FO–MD integrated process for nitrate removal from contaminated groundwater using seawater as draw solution to supply clean water for rural communities

Abstract

Access to clean water has become a global concern in recent years, especially in rural communities due to the contamination of groundwater induced by intensive anthropogenic activities. The current study proposed a solution for this issue by the evaluation of the feasibility of forward osmosis (FO) coupled with membrane distillation (MD) to treat nitrate-contaminated groundwater using seawater as draw solution. The studied groundwater had high nitrate levels of 150 mg/L. The evaluation of different operating conditions indicated that working at lower FS concentration, higher DS concentration, higher DS temperature and under active layer draw solution (AL-DS) mode had positive effects on FO water flux. However, reverse solute flux and nitrate flux showed an increment with increasing FS concentration, DS concentration and DS temperature. Application of optimal operating conditions on real groundwater using seawater as DS, during 15 h of continuous operating time, led to obtain FO water flux of 6.25 LMH, MD permeate flux of 12.44 LMH, nitrate flux of 0.69 gMH, reverse solute flux of 20.24 gMH, FO rejection rate of 98.34% and MD salt rejection rate of 99.05%. Moreover, FO–MD process produced freshwater with almost free-nitrate content and very low conductivity of 78 µS/cm suitable for drinking and irrigation purposes. Thus, the integrated FO–MD process can be applied efficiently to remove nitrate from contaminated groundwater.