Mechanism Study Of The On-site Sludge Reduction In A Biological Process With Repeated Coupling Of Aerobic And Anaerobic Conditions And Its Application

Reduction of excess sludge is one of the biggest challenges in biologicalwastewater treatment processes. An ideal way to solve the problem is tominimize excess sludge production during the wastewater treatment ratherthan treat the sludge after its generation. Our previous studies have shown that abioreactorsystemconsistingofrepeatedcouplingofaerobicandanaerobicconditions(rCAA)couldachievegoodeffluent qualityaswellastheon-sitesludgereduction. Inthis study, a baffled rCAA reactor consisting of 3 coupling series of aerobic andanaerobic compartments was constructed and the mechanism of on-site sludgereduction was elucidated systematically. This rCAA process was also applied to thetreatmentoffermentationwastewater.TheresultsshowedthatattheinfluentCODof700-800mg·L-1 and HRT of 15h, the COD removal efficiency in average maintained over 89% and the sludgeproductionintherCAAsystemwas0.09kg-SS·(kg-COD)-1 whichwasabout33.3%of that in the conventional activated sludge process during the 3-year running period.By analyzing the changes in soluble components, sludge characteristics,microorganism community and metabolic activities in the rCAA system, weconcluded that when the sludge in the aerobic zone flowed into the anaerobic zone,the sludge destruction and degradation occurred. Then intracellular organicsubstances, such as proteins, were released and further hydrolyzed into smallmolecular substances such as volatile fatty acids (VFAs). These intermediatesubstances were degraded in the subsequent aerobic compartments. This rCAAprocess could rationally control the microbial community along the bioreactor andalso enhance the cryptic growth of sludge which could contribute to the sludgereduction.Thecomplete biotransformationoforganicsubstances inthewastewatertoCO2andN2wasachievedbytherCAAprocess.In order to characterize the destruction process of microorganisms during thesludge transfer from aerobic compartments to anaerobic compartments, a novel method by using the GFP bacteria as the indicator was proposed. When the GFPbacteria were resuspended in the supernatant from the anaerobic compartments andthe downstream aerobic compartments, the intracellular GFP was released from thebacteria, demonstrating that the supernatant from these compartments could greatlyimprove the release of intracellular GFP. This indicated that the supernatant fromthesecompartmentshastheabilityofcelllysis.A mathematic model was proposed to simulate the rCAA process. In the aerobiccompartments the growth of microorganisms and the elimination of substances weredescribed on the basis of Monod equation, while in the anaerobic compartments amodel based on sludge solubilization and transformation was proposed. Theparameters in the model were calculated byusing Matlab software. This model coulddiscribethereactionprocessoftherCAAsystemwell.Finally, the rCAA system was successfully applied to the treatment of practicalavermectinfermentation wastewater.On thebasis oflab-scale andpilot-scalestudies,we reconstructed the wastewater treatment system bycombining flocculation processwith rCAA reactor to treat the effluent of UASB reactor. The results showed that thevalue of the effluent COD was below 300 mg·L-1when the influent COD was about1500 mg·L-1. In addition, the effect of decolorization was notable by using thisprocess.