Seasonal Water Quality Assessment of the Ayad River and Remediation Potential of Sunlight-Driven TiO₂ Photocatalysis: A Comparative Pre- and Post-Treatment Study

Abstract

Urban and peri-urban rivers in semi-arid regions are increasingly dangered by continuous anthropogenic discharge and seasonal hydrological extremes. The Ayad River in Udaipur, Rajasthan, follows this pattern of progressive water quