Processes Control On Partial Nitritation Coupled With Anaerobic Ammonium Oxidation And Its Application To Nitrogen Removal From Landfill Leachate

Leachate generated from landfill contains high concentrations of ammonium and organic compounds, varies significantly in composition and flow rate, thus making its treatment energy-gobbling and highly expensive when using conventional nitrification and denitrification processes. Due to the high cost-effectiveness and efficiency, combined partial nitritation （PN）-anaerobic ammonium oxidation （ANAMMOX） process, is a promising alternative to conventional nitrification and denitrification for nitrogen removal from landfill leachate. However, the PN-ANAMMOX technology has not yet been fully investigated; there have still been some barriers remained to be solved. Both ammonia oxidation bacteria （AOB） and ANAMMOX bacteria （AnAOB） are slow growers, and are susceptible to the variation in wastewater compositions and operational conditions, thus resulting in a slow reactor startup and a difficult process control and a frequent instability in operation.The overarching goal of this research was to solve the above issues:to investigate the fast startup, loading enhancement and process control of the PN and ANAMMOX units, to examine the rules of the process control on combining PN-ANAMMOX by means of two-stage and one-stage modes. The results are listed as follows.（1） By using conventional fixed-time control in a sequencing batch reactor （SBR）, partial nitritation of landfill leachate was achieved under both intermittent and continuous aeration modes. The adjustment of total air flux （TAF）/influent loading rate （ILR） ratio was observed to be effective to inhibiting nitrate formation. The effluent pH was found to be an indicator for effluent NO2--N/NH4+-N molar ratio. Due to more granules formed in the reactor operated under intermittent aeration mode, the nitrogen and COD removal performance were superior to those observed in continuous aeration mode.（2） During the PN experiment in an SBR with a10times bigger volume （50L）, combiantion of partial nitritation and denitrification was achieved by using flocculent activated sludge. Inhibition of nitrate formation can also be achieved by adjusting the TAF/ILR ratio; effluent pH was also observed as an effective indicator for effluent NO2--N/NH4+-N molar ratio. The analysis of the state in an SBR cycle showed that simultaneous nitrification and denitrification occurred in the first aeration stage.（3） Endpoint pH control technique was used in the PN-SBR system for landfill leachate treatment by combination of partial nitritation and denitrification, resulting in a stable performance during long-term operation. Dynamically setting a suitable endpoint pH was the key to achieving optimal effluent NO2--N/NH4+-N molar ratio. Air flow rates at0.8,1.2and 1.6m3/h had unnoticeable effect on effluent NO2--N/NH4+-N molar ratio. Reaction temperatures at30℃,33℃and36℃had also unnoticeable effect on effluent NO2--N/NH4+-N molar ratio. Influent flow rate had no obvious effect on effluent NO2--N/NH4+-N molar ratio as well.（4） By using the activated sludge in the PN-SBR and a small amount of ANAMMOX sludge from a UASB, fast startup of ANAMMOX reactor with NRR of6.2kg N/m3/d on day91was achieved. The pH, conductivity and effluent nitrate concentration can be the performance indicators of ANAMMOX reactor. Influent pH and NO2--N/NH4+-N molar ratio were found to significantly affect the ANAMMOX performance. Therefore, it is necessary to impose an equalization tank between the PN and ANAMMOX units for two-stage PN-ANAMMOX process. The optimal influent pH was7.0-7.5and NO2--N/NH4+-N molar ratio was1.25-1.35.（5） The effect of organic compounds on AnAOB was investigated by adding raw landfill leachate as organic compounds in the ANAMMOX feed. The results showed that ANAMMOX performance was fluctuated and it was unable to achieve high rate nitrogen removal owing to the inhibition of organic compounds in the leachate. In contrast, it is successful to attain high rate nitrogen removal from the diluted PN-treated leachate, leading to development of reddish ANAMMOX granules. When the organic COD in the influent was around200mg/L, the NRR reached8.9kg N/m3/d, which is much higher than that reported in other related studies. Moreover, pH, conductivity and effluent nitrate can be used as indicators of performance of ANAMMOX reactor fed with diluted PN-treated leachate.（6） Two-stage PN-SBR and ANAMMOX-UASB process was able to achieve efficient nitrogen removal from landfill leachate. Despite the significant variation in composition of landfill leachate, stable PN performance was witnessed in the PN-SBR using dynamic endpoint pH control technique. During the treatment of100%of PN-treated leachate in the ANAMMOX-UASB, high rate nitrogen removal can be achieved. Later on, after shock of high influent pH due to lack in reactor operation, the reactor performance is fluctuated and unstable during treatment of100%of PN effluent. Finally,85±1%of nitrogen removal and0.75±0.12kg N/m3/d of NRR were achieved when the ANAMMOX-UASB was operated under lower nitrogen load. Cloning analysis of the activated sludge in the PN-SBR indicated that one operational taxa unit （OTU） was99%related to the AOB species of Nitrosomonas sp. IWT514, one OTU was96%related to Nitrosomonas eutropha （NR₀27566） and two OTUs were96%related to Nitrosomonas eutropha （CP000450）. A variety of uncultured bacteria, however, no nitrobacter were found in the PN-SBR. AOB only accounted for0.24%of the total bacteria, surprisingly, AnAOB accounted for0.04%of the total bacteria, but no nitrobacter were found. The AnAOB in the ANAMMOX-UASB were highly related to Kuenenia stuttgartiensis （CT573071）, and accounted for8.34%of total bacteria, while AOB accounted for0.1%of total bacteria, no nitrobacter were observed.（7） By using floc-like AOB and granular AnAOB as seeds for the completely autotrophic nitrogen removal over nitrite （CANON） reactor, and adding a small amount of nitrite in the feed during the first45days, fast startup of CANON reactor was achieved. Proportion of addition of landfill leachate in the feed was then gradually increased till100%of raw leachate （C/N ratio of0.80-0.95）; the nitrogen removal performance was stepwise improved. On day101, NRR reached1.32kg N/m3/d, and the nitrogen removal efficiency was81%. The qPCR analysis showed that AOB accounted for only1%-3%of the total bacteria in the CANON system, AnAOB accounted for a lower proportion （0.3%） of total bacteria. There were a variety of other bacteria in the CANON sludge, indicating the great bacterial diversity in the system.