Sludge Treatment

SLUDGE TREATMENT….

Pakistan Council of Scientific & Industrial Research Laboratories Complex, KarachiOff: University Road, Karachi-75280.

Pakistan Council of Scientific & Industrial Research Laboratories Complex, Karachi

Off: University Road, Karachi-75280.

Introduction…

Sludge refers to the residual, semi-solid material left from industrial wastewater, or sewage treatment processes.Waste water sludge is the mixture of waste water and settled solids.Depending upon the source it may be primary, secondary, excess activated sludge.

Pakistan Council of Scientific & Industrial Research Laboratories Complex, Karachi

Off: University Road, Karachi-75280.

Objectives…

To reduce the volume of the material to be handled by removal of liquid portion.

To decompose the organic matter and inorganic compounds for reduction in the total solids.


GOALS OF SLUDGE TREATMENT…Volume

reduction • Thickening • Dewatering

Elimination of pathogenic germs

• If used in agriculture as fertiliser or compost

Stabilisation of organic substances

Recycling of

substances

• Gas production • Reduction of dry content

• Improvement of dewatering

• Reduction of odour • Nutrients, fertiliser

• Humus • Biogas


Sludge handling and disposal includes:-

Collection of sludge Transportation of sludge Processing of sludge to convert it to

a form suitable for disposal Final disposal of the sludge


Composition…

Sludge from plain sedimentation tank- settable solids (raw sludge)

This gray in color contain garbage, fecal solids, debris.

Bad odor.From sec. settling tank following a

trickling filter consists of partially decomposed organic matter.

Dark brown in color, less odor than raw sludge.


Sludge types…Primary sludge

3 to 8 % solids About 70% organic material

Sec. sludge Wasted microbes and inert materials 90% organic material

Tertiary sludge If sec. clarifier is used to remove

phosphate, this sludge contain chemical precipitates.


Overview Wastewater treatment

Primary, secondary, tertiary sludge

Thickening

Stabilisation

Thickening

Dewatering

Drying

Incineration

Biogas

Agriculture

Disposal site

Construction industry

Atmosphere

Pro

cess

wa

ter


Thickening (volume reduction) by Gravity Gravity separation, similar to settling tank Additional mechanic stirring to enhance

flocculation and extraction of water and gas Supernatant is introduced to primary clarifier

or – if floatables and grease contents are high – to grid chamber Thickened sludge is withdrawn from hopper and introduced to sludge treatment

For an efficient thickening process the development of gas bubbles must be prevented


Gravity Thickener

Scum scimmerInflow

Sludgeliquor

Thickened sludge


Thickening by FlotationPre treatment: mostly chemical flocculation Sludge is placed in contact with air-saturated water (full flow or recycle pressurization) Air bubbles attach to solid particles

Floating Sludge bubble composite is collected

at the surfaceWater is recovered under a scum baffle and removed .


Thickening by Flotation


Sludge stabilization (mass reduction)

Aerobic digestionAnaerobic digestionAerobic sludge digestion may be

used to treat only Waste activated sludge Mixtures of waste activated siudge

and primary siudge Activated sludge treatment plant

without primary settling


Advantages Volatile solids reduction is equal that

obtained anaerobically Lower BOD concentrations in

supernatant liquor Production of an odorless, humus-like,

biologically stable end Operation is relativeluy easy Lower capital cost


Disadvantages A high power cost is associated with

supplying the required O2

A digested sludge is produced with poor mechanical dewatering characteristics

A useful by-product such as methane is not recovered


Process designFactors taht must be considered in designing

aerobic digesters include;

Solid reduction

Hydraulic retention time

Oxygen requirements

Energy requirements for mixing

environmental condition such as pH,

temperature.


Anaerobic digestion Sludge held without aeration for 10-90 days Process can be accelerated by heating to 35-

40oC These are called High Rate Digesters (10-20

days) Advantages

low solids production useable methane gas produced

Disadvantages high capital costs susceptibility to shocks and overloads


Basic Components of Anaerobic Digesters

Raw Sludge

Heat ExchangerCirculating Pump

Digester Gas

Digested Sludge

Mixing


Anaerobic digestion process

Complex Organics

CH4 and

CO2

Organic acids and

H2 Acid producing bacteria

(acidogens)

Methane producing bacteria

(methanogenics)


Three Mechanisms Occurring:Hydrolysis Process – conversion of insoluble high

molecular compounds (lignin, carbohydrates, fats) to lower molecular compounds

Acidogenesis Process – conversion of soluble lower molecular components of fatty acids, amino acids and sugars (monosaccharide) to lower molecular intermediate products (volatile acids, alcohol, ammonia, H2 and CO2)

Methanogenesis Process – conversion of volatile acids & intermediate products to final product of methane and CO2


Steps in anaerobic (oxygen-free) digestion:Particulate and complex organics

Soluble simple organics

Soluble simple organics Short organic acids

Short organic acids CH4 & CO2

Hydrolysis

Acidogenesis

Methanogenesis


Conventional anaerobic digesterHigh rate anaerobic digester



Anaerobic Digester Design Mean Cell Residence Time Volumetric Loading Factor Observed Volume Reduction Loading Factors Based on

Populations


Sludge dewatering Dewatering aims to reduce the water

content further. The sludge can then be handled like a

solid. Dewatering can be done mechanically

using a filter press (employing pressure or vacuum), or a centrifuge.

Also be done using drying beds.


Drying bedsMost popular methods.A drying bed consists of a 30 cm bed of

sand with an under-drainage .Sludge is applied on the sand bed and

is allowed to dry by evaporation and drainage of excess water over a period of several weeks depending on

climatic conditions.


Bacterial decomposition of the sludge takes place during the drying process while moisture content is sufficiently high.

During the rainy season the process may take a longer time to complete.


THANK YOU!!!

NIAZ AHMEDSOCES

PCSIR LAB COMPLEXCELL NO.

03333259613

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Sludge Treatment