Study On The Microbial Characteristics In The A+OSA Excess Sludge Reduction System

Municipal wastewater treatment is mainly performed with the conventionalactivated sludge （CAS） process in which up to50%of the organic materials in thewastewater is converted into biological sludge. The associated high sludge processingcosts of up to50%–60%of the operational costs of wastewater treatment plants havealso led to an increased interest in sludge reduction techniques. The oxic-settling-anaerobic （OSA） process decreases excess sludge well, and reduces energyconsumption without chemical addition. The OSA process is becoming an attractiveapproach for solving sludge-associated problems by reducing sludge production in thewastewater treatment process itself rather than in other treatments. Domestic andforeign research on OSA focused on operation parameters, sludge reduction efficiencyand mechanism of sludge reduction, little study was referred to microbial communitystructure. A deep understanding of microbial populations, characteristics of communitystructure and dominant function in activated sludge should be studied to improve andcontrol efficiency of this kind of reactor. Moreover, this research will be conducive toexplore the mechanism of wastewater biological treatment process and coordinationcontradictions between macro regulation and microbial and biochemical reaction.A bench-scale anoxic+OSA （A+OSA） sludge reduction system and an anoxic-oxic（AO） reference wastewater treatment system were employed. These systems were usedto investigate the effects of inserting a sludge holding tank into a sludge return pipeline.Polymerase chain reaction amplification and denaturing gradient gel electrophoresis（PCR-DGGE） was used to analyze microbial community characteristics and communitystructural diversity. Moreover, molecular biology techniques and conventionalculture-based methods were combined to isolate and identify the so-called“differentiation bacterial strains”, which were only existence in A+OSA system and notfound in the AO system. The ability of decomposition of the synthetic wastewater andsewage sludge by the “differentiation bacterial strains” were also tested in this study.The main conclusions are listd as follows:1) During the121d operation experiment, the excess sludge production rate was2.53g·d^-1in the AO system, while in the A+OSA process, which retained sludge for 7.14h in the holding tank, the sludge production rate dropped to1.22g·d^-1. Sludgereduction rate of51.24%had been achieved. The121d operation data further confirmedthat the A+OSA system can effectively reduce excess sludge production.2) The results of sludge microscopy and scanning electron microscopy showedthat the sludge microstructure and sludge microbial community were directed affectedby the environment in turn of the oxic-settling-anaerobic. There are both abundantmicrobial in actived sludge in A+OSA and AO systems. Compared to the AO sustem,the richness index and the shannon diversity index decreased in the anoxic and oxictanks in terms of some lanes disappeared in DGGE profiles with the insert of sludgeholding tank in the return line. In the A+OSA system, the richness index and theshannon diversity index in aerobic tank is the highest, and the next is in anoxic tankfollowed by the sludge holding tank. The DGGE profiles in the sludge holding tankshow that there are hydrolytic-fermentative bacteria in the tank related to sludge decay.3) Four “differentiation bacterial strains”, named J₁, J₂, J₃and J₄, were isolatedand slected from the A+OSA system. J₁, J₂, J₃and J₄were inentified as bacillusamyloliquefaciens, rahnella aquatilis, uncultured bacterium clone and bacillusvallismortis.4) In batch experiment, the sterilized sludge as substrate was treated by J₁, J₂, J₃and J₄bacterial strains respectively. Probably as a result of sludge adsorption, CODconcentration decreased obviously at first. COD concentration is maintained at arelatively stable value by J₃bacterial strain without obvious sludge disintegration. Whilecharacteristics of decomposition sludge were exhibited by J₁, J₂and J₄bacterial strain, asthe phenomenon of the COD concentration increment were observed. Microbial activityleads to a decrement in mixed liquor suspended solids （MLSS）. Therefore, sludge decayin the sludge holding tank that retains thickened sludge under the no air supplycondition can be realized.5) After inoculation to the sterilized synthetic wastewater, J₁, J₂, J₃and J₄bacterialstrains were directly into the exponential phase. The four bacteria strains have beenperfectly adapted to the nutrient substance in wastewater. COD removal efficiency were40%and44%respectively by J₁and J₄bacteria strains, while COD removal efficiencyreached61%and75%respectively by J₂and J₃bacteria strains.6) J₁, J₂, J₃and J₄bacterial strains in exponential phase reached maximum growthrate of0.046and0.14,0.094and0026h^-1, respectively. When consuming the sameamount of COD, J₁, J₃and J₄bacteria strains obtain slow bacterial growth compared with J₂, and also produce less excess sludge. Four bacterial strains aerobic yields arelower than that of aerobic heterotrophic microbes.This subject is supported by the National Natural Science Fund project （51178484）.The author thanks for their financial support.