Research On Shifting Of Nitrogen Removal Microbes In Aged Refuse Bioreactor Treating Landfill Leachate

Landfill leachate is one kind of highly concentrated ammonia organic wastewater, and hard to treat all the time. Traditional treatment process like nitrogen stripping and chemical precipitation usually cause secondary pollution and need a mount of chemicals, which would cost too much. Aged refuse has unique physical, chemical and biological properties, with a great number of microorganisms. The bioreactor with aged refuse has a good pollutant removal effect on landfill leachate, and has been applied in practice. However, previous studies have focused mainly on pollutant treatment performance of leachate, there are less research focused on the relationship between nitrogen removal microbial and environmental factor and treatment efficiency. Therefore, studying the changes of amount of nitrogen removal microbia is very important for optimizing the bioreactor system.In this paper, the aged refuse and slag were used as packing to build aged refuse bioreactor (complex and Anammox bioreactor) to treat the landfill leachate. The community structure of nitrogen removal microbes of the aged refuse bioreactor under different environmental factor was studied by fluorescent in situ hybridization (FISH) and traditional microbial counting methods, the relationship between the number of nitrogen removal microbial and treatment effect was analysed as well. The conclusions were drawn as follows:(1) The NH4+-N removal rate of the complex refuse bioreactor remained above99%, and operating condition had little impact on it; When hydraulic load increased from0.0085L/L D to0.017L/L D, the CODCr and NH4+-N removal rate improved; recirculation is unfavorable to the CODCr and NH4+-N removal, but high recirculation ratio (200%) is helpful to improve the TN removal rate; The additional carbon source was helpful to TN removal, but the CODCr removal rate would reduced; the bioreactor with aged refuse was benefit to the CODCr and TN removal; higher temperature is helpful to improve the CODCr and TN removal rate.(2) The number of nitrifying bacteria dropped with the increasing of hydraulic load in complex refuse bioreactor, while the number of heterotrophic bacteria, nitrosobacteria and denitrifying bacteria increased when the hydraulic loading increased from0.0085L/L D to0.017L/L D. When the hydraulic loading was low and recirculation ratio was100%, the number of heterotrophic bacteria, nitrosobacteria, nitrifying bacteria and denitrifying bacteria increased compared with no recirculation, while it decreased when recirculation ratio was excessively high (recirculation ratio:200%). Additional carbon source was helpful to increase the number of heterotrophic bacteria, nitrosobacteria, nitrifying bacteria and denitrifying bacteria. There were more heterotrophic bacteria in bioreactor with aged refuse, while bioreactor with slag and aged refuse was benefit to the growth of nitrosobacteria and nitrifying bacteria, moreover, packing materials has little impact on the number of denitrifying bacteria. The number of heterotrophic bacteria, nitrosobacteria, nitrifying bacteria and denitrifying bacteria all increased when the temperature increased.(3) The NH4+-N removal remained fine when the TN load between0.74g(TN)/kg*(vs)*d to0.95g(TN)/kg*(vs)*d in the aged refuse Anammox bioreactor, but reduced when the TN load was too high. The number of heterotrophic bacteria increased with the increasing of hydraulic loading. The number of nitrosobacteria was large when the hydraulic loading was0.049L/L D and the TN load was0.95g(TN)/kg*(vs)*d, it increased when the hydraulic loading increased, decreased when the TN load increased, which illustrate that the larger hydraulic loading was benefit for nitrosobacteria, while larger TN load was not benefit fornitrosobactia growth. The number of nitrifying bacteria and denitrifying bacteria was large when the hydraulic loading and TN load were low(respectively was0.033L/L D and0.74g(TN)/kg*(vs)*d), their number decreased when the TN load increased. The number of nitrosobacteria, nitrifying bacteria and denitrifying bacteria in the upper of the aged refuse Anammox bioreactor were higher than that in the bottom, the distribution of heterotrophic bacteria had no obvious rule, all above illustrated that the upper environment is suitable for nitrosobacteria, nitrifying bacteria and denitrifying bacteria.(4) The result of FISH showed that the existence of partial anaerobic condition in the complex refuse bioreactor which was suitable for Anammox bacteria, but the number of Anammox bacteria was not large. Nitrifying bacteria usually grow close together, while nitrosobacteria grow dispersively. Anammox bacteria existed in the aged refuse Anammox bioreactor and distributed uniformly in the upper and bottom at first; the number of Anammox bacteria was large when the TN load was medium and NH4+-N:NO2-N was between1～1.32, it decreased when the TN load was too high.(5) The number of heterotrophic bacteria had positive significance correlation with CODCr removal rate(r=0.825,p<0.01), the correlation between the number of denitrifying bacteria and the TN removal rate was found positively significant too(r=0.762,p<0.05), the correlation between other denitrificationl microbial and water quality removal rate was not significant.This study showed that increasing the hydraulic load properly was benefit for increasing the number of heterotrophic bacteria, proper recirculation ratio was also helpful to increase the number of denitrifying bacteria and the TN removal rate, additional carbon source and raising temperature properly could increase the number of denitrification microbial, and low TN load could increase that number as well, Anammox bacteria could exist in aged refuse bioreactor, adjusting NH4+-N:NO2-N could increase the number of Anammox. The correlation between the number of heterotrophic bacteria and CODcr removal rate, the number of denitrifying bacteria and TN removal rate was positive significant, which indicates that increasing the number of the heterotrophic bacteria and denitrifying bacteria was benefit for increasing the CODCr and TN removal rate.