Study On VFAs Yield By Using Thermophilic Anaerobic Acidification Of Waste Sludge And The Synthesis Of Poly-hydroxyalkanoates

The goal of this thesis is the reduction and utilization of waste activated sludge produced by municipal wastewater treatment plants. Through the lab-scale and the pilot-scale experiments, two tasks were studied thoroughly. The first task is the VFAs yield from waste activated sludge(WAS) by using thermophilic anaerobic hydrolysis and acidification(TAHA). The second task is that the group of Poly-hydroxyalkanoates(PHAs) synthesis microbial floras were acclimatized by fermented filtrate from the TAHA experiments.Degradation behaviors and characteristics of macromolecular organics were investigated through the multifaceted comparison between mesophilic and thermophilic anaerobic hydrolysis and acidification step. The results showed that TAHA process had more evident advantages than mesophilic process. And it acquired the optimal operating parameters. After that, Qualitative identification of VFAs yield from protein and carbohydrate and quantitative calculation on contribution rate by using stable 13 C isotope method have been studied. Several control strategies of the anaerobic hydrolysis and acidification stage was proposed to satisfy the requirements of directional VFAs production as the process of PHAs synthesis need different kinds or concentration of VFAs.The diversity and variation of biological community in anaerobic hydrolysis and acidification stage were investigated by means of 454 pyrosequncing. The results demonstrated that there were considerable different of microbial community between mesophilic and thermophilic anaerobic hydrolytic-acidification process. The diversity and variation of the mesophilic biological community is similar to the raw sludge. However, it could acclimatize the unique predominant biological community in the thermophilic anaerobic fermentation process. More VFAs were produced in thermophilic anaerobic fermentation reactor because of the existing of these unique predominant bateria. In addition, based on the result of Redundancy Analysis(RDA), it found that n-Butyric acid(n-HBu), Hydraulic Retention Time(HRT) and Temperature(T) were the most important environmental factors as these factors seriously impacted on the microbial community. By adjusting T, HRT and the volumetric loading of VFAs yield(FVFAs), the large numbers of bacterial community with the ability of producing VFAs were found in the reactor, which including some special thermophilic microbes. At the same time these factors could improve the decomposition of thickened waste activated sludge(TWAS) floc and the dewatering performance of TWAS.The low carbon/nitrogen(C/N) ratio of substrate was used to acclimatize bacteria in Aerobic Dynamic Feeding(ADF) module for PHAs synthesis, and further to gain M150 bacterial consortia which could obtain maximum PHAs synthesis rate(w PHA). The results showed that the maximum w PHA of the lab scale and pilot scale were 23.47% and 59.46% respectively when fermentation liquid was taken as carbon source for the M150 bacterial consortia. As w PHA is not suitable to evaluate the process of PHAs sythesis when the organic carbon source is limited. However, PHAs synthesis velocity(υ PHA) and PHAs yield coefficient( YPHA/SCOD)could be adopted for the assessment of PHAs synthesis result under the condition of limited organic carbon source. Finally, it could cut the cost of sludge treatment if combined thermophilic anaerobic hydrolysis acidification(TAHA) with PHAs synthesis by mixed microbial floras.