The Application Of Using Polyepoxysuccinic Acid As Novel Draw Solution In Forward Osmosis Process

Forward osmosis(FO)is recently an emerging membrane technology for wastewater treatment.In FO,pure water permeates from feed solution(FS)to draw solution(DS)through a semi-permeable membrane due to the osmotic pressure differences.Due to the absence of applied pressure,FO has some potential advantages over current technologies,which can be summarized as low energy,low and reversible membrane fouling.The polyelectrolytes used as draw solutions are gaining much interest recently.In our study,polyelectrolyte of polyepoxysuccinic acid(PESA)is selected as draw solution in forward osmosis process.As a green corrosion scale inhibitor,PESA can been used in many cooling water systems and shows excellent scale performance.So the diluted PESA solution could be used to cooling systems without any post treatment.In this study,the water flux,reverse solute flux and the ratio of reverse solute flux to water flux(specific water flux)were measured using PESA as DS.These figures were also compared with NaCl(traditional inorganic draw solution)and ployaspartic acid(PASP,a polyelectrolyte draw solution).The effects of membrane orientation,temperature and cross velocity on the water fluxes were studied.For the cooling water reuse test,three kinds of substances PASP,PESA and ammonium bicarbonate(NH4HCO3)were added into the cooling water to increase the osmotic pressure of draw solution.The effect of membrane orientation and temperature were measured and compared.The membrane fouling studies were conducted using secondary effluent as feed solution(FS).The results showed that the effect of temperature on water flux was obvious,but the water flux increased more from 25? to 35? than that from 35? to 45? in both PRO and FO mode.The cross flow rate can influence the water flux due to its effect on concentration polarization,but the influence was not obvious.Compared to FO mode,the water flux increased faster in PRO mode at high flow rate,due to the reduction of the concentrative internal concentration polarization(CICP).Compared with PASP and NaCl,the water flux of PESA was less under the same condition.But the PESA had the lowest value of specific reverse solute flux(Js/Jw)at both membrane orientations.For example in FO mode the value was 0.46 g/L,while those of NaCl and PASP were recorded as 1.12 g/L and 0.74 g/L,respectively.In cooling water reuse tests,the draw solution contained PESA had the highest water flux on both membrane orientations(6.26 LMH and 5.04 LMH at PRO and FO mode,respectively),the following order was draw solution contained PASP and NH4HCO3.The higher temperature(35? and 40?)could promote the water flux obviously when using the PESA and PASP based draw solutions.But the water flux of the NH4HCO3 based draw solution showed a decreased trend when the temperature was above 35? because of the decomposition of NH4HCO3.The membrane fouling tests showed that reversely flowed polymeric anions from draw solution could effectively control membrane scaling.