Question

Define Give detention time and give reasons why wastewater needs to stay in the

clarifier longer. What is the implications having the tank (clarifier) smaller for the

amount of flow?

4 marks

b. In the oxidation of ammonia by nitrifying bacteria, considerable quantities of oxygen

can be utilised, which can represent a significant fraction of the total oxygen demand of

a wastewater. Name these bacteria (2) and give equations to illustrate the process

8 Mark

Answer 1

detention time of a clarifier:-

it is defined as the time period for which waste water is being treated in clarifier tank (or) time period for which waste water stays in the tank.

* watse water needs to be stay in clarifier for longer times for effective removal of suspended particles.

* the detention time should be designed such that the particle settings velocity should be less than the dention period of the clarifier to provide enough time to suspended matter for settling.

*if smaller tanks are provided,it's volume gets decreased in turn results in lower detention periods. as the formula for detention period is

T = V/Q. so lower detention periods result in lesser efficiency of Particle removal.

b) Nitrification is the process of biological conversion of ammonium to nitrate nitrogen in the presence of air.

in this process mainly two types of bacteria are used one is nitrosomonas bacteria converts ammonium to nitrites. another one is nitrobacter which converts nitrites to nitrates which finishes the process.

the reactions involved in the nitrification process are as follows

from the above nitrification reactions we can obtain that for every kg of ammonium oxidized to nitrate,

4.18 kg of oxygen is consumed.

7.14 kg of alkalinity as CaCO3 is required.

thank you.