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Manual on Disposal of Refinery Wastes

Volume on Solid Wastes

Refining Depadment

FiRST EDITION, SEPTEMBER 1980

American Petroleum Institute

.

Nothing contained in any API publication is to be construed as granting any right, by implication or otherwise, for thc manufacture, sale, or use in connection with any method, apparatus, or product covered by letters patent, nor as insuring anyone against liability for infringement of letters patent.

API publications may be used by anyone desiring to do so, and every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them. However, the Institute makes no representation, warranty, or guarantee in connection with API publications and hereby expressly discfaims any liability or responsibility for loss or damage resulting from their use; for any violation of any federal, state, or municipal regulation with which an API publication may conflict; or for the infringement of any patent resulting from the use of an API publication.

Copyright O 1980 American Petroleum Institute

FOREWORD

The API Committee on Refinery Environmental Control has with this volume

The manual in three volumes is organized as follows: completed the updating of the Manual on Disposal of Refinery Wastes.

Liquid W a s t e d o m p l e t e d in 1975. Atmospheric Emissions-Completed in 1977. Solid W a s t e d o m p l e t e d in 1980.

The chapters comprising each volume are individual units to allow for their easy removal from the binder and to facilitate their use.

It is the Institute’s belief that this format enhances the value of the information and enables API to revise and update information as it becomes available. Refiners are urged to contribute to the success of this manual by submitting information on waste disposal practices to the director of the Refining Department, American Petroleum Institute, 2101 L Street, N.W., Washington, D.C. 20037.

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CONTENTS

CHAPTER 1-INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PAGE

. . . 1-1 1.1 1.2 1.3 1.4 1.5

' 1.6 1.7 1.8 1.9

Scope The Resource Conservation and Recovery Hazardous Wastes . . . . . . . . . . . . . . . . . . . . . Nonhazardous Wastes . . . . . . . . . . . . . . . . . . Imminent Hazard Situations . . . . . . . . . . . . Subtitle C Impacts on a Refinery . . . . . . . . . Subtitle D Impacts on a Refinery . . . . . . . . . Onsite vs . Offsite Disposal . . . . . . . . . . . . . . General Considerations . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Act . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . 1.1

. . . . . . . . . . 1.1 . . . . . . . . . 1-1 . . . . . . . . . 1.2 . . . . . . . . . 1-2 . . . . . . . . . 1-2 . . . . . . . . . 1-3 . . . . . . . . . 1-3 . . . . . . . . . 1-3

CHAPTER 2 4 E N E R A L ADMINISTRATION

CHAPTER 3-SOURCES, SEGREGATION,

AND CONTROL OF SOLID WASTE . . . . . . . . . . . 2-1

QUANTITIES, AND CHARACTERISTICS OF SOLID WASTES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3.1 Sources and Classification 3-1 3.2 Segregation of Wastes 3-1

3.2.1 Oily Process Sludges 3-1 3.2.2 Nonoily Wastes 3-1 3.2.3 Biological Sludges 3-1 3.2.4 Miscellaneous Wastes 3-1 3.2.5 Sanitary Wastes 3-1 Typical Quantities and Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3

CHAPTER &SOURCE REDUCTION 4.1 Tank Cleaning .......................... 4.2 Biosludge From Water Treatment . . . . . . . . .

4.2.1 Sludge Age ...................... 4.2.2 Aerobic Digestion . . . . . . . . . . . . . . . . 4.2.3 Hydrolysis ....................... 4.2.4 Air Flotation Float Recycle . . . . . . . . 4.2.5 Beneficial Combination . . . . . . . . . . . . 4.2.6 Shutdown Planning . . . . . . . . . . . . . . . .

4-1 . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4-1 . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 . . . . . . . . . . . . . . . . . . . . . . . . . J-1 . . . . . . . . . . . . . . . . . . . . . . . . . J-1

4-1 . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

. . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . .

CHAPTER 5-RESOURCE RECOVERY . . . . . . . . . . . . . . . . . . . . . 5-1 ...

5.1 Oil Reclamation 5.1 5.2 Catalyst Reuse 5.1 5.3 Acids . and Caustics 5.1 5.4 Biological Sludges :5-1 5.5 Filter Clays 5.1 5.5 Chromate Inhibitor Reuse 5.1

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CHAPTER &TREATMENT PRIOR TO

6.1 ULTIMATE DISPOSAL . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

The Importance of Waste Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

V

.

6.2 Sludge Concentration by Gravity Diffirential Methods . . . . . . . . . . . . . . . . 6-1 6.2.1 Gravity Thickening or Settling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1 6.2.2 Air Flotation Units .............................. 6.2.3 Chemical Flocculation . . . . . . . . . . . . . . . . . . . . . . . . . . . Sludge Concentration by Mechanical Dewatering . . . . . . . . . . . . . . . . . . . . . 6-3 6.3.1 Centrifugation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3 6.3.2 Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6 Sludge Concentration by Incineration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7 6.4.1 Burner-Type Incinerators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7 6.4.2 Fluid Bed Incinerators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8

6.4.4 Monoheanh Incinerators

6.4.6 Rotary Kilns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9

6.4.8 Pyrolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10

6.3

6.4

6.4.3 Multiple Hearth Incinerators . . . . . . . . . . . . . . . . . . . . . . 6-9

6.4.5 Grate-Type Incinerators . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9

6.4.7 Incinerator Design Considerations . . . . . . . . . . . . . . . . . . . . . . 6-10

. . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9

CHAPTER 7-ULTIMATE DISPOSAL . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 7.1 Landfill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.1.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 .7. 1.2 Sand-Lime Stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 7.1.3 Chemical Fixation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 Landfarming of Oily Sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

.7. 1.2 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 7.2.1 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2 7.2.3 Site Selecticn and Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

. 7.2.4 7.2.5 Sludge Distribution and Tilling Frequency . . . . . . . . . . . . . . . . . . . . 7-2

.7. 3.1 General ................................................... 7-3 7.3.2 Landfarming Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

7.2

Oil Loading and Nutrient Addition . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

. Landfarming of Biological Sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3 7.3

LIST O F ILLUSTRATIONS Tables

3-1-Sources and Characteristics of Refinery Solid Wastes . . . . . . . . . . . . . . . 3.2 3-24ompar i son of API and Jacobs Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 3-3--Comparison of API and Jacobs Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 6-1-Sludge Source versus Solids Concentration . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 6-2--Ranges of Solids Removal for the Dissolved Air Flotation Process . . . 6.2 6-%Typical Dissolved Air Flotation Process Design Parameters . . . . . . . . . . 6.2 6-4-Gravity Differential Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3

Figures 6-l-centrifugal Separator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6-3-Scroll Centrifuge ........................ . . . . . . . . . . . . . 6-&Imperforate Basket Centrifuge . . . . . 6-%-Rotary Drum Vacuum Filter . . . . . . . 6 - W r a v i t y Belt Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7-Fluid Bed Incinerator . . . . . . . . . . . . . 6-$--Typical Multiple Hearth hcinerator . . . . . . . . . . . . . . . . . 6-eRota r -y Kiln Including Afterburning System 6-10-Infrared Incineration System . . . . . . . . . . . . . . . . . . . . . . . 7- 1-Graph for Estimating Oil Loading an

6-2-Disc Centrifuge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4

. . . . . . . . . . . . . . . . . . . . 6-5 . . . . . . . . . . . . . . . . . . . . . . . . 6-6

. . . . . . . . . . 6-9

vi


Volume on Solid Wastes Chapter 1-Introduction

FIRST EDITION, SEPTEMBER 1980

t

American Petroleum lnstihrte

c Manual on Disposal of Refinery Wastes


CHAPTER l--INTROOUCTION

1.1 Scope The manual is intended as a primer for a petroleum

refinery engineer just starting to consider solid waste treatment and disposal. It provides a general description of a possible refinery organization, waste characteristics, and techniques used for waste treatment and disposal. The manual does not provide all of the de- tailed information that is needed for design and operation of a refinery solid waste system. However, it does contain comments and cautions which are specific to treatment of refinery wastes which are generally not found in other sources.

1.2 The Resource Conservation and Recovery Act

The treatment and disposal of refinery wastes are becoming inneasingiy important because of the added cost and legal liabilities which maybe incurred. This is largely a result of the Resource Conservation and Re- covery Act (RCRA). It will be useful at the outset to briefly review the statute. The objectives are (1) to protect human health and the environment and (2) to encourage resource recovery.

Certain key words are defined in the act. The following definitions from the act will be used throughout this manual. Solid waste is any garbage, refuse, or sludge from a

waste treatment plant, water supply treatment plant. or air pollution control facility, or other discarded material, inciuding solids, liquids, semisolids, or contained gaseous material resulting from industrial, commercial. mining, and agricultural operations and from commu- nity activities. Under the act, solid waste does not include solid or dissolved material in domestic sewage, solid or dissolved materials in imgation return flows. or industrial discharges which are point sources subject to permits under Section 402 of the Federal Water Pollu- tion Control Act. In addition, solid waste does not include source, special nuclear, or byproduct material as defined by the Atomic Energy Act.

Discarded material is used or spent material which is not reused in any way and that is committed to final disposition. Used materials which, although of no further utility to the generator, are recycled, regen-

r

erated, or reused by others are not discarded and. therefore, are not subject to rcgulation under the act.

Hazardous wasre is solid waste which poses specified health and environmental hazards.

Disposal is the discharge, deposit, injection, dumping, spilling, leaking, or placing of any solid waste or hazardous waste into or on any land or water so that such solid waste or hazardous waste or any constituent thereof may enter the environment, be emitted into thl: air, or be discharged into any waters, including ground waters. Therefore, waste deposited in a landfill. land- farmed wastewater discharged to a basin or surface impoundment, or stormwater runoff diverted to a percola- tion or settling pond is disposal. Incineration is considered treatment under RCRA.

An open dump is a facility that does not meet the criteria for a sanitary landfill and is not a facility for disposal of hazardous waste.

Confamindon is the introduction into the groundwater of any substance which would cause the concentration of that substance in the groundwater to exceed the maximum contaminant levels under the National Interim Drinking Water Standards (40 CFR 141).

1.3 Hazardous Wastes The Subtitle C or hazardous waste program under

RCRA will be accomplished by a series of nine regulations.

