Journal of environmental management | 2021
Promising integrated technique for the treatment of highly saline nanofiltration rejected stream of steel industry.
Abstract
This work presents a novel concept for the integration of closed-circuit reverse osmosis (CCRO) technology and solvent-based precipitation as a means of producing an exceptional quality of water by separating the salts especially chlorides and sulphates from highly saline nanofiltration (NF) rejected stream of the steel industry. The NF rejected stream was extremely concentrated with salts like chloride (1560\xa0mg/L), sulphate (4212\xa0mg/L), manganese (28\xa0mg/L), sodium (418\xa0mg/L) and total dissolved solids (TDS), as high as 8100\xa0mg/L, which are well above the permissible limit for surface discharge. The outcome of this work showed that reverse osmosis (RO) with continuous brine recycling achieved excellent desalination performance. Miscible organic solvents such as diisopropylamine (DIIPA), isopropylamine (IPA), and ethylamine (EA) were found to be effective in precipitating chloride and sulphate ions from highly concentrated RO brine. The overall removal efficiency of sulphate and chloride was found to be 99.88% and 91%, respectively. Preliminary treatment cost was estimated and found to be around 7.35 $/m3. The treated water can either be recycled in the system or safely released into the environment. The readers of this research article will be benefitted by gaining a thorough understanding of the treatment of concentrated brine from nanofiltration using an integrated RO-precipitation technique.