Domestic Wastewater Treatment By Modified UASB Reactor And Subsequent Systems For Nitrogen Removal

In recent years,domestic treatment using UASB reactor has been widely applied. However,the effluent COD concentrations of domestic sewage from UASB reactor are still high,difficult to reach the national emission standards of domestic sewage treatment plants(level 2) and a higher concentration of effluent sulfide.Studies showed that a large portion of the anaerobic treated effluent COD was contributed to sulphide and the anaerobic biological treatment of waste water in basically did not remove ammonia nitrogen.Therefore,the efforts of improving the anaerobic process in order to reduce effluent COD have great practical significance to promote the anaerobic treatment of domestic sewage.Appropriate follow-up processes are also needed to solve the problem of ammonia nitrogen in effluents,so that anaerobic treatment can be better applied in domestic sewage water treatment.This study discussed the removal of sulfide and its mechanisms after adding iron particles into UASB reactor,and the overall improved performance of UASB reactor. This study also researched the removal of ammonia nitrogen through two kinds of follow-up process of UASB reactor(electrochemistry and absorption) and their feasibilities.The main results are as follows:1.After adding iron shavings into UASB reactor,the average COD,sulfide,SS in the effluents were 47,8 and 8 mg/L,respectively,reduced by 55,12 and 13 mg/L, respectively,comparing with the values before adding iron shavings.Both reach the national emission standards of domestic sewage treatment plants(level 1A).Iron shavings formed Fe²⁺ in UASB reactor,and S^2- generated by sulfate reduction formed FeS precipitation,thus reducing the effluent sulphide;hydrated compounds formed by dissolved iron in some parts have led to the decreases of effluent SS,color and turbidity,significantly improved the apparent traits of effluents.2.In Electrochemical treatment of UASB reactor effluents,the ammonia nitrogen removal efficiency increased with the raises of current density,chloride ion concentration and HRT.If the current density was 15.4 mA·cm^-2,the effluent ammonia nitrogen reduced to 17,10,5 mg/L,when HRT was 30,60,90 minutes, respectively,reaching the national emission standards of domestic sewage treatment plants(level 2,level 1B and level 1A,respectively).If HRT was 90 minutes,the effluent ammonia nitrogen could reach the national emission standards of domestic sewage treatment plants(level 2,level 1B and level 1A,respectively),when the current density was 7.6,11.6,15.4 mA·cm^-2,respectively.In accordance with the actual use of energy consumption and emission standards,appropriate process conditions were chosen.The initial COD concentration in wastewater had influence on electrochemical removal of ammonia nitrogen,to a certain extent.The higher the COD content was,the slower the removal rate of ammonia nitrogen was,and vice versa.3.In the static adsorption study,the adsorptions of ammonia nitrogen by four kinds of materials followed Freundlich or Langmuir isotherm,especially Langrnuir isotherm.The static saturated adsorption capacity of Zeolite and Na-zeolite was 8.09 and 13.55 mg/g,respectively,much higher than that of vermiculite.Na-modification of Zeolite significantly increased its adsorption capacity and adsorption effect,which is of high value.In the dynamic adsorption study,the adsorption rate of adsorption column had relationship with influent concentration of ammonia nitrogen.The higher the influent concentration was,the shorter the time of zeolite reaching saturated adsorption was.The new technique of electrochemical regeneration of saturated zeolite was proposed for the first time.Zeolite was used in 213 mg/L ammonia nitrogen solution.The regeneration of zeolite by electrochemistry cost only 3 h,while it would cost around 15 h using NaCl,and 3.5 h using NaCl + NaOH(weight ratio of 3:7).In electrochemical process,ammonia nitrogen could be oxidized into nitrogen, resolving the difficulties of renewable liquid treatment,and realizing no ammonia nitrogen emissions.