Municipal-to-Industrial Water Reuse via Multi-Stage and Multi-Pass Reverse Osmosis Systems: A Step from Water Scarcity towards Sustainable Development

Abstract

Wastewater reclamation is a promising solution to growing pressure on limited water resources. In this study we evaluated the efficiency of boron removal from effluent at a water resource recovery facility (WRRF) using a two-stage/two-pass RO membrane system. We propose using measurements of electrical conductivity (EC) as a proxy for boron concentration. We tested our approach to boron estimation and the proposed split partial second pass (SPSP) system at an established WRRF and a pilot plant we constructed at the same location. Results showed that boron in the effluent was directly related to the concentration of EC. The proposed regression equation (y = 4.959 × 10-5x + 0.138) represents a rule of thumb for wastewater plant operators. The proposed SPSP system was optimized through manipulation of operating conditions, achieving a promising total water recovery of 64% at maximum boron rejection (over 85% removal) in a manner that was both cost-effective and flexible. This study demonstrates that two-stage/two-pass split-partial permeate treatment with a high pH for boron removal offers a sustainable freshwater supply option suitable for use by the semiconductor industry.

Reverse Osmosis with Intermediate Chemical Demineralization: Scale Inhibitor Selection, Degradation, and Seeded Precipitation

“…For concentrates containing high CaSO 4 , suitable scale inhibitors were selected from the following three aspects: Ca 2+ concentration in the concentrate, macroscopic scaling amount, and microscopic CaSO 4 precipitation morphology. RO-400, being the preferred scale inhibitor, shows an effective inhibition effect across a wide range of SIg (2.3-6) and pH (5)(6)(7)(8)(9)(10)(11) values. In the UVD process, a 40 W UV light with 70 mg/L H 2 O 2 can degrade RO-400 completely in 15 min.…”

“…Secondary reverse osmosis (SRO) can further treat the salt-containing concentrate to reduce the amount of high-concentration brine. The two-stage RO process integrating RO desalination with intermediate concentrate demineralization (ICD) is one of the promising strategies to overcome the recovery limitation caused by mineral scaling during RO desalination [6][7][8][9][10][11]. ICD can reduce the concentration of calcium sulfate in the RO concentrate, allowing it to be further desalted in a subsequent SRO process [6,12].…”