Influence Of Cu(Ⅱ) On Bio-nitrification Process And Structure Of Nitrifying Bacteria Community

Many wastewater treatment plants receive a large amount of industrial wastewater.When the high concentrations of heavy metals in the influent shock the bioreactor, thenitrification efficiency of the bioreactor declines sharply. Moreover, it is difficult fornitrifier to recover their nitrification capacity in a short term so that the NH4+-Nconcentration in the effluent of wastewater treatment plants will not meet the standard.In this paper, a typical heavy metal copper (Cu2+) was chosen as an inhibitor, and theinhibition of Cu2+on nitrification and nitrifier was investigated by static tests, shockload tests, sustained load tests and gradually increased Cu2+load tests in sequencingbatch activated sludge process (SBRs). The influences of Cu2+on the nitrificationefficiency were examined during and after the Cu2+loading by analyzing nitrogenconcentrations, microbial activities (SOUR), and the distribution of cooper. To furtherexplore the diversity and structure of nitrifying microbiota and functional genes underthe different Cu2+loadings, polymerase chain reaction-denaturing gradient gelelectrophoresis (PCR-DGGE) and real-time quantitative (q-PCR) technique were used.In shock load and static tests: the inhibition effects on nitrifier increased withincreasing concentrations of Cu2+and the loading time. Cu2+with concentrations of30~150mg/L inhibited the activities of heterotrophic bacteria, ammonia-oxidizingbacteria (AOB) and nitrite-oxidizing bacteria (NOB). The inhibition order wasAOB>NOB>heterotrophic bacteria. The distribution of cooper showed that copper wasquickly adsorbed on the activated sludge. As the reaction proceeded, the copperadsorbed on the surface of the activated sludge moved into the inside of the activatedsludge. With the low Cu2+loading, the recovery of NOB was faster than that of AOB.However, with the high Cu2+loading, the recovery of AOB was earlier than that ofNOB. Sustained load tests show: the inhibition on the ammonia nitrogen removal ratebecame significant as the Cu2+loading concentration and run cycle increased. In therecovery period, the recovery rate of AOB and NOB decreased with the increases ofthe Cu2+dosage. The nitrification inhibition rate and dissolved copper concentrationswere positively correlated. Gradually increased Cu2+load tests showed that: sludgeactivities (SOUR) decreased in the inhibition phase and then increased in the followingrecovery phase. During operation, heterotrophic bacteria and nitrifying bacteria were gradually domesticated. In the inhibition period, the newly entered Cu2+accumulatedin the liquid phase, which inhibited the nitrification efficiency. At the end of the lastthree recovery periods, the copper in the liquid, in the sludge and on the surface of thesludge all decreased gradually. And then nitrification performance recovered gradually.Molecular biology tests showed: Cu2+destroyed the diversities of AOB and NOBand higher Cu2+loading concentrations caused lower diversities. DifferentNitrosomonas and Nitrobacter strains had different tolerance degrees to Cu2+. In theabove three different Cu2+loading methods, new species of AOB bacteria (Nitrosopira)emerged in the system, which indicates that some Nitrosopira had strong tolerance toCu2+. During the recovery process, the diversity and similarity degrees of NOBrecovered more than AOB. The gene expressions of AOB and NOB were verysensitive to Cu2+. In the beginning of the Cu2+loading, the gene expression wasseverely inhibited, which is earlier than the inhibition of nitrification performance andmicrobial activity. Due to the microbial stress response, the gene expression graduallyincreased and then even over expressed. The gene expressions of AOB and NOBseverely inhibited by50mg/L Cu2+, and can recovered after a long-term recovery(47cycles).