Removal of Naturally Occurring Strontium by Nanofiltration/Reverse Osmosis from Groundwater

Abstract

Removal of naturally occurring strontium (Sr) from groundwater is vital as excessive exposure may lead to bone growth problems in children. Nanofiltration/reverse osmosis (NF/RO) is commonly used in groundwater treatment due to the high effectiveness and simple maintenance of these pressure driven membrane processes. In this research, a pilot-scale NF/RO system was used to desalinate a natural groundwater sample containing high Sr concentration (10.3 mg/L) and “old” groundwater organic matter (70.9 mg/L) from Esilalei in northern Tanzania to understand the removal of strontium by NF/RO. The impact of applied pressure (10–15 bar) and groundwater pH (3–12) on the membrane performance including permeate flux, strontium and total organic carbon (TOC) flux and removal was investigated. Increasing applied pressure was found to enhance the flux by increasing the driving force and enhance Sr and TOC removal by dilution effect (water flux higher than Sr passage). The alkaline pH caused severe flux decline likely due to membrane fouling and scaling, while it slightly enhanced Sr removal of RO membranes, but weakened the TOC removal. In contrast, acidic and neutral pH of groundwater enhanced TOC removal. These findings suggest that appropriately high applied pressure and acidic pH condition of groundwater are recommended to apply to the NF/RO membrane system in groundwater desalination to achieve better membrane performance.

Progress in Research and Application of Nanofiltration (NF) Technology for Brackish Water Treatment

“…The permeate water of NF and RO are mixed to form the final permeate water. Cai et al constructed a pilot-scale NF-C-RO system to desalinate natural ground brackish water containing high Sr concentration (10.3 mg/L) in Tanzania [ 130 ]. It was found that the NF unit only had a Sr rejection of 55–67%, while RO can remove almost 100% of Sr, so the mixture of NF permeate and RO permeate can meet the USEPA guideline of 1.5 mg/L.…”

Euler’s Numerical Method for Ions Rejection Reassessment of a Defect-Free Synthesized Nanofiltration Membrane with Ultrathin Titania Film as the Selective Layer

“…where , is the hindered diffusivity; , is the hindrance factor for convection, which are dimensionless coefficients in Nernst-Planck equations. They are made explicit in Equation (12) and Equation ( 13):…”

“…For both plots shown in Figure 6a,b, the concentration of the solute particles Cl − and Mg 2+ in the target layer of NF_PAN_Ti decreased as the particles moved from one side (feed) to another (permeate) (Table 3). solute particles' removal is the pore size rp of the NF_PAN_Ti active layer related to both hindrance coefficients already explained in the mathematical modeling equations, namely Ki,c for convection and Ki,d for diffusion, as it was clarified in Equations ( 8), (12), and (13) In…”

“…Even comparative and cost-effectiveness studies have been carried out on NF and RO membranes, and it emerged that NF membranes have tremendous advantages, especially with the use of nanoparticles, as they can be modified and adapted for several uses [8,9]. Due to their typical features, the NF process has aroused a great interest in the scientific world and many applications have been made, including enantiomeric ibuprofen rejection [10], tannery effluent treatment [11], natural occurring strontium removal [12], fouling [13], modeling [14], industrial wastewater treatment [15], and drinking water supply in critical places, such as Sri Lanka [16]. Novel NFMs have been synthesized for the first time, extremely loose or displaying excellent rejection performance, and even in some cases both at the same time.…”

Enhancing the Efficiency of Membrane Processes for Water Treatment

“…Nevertheless, there are various aspects that require intensive research toward better understanding of the processes involved, further optimization of the technology, and increasing the applicability in other fields. For instance, the influences of operating pressure and groundwater pH on permselective properties of NF and RO membranes were studied in a pilot study by Cai et al [ 1 ]. The feed water was a natural groundwater from the Eslalei region in northern Tanzania with high strontium and organic matter contents.…”