Wastewater Engineering – (Info Gathered Online)

1) Sewage Characteristics 

 

Sewage is characterized in terms of its physical, chemical and biological composition. The main physical, chemical and biological constituents of domestic sewage may be summarized as follows: 

Physical Properties : Colour, Odor, Solids, Temperature 

Chemical Constituents : Organic - Carbohydrates, Fats, Oil, Grease, Proteins, and Surfactants Inorganic - pH, Chlorides, Citrogen, Phosphorus, Sulfur Gases - Hydrogen Culphide, Methane, Oxygen

 

2) Sewage Treatment Objectives

As populations increase by leaps and bounds, it places more pressure on the environment and threatening sources of fresh water supplies, it was recognized that the problem of 'human waste' needed proper management.

From the early 1900s there has been a steady evolution of sewage treatment into today's modern sewage treatment plants producing high quality effluent, which can be safely discharged to the environment or reused.

More recent developments in sewage treatment have been to improve the reliability and efficiency of treatment systems to treat sewage to meet standards and reduce the land area occupied by treatment works through accelerating natural treatment rates under controlled conditions.

However, despite these developments sewage treatment systems are still mainly concerned with the removal of suspended and floatable materials, the treatment of biodegradable organic and in some cases the elimination of pathogenic organisms.

Sewage treatment methods may be classified into physical unit operations, chemical unit processes and biological unit processes.

 

 

Physical Unit Operations Physical unit operations are treatment methods, which use the application of physical forces to treat sewage. These include screening, mixing, flocculation, sedimentation, filtration and flotation.

   

Chemical Unit Processes

Treatment methods in which the removal or conversion of pollutants by the addition of chemicals or by chemical reactions are known as Chemical Unit Processes. These include precipitation, adsorption and disinfection.

Biological Unit ProcessesBiological unit processes describe methods, which remove pollutants by biological activity. Biodegradable organic substances are converted into gases that escape to the atmosphere and cell tissue is removed by settling.

 

Oxidation Pond

Basic Biological Reaction in an Oxidation Pond

3) Sewage Treatment Methods

Historically unit operations have been grouped together to provide various levels of treatment. Preliminary and/or Primary Treatment refers to physical unit operations and is the first stage of treatment applied to any sewage. Secondary Treatment refers to biological and chemical unit

processes, while Tertiary refers to combinations of all three. Preliminary Sewage TreatmentPreliminary sewage treatment is defined as the removal of sewage constituents that may cause maintenance or operational problems with the treatment operations. This includes screening and comminution (grinding) for the removal of debris and rags, grit removal by sedimentation and flotation for the removal of excess oil and grease.

  Primary Sewage TreatmentIn primary treatment screening and sedimentation remove some of the suspended solids and organic matter. The effluent from primary treatment will contain high amounts or organic matter.

 Secondary Sewage TreatmentSecondary sewage treatment is directed at the removal of biodegradable organic and suspended solids, mainly using biological unit processes. Disinfection may be included in secondary sewage treatment.

 Tertiary Sewage Treatment

Tertiary sewage treatment includes the removal of nutrients, toxic substances including heavy metals and further removal of suspended solids and organic. Effluent from tertiary treatment is of a high standard and suitable for reuse.

There is no plan to build tertiary treatment systems in Malaysia. The focus has been providing a basic standard of preliminary, primary and secondary treatment.

 Sewage inflow

Preliminary Treatment

Primary Treatment

Secondary Treatment

Tertiary Treatment

effluent discharge

 

       

 

screening sedimentation activated sludge filtration grit removal floatation biofiltration disinfection grease tank

 

sedimentation tertiary ponds pre-aeration

   flow measurementflow balancing

removal of rags, rubbish, grit, oil, grease

removal of settleable and floatable materials

biological treatment to remove organic and suspended solids

biological and chemical treatment to remove nutrients and pathogens

4) Sewage Treatment Systems

Various methods of sewage treatment systems have been developed over the last fifty years to meet the need to protect public health and the environment. For urban centres where the population is concentrated and the receiving environment is not able to cope with the waste discharge, sophisticated treatment systems have evolved, which produces a high quality effluent. Simpler systems have been used to service small communities although ever increasing environment standards means that even these areas must eventually install better treatment systems.

 Sewage Treatment Systems For Urban AreasTreatment processes are divided into treatment, which utilises oxygen to breakdown organic matter (aerobic) and treatment, which doesn't utilises oxygen (anaerobic). The breakdown of organic matter can occur while in suspension (suspended growth) or on the surface of some type of media (attached growth). In addition, processes using ponds are also sometimes used where large areas of land are available. Treatment processes are categorised in this manner as shown in Table 1.

 

Table 1 Major Biological Sewage Treatment Processes

Aerobic Processes Suspended Growth Activated Sludge

   

- plug flow - complete mix- sequencing batch reactor - extended aeration * - oxidation ditch * - deep shaft * -Aerated Lagoons *

  Attached Growth Trickling Filters

   - low rate- high rate * - Rotating Biological Contactors * - Submerged Biological Contactors *

  Combines Biofilter Activated Sludge

    * Trickling Filter Activated Sludge

Anaerobic Process Suspended Growth Attached Growth

Anaerobic Contact Anaerobic Filter Expanded Bed

Pond Processes    

   Aerobic Stabilization (Oxidation) Facultative Anaerobic

 * Systems used in Malaysia.   Activated sludge, aerated lagoons, rotating biological contactors and trickling filters are the treatment systems most commonly used.

 Sewage Systems For Small CommunitiesBecause of their size, small communities have traditionally faced the problems of high per capital costs, limited finances and limited operation and maintenance budgets for sewage treatment.

Where populations are less dense, the receiving environment is able to cope with lesser level of treatment, often only primary treatment will be provided. However as population increases, these primary treatment systems must be replaced with secondary treatment systems.

Sewage treatment plants for small communities are now prefabricated before delivery to site and these are commonly known as "package plants". They are only suitable for small communities. Treatment processes are categorized in this manner as shown in Table 2.

