Research On Nitrogen Removal Efficiency And Microbial Properties Of PN-ANAMMOX Combination For Low Strength Wastewater Treatment At Ambient Temperature

The current wastewater treatment systems are required for removal ofnitrogenous compounds, which could cause eutrophication of surface water bodies.Compared with the conventional nitrification/denitrification process, partialnitrification （PN） coupled with anaerobic ammonium-oxidizing （ANAMMOX）process is an ideal biological nitrogen removal choice. It could save aeration energyconsumption, as well as less biomass production and without organic carbonconsumption. However, most of PN-ANAMMOX processes focused on treatingwarm （>30℃） and concentrated （>500mgN/L） waste streams. On the other hand,the key of promotion process relies on knowing the microbial communityinvolvement. Ammonia oxidizing bacteria （AOB） and ANAMMOX bacteria arefunctional microorganisms in PN-ANAMMOX process. Analysis of microbialcommunity structures and functional microorganisms will contribute to PN andANAMMOX processes optimization. Hence, the aim of the present study was toprovide theoretical guidance for PN-ANAMMOX process treating low strengthwastewater at ambient temperature.Partial nitrifying experiments were carried out basing on sequencing batchbiofilm reactor （SBBR） and sequencing batch reactor （SBR）, which were used forcomparison partial nitrification treating low strength nitrogen wastewater at ambienttemperature. Partial nitrification of SBBR and SBR could be rapidly realized sinceAOB were domesticated in low strength wastewater as influent ammoniumconcentration gradually decreased. Free ammonia （FA） was the key factor affectingmicrobial community of both SBBR and SBR. Nitrosomonas were predominantAOB in SBR with low ammonia influent. The microbial characteristic ofpredominant AOB and less NOB contributed to stable partial nitrification of SBRtreating low strength wastewater at ambient temperature.Experiments of ANAMMOX were carried out under low temperature, with theaim to provide a reference for ANAMMOX process running and optimization inwinter time. The biofilter filled with volcanic rocks had higher nitrogen removalcapacity than that of ceramic packed biofilter at low temperature （15-16.5℃） inwinter. Total nitrogen removal rate of B2was1.57kg/（m³d）, which was muchhigher than that of B1（0.52kg/（m³d））. The genus of ANAMMOX bacteria was bothCandidatus Kuenenia stuttgartiensis in two reactors. However, ANAMMOXbacteria had more densely distribution in volcanic rocks biofilter, which indicatedthat volcanic rocks were more suitable for ANAMMOX bacteria enrichment in biofilters. Nitrogen removal rate along volcanic ANAMMOX biofilter wasinvestigated. Results showed that a large proportion of ammonia and nitriteproportional disappeared in the middle part of biofilter. It was owed to theproportion of ANAMMOX bacteria in middle of biofilter was bigger than that inother parts by FISH analysis. There was only one type of ANAMMOX bacteriumand AOB present in different parts of biofilter, which were identified as CandidatusKuenenia stuttgartiensis and Nitrosomonas sp. ENI-11, respectively.Based on previous volcanic ANAMMOX biofilter, experiments were carriedout to investigate nitrogen removal rate of bioreactor for low strength wastewatertreatment at ambient temperature （14.5-24.5℃）. The results showed ANAMMOXbiofilter had the ability to maintain high capacity of nitrogen removal rate underlow ammonia concentrations of periodⅠ（78.7mg/L） and periodⅡ（46.5mg/L）. Forexample, average and maximum total nitrogen removal rates were2.26kg/（m³·d）and3.04kg/（m³·d） at periodⅡ. The sequence of ANAMMOX16SrRNAidentification revealed that Candidatus Kuenenia stuttgartiensis occurred in all highand low matrix periods. However, it had a little difference of relative proportions inthree periods, which were accounted for41.6%、37.9%and36.3%. Nitrogenremoval rate along biofilter showed that a large proportion of ammonia and nitriteproportional disappeared in the middle part of biofilter. Candidatus Kueneniastuttgartiensis had wide adaptability to variable temperature and substrateconcentrations, which indicated that it had potential to apply such ANAMMOXbacteria for low strength wastewater treatment at ambient temperature.On the basis of independent running partial nitrification and ANAMMOXreactors, PN-ANAMMOX experiments were developed for sewage treatment atambient temperature. After PN unit start-up, plug-flow continuous stream runningwas carried out with low DO concentration （0.1to0.6mg/L）. EffluentNO₂^--N/NH₄⁺-N of PN was relatively stable, which was suitable for subsequentANAMMOX unit. Biofilter was successful started up after25days by addingmature ANAMMOX sludge. The bioreactor had a satisfactory nitrogen removalpotential with maximum nitrogen removal rate of0.99kg/（m³·d） and maximumnitrogen removal efficiency of85.6%. Analysis of PN-ANAMMOX couplingfactors showed that NO₂^--N/NH₄⁺-N was the key factor, which could affect nitrogenremoval of ANAMMOX biofilter. The outlet water quality of ANAMMOX unitsatisfied the Standard A of the first class in “Discharge standard of pollutants formunicipal wastewater treatment plant （GB18918-2002）” when the ratio ofNO₂^--N/NH₄⁺-N was between1.01to1.45.After PN-ANAMMOX successfully coupled, spherical and short rod bacteria were predominant in partial nitrifying sludge, in which AOB was the dominantbacteria. The genus of AOB was Nitrosomonas sp., which could be coexisted withother heterotrophic bacteria harmony in PN unit. Combining FISH analysis withSEM observations confirmed the superiority of ANAMMOX bacteria in thecultivated biofilm. The principal anammox bacteria shifted from members related toCandidatus Kuenenia stuttgartiensis present in the initial inoculum to membersrelated to Candidatus Brocadia fulgida in biofilm. Candidatus Brocadia fulgidawere the functional ANAMMOX bacteria in the reactor, which could survivecomfortably in sewage with a limited amount of COD. AOB and denitrifyingbacteria were also found in the bifofilm, which were the members of microbialcommunities living together with ANAMMOX bacteria. The functional microbialpopulations contributed to stable nitrogen removal rate of ANAMMOX unit toaccommodate the slight fluctuation of influent NO₂^--N/NH₄⁺-N.