I treated the sewage waste water by Diatomaceous earth. Every parameters were successfully reduced without BOD and COD. How to reduce them now? I want to use any biological method for the operational inconveniences.
it just shows that Diatomaceous earth can not absorb the carbon present in the wastewater, which is not unusual. There are various way you can reduce the carbon content of the wastewater. The best is activated sludge treatment but if you want something simpler, you can go for activated carbon treatment.
There are different ways you can use to reduce COD. Chemically, Chlorination or hydrogen peroxide would reduce the COD. Biologically you could use the conventional activated sludge process, which is an aerobic biological process. Of course the quality and quantity of your wastewater will give an idea of a possible route you can follow.
Your question is very complex....You need to know what are the compounds giving your BOD and your COD. Furthermore in which state you have them...particulate, colloidal, soluble....then you can have an idea on how to proceed to treat your water in question.
As stated by Fabio Kaczala, you should first get more information about your treated waste water. As you say that other parameters have been reduced, I guess you might be referring to suspended solids, and if your turbidity is low too, then you can probably go for activated sludge, which is quite simple, you just need to get some activated sludge from a wastewater treatment plant and inoculate your wastewater with it, depending on the values of your COD and BOD you might need longer or shorter treatment or using older or younger sludge.
Most Chemical Oxoidation methods like Ozonation or dosing H2O2 followed by adsorption on GAC or PAC will do the job, but since you give no hints of the concentrations to treat and the targeted effluent values it is difficult advise more precise.
Yes...just like Drizo puts it..the constructed wetlands or biofilters can do a wonderful job at stabilizing the effluents especially in terms of reducing the BOD and COD values. We have done quite some work on this and the manuscripts are here. We tested different sand filters for their efficiency in terms of removal of most pollutants in water including bacteria and BOD and the results were remarkable but were all dependent on the sand bed depth, sand grain size and retention time.