 

Table 2: Commonly Used Treatment Systems for Small Communities

Primary Treatment

 Individual Septic Tanks Communal Septic Tanks Imhoff Tanks  

Secondary Treatment

 Package (pre fabricated) Plants- activated sludge systems- sequencing batch reactors- contact stabilization - rotating biological contactors  Individually Designed Plants- activated sludge systems (most popular) - oxidation ponds- sequencing batch reactors- rotating biological contactors- trickling filter- facultation lagoons - aerated lagoons  

 The use of package plants will be strictly controlled to ensure their long-term viability. In urban areas Individual Septic Tanks (IST), Communal Septic Tanks (CST) and Imhoff Tanks (IT) will be phased out.

5) PUBLIC SEWAGE TREATMENT PLANTS IN MALAYSIA

In Malaysia extensive use has been made of primary treatment systems such as communal septic tanks and imhoff tanks and unreliable low cost secondary systems such as oxidation ponds. In addition, large urban areas utilize Individual Septic

Tanks (IST). It is estimated that there are over one million individual septic tanks in Malaysia.

These tanks only partially treat sewage, discharging an effluent still rich in organic material. This has the potential to create public health and environmental problems, particularly in urban areas.

IWK is responsible for planning and rationalizing the public sewerage facilities to reduce the number of treatment plants using the "multipoint concept" or regionalization. Finally, sewerage pipeline networks will be layed in urban areas currently serviced by IST to convey the domestic sewage to modern secondary treatment facilities.

In Malaysia, 38% of public sewage treatment plants in the country are mechanical plants. These plants operate using mechanical equipment that accelerates sewage break down.

It is hoped that in the long-term, Malaysia's sewerage system will be made more efficient through the standardization of the types of plants used.

These extensive programs are nothing short of a revolution in the management of domestic sewage in Malaysia. The entire sewerage infrastructure can expect to undergo changes. Estimates have been made of the number and type of public treatment plants currently in Malaysia.

 

Table 1 : Public Sewage Treatment Plants in Malaysia

 No. Types of Sewage Treatment Plant As At Dec 2008

1 Imhoff Tank 760

2 Oxidation Ponds 436

3 Mechanical Plants 4,026

4 Network Pump Stations 668

  TOTAL 5,890

COMMUNAL SEPTIC TANK 3,635

 

The trend will be moving towards "mechanical plants" such as Extended Aeration (EA), Oxidation Ditch (OD), Rotating Biological Contactors (RBC), Sequenced Batch Reactors (SBR) and Trickling Filters. Careful management of this change will ensure the future of Malaysia's public sewerage systems.

 Domestic sewage treatment is mainly designed to produce an effluent low in solids and organic. However, other treatments, which remove the nutrients alter the pH or disinfect the effluent may be added depending on the receiving environment for the effluent.

Standards have been established for the quality of effluent discharged from treatment plants to receiving waters. These take the form of acceptable upper limits for various effluent contaminants. Effluents from treatment plants are regularly sampled and tested in laboratories to ensure that these standards are being met and that treatment plants are being operated correctly.

Effluent from Sewage Treatment Plant (STP) must meet standard A if there is water intake downstream of discharge point. Otherwise, standard B is sufficient. These standard was set by Department of Environment DOE)

 

Parameter Unit Standards

A B

Temperature C 40 40

pH Value - 6.0-9.0 5.5-9.0

BOD5 at 20C mg/l 20 50

COD mg/l 50 100

Suspended Solids mg/l 50 100

Mercury mg/l 0.005 0.05

Cadmium mg/l 0.01 0.02

Chromium, Hexavalent mg/l 0.05 0.05

Arsenic mg/l 0.05 0.10

Cyanide mg/l 0.05 0.10

Lead mg/l 0.10 0.5

Chromium, Trivalent mg/l 0.20 1.0

Copper mg/l 0.20 1.0

Manganese mg/l 0.20 1.0

Nickel mg/l 0.20 1.0

Tin mg/l 0.20 1.0

Zinc mg/l 1.0 1.0

Boron mg/l 1.0 4.0

Iron (Fe) mg/l 1.0 5.0

Phenol mg/l 0.001 1.0

Free Chlorine mg/l 1.0 2.0

Sulphide mg/l 0.50 0.5

Oil and Grease mg/l Not Detectable 10.0

  The pollutants in sewage are measured in order to better understand and thus facilitate the treatment of sewage as well as to examine the effects of effluent or treated sewage on the environment. Effluent from all public sewage treatment plants is sampled at regular intervals and tested in modern laboratories to ensure that it meets the required standards. Tests are carried out as part of a monitoring programme in keeping with Indah Water's operational license conditions and to ensure the efficient operation of treatment processes.

This provides for a cleaner and safer environment that improves the living conditions of Malaysians. The two most important parameters measured are Biochemical Oxygen Demand (BOD) and Suspended Solids (SS).

BOD is a measure of the amount of oxygen that sewage consumes over a given time. High BOD is significant because it means that sewage will rapidly consume all the naturally-dissolved oxygen in streams, rivers and lakes, thus killing off all aquatic life, and rendering the water septic and foul-smelling. SS is a measure of the undissolved material in sewage. High SS leads to sludge deposits in the waterways, thus causing significant environmental deterioration.

Effluent that is discharged upstream of a water supply intake should meet Standard A , while effluent that is discharged downstream has to meet Standard B. These standards are set by the Environmental Quality Act 1974.

Standard BOD (mg/L) SS (mg/L)

A 20 50

B 50 100

 

 6) Individual Septic Tanks (IST)

Individual Septic Tanks is one of the simplest forms of sewage treatment and dates back to the sewerage system development in France in 1860.

An IST comprises two chambers connected in a series. In the first chamber, solids from the incoming sewage settle forming a "sludge", while greases and oils float to the surface forming a "scum" layer. Effluent from between the scum and sludge layers then passes into the second chamber where further sedimentation occurs. Finally, the effluent leaves the second chamber and is discharged into a drain or allowed to percolate into the soil.

The sludge in the tank undergoes anaerobic digestion and is converted into more stable organic compounds and gases such as carbon dioxide (CO2), methane (CH4) and hydrogen sulfide (H2S). ISTs are usually designed for a 24-hour retention time. Enough storage capacity is provided so that scum and sludge can be deposited in the tank for up two years after which it must be desludged to keep the tank operating satisfactory.

