Optimization of pilot scale forward osmosis process integrated with electrodialysis to concentrate landfill leachate

A forward osmosis (FO) – electrodialysis (ED) pilot was built and tested for landfill leachate (LL) concentration and draw and water recovery. 70% water extraction from high salinity (35mS.cm−1) LL was achieved through FO in batch operation; no fouling or clogging were observed during the operation of the pilot. Operating with constant high salinity draw solution (>100 mS.cm−1) was required to reach 70% water extraction especially for the final step of LL concentration. FO allowed for high rejection (>90%) of most LL compounds and their effective concentration in the concentrated LL except for ammonium which was partially lost through the membrane or by stripping. Lowering the pH of the LL (from 8.3 down to 6.5) allowed to reduce losses by stripping but led to higher overall losses due to longer filtration time required (higher salinity of the feed solution following hydrochloric acid addition for neutralization). Ultimately, tests in continuous mode (one pass through the FO module) demonstrated that ammonium losses can be reduced significantly (below 15%), thus allowing for efficient operation in counter current mode, resulting also in a better usage of the osmotic pressure. Regeneration of the draw solution and production of a dilute water stream within the discharge requirements (<6 ms.cm−1) was achieved by ED. Energy consumption of the FO-ED system remain below 8 kWh.m−3 allowing the process to be energetically competitive in comparison with other LL concentration technologies and other FO hybrid systems. © 2021