Section 3001 regulations identify the characteristics of hazardous waste and, using the characteristics, lists some specific waste streams. The hazardous characteristics proposed include toxicity. corrosivity, reactivity, and ignitability.

Section 3002 mandates standards for generators of hazardous waste. The requirements include recordkeeping, reporting, labeling, proper containerization. and initiation of a manifest system to track a hazardous waste from its generation to its ultimate disposal. or “cradle to grave” as the Environmental Protection Agency (EPA) puts it. Note that the manifest requirement is not applicable to hazardous waste that a generator treats, stores, or disposes of onsite.

Section 3003 mandates standards for transporters of hazardous wastes. These requirements include recordkeeping, delivery only to a permitted facility, reports. I

1-1

.

1-2 DRW MANUM-SOLIO WASTES

and compliance with the manifest system. Section 3004 mandates standards for treatment, stor-

age, and disposal facilities. These standards include requirements for recordkeeping; reporting, monitoring, inspection and compliance with the manifest system; facility operating methods; site selection and design criteria; contingency plans; maintenance of operations and requirements as to ownership. continuity of operations, and personnel training; financial responsibility; and compliance with the permit requirements.

Section 3005 requires each facility treating, storing, or disposing of waste to obtain a permit. A facility in existence when the final regulations under 3001 and 3004 are promulgated is entitled to interim status and may continue to conduct hazardous waste activities pending final action on its permit application if it makes proper notification in accordance with Section 3010 and applies for a permit. Any facility not in existence must obtain a permit before commencing construction. It appears that “in existence” will be interpreted narrowly. It will include a facility in operation, under construction, or one which has obtained all necessary permit approvals and has made a commitment that cannot be rescinded or modified without a substantial financial penalty.

Section 3006 provides for state administration of the hazardous waste program in lieu of EPA. A state which wishes to administer its own program must develop a plan that is equivalent to the federal program, that is consistent with the federal and state programs applicable in other states, and that provides for adequate enforcement.

Section 3007 authorizes EPA and state officials (where the state has an authorized program) to enter any facilities where hazardous wastes are generated. stored, treated, or transported from or disposed of and to inspect and obtain samples of any wastes.

Section 3008 authorizes the issuance of compliance orders for violation of any requirements under Subtitle C. provides for public hearings, and establishes civil and criminal penalties for violations. Civil penalties are set at 525,OOO for each day of continued noncompliance after the date specified in a compliance order issued by EPA. Criminal penalties of S25,OOO for each day of violation and up to 1 year imprisonment, or both, are set for conviction of knowingly (1) transporting a hazardous waste to a nonpermitted facility, (2) treating, storing, or disposing of a hazardous waste without a permit, or (3) making false statements in any application, label, manifest, permit, report, or other document maintained under Subtitle C. Second offenses are punishable by a 550.000 a day fine and up to 2 years imprisonment, or both.

Section 3010 requires any person generating or trans- I

porting hazardous waste or any person using or operating a facility for the treatment, storage. or disposal of hazardous waste to notify EPA or the authorized state of such activities, stating the location and general description of the activity and the identified or listed hazardous wastes handled by such person. This is a one time notification to be given within 90 days after final regulations are promulgated under 3001. No hazardous waste may be transported, treated. stored, or disposed of unless such notification is given.

1.4 Nonhazardous Waste The Subtitle D scheme for nonhazardous waste is less

pervasive but more circuitous than that of Subtitle C. If a state wishes to avail itself of the federal technical and financial assistance provided by Subtitle D, it must develop a state solid waste plan that meets certain minimum requirements. The state plan must provide for the upgrading or dosing of all existing open dumps (see 1.2). One year after promulgation of the criteria for a sanitary landfill, EPA must publish an inventory of all facilities which are open dumps within the meaning of the act. In accordance with any applicable state Subtitle D program, open dumps must be retrofitted to comply with the sanitary landfill criteria or close within 5 years from the publication date of the inventory.

It must be noted, however, that states are not required to adopt Subtitle D solid waste programs at all, and EPA is not authorized to devefop a state program if the state fails to do so or fails to receive approval for its program. The state simply will not be entitled to receive federal financial and technical assistance. There is no federal enforcement of Subtitle D requirements.

i

1.5 Imminent Hazard Situations In addition to other authority and remedies provided

under the RCRA, EPA may bring suit to immediately restrain any person from conducting a waste handling activity which is presenting an imminent and substantial danger to health or the environment and to take such other action as may be appropriate.

1.6 Subtitle C Impacts on a Refinery The proposed 43001 regulations list the following

specific refinery wastes as hazardous: 1. Leaded tank bottoms. 2. Neutralization hydrofluoric alkylation sludge. 3. Disolved air flotation unit sludge. 4. Kerosine filter cake. 5 . Lube oil filtration clays.

INTF4owcTIoN 1-3

. i 6 . Slop oil emulsion solids. care would accumulate over the life of the waste facility by annual contributions to a trust fund. 7. Exchanger bundle cleaning solvent.

8. API separator sludge. A refinery may, by performing a specified series of 1.7 Subtitle D Impacts on a Refinery tests, demonstrate to EPA that a listed waste from a particular refinery is not hazardous.

In addition to listed wastes, any other wastes which meet the hazardous criteria must be handled in accordance with Subtitle C, for example, pipeline cleaning residues and adsorbents used for spill cleanup. On the other hand, recycied or regenerated wastes, such as spent catalyst sent to a manufacturer for regeneration and metal recovery or used automotive oil sent to a re-refiner, do not fall within the scope of RCRA because they are not discarded.

As a generator of hazardous waste, a refinery must comply with the applicable 93002 standards. Further, some refiners will also be subject to the § 3 W standards for treatment, storage, and disposal facilities and will require a RCRA permit. Even if a refinery sends most of its listed wastes to an offsite disposer, it may need a RCRA permit for its National Pollution Discharge Elimination System (NPDES) facility. Wastewater treatment systems receive wastewater streams which may fall within the 93001 criteria. Although the NPDES effluent is specifically excluded from .RCRA coverage, a basin or surface impoundment associated with such a facility is subject to RCRA if the waste stream entering such basin or impoundment is hazardous according to

If the refinery is also a treatment, storage, or disposal facility, it will have to meet the $3004 standards, including proposed stringent financial responsibility requirements for the liability arising out of operation of such a facility. For example, if a refinery’s wastewater treatment system is considered a RCRA facility, the refinery would have to provide evidence of financial responsibility of $5 million per occurrence for claims arising out of injury to persons or property from the sudden and accidental release of hazardous waste into the environment. Additionally, the refinery would have to maintain financial responsibility of $5 million per occurrence for claims arising from nonsudden releases, such as the gradual pollution of groundwater by seepage or leaking. These specified levels of financial responsibility do not mean, however, that the refinery’s liability would be limited. The refinery would remain liable for the full amount of damages it may cause.

The statute and the regulations do not cover financial responsibility or liability for sudden and nonsudden releases following closure. The proposed regulations provide for post-closure monitoring and maintenance for up to 20 years after closure. The money for post-closure

!

. the 93001 criteria.

!

If a refinery can demonstrate that its waste is nonhazardous and if the state in which the refinery is located adopts a Subtitle D program, the refinery’s onsite disposal sites must meet the criteria for a sanitary landfill. If they do not, they must be upgraded to comply or must be shut down. The criteria for a landfill have been promulgated (4.0 CFR 257, 44 Fed. Reg. 53438, Sep- tember 13, 1979) and prohibit contamination (see 1.2) of underground drinking water beyond the solid waste boundary. Where the level of a substance identified in the National Interim Primary Drinking Water Stand- ards is already exceeded in the groundwater, no discharge to the groundwater is permitted.

1.8 Onsite vs. Offsite Disposal As previously discussed, a refinery may need a

RCRA permit for its NPDES facility. The decision as to whether to handle the remaining wastes onsite or offsite is a complex one and involves a review of existing law as well as consideration of proposed changes in that law.

A permit for any pollutant discharge-whether it be an NPDES permit, an air permit, an underground injection control permit, or a R C M pennit-does not make the refinery immune from nuisance and damage actions, and there are no limits to this liability. A claimant must, however, show that the refinery discharged or released the pollutant and that the claimant was damaged in some way by that release. For example, actions have been brought against aluminum smelters for fluoride damage to surrounding vegetation even though the emissions were not in violation of applicable air regulations. Therefore, although a refinery may dispose of wastes in a landfill which meets all the requirements of its RCRA permit, if there is a release from that landfill (for example, contamination of groundwater), the refinery could still be held liable for the full extent of the proven damages.

1.9 General Considerations 1. Review relationships with independent off5ire wave managers. Contracts should provide that the waste management firm agrees to comply with all environmental laws, federal and state, relating to its operations.

On a longer term basis, i t would also be advisable to determine if the sites presently used could be upgraded

1 - 4 DRW MWAL-SCUD WASTES ~ ~-

to meet the new RCR4 standards. If they cannot, every stringent regulations are developed, and the shortage of effort should be made to seek other means of handling sites increases, the cost of waste management will be- the waste. . come increasingly more expensive. Thus, recycling, re- 2. Consider onsire treatment, storage, or disposal. Some existing sites, which cannot or will not be retrofitted to meet the stringent requirements, will be required to close. This will further exacerbate the existing shortfall of available hazardous waste management facilities. Permits for new sites will be extremely difficult to obtain. If land is available on refinery property, it seems advisable to determine whether the waste can be man- aged on site. 3. Determine if there are alternatives ro disposal. Energy conservation has increased dramatically in the past several years. As energy costs rapidly escalate, it becomes clear that one of the best rates of return can be realized on funds expended for energy efficiency. Sim- ilar economics will shortly create the same climate in the area of hazardous waste management. When regulation was minimal and hazards were unknown, waste disposal was cheap. As new hazards are recognized,

generation, resource recovery, or incineration, which may have been economically unattractive under pre- vious regulatory regimes, may become cost-effective. It is advisable to complete this review now before there is an extraordinary demand for incinerators, recyclers, regenerators, and so forth, which will drive up the cost of such services. In addition, the opportunities offered by waste exchanges should be explored. Remember, used materials which are recyded. regenerated, or reused are not subject to Subtitle C requirements even if they are hazardous. 4. Consider the economics of segregating wastes. The simple segregation of waste, hazardous and nonhazardous, may result in significant savings even though the economics would not have been considered cost- justified in the past. In addition, future legislation may impose a waste fee of $10 per ton or more to provide funds for emergency containment or clean-up.


