Study On Nitrite Pretreatment For Anaerobic Acidification Of Waste Activated Sludge

Anaerobic digestion is an important method for the reduction of waste activated sludge.The limitations on anaerobic hydrolysis and acidolysis of this waste would result in a longer retention time to 25 days and a lager digester volum.The organic matter of the waste activated sludge mainly exists in the microbial cells,but it is difficult to break the cell wall to release intracellular organic substances.Therefore,before the anaerobic acidification of waste activated sludge,it needs to break cell wall to release intracellular organics.Traditional pretreatment technologies,including ultrasonic pretreatment,thermal pretreatment,acid-base pretreatment,etc.,require additional dosing or new equipment,which has the disadvantages of higher investment,larger energy consumption,and easier corrosion of equipment.Nitrite pretreatment of waste activated sludge can not only improve the hydrolysis effect,but also increase acid production and increase sludge reduction,and the sewage treatment plant can produce nitrite in situ.This study aims to explore the effect of pretreatment time,concentrations of nitrite(NO2~--N),and pH on anaerobic acidification of waste activated sludge.Response surface methodology was conducted for parametric optimization.The main results are as follows:(1)Single factor analysis was used to investigate the nitrite concentration,pretreatment time,and pH of waste activated sludge,and the changes in organic matter and volatile fatty acid(VFA)production during the subsequent ten days anaerobic acidification were characterized.In the range of 200~600 mg/L,time 4~10 h,and pH5.5~6.5,the effect of organic matter dissolution and anaerobic acidification of waste activated sludge was significantly improved.(2)The optimal pretreatment conditions were obtained by response surface optimization method:treatment time 7 h,pH=6.0,and agent concentration 400 mg/L.The effect of three factors on the 3-day cumulative amount of VFA was:agent concentration>pH>treatment time.Under the optimal pretreatment conditions,the starting point of anaerobic acidification of SCOD and the cumulative amount three days of VFA reached 1960 mg/L and 3181 mg/L,respectively.(3)The continuous anaerobic acidification reactor was started and run,and the waste activated sludge was pretreated with anaerobic acidification for 15 days under the optimum conditions of response surface.The VS removal rate reached 46%;the mean values of SCOD and VFA reached 1975 mg/L?1457 mg/L,respectively,increased by 28%and 23%relative to the control phase.The nitrite pretreatment of waste activated sludge by anaerobic acidification of organic matter produced significant acid reduction and sludge reduction.