Study On Wastewater Biological Treatment Technologies With Excess Sludge Reduction And Microbial Community Characteristics

Activated sludge process and biofilm process with high efficiency and low cost have been applied worldwidely in municipal and industrial wastewater biological treatment. However, the most serious drawbacks of conventional biological wastewater treatment technology are tremendous production of excess sludge and the rising costs for final sludge treatment. So how to solve essentially the problem of excess sludge production is generating a real challenge in the field of environmental engineering technology. An ideal way to solve sludge-associated problems is to reduce sludge production in the wastewater treatment rather than the post-treatment of the sludge. The oxic-settling-anaerobic (OSA) process is a modified conventional activated sludge (CAS) process and reduces excess sludge by adding an anaerobic sludge tank in sludge return line. The OSA process is in accord with sustainable wastewater treatment model and reduces excess sludge by lower operational and investment cost for not adding any chemical and expensive equipments. The OSA process can be conveniently used to rebuild CAS process by inserting an anaerobic sludge tank in recycled sludge course, which is puzzled by heavy excess sludge production. So the Oxic-Settling-Anaerobic process provides a promising technique for industrial scale application.Performance of the OSA process has been systematically studied, including efficiency of wastewater treatment and sludge reduction, its affecting factors, and mechanism of minimization of excess sludge. For the first time, denaturing gradient gel electrophoresis (DGGE) and fluorescent in situ hybridization (FISH) were used to analyze microbial community characteristics, predominant community transformation by change of operational condition in OSA process. A new endogenous denitrifying phosphorus removal process with excess sludge reduction was developed. Efficiency of wastewater treatment and sludge reduction and its affecting factors were discussed. Efficiency and characteristics of denitrifying dephosphatation in the endogenous phosphorus removal process were studied emphatically. DGGE and FISH were used to investigate the relationship between microbial characteristics and treatment efficiency in various units of the endogenous denitrifying phosphorus removal process.In comparison with the CAS process, internal mechanism of excess sludge reduction was stressly discussed in the OSA process. As a result, the decisive cause of reducing excess sludge production is the increasing maintenance endogenous metabolism in the OSA process, which include sludge decay and anaerobic reactions with low sludge yield. It has been confirmed that sludge decay is the main cause in the OSA process, accounting for 66.7% of sludge reduction. These anaerobic reactions in sludge anaerobic tanks have lower sludge production than aerobic oxidation when equivalent SCOD is consumed, which may lead to approximately 23% of sludge reduction in the OSA process. There was energetic uncoupling in the OSA system since microorganisms were exposed to alternative anaerobic and aerobic environment, but which was a minimum factor, leading to about 10% of sludge reduction.The results of DG-DGGE profile and FISH analysis showed that there was more abundant microbial diversity in OSA sludge than that in CAS sludge. 11 predominant bands was excised from DG-DGGE and blasted in GenBank. Results showed that 7 clones represented by dominant bands in the DGGE gel of the OSA sludge were similar to bacteria isolated from denitrifying sludge and EBPR sludge. The finding explained that anaerobic sludge tank inserted in recycled sludge line provided a favorable environment for endogenous denitrifying bacteria and phosphorus removing bacteria. Phylogenetic tree of predominant DG-DGGE bacteria indicated thatβ-proteobacteria was the main community in the OSA sludge.A new endogenous denitrifying phosphorus removal process was developed. It was stably running when Ns was 0.87kgCOD/kgMLSS·d, ratios of system return sludge and denitrifying return sludge were 25% and 35%, respectively. Under the best conditions, sludge production was 4.78g/d and Yobs was 0.30gMLSS/gCOD while COD removal efficiency was about 90% and the percentage of NH4+-N, TN, TP was about 86%, 84% and 80%, respectively. Denitrifying phosphorus removal bacteria occupied 35%~44% of phosphorus accumulating bacteria in the endogenous denitrifying phosphorus removal process. Phosphorus content of sludge could be increased by extending SRT, which relaxed the contradiction between the production of excess sludge and TP removal efficiency.Analyzing and blasting the predominant bacteria represented by dominant bands in the DGGE gel of the endogenous denitrifying phosphorus removal process, it was detected that there were abundant microbial community.α-proteobacteria,β-proteobacteria,γ-proteobacteria,CFB-group bacteria,low G+C gram-positive bacteria were the main subclasses.β-proteobacteria was the predominant subclass, accounting for about 48%. FISH by PAOmix probe showed that phosphorus accumulating bacteria accounted for 40% of total bacteria in anoxic sludge and 33% of total bacteria in anaerobic sludge.