Study On Enhanced Biological Denitrification Of Wastewater By Ultrasound-Hydrolysis Acidification Surplus Sludge

Activated sludge treatment technology,as a one-hundred-year process,is widely used in municipal domestic sewage treatment nowadays.However,due to the low carbon-nitrogen ratio of municipal domestic sewage and the difficulty of disposal of excess sludge accompanied by biological treatment of sewage,it has become a bottleneck restricting its process development.Pretreatment of excess sludge is used as a carbon source to reuse sewage treatment system to enhance the efficiency of sewage denitrification.On the basis of realizing the reduction of excess sludge,the utilization of excess sludge is carried out,which meets the needs of water environment in China at this stage.In this paper,the activated sludge from the aeration tank of plant Jinan Guangda was pretreated by ultrasonic cell lysis and anaerobic hydrolysis acidification was carried out.From the point of view of sludge cell lysis rate,sludge dissolution matrix and sludge particle size in sludge liquid phase,the optimum parameters of cell lysis condition for the treatment of excess sludge by Ultrasound-Hydrolysis Acidification(UHA)were explored.Taking domestic sewage disposal as an object of study,the UHA product of excess sludge was used as carbon source to sink into AAO system to explore the system's denitrification and pollutant removal efficiency,and the microbial community status and species in the system were analyzed by means of SEM,PCR and other technologies.The main conclusions are as follows:Ultrasound cell lysis test of excess sludge shows that ultrasound can effectively break up sludge cells and release a large amount of organic matter into the liquid phase.The organic matter such as SCOD,proteins and polysaccharides of sludge increased with time at different acoustic energy densities.The growth trend was linear in 0~30 minutes and slowed down after 30 minutes.The data show that ultrasonic pretreatment can effectively destroy sludge flocs.Through the analysis of sludge particle size,when the effect of acoustic energy density is greater than 1W/mL,the sludge particle size decreases from 260~300 micron to 10~11 micron in 30 minutes,but with the time going on,the sludge particle size does not change,which indicates that there is a certain limit value for ultrasonic treatment over sludge.In order to make the small molecule degradable carbon source required by microorganisms in wastewater biological treatment,the sludge treated by ultrasound was hydrolyzed and acidified for 10 days at room temperature of 25? It was found that the best time for the accumulation of volatile acids was on the 7th day,and the volatile acids at different acoustic energy densities(0.50,0.80,1.00,1.60,2.00 W/mL)were 645,1012,1279 and 1413 mg/L,respectively.By comparing and analyzing the changes of SCOD,sludge particle size and volatile acid concentration in the liquid phase,it was found that the smaller the sludge particle size in the liquid phase and the higher the SCOD concentration,the higher the concentration of volatile acid,the more the small molecule degradable carbon source.In order to explore the denitrification performance of UHA products in excess sludge,the denitrification efficiency of UHA products was compared with sodium acetate as carbon source.It was found that UHA products contain a large amount of small molecular substances,which provides good carbon for denitrifying bacteria.The source effectively strengthens the denitrification capacity of the denitrifying bacteria.The denitrification test is carried out for the reactor with the UHA product as the carbon source and the reactor with the sodium acetate as the carbon source for 240 min.The nitrate yield of the UHA product reactor is slightly higher.For sodium acetate,the denitrification rate of UHA product is 801.69mgNO3-N/(mg MLSS·min)which is slightly lower than the denitrification rate of sodium acetate reactor is 868.32mgNO3-N/(mg MLSS·min).The reason for the analysis is due to the presence of UHA product.Large molecular substances such as proteins provide a carbon source for other bacteria,which hinders the further strengthening of denitrifying bacteria.The treated product of UHA(1.5W/mL,30 min,hydrolysis and acidification for 7d)was used as a carbon source for reuse in the AAO reactor.The continuous operation was carried out for 40 days.The effluent TN and ammonia nitrogen concentrations were respectively obtained from the UHA before the addition.14.90mg/L and 13.50mg/L were reduced to 5.30mg/L and 2.80mg/L,and the corresponding removal rates increased from 62.20% and 62.60% to 88.93% and 89.60%.The SEM observation of the system showed that after the UHA product was added,the number of rod-shaped bacteria in the anoxic area was more densely distributed;the microbial community in the aerobic area was transformed from a coagulated cocci into a relatively dense spheroid.Sequencing analysis of microbial community structure by PCR molecular technology revealed that the addition of UHA product had an effect on the microbial community structure in the system.Denitrifying bacteria such as Betaproteobacteria and Alphaproteobacteria increase with the addition of UHA products,which enhances the nitrogen removal efficiency of sewage biological treatment.