SLUDGE TREATMENT AND DISPOSAL

Presented to :-

Dr. Baljinder kaur

Presented by :- sudha chib

Roll no :- 130181107

CONTENTS

SLUDGE CHARACTERISTICS

SLUDGE THICKENING

SLUDGE DIGESTION

SLUDGE DISPOSAL

SLUDGE

Sludge is the concentrated impurities of waste water into solid form

Secondary

Organic

Inorganic

WastewaterPre

Treatment

Rock

Grit

Plastic

Etc.

PrimaryClarifier

Settleable

Suspended

Dissolved

Suspended

Dissolved

SecondaryClarifier

Effluent

SLUDGE CHARACTERISTICS

Primary settling remove the settleable fraction of raw wastewater solids , the quantity of this solid on the dry mass basis can be determined as:-

Mp = ᶓ *SS * Q

Where Mp= mass of primary solids;kg/d

ᶓ = efficiency of primary clarifier

SS=total suspended solids in effluent

Q = flow rate ; m3/d

Secondary sludge is composed primarily of biological solids , the quantity of which can be estimated by:-

Ms= Y × BOD 5× Q

Where Ms = mass of secondary solids , kg/d

Y = biomass conversion factor

BOD5 =BOD5 removed by secondary treatment

kg/m3

Q = flow rate , m3/d

CHARACTERISTICS

Specific gravity :- sludge have specific gravity of 1.0

Solid concentration:- it defines the relative fraction of solids and liquids in a slurry and expressed as mg/l

Particulate size

SLUDGE THICKENING

Thickening is a procedure used to increase the solid content of sludge by removing a portion of the liquid fraction

Thickening is generally acomplished by physical means including gravity settling , flotation , centrifugation etc

Location of the thickener in a wastewater treatment plant is important.

A thickener operates like a settling tank

The feed enters from the middle , are distributed radially

The settled sludge is collected from the underflow

The effluent exits over the weirs

The thickening process takes place in settling tank with long enough solids retention time

GRAVITY THICKENER

Gravity thickeners contain pickets on the scraper cause a horizontal agitation .

It helps to release water trapped in the flocculent structure of the sludge

These are commonly used when suspended culture system sludges are to be thickened

These thickeners have ability to double the solid content of the sludge

SLUDGE DIGESTION

Sludge digestion serves both to reduce the volume of the thickened sludge still further and to render the remaining solids and relatively reduce pathogen

These goals can be achieved by :-

Anaerobic digestion

Aerobic digestion

ANAEROBIC DIGESTION

Anaerobic digestion is the most common method for dealing with the waste water containing primary sludge

The principle function is to convert as much of the sludge as possible to end products such as liquid and gases

Very less residual biomass as possible is produced

The anaerobic sludge digestion often divides the organisms into broad groups :-

Acid formers

Methane formers

ACID FORMERS

The acid formers consist of facultative and anaerobic bacteria and include organisms that solubilize the organic solids through hydrolysis

The soluble products are then fermented to acids and alcohols of low molecular weight

METHANE FORMERS

Methane formers consist of strict anaerobic bacteria

Acids and alcohols along with hydrogen and carbon dioxide are converted to methane

Pathway and products of anaerobic digestion

Sludge is fed into the digestor on an intermittent basis and supernatant is withdrawn and returned to secondary treatment unit

A typical standard rate anaerobic digester consisting of a single – stage operation

The conical bottom facilitates sludge withdrawal

Floating cover accommodate volume change due to sludge addition or withdrawl

Sludge separates in the reactor

Although some mixing occur in the zone of active digestion and in the supernatant

HIGH RATE DIGESTERS

These are more efficient

Require less volume

The contents are mechanicaly mixed to ensure better contact between the organics and the microorganisms

Unit is heated to increase the metabolic rate of the microorganisms

Optimum tempurature is around 35 ̊ C

Little gas is generated in the second stage

But the second stage is covered and is equipped for gas recovery

The second stage reactor is not heated

ADVANTAGES

Waste stabilisation

Odour reduction

Scalable technology

Low capital cost

Fuel based renewable/pack generation

DISADVANTAGES

No useful byproduct

Required expertise

Affected by changes in loading and conditions

AEROBIC DIGESTION

This process is essentially a continuation of the aeration process , with the volume being reduced by thickening in the secondary clarifier and sludge thickener

It is an endogenous respiration process

ADVANTAGES

The process is easy to control

It usually has lower ammonia concentration

Explosive gases are not produced

DISADVANTAGES

Aerobic digestion is energy consumptive

Temperature dependent

Aerobic digestion does not produce energy

SLUDGE DISPOSAL

Several options are available for the ultimate disposal of wastewater sludges, these include:-

Incineration

Placement in sanitary landfill

Incorporation into as a fertilizer

INCINERATION

Combustion process

PLACEMENT IN SANITARY LANDFILL

Disposal in landfills

INCORPORATION INTO AS A FERTILIZER

Injection of sludge into soil

REFERENCES

Environmental engineering by Howard S .Peavy

mimoza.marmara.edu.tr/~orhan.gokyay/enve425/ch2.pdf

www.eea.europa.eu/publications/GH-10-97-106-EN-C/download

http://www.lenntech.com/library/sludge/drying/sludgedrying.htm

www.maths.tcd.ie/~jlennon/miniprojects/biomass.doc

http://www.wrights-trainingsite.com/aerodigestion.html