Influence of physicochemical properties and ionic composition on bacterial abundance in treated wastewater and post-irrigation agricultural drainage water: a case study from Al-ahsa, Saudi Arabia

Abstract

This study investigated the relationships between physiochemical properties and bacterial abundance in treated wastewater and post-irrigation agricultural drainage water in Al-Ahsa, Saudi Arabia. Six water samples were collected from treated wastewater (n = 3) and agricultural drainage water (n = 3), and four tap water samples were included as a microbiological reference. Major ions, trace elements, organic matter, total viable counts (TVC), and total coliforms were determined. Agricultural drainage water exhibited higher salinity, sodium dominance, chloride (1,520–1850 mg/kg), sulfate (820–980 mg/kg), and organic matter (0.65%–0.72%) than treated wastewater (chloride = 314–333 mg/kg; sulfate = 206–218 mg/kg; organic matter = 0.17–0.19%). Despite these physiochemical differences, both water sources contained comparable microbial abundance, with TVC ranging from 2.51 to 3.17 log 10 CFU/mL and total coliforms from 1.93 to 2.87 log 10 CFU/mL. Conversely, tap water contained consistently low microbial counts (0.70 log 10 CFU/mL). Spearman’s correlation analysis revealed significant positive relationships between total coliforms and major ions, while principal component analysis (PCA) clearly separated agricultural drainage water from treated wastewater based primarily on physiochemical parameters. The findings demonstrate that microbial abundance is associated with multiple interacting physiochemical factors rather than individual ions alone. The findings also provide baseline information to support water quality monitoring and sustainable wastewater reuse for agricultural irrigation in the Al-Ahsa region.