SLUDGE TREATMENT AND DISPOSAL

Presented to :- Dr. Baljinder

kaur

Presented by :- sudha chib

Roll no :- 130181107

CONTENTS

SLUDGE CHARACTERISTICS SLUDGE THICKENINGSLUDGE DIGESTION SLUDGE DISPOSAL

SLUDGE

Sludge is the concentrated impurities of waste water into solid form

Secondary

OrganicInorganic

WastewaterPre

Treatment

RockGritPlasticEtc.

PrimaryClarifier

SettleableSuspendedDissolved

SuspendedDissolved

SecondaryClarifier

Effluent

Sludge Sludge

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 fracction of solids and liquids in a slurry and expressed as mg/l

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 reactorAlthough some mixing occur in the zone of

active digestion and in the supernatant

HIGH RATE DIGESTERS

These are more efficient Require less volumeThe 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 recoveryThe second stage reactor is not heated

ADVANTAGES

Waste stabilisationOdour reductionScalable technologyLow capital costFuel based renewable/pack generation

DISADVANTAGES

No useful byproductRequired expertiseAffected 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 controlIt usually has lower ammonia concentration Explosive gases are not produced

DISADVANTAGES

Aerobic digestion is energy consumptiveTemperature dependentAerobic digestion does not produce energy

SLUDGE DISPOSAL

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

IncinerationPlacement in sanitary landfillIncorporation 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