| Sewage sludge fermentation for acid is one of the important methods of sludge treatment. However, there exists many restraining effects, resulting in low substrate conversion rate and acid yield. In this study, sludge fermentation for acid was conducted in a self-dynamic membrane bioreactor. Based on the principle of selective intercept by self-dynamic membrane bioreactor, residual organic matters are intercepted and inhibitors of acids and ammonia nitrogen were efficiently discharged out from reactor in time, which improved substrate conversion rate and acid yield. The detailed research contents and main achievements were listed as following.1. The reasons to the low conversion rate of the sewage sludge and the residual organic matter were explored in the anaerobic fermentation process. In this study, poor biodegradability of proteins and fast decrease of the indigenous hydrolase activity in the residual were found to be the major reasons. With the addition of trypsin and alkaline protease in residual post-fermented sludge after primary alkaline fermentation, degradation efficiency of refractory protein was increased by 33.6% and 34.8%, respectively. Accordingly, the VFAs yields were improved by 69.7% and 106.1%, respectively. Furthermore, the activities of added trypsin and alkaline protease could maintain at 13.52 U/m L and 19.11 U/mL in the alkaline fermentation process. This study demonstrated that exploiting the refractory proteins in residual post-fermented sludge by protease addition seems to be a very promising way for improving VFAs yield of conventional alkaline fermentations with waste activated sludge.2. Operating conditions of self-dynamic membrane bioreactor, formation mechanisms of dyanic membrane and acidogenesis effect of reactor for acid fermentation under stable operation were studied. Results showed that when the influent sludge concentration was about 15 g/L, the flux was 1.2 ml/min, the rotate speed was 100 r/min, stable operation and high acid yield were simultaniously obtained. Then, through the long-term stable operation, the reliability, performance and mechanisms of the improved acid yield by self-dynamic membrane were investigated. Results showed that comparing with stirring reactor, acid yield could be improved 50% by the application of self-dynamic membrane bioreactor. The activity of protease and β-glucoside in self-dynamic membrance bioreactor could reach 6 U/mL and 22 μ mol/l·h, respectively. In addition, after 14 ds operation, the genus such as Alkaliphilus, Anaerobranca, Corynebacterium, Acinetobacter, etc, were enriched. In conclusion, the results showed that biological factors in self-dynamic membrane bioreactor was the most crucial effectors contributing to the improvement of acids production from sludge anaerobic fermentation, due to the improved activities of hydrolytic enzymes and the enriched microorganisms for releasing secrete hydrolase.3. The efficiency and mechanism of the catalytic protein degradation process were investigated by simultaneously applying self-dynamic membrane and protease on sludge fermemtation. In order to promote the degradation of the intercepted organic matter, especially for protein, alkaline protease was added into in dynamic membrane bioreactor. Results showed that after adding alkaline protease, acids yield was 1.44-folds than that without protease addition. Moreover, without adding the protease, the protein and polysaccharide were slowly accumulated, but their concentrations could maintain stable after adding protease. Results of mechanism researches indicated the addition of alkaline protease increased the activities of protease hydrolysis enzyme in the reactor, which is as large as four times of that with protease addition. Furthermore, by applying protease on sludge fermentation, the abundance of hydrolysis fermentation bacterias such as Paludibacter, Proteiniphilum would decrease while the abundance of pure fermentation bacteria such as vadinBC27 wastewater sludge group, etc would increase. |
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