Advanced Nitrogen Removal From Landfill Leachate Treatment Via SBR Technology Without Extra Carbon Source Addition

Landfill leachate is a kind of refractory wastewater, which is characterized bycomposition complexity of organics, high concentration of ammonium （NH⁺₄-N）,gerneral existence of heavy mantal ions and dispropoertionality of nutrients.Considering the above specifics, the application of biological processes in landfillleachate treatment is limited. Among the biological processes, sequencing batch reator（SBR） technology is widely used in special organic wastewater treatment due to itssimple construction, flexible operation conditions, excellent sludge settleability andoutstanding resistance to shock loads. In order to estimate the fesibility aboutadvanced nitrogen removal from real landfill leachate via SBR technology andresearch the mechanism and influencing factors of nitrogen removal course,SBR-ASBR, single stage pulsed SBR and ASBR-pulsed SBR systems treating reallandfill leachate were builded on the basis of experimental analysis and relativetheories. In such a case, the anaerobic ammonium oxidation （Anammox） andendongeous denitritation processes were explored for landfill leachate treatment.Based on the research of treaement performance, nitrogen removal mechanism andinfluencing factors, several results were obtained as follows:1) With regard to mature, middleage and immature landfill leachate,advanced nitrogen removal was achieved via these different systems.a) SBR-ASBR system. Take low COD/TN （C/N） ratio that mature landfillleachate had into consideration, a process combined nitritation （SBR） with Anammox（ASBR） was used. When the total nitrogen （TN） load kept around1.2kgN·m^-3·d^-1,effluent NH⁺₄-N and nitrite （NO^-₂-N） concentration were both blew3mg·L^-1, andeffluent NO-3-N concentration also kept less than60mg·L^-1, which resulted in the TNremoval ratio of more than90%. In addition, continuous feeding mode was proposedfor ASBR to weaken the inhibition from free nitrite acid （FNA）.b) Single stage pulsed SBR. As for middleage landfill leachate with the C/N ratioof3-5, single stage aerobic process would be suitable to treat it. This system realizedNH⁺₄-N and TN removal ratio of more than95%and90%, respectively, and effluentTN was always less than40mg·L^-1which met the new landfill leachate dischargestandard （GB16889-2008.07.01）. Consequently, advanced nitrogen removal wasachieved without extra carbon source addition. The three equal feeds mode applied by pulsed SBR reduced the inhibition from free ammonia （FA）, and promoted theapplication of organics in raw leachate as the electron donor for denitritation.c) ASBR-pulsed SBR system. Traditional nitritaion/denitritation process wasapplied for immature landfill leachate treatment due to its high C/N ratio （7-9）. TheCOD and TN removal ratio reached89%and97%, respectively, under the influentCOD and TN concentration of7341-10448mg·L^-1and1279-1578mg·L^-1,respectively. Advanced nitrogen removal was also achieved without extra carbonsource addition and physicochemical pre-treatment.2) The segmental mechanism of endogenous denitritation from landfillleachate treatment was analyzed.Polyhydroxybutyrate （PHB） and glycogen were verified as the main electrondonors used by endogenous denitritaion through the standard cycle tests of pulsedSBR belonging to the immature landfill leachate treatment system, but extracellularpolymeric substance （EPS） was not the available carbon source for endogenousdenitritaion. Microorganism prefer to utilize PHB to reduce NO^-₂-N into N2at first,then glycogen would take over the role of internal carbon source as long as PHBcould only be used for biomass metabolism. As a result, the internal carbon sourcetype alteration used by endogenous denitritation would make the specific denitritationrate （DNR） changed from fast to slow. Moreover, a hypothesis was presented todemonstrate the existence of denitrifying glycogen-accumulating organisms（DNGAOs） what might be the dominant culture with respect to endogenousdenitritation.3) The influencing factors affecting organics and nitrogen removalperformance from SBR technology was discussed.a) The effects of NH⁺₄-N concentration on anaerobic digestion. As for CODremoval ratio and methane production rate of ASBR, the inihibition from highNH⁺₄-N concentration was found through improving the influent NH⁺₄-Nconcentration of ASBR step by step. The reason why NH⁺₄-N would suppressanaerobic digestion appeared to be that high NH⁺₄-N concentration would change thefermentation type of acid formation bacterias from acetic into propionic, and reducethe abilities of propionic acid utilization for methanogens. Opposite to that, NH⁺₄-Nconcentration didn’t has a significant influenc on acetic acid utilization formethanogens. b) The effects of influent C/N ratio on nitrogen removal performance in apost-denitritation SBR. Higher influent C/N ratio was in favor of nitrogen removalperformance. PHB degradation rate was the rate-limiting step for simultaneousnitritation and denitritation （SND） and endogenous denitritation during the famineperiod （organics presented in wastewater）. Higher influent C/N ratio benefited PHBreservoir of organisms, so it would facilitate TN removal ratio in oxic stage andendogenous DNR in anoxic stage.c) The effects of oxygen supply on nitrogen removal performance for SBR. Theresult that stronger oxygen supply would encourage nitrogen removal performance ofSBR was determined via providing4different oxygen supplies during the oxic stageof the post-denitritation SBR. For SND, the percentage and rate of SND of faminephase had a compromising relationship when volumetric oxygen transfer coefficient（KLa） increased from3.64to16.82h-1, but they both decreased under the increasedKLa to28.17h-1. For endogenous denitritation, higher KLa in aerobic stage providedmore PHB at the beginning of anoxic stage, which also led to the higher rate constantsfor PHB degradation. On the basis of that, endogenous DNR was facilitated.Consequently, build-up of high levels of PHB and reasonable oxygen managementwould improve PHB-driven nitrogen removal.