Volume on Solid Wastes Chapter 2-General Administration and Control

of Solid Waste

FlRST EDITION, SEPTEMBER 1980

Institute

Manual on Disposal of Refinery Wastes Volume on Solid Wastes

CHAPTER 2 4 E N E R A L ADMINISTRATION AND CONTROL OF SOLID WASTE

In recent years refinery solid waste management technology has become more complex and the consequences of improper techniques more severe. Invest- ment and operating costs have increased for complex equipment such as centrifuges, filters, and incinerators. Along with this, the need for skills in such areas as mechanics, chemistry, biology, heat transfer, and materials engineering has increased. To achieve compliance with environmental regulations at a reasonable cost, it is incumbent upon refinery management to train process engineers in the techniques of developing and operating solid wastes programs. To achieve this goal it is especially important that refinery waste control have active management support.

An effective program requires that plant personnel clearly understand their responsibilities. It is preferable to delegate overall responsibility to a single person who has the authority to enforce established preocedures. Experience has shown that indiscriminate mixing of wastes and unreported spills to refinery sewers are the types of events which frequently result in regulatory violation and decreased cost. The person with overall responsibility should be certain that personnel understand their individual responsibilities. He should also establish cost and quality standards which can be re- viewed to see that goals are met. The consequences of improper solid waste disposal are not as immediately visible as a smoky flare. The sampling is not as simple as sampling water effluents. However, the consequences of improper procedures can be every bit as

Operating units and maintenance departments should be held responsible for controlling their own generation of solid wastes. They should advise the proper plant authority, by established procedures, of anticipated changes in quantity or characteristics of their waste. This will enable measures to be taken to prevent adverse effects on the overall solid waste program. Plant personnel must recognize that responsibility for a solid waste does not end at the plant gate. Environmental regulations require that the waste generator properly notify the hauler and waste disposer of the properties of a waste. The generator may be held responsible if wastes are not clearly described.

The first step in establishing an effective waste management program is to conduct a solids survey to define

i

costly.

the problem in terms of waste quantities, characteristics, sources, costs, and disposal options. This is described more fully in subsequent chapters of this manual. The second step is to establish procedures for segregation. waste reduction, and resource recovery. These procedures should include contingency plans, short and long-range, in the event that waste characteristics or regulations change or that a contractor is no longer able to handle the waste. In developing these plans, bear in mind the ultimate objectives of resource recovery and sound environmental practice at reasonable cost.

Combining wastes is frequently the most expedient way to remove an unwanted material from a process unit. However, i t can readily be understood that adding a solid waste to a liquid may make the entire waste unpumpable or adding an oily waste to a nonoily waste makes the entire waste oily. Mixing affects how the entire waste must then be treated and disposed. In almost all cases, combining wastes increases costs. Com- bining wastes in a random manner also requires that individual consideration be given to how that specific waste container will be treated. Again, this increases costs.

The second important point is waste reduction. In almost all cases, cost of treatment and waste disposal are directly related to waste volume. Waste reduction also makes the possibility of resource recovery more likely. For example, if a slop oil has less water it may be autogenous and not require the use of auxiliary fuel for incineration. Likewise, i t may be economically feasible to break an emulsion if the total amount of the emulsion is reduced.

Once a survey has been completed and procedures established, refinery personnel at all levels must be in- formed of their responsibilities. They must understand the effect of their actions on costs and the operating problems that may be created in other areas.

A complete waste managemenl program should include plans for the future. Contingency plans for truck strikes, for the inability of a contractor to process a waste for short or indefinite periods, and for the need to meet new federal or local environmental regulations are examples of considerations to be included in future plans.

Finally, consideration should be given to resource

2- 1

2-2 DRW Mucuu-Souo WASTES

recovery. Many so called “wastes” are now recovered. Some spent catalysts and coker residues are being recovered for their metals content. In some cases waste oils are being reclaimed. These are examples of resource recovery and such recovery and reuse are the stated objective of the Resource Conservation and Re-

covery Act. Regulations and increasing waste treatment and disposal costs will increase the incentive for resource recovery. In the end, resource recovery is the ultimate soiution to waste disposal problems and should continue to receive serious attention.


Volume on Solid Wastes Chapter 3--Sources, Segregation, Quantities,

and Characteristics of Solid Waste





CHAPTER 3-SOURCES, SEGREGATION, QUANTITIES, AND \ CHARACTERlSTlCS OF SOL10 WASTE

There are numerous sources and types of refinery solid waste. Most wastes can be segregated at the source for more efficient handling before reclamation or disposal.

Because of varied refinery configurations, each refinery will have problems specific to its location, process, and local regulations. Even considering the indi- viduality of refineries, there are basic waste materials produced which are common to most refining processes and, therefore, can be handled similarly for resource recovery or disposal. Besides these basic wastes, there are other wastes with characteristics and in quantities not easily defined. A list of waste sources and dassifica- tion of wastes is presented in Table 3-1. Obviously such a list cannot be all inclusive. ,

I 3.1 Sources and Classification

Some of the more easily defined waste materials found in Table 3-1 are listed by refinery unit source and

, classified into combustibles, noncombustibles, and bio- degradables.

3.2 Segregation of Wastes By studying Table 3-1 and relating it to a particular

operation, prudent segregation practices that can reduce the cost and effort of handling become apparent.

The following catagories for segregation are sug- gested: 1. Oily process sludges. 2. Nonoily wastes. 3. Biological sludges. 4. Miscellaneous. 5 . Sanitary wastes.

Using the segregation guide along with the source table, materials that arc compatible and that may possibly be mixed prior to processing for resource recovery can be identified.

3.2.1 OILY PROCESS SLUDGES

Oily sludge is the most difficult to handle. Oil sludges are obtained as sediments from storage tanks. crude desalters. sewer cleaning, vessel cleaning. oil-water sep-

arators, dissolved air flotation, lube oil processing, and alkylation. X very thorough study is required to determine which wastes are compatible for mixing prior 'to recovery.

3.2.2 NONOILY WASTES

Nonoily wastes are much easier to handle. These wastes come from storm sewer cfeanings. grit chambers, tank cleaning, cooling tower cfeanings, water treating, and catalyst replacement. Used catalyst is the most likely candidate for resource recovery.

3.2.3 BlOLOGlCAL SLUDGES

Biological sludges are those obtained from biological wastewater treatment plants. These sludges are concentrated by various methods, and when the quality allqws, may be used as soil conditioners. Methods of concentration are discussed in Chapter 6 .

3.2.4 MISCELLANEOUS WASTE

Miscellaneous solid waste materials not related to oil processing can generally be disposed of in municipal landfiils.

3.2.5 SANITARY WASTES

The sanitary sewage collection and disposal system should be segregated from the process wastewater system to eliminate the requirement to chlorinate the treated water effluent. Where refineries do operate sanitary waste treatment systems, adequate information is available in the literature to answer solids disposal questions.

3.3 Typical Quantities and Characteristics In 1974, the U.S. Environmental Protection Agency

contracted with Jacobs Engineering for a survey of the refining industry to characterize and quantify the solid waste materials produced by refineries. Subsequent to that report in 1976, the American Perroleurn Institute conducted a separate survey to better quantify wastes through a broader data base.

3- 1

3-2 DRW MANUM-SOLID WASTES

Table 3-1 --Sources and Characteristics of Refinery Solid Wastes

Classification Source Combustible Noncombusti ble’ Biodeqadablc

Rdlnlng P r o u w a

Crude oil storage

Crude processing Product Storage

Wax bottoms Sand, rust, slit TEL sludge. sand, rust, silt Sand. rust, silt, salt. slop oil emulsions

Separator coke Thermal cracking Catalytic cracking Catalytic reforming Polymerization Alkylation HF alkylation Asphalt manufacture

Product treating Cooling

Spent catalyst Spent catalyst Spent catalyst Corrosion products (sludge. tar) Calcium fluoride sludge Asphalt emulsions Asphalt drips

Coke fines, wax tailings Add sludge Adsorbents

Slops, drips Soaps

Emulsions, light solvent

Lead sludge Adsorbents Clay Lubes and grease

WaX

Smrvlt. Functlonr

Carpenter Welding Machine Maintenance Electrical Cafeteria

Shops

Laboratory

Wood ,Metal scrap Metal scrap Metal m a p Metal scrap. insulation Metal scrap Broken glassware cans, bottle Garbage Scrap equipment. catalyst Sanitary wastes

Rubber, plastic Waste paper Waste paper. asphalt. samples, boxes Waste paper. boxes Waste paper, discarded clothing

Scrap equipment Sanitary wastes Sanitary wastes

Office Lodter Rooms

Nonrdlnlng Opmtlon8

Steam generation Feedwater treatment Cooling towers

Utilities

Wartewatw Pollutlon Control API separators

Boiler blowdown sludge Lime sludge Suspended solids

Oily sludges. heavy hydrocarbons Oily froth Bio. floc.” Floc.

Sand. silt Oily coated inert solids

Air flotation Clarifiers Flocculation Filters Biological oxidation

Bio floc. Flocs. Clay Filter cake

Bio. floc. Bio. sludge

Alr Pollutlon Control Bas filters Electrostatic precipitators

Catalyst dust Catalyst dust

‘In many cases the noncombustibles arc associa~ed with combustibles and ihc whole mass must be

‘Biological flocculation. roccssed to remove the combustible before disposal of the inen residue.

SOVRCES, SEGREGATION. QUANTIES, AND CHARACTERISTICS 3-3

Table 3-2 shows a comparison of the two surveys for (see Table 3-3). Unfortunately. no meaningful correla- total quantities of wastes produced from various tion could be made between refinery size. barrels per sources. day of crude processed. and the amount of waste gener-

The surveys concluded that emphasis on waste oil ated. recovery is justified. Further analysis showed that the metallic content of

The surveys indicated that the major sources of wastes varies widely between refineries. however the metallic constituents are API separator bottoms. ais- total quantity of metals discharged to the environment solved air flotation units, waste biological sludge, storm is insignificant when compared to municipal sludges. silt, and waste fluid catalytic cracking (FCC) catalyst

c

!

