Permeate quality, advanced oxidation process treatability, and cost for two concentrate treatment technologies to enhance recovery for potable reuse

Closed circuit reverse osmosis (CCRO) and forward osmosis-RO (FO-RO) were evaluated at a pilot scale to generate additional permeate from RO concentrate – achieving a recovery of 61% for CCRO and 35% for FO-RO – at a full-scale advanced water purification facility. This study assessed permeate water quality, suitability of the permeate for treatment by an ultraviolet-advanced oxidation process (UV-AOP), and cost/footprint for a conceptual 10- or 20-mgd system. Both technologies demonstrated inorganic, organic, and microbiological constituent removal suitable for blending with primary RO permeate. Virus challenge testing with MS coliphage demonstrated greater than 5-log removal by both technologies. Pilot-scale UV/hydrogen peroxide AOP treatment of CCRO or FO-RO permeate yielded similar performance (∼1.4-log N-nitrosodimethylamine removal and ∼0.5-log 1,4-dioxane removal) as the full-scale UV-AOP that treats the RO permeate from the purification facility. The estimated full-scale total unit cost (capital plus operation and maintenance costs) of product water produced by the two technologies was estimated to range from $0.91 to $1.12 per cubic meter, depending on the design flow rate of RO concentrate treated, and is estimated to be similar between the two technologies given the +50%/–30% expected accuracy of the Class 5 cost estimate.