Enhancing Microbial Cryptic Growth By Ultrasonic Cell Lysis

The conventional activated sludge process(CAS)is easy to produce a large amount of excess sludge.Lysis-cryptic growth sludge reduction technology results in sludge reduction by dissolving the microbial cells and releasing cellular material,which is used as a second-stroma for activated sludge microbes to digest and grow when returned to the aeration tank.During the lysis pretreatment,the release of microbial cell material is one of a key factor which influences sludge reduction based on cell lysis.While the release of cellular material is accompanied by changes in microbial structure.A full understanding of the properties of the structural variation and release of microbial cell material during lysis pretreatment will provide an early period guidance for cryptic growth.An ultrasonic cell breaker was used to treat sludge sample,which derived from the secondary sedimentation tank of a sewage plant.Fractal theory is employed here for the study of sludge fractal structure characteristics and dissolution mechanism of organic matter indifferent ultrasonic reaction time(1,2,3,5,1Omin)and power density(0.3,0.6,0.9,1.2,1.5W/mL).Then,the optimal ultrasonic parameters were determined.On this basis,the effluent quality,sludge properties and sludge yield of the CAS with and without ultrasonic sludge recirculation were investigated during 40 days.The main conclusions are as follows:Lysis pretreatment experiment showed that ultrasonic could break the sludge effectively,releasing organic matter to liquid phase.SCOD and DDcoD were rose by stages with ultrasonic reaction time under different power density,which reached the maximum 1189.4mg/L and 28.6%at 5min,1.5W/mL.Besides,TP,NH4+-N,protein and polysaccharide in sludge supernatant all increased to a certain degree with different speed with the increase of ultrasonic reaction time or power density.Polysaccharide and TP mainly affected by reaction time,while power density had great impact on protein and NH4+-N.The dissolution of organic matter suggested that ultrasonic is benefit for the biodegradability of sludge,which can enhancing the following cryptic growth.d0.5 were dropped with the increase of ultrasonic reaction time or power density,while SSA showed a reverse trend,which indicated that ultrasonic could cut down the particle size of sludge and disperse floc.A turning point of do 5 and SSA appeared at 5min.If below this point,d0.5 and SSA were significantly affected by the ultrasonic reaction time,and if exceed this point,the reaction time would hardly affectd0.5 and SSA.Under different ultrasonic power density,D2 and D3 were both dropped with the reaction time.Taking into account of the variation of dissolved substances and fractal structure,and considering energy consumption,we selected 1.2W/mL,5min as the optimal ultrasonic condition.The results of pearson correlation analysis showed that both SSA and D3had a significant with SCOD.Generally,SCOD could well reflect the dissolution state of sludge,while D3 and SSA could screen effectiveness of cell lysis by micromorphology.So,the structural parameters D3 and SSA measuring online can reflect the effects of sludge lysis indirectly,which will provide an early period guidance for the practical production.Within 40 days of stable operation,the effluent SS,COD,TP,NH4+-N of test CAS(with ultrasonic pretreatment sludge return)were 13.1mg/L,20.6mg/L,0.57mg/L and 4.3mg/L respectively.Though the effluent SS,COD,TP of test CAS were a little higher than control CAS(no ultrasonic pretreatment sludge return),the test CAS remained stable.The effluent quality of test CAS could reach the standard B of level one of GB 18918-2002.During 40 days of stable operation,the MLSS in the aeration tank of test CAS were slightly higher than control CAS,but always remained in a stable condition,indicating that ultrasonic pretreatment sludge recirculation didn't cause sharp increase of microbial quantity.In addition,both SVI and SOUR in the aeration tank of the 2 CAS had little differences,suggesting that the settleability and bioactivity of sludge were rarely affected by ultrasonic pretreatment sludge recirculation.Ultrasonic lysis for 80%excess sludge recirculation could enhance cryptic growth in CAS to achieve sludge reduction effectively.After 40 days of operation,the observation yield of test CAS and control CAS were 32g and 126g,the reduction efficiency of test CAS was 67.2%.Besides,the total sludge production of test CAS was 159g,33g more than control CAS.Mainly since the accumulation of unbiodegradable cell wreckage and inert inorganic matter,and the increment of cryptic growth.