Construction And Properties Of Mixed Microbial Consortium In Alkaline Anaerobic Fermentation Of Excess Sludge

As a concomitant of sewage treatment plant, the sludge is also a kind of high ly available secondary resources. However, with the increasing of municipal sewage sludge production, sludge treatment and disposal are imminent. Sludge is rich in organic compounds, nitrogen, phosphorus, and other nutrients, some of which can produce volatile fatty acids(VFAs) by anaerobic digestion. VFAs are the favorable organic carbon sources for biological nutrients(nitrogen and phosphorus) removal processes in wastewater treatment plants. Therefore, the acquirement of VFAs during the acidogenic phase of anaerobic digestion is an effective approach for the beneficial utilization of sludge.The optimal p H for VFAs accumulation and the bacterial community structure in the bio-production of VFAs from excess sludge(ES) was determined. Bacteria capable of protease-producing were isolated from ES under the optimal condition for VFAs accumulation. A mixed microbial consortium capable of protease-producing was constructed by the isolated bacterial strains. In addition, the semi-continuous operation mode was conducted to further analyse the influence of the mixed microbial consortium capable of protease-producing on the dissolution of organic compounds, nitrogen and phosphorus under alkaline anaerobic fermentation of ES. At the same time, the bacterial community structure of different fermen tation systems were analyzed by Mi Seq high-throughput sequencing technology. It reveals the relationship between the dissolution of organic compounds, nitrogen and phosphorus, and the bacterial community structure under alkaline anaerobic fermentation of ES. This study provides a new way for the rapid start-up and stable operation of alkaline anaerobic fermentation of ES. Meanwhile, it has an important significance for improving the resource utilization, reduction, stabilization of ES.The effects of p H on the dissolution of VFAs, nitrogen and phosphorus under alkaline anaerobic fermentation of ES showed that alkaline fermentation conditions were more conducive to VFAs dissolution, and the amount of dissolved VFAs and NH4+-N were the highest at p H 10.0. However, the acid fermentation conditions were more conducive to the solution of PO43--P. Denaturing gradient gel electrophoresis(DGGE) analysis revealed that the bacterial community structures were different under anaerobic fermentation of ES at different p Hs, and the dominant bacteria were Pseudomonas sp., Clostridium sp., Variovorax sp., and uncultured bacteria. Two alkali-tolerant bacterial strains(HIT-01 and HIT-02 strains) capable of protease-producing were isolated from alkaline anaerobic fermentation of ES and were identified to Bacillus subtilis and Bacillus sp. The optimal protease-producing fermentation conditions of the two strains were the same.The static mode of operation research showed that VFAs accumulation were able to accelerate to some extent by inoculation of protease-producing strains HIT-01 or / and HIT-02 under alkaline anaerobic fermentation of ES. DGGE analysis revealed that HIT-01 and HIT-02 strains became predominant in the bacterial community and successfully established the mixed microbial consortium capable of protease-producing during alkaline anaerobic fermentation. On the basis of the dissolution of organic compounds, nitrogen and phosphorus, a mixed microbial consortium capable of protease-producing was constructed, and the optimum conditions of acidogenic fermentation of ES was determined. The fermentation start-up phase was shortened by 2 days. All the concentrations of organic compounds reached the peak values on the 8th day of fermentation, the concentrations of soluble protein and total VFAs accounted for 29.87% and 44.54% of total SCOD concentration, respectively.The semi continuous mode of operation research indicated that the concentrations of all the organic compounds were the highest in reactor JWG-G(inoculated with HIT-01 and HIT-02 strains), and the SCOD(t-N-P) were 125.22 times, 1.44 times, 1.31 times, and 1.19 times higher than the values that from reactor JWG-0, JWG-A, JWG-E(inoculated with HIT-01 strain), and JWG-F(inoculated with HIT-02 strain), respectively. It showed that inoculation with both HIT-01 and HIT-02 strains under alkaline condition was more beneficial to the dissolution of organic compounds during ES fermentation process. The average concentration of VFAs in reactor JWG-E, JWG-F, and JWG-G were 1.21 times, 1.14 times and 1.46 times higher than the values that from reactor JWG-A, respectively, and were 57.61 times, 53.90 times and 69.30 times higher than the values that from reactor JWG-0, respectively. It showed that VFAs accumulation was affected not only by the fermentation conditions of ES, but also by the microbial community of ES. The order of CST in each reactor follows as: JWG-A > JWG-F > JWG-E > JWG-G > JWG-0. It showed that the microbial community structure might affect the dewatering performance of sludge to a certain extent.MiSeq high-throughput sequencing analysis showed that the microbial communities of the 6 reactors can be divided into non-alkaline conditions(JWG-S and JWG-0) branch, pure alkaline condition(JWG-A) branch and inoculation of protease-producing strains alkaline conditions(JWG-E, JWG-F and JWG-G) branch. To a certain extent, HIT-01 and HIT-02 strains can affect the microbial community composition in the ES. The most obvious differences of the microbial communities in the 6 reactors was the proportion of Bacillus, Proteiniclasticum, Peptostreptococcaceae and Dechloromonas accounted for the microbial communities of each ES sample. Bacillus was the dominant bacterial community in the reactors inoculated with protease-producing strains. It revealed that HIT-01 and HIT-02 strains could be competitive with indigenous microorganisms and successful be colonized in ES, and became predominant in the bacterial community, to play their biodegradation role greatly and facilitate the production of VFAs during alkaline anaerobic fermentation.