Study Of Bacterial Community Stability And Competition Of Bioenhanced Activated Carbon Process

The insurance of water supply security has in face of challenge because of water shortage and pollution. Bio-enhanced activated carbon (BEAC) is a kind of advanced drinking water treatment process, which fixed the isolated bacteria on activated carbon. The use of BEAC has become a matter of concern to many researchers, because it can improve organic pollutants removal efficiency. At present, the study of BEAC focuses on activated carbon properties in use and proper parameters of the process. The purpose of these studies are keep the dominant bacteria and BEAC process stable by means of improving the growth of dominant bacteria, preventing external bacteria from invading, keeping dominant bacterial quantity and activity. However, these studies did not concern about the importance of dominant bacteria, including the dynamics of dominant bacteria and relationship between these bacteria.In this study, three different DNA extraction protocols were used for evaluating the DNA extraction efficiency of bacteria attached on activated carbon by DGGE analysis. The results showed that method C with 120 seconds ultra-sonication under 20 kHz and 40 W input energy could produce the intact bacterial profiles, which was the most proper DNA extraction protocol. After comparison with three different fluorescence in situ hybridization methods, the results showed that 120 s ultra-sonication pretreatment was benefit for bacteria separated from activated carbon. The most proper hybridization condition was that the samples were hybridized for 3 hours in 8μL hybridization solutions with 50 ng probes at 40°C, then eluted in hybridization for 20 minutes at 42°C.With the most proper DNA extraction and FISH methods described above, bacterial community of BAC filter operated for 300 days was tested, and dominant bacteria were isolated and screened. It was found that five bacteria (SRO 2, SRO 11, SRO 19, SRO 20 and SRO 30) biodegraded TOC with higher efficiency, grew faster, and activated with higher dehydrigebase activity.Five bacteria were combined and fixed on activated carbon to form BEAC process. Parameters of BEAC process were tested by comparing with BAC, including water qualities of influent and effluent water, bacterial activity, structure and dynamics with DNA extraction, ATP, SEM and FISH analysis. The results showed that dominant bacterial played an important role in improving pollutants removal efficiency and stable operation of process. Bacterial activity of BEAC filter was higher than that of BAC filter. On the 90^th day of BEAC process, bacterial activity was above 1000 ngATP/g carbon. On the 180^th day of BEAC process, bacterial activity was above 1500 ngATP/g carboon, while the highest bacterial activity was 1023.5 ngATP/g carbon during BAC process. Bacterial activity of the BEAC filter increased faster than BAC because of the dominant bacteria attached on BEAC with the properties of strong metabolism, high biological activity and low growth time. The average increase rate of bacterial activity in BEAC filter was 7.70 ngATP·g^-1carbon·d^-1, while it was 5.12 ngATP·g^-1carbon·d^-1 in BAC filter. The higher biological activity of BEAC improved pollutants removal efficiency. During BEAC operation, average TOC removal efficiency of BEAC was 76.24%, while its of BAC was only 58.97%. Bacterial distribution along the BEAC filter was relatively more uniform than BAC, which made bacteria on each layer of the filter act and promoted the removal efficiency.On the 180^th day of BEAC operation, the amount of SRO 30 was the highest, with 50% of total biomass. The ammount of SRO 19 was 25% of total biomass. The amount of dominant bacteria was increased during BEAC process, while the amount of SRO 11 was decreased and eliminated on the 180^th day of operation. The study of competition between dominant bacteria on BEAC showed that the competition was related to the minus required resource (R^*). The organic resouce in influent was lower than R^* of SRO 11, so it limited the growth of SRO 11.The competition between SRO 2, SRO 11, SRO 19 and SRO 20 of Pseudomonas genus is exploitative. The competition between SRO 2, SRO 11, SRO 19, SRO 20 and SRO 30 is interfering. The environmental load of Pseudomonas genus SRO 2, SRO 19, SRO 20 and Bacillus subtilis SRO 30 are represented by K₁ and K₂ respectively. The competition coefficient of Pseudomonas genus SRO 2, SRO 19, SRO 20 and Bacillus subtilis SRO 30 are represented byαandβ. K₁, K₂,αandβwere calculated by using Lotka-Volterra fomula. The results showed thatαwas lower than K₁/K₂, andβwas lower than K₂/K₁, which indicated that Pseudomonas genus SRO 2, SRO 19, SRO 20 and Bacillus subtilis SRO 30 could coexist in the BEAC process.After the above study, the most proper DNA extraction and FISH methods were constructed, which could provide the reliable technologies for future study of bacteria on BAC or BEAC. It has been confirmed by this research that Bacillus subtilis SRO 30 and Pseudomonas pertucinogena SRO 19 obviously dominant achieved in BEAC ecosystem. The reasons about the dominance of BEAC were pointed out. The choice of dominant bacteria is important for BEAC process stability, during which should avoid overlapping resource, choose bacteria with low minus required resource (R^*), minimize internal competition. The forecasting results of dominant bacterial competition by using methametic fomula showed that Pseudomonas genus SRO 2, SRO 19, SRO 20 and Bacillus subtilis SRO 30 could coexist in the BEAC process, forming stable bacteria community.