Study On The Treatment Of Ethanol Wastewater By Membrane Separation Method

With the growth of demand for fossil oil resources,using renewable fuel ethanol to replace non-renewable fossil oil resources is receiving more and more attention.However,ethanol production process generate large volumes of wastewater.The ethanol wastewater,which contained complex components and high pollution load,was difficult to handle.At present,ethanol wastewater is usually treated with anaerobic digestion followed by aerobic digestion.However,operation costs of the aerobic digestion are high and the disposal of the aerobic sludge is still a hard task.Therefore,the effective treatment methods of wastewater becomes the key to decrease the cost of ethanol production.The ethanol wastewater,provided by the Henan Tianguan Co.,Ltd.,China,was the anaerobic digestion effluent after high temperature and medium temperature anaerobic fermentation process.This research focuses on investigating the treatment of ethanol wastewater by membrane separation methods.Firstly,the microfiltration and ultrafiltration membrane were used to treat ethanol wastewater.The effects of operating conditions such as operating pressure and pH on the wastewater treatment process were investigated.The process conditions for ethanol wastewater treatment by membrane separation were optimized.The effect of cleaning methods on the recovery rate of microfiltration and ultrafiltration membrane flux were explored.The experimental results showed that the nylon 66 microfiltration membrane had the highest membrane flux and the best treatment effect on ethanol wastewater at pressure of 0.15 MPa and pH of 8.Four different ultrafiltration membranes were selected for ultrafiltration of wastewater.The polyamide composite membrane with a molecular weight cut off of 1 kDa was selected by comparing the removal effects.When the operating pressure was 0.45 MPa,the ultrafiltration membrane had the highest flux and the best removal effect on the COD,chromaticity,ammonia nitrogen and total phosphorus of wastewater.Using backwash of tap water could restore the wastewater flux of microfiltration membrane by 88%.The ultrafiltration membrane flux could be effectively restored by using the combined cleaning of 2% hydrochloric acid+1% sodium hydroxide+5% effective chlorine content of sodium hypochlorite solution,ultrafiltration membrane pure water and wastewater membrane flux recovery rate could reach to 93.74% and 91.55%,respectively.The cleaned microfiltration membrane and ultrafiltration membrane can be reused,and the effluent water quality was stable.Secondly,the spiral type ultrafiltration membrane module(polyamide composite membrane with a molecular weight cut off of 1 kDa)was used to treat ethanol wastewater.The effects of the treatment pressure,temperature,pH,feed concentration on the COD and color removal were investigated.The cleaning methods of spiral type membrane module was explored further.The results showed that the spiral type membrane module had the best treatment effect on ethanol wastewater at the pressure of 0.50 MPa,temperature of 40 °C and pH of 8.The membrane flux of the membrane module could be effectively restored by the mixed reagent(the pH of mixed solution of sodium hydroxide and sodium hypochlorite is 12).The recovery rate of pure water flux couldreach to 92.5%.The spiral type membrane module had stable performance in continuous use.Finally,multiple analytical techniques such as GC-MS and ICP-OES were employed to examine the pollutions in the ethanol wastewater before and after the membrane separation treatment.The main organic species and metal ions of the wastewater were determined.The composition of ethanol wastewater before and after membrane separation were analyzed by the Chinese standard method.The results showed that the values of COD,BOD,suspended solids,pH and color of the effluent treated by the membrane separation methods meet the national indirect discharge standard(GB27631-2011).The research on the treatment of ethanol wastewater by microfiltration,ultrafiltration two-stage membrane separation and membrane module separation provides theoretical support for the industrial application of membrane separation technology.