Table 3-24omparison of API and Jacobs Results Results in Id Metric TonsA'ear Extrapolated" to the Total Industry

0 1 1 Solids 011 and Solids Stream API Jacobs API Jacobs - )\PI Jacobs

Once-through cooling sludge 5 0 2 44 28 2 9 28

sludge 0 4 0.002 5 0 1 5 0 1

API separator bottoms 28 2.5 53 33 81 58

Air flotation float 12 9 28 11 40 20

Waste biological solids 6 0.2 14 1 1 20 1 1

Storm water silt 2 1 24 33 26 24

Storage tankb bottoms - - - - - - Waste FCC catalyst - 0.06 64 31 64 31

Cooling tower

- _ _ _ _ _ _ ----- __ .

HF alkylation sludge - 1 7 8 7 9

Treating clays 19 4 46 55 65 59

Total 72 40 285 200 357 240

'Extrapolation from industry survey base which consisted of 57 percent oi the U.S. refinery capacitv bInsufficient data for extrapolation.

3-4 DAW MANUAL-SOLIO WASTES

Table 3-3-Comparison of the API and Jacobs Survey Total Quantities of Metals in Each Solid Waste for All U.S. Refineries in Metric Tons Per Year

Once-Through Cooling API Air Waste Storm Storage Waste Metals Cooling Tower Separator Flotation Biological Water Tank FCC Treating

Sludge Sludge Bottoms Float Solids Silt Bottoms' Catalyst Clays' Total

Arsenic API Jacobs

Cadmium API Jacobs

Chromium API Jacobs

Copper API Jacobs

Lead API Jacobs

Mercury API Jacobs

Nickel API Jacobs

Selenium API Jacobs

' Vanadium API Jacobs

Zinc API Jacobs

Total

API Jacobs

0.06 0.02

0.04 o.ooo1

1.85 2.4

2.09 5.7

1.61 2.1

0.008 0.02

0.62 1.3

0.12 0.06

0.49 1.5

2.18 4.1

9.07 17.8

0.04 0.004

0.005 0 . m 1

4.33 0.3

0.85 0.02

0.24 0.M

O.ooo6 5 -

0.08 0.003

0.008 c -

0.06 0.004

2.45 0.3

8.06 0.6

0.11 0.4

0.06 0.03

8.56 17.6

3.23 1.4

2.39 1.2

0.02 0.03

0.95 1.3

0.01 0.07

1.20 0.7

11.7 20.7

28.2 43.4

0.001 0.1

0.02 0.0003

5.32 8.4

0.43 0.4

0.23 0.5

0.003 0.03

0.17 o.co1

0.003 0.1

0.13 0.003

5.88 6.3

12.2 15.8

0.02 0.3

0.004 0.02

4.09 22.0

0.22 0.8

0.46 0.4

0.001 0.2

0.10 0.002

0.01 0.008

0.10 0.004

3.09 9.9

8.09 33.6

0.07 0.2

0.03 0.007

3.6 10.2

1.75 0.8

4.37 1.6

0.02 0.02

0.58 2.4

0.02 0.05

0.51 2.1

4.97 6.9

15.9 24.3

0.06 0.06

0.13 0.001

3.0 2.6

1.47 0.5

2.56 1.5

0.01 (3)

12.16 7.4

0.06 0.0003

14.7 7.4

2.37 1.6

36.5 21.1

0.07 0.08

0.10 0.071

1.66 2.11

0.51 0.45

0.51 0.1'4

0.005 0.02

0.69 1 .o

0.06 0.10

1.29 3.2

1.89 5.5

6.79 12.7

0.43 1.2

0.39 0.1

32.4 65.6

10.6 10.1

12.4 7.5

0.068 0.3

15.4 13.4

0.29 0.4

18.5 14.2

34.5 55.9

125 169

'Insufficient data for extrapolation. bIncludes lube and jet fuel treating clays. 'Less than 1.0 Ib/hr.

NOTE: Other comparisons are made from the surveys and can be found by reference to the original document.

Ihlanual on Disposal of Refinery Wastes

I.

Volume on Solid Waste Chapter &Source Reduction


American Petroleum InsttMe


CHAPTER 4-SOURCE REDUCTION METHODS

A major tool in the management of solid wastes is the modification of process and operating procedures. This is done to reduce the quantity of waste solids and to alter their characteristics to make disposal less costly. Many such modifications have been put into practice, and refinery management is continually on the lookout for additional methods.

4.1 Tank Cleaning Variable angle mixers installed in storage tanks can

be used in conjunction with selected solvents (such as, crude, light cycle oil. and water) to reduce the time, manpower, and cost of removing residual solids from storage tanks.

The selected solvent is added to the tank to be cleaned and the mixers are operated for 5 to 15 days in

either side of the center line. This sweeps all parts of the tank floor and lifts the solids so that solvent and oily solids are in intimate contact. The resulting deoiling of the solids recovers valuable hydrocarbon for reuse. It also reduces the oil content of the residual solids making them less difficult to dispose of ultimately and reduces the quantity of residual solids by removing the oil and wax content of the solids. An additional advantage of this technique is the greater safety afforded by conducting the major portion of the cleaning activity from outside of the tank.

i various positions typically ranging 30 degrees from

,

4.2 Biosludge From Water Treatment Several techniques are available to reduce the quan-

tity of waste biosludge from wastewater treatment.

4.2.1 SLUDGE AGE

The sludge age in the biological treatment system can be increased. To accomplish this without creating sludge settling problems usually requires careful pretreatment to remove colloidal material in the wastewater entering the biounit. Removal may be accomplished by use of a well-operated air flotation or sand filter system. The sludge age can usually be increased sufficiently to reduce sludge wastage to very low levels.

4.2.2 AEROBIC DIGESTION

Aerobic digestion of the waste biosludge will result in a significant reduction in the quantity of sludge. It is also a necessary pretreatment step for landfarming of biologicai sludge to prevent odor problems.

4.2.3 HYDROLYSIS

Other methods of reducing waste biological sludge include chemical treatment, such as acid treatment. to break down the biological cell wall. Thus, organics can be oxidized and the resultant biological studge is more easily dewatered for ultimate disposal.

4.2.4 AIR FLOTATION FLOAT RECYCLE

Air flotation units are usually operated with chemical additives to improve their efficiency. Alum, ferric chloride, lime, and polyelectrolytes are typical chemical agents used. If possible, the chemical usage should be limited to polyelectrolytes since alum, lime, and ferric chloride type treatment creates a significant volume of oily solids for disposal.

The use of polyelectrolytes alone opens the possibility of recycling the float, which is now primarily oil. to the front of the system thus reducing the quantity of solid material for disposal.

4.2.5 BENEnClAL COMBINATION

Some wastes may be combined to advantage. For instance, lime from boiler feed water treatment can be used for pH control on landfarm operations.

4.2.6 SHUTDOWN PLANNING

The environmental department should be involved in the planning for all types of shutdowns so that the quantities and characteristics of wastes to be generated by the shutdown are anticipated. The shutdown pian- ning should assure that all possible steps are taken to keep quantities to a minimum, to control the characteristics of the waste to simplify its disposal. and to plan the disposal techniques to be used.

Reference Knowlton. H. E.. “Source Control in Petroleum Refincnes.” paper

presented at the National Petroleum Refiners Association Annual Meeting. A M 78-41. March 1978

4-1


Volume on Solid Waste Chapter 5-Resource Recovery

F!RST EDITION, SEPTEMBER 1980



CHAPTER 5-RESOURCE RECOVERY

Resource recovery is a very important part of a waste management program. With the ever increasing price of crude oil. the goal must be the recovery of every usable barrel of oil. Aside from the profit motive, one must consider the regulatory requirements for waste disposal and factor these associated costs into a resource recovery program. Whether the recoverable product be oil, catalyst, or digested sludge the process of recovery for reuse nearly always reduces the quantity of waste material for disposal. Of the waste streams identified in the Jacobs and API waste surveys, the main items which are recoverable and reusable include oil, catalyst, acids, caustics, digested biological sludges. filter clays. and. in some cases, chromate inhibitors used in cooling tower treatment. Almost every refinery can identify recoverable items from waste generated by processes which are individual to that refinery.

5.1 Oil Reclamation All refineries practice the recovery of waste oils to

some degree. The recovered oils may be reintroduced into various process feed streams or sold directly for fuel or other uses. The techniques for recovery include simple gravity separation, emulsion breaking with chemicals and heat, and the use of lighter oils and solvents to aid in emulsion breaking and thinning of heavier oil fractions. There are a number of patented processes on the market for the recovery of oil from waste streams. The chemical companies which special- ize in emulsion breaking chemicals offer engineering services directed at maximizing the recoverable oil from a given waste material. After the oil is recovered. the residual waste is amenable to landfarming as the ultimate method of disposal. If a sludge is to be land- farmed, oil should be recovered until the oil content is no more than 15 percent. Since oil concentration is a limiting factor for the quantity of waste to be applied to a plot of land, the less oil a waste contains the smaller the land area required for landfarming.

,

5.2 Catalyst Reuse

i The metal content of many catalysts is frequently of sufficient quantity to allow the catalysts to be repro- cessed for resale or metal recovery. This may be done

by catalyst manufacturers or companies specializing in metal recovery from waste materials. If a catalyst supplier will not take the spent catalyst for reprocessing, the supplier may heip the refinery find a market for the catalyst. Most spent catalvsts are stable enough that ultimate disposai can be accomplished by landfilling. I t is a good practice not to mix spent catalyst with other wastes in a landfill. In many cases, landfills become acceptable means for disposal if they are dedicated completely to a particular waste material.

5.3 Acids and Caustics It is a common practice to match these waste ma-

terials for neutralization prior to disposal. Reacting waste chemicals in this manner reduces the amount of fresh chemical required for neutralization and can be defined as a reuse process. Waste caustics saturated with phenolic compounds can usually be sold to chemical companies specializing in the recovery of phenolics. Neutralized acid and caustic solutions can be discharged into the wastewater treatment system whenever the total dissolved solids limit of the NPDES pennit is not exceeded. Spent alkylation acid can be returned to sul- furic acid manufacturers for reprocessing.

