Biological Phosphorus Removal For Low C/N Ratio Domestic Wastewate

As the promulgation of"discharge standard of pollutants for municipal wastewater treatment plant GB18918-2002", it puts forward higher request for the nitrogen and phosphorus emission to urban sewage treatment plant of our country. But at present, for the low C/N urban sewage treatment, the effects of nitrogen and phosphorus removal are not ideal, so the effluent TP cannot reach the A standard. The main reasons are as follows:In the traditional nitrogen and phosphorus removal process, generally, it adopts single sludge system, in which microorganism grow in the form of mixture and suspension. In the biological denitrification and dephosphorization process, Nitrosomonas and PAOs coexist in the same activated sludge system. Due to the large difference of their generation periods, when SRT controlled by mudhole ,it is hardly to guarantee two bacteria'biological activity are in the optimum condition groove, causing some disadvantages, for example, denitrification and dephosphorization effect are not ideal, and sludge sedimentation become worse, etc.The test mainly carried out start-up, running and sludge characteristics research of two-sludge system basing on BAF nitrification. The running cycle was 7.5 h, via 20 days cultivation under the condition of anaerobic-aerobic, PAOs became dominant species, after anaerobic-anoxic for 27 days, DPB became dominant in the activated sludge.The results show that: (1) The main pollutants removal could achieve high levels, phosphorus removal could reach 90%, COD removal could reach 89%, and ammonia nitrogen removal rate could reach 73%, nitrate-nitrogen and nitrite-nitrogen were below 1mg/L. After the final improvement of the process, the main pollutants finally achieved GB18918-2002 level A standard. (2) DPB performance was stable, the amount of phosphorus release increased with the increase of pH. The content of released phosphorus increased with the temperature increased, but should not too high, the best temperature was about 30 degrees. Acetic acid was the best for anaerobic phosphorus release followed by glucose, ethanol, methanol. Existence of NO3- inhibited the anaerobic phosphorus release, only when denitrification finished then anaerobic phosphorus release could occur. Appropriately increase the sludge organic load could help increase the amount of anaerobic phosphorus release, but should not too large, the limit of organic loading was 0.12gCOD/gMLSS. If we continue to add COD beyond this range, the effect was very little. (3) Compared with the traditional process which depended obligative aerobic bacteria for phosphorus removal, denitrifying phosphate bacteria could save about 50% COD and 30% of the consumption of oxygen and residual sludge amount could correspondingly reduced by 50%.Compared with the traditional process, the advantages of this process were"a carbon for dual purpose", saving aeration, low sludge yield and different bacterium could be cultivated separately, which solved the conflict of dephosphorization and denitrification. The process achieved high phosphate removal and effluent phosphate concentration reach the A standard.