Sustainable Groundwater Treatment: Enhancing NF and UF Membrane Efficiency with Agro-Waste-Derived Crystalline Nanocellulose

Abstract

Qatar is located on the eastern edge of the Arabian Peninsula and is characterized by an arid climate with minimal rainfall. In the absence of surface water resources, groundwater represents the country’s primary natural freshwater supply, with approximately 92% of extracted groundwater utilized for agricultural purposes. Prolonged overextraction has contributed to the deterioration of groundwater quality, with elevated concentrations of trace elements such as molybdenum (Mo), boron (B), and lithium (Li) reported in several wells across Qatar. Although membrane filtration is widely applied for groundwater treatment, its performance is often hindered by membrane fouling, underscoring the need for surface modification strategies to enhance treatment efficiency. This study evaluated the physicochemical quality of groundwater collected from ten farms in Qatar and employed spatial interpolation analysis using ArcGIS to assess contaminant distribution. The results revealed that Mo, B, and Li, along with other water quality parameters, exceeded guideline limits established by the World Health Organization (WHO), Gulf Standardization Organization (GSO), Qatar drinking water standards, and United States Environmental Protection Agency (US-EPA) health advisories. To address these challenges in a sustainable manner, crystalline nanocellulose (CNC) was extracted from date-pit agro-waste and utilized to modify ultrafiltration (UF) and nanofiltration (NF) membranes. X-ray diffraction (XRD) analysis confirmed the crystalline structure of CNC, with characteristic peaks at 15.5° and 22.5° and a crystallinity index of 39.5%. Fourier transform infrared spectroscopy (FTIR) verified the presence of functional groups, while atomic force microscopy (AFM) and scanning electron microscopy (SEM) analyses confirmed successful CNC coating on the membrane surfaces. The CNC-modified NF membrane (NF-CNC) exhibited a reduction in surface roughness from 37.8 to 19.8 nm, whereas the CNC-modified UF membrane (UF-CNC) showed an increase in roughness (35.56 to 44.50 nm) accompanied by improved hydrophilicity following surface modification. Filtration experiments conducted at operating pressures of 5 bar for NF and 2 bar for UF demonstrated that UF-CNC outperformed all other membranes, achieving greater than 90% rejection of B, Li, and Mo. These results were statistically validated using Tukey’s post-hoc test. The dominant removal mechanisms were attributed to Donnan exclusion for Mo, hydration-layer interactions and electrostatic interaction for Li, and hydrogen bonding for B, indicating the role of adsorptive membrane filtration. When applied to real groundwater samples, UF-CNC successfully reduced Li and B concentrations to permissible levels of Qatar while simultaneously lowering additional contaminants and maintaining stable performance with minimal fouling. Overall, this study demonstrates the dual functionality of CNC-modified membranes in enhancing pollutant removal efficiency while sustaining membrane performance, highlighting their potential for sustainable groundwater treatment in arid regions.