Process And Mechanism Based On Anammox Treating Mature Landfill Leachate

Although the disposal of solid waste in landfills served as the most common method of waste management,the produce of leachate is inevitable.The treatment of sanitary landfill leachate constitutes one of the major obstacles for the community,mainly due to the high amount of ammonia and recalcitrant organic substances.Thus,developing an effective and cost-saving removal method is of great importance.As a new biological nitrogen removal technology,anammox has the characteristics of low consumption and high efficiency,which can solve the problem of low biodegradability of mature landfill leachate.However,the reaction substrate NO₂^-of anammox process is difficult to obtain stably,and 11%of TN exists in the form of NO₃^-in the effluent,making it difficult for the effluent to meet the discharge standard.In view of the above problems,starting from the acquisition of anaerobic ammonium oxidation reaction substrate NO₂^-,this study first investigated the influence of different factors on the realization of partial nitrification in two parallel SBR.Secondly,the feasibility of enhanced nitrogen removal of mature leachate was investigated by starting the partial denitrification and anammox（PD/A）process in a single-stage SBR.On the basis of the previous work,A combined process PN/A+PD/A（constructed by continuous flow partial nitrification reactor,annamox reactor and PD/A reactor）based on anammox was established to realize the enhanced nitrogen removal from mature landfill leachate.A strategy of rapid short-cut nitrification with continuous addition of hydroxylamine and real-time control was proposed.Nitrite accumulation was investigated under different DO conditions and different hydroxylamine addition methods in two parallel sequencing batch reactors.The nitrite accumulation rate during with DO concentration of 2.0 and4.0mg/L increased to 44.8 and 66.7%in 20 days.During hydroxylamine addition,the NAR increased over 90%under the continuous and intermittent hydroxylamine addition.Continuous hydroxylamine addition could result in a more efficient and rapid nitrite accumulation.The findings suggested that comammox could be the main reason for the failure of partial nitrification in a low DO environment（<0.5mg/L）.The nitrogen variation during typical cycles showed that the continuous hydroxylamine addition suppressed the activity of NOB and the ammonia oxidation rate.Further,the q PCR results indicated that the abundance of comammox amo A（ranged from 6.25×10⁷ to 4.16×10⁸copies/g VSS）was higher than those of AOB amo A and Nitrobacter in sludge samples.This study proposed an economical process for enhancing nitrogen removal from nitrate-rich leachate which combined partial-denitrification and anammox（PD/A）in a SBR.Under the concentration of influent ammonia and nitrate of 47.5mg/L and 93.7mg/L on average,TN removal efficiency of 84.8%was obtained with the effluent TN less than20mg/L.It was found that enhanced nitrogen removal of mature landfill leachate through PD-anammox was estimated to save 40%organic carbon addition and reduce the cost of sludge treatment in this study.Moreover,the ORP and p H could potentially be used as control parameters to maintain the stability of combined process.A novel continuous-flow combined process of partial nitrification,Anammox（PN/A）and partial denitrification-Anammox（PD/A）was established to achieve enhanced nitrogen removal from landfill leachate.The NH₄⁺transformation rate and NO₂^-accumulation rate in the PN reactor reached 93.4%and 91.5%,respectively.The nitrite generated from the PN reactor was combined with influent（38%）and fed into the Anammox reactor.The nitrate produced in the Anammox reactor was then discharged to PD/A reactor,where nitrate was transformed to nitrite and removed via Anammox.Under a COD/NO₃^--N ratio of 4.0,the NO₃^--to-NO₂^-transformation ratio（NTR）and Anammox contribution rate reached 60.4%and 57.1%in PD/A reactor.The final effluent TN concentration was 15.7mg/L,and the efficiency of TN removal could reach 98.8%.By combining PN/A with PD/A,enhanced nitrogen removal from landfill leachate was achieved successfully with an external carbon source addition（COD/NH₄⁺-N）of 0.28.