Sludge dewatering

Wolfgang Stump

Öko-control GmbH; Burgwall 13a;

D – 39128 Schönebeck

Telephone: +49 (0)3928/42738; Fax: 42739

E-Mail: wolfgang.stump@oeko-control.com

Sludge dewatering

Outline:

1) The method of sludge dewatering

1a) Natural method

1b) Artificial methods

2) Need for (mobile) sludge dewatering

3) Problems with the (mobile) sludge dewatering

1a) Natural methods of sludge dewatering

Steps Treatment Effective by Individual processes

1. Step thickening gravitation continuous or

discontinuous operated

thickener

2. Step dewatering gravitation

evaporation

sludge basin

sludge drying bed

sludge lagoon

3. Step drying thermic forces sludge drying bed

(only in warm regions)

Sludge dewatering

Sludge lagoon

Sludge dewatering

1a) Natural methods of sludge dewatering

Sludge basins

– a nightmare for mobile sludge dewatering

Sludge dewatering

1a) Natural methods of sludge dewatering

Construction of a dry reed bed

Sludge dewatering

1a) Natural methods of sludge dewatering

Reed bed

Sludge dewatering

1a) Natural methods of sludge dewatering

Sludge dewatering

1a) Natural methods of sludge dewatering

Reed bed (gras)

Site clearance of a dry reed bed (reed)

Sludge dewatering

1a) Natural methods of sludge dewatering

Steps Treatment Effective by Individual processes

1. Step thickening gravitation continuous or

discontinuous operated

thickener

2. Step dewatering static methods

(Pressure differences

compared to the

atmosphere by low or high

pressure in the machine

dynamic process

Gravity (artificial gravity

field)

static methods

Vacuum filtration,

Belt filter presses

(Over) pressure

filtration

dynamic process

Centrifuges /

Decanters

3. Step drying Thermic forces dryers / dehydrators

(any sort / type)

Sludge dewatering

1b) Artificial methods of sludge dewatering

Static thickener – operated with moving turbid water pump or

with float and suction pipe

Sludge dewatering

1b) Artificial methods of sludge dewatering

Sludge storage with sample line for liquid removal

or connection for mobile dewatering; mobile belt filter press

Sludge dewatering

1b) Artificial methods of sludge dewatering

Stationary belt filter press

Sludge dewatering

1b) Artificial methods of sludge dewatering

Mobile Chamber Filter Press

Sludge dewatering

1b) Artificial methods of sludge dewatering

Filter cake from a chamber filter press

Sludge dewatering

1b) Artificial methods of sludge dewatering

Sludge storage and mobile decanter centrifuge with sludge storage

Sludge dewatering

1b) Artificial methods of sludge dewatering

Decanter centrifuge

Sludge dewatering

1b) Artificial methods of sludge dewatering

Stationary decanter centrifuge and sludge storage

Sludge dewatering

1b) Artificial methods of sludge dewatering

Sludge transport…

Sludge dewatering

1b) Artificial methods of sludge dewatering

2.) Necessity of (mobile) sludge dewatering

The only way for recycling of liquid sewage is the agricultural use

- Conservation of resources for society (savings of landfill space) and for agriculture

(replacement of mineral fertilizers)

- Recycling of organic matter and nutrients in agriculture as recycling process

corresponds to the cycle principle

- Agricultural use is a process with long-term experience on a secure legal and

scientific basis

- Recycling in agriculture is, in comparison to other means of disposal, a cost-efficient

solution

- Efficient organization and qualified service providers enable effective monitoring for

low-risk agricultural recycling

Sludge dewatering

The only way for recycling of liquid sewage is the agricultural use

Theses against the use of sewage sludge in agriculture:

- Risk of pollutant dispersion and enrichment in the environment and in the food chain

- Significant exposure to viruses, bacteria and hormones

- Through coincineration of sewage sludge fossil resources can be replaced

- Phosphorus compounds are, by additives in wastewater treatment, often not

available in the soil

Sludge dewatering 2.) Necessity of (mobile) sludge dewatering

The only way for recycling of liquid sewage is the agricultural use

The agricultural use is not always possible:

- High pollution load of the sewage sludge (exceedances of limits for metals, trace

organic substances)

- Acceptance problems among farmers and businesses in the food industry

- Adequate supply of nutrients in the soil - no / low fertilizer requirements

- No sewage sludge application during the growing season (just after harvest and

before sowing)

Sludge dewatering 2.) Necessity of (mobile) sludge dewatering

Any other recycling method for sewage sludge requires a solid state

of the sludge

- Composting

- Landscaping and reclamation

- Landfilling (banned in Germany)

- Combustion (coincineration or mono incineration)

Sludge dewatering 2.) Necessity of (mobile) sludge dewatering

3.) Problems of the (mobile) sludge dewatering

Depending on the type of sludge and the wastewater and sludge

treatment sludge can be dewatered good or bad

Factors:

- dry solids, organic content

- pH and organic acids

- fats / lipophilic substances

- sediment content, grain size

- binding forms of water to the sludge flocs

Sludge dewatering

In order to separate the sludge from the water well, flocculants – e.g. organic polymers – are added

- Flocculants to improve the separation of sludge and water

- Goal: high dry matters of the dewatered sludge and "clean"

sludge water (centrate, filtrate)

- the use of flocculants must be optimized; different sewage

sludges and fluctuating characteristics of the sludge require

different substances

Sludge dewatering 3.) Problems of the (mobile) sludge dewatering

Dewatered sludge is to be recycled as soon as

possible.

Sludge dewatering 3.) Problems of the (mobile) sludge dewatering

The sludge water (centrate, filtrate) is recycled to the wastewater treatment plant inlet and generates a high return of the plant load

- sludge water has high concentrations of chemical oxygen demand, total nitrogen

and ammonium nitrogen, phosphorus and suspended solids

- small WWTP often do not have the capacity of co-treatment of the sludge water

- private companies for mobile sludge dewatering are interested in a high throughput

and produce sometimes significant impact loads for the WWTP

Sludge dewatering 3.) Problems of the (mobile) sludge dewatering

Concentrations in sludge water and municipal wastewater

parameter sludge water

minimum

mg/l

sludge water

maximum

mg/l

Municipal waste-

water average

mg/l

CSB 400 8.000 500

BSB5 200 6.000 250

Nges 150 1.600 55

NH4-N 100 1.200 45

Pges 20 200 8

Sludge dewatering 3.) Problems of the (mobile) sludge dewatering

Sludge dewatering increases the possibilities of sludge disposal and reduces the cost at a reasonable cost

Opportunities:

- Profit from disposal of sewage sludge safety

- Saving of transport costs

- Reduce the amount to be disposed of

Risks

- Charge back to the wastewater treatment plant through sludge water

- Cost factor for sludge dewatering

Sludge dewatering 4.) Conclusion and Summary

Notes from the field - for smaller WWTP: Set quality criteria and dicharge load limit for sludge water

- accounting basis should be the tonnage of the dewatered sludge

- the dry solids content of the raw sludge and the dewatered sludge should be fixed in

a contract

- parallel provisions of the drainer and operator of the system in the dry matter

content

- limit the amount of daily sludge to be dewatered

Sludge dewatering 4.) Conclusion and Summary

4.) Conclusion and Summary

Sludge dewatering

Thank you for your attention and I look forward to your questions.

Wolfgang Stump

Öko-control GmbH Schönebeck

Phone: +49 (0)3928 / 42738