Engineering A Fertilizing Draw Solution For Irrigation Using Forward Osmosis / Reverse Osmosis Hybrid System

Abstract

Large volumes of fresh water are consumed in the human’s daily activities, producing large volumes of highly contaminated wastewater which exhibits a major environmental problem. Wastewater is treated using multiple technologies to produce Treated sewage effluent (TSE) which is considered to be less contaminated but unusable by human daily activities. This work investigates the application of a hybrid system that combines forward osmosis (FO) and reverse osmosis (RO) processes for the supply of a fertilizing solution that could be used directly for irrigation purposes. In the forward osmosis process, treated sewage effluent (TSE) is used as the feed solution and two different types of draw solutions were investigated namely, 0.5M NaCl solution and 0.5M NaCl and 0.01M diammonium phosphate ((NH4)2HPO4) solution. The impact of the feed solution and the draw solution flowrates and the membrane orientation on the membrane flux were investigated in the forward osmosis process. In the reverse osmosis process, seawater RO membrane (SW30HR) and brackish water RO membrane (BW30LE) were tested for the regeneration of the draw solution. In the forward osmosis process, it was found that the highest membrane flux was 13.2 LMH achieved at a flow rate of 2 LPM for the feed solution and the draw solution and when the 0.5M NaCl and 0.01M diammonium phosphate solution was used as the draw solution in the FO mode membrane orientation. The FO process had high rejection rates for total phosphorus and ammonium which were 99% and 97%, respectively. Reverse osmosis achieved 99% total salts rejection rate using the seawater RO membrane. The final product water had high quality in terms of total dissolved solids and nutrients concentration. The final product meets the irrigation water quality.