ISTs are suitable for single dwellings or individual buildings with a population equivalent (PE) up to 150 and installed where there is no central sewerage systems and where effluent discharges will not adversely effect the environment. It is a cheap solution to disposing of sewage. However, ISTs only partially treat sewage and concentrated groups of tanks can overload the capacity of the receiving environment creating health and odour problems. There are currently over one million ISTs in Malaysia, making it by far the most common type of sewage treatment system. The figure below show the effluent from IST’s does not even meet DOE’s standard B (BOD effluent of 150-200, so far from BOD of 50 required)

Typical figures for ISTs are as follows: -

 (mg/L) Raw Sewage Effluent DOE Standard B

Biochemical Oxygen Demand 200-400 150-200 50 } not applicable to

Suspended Solids 200-350 50-100 100 } ISTs.

 

 

Population Equivalents (PE) In order to design pipe network, pump stations and sewage treatment plants, estimates need to be made of the volumetric flow rate which will be expected to be carried, pumped and treated. Such flow rates are measured in cubic metres per second and need to be calculated for both existing land use and for expected future development.

There are many methods for calculating expected flow rates. One method is to calculate a design parameter called the "population equivalent" (PE) of a catchment and convert this to a flow rate. The PE is an estimate of the usage made of sewage facilities. It is not a measure of population.For residential areas the population equivalent is calculated as five per dwelling and is a direct measurement of the population in an area.However for commercial areas it is calculated from the floor area, which is considered to be proportional to the number of people using a premises during the day. In this case it does not reflect the population living in an area.

The following table shows how the PE is calculated.

Type of Establishment Population Equivalent

Residential 5 per house

Commercial 3 per 100m2 area

Educational Institutions  

- Day Schools 0.2 per student

- Residential Schools 1 per student (residential)

Hospitals 4 per bed

Hotels 4 per room

Factories 0.3 per employee

Market (Wet Type) 3 per stall

Market (Dry Type) 1 per stall

Petrol Stations 18 per service bay

Bus Terminal 4 per bus bay

Taxi Terminal 4 per taxi bay

Mosque 0.5 per person

Church or Temple 0.2 per person

Stadium 0.2 per person

Swimming Pool or Sports Complex 0.5 per person

Public Toilet 16 per WC (water closet)

Airport 0.2 per passenger/day

Airport 0.3 per employee

Laundry 10 per machine

Prison 1 per person

Golf Course 20 per hole

  The PE may be converted to a flow rate using a simple formula such as set out in Malaysian Standards 1228 (MS1228).

Water Cycle ( note the suggested location of WTP and the STP.... Why? )

 

 

7) Oxidation Pond (OP)

Oxidation Ponds (or Stabilization Ponds) are a popular sewage treatment method for small communities because of their low construction and operating costs. Oxidation ponds represent 12 per cent (500 numbers) of all sewage treatment plants. New oxidation ponds can treat sewage to Standard B effluent level but require maintenance and periodic desludging in order to maintain this standard.

OPs may comprise one or more shallow ponds in a series. The natural processes of algal and bacteria growth exist in

a mutually dependent relationship.

Oxygen is supplied from natural surface aeration and by algal photosynthesis. Bacteria present in the wastewater use the oxygen to feed on organic material, breaking it down into nutrients and carbon dioxide. These are in turn used by the algae. Other microbes in the pond such as protozoa remove additional organic and nutrients to polish the effluent.

There are normally at least two ponds constructed. The first pond reduces the organic material using aerobic digestion while the second pond polishes the effluent and reduces the pathogens present in sewage. Sewage enters a large pond after passing through a settling and screening chamber. After retention for several days , the flow is often passed into a second pond for further treatment before it is discharged into a drain. Bacteria already present in sewage acts to break down organic matter using oxygen from the surface of the pond. Oxidation ponds need to be desludged periodically in order to work effectively.

OPs require large amounts of land and the degree of treatment is weather dependent. They are incapable of achieving a good standard of effluent consistently. It is this variation in performance, which require the gradual phasing out of this type treatment plant.

Depending upon the design. OPs must be desludged approximately every 10 years.

Typical figures for OPs are as follows: (note the BOD of effluent is much better compared to IST)

 (mg/L) Raw Sewage Effluent DOE Standard B

Biological Oxygen Demand 200-400 20-100 50

Suspended Solids 200-350 30-150 100

 

 8) IMHOFF TANKS (IT)

Imhoff Tanks are simple form of sewage treatment plants requiring very little operator skill. There is no mechanical equipment to maintain and operation consists of removing scum, reversing the flow to keep an even distribution of sludge and removing sludge.

Imhoff tanks constitute 24 per cent (800 numbers) of all sewage treatment plants in Malaysia and are the second most common form of treatment plant. They provide limited treatment of sewage and are not a suitable long-term solution. The effluent from Imhoff tanks can rapidly deteriorate if the tanks are not properly maintained.

An IT comprises two chambers positioned one above the other. In the upper compartment sedimentation occurs with solids passing through an opening into the lower chamber. Settled solids form sludge in the lower chamber and undergo anaerobic digestion. Gases from the lower tanks are discharged to the air. Scum is accumulated in the upper tank.

Sewage from the connected premises enters the sedimentation tank where settlement of solids occurs. Heavier solids settle at the bottom of the tank as sludge. Liquid effluent from the sedimentation tank then trickles through a rock filter bed. The sedimentation tank needs to be desludged regularly. Organisms living in the rock filter feed on the sewage, treating it in the process. Treated effluent is collected and discharged into a nearby drain. Usually, the sedimentation process in the upper chamber is followed by percolating effluent over a coarse stone media before discharge to a receiving water.

ITs are normally used to service small communities up to a population equivalent (PE) of 1,000. They are relatively cheap to install, operate and maintain. However, ITs, like ISTs, only partially treat sewage. The effluent from these tanks will not meet the environmental requirements of the Department of Environment (DOE). Small package treatment plants have more recently sur-planted ITs as the popular method of servicing small communities.

Typical figures for ITs are as follows: (note the BOD of effluent is still so high)

 

(mg/L) Raw Sewage Effluent DOE Standard B

Biological Oxygen Demand 200-400 50-150 50

Suspended Solids 200-350 30-150 100

  

 

 

 

9) PACKAGE PLANTS /MECHANICAL SEWAGE TREATMENT PLANTS Commercially available prefabricated treatment plants known as "package plants" are often used to serve small communities up to population equivalent (PE) of 5,000. Package plants require little design work and can be installed quickly although they require the same operational and maintenance care as conventional treatment plants. Claims that package plants produce no sludge is incorrect.Care must be taken in using package plants where large variations in flow (hydraulic shock are experienced), in addition adequate provision must be made for sludge removal, scum and grease removal and the proper control of air supply.

