Performance Of Abr Process For Catering Wastewater Pretreatment At Normal Temperature

With the rapid development of the catering industry,a large amount of untreated catering wastewater is discharged into the municipal sewage pipe network,putting pressure on the operation of urban sewage treatment plants.The anaerobic baffled reactor?ABR?was extended to pretreat catering wastewater from a western fast food restaurant,where the effects of HRT?24h?6h?on performances was investigated at normal temperature?8?-31??.Aiming at the poor water quality of ABR in autumn and winter,the effluent reflux optimization measures are adopted to provide theoretical guidance for the application of ABR at normal temperature.By inoculation of anaerobic/aerobic mixed sludge and controlling of the initial conditions(i.e.,HRT 24h,volumetric load 1.7 kg COD·m^-3·d^-1),ABR successfully started after 55d,the effluent COD removal rate is above 40%.During the continuous 243d operation in normal temperature,the overall COD removal rate of reactor is 30%-81%.The results showed that HRT and temperature had a synergic effects on COD degradation,and the removal loading rate,gas production and methane ratio reached their respective maximum of 3.9 kg COD·m^-3·d^-1,219 mL CH₄·g^-1 COD and 37%at HRT 12h and 25?.The effluent COD,BOD₅,SS,animal and vegetable oils could also meet the discharge standards.Changes in pH and gas production at different temperatures and HRT indicate:low temperature or hydraulic shock in autumn/winter inhibited the conversion and removal of carbon,and thereby made acidogenic phase in compartments to move backward with an increasing effluent pH value and simultaneous accumulation of propionic acid,butyric acid and valeric acid.It further resulted in the deterioration of operational performances,in terms of COD removal,gas production,CH₄ generating efficiency and its volume ratio,and which would adversely affect the application of ABR at normal temperature.There is sludge granulation in ABR,but the degree of granulation is low and the particle size is small.The size,color and properties of sludge in each compartment along the direction of water flow are greatly affected by organic load.Along the compartment direction,VSS/SS increases,VFA decreases,and specific methanogenic activity of sludge enhance.Each compartment also exhibits different microbial features,with the front compartment being dominated by bacilli and filamentous bacteria,and the rear compartment being dominated by cocci.And the ABR has achieved phase separation of acid production and methanogenesis.To overcome the effects of low temperature in autumn and winter on sludge activity and mass transfer reaction,this paper optimizes the water quality of ABR effluent through comprehensive supporting measures such as effluent reflux and three-phase separator setting.At the optimum reflux ratio of 70%,the COD removal rate is increased to about 70%.And the effluent water quality meets the discharge standards.The results show that proper effluent reflux ratio can ameliorate the VFA accumulation in the reactor.The acetic acid and propionic acid contained in the reflux are beneficial to the utilization of methanogenic bacteria in the front compartment,enriching the microbial population in each compartment,and improving the stability of ABR.