| Recirculation can utilize landfill bioreactor for treating concentrated leachate, but pollutants in concentrated leachate might inhibit microbial activities in landfills and thus affect landfill stablization. In this study, different ways of recirculation and the combination of microaerobic reactor ex-situ was conducted to investigate the effects of concentrated leachate on landfill stabilization. In addition, pyrosequencing was applied to analyze succession characteristics of microbial community during landfill stabilization. The main results are listed as follows.(1) Compared with the traditional anaerobic landfills, leachate and concentrated leachate recirculation might accelate the degradation of landfilled waste, reduce the volume of leachate and concentrated leachate, and decrease the discharge amount of pollutants. As the recirculated hydraulic load rate of leachate and concentrated leachate increased from 7.5 to 22.5 L/m3d, the released amounts of chemical organic demand (COD) and total nitrogen (TN) from landfills increased. Compared with the same hydraulic load rate (7.5 L/m3·d) of the mixture of leachate and concentrated leachate, the direct recirculation of concentrated leachate might inhibit the degradation of landfilled wate due to high concentrations of refractory organic matters, metals and salinity in concentrated leachate. However, NO2-N and NO3-N in concentrated leachate could be well removed in landfill bioreactors and the discharge amount of TN dropped in the landfill system with concentrated leachate recirculation.(2) The removal efficiencies of COD and TN of leachate were 80～92% and 60～70%, respectively, when the influent organic loading rate and dissolved oxygen (DO) were 2.0-3.3 kg COD/m3d and 1.0-2.0 mg/L in the microaerobic reactor. The main nitrogen compounds were ammonia and organic nitrogen in the microaerobic reactor. At the later stage of the experiment, the main organic matters in the microaerobic reactor were refractory, which caused the competition of carbon source between denitrifying bacteria and the heterotrophic bacter, leaded to the increase of nitrate and nitrite concentrations in the effluent.(3) The recirculation of one part of leachate pretreated by a microaerobic reactor to landfills not only relieve the effect of the fluctuation of quality and quantity of leachate during the landfill stablization, but also reduce the inhibitory effect of acidic pH on neutral microorganisms such as methanogenic bacteria for the recirculated liquid was neutral or slightly alkaline, and accelerate the degradation of landfilled waste.(4) The recirculation of leachate and concentrated leachate could reduce the discharge amount of pollutants in the leachate by the purification of landfills. On day 390, the discharge amount of COD and TN in the landfill system with leachated pretreated by a microaerobic reactor was 7.4 g and 0.9 g, respectively, which accounted for 0.7% and 2.6% of COD discharge amounts,1.9% and 7.5% of the TN discharge amount in the landfills without recirublation and directly recirculated with leachate.(5) Pyrosequencing analysis showed that there was a relationship between the index of richness and diversity and the recirculation of leachate and concentrated leachate, and the stabilization phase of landfills. Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria dominated in landfills. Comamonas, Stenotrophomonas and Pseudomonas, belonging to the Proteobacteria, accounted for 29.2% of the total bacteria. The composition and richness of the denitrifying bacteria varied with the time of landfill. Comamonas was the main denitrifying bacteria in traditional anaerobic landfills. On day 30, the main denitrifying bacteria were Comamonas, but Rhodanbacter dominated at the later stage in the landfill system with leachate recirculation pretreated by a microaerobic reactor. |
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