5.4 Biological Sludges Digested biological sludges have long been used as

soil conditioners for lawns and flower beds. Most refineries have lawns and shrubbery on which dried biological sludge can be used. Usually the amount of biological sludge generated exceeds the requirements for grounds beautification. Biological sludge should not be used for growing food products but waste sludge may be spread in tank farm areas.

5.5 Filter Clays Filter clays used for oil and wax purification can be

regenerated in multiple hearth furnaces for reuse. A particular clay will withstand several regeneration cycles before particle size and reaction surface deteri- orate.

Waste filter clay is nonreactive and is amenable to landfill as an uitimate disposal method.

5-1

5-2 DAW MANUM-SOLVJ WASTES

5.5 Chromate Inhibitor Reuse ion exchange process. Stringent wastewater regulations I

have made this reuse process more attractive. The refinery engineer must always consider reuse of

waste materials in the design and development of his refining processes. Maximum recovery might be the difference between success or failure for a par- titular project.

Chromate continues to be one of the most effective corrosion inhibitors for cooling systems. Because of NPDES restrictions, the reduction of chromium content in wastewater has become imperative. Chromate can be recovered from cooling tower blowdown for reuse in the make-up water. This is accomplished by the


Volume on Solid Wastes Chapter &Treatment Prior to Ultimate

Disposal




CHAPTER &TREATMENT PRIOR TO ULTIMATE DISPOSAL

The largest volume of refinery wastes consists of sludges that result from wastewater treatment. tank cleanings, and flue gas scrubbing. These wastes contain hydrocarbons, water, and solids which must be reduced in volume prior to ultimate disposal. The objective of this volume reduction is to reduce overall disposal cost and to reduce technical problems in subsequent treatment steps. There are generally three steps, done in series, for the volume reduction of these oiVwaterlsolids sludges.

The first step generally utilizes gravity differential. that is gravity thickening or flotation. These are relatively low cost operations per volume of waste treated. They result in large sludge volumes for which disposal costs are usually prohibitively expensive. Therefore the next step is usually mechanical dewatering, such as centrifugation or vacuum. pressure, or gravity filtration. This mechanical dewatering equipment is inherently more expensive per ton of sludge treated. Investment. operating, and maintenance expenses are all generally higher. The final treatment step might be chemical fixation, incineration, landfarming, or composting which can be done prior to or as a part of ultimate disposal.

f ' 1.

6.1 The Importance of Concentration The importance of concentrating solids is easily un-

derstood when one considers that the doubling of solids concentration results in halving the volume for ultimate disposal. Therefore, increasing concentration from 1 to 2, or from 2 to 4 percent, is especially important because of the large reduction in volume. However, as the solids concentration is increased, the economic incentive decreases, because each percent increase in concentration is not as significant in terms of volume reduction. Also, the cost of further concentration becomes higher.

Because of new effluent regulations, wastewater treatment sludges have become the single largest source of sludge. These sludges are difficult to process because they are often gelatinous or oily. Furthermore, the phy- sical properties of wastewater sludge may change frequently because of turnarounds or changes in refinery

Selection of the concentration process depends on the characteristics of the sludge and the ultimate disposal methods available at the specific location. For

, operations. i

example, the sludge may be heavy and easily settled or light and easily floated. Land may be readily available at low cost for landfill or fanning, making the concentrating step less important. Or. land may be expensive and incineration may then be required to reduce sludge volume as much as possible. In the latter case, the concentrating step is quite important because of the high cost of incineration.

6.2 Sludge Concentration by Gravity Differential Met hods

6.2.1 GRAVITY THICKENING OR SElTLlNG

Dilute refinery slurries can be concentrated to approximately 1-7 weight percent by gravity. Concentra- tions of 1-2.5 percent are typical for biological sludges and 5-7 percent for oily pretreatment sludges which contain solids, such as rust and silt. Some sludges. such as lime sludge, coal ash. or incinerator ash, settle to higher concentrations and care must be taken if they are to be kept pumpable. Gravity thickeners may be round or rectangular and sludge is removed from the bottom by rakes or suction piping. Parallel plate devices used for streams handling dilute solids are generally not used for sludge concentration where the more concentrated feed may result in blocking flow between the plates.

Batch settling tests, using small sludge samples and laboratory glassware, can be conducted to determine the size of full scale equipment. These tests can be used to estimate final solids concentration in the underflow and the need for flocculation polymers. They also define the required area by providing information on whether the initial settling rate or the mass flux of the solids is the limiting parameter.

Final solids concentration obtained by gravity settling is a function of initial feed composition and depth of the settled sludge blanket. Other factors affecting sludge blanket concentration are listed here. 1. A higher oil-to-solids ratio in the feed results in less dense sludge. 2. Entrained air results in less dense sludge. 3. Use of polyelectrolytes increases the settling rate but decreases final sludge density. The extent to which polymers affect final sludge density varies greatly from one polymer to another. 4. Long retention time for biological sludge may result in an anaerobic biological growth and in merhane gas

6- 1

6-2 DRW M A N U A L ~ ~ L I O WASTES

-. Table 6-1-Sludge Source versus Solids Concentration

Initial Solids Final Solids Concentration Concentratton Solids Rate

Sludge Source ( W t c l o ) (wt%) ( Ibs/ft2/dav) (kgm’/dav) Filter backwash 0 1-1.0 4 0-8 0 6-8 3 0 4 0 DAF float 2-3 4 0-6.0 4-5 20-25 Biological sludge 0 5 1 .O-2.5 1-2 5-10

formation. The sludge blanket will become less dense and even rise. 5. Deeper sludge blankets. at equal retention time, will result in greater sludge density. However, above 3 feet (1 meter), the increase in density becomes less pro- nounced. ing total feed pressurization. Design values depend upon Ihr: specific sludge to be thickened; however, the values listed in Table 6-1 are typical.

feed pressurization, and (3) pressurization of a portion of the effluent, which is then recycled back to the feed. The recommended mode of operation is recycle pressurization. Recycle pressurization avoids problems with emulsification and floc shearing, which can occur dur-

Air flotation is the most effective means for removing free oil from process waste streams. At times. when using inorganic coagulants, suspended solids may increase. Use of polymers generally reduces suspended

6.2.2 AIR FLOTATION UNITS solids but may reduce oil rimoval efficiency. The oil-to- solids ratio of a Darticular waste will affect solids re-

After removal of the majority of free Oil in an moval and can ilso affect overall oil removal. The ranges of removals listed in Table 6-2 can be expected. Typical dissolved air flotation process design parameters are described in Table 6-3.

separator, the remaining 50-100 PPm free 0‘1 together with colloidal emulsions and suspended solids may be further reduced in a dissolved or induced air flotation unit (DAF or IAF). These units typically concentrate ’

sludge to 4-5 weight percent. The basic principle of either DAF or IAF is that air

bubbles attach to the suspended oil or solids causing the particles to float to the surface where they can be skimmed.

In dissolved air flotation, small bubbles are formed by dissolving air in water under pressure and then re- leasing the pressure to form small bubbles as the water becomes supersaturated. In induced air flotation. air is dispersed in the water at the vortex of a mechanical agitator. This reportedly results in a greater number of large size bubbles than that for dissolved air flotation.

To improve the flotation process, the suspended solids and oil are usually coagulated by addition of inorganic coagulants (usually alum) or organic flocculants (synthetic polyelectrolytes), or both, before introduction of the bubbles.

In dissolved air flotation, bubble formation can be obtained by (1) total feed pressurization, (2) partial

Table 6-24anges of Solids Removal for the Dissolved Flotation Process

oilm Suspended Solids Low High Low High

Effluent concentration. mg/l 6 37 3 37

Removal. percent 81 91 0 87

6.2.3 CHEMICAL FLOCCULATION

Chemical flocculation is another pretreatment or roughing treatment used for removing oil and solids. Because it involves settling. it is best suited where there is no opportunity for high oil content in the feed.

Chemical coagulation consists of adding chemicals to a coagulant chamber. Flocculated sludge is then al- lowed to settle. Some of the settled sludge is recir-

