Effects Of Free Ammonia (FA) On Activity And Variation Of Nitrobacterium Community

Many wastewater plants sometimes suffer shock load of high ammonia-nitrogenwastewater, which will produces short-term inhibition of biological nitrificationprocess, affect the effluent quality, and cause the wasterwater plants fail in meetingthe discharge standards. In this research sitimulated wastewater was used to study theeffects of ammonia-nitrogen loads on biological nitrification process and activity ofnitrobacterium communities in a sequencing batch reactor （SBR） under differentconditions. To investigate the influence mechanisms and confirm critical inhibitionconcentrations of free ammonia （FA） under different influent conditions, ammoniaspecific degradation rates and nitrate nitrogen specific growth rates were determinedand PCR-DGGE and FISH analyses for nitrifying bacteria communities wereconducted.The shock load experiment of free ammonia nitrogen （FA） showed that when FAwas no more than8.0mgN/L （a critical inhibition concentration）, the activities ofnitrifying bacteria communities were promoted obviously. Ammonia specificdegradation rate （qmax0） and nitrate nitrogen specific growth rate （μmax0） showed anincreasing trend with the concentrastions of FA and the max0imum values were10.88and3.22times of the control ones respectively. When FA was more than the criticalinhibition concentration, inhibition effects of FA on nitrifying bacteria communitieswere observed obviously. max0and max0decreased with the concentrations ofFA. Ammonia-oxidizing bacteria （AOB） is more sensitive than nitrite-oxidizingbacteria （NOB） cause we found the reduce degree of μmax0was more lower thanqmax0.The sustained load test without adjusting influent pH, showed that when FA wasno more than4.0mgN/L （the critical inhibition concentration）, the activities ofnitrifying bacteria communities were promoted obviously. qmax0’ and μmax0’ showed an increasing trend with the concentrastions of FA and the max0imumvalues were1.36and1.23times of the control ones respectively. When FA was morethan the critical inhibition concentration, inhibition effects of FA on nitrifying bacteriacommunities were observed obviously. AOB was more sensitive than NOB underhigh free ammonia nitrogen.The sustained load test with influent pH equal to8.0, showed that the tolerant abilities of AOB and NOB for FA increased obviously and the critical inhibitionconcentration （21.1mgN/L） improved. When FA was no more than21.1mgN/L, theactivities of AOB were promoted obviously. When FA was more than the criticalinhibition concentration, inhibition effects of FA on nitrifying bacteria communitieswere observed obviously, which made the NH₄⁺-N cutting capacity decreased. Sincethe accumulation of NO₂^--N was not found, the inhibition effect of FA on NOB wasnot as much as on AOB. Moreover, the activity of NOB increasedthe inhibitory actiondoes not observed in NOB, with the concentraions of FA.The sustained load test with influent pH to8.0and adequate alkalinity showedthat the critical inhibition concentration of AOB （15.0mgN/L） decresed. When FA wasmore than15.0mgN/L, inhibition effects of FA on nitrifying bacteria communitieswere observed obviously. NOB was inhibited with the concentration and theinhibitory theory need to be study further more.PCR-DGGE and FISH showed that for AOB, the sustained load test withoutadjusting influent pH product the most serious effect, which mean a lot of bacteriumdisappeared and biological diversity reduced. When we took some actions, such ascontrolling the pH and alkalinity, the disappeared bacterium recovered again. On thecontrary, for NOB, when controled the influent pH, the NOB bacterium increasedobviously but when controled the influent alkalinity, they disappeared obviously.