Study On In-situ Sludge Reduction Effect Of BM In Activated Sludge Process And Its Mechanism

Activated sludge process,which relies on a large amount of activated sludge to purify sewage,is a common standard method.At present,this method has been widely used all over the world.Due to the characteristics of the activated sludge process,a large amount of sludge will be produced with the treatment of sewage,and the treatment cost will be high.Otherwise,it will cause new pollution to the environment.Adding compound microbial preparation can achieve in-situ sludge reduction effect in the normal operation of the system,and has the advantages of simple operation,obvious sludge reduction effect and low operation cost.And the water quality and the process flow of different urban sewage plants are different,and the condition of adding the microbial agent is not consistent.In this paper,the effect of sludge yield change under different reaction conditions was studied,and the actual sludge reduction effect of BM compound microbial preparation in A~2O,AO,and AS systems was also explored.Through the changes of effluent water quality,sludge index and microbial community,the mechanism of sludge reduction by BM was further explored.The main results are as follows:(1)through single factor experiment,the effect of BM compound microbial preparation on sludge yield was analyzed,including the dosage of BM,the concentration range of COD,the reaction time of pH,and the suitable conditions of adding BM agent were obtained.The operating parameters of the subsequent reactor are determined.The results showed that when 1%BM was added,pH was about 7.5,COD concentration was within 200~600 mg/L,and reaction time was 8 h,BM was the most effective agent for reducing sludge yield in the system.(2)Adding BM compound microbial preparation to different processes and comparing its effect.Under the condition that the effluent quality of the reactor reached the standard,the mixed BM agent was added to the experimental group——A~2O,AO and AS process systems,and the sludge concentration of the experimental group and its control group was monitored by monitoring the sludge discharge condition of the experimental group and its control group.The effect of adding BM agent on sludge reduction was compared,and the reduction rate of sludge concentration in different reactor was analyzed by BM agent.The results showed that the sludge concentration of both A~2O system and AO system decreased obviously with the addition of BM.The reduction rates of MLSS and MLVSS in A~2O system were 28.26%and 24.85%,respectively.The reduction rates of MLSS and MLVSS in AO system were 26.27%and 36.13%,respectively.In the AS system,the sludge reduction effect was not significantly improved.The reduction rates of MLSS and MLVSS were 5.4%and 3.5%,respectively.At the same time,the effluent water quality was observed after adding microbial agents in different reactors,while reducing the sludge in the reactor.It was found that the removal of COD was greatly improved by adding microbial agents,which were reflected in A~2O,AO and AS reactors.In A~2O system and AO system,the removal rate of TN in effluent has also been improved.The phosphorus removal ability of A~2O system was also enhanced.The COD,TN of the effluent meets the first class A standard.(3)By observing the changes of sludge indexes in AO system during the experiment,the mechanism of reducing sludge concentration was analyzed.The morphology of activated sludge in the two groups was observed by scanning electron microscopy,and it was found that the structure of the sludge in the microbial group was smaller and denser.Moreover,the activity of enzyme in the sludge of the system was enhanced by BM agent.The dehydrogenase activity in the system added BM increased to 50.4?g/mL·h,and that in the control group was about36.7?g/mL·h.In the initial stage of the experiment,the polysaccharide content of the two groups remained about 21 mg/L.After 60 days of culture,the polysaccharide content of sludge in the microbial group decreased gradually to 13.21 mg/L.And the content of polysaccharide in the sludge of the control group fluctuated to a certain extent,but all remained about 25 mg/L.The initial protein contents in EPS of two groups of reactors were 29.06 mg/L and 30.21 mg/L.The protein content in the bacterial group decreased slightly during the experiment and remained at 23.28 mg/L at the end of the experiment.The control group rose to 34.21 mg/L.The results showed that the content of polysaccharide and protein in the system EPS could be decreased by adding the inoculant.Through the analysis of different levels of microorganism,it was found that the composition of microbial species changed after the action of BM agent.Because of the increase of Pseudomonadales,Thauera and other bacteria,it is beneficial to the secretion of protease and decrease of extracellular polymer,thus reducing the amount of sludge in the system.And the improvement of Proteobacteriac,Betaproteobacteria,Rhodocyclaceae and other bacteria in the system enhanced the nitrogen removal capacity of the system.