Table 6-+Typical Dissolved Air Flotation Process Design Parameters

~~~~ ~

Parameter Design Value Flotator nse rate 1.s2.0 gpm/ftl

Saturator tank presser

(3.7-2.9-m’lhr. m2)

5 0 6 5 psig (4.5-5.5 bar)

Recycle rate, percent of feed

Air supply rate to saturator

30-100

1.0 SCFllOO gal feed (0.075 m’lSTPlm’ feed)

15-20 min Flocculation tank holdup time

Coagulant dosage 30-ZM) ppm alum

Polvelcctrolyic dose 1 - 3 PPm

Float produciion percent bv volume on feed 0 . 5 3 . 0 % ’Extraction-infrared analysis.

TAUTMENT PRI~R TO ULTIMATE DISPOSAL 6-3

Table 6-4-Gravity Differential Processes

Dissolved Gravitv Air Chemical

Factors Thickening Flotation Flocculation Relative investment LOW Medium Low

Effluent water quality L O W ,Medium Medium

Operating cost LOW High Medium

Feed to which best suited Constant flow Contaminant Easily coaylared and sludge lighter than sludge heavier heavier than water than water water

NOTE: Induced air flotation has slightly lower investment. water quality. and operating cost than dissolved air flotation.

culated to the feed where it comes in contact with incoming contaminants and drags them down to the sludge blanket. The advantage of chemical coagulation is that the sludge blanket may contain a high solids concentration. The disadvantage is that an upstream oil spill may cause the sludge blanket to float and be discharged with the effiuent water. Furthermore, re-establishing the sludge blanket and efficient removal may require as much as a week, during this time contaminant removal efficiency is low.

Gravity differential processes producing sludge for further concentration are summarized in Table 6-4. <

the inner spiral of the vortex with most of t..e liquid and escape through the vortex finder opposite the apex end.

Liquid cyclones do not have high solids recovery efficiency. Many of the finer solids escape in the centrate. and the solids that are recovered are in a dilute suspen- sion. The advantage of liquid cyclones is their relatively low cost and the absence of moving parts.

Liquid cyclones have been utilized €or primary separation to remove coarse solids from tank bottoms or separator sludges. They have also been used to remove

6.3 Sludge Concentration by Mechanical Dewatering

6.3.1 CENTRIFUGATION Three types of centrifuges are used for processing

high solids content sludges-scroll, imperforate basket. and disc. Scroll centrifuges are frequently called solid bowl centrifuges; however, this is confusing since imperforate basket centrifuges also have a solid bowl.

Oily wastes containing a wide range of solids, oil, and water can be processed by centrifugation. Units have also been designed to process emulsions and oily sludges with high solids content, such as separator and tank bottoms.

6.3.1.1 Centrifugal Separators

A centrifugal separator, or liquid cycfone, is a com- pact, cylindro-conical classification unit, as shown in Figure 6-1, which utilizes centrifugal force in place of gravity. Feed enters the cylindrical section tangentially at suff-icient velocity to support the vortex action of the slurry in the uni t . Coarse solids thrown to the wall travel a spiral path axially to discharge at the apex end. Fine solids. less affected by the centrifugal forces, move to

SOLIDS 1 REJECTION

APEX

Figure 6-l-Centnfugal Separator

6-4 DRW MANUM-SOLID WMXS

UNOERFCOW

Figure 6 - 2 4 i s c Centrifuge

coke fines from water and reportedly do a good job so long as the water flow is kept at the required velocity and volume. Liquid cyclones are available in sizes ranging from 10 millimeters to 2 meters in diameter. At equal inlet velocity, finer classifications are achieved in the smaller sizes because of the greater centrifugal force. Large production volumes are readily handled by manifolding units in parallel, as required. The capacity of any cycione is a function of the pressure differential between feed inlet and overflow outlet. Standard units have certain fixed dimensions, such as cyclone diameter, feed inlet diameter, and cone angle. These factors set overall limits on the capacity and size for a specific application, which is a further limitation. The apex outlet may be controlled during operation to restrict the amount of discharge. The most important factor controlling separation is the relative specific gravities of the solids and the liquid. Other important factors include viscosity, solids concentration. particle size distribution, particle shape, and the generally complete absence of gas phase in the feed.

’

6.3.1.2. Disc Centrifuges

The disc centrifuge consists of a vertical bowl containing a concentrically mounted stack of inverted conical discs. as shown in Figure 6-2. Both the bowl and discs rotate at high speed and develop a separation force approximately 6OOO times that of gravity. The bowl contains peripheral novles or ports for discharge of the solids-containing stream.

Feed is introduced a t the top and flows downward and radially outward between the discs. Nozzles along ,he outer circumference of the bowl mamtam a back

pressure but allow heavier solids and some liquid to escape. To keep these small nozzles from plugging, most of the flow is recycled back through the bottom of the bowl. This results in high velocity and abrasion of the nozzles. Liquids and less dense solids, which do not escape through the nozzle, flow inward between the stacked discs. Effective separation takes place between these discs because of the short distance between plates that the heavier material has to travel.

One advantage of the disc centrifuge is that high gravitational force is applied and there is little turbulence between the discs. The disc centrifuge is well suited for separating two liquids having different densi- ties but is not well suited for separating solids from liquids, because of the tendency of solids to plug the small nozzle openings and the space between the discs. Another disadvantage is that maintaining flow through the nozzles requires that the solids discharge stream be rather dilute. The solids concentration of this discharge stream is about half of that obtained with other types of centrifuges.

)

6.3.1.3 Scroll Centrifuges

The scroll centrifuge consists of a bowl which may be vertical or horizontal. A helical conveyor. called the scroll or screw, is located within the bowl. It is driven by the same drive but is geared to rotate 75-100 revolu- tions per minute slower. As seen in Figure 6-3, sludge enters the centrifuge through the hollow conveyor shaft and discharges through a port about halfway down its length. Dense solids are carried by centrifugal force to the bowl wall and are then conveyed along the bowl wall by the conveyor toward the beach. The beach is the conical section of the bowl where liquid drains from the solids. The liquid drains to the cylindrical section of the bowl and discharges through overflow ports.

The scroll centrifuge is a relatively high feed capacity, low gravity-force machine, useful in separating heavy coarse solids at high feed rates. The discharged solids have a high solids concentration and are frequently not pumpable. A disadvantage of a scroll centrifuge is that the differential speed of the bowl and scroll causes turbulence. This affects solid-liquid separation and may require addition of polymers to assist in solid-liquid separation.

Because of its high feed capacity and relatively low solids recovery ability for oily or biological sludge. a scroll centrifuge may be used as a scalping machine before an imperforate basket centrifuge is used.

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6.3.1.4 Imperforate Basket Centrifuge

An imperforate basket centrifuge, shown in Figure 6-4, consists of a vertically mounted rotating bowl which

6-5 TREATMENT PRIOR TO ULTIMATE DtSWSi.

COVER

OlFFEAENTlAL SPEED

BASE NOT SHOWN CENTRATE SLUCGE CAKE DISCHARGE OISCHARGE

I 1

Figure 6-3-Scroil Centrifuge

c

ir

Figure 6-4-Imperforate Basket Centrifuge

6-6 DRW MANUAL-~LID WASTES

is open at the top and the bottom. Feed is introduced through a downcomer that directs the flow toward the wall near the bottom of the basket. Rotation of the bowl and fluid develops a force approximately 10oO to 1800 times that of gravity which forces solids to the outer bowl wall. Clarified liquid escapes at the top of the bowl, overflowing the lip. When the solids buildup reaches the capacity of the basket, the feed is stopped and pumpable solids are removed by a skim pipe. The basket speed is then slowed. and heavier solids are plowed out into a hopper or conveyor. Solids discharge is intermittent and consists of two types of solids, skimmed or pumpable and plowed or nonpumpable.

The imperforate basket centrifuge does not have the fine passages of a disc centrifuge and is, therefore, less apt to plug. Also, there is less turbulence than in a scroll centrifuge and this results in less abrasion and less need for coagulating polymers. The disadvantage of an imperforate basket centrifuge is the relatively low feed rate of generally 34-60 gallons per minute. Because of the automatic cyclic operation, smooth operation depends on the reliable operation of electro-mechanical components during the hundreds of cycles each day.

6.3.2 FILTRATION

The various types of mechanical filters which are generally used to concentrate sludges that have previously been gravity settled or floated are described here. Pres-

’ sure filters, vacuum filters, and gravity belt filters are included. Granular media filters which are used for water treating are not included. Granular media filters require a more dilute feed and do not concentrate to as high a solids concentration.

6.3.2.1 Pressure Flltratlon

A pressure filter consists of metal plates covered by a fabric filtering medium. The covered plates are hung in a frame equipped with both a fixed and a movable head. The plates are forced together with a chamber left between the cloth surfaces. Sludge is pumped through a central opening in the plates to the cloth-lined chamber. Sludge is retained on the fabric and liquid is forced through the fabric to the plate surface where it drains away. At the end of the filtration cycle. the plates are separated, and the sludge cake is discharged from the unit. Feed pressures ranging between 80 and 225 pounds per square inch gage are common.

Pressure filters of the plate and frame type are generally not used for filtrarion of oily sludges or oily slurries because the filter media plugs rapidly This severely limits the filtration rate. If spent inert solids, such as

lime sludge, are available, they may be mixed with the waste to provide porosity and improve the ease of removal of the cake from the filter media.

6.3.2.2 Vacuum Filtration

The typical filter installation consists of a horizontal compartmented drum, which supports the filter media on its outer surface. The drum is rotated, partially sub- merged, in a tank containing the waste sludge. As each section of the drum passes through the tank. vacuum pulls the liquid inward and the solids are retained as a thin cake on the filter media covering the outer drum surface. As each section emerges from the liquid, a vacuum is maintained to dry the wetted cake. Cake is removed from the drum before the section reenters the tank, where the cycle is repeated. Because the drum has multiple sections, filtrate flow is continuous. Filtrate passes through a vacuum valve to a vacuum receiver, where it is disengaged from the air that enters the drum from the upper exposed portion of its travel (drying section). Filtrate is generally removed by a pump. Vacuum is usually applied to the drum through the filtrate receiver by vacuum pumps, although steam jet ejectors can be used. The feed tank is generally equipped with an agitator to maintain the solids in sus- pension. The filter media and method of cake discharge are selected to suit the particular application.

The filter media may be one of a variety of natural or synthetic fiber fabrics available in numerous weaves. With a fabric filter media, cake may be discharged by applying pneumatic pressure from inside the drum to loosen the cake at the end of the drying period just before it reaches a knife, which scrapes the cake from the surface. Some cloth-covered filters use a “string discharge” to remove cake. A series of strings wound around the drum lift the cake from the surface before the drum re-enters the liquid. Rates of 2 to 6 pounds of dry solids per hour per square foot of filter area are obtained when filtering biological sludges. Moisture content of the cake will vary depending upon conditioning and sludge type. For oily sludges, vacuum filtration may require adding an amount of inert solids to the feed equal to the dry solids content of the wastewater sludge.

