Study On The Treatment Of Aquaculture Wastewater By A New Biofilm Reactor

In recent years, with the rapid developing of biofilm technology in treating wastewater, developing high efficiency and stable biofilm reactors for the treatment of different kinds of wastewater have important significance for the environmental protection. In this paper, a new biofilm reactor was designed for the treatment of aquaculture wastewater. And it was investigated that the influence of different start-up methods on the start-up efficiency and bacterial diversity. What’s more, it was researched that the influence of organic loading rate, C/N ratio and the reflux ratio on the removal efficiency of this reactor.With the sequencing batch type operation strategy, it was compared that the difference in removal efficiency and the structure of successful biofilm which started-up by two different methods, natural start-up and start-up by adding activated sludge. The results showed that both of the two methods could started-up the biofilm successfully, and their removal efficiencies of COD and NH4+-N were above 85%. But it took only 13 days when start-up with the addition of active sludge, while the natural start-up strategy required 24 days. According to the results of the optical microscope and scanning electron microscope, it was found that the biofilm which started-up by adding active sludge have more compact structure and stronger adhesion than that of natural-started biofilm. And in the aspect of microbial species, the former is much richer than the latter obviously.Secondly, it was also investigated that the bacterial community shifts during the start-up, and the variation of bacterial between the two start-up methods by PCR-DGGE. The results showed that, during the biofilm start-up process, the bacterial community changed obviously no matter in which start-up methods, the comparability index of bacterial community were only 32.7% and 42.5%, respectively. After start-up, there was no much similarity of bacterial community between the two start-up strategy, and the maximum comparability index was only 25.2%. In addition, part of the biofilm microbial community of dominant bacteria was analyzed through the methods of cloning and sequencing, and 15 bacterial 16 s r DNA sequences were identified in the both of two start-up methods, and with a homology over than 95% when compared with the bacteria of Azoarcus sp.、Bacteroidetes bacterium、Aeromonas caviae 、 Lactobacillus sp. 、 Bergeyella sp. 、 Tolumonas osonensis 、 Duganella sp. and Trichococcus pasteurii., these strains played a very important role in the process of removing organic pollutants. Phylogenetic tree was further builded, it was found that in the mature biofilm of two start-up methods, some dominant bacteria had a very close relationship, their mechanism of organic removal may be the same or similar.After the reactor had been started-up, the effects of operating conditions inluding COD loading rate, C/N ratio and reflux ratio on the treatment efficiency of the biofilm reactor was investigated. The results showed that, with the COD loading rate increased from 15 g/(m2?d) to 30 g/(m2?d), the removal efficiency of COD and NH4+-N tended to rise before they were stable, and reached 89.5% and 86.4% respectively, at 25 g/(m2?d), the effluent COD and NH4+-N concentration were 10.47 mg/L and 1.26 mg/L, respectively. During the process of C/N ratio increased from 5.3 to 14.6, the removal efficiency of COD and NH4+-N presented the opposite shifts, the removal efficiency of COD increased with the growth of the C/N ratio, reached the maximum value 90.11% at 14.6, while the removal efficiency of NH4+-N decreased, and its maximum value reached 85.4% when C/N was 10.4. For reflux ratio, when it increased from 6.38 to 10.56, the removal efficiency decreased after a rapidly increased, at 9.17, the reactor got the highest COD and NH4+-N removal efficiency, which was 91.5% and 88.7%, respectively.