ECOLOGICAL RISK ASSESSMENT OF BRINE AND MITIGATING RISKS WITH OPTIMIZED PAN MEMBRANE IN FORWARD OSMOSIS

Abstract

Desalination of both freshwater and seawater has been regarded as a practical and effective means of providing safe and dependable drinking water. Desalination is the process of purifying water to make it acceptable for human consumption by eliminating excess salt and other dissolved particles. However, seawater reverse osmosis (RO) desalination inevitably produces brine, a substance that comprises salt and various ions and elements that can potentially impair the local marine ecology and its biodiversity. The adverse impacts of brine, resulting from its high salinity, have emerged as a significant issue due to its inadequate disposal into marine environments. The initial objective of this research was to assess the efficacy of a chemically modified polyacrylonitrile (PAN) based nanocomposite membrane in the context of forward osmosis, with the specific objective of minimizing the adverse effects caused by reject brine. The forward osmosis (FO) experiments were conducted, and the modified nanocomposite membrane showed superior performance compared to the commercial membrane in terms of flux, reverse solute flux (RSF), specific reverse solute flux (SRSF), and salt rejection (R%). The optimal operational parameters in FO were determined by considering the pressure on the feed sides, the flow and concentration of draw side (DS), and the type of DS salt. Additionally, the utilization of RO brine and synthetic brine in FO was investigated, revealing that the nanocomposite membrane exhibited optimal values of RSF at 0.5487gMH and 0.4400gMH, respectively. On the other hand, it was noted that the commercial membrane exhibited low flow and high RSF values for RO brine, measuring at 25.24 LMH and 11.02 gMH. This can be explained due to the occurrence of internal concentration polarization (ICP) that might result in fouling and a reduction in flow. Subsequently, an ecological risk assessment was conducted to examine the ecological consequences of the brine before and after FO. The exposure assessment involved evaluating the physicochemical properties of brine. The ionic and elemental composition of synthetic and RO brines was analysed both following and prior to FO and was better understood using ICP-OES and IC analysis. The findings conveyed that the dilution percentage of the ions and elements was higher for the GOMPDHPAN membrane compared to the PAN membrane. Furthermore, the salinity parameter is an appropriate representation of both elements and ions in brine, as the bulk of elements consist of alkali and alkaline earth metals. The initial salinity of the RO brine significantly decreased with the use of the commercial membrane and reached its lowest level with the modified membrane. The exposure evaluation resulted in the generation of exposure concentrations that were directly linked to marine toxicity in the effects assessment, based on salinity. Subsequently, hazards associated with brine were determined by establishing a safe limit or benchmark for specific marine species based on the literature review. The results of the study indicated that salinity has frequently been employed as a measure of the marine toxicity of brine. Additionally, the concentrations of trace metals Mo, Cu, and Li were found to be below established benchmark limits, suggesting that they are not deemed toxic to the marine environment. The deterministic risk characterization approach was employed to assess the effects and exposure concentration in order to determine the risk quotient (RQ). Subsequently, probability distribution graphs were generated to illustrate the RQ, with point estimates serving as reference values. These estimates were utilized to depict the probability of risks resulting from brine exposure on the species. The results demonstrated that the chemically modified membrane efficiently diluted the concentration of harmful substances in brine. Additionally, the characterization phase of the ecological risk assessment (ERA) indicated that the use of the modified membrane lowered the risks of detrimental effects on the selected species or assessment endpoints.