The most common types of package plants use Extended Aeration, Contact Stabilisation, Bio-Filter, Sequenced Batch Reactors and Rotating Biological Contactor processes.

 

  The performance of package plants can be improved by sizing the components conservatively. In general, the careful selection of the right process should lead to an adequate plant for small isolated communities requiring sewage treatment. A plant such as the one using an "Extended Aeration Activated Sludge" process should produce a good effluent quality, have low sludge yield and be easy to operate.

There are now a large number of package plants in the market using a variety of equipment. Uncontrolled selection of plants can lead to problems with operational knowledge and supply of spare parts. Hence, some form of regulation for the use of these plants will be employed to ensure overall industry efficiency.

Further, market forces have driven the manufactures to make optimistic claims for the treatment capacity of small package plants, leading to plants designed in the high rate activated sludge

mode in order to reduce the capital cost of construction. This often leads to high operational, maintenance and operator costs due to the need for high operator involvement to keep the plants running within the design parameters.

 

 

Package Plants (the various types)Aerated Lagoons

Extended Aeration Systems

Oxidation Ditch

Rotating Biological Contractors

High Rate Trickling Filter

 

 9a) Aerated Lagoons (AL)

 Aerated Lagoons are relatively simple plants to operate and maintain. However, they require large land areas and are therefore rarely found in densely populated urban areas.

The AL process normally comprises two or three lagoons in a sequence. The first lagoon has surface aerators, which are like large "paddle mixers". The aerators float on the surface of the pond and continuously stir the incoming sewage, serving to maintain oxygen content in the sewage and preventing any solids from settling.

Sewage has an average retention in the first pond of five days. During this time, bacteria consumed the oxygen to breaking down the organic material in the sewage.

Effluent is passed into the second pond where the degraded organic matter and sediments are settle out to form sludge. The effluent may then pass to a third pond for polishing or be discharged to a receiving waterway. The average retention time in the second pond is one day.

Care must be taken in managing the settling pond in warm climates. These ponds can suffer from algal growth and/or odour generated by anaerobic digestion of the sludge at the bottom of the pond. Depending upon their design these ponds must be desludged approximately every 10 years. Typical figures for effluent of ALs are as follows:

 (mg/L) Raw Sewage Effluent DOE Standard B

Biological Oxygen Demand 200-400 20-80 50

Suspended Solids 200-350 40-100 100

 There are approximately 40 AL sewage treatment plants in Malaysia.

 

9b) Extended Aeration Systems

 Fine Bubble Diffused Air Extended Aeration Systems (FBDAEA) are mechanical secondary treatment systems. FBDAEA systems are robust and can withstand surges in hydraulic or organic load.

To breakdown the organic material in sewage, bacteria require oxygen. This may be introduced by agitation (using surface aerators) or by submerged "diffusers".

As the name implies FBDAEA systems introduce air in the form of fine bubbles through

submerged diffusers. Fine bubbles promote higher oxygen transfer efficiency and are therefore used in preference to coarse bubbles.

Sewage entering a plant in passed through primary treatment where coarse material and grit is removed. The sewage then passes to secondary treatment in the form of any aeration tank where it is injected with fine bubbles of air from submerged diffusers.

Solids in the sewage are held in suspension by the bubbles and bacteria in the sewage break down organic materials. Sewage is held in the aeration tank between 18-24 hours.

The effluent with suspended material is then passed into a "clarifier" (sedimentation tank) where the material settles as a sludge. The sludge is drawn off with some being returned to the aeration tank to ensure enough bacteria are present in the tank to continue the process of breaking down newly introduced sewage.

The effluent is then polished and/or discharged to the receiving environment.

Typical values for FBDAEA plants are as follows:(note the BOD of effluent is very low)

 (mg/L) Raw Sewage Effluent DOE Standard

A

Biological Oxygen Demand 200-400 10-30 20

Suspended Solids 200-350 15-40 50

 FBDAEA systems can consistently produce a high quantity effluent. By monitoring the influent and effluent, the activity in the aeration tank can be adjusted to cater for variations in hydraulic or organic load. These plants only require moderate areas of land.

There are currently approximately 60 extended aeration systems in Malaysia and this is expected to significantly increase to some 200 plants as older systems are phased out.

9c) Oxidation Ditch

 The Oxidation Ditch (OD) is a modified form of the activated sludge system. Oxidation ditches are mechanical secondary treatment systems which are tolerant of variations in hydraulic and organic loads.

The OD consists of a "ring or oval shaped channel" equipped with mechanical aeration devices. Screened wastewater, which enters the ditch is aerated and circulated. ODs typically have long detention times and are capable of removing between 75% and 95% of the Biological Oxygen Demand (BOD).The proprietary "Orbal System" uses three channels or ditches concentrically placed. Each channel is independently aerated and can be configured to act in parallel or series with the other channels, depending upon the degree of treatment required.

After screening and grit removal, sewage enters the outer channel where most of the biological reaction takes place. The second channel is held at a slightly higher dissolved oxygen content for further BOD and nutrient reduction. The innermost channel is used for polishing the effluent before it passes to a clarifier.

Typical figures for ODs are as follows:

 (mg/L) Raw Sewage Effluent DOE

Standard A

Biological Oxygen Demand 200-400 10-30 20

Suspended Solids 200-350 15-40 50

 The ODs can be easily adjusted to meet most combinations of incoming sewage and effluent standards. This system achieves both high BOD reduction and some nutrient removal.

ODs require more land than other processes but can be cheaper to construct and operate. There are currently approximately 30 ODs in Malaysia. The new modified ODs in Malaysia are located in Sg. Besi - Kuala Lumpur, Bayan Baru - Penang and Cyberjaya.

9d) Rotating Biological Contractors (RBC)

 Rotating Biological Contactors (RBCs) are mechanical secondary treatment systems, which are robust and capable of withstanding surges in organic load. RBC's were first installed in Germany in 1960 and have since been developed and refined into a reliable operating unit.

Sewage entering a plant is passed through primary treatment where coarse material and grit is removed. The sewage then passes through one or more RBC units, which have historically been built in a variety of configurations.

An RBC unit comprises a series of closely spaced "circular disks" normally made from a plastic material. The disks are partially submerged in the sewage and are slowly rotated through it.

