Electrocoagulation-gravity Driven Membrane System (EC-GDM) For Grey Water Treatment

Grey water（GW）is of larger quantity and less pollution in domestic sewage,which is of great value to reuse.A reasonable grey water treatment and reuse process can not only achieve the purpose of removing pollutants,but also effectively increase the utilization rate of water resources,and promote progress development of semi-centralized sewage treatment systems.This paper summarizes the current grey water treatment technology,and proposes a low-energy,low-maintenance electroflocculation-gravity membrane filtration system（EC-GDM）for preliminary exploration of grey water treatment.The influences of reactor electrode combination,plate spacing,current density,residence time,initial pH,as well as the electrolyte Na₂SO₄ dosage were investigated,which accepts the removal rate of LAS,COD_Crr and turbidity,final pH stability and effluent flux as the evaluation index,in simulated light grey water.This article invertigate the cleaning and the membrane flux recovery rate of gravity membrane filtration system under the optimal operation conditions.The stability was verified,and the removal of TP and NH₃-N was investigated as an extr on the continuous operation of the EC-GDM unit.The experimental results show that:（1）First,the effect of EC-GDM on the grey water treatment under different conditions was investigated.The results show when using the Al-Fe-Fe-Al plate combination method,the effect of comprehensive removal of LAS,COD_Crr and turbidity is better than the case of Al-Al-Al-Al,Fe-Fe-Fe-Fe,Al-Fe-Al-Fe and Fe-Al-Fe-Al,and also have a stable effluent pH.In the process of reducing the distance of the plate from25mm to 15mm,the removal rate of LAS and COD_Cr in the effluent is obviously improved.It is not obvious to improve the removal rate of pollutants when continue to diminish the plate space,and it will easily lead to poor circulation and excessive flocs between plates.When the current density increases from 5.714mA/cm² to 7.143mA/cm²,the treatment effect of the contaminants in the grey water increases significantly.In the process of increasing the current density to 10.00mA/cm²,the removal rate of COD_Cr is not significantly improved,and even have an adverse effect for the removal of LAS.There is little difference in the stable removal effect of the reactor for LAS when the effective residence time is not less than 18min,however,the maximum COD_Cr removal efficiency at the T=22.5 min,and the best effective residence time in the electrocoagulation reaction zone is 22.5min.The flocculation,floatation and oxidation of the initial pH value of grey water in the neutral conditions are superior to the acidic and alkaline conditions,because the electrocoagulation produces more efficient hydrolysates and smaller size H₂ and O₂ microbubbles.At any influent pH,with the continuous operation of the reactor,the effluent pH value tends to be close to neutral.Appropriate addition of Na₂SO₄（50mg/L）can promote the flocculation reaction and shorten shorten the stabilizing time of the systems.Nevertheless,there was no significant improvement in the maximum removal efficiency,and adding too much Na₂SO₄ will reduce the efficiency of pollutant treatment.Under all conditions,changing the operating conditions of the reactor has little effect on the turbidity of the effluent,and low turbidity water can be obtained,and the effluent flux of the reactor decreased first and then slowly decreased until it became stable with the prolongation of operation time.When all operating conditions were adjusted to the optimal operating parameters,the water quality and membrane flux of the reactor were basically stable after 80minutes operation.（2）Pure water was used for the 160-minute membrane flux test.The result show that pure water stable flux of the pvdf membrane under t head of 0.8m was about 0.56mL/（min.cm²）.The article suggests that the optimal test conditions are Al-Fe-Fe-Al electrode combination,plate distance of 15mm,current density of 7.143mA/cm²,residence time of 22.5min,maintaining the pH of raw water,adding 50mg/L Na₂SO₄,and the cleaning cycle is 80min.Under this conditions,the recovery rate of membrane flux reached 80.4%after the initial cleaning,the decreasing trend of flux was consistent and the flux of the membrane under the corresponding sampling time decreased in each cleaning cycle.（3）Continuous operation for 4 cycles（320min）under optimal operating conditions,the removal rate of turbidity reached 97.6%over the entire operation process.The removal rate of LAS,COD_Cr,and TP after the effluent of the reactor was stable reached93.1%,62.8%,and 92.5%,respectively,the highest removal rate for NH₃-N was 32.4%.However,the long running time is not conducive to the removal of pollutants.The effluent LAS,turbidity,NH₃-N and pH basically reached the national urban mixed water quality standards of GB/T 18920-2002,it also has a good effect on TP but the removal on COD_Cr is rough,in the stable operation of the reactor.