Dear Weam,

Algae is as expected related to the ratios of excess nitrogen (N) and phosphorous (P) in the stream. Even minor concentration of phosphate (e.g. 0.01 mg./l) may support plankton development, while higher concentrations (e.g.0.03 to 0.1 mg./l) can trigger algae blooms (USEPA, 1986; Dunne and Leopold, 1978).

There are also types of algae that bloom in the presence of high BOD (e.g. Cyanobacteria, cases with BOD >15mg/L) in the presence of intense sunlight. Would it be possible to increase the number of bacteria (MLVSS) in the tank to reduce a little further the organic material?

Temperature and D.O. may also affect growth. What is your D.O.? can that be somehow increased? Bear in mind that oxygen transfer reduces the higher the temperature gets.

I hope the above give an indication of potential problems that may contribute to the situation you have.

Good luck,

Evangelos

Simply saying there is insufficient oxygen supply in the secondary treatment unit which carries the untreated algae to the secondary Sedimentation tank, produced due to the excess loading of nitrogen / phosporous content.

Dear Evangelos,

thanks a lot for your answer.

the Dissolved Oxygen in our WWTP about 2 mg/l. What do you think about this Concentration. what is the range of Dissolved Oxygen must be in such WWTPs that treated the Nitrogen and Phosphorus Biologically.

And Do you have any idea about good books that may help me in the processing of WW treatment in such kind of WWTPs

thank you very much.

Dear Saravanan,

Thanks a lot for your answer.

What is the range of DO should be ?

This discussion on dependency of Oxygen is rubbish. If Algae is present in the secondary settler it is as Evangelos rightly wrote due to the presence of Nutrient, but the second very important factor is sunlight. If there is sunlight the O2 that might be present will be coming from the Algae them selves. This mean also that you must have a very good settling sludge since you get a good penetration of the light into the tank.

Two solutions: Go for getting a limiting concentration of Phosphorous (

Mr. Soerensen.

Thank you for you helpful and valuable answers. and thank you for your time.

When you have Advanced WWTP with BNR + BPR process , algal growth shows that the plant is not working prperly . Algal growth should not take place if you strictly follow the design parameters of combined Biological Nitrogen and Phosphorus removal process.

In a Bardenpho process there are 5 stages in process- anaerobic anoxic and aerobic zones with sludge and internal recycling. Under optimum conditions the BNR system with multiple zone is capable of producing effluent with Phosphorus and ammonia to 0.5 and 0.1 mg/L However effluent from the BNR process will typically contain a soluble organic nitrogen concentration of 0.5-1.0 mg/L respectively and an NO3-N concentration in the range of 5-8 mg/L. Further removal of organic nitrogen is possible using activated carbon treatment

By controlling process parameters in operation of treatment process, algae should not develop.

Dear Weam, the denitrifiers require an anoxic environment NO3 and N02 present and DO absent Extreme care should be taken to minimize the entry of DO.

Nitrifiers on the other hand need aerobic conditions- min 2 mg/L of DO is desirable for high activities of denitrifiers. At an average 4.6 mg/L of DO are needed per mg/L NH4-N nitrified.

Dear Dr. Sheth,

Thank you for your answer.

Also I want to ask you How Can Minimize the entry of DO to the Anoxic Tank ??

and what is the other parameter that I should care about it ??

Regards,

the first finding is an imbalance of nitrogen and phosphorus in the environment

valuable information.