Environmental Engineering Department

Firat University- Elazig

Activated sludge

prepared by : Shaimaa F. Tayb

Activated sludge Environmental Engineering department

Firat University – Elazig, Turkey Prepared by:

Shaimaa F. Alsadawi

Content 1 -Introduction

2 -the steps of the process

3 -the factors that effect ASP

4 -The benefit of ASP

5 -the problems that we found in ASP

Introduction The activated sludge is a process for treating sewage and  industrial wastewaters using air and a biological floc composed of bacteria and protozoa. Then mixture is aerated. After a certain amount of time, the activated sludge is allowed to settle out by sedimentation and is disposed of (wasted) or reused Sludge means the particles that produced in wastewater by the growth of organisms in aeration tanks .

The term ‘activated’ comes from the fact that the particles teem with bacteria, fungi, and protozoa .

The history of A.S. processesAs generally known, the activated sludge process was invented in England in 1913 – 1914. there were carried out lab-scale experiments at the Manchester for wastewater treatment plant. The experiments were prepared and performed by William Lockett . The ASP found soon its application also outside the UK. The first experimental activated sludge plant in USA was built in 1915, Even before World War II the ASP reached other continents then Europe and America. Thus the activated sludge process was installed for instance in Bangalore, India, Australia and South Africa.

The purpose of ASPIn a sewage (or industrial wastewater) treatment plant, the activated sludge process is a biological process that can be used for one or several of the following purposes:

1-oxidizing carbonaceous biological matter.

2-oxidizing nitrogenous matter: mainly ammonium and nitrogen in biological matter.

3-removing nutrients (nitrogen and phosphorus).

The steps of ASP -The process involves air or oxygen being introduced into a mixture of industrial wastewater combined with organisms known as mixed liquor. which reduces the organic content of the sewage.

-Once the wastewater has received sufficient treatment, excess mixed liquor is discharged into settling tanks for undergo further treatment before discharge. 

The processes-Part of the settled material (sludge), is returned to the head of

the aeration system to maintain bacteria population . -This fraction is called return activated sludge (R.A.S.). Excess

sludge is called surplus activated sludge(S.A.S.) or waste activated sludge(W.A.S).

-The function of the secondary clarifier is to separate the activated sludge solids from the mixed liquor .

Aeration Tank

Secondary Clarifier

Primary

Effluent

ReturnSludge

The factors that effects ASP These include:

1 .temperature 2.amount of oxygen available

3 .amount of organic matter available4 .pH

5 .waste flow rates 6 .aeration time

7 .wastewater toxicity

The benefit of ASP -Diverse; can be used for one household up a huge

plant-Removes organics-Oxidation and Nitrification achieved-Biological nitrification without adding chemicals-Biological Phosphorus removal-Solids/ Liquids separation-Stabilization of sludge-Capable of removing ~ 97% of suspended solids-The most widely used wastewater treatment process

The problems that we found in ASP -Does not remove colour from industrial wastes and may

increase the colour through formation of highly colored intermediates through oxidation.

-Recycle biomass keeps high biomass concentration in aeration tanks.

-Operation cost is high and required large scale

on large -This process is sensitive

to certain industrial wastes-Skilled supervision is

required to check that the returned sludge remains active