When the sludge to be filtered contains material which trends to clog or “blind” the openings in the filter media, firtration rates are very low.. The precoat filter may then be used. A typical schematic diagram of precoat vacuum facilities is shown in Figure 6-5.

Precoating requires applying a layer of solids over the fabric as a filter media. A slurry of the precoat material, usually diatomaceous earth, is charged to the filter until a layer of solids, say 3 inches thick, is built up on the drum. In operation, the vacuum is maintained con-

TREATMENT PRIOR TO ULTIMATE DISPOSAL 6-7

3) SLUR& FEED AIR BLOW-BACK UNE

Figure 6-!%-Rotary Drum Vacuum Filter

tinuously. The solids are retained on the precoat surface while the liquid passes through and is discharged. As the drum is about to re-enter the filter tank, a doctor blade shaves off the accumulated solids plus a thick layer of the underlying precoat. The shavings drop to a hopper or conveyor. A mechanism is provided which continuously advances the blade as the filter drum ro- tates. The optimum advance rate of the blade allows maximum filtration rate at a minimum rate of precoat consumption. The advance rate can usually be adjusted over a range of 0.001 to 0.01 inch per revolution. In practice, dependent upon feedstock viscosity, a precoat may last anywhere from 10 hours to several days before the “heel” must be removed and a new precoat applied.

Vacuum filters can also be operated by adding the inert material to the feed forming a slurry, which is fed to the filter. By this feed conditioning, operations are similar to that of a precoat filter.

‘

6.3.2.3 Gravity Belt Filtration Gravity belt filtration is a newer technology for con-

centration of oily and biological sludges (see Figure 6-6). This process depends on the use of high molecular weight, usually electrically charged, polymers to coagu- late the sludge. After mixing sludge and polymer, the coagulated sludge is poured on a porous screen where free water drains. After the free water is drained, the remaining sludge can be pressed, removing water trapped in the floc, without forcing the sludge through the screen. The significant difference between gravity

belt filtrarion and pressure or vacuum filtration is that free water drains through the screen before pressure is applied to compress the sludge and blind the screen. Also, because a flocculation polymer is used to form large floc, the screen openings are much greater and. therefore, less apt to plug.

One advantage of gravity belt filtration is that slower speeds result in less maintenance than that required for centrifuges. The disadvantage is that the process depends on high-cost polymers, which are sensitive to pH and other changes in sludge characteristics.

6.4 Sludge Concentration by Incineration Incineration is the ultimate in volume reduction. It

results in an ash which must be landfilled. Gases are passed out the stack where particulates and acid vapors (CO,, SO,, and HC!), if present, are removed. Hydro- carbons present in the sludge reduce the amount of auxiliary feed required. The chief disadvantages are the high capital and operating costs. These costs, per ton of waste incinerated, are especially high for small incinerators and for large incinerators if not used to their full capacity. Therefore in evaluating the need and economics for incineration. three basic steps are required. First. make an accurate estimate of the amount and characteristics of the waste to be incinerated. Second. evaluate alternative disposal methods and types of incinerators. Finally, make an economic and environmental comparison of the alternatives. I

6-8 DRW MANUAL-SOLIO WGES

POLYMER FROM DILUTION NO STOPPAGE SYSTEM

FLOCCULATION

GRAVITY DRAIN

I I

I COMPRESSION ZONE I PRESSZONE 1 SHEAR ZONE 1 Figure 6-6-Gravity Belt Filter

A brief description of major types of incinerators and their application is included in 6.4.1 through 6.4.8.

6.4.7 BURNER-TYPE INClNERATORS

Burner type incinerators include several designs using steam or air to atomize wastes into a refractory- lined combustion chamber. With heavy sludges, rotary cup burners replace the atomizing nozzle. The refractory enclosure can be a simple open-ended retort, a

,vertical-cyiindrid fumace, or a rotary kiln. One advantage of the bumer-type unit is that its simple design and low cost favor several small incinerators located near process units rather than a large central disposal facility. However, its use is limited to applications where the waste can be atomized and combustion is essentially complete within the flame, that is, liquid wastes of high heat content.

6.4.2 FLUID BED INCINERATORS Fluid bed incinerators consist of a refractory-iined

cylindrical reactor containing a heated, fluidized sand bed (see Figure 6-7). Waste is injected into the 1600-1800 F bed where thermal cracking and burning occur. Combustion of light ends is completed in the after-burning section above the sand bed. Heat contained in the flue gas may be exchanged with incoming combustion air. Because fines from the sand bed are carried by the flue gas, a cyclone or a wet scrubber, or both, are usually required to remove particulates. Sand attrition and carryover require a periodic quartz or alu- mina sand makeup.

This type of incinerator generally handles all ma- rerials that can be injected into the bed using a progres-

sive cavity (screw) pump or screw-type feeder. Wastes that become tacky prior to combustion can be burned if sand particle diameters are large enough to avoid ag- glomerization. Solid waste may also be pneumatically conveyed or fed through the top of the incinerator. The major advantage of this unit is its low sensitivity to varying waste heating content because of the intense agitation and the large heat sink of the fluidized bed. High investment cost is a major disadvantage. Another disadvantage is that the amount of air to fluidize the bed is a constant. This air must be preheated and may re- - I l I I L F I Ill

Figure 6-7-Fluid Bed Incinerator

TREATMENT PRIOR TO ULTIMATE DISWSM 6-9

quire 50 percent of the heat input. This makes fuel utilization very inefficient when the incinerator is operated at reduced sludge feed rates.

6.4.3 MULTIPLE HEARTH INCINERATORS

The multiple hearth incinerator consists of a series of circular hearths placed on above the other and enclosed in a refractory shell (see Figure 6-8). Sludge is fed to the outside of the top hearth and moved by rotating rabble arms to the center, where it drops to the next level. Rabble arms move the sludge on this hearth in a spiral path to the periphery, where it drops through openings to the third hearth and so on. In a standard six hearth model, sludge is dried on the first and second hearths, burned on the next three, and the ash cooled in the sixth. Combustion air is preheated as it cools the center shaft and rabble arms. It is further heated as it cools ash on the bottom hearth before warming the incoming sludge. These features increase the thermal efficiency of this design and reduce auxiliarj fuel requirements.

The multiple hearth has long been used for municipal sludge disposal with more than 100 installations in the United States. Wastes with large particles (approximately 1 inch or larger) or wastes which become sticky and form crusts when heated may interfere with rabble arm operation and are not recommended for multiple hearth disposal. Wastes which are too soupy to form ci

A/coouffi MSCHAAGE

FLOATING DAMPER SLUDGE

/INLET

FLUE GASES

COOLING AIR FAN

Figure 6-&Typical Multiple Hearth Incinerator

furrows when rabbled are also not suited for multiple hearth incineration. Another disadvantage of multiple hearth incinerators is that moving parts in the high temperature zone are susceptible to thermal damage and corrosion.

6.4.4 MONOHEARTH INCINERATORS

The monohearth or single hearth incinerator with rotating rabble arms is also available. Waste is fed from above to the grate where rotating arms agitate the waste and move ash outward toward hinged grates at the hearth’s periphery. At intervals the outer grates are dropped, dumping ash into a hopper below. Off-gases pass through a refractory stack. This type of incinerator has also been widely used in the United States for municipal refuse disposal with over seventy installations completed. The major disadvantage is its size; the smal- lest available unit is rated at 50 tons per day of refuse. Few refineries generate sufficient waste to justify this size incinerator.

6.4.5 GRATE-TYPE INCINERATORS

Grate-type incinerators are used for trash destruction. These incinerators are not suited to most refinery sludges since the unburned sludge runs through the grate.

6.4.6 ROTARY KILNS The rotary kiln is a slightly-inclined, refractory-lined

rotating cylinder (see Figure 6-9). Thick sludges and solids are fed via a belt or screw conveyor; pumpable wastes can be sprayed into the kiln with an atomizing nozzle. The rotary kiln is suitable for disposing of large solid waste containers, for example, fiber drums. I t can also handle liquid wastes but at a reduced capacity. The waste is heated and dried in the first few feet of the kiln and burned in the remainder. Auxiliary fuel burners in the afterburning chamber complete the combustion of soot and vapors liberated in the kiln. The rotating action of the kiln agitates the waste, thereby exposing each waste panicle to 1400 F gases in the kiln.

The design of a rotary kiln is complex; computers are commonly used to optimize designs. The objective is to completely bum the maximum waste quantity and particle size expected. This is a function of temperature. retention time, and degree of agitation. These latter two variables in turn depend upon kiln diameter, length, inclination, and speed of rotation. In addition, the size of the afterburning chamber is based on the combustion characteristics of the soot and vapors liberated in the kiln. An advantage of this design is its flexi- bility in handling wastes with wide!? varying character-

6-10 DRW MANUAL-SOLID WASTES

FUEL

Figure 6-&-Rotary Kiln Including Afterburning Facilities

istics. The major drawback is the potential mechanical * problems inherent in rotating the large (typically 5 to 10

feet in diameter) kiln. Problems have been reported with wastes that ball up in the kiln or cake on the refractory, resulting in incomplete combustion and smoke and odors.

6.4.7 INCINERATOR DESIGN CONSlDERATlONS

Incinerator design requires close cooperation with the incinerator vendor after the characteristics and amount of sludge are known. Specific design considerations depend on the type of incinerator being considered. General factors include: 1. The quality of the feed, including variations in composition, production rate, and combustion characteristics. For example, will the feed to a fluid bed incinerator form a low melting eutectic which will bog a fluid bed or will corrosive fumes attack metal rabble arms. 2. Control of incineration temperature to ensure complete and safe combustion with minimum maintenance and operating costs. The need for auxiliary fuel, the control of excess air, turbulence, or mixing heat transfer and residence time in the combustion zone must be considered. 3. Control of air pollution due to incomplete combus-

tion, emission of particulates, or the generation of nox- ious gases. Care must be taken not to create a water pollution problem when seeking to control the air pollution problem. 4. Selection of a proper and workable feeding mechanism. 5 . Proper design of grates or other means of controlling the passage of solids through the combustion zone and subsequent discharge of ash. 6. Provision of adequate facilities for handling ash without emitting dust. 7. The economics of heat recovery.

6.4.8 PYROLYSIS

Pyrolysis is defined as heating of the waste in the presence of less air than would be required for complete combustion. By doing this some of the hydrocarbon is utilized and some may be partially oxidized. These materials along with complete products of combustion are burned in an afterburner for heat recovery or, by con- densation, some material may be collected as a liquid For subsequent use as a heat or hydrocarbon source. Regeneration of activated carbon is also a pyrolysis process with the limited oxygen being used to prevent complete destruction of the carbon.

TREATMENT PRM TO ULTIMATE DISPOSAL 6-1 1

To date multiple hearth incinerators have been commonly used for pyrolysis since: (1) Counter current flow of sludge and gas increases efficiency; and (2) a minimum air flow for fluidization of a bed is not required.

Pyrolysis is most effective for wastes with high organic content and low moisture. If water exists in the feed, more of the organic matter in the feed must be used as fuel to heat and vaporize the water. This in turn requires the use of more air and thus more energy to heat the air. Preheating of combustion air with flue gas can minimize this.

An energy balance should be the first step in evaluating pyrolysis. The second step would be a laboratory evaluation, called differential thermal analysis, to estimate how much hydrocarbon might be recovered. During this procedure, a small sample is heated slowly

-

in a muffle furnace, and the off gases are collected and analyzed.

Recently an infrared incinerator has been introduced for activated carbon regeneration and sludge incineration. This incinerator shown in Figure 6-10 consists of a metal mesh belt traveling through a well insulated chamber. Silicon-carbide rods heat the sludge or carbon. For activated carbon, a limited amount of air flows cocurrent to the carbon. For sludge incineration, air flow is countercurrent. The advantage claimed for this incinerator is that air flow, sludge. or carbon residence time and temperature can be controlled independently. This incinerator seems to have promise for pryolytic processes such as carbon regeneration or sludge pyrolysis when the sludge is nearly autogeneous.

Figure 6-1 0-Infrared incineration System

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Volume on Solid Waste Chapter 7-Ultimate Disposal


American Petroleum institute



CHAPTER 7-ULTlMATE DISPOSAL

.

7.1 Landfill 7.1.1 GENERAL

.A landfill is essentially a well operated, environmen- tally safe disposal area. It is not an open dump. In a proper landfill, groundwater is protected by providing a low permeability layer of natural or artificial material in the bottom of the site or by locating the dump where such a natural bam‘er exists. Regulations will probably require a leachate collection and treatment system arid a system of monitoring wells to assure the integrity of the groundwater protection program. The air is protected and vectors are controlled by periodic covering, at least daily, of the wastes with soil as they are deposited. Surface water is protected by diversion of storm runoff from the disposal site and by collection and freat- ment of runoff from active portions of the landfill.

A major concern of the landfill operator is the potential hazards presented by the diverse wastes to be handled. Such hazards include flammability, corrosi- tivity, toxicity, reactivity, compatibility, and patho- genicity.

The generator of wastes will be required to define these hazardous characteristics so the disposal site operator can provide appropriate handling. It is expected that the ultimate responsibility for the safe disposal of wastes will be shared by the generator and the disposal site operator. Therefore, it is important for the generator. to maintain dose contact with the disposal site operator to be assured that the operation continues to be conducted in a satisfactory manner.

7.1.2 SAND-LIME STABILIZATION

Sand-lime stabilization is a process for converting viscous oily semi-liquid sludges into dirt-like landfill material. The process can be used to convert “silt ponds” into soil suitable for construction.

Specific formulations must be determined by laboratory testing of representative sludge. In general, SO percent dry sand is mixed with 5 percent calcined lime (CaO) with the balance being the sludge to be stabilized. Belt conveyors, with continuous belt scales. meter the sand, lime, and sludge to a mixer (the pug mill). The mixer intimately mixes the components and deposits the mix on a conveyor from which i t is deposited in piles on the ground. There is no immediate

change in appearance or texture: however, after several days the material cures. A distinct color change marks the curing process. The oily appearance is lost. and physically the material has the texture of soil. It may then be used as backfill.

The process doubles the volume of material and is generally economical only if there is a nearby low cost source of suitable sand. There is some fixation of oil, possibly chemical; however, it is not as effective as in higher cost chemical fixation techniques.

7.1.3 CHEMICAL FiXATION

The use of fly ash as a component of concrete is a form of chemical fixation of a solid waste. The addition of lime and cement to a mass of wet sludge solids will yield a solid approaching the criteria for ultimate disposal. However, the resulting large increase in volume. about 100 percent, is a serious disadvantage. In recent years proprietary methods of chemical fixa-

tion have been developed. Methods used to stabilize flue gas scrubber sludges

employ lime and blast furnace sludge and result in a handleable solid material of improved leachate stability and suitable for landfill or cover on municipal disposal sites.

Another more costly method employs soluble silicates and has been used with limited success for oily sludges. Polyvalent metals contained in the sludge react with the silicates to form insoluble silicates in the form of a gel. The gel formation entraps the sludge particles (solids and oil) and water is retained in the gel mass in somewhat the same manner as it is retained in a sponge. The additive acts as a setting agent and can be propor- tioned to obtain either rapid or slow setting. Leachate studies on inorganic sludges stabilized in this manner have shown excellent chemical stability. Caution should be used for oily sludge since the oil may become mobile over a period of time.

7.2 Landfarming of Oily Sludge 7.2.1 GENERAL

Landfarming is a disposal process in which naturally occurring soil bacteria are used to degrade either biological or oily sludges. This process is similar to the

7-1

7-2 DAW MANUAL-SCLIO WASTES

decomposition of leaves in a mulch pile or the disap- pearance of grass clippings from a lawn. In each of these processes, bacteria use the organic materials as a food. producing carbon dioxide and additional bacterial cells.

To develop a successful landfarm operation. it is necessary to provide the proper environment for bacterial growth. The major parameters which limit growth in the presence of a feed substrate are oxygen. nutrients, the soil pH, and temperature. Oxygen is supplied to the soil by disking, rototilling, or blading with a bulldozer. It is also supplied by natural oxygen transfer as the soil "breathes." In addition to oxygen transfer, the mixing or tilling of soil facilitates degradation by dispersing the sludge. Micronutrients such as calcium, magnesium, and boron are generally available from the soil; however, the level of the macronutrients, nitrogen, potassium, and phosphorus, is generally below that required to obtain maximum degradation rates. These nutrients can be added by applying an agricultural fertilizer to the landfarm area. Several studies in both laboratory and full-scale operations have shown substantial increases in degradation rates with the addition of fertilizer.

Similarly, soil pH can be raised by the addition of agricultural limestone to acidic soils. The maximum degradation rate will be obtained in the.pH range of six to eight. Lower pH should be avoided to reduce solubility of metals.

The soil temperature is an uncontrollable parameter. If possible, landfarm operations for oily sludge should be initiated during the spring and summer months. Once started bacterial growth, like crop growth. occurs over a wide range of soil temperatures.

7.2.2 PROCEDURE

A successful landfarming operation can be ensured by proper site selection, pH control, controlled oil-in- soil loadings (the amount of oil added per acre), nutrient addition, and aeration by tilling of the soil.

7.2.3 SITE SELECTlON AND DEVELOPMENT

The landfarm site should be relatively flat and the ground water level should be at least several feet below the surface. A wide range of soils has been used success- fully, but a loamy type is ideal. Problems have been encountered using soils with either a high clay or a high sand content. Clay soils tend to remain wet, thus ex- cluding oxygen and creating anaerobic conditions. Also, clay soils that do not drain well are generally difficult to t i l l . They do not aerate as well and maintaining traction of mechanical equipment is difficult.

Contamination of surface water by storm water runoff from a landfarm site must be prevented. The runoff can be controlled by providing berms around the perim- eter of the landfarm and by using a gate valve to control runoff which must be routed to a water treatment system. In the event of a storm soon after sludge application, this gate valve can be ciosed to prevent sludge from washing from the landfarm. Fish kills and con- taminations of surface waters have occurred when these precautions have not been taken.

\

7.2.4 OIL LOADING AND NUTRIENT AODlTlON

In the past little attention has been directed to the amount of sludge or to the oil content of the sludge added to a landfarm area. The generally-accepted procedure has been to add sludge to a depth of 1-6 inches and to allow it to dry (forming a thick cracked cake) before disking the oily sludge into the soil. Laboratory and full-scale tests have shown that thr: maximum rate of degradation is obtained when the initial oil-in-soil loading is maintained between 5 and 10 percent oil-in- soil. Oil levels of about 10 percent or higher, can pro- duce oxygen transfer and tilling problems. Higher oil levels have been applied where less-than-optimum degradation rates can be tolerated.

After analysis to determine the oil content of a sludge, the amount of sludge which should be added to obtain a given oil loading can be determined by use of a nomogram (see Figure 7-1). This nomogram was con- structed for a soil disking depth of 4 inches. The use of a different depth would require a proportional change in the amount of sludge added.

As shown by the dashed line (Figure 7-1). 1200 barrels of sludge per acre (1.86 acre-inches) of 24 percent oil-in-sludge would be required to give an oil loading of 7 percent. The amount of fertilizer required for nutrient addition is also given by this line. For a disking depth of 4 inches, 4066 pounds of 10-5-5 fertilizer are required. The weight percent of nitrogen, phosphorous, and potassium are indicated by 10, 5 , and 5 , respective!?.) Better results would be obtained by the use of two or more fertilizer dosages instead of one large addition. High fertilizer loadings can result in ground and surface water contamination.

7.2.5 SLUDGE DlSTRlBUTlON . AND TlLLlNG FREQUENCY

The sludge viscosity and distance to the landfarm will dictate the application method. For fluid sludges, a mud pump and irrigation pipe or fire hose can be used for short distances. but longer distances require the use of a vacuum truck. The flow and depth of iluid sludges can

L

30 4007062 1 7 4 2 3

26 ;4 ’ \

“s$2*4, y .?

,, 800 1900 zoo0 309

2 2 0 0 3 3 40

12

10 5808- 10

Figure 7-l-Graph for Estimating Oil Loading and Nutrient Requirements

be controlled by constructing mini-dikes two or three times the sludge application depth in each landfann plot. The sludge drying rate will be increased by disking prior to sludge application.

On the other hand, viscous or semisolid sludges, such = as tank bottom sludges, can be hauled by dump truck

and spread with a bulldozer or grader. All landfarms should be tilled at 2-to4 week intervals

between the last and first frosts or until the oil level in the soil decreases to 2 to 3 percent.

(

7.3 Landfarming of 8iological Sludge 7.3.1 GENERAL

Although landfanning has been used as a disposal method for biological sludges for many years, regulatory agencies have not as yet established design criteria (solids-soil loading levels, monitoring procedure, and so forth). The main requirement is that the sludge be stabilized to eliminate the possibility of odors or vector breeding within a landfann area.

Aerobic digestion is generally the method used to stabilize biologicai sludge. In this process the solids are aerated for periods up to 20 days. Durin: this period the bacteria utilize the accumulated cellular material. leav- ing the cell walls or “bacteria bones.” This material is nonputresible and resembles peanut hulls after drying.

7.3.2 LANDFARMING PROCEDURE

The design of a biological sludge landfarming area is the same as that given for oily-sludge landfarming (see 7.2). However, nutrient addition is not required since biological solids will contain nitrogen, phosphorus, and potassium.

Although data are limited. a loading of 20 tons of dry solids per acre per year appears realistic. The sludge may be applied as thickened or dewatered solids: however, application of the dilute sludge is just as effective and may be more economical providing the soil is kept aerobic; Aeration is not essential once the sludge is incorporated into the soil. However, periodic tilling of the soil does increase the degradation rate by maintaining aerobic conditions. It is expected that each state will adopt regulations with respect to loading, monitoring of the groundwater, and the metal content of the sludge.

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