Selective removal of arsenic and monovalent ions from brackish water reverse osmosis concentrate

• Published in: Journal of hazardous materials 2013-09, Vol.260, p.885-891
• Main Authors: Xu, Pei, Capito, Marissa, Cath, Tzahi Y.
• Format: Article
• Language: English
• Subjects: Adsorption; Anion exchanging; Anions; Applied sciences; Arsenic; Arsenic - analysis; Arsenic - chemistry; Arsenic removal; Beneficial use; Chemical engineering; Chlorides - analysis; Chlorides - chemistry; Concentrate treatment; Current density; Desalination; Drinking Water; Drinking water and swimming-pool water. Desalination; Electrodialysis; Energy management; Exact sciences and technology; Exchange; Ferric Compounds - analysis; Ferric Compounds - chemistry; Filtration; Groundwaters; Hydroxides - chemistry; Ions - analysis; Ions - chemistry; Magnesium; Membrane separation (reverse osmosis, dialysis...); Membranes; Membranes, Artificial; Natural water pollution; Osmosis; Pollution; Reverse osmosis; Sewage; Water; Water Pollutants, Chemical - analysis; Water Pollutants, Chemical - chemistry; Water Purification - methods; Water treatment and pollution
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2013.06.038

•Arsenic was effectively removed by coagulation with ferric salts.•Adsorption with ferric sludge provides a “waste treat waste” method for arsenic removal.•Coagulant dose requirement for RO concentrate was higher than low salinity water.•Increase in current density does not affect significantly selectivity of monovalent anions over di-, multi-valent anions.•Transport of divalent cations increases with increase in current density. Concentrate disposal and management is a considerable challenge for the implementation of desalination technologies, especially for inland applications where concentrate disposal options are limited. This study has focused on selective removal of arsenic and monovalent ions from brackish groundwater reverse osmosis (RO) concentrate for beneficial use and safe environmental disposal using in situ and pre-formed hydrous ferric oxides/hydroxides adsorption, and electrodialysis (ED) with monovalent permselective membranes. Coagulation with ferric salts is highly efficient at removing arsenic from RO concentrate to meet a drinking water standard of 10μg/L. The chemical demand for ferric chloride however is much lower than ferric sulfate as coagulant. An alternative method using ferric sludge from surface water treatment plant is demonstrated as an efficient adsorbent to remove arsenic from RO concentrate, providing a promising low cost, “waste treat waste” approach. The monovalent permselective anion exchange membranes exhibit high selectivity in removing monovalent anions over di- and multi-valent anions. The transport of sulfate and phosphate through the anion exchange membranes was negligible over a broad range of electrical current density. However, the transport of divalent cations such as calcium and magnesium increases through monovalent permselective cation exchange membranes with increasing current density. Higher overall salt concentration reduction is achieved around limiting current density while higher normalized salt removal rate in terms of mass of salt per membrane area and applied energy is attained at lower current density because the energy unitization efficiency decreases at higher current density.