Magnetic Coagulation Biological Combination Of Process Study On City Malodorous River

Due to the lagging construction of urban wastewater treatment facilities,urban river water bodies have been widely polluted.In order to improve the quality of urban water environment as soon as possible,setting deadlines for eliminating black-colored and odorous water bodies in built-up areas is reinforced.Although the coagulation magnetic(Co Mag)technology which has got extensive application nowadays can greatly reduce the footprint and effectively remove TP and SS,the removal effect to NH4+-N and dissolved COD is low.By contrast,biological methods exhibit significant advantages.In present work,combination of Co Mag and different biological methods including biological aerated filter(BAF)and membrane bioreactor(MBR)were taken as cases to study their efficiencies to treat the polluted river in urban areas,and highly effective integrated system was then proposed.The operational parameters of Co Mag are optimized by static and dynamic tests.Best results were obtained when coagulant PAC and anionic coagulant aid PAM were selected,each with the dosage of 30 mg/L and 1.5 mg/L,respectively.300 mg/L Fe3O4 magnetic powder with the diameter of 45~75 ?m was recommended.And the dosing sequence is magnetic species and PAC added simultaneously first,and then PAM.The optimum field strength and disk speed were 3500 GS and 4 r/min.The effluent concentration dropped from 3.22 to 0.40 mg/L for TP,and from 120 to 9 mg/L for TP respectively for HRT of 9 min.In addition,the dosage of PAC,PAM and magnetic seed were also optimized under different water quality conditions.Based on the batch experiments,the bioassay parameters of BAF and MBR devices were optimized and comprehensive comparison was carried out to determine the suitable biological treatment stage combined with Co Mag.The results showed that both the BAF and MBR had excellent removal efficiencies of NH4+-N and dissolved COD,guaranteeing the five kinds standards of the national groundwater environmental quality.However,as a comparison of MBR,BAF exhibited more advantages in energy saving,operating cost and start-up cycle.Therefore,BAF was chosen as the biological segment to be coupled with Co Mag.Taking the practical Co Mag effluent from the field as a case,the operational parameters of pilot scale BAF were further optimized and the removal efficienc y of the integrated process was investigated.The results showed that the optimum HRT and air-water ratios of BAF were 0.5 h and 3:1,respectively,with influent COD and NH4+-N values of 47 mg/L and 14 mg/L.In order to ensure effluent quality,the layer thickness should be 3.5 m at least.Effective removal of various contaminants could be achieved by the combined process with HRT of 9 and 30 min for Co Mag and BAF,respectively.The corresponding effluent COD,NH4+-N,TP and SS reached 16,1.11,0.12 and 10 mg/L,meeting the five kinds standards of the national groundwater environmental quality.