Research On Halophilic Denitrification Complex Microbial Inoculants And Their Bioaugmentation Effects

When wastewater containing high concentration of chloride ion, high environmental osmotic pressure would lead to destruction of bacterial enzymes and microbial cell membrane, inhibition of microbial activities and undermining of microbial physiological activities. All of them have deleterious effects on biological wastewater treatment system, resulting in a decline in carbon and nitrogen removal rate.Microorganism in acclimated activated sludge has limited tolerance range of chloride ion and is sensitive to environmental variation. This study aims to build efficient halophilic denitrification complex microbial inoculants. We investigated that effects of C/N?pH?salinity and temperature on the nitrogen removal rate of halophilic denitrification complex microbial inoculants and the optimal cultivation condition. Through the optimization of dosing quantity of halophilic denitrification complex microbial inoculants and the system operation cycle, we provided appropriate process parameters for the practical bioaugmentation. These results are very important to improve the efficiency of high salt wastewater denitrification and the stability of the biological process operation.There were total 35 strains of salt-tolerant denitrifying bacteria(Halomonas sp.), salt-tolerant nitrifying bacteria(Bacillus sp.) and salt-tolerant bacteria(Halomonas sp.) isolated from mature salt-tolerant activated sludge domesticated by biological contact oxidation process. In this paper, salt-tolerant denitrifying bacteria F2, F3, F5, F10, salt-tolerant nitrifying bacteria X23 and salt-tolerant bacteria N39 were chosen. By testing the denitrification and growth characteristics of complex microbial inoculants with different proportions, we finally obtained halophilic denitrification complex microbial inoculants with the F3:F5:X23:N39 proportion of 1:1:10:60. The complex microbial inoculants have simultaneous nitrification and denitrification ability, without the accumulation of nitrate nitrogen in the reaction process.The study of influencing factors of halophilic denitrification complex microbial inoculants indicated that under certain conditions, the optimum C/N was 15:1, the optimum initial concentration of NH4+-N was 100 mg/L, the optimum salinity was 3%, the optimum pH was 7, and the optimum temperature was 30?. The appropriate salinity range was 3%-7%. The denitrification ratio reached 98.57% under ideal conditions.The study of the impact of NH4+-N, C/N and dosing quantity on the denitrification rate of halophilic denitrification complex microbial inoculants by response surface method, suggested that the impact of three factors was not a simple linear relationship, while the interaction terms and quadratic terms had significantly effects. And the response value of denitrification rate was up to 99.63%, the best conditions were initial NH4+-N concentration of 121.51mg/L, C/N of 14.95 and dosing quantity of 5.4%.After halophilic denitrification complex microbial inoculants added to high salt wastewater treatment system, a comparative study of the bioaugmented system and the contrast system was carried out to analyse the nitrogen transformation and parametres variation. On this basis, the optimal operation cycle of SBR process was determined as follow:the fill time for 30 min, aeration time was 6 h, mixing time of 1 h, precipitation time of 1 h, and the drainage for 30 min.Salinity shock tests were conducted between the bioaugmented system and the contrast system. When the systems were suffered from 5% and 7% salinity shock respectively, the denitrification rate of each system dropped dramatically. After restoring to original salinity, activated sludge in the bioaugmented system restored original activity ahead of the contrast system, and total nitrogen in the effluent of recovered bioaugmented system could reach level A of water discharge standards. When systems were shocked by 0% salinity, activated sludge in the contrast system was inactive, and was unable to restore; while adding a small amount of halophilic denitrification complex microbial inoculants, the bioaugmented system could quickly recover activity, and total nitrogen reached level A of water discharge standards. It demonstrated that the salt-tolerant activated sludge had a minimum tolerance value to feed water salinity. When salinity of influent was lower than a centain concentration, microorganism swelled and died, and eventually the activated sludge lost its activity; while activated sludge system bioaugmented by halophilic denitrification complex microbial inoculants had a characteristics of strong salinity shock resistance and favourable system stability.