The rotating disks support the growth of bacteria and micro-organisms present in the sewage, which breakdown and stabilise organic pollutants. To be successful, micro-organisms need both oxygen to live and food grow. Oxygen is obtained from the atmosphere as the disks rotate. As the micro-organisms grow, they build up on the media until they are sloughed off due to shear forces provided by the rotating discs in the sewage.

Effluent from the RBC is then passed through final clarifiers where the micro-organisms in suspension settle as a sludge. The sludge is withdrawn from the clarifier for further treatment.

The Submerged Biological Contactor (SBC) is the modified version of the conventional RBC where the disks are 80% -100% submerged and forced air is introduced.

Typical values for RBC's are as follows:

 (mg/L) Raw Sewage Effluent DOE

Standard A

Biological Oxygen Demand 200-400 10-30 20

Suspended Solids 200-350 15-40 50

 RBC units are suitable where land is restricted. They are quite and consistently produce a high quality effluent. Because they are modular they are also suitable for a staged development. Operations and maintenance costs are lower than for other forms of mechanical treatment.

There are currently approximately 40 RBC plants in Malaysia

9e) High Rate Trickling Filter (HRTF)

 The first trickling filter was brought into operation in England in 1893.

The modern trickling filter comprises a bed of highly permeable medium to which micro-organisms are attached. Sewage is percolated or trickled through this media which is made from rocks (2cm to 10cm in size) or specially designed plastic.

Rock beds are typically 2 meters deep and are circular. A revolving arm is used to distribute the sewage over the media. Plastic media varies in design with depths ranging from 4 to 12 meters depending upon the organic load.

Filters under the media drain the effluent and biological solids, which have become detached from the media. Air is circulated back through the drainage system to the media. The effluent from the drain is settled before discharge to the receiving environment.

Some effluent from the drain is recycled to dilute the strength of the incoming sewage and to ensure the media remain moist.

As the effluent passes through the media organic material is absorbed onto the biological film or slime layer covering the media. Here is it degraded by aerobic micro-organisms. As the slime layer grows an anaerobic environment is created near the media interface. Eventually the micro-organisms at the media interface loose their ability to cling to the media and the slime is washed off. A slime layer begins to grow again and the cycle is repeated.

Filters are classified by hydraulic or organic loading rates. Classifications are low rate, intermediate rate, high rate, super high rate and roughing. Re-circulation of filter effluent permits higher organic loadings in high rate filters.

Typical figures for high rate trickling filter are as follows:-

 (mg/L) Raw Sewage Effluent DOE Standard

A

Biological Oxygen Demand 200-400 10-30 20

Suspended Solids 200-350 15-40 50

 High rate trickling filters remove between 65% to 85% of the organic load. They are used where there is sufficient land available and where a quiet operation is required. They can sustain some variation is hydraulic or organic load

10) Confined Space

SEWERAGE SYSTEMS CONFINED SPACE ENTRY COURSE (AGT lll) Many lives have been lost in 'confined spaces' throughout the world caused by poisonous gas related accidents. Most of the victims were wither overcome by toxic fumes or die of gas explosions. Almost all of the deaths were caused when working in 'confined space' or through the explosion of flammable gases, which could have been prevented or avoided.

 DEFINITION OF CONFINED SPACE (Department of Workers Safety & Health - JKKP(1) 04/98) A space, which:

• Is not intended as a regular work place i.e. continuous employee occupancy.

• Has restricted means of entry or exit

• Is large enough and so configured that an employee can bodily enter & perform assigned work and

• Is at atmospheric pressure during occupancy

 CHARACTERISTICS OF CONFINED SPACE

• contains or has a potential to contain a hazardous atmosphere

• contains material (solid or fluid substance) that has potential for engulfing an entrant

• has an internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls or by a floor, which slopes downwards and tapers to a smaller cross section or

• contains any other recognized serious safety or health hazards, e.g. rotors

 CONFINED SPACES

Some examples of confined spaces are sewers, manholes, chambers, wet and dry wells, sewage and sludge tanks, septic tanks, tanker barrels, air filter houses, chemical storage tanks, tidal storage tanks, underground tanks and reservoirs. Audits and tunnels, pipelines, bore-holes, reaction surge vessels, boilers, road tankers and the like.

Nearly all deaths involved in confined spaces are due to :-

• suffocation due to lack of oxygen

• poisoning caused by inhalation of toxic gases

• injuries caused by an explosion due to ignition of flammable gases

 

11) Ammonia

 Ammoniacal Nitrogen (NH3) 

 It is component of nitrogen referred as ammoniacal nitrogen, which is adopted as an indicator to determine pollution by sewage. Other component of nitrogen includes organic nitrogen, Kjeldahl Nitrogen, Nitrate and Nitrite. It is a natural product of decay of organic nitrogen compounds and one of the many contaminants in water supplies.

Ammoniacal Nitrogen is extremely soluble in water, reacting with water to produce ammonium hydroxide and one of the transient constituents in water as it is part of the nitrogen cycle, which is influenced by biological activity. The total nitrogen (TKN) content amounts to about 15% to 20% of the BOD5 in domestic effluent. Appended below is an approximate composition of medium strength domestic wastewater in terms of Nitrogen and its constituents.

 

Parameter mg/L

Total Nitrogen 35

Kjeldhal Nitrogen 35

Ammonia Nitrogen 25

Organic Nitrogen 10

Nitrate 0

Nitrite 0

 There are various sources of ammonia in rivers as follows:-

• fertilizers for land and agricultural developments

• uncontrolled landfill leachate and land development

• untreated sewage from poultry farms, reverine squatters, septic tanks, factories, makeshift and toilets at construction sites

• wastewater discharges from domestic, commercial, institutional and similar facilities

• wastewater and toxic chemicals discharges from different types of industries

• surface runoff and washouts resulting from rainfall

• oil, sullage (wastewater) from bathrooms and kitchens

•municipal sewage treatment plant effluent

 

 

 Under anaerobic conditions, ammonia is oxidized to nitrite and further oxidized to nitrate through nitrification process. Under anoxic (without oxygen) conditions, nitrate formed is then converted to nitrogen gas with no oxygen present through denitrification.

Excessive ammoniacal nitrogen in waterways can cause taste and (pungent) odor problems, apart from introducing a psychological problem to consumers, who will be under the impression that the water source is contaminated with sewage, even though this is not the case.

