Study On The Process Characteristics Of Anaerobic Membrane Bioreactor Coupled With Anammox In Municipal Wastewater Treatment

The development and application of high-removal,low-carbon and energy-generation technologies that integrate pollutant reduction and simultaneous energy recovery have become a new trend in the development of municipal wastewater treatment.Anaerobic membrane bioreactor?AnMBR?and anaerobic ammonium oxidation?Anammox?are two new technologies developed in this context.AnMBR,which integrates membrane filtration units into anaerobic digestion,has been suggested as a promising strategy for wastewater treatment.AnMBR produces effluent of superior quality by membrane separation,and a quite low sludge growth rate because of the anaerobic environment,thereby a low level of excess bio-solid emission and disposal.Anammox is a biological reaction process in which NH₄⁺-N can be removed by anaerobic ammonia oxidizing bacteria?anammox?under anaerobic conditions.Since no extra organic matter and oxygen are required,this process is more efficient than the traditional nitrification-denitrification process.In municipal wastewater treatment,AnMBR and Anammox have good complementarity.Therefore,this study proposes to couple the AnMBR and Anammox to achieve the purpose of energy recovery and autotrophic nitrogen removal.In this study,the treatment performances of coupled AnMBR-Anammox treatment process were firstly studied,Next,sludge properties and microbial community in each reactor.properties of mixed liquor were analyzed.First,a 6 L AnMBR and 1 L Partial Nitrification/2.3 L Anammox?PN/A?reactors were respectively started-up.After the two reached steady state,they were coupled into a new process called“AnMBR-PN/Anammox”to achieve Anterior methanation and posterior autotrophic denitrification.Then,the COD and N removal efficiencies and mass balance analysis of the AnMBR-PN/A coupling process during stable operation were investigated,the fouling behaviors in AnMBR were monitored,and the characteristics of organic matter in the effluent at coupling process were examined.Finally,the sludge properties in each reactor were studied such as MLVSS,particle size distribution and specific activities.And the mechanism of microbial community in different reactors was analyzed using Illumina-Miseq high-throughput sequencing technology.The main work and conclusions are as follows:?1?The fast startup and stable operation of the An MBR-PN/A coupled system was successfully achieved.Organic matter removal reached stability 6 days after AnMBR was started,and methane production efficiency reached stable at 113 L/L-reactor/d after 28days.Total nitrogen?TN?removal rate reached more than 70%after 51 days of PN/A startup,successfully achieving quick start in segments.After coupling,at HRT=7.8 h?AnMBR organic load OLR=2.4 g-COD/L/d,PN/A nitrogen load NLR=1.54 g-N/L/d?,the removal rate of COD and TN at the AnMBR-PN/A process reached 97%and 72.9%respectively,and the average effluent COD and TN concentrations were about 17.0 and13.4 mg/L.The methane yield in the AnMBR section was 0.33 L-CH₄/g-COD_removed,and the energy recovery rate was 84.6%.?2?AnMBR contributed more than 96%of the COD removal rate,of which more than 85%of the COD was eventually recovered as CH₄,and the effluent COD remained below 30 mg/L.In this coupled process,the methanation was dominated by the acetic acid pathway,and its methanogenic potential reached 0.454 g-COD/g-MLVSS/d at HRT_AnMBR=7.2 h.The methanogenic potential of the H₂/CO₂ pathway increased significantly with shortening HRT?increasing organic load?,but it still was the auxiliary pathway.When HRT_AnMBR was shortened from 7.2 h to 5.0 h,the concentration of SMP and EPS in the mixed liquor increased,the protein to polysaccharide ratio decreased,but the protein ratio in the membrane fouling layer increased significantly.HRT was shortened,the lag force enhanced,and proteins and microorganisms in the mixed liquor were adsorbed on the membrane surface to form a compact cake layer.?3?In the AnMBR-PN/A coupled system,the PN/A completed the transformation of the N form and the final removal of the TN.The PN-SBR converted 53.5%of NH₄⁺into NO₂^-,which achieved the optimal NO₂^-/NH₄⁺ratio required for subsequent Anammox reactions.In addition,the small-growth anammox activity in the PN-SBR contributed to a certain TN removal rate.The contribution of Anammox-UASB reactor to TN removal was about 87%,of which the sludge at the bottom of the reactor had the largest contribution;a small amount of COD in the influent promoted partial denitrification in the Anammox-UASB reactor?NO₃^-?NO₂^-?,which realized the secondary supply of NO₂^-,then strengthened the activity of anammox and the removal of TN.The results of activity experiments showed that the SAA of anammox bacteria gradually weakened from the bottom to the top of the reactor,ranging from 373.8-648.9mg-N/g-MLVSS/d.The SDA of denitrifying bacteria was significantly lower than that of SAA,but the activities at different heights of the reactor were basically similar,indicating that the denitrifying bacteria are evenly distributed at different heights of the reactor.?4?Microbiological community analysis results showed that Actinomycetales,Anaerolineales,Selenomonadales,Clostridiales and other bacteria were mainly involved in the hydrolysis and acidification of organic matter in AnMBR;Methanothrix?58.45%?and Methanolinea?29.99%?were the main methanogens,accounting for 88%of all archaea,and it was confirmed that the methanation process in AnMBR was dominated by acetation.The predominant bacterium Nitrosomonas was an important functional flora in the PN-SBR and its abundance was 7.45%,which can oxidaize NH₄⁺to NO₂^-.At the same time,a small amount of anammox?Ca.Brocadia?and denitrification microorganisms?Thriotix?also had a certain abundance.The enrichment of these microorganisms was the main cause of TN removal in the PN-SBR reactor.Ca.Brocadia was the dominant microorganism in Anammox reactor,with a maximum abundance of7.77%at the bottom;in addition,a certain amount of denitrifying bacteria Thermomonas and Dokdonella were evenly distributed in the reactor,and its abundance was 0.20±0.08%.These bacteria provided anammox with additional nitrite nitrogen,further enhancing the contribution of anammox to total nitrogen removal.