Experimental Study On Swim-bed Anoxic And Oxic Process For Wastewater Treatment

Activated sludge/biofilm process coexisted of the suspended and attached microorganisms includes the advantages of activated sludge and biofilm.Swim-bed biological treatment technology is a kind of novel biofilm technology which being combined with activated sludge will have many advantages such as high MLSS,more pollutants removal, strong resistance to overload shock,less sludge yield,stable operation,easy control and so on, because of the special biological carrier of biofringe.As a small pilot scale study for project application,this experiment was done to treat Dalian Bay fishery wastewater and Dalian Economic and Technological Development zone integrated wastewater in anoxic-oxic swim-bed reactors by preanoxic nitrogen-removal process with BF materials packed in anoxic and oxic tanks and only in oxic tanks respectively. The study has investigated two kinds of wastewater treatment performance with different technical parameters including BOD₅ volumetric loading,mixed liquid recycle ratio,HRT, BOD₅/TN and sludge performance,all of which is used to provide design base for actual project.The two experiments last for 87 days and 112 days respectively,and results are as follows:(1) In the treatment of Dalian Bay fishery wastewater,under the condition of BOD₅ volumetric loading of 1.5 kg/(m³Â·d),the HRT of 5.9-4.7 h,DO in aerobic tank of 4.5 mixed liquid recycle ratio of 1.0 and the temperature of 20-27℃,the average removal efficiencies of COD,TN and NH₄⁺-N reach to 93.6%,72.7%,98.9%respectively,with effluent average concentration of 34.1 mg/L,19.5 mg/L,0.7 mg/L.TN removal effect has no obvious improvement by changing mixed liquid recycle ratio from 1.0 to 2.0.Taking the cost into account,the optimal mixed liquid recycle ratio is 1.0.Simultaneous nitrification and denitrification can occur in the oxic-swim-bed biofilm reactor,because there exists different micro-environment inside the biofilm on the biofringe carrier,which is beneficial to the removing of TN.(2) In the treatment of Dalian Economic and Technological Development zone integrated wastewater,the average removal efficiencies of COD and NH₄⁺-N reach to 68.4%and 95.5%, with effluent average concentration of 49.1 mg/L and 1.7 mg/L.Due to the low BOD₅/TN of 2.4 of influent,TN average removal efficiencies is only 34.1%,with effluent average concentration of 26.2 mg/L.The removal efficiencies of TN rise with the increase of BOD₅/TN in the experiment,therefor we can increase the organic content in it to improve the TN removal rate.(3) The study finds that the swim-bed A/O system has many advantages,including easy biofilm attachment,quick start-up,high MLSS(more than 10,000mg/L),and the low value of SVI and sludge production rate(0.1891 and 0.1513 kgMLSS/kgCOD_removal respectively in two experiment),as well as the microbial populations in aboundance,thereby it greatly saves the area of the reactor footprint,reduces sludge disposal costs,and it can be easy-manage,high economic returns,and suited for practical applications in engineering.