The self-purification capability of the waterways is an important concept. By understanding this concept, it will be clear as to why permissible limit of pollutants are discharged to the waterways. Otherwise, excessive discharges of pollutants will “kill” the natural waterways.

Some of the methods used for ammoniacal nitrogen removal are air-stripping (volatilization of gaseous ammonia), breakpoint chlorination (adding chlorine to oxidize ammonia) or ion exchange (type of clay – clinoptilolite for removal of ammonia). It can also be removed from water sources at the raw water intake point or in a wastewater treatment plant. The rate of removal of ammoniacal nitrogen is dependent on the self purification of the waterways/rivers, requirements of the effluent discharge or state of the art technology adopted by potable water treatment plants.

Currently, there is no standard for ammoniacal nitrogen discharge and all existing sewage treatment plants in Malaysia are not designed for the removal of ammoniacal nitrogen. However, on the average, the public sewage treatment facilities comply to the stipulated Standard “A” and “B” requirements as follows:

 

Parameter Standard A (mg/L) Standard B (mg/L)

Temperature (Celcius) 40 40

pH Value 6.0 - 9.0 5.5 - 9.0

Biological Oxygen Demand 20 50

Chemical Oxygen Demand 50 100

Suspended Solids 50 100

Ammoniacal Nitrogen 15 25

 The ammoniacal nitrogen in effluent discharged from sewage treatment plants is gradually diluted in the waterways and is reduced to a less toxic compound.

One of the most critical sources of pollution is from septic tanks and pour flush lactrines. There are over 1.2 million septic tanks in Malaysia and only 30% are well maintained i.e. sludge is removed regularly from the tank. Many users of this system neglected their responsibility to ensure that the sludge is removed regularly. Hence, accumulated sludge pollutes the waterways.

 

 

12) Green Technology  Bioeffluent. We can recycle wastewater for use as water supply. 

 

13) The Evolution Of Sewage Treatment

As societies moved from nomadic cultures to building more permanent sites, the concern over waste (solid and wastewater) disposal became an important concern. As we will see it has been an issue that has been dealt with many different ways and knowledge has been lost and regained. When groups were living as hunters and gatherers, the natural decomposition dealt with refuse and human wastes naturally. As cities developed other mechanisms were necessary to address waste issues. What we must understand "until recently, wastewater sanitation focused on minimizing health risks, primarily infections diseases. More recently, the scope of wastewater management issues has broadened to include chronic health risks and environmental concerns" (Burks & Minnis, 1994:1).

 Domestic Wastewater Treatment In The Ancient World> 3500 Before Common Era (BCE) To 500 Common Era (CE)During the Neolithic period (10,000 BCE) movement by nomadic tribes addressed the waste created by human activities. This nomadic movement allowed the earth or the soils treat the waste. In the ancient world cultures or societies developed waste treatment technologies. These varied by the skills the various cultures developed. The City of Ur, by 3500 BCE, had an average population of 65,000 people per square mile (a high population density which produced considerable waste). The populace of the city dealt with their waste problem by simply sweeping their wastes into the streets. This caused the street levels to rise and would require, every so often the raising of house doors. These "[practices that were satisfactory in semi-permanent small villages were not necessarily suitable in an urban environment" (Savas, 1977:11). Nor are these practices acceptable today. We can compare this to cities of the Indus Valley (present day Pakistan) from about 2500 to 1500 BCE Some houses had bathrooms with water flushing toilets. They had well-designed drainage systems. Houses had rubbish chutes, and there were rubbish bins placed around the city for refuse disposal. This was a great leap in waste treatment. (Kahn, 2000:119; Savas, 1977:11).

Moving back to the Mediterranean cultures, we see developments in waste treatment technologies. In the Egyptian city of Herakopolis (BCE 2100), the average person treated their wastes much like those in Ur, they threw the wastes into the streets. However, "in the elite and religious quarters, there was a deliberate effort made to remove all wastes, organic and inorganic to locations outside the living and/or communal areas, which usually meant the rivers." There is also religious teachings that dealt with waste. Mosaic law (BCE 1300) tells "to remove his own refuse and bury it in the earth." Nehemiah tells of rebuilding Jerusalem where there was a refuse gate where the city wastes were to be dumped. And the Talmud called for the streets of Jerusalem to be washed daily (Savas, 1977:12).

The Minoan Culture on the Island of Crete between 1500-1700 BCE had a highly developed waste management system. They had very advanced plumbing and designed places to dispose of organic wastes. Knossos, the capital city, had a central courtyard with baths that were filled and emptied using terra-cotta pipes. This piping system is similar to techniques used today. They had flushing toilets, with wooden seats and an overhead reservoir. "Excavations reveal four large separate drainage systems that emptied into large sewers built of stone." The Minoan royals were the last group to use flushing toilets until the re-development of that technology in 1596 (Kahn, 2000: 119-120).

The first 'dumps' was developed by the Greeks (Athens) circa 500 BCE In the development of waste management, Athens, in 320 BCE, passed the first known edict banning the disposal of refuse in the streets. In the continued development of waste management, by 300 BCE, one of the responsibilities of the Greek city-state was the removal of waste. "The expenses [for waste removal were] covered by levees on landowners. This system was sufficiently viable to last for eight hundred years, until the general breakdown of civic order"(Savas, 1977:13). In the use of water the early Greeks understood the relationship between water quality and general public health. This concern was passed onto the Romans.

The Romans' waste treatment management practices were the most developed of any civilization prior to the nineteenth century. In fact, the Romans' waste management systems were better than those in the middle age. The Romans were very advanced technologically. We see the evidence of this in their buildings, roads, and aqueducts that are still standing and in some cases still in use. The Romans' concern for water is best illustrated in their aqueducts. They developed them to provide water to their cities. The water was used for baths, fountains, public conveniences, and for flushing sewers. The Romans were concerned with locating good

water supplies, and they were concerned with obtaining pure water, as stressed by ancient physicians and engineers (History of Technology Vol. II., 1956: 660-674).

The early Roman Republic was concerned with the extension of the city's water supply, as well as the construction of aqueducts. In fact by 125 BCE, the city's water supply had been doubled to meet the rapid expansion (History of Technology Vol. II., 1956:670). The development of these aqueducts required engineering skills. What we must understand, is the aqueduct systems developed by the Romans were vast. In every part of their Empire they built aqueducts, and the majority of the systems were underground. What we see today is just the tip of the iceberg. As we have seen the Romans put the water to many uses. Particularly in Rome, they used the water to flush their sewers. "The Romans employed water-carrying devices to send most of their wastes to nearby the River Tiber via open sewers as early as the 6th century B.C.[E.]. By the 3rd Century, the sewers in Rome were vaulted underground networks called the Cloaca Mixima" (Burks & Minnis, 1994:1). These building projects continued and "by the 4th Century [C.E.], Rome had 11 public baths over 1300 public fountains, and 856 private baths. Not only were there private water-flushed toilets, there were public ones. In [C.E.], 315 Rome had 144 [public water-flushed toilets]" (Kahn, 2000:121).

Even with all these advances and waste management, Rome was still an unhealthy city. Disposal of the sewage to the Tiber River and dumping wastes outside the city still caused health concerns (Savas, 1977:14). The fall of Rome, in the fifth century C.E., brought an end to plumbing development (Burks & Minnis, 1994:2). In fact "with the fall of the [Roman] Empire the lack of central authority and consequently of adequate public funds led to the decline of all public services. Their organization was left to private citizens or to municipal authorities. Only in certain large urban centers did even remnants of Roman systems survive" (History of Technology, Vol. II, 1956:689).

  Domestic Wastewater Treatment In The Middle Ages > 500 Common Era (CE) To 1500 Common Era (CE)The fall of the Roman Empire in the west turned an urban society into a rural one. "By 500 [C.E.], 'the taps were being turned off all over Europe; they would not be turned on again for nearly a thousand years: Sanitation technology entered its dark ages'" (Kahn, 2000:121). There was massive depopulation of Rome and most of the western Empire. The deurbanization of the west changed waste treatment. "The reduced population density, therefore, rendered traditional methods of waste disposal (tossing it out of the house) more viable" (Savas, 1974:14). Also, without monitoring the sewers and streets, hygienic conditions fell below the Imperial Roman Standards (History of Technology, Vol. II., 1956:689-690). This demise in sanitation brought back "the outhouse, open trenches, and the chamber pot ... at all levels of society" (Kahn, 2000:122).

This loss of knowledge and hygienic practice brought many problems. During the middle ages, "the ages-old practice of separating drinking water and human wastes was largely abandoned, and human wastes could easily migrate from waste pits into wells. Epidemics raged in the cities, but the relationship between excrement and disease was not recognized" (Burks & Minnis, 1994:2). In the middle ages people simply threw their waste into the streets. "Open gutters in the middle of the streets carried refuse, while rain-water pouring from the roofs was not properly drained. The streets, seldom paved, were often mud-pools from which the excreta of pigs and other animals leaked into wells and private plots" (History of Technology Vol. II, 1956:690). The habits of rural life, which might be harmless on the farm, could and did prove to be fatal in the growing towns of Medieval Europe. Over time in the Medieval era, cities began to grow. The size of the city was determined by the walls; this increased the population density, and with people still practicing their rural habits, the potential for disease developed. In this period the rivers of the two major European cities, London and Paris, were open sewers (Savas, 1974:14 and Kahn, 2000:122-124).

The sanitary conditions in medieval cities lead to rampant disease and death during the middle ages. The waste and excrement provided food for the rats, thus bringing disease-carrying ticks and fleas into human contact. "[D]iseases directly related to human wastes wiped out many hundreds of thousands of people in the Middle Ages. This included dysentery, typhus (which comes from bad sanitation and is highly contagious), and typhoid fever (from human feces and urine)" (Kahn, 2000:124). The conditions in medieval towns and cities as urbanization developed were very poor. The Greek and Roman concern with safe water was lost in this period. The technology to secure safe water was also lost.

As the middle ages went on, changes did occur. Most of the water changes in water issues were speared-head by religious orders. "Near Milan, the Cistercians introduced the use of city refuse and sewer water as fertilizers on their land about 1150 C.E. (History of Technology Vol. II, 1956:681-690). Even during the unwashed period, "many abbeys in Britain had piped water before 1200 [C.E.]. The Christchurch Monastery at Canterbury, for example, had running water, purifying tanks, and wastewater drainage from toilets, and the monastery was spared from the Black Plague in

1349" (Kahn, 2000:122).

By the end of the 12th and the beginning of the 13th centuries, changes began to take place. Following the major plagues of the 12th century, waste management became a priority. In 1372 Edward the Third of England proclaimed that "throwing rushes, dung, refuse and other filth and harmful things into the [Thames] shall no longer be allowed" (Savas, 1974:15). Following this line, in 1388 an act of Parliament "forbade the throwing of filth and garbage into ditches, rivers, and water" And by the late 14th century London had an organized scavenger system (people would go around and pick up dead animals); yet "[u]ltimately , legislation and scavenging tended to be relatively ineffective. This was not, however, because of ignorance but rather because offenders and offended alike were unable to devise adequate alternatives to the available methods of collection and disposal. Moreover, except for those in heavily polluted areas, popular opinion was very much against such measures" (Savas, 1974:15-16, History of Technology Vol. II, 1956:691).

During the Renaissance more concern was given to health and water issues. The cesspool was one of the technical developments of the Renaissance. It is a simple pit, which allowed solids to settle and the liquid to seep into the ground. Periodically, the cesspools would have to be cleaned out (Burks & Minnis, 1994:3). As the 15th century came to a close, there were other management changes that impacted sanitation. Henry the VI (England) established a Commission of Sewers, which "provided for severe penalties for the pollution of streams and made special provisions for the disposal of tanner and brewers wastes." Henry the VII outlawed slaughterhouses in cities or towns, because of the danger of disease for the people (Savas, 1974:16). There was a new awareness of the role that human and animal wastes played on human health by the end of the 15th century.

 Domestic Wastewater Treatment In The Modern World: 500 CE To 1900 CEIn the early modern period there was still little change in the understanding and disposal of human wastes. Wastes were still disposed of in rivers, and water sources were being contaminated. These practices were brought to the New World. As developments grew to cities, the Colonies had to address waste issues. In 1644 eighteen years after taking control of Manhattan Island, "residents were directed to take all wastes out of the fort," and in 1648 a law was passed prohibiting hogs and goats from running in the streets (Savas, 1974:17-19). The major changes in waste treatment came in the 19th century.

In 1860 Louis Moureas invented the "septic tank"; however, it would not be given this name until 1895. Septic tanks at this stage were large and were used to treat sewage from communities. "The main purpose of these tanks was to remove gross solids before discharge into the nearest stream or river." Here we see an understanding of removing the solids, a potential problem for public health. Nevertheless, a problem remained: "effluent was largely untreated and caused pollution of streams and rivers" (Kahn, 2000:135-136). The pollution of water was not solved by a septic tank. Even with pre-treatment, the need for disposal technology was becoming evident.

Edward Frankland, in 1868, developed trickling sand filter technology. He devised a system consisting of six-foot high, ten-inch wide cylinders, filling each with different medias like sand and soil. He then ran sewage at different doses through the different tanks. He calculated the capabilities of the different media in purifying the wastewater. Unfortunately, little data is available to report on at this time. The Experimental Station at Lawrence, Massachusetts, created in 1887, by the Massachusetts State Board of Health worked on disposal issues. "At the station in 1893, a sand bed was first used to filter the effluent from a septic tank , reducing the land areas needed for sewage disposal. The land acceptance rates were established to maintain an efficiently-working sand-filter" (Burks & Minnis, 1994:3-5).

What was driving these changes? Disease -- it pushed plumbing and disposal development. The scourge of the 19th century was cholera. The urbanization of cities and the industrial revolution also increasing city populations lead to increased human waste. In the mid-19th century a world-wide epidemic of cholera occurred. Cholera was worse in the poor areas, but even the wealthy were not immune (Kahn, 2000:123-125). The English physician John Snow discovered the relationship of cholera to water. He traced this disease from its origins in India and the path it took to Europe. Snow traced the contamination to public wells, which were being contaminated by privy vaults in the epidemic of 1854 in London (Kahn, 2000:125, Burks & Minnis, 1994:2-4). Thus, the sewer was developed. "The British engineers led the way in sewer construction and separation of wastes from drinking water" (Kahn, 2000:125). But this only took the issue of sanitation to the river. The pollution of the rivers, especially the Thames in London, began the call for sewage treatment. The need to solve this health care concern in large cities marked the 19th century as the beginning of municipal socialism (Savas, 1974:19-20). The classic example of this effort is New York City.

 A Case Study - The Development Of Wastewater Treatment In New York City

New York City provides an excellent case study in the development of wastewater management. In the 19th century New York City was a developing urban center, which lacked the infrastructure to deal with its wastewater. In the city in the early part of the century, "people obtained their own water from wells and cisterns and were responsible for discarding their wastes" (Goldman, 1997:11). Both water supply and waste disposal were private matters in the city. The city's efforts to manage waste were particularly ineffective. Each house was responsible for its waste disposal, which meant they built privies. "Regulations mandated that privies be constructed of stone, mortar, and brick and be dug at least five feet deep." The completed privies were also to be inspected. Even with what appeared to be a rigorous code, petitions for wood privies were regularly approved. The city would only get involved if privies overtly were a threat to public health. The other concern was privy vaults were meant to function as temporary storage for wastes, they were not for permanent disposal (Goldman, 1997:19-21).

The understanding of treatment of waste was very limited at this time. "The belief that running water purified effluents was widely held during the first half of the nineteenth century, so the potential for water pollution did not raise the concern that the 'nuisances' on land had" (Goldman, 1997:22). We see that, from time to time, the treatment was to dispose of particular obnoxious effluent from privies directly to the river. The treatment of on-site waste was, in a sense, vault and haul. Yet, the city did have a sewer system. The system that did exist in the early nineteenth century was developed to handle storm water. There was limited access to these sewer systems because of the limited access to water, which was needed to flush waste through the sewers. Before 1840 there were limited sewer developments; with the exception of a few wealthy neighborhoods, most of the city was left to wallow in dampness. The flood water carried street debris and animal wastes through the streets. "The earliest sewers were merely open trenches placed together in the center on the sides of a street." This was a health problem, because the sun would heat the standing water and quicken decomposition, producing an unhealthy brew (Goldman, 1997:40-45). In the early part of the nineteenth century, the treatment of waste in New York City was little different from the late middle age.

During this period sewers were done on a street-by-street basis. This could even be blocked if a people on the street were opposed to sewering. At this time those opposed to sewers "feared that sewers were unhealthy and generated offensive smells." This system precluded any possibility of an organized and integrated system. There was no overall design for the city to dispose of storm water, much less wastewater (Goldman, 1997:44-46). The limited water supply made a water-based waste disposal system unacceptable. However, with the arrival of the Croton aqueduct, water overwhelmed the existing sewer systems. This required a change in thinking regarding a water-based disposal system.

By the end of the 1860's physicians and engineers were part of the city management on full-time, year-round basis (Goldman, 1997:146). This change greatly impacted the development of public health issues and the development of sewering the city. The Croton Aqueduct Department laid 39,000 linear feet of sewers in 1865. By the end of the decade the department had laid an additional 271,000 linear feet. They were draining the city. "Each district was approached as an entity and treated in its entirety. A system of intercepting sewers was planned that took into consideration street grade and anticipated sewage volume. The goal was to ensure the smooth and continuous flow of sewage from small pipes into larger ones and finally to a limited and specified number of sites for disposal into the rivers" (Goldman, 1997:158).

The city put the economic resource to build sewers in the engineers' hands. And they built a comprehensive wastewater disposal system. Yet, even into the 1880's their project was still not complete. In some affluent neighborhoods problems still existed. "Property owners had built house drains but never connected them to sewers, so that the sewage discharged into the loose rock filling the streets. At other times, house drains emptied their contents into underground watercourses. All too often, property owners sought economy at the expense of efficiency and effectiveness" (Goldman, 1997:162). The task of sewering New York was a long and arduous task. The goal to sewer the city was achieved by public funding pushed by public health concerns.

The problems of wastewater treatment and reuse will always be a part of society's concern. The development of large or municipal treatment plants, which was considered the solution in mid-19th century, is no longer considered the answer. The cost of constructing these plants is too high, and most local municipalities cannot afford to build them, and the national government is not looking to help fund new plants. This is evident in the 1997 Environmental Protection Agency's Response to Congress On Use of Decentralized Wastewater Treatment Systems (EPA 832-R-97-001b).