Question

Q4. You are working in a waste water treatment plant, once your treatment plant receives sewage water with more colloidal or dissolved organic materials. As an Engineer what type of treatment will you prefer for this sewage water? Justify and explain the method selected by you.

Answer 1

There are several factors to be considered before choosing a treatment method.They are the quality and and quantity of sewage generated,The quality that should be maintained for the effluent generated which depends on disposal method of the efflent,The availability of land and money etc.Here the only information given is the sewage with more colloidal or dissolved organic materials is to be treated.Conventional Biological treatment methods like Activated sludge process are found very effective in treating these kind of wastewater.

Another option I would suggest is Constructed wetland.These are more cheap alternative to conventional treatment methods like Trickling filter and Activated sludge process because of less operational and maintenance cost.Constructed wetlands are engineered systems which are designed to work through the same processes that would occur in a natural wetland ,but in a controlled manner by the combined action of vegetation,soil, algae and other microbes in a controlled environment.Figure shows a schematic diagram of a vertical flow constructed wetland.

Macrophytes are planted over a bed media( like gravel).An imperveous layer is given at the bottom.Influent is fed from the top and effluent after treatment is collected from the bottom

The aerobic and anaerobic microbes will decompose the dissolved and coilldal matter.The plant can utilize the nutrients present in the influent for it's growth.Apart from these physical processes like filtration and sedimentation also occur in the wetlands which will help to improve the quality of effluent

Constructed wetlands have shown good efficiency in removing COD,BOD nirogen and phosphorus and suspended solids up to 98 percent.The efficiency may vary according to the wastewater characteristics and the type plant and filter media