The Study Of Electroplating Rinsing Wastewater Reutilization By Membrane Technology

The electroplating wastewater is generally treated by conventional techniques such as chemical sedimentation,ion exchange process,adsorptive process and electrolytic process,but these technologies have respective limit and are difficult to recover the water and heavy metals simultaneously.Membrane separation technology can treat the wastewater by physical method and recover the heavy metal and water,so it develops quickly.The homemade equipment was used to study the use of reverse osmosis(RO)membrane,nanofiltration(NF)membrane and the hybrid membrane on electroplating wastewater treatment,considered the influence of several factors on the treatment,and analyzed the energy consumption,costs and environmental impact of equipment.The style of RO and NF membrane was ESPA2-4040 and ESNA1-4040 separately.The experiment studied the treatment of artificial electroplating wastewater by RO and NF membrane first.The results showed that the rejection heavy metal and flux of permeate water were affected by operation pressure,temperature,concentration of Ethylene Diamine Tetraacetic Acid(EDTA)and concentration.Besides,NF process could also be affected by p H and anions.Flux of permeate water increased with the pressure,but the rejection of RO membrane kept stable closing to 100% and NF membrane firstly increased and the decreased and came to the highest at 0.7 Mpa.The flux of permeate water and quantity of Cu2+ would increase with the temperature,but rejection was determined by the trade-off and the result was that it decreased with the temperature.When the concentration of EDTA increased,the flux of permeate water increased,but the rejection decreased.Besides,the flux of permeate water would decreased with the increase of feed concentration,but the rejection of RO membrane had no significant change.When it came to NF membrane,the rejection would increase at the lower feed concentration and decrease at the higher feed concentration.The experiments on the NF of artificial copper electroplating wastewater were conducted on the Cu SO4,Cu Cl2 and Cu(NO3)2 solutions.The results showed that the Cu2+ rejection in different solution was in the following sequence: Cu SO4 > Cu Cl2 > Cu(NO3)2.The varying of p H values of feed solution caused the great varying of heavy metal rejection and permeate flux.The rejection was the lowest at natural p H,but the permeate flux had opposite status.In the experiments,concentratiuon of permeate of NF was over 0.5 mg/L and exceeded the recovery standard,and concentration of permeate of RO was below 0.5 mg/L when feed concentration was less than 500 mg/L.Besides,permeate flux decreased with the increase of concentration ratio.The treatment of the hybrid membrane systems,RO-RO,NF-NF,RO-NF and NF-RO system,was analyzed,and the results implied the sequence of recovery was: RO-RO > RO-NF> NF-RO > NF-NF system,but the sequence of concentration ratio was NF-NF > RO-NF > NF-RO > RO-RO system.The energy consumption of hybrid membrane systems was analyzed.The results showed that the specific entropy production(SEP)increased with the operation pressure and feed concentration,but decreased with the temperature.By comparison,the RO-NF system was better than NF-RO system referring to SEP.The experiment analyzed the exergy destruction contribution of every part to compare the four systems,determine the process of the most exergy destruction and calculate the exergitic efficiency.The environmental impact and economic assessment of RO-NF and NF-RO system was discussed based on Life Cycle Assessment(LCA),the results showed RO-NF system had advantages over NF-RO system on economic benefit,social benefit and environmental benefit.