Nitrogen Removal From Landfill Leachate By A Combined Ex Situ And In Situ Biological Processes

The "sanitary" landfill technique, as it is practiced today, is one of the most important methods for municipal solid waste disposal in China. In recent years, more stringent discharge standard for landfill leachate (GB16889-2008) is imposed by the Chinese government. However, treatment of landfill leachate produced from the landfill, which is characteristic of high COD and ammonia concentration, becomes the bottleneck of sustainable development of sanitary landfill. Therefore, it is imperative to develop economic and efficient technology for landfill leachate treatment. Bioreactor landfill, which consists in controlling moisture through the recirculation of the leachate or by other means, lays the foundation for combined ex situ and in situ process. The objectives of this study were:(1) to assess the nitrogen removal performance by a combined process with ex situ nitrification/in situ denitrification/MAP precipitation/coagulation/soil infiltration;(2) to establish the correlation between the abundance of nitrifiers and nitrification performance;(3) to explore primary functional denitrifiers in the landfill bioreactor;(4) to assess the nitrogen removal performance by Anaerobic fermentation/Sharon/Anammox process. The obtained results will provide profound role in nitrogen removal from landfill leachate by combined ex situ and in situ biological process. The primary results of this study are summaried as follows.(1) A combined process consisting of ex situ nitrification and in situ denitrification in landfill refuse was studied in pilot scale for nitrogen removal from municipal landfill leachate. The results showed that simultaneous organic matter removal and complete ammonia oxidation was accomplished in a single aerobic reactor at COD loading rate of2.48Kg/(m3·d) and NH4+-N loading rate of0.37Kg/(m3·d). Above80%of partial nitrification ratio and an average COD loading rate of1.50Kg/(m3·d) were steadily maintained under DO concentrations of1.00-1.70mg L-1Quantitative PCR results indicated that the abundance of ammonia oxidizing bacterial (AOB) amoA and nitrite oxidizing bacterial (NOB) nxrA genes were highly correlated with the specific ammonia removal rate and specific nitrate production rate. The gene copy number of amoA ranged from9.08×108to6.71×109copies/g VSS, and gene copy number of nxrA ranged from1.53×107to1.54×109copies/g VSS.(2)7-year-old landfilled refuse exhibited high denitrification capacity. Nitrified landfill leachate could be denitrified in the landfill bioreactor with total oxidizing nitrogen (TON) removal rate ranging from16.4-67.2g N/(t-TSwaste d). Clone and sequencing analysis of denitrifying bacterial nirS gene inferred that heterotrophic Azoarcus tolulyticu was the primary denitrifier in the landfill bioreactor. The combined process consisting of ex situ nitrification/in situ denitrification/MAP precipitation/coagulation/soil infiltration showed high COD and ammonia removal. When the influent COD and ammonia of leachate were2983-11780mg/L and910-1731mg/L, respectively, the effluent of COD lower than500mg/L, ammonia lower than25mg/L and TN lower than60mg/L was achieved.(3) A microbial community on two sludge samples from a SND reactor and Sharon reactor was analyzed by high throughput sequencing. The obtained results indicated that the corresponding most dominant phylum in the two samples are Betaproteobacteria, Gammaproteobacteria, Bacteroidetes. However, different bacterial composition at genus level was found in the two samples. The dominant process in the SND sludge was heterophic denitrification, autotrophic denitrification, ammonia oxidation, organic decomposition, and bulking, as well as potential anammox. The dominant genus was Thauera, Nitrosomonas, uncultured Anaerolineaceae, Saprospiraceae and Planctomycetes. While the dominant process in the Sharon sludge was heterophic denitrification, autotrophic denitrification and ammonia oxidation. The dominant genus was Rhodanobacter, Ottowia and Nitrosomonas.(4) A combined process consisting of in situ anaerobic fermentation and ex situ Sharon/Anammox was studied for methane recovery and nitrogen removal from municipal landfill leachate. The results showed that COD removal rate was1.0Kg/(m3·d) and methane production rate was0.47L/g COD. Stable short-cut nitrification could be achieved at FA concentration of1-280mg/L in Sharon reactor. The effluent NO2-/NF4+ratio could be adujusted by the ratio of influent alkalinity/NH4+. Anammox was started up successfully using SND sludge from landfill leachate treatment. In the phases of sluggish, it is helpful for rapid start-up of Anammox at nitrite concentration lower than60mg/L. Low percentage of effluent from Sharon reactor could promote the Anammox activity, while the presence of biodegradable organic matter could inhibit the Anammox activity. When the influent ammonia and nitrie concentration ranged from550to620mg/L, the effluent ammonia and nitrie concentration were lower than5mg/L, nitrate concentration was lower than100mg/L. Nitrogen removal rate could reach at about200mg/(L-d).