Nitrogen Removal Of Sludge Digester Liquor Based On Simultaneous Partial Nitrification/anammox/denitrification(SNAD) Process

Recently,the biological denitrification technology based on anammox process has been the research focus in the low C/N wastewater treatment.However,anammox activity is susceptible to environmental conditions,such as organic carbon,DO,and NO2--N.The long double time of anammox bacteria(11d)results in long start-up period problem of anammox process.The above problems limit the full-scale application of anammox process.In this study,a low-energy side stream biological treatment process based on simultaneous partial nitrification,anammox and denitrification(SNAD)process was designed to treat sludge digester liquor,which was also aimed to break the bottleneck of anammox industrial application.The first full-scale SNAD reactor for sludge digester liquor treatment was established in China.The fast start-up of anammox process and the feasibility of SNAD prcess were mainly investigated.The optimal operating parameters and change of the microbial community in the SNAD process were studied.The start-up and operation strategy of the full-scale application of SNAD process were detailed introducted.The main innovative research results of this study have been obtained as follows:(1)The activity of anammox bacteria stored at 4 ? reactivated faster than the anammox bacteria stored at the room temperature through the contrast experiment,and the sludge characters during the reactivating process,including settleability and particle size,were also better.Adding 0.1 g/L graphene oxide(GO)promoted the reactivation rate of the anammox bacteria and contributed to forming anammox granules which showed good settleability.(2)The operating parameters of the intermittent aeration SNAD-MBR(influent carbon to nitrogen ratio(C/N),alternating aerobic/anaerobic(Tae/Tan)period and air flow)were optimized through response surface methodology(RSM).The optimal operating parameters were:a C/N of 0.42-0.55,a Tae/Tan of 1 min/(2.5-3.1)min and an air flow of 0.48-0.51 L/min.Under these conditions,the TN and COD removal efficiencies was 92.4%and 98.1%,respectively,and indicating that a reasonable control operation model and nitrogen removal process by the cooperation of partial nitrification,anammox and denitrification were established.In the SNAD process,the total nitrogen(TN)removal by anammox process was 76.1%,and the denitrification process contributed to 19.0%of TN removal and 95.0%of COD removal.The spatial distribution of microbial community in the SNAD granules depended on the DO concentration.FISH(fluorescence in suit hybridization)analysis showed that the biomass in the outer part of the SNAD granule was mostly AOB,while ANAMMOX and denitrifiers were in the inner anoxic part.In this study,the recycling gas(air and biogas)sparging for controlling low DO concentration and relieving membrane fouling was successfully operated to realize the long-term operation of the anerobic membrane.(3)A pilot-scale partial nitrification-anammox(PN/A)reactor was successfully started up for sludge digester liquor treatment.An efficient PN process was obtained by controlling the concentration of DO(0.3-0.8 mg/L),free ammonia(0.7-8.4 mg/L)and free nitrous acid(0.02-1.0 mg/L).A stable anammox-suited effluent was obtained through the PN process.During the start-up of anammox process,adding 3.5 mg/L hydroxylamine enhanced the anammox reactivation rate.On day 148,the nitrogen removal rate(NRR)of anammox reactor was 1.24 kg N/(m3 d)and the specific anammox activity(SAA)was 1.01 kg N/(kg VSS.d).The bacteria exhibited improved granule properties at a specific input power between 0.065 and 0.097 kW/m3.The heme c content in the anammox sludge increased from 0.42 ±0.10 to 5.77± 1.00 ?mol/g VSS from day 0 to 120.And the heme c content in the anammox granule sludge is higher than that in the flocculent sludge.High-throughput sequencing techniques demonstrated that Candidatus Brocadia was the dominant genus in the anammox reactor.Keeping a constant influent nitrogen load rate(NLR),low hydraulic retention time(HRT)can promote the growth rate of the anammox bacteria.(4)The start-up of full-scale sludge digester liquor treatment process based on SNAD-MBBR was divided into two stages.Firstly,the tandem-type PN/A process were started up for the proliferation of anammox bacteria;secondly,the integrated SNAD process was started up.After biofilm developing on the carriers,the carriers were transfered from the pilot-scale anammox reactor to the full-scale reactor,which was favorable for the fast start-up of full-scale anammox reactor and enrichment of anammox bacteria.The anmmox process with a good nitrogen removal performance was successfully started up by mixing the nitrification sludge and anammox sludge as inoculum.According to the biomass concentration in the anammox reactor,the nitrosation sludge and anammox sludge were gradually mixed to start up the SNAD process.After 2 months,the nitrogen removal efficiency of the SNAD reactor 1 and 2 reached 68%and 71%,respectively,and the COD removal efficiency reached 55%and 60%,respectively.High-throughput sequencing techniques demonstrated the coexistence of ammonia oxidizing bacteria,anammox bacteria and denitrifying bacteria in the SNAD reactor,indicating the successful start-up of the SNAD process.In addition,Candidatus Brocadia was the dominant anammox genus in the SNAD reactor.