Microbial Community Succession Of Excess Sludge Acidification Process Contral In Bench Scale

With the increasing scale of wastewater treatment, more and more sludge were produced, the problem of sludge treatment and disposal has become an important and difficult problem in the field of wastewater treatment. In the acidification phase of sludge anaerobic fermentation, much volatile fatty acids(VFAs) could be produced, which could be used as carbon source of enhanced biological nitrogen and phosphorus removal, and that would solve the shortage of carbon source in nitrogen and phosphorus process. Althoug much work had been done adout sludge alkaline fermentation, there was no detail report about organic matter degradation and the relationship between microbial community and VFAs accumulation, study about fermentation sludge as seed sludge to produce CH4 was few.The changes of organic matter and the relesse of ammonia nitrogen and orthophosphate were studied at 35℃, p H10.0 with expanded granular sludge blanket reactor(EGSB). The production and composition of VFAs were also studied to find out the optimal excess sludge(ES)hydrolysis and fermentation time. Furthermore, different solids retention time(SRT) ES were discussed as seed sludge to produce methane. In the end, high throughput sequencing menthod was used to analysis the microbial community succession during the anaerobic alkaline fermentation, which could indicate the mechanism of alkaline conditionenhancing VFAs production in microbial view.Results showed that soluble chemical oxygen demand(SCOD) increased during the whole fermentation period, specially in the first 8 days. Ammonia nitrogen, orthophosphate and VFAs concentration increased in in the first 8 days and then decreased gradually with extention time of SRT,therefor 8 days were the optimal hydrolysis and fermentation time. VFAs were composed of acetic acid, propionic acid, iso-butyric acid, n-butyric acid, iso-valeric acid and n-valeric acid, and acetic acid(82%) was the most dominant, followed by propionic acid(12%), the other four acids only occupied about 5%. The changes of VFAs was corresponded with the microbial community structure analyzed by high throughput sequencing.Total chemical oxygen demand(TCOD), suspended solids(SS) and volatile suspended solids(VSS) showed the trend of decreasing during the fermentation period, and about 20% TCOD were removed. SS and VSS decreased obviously in the first 8 days, and then reduced slowly, thus 8 days was the appropriate sludge reduction time. In addition, 8 days fermented sludge could produced more methane than 2 days and original ES.Firmicutes、Proteobacteria and Actinobacteria were the most prevalent microbal phylm during ES anaerobic alkaline fermentation, they increased rapidly to 94.6% in the first 2 days, and then slowly decreased to 87.7% in 8 days fermentation time. On 8th day, Clostridiawas the most dominant, next were Actinobacteria, followed by Anaerolineae and Betaproteobateri. Mass of Gammaproteobateria would propagate when fermentatiom time was more than 8 days, which contained plenty of pathogenic bacteria.During the first 8 days of fermentation period, both TVFAs and total acid-producing bacteria increased with fermentation time, and they showed positive correlation relationship, 8 day was the best time to produce VFAs. Clostridium、Bacillus、Amphibacillus and Peptostreptococcaceae were the dominant bacteria genus to produce VFAs. Within the total acid-producing bacteria, most genus bacteria could produce acetic acid, so it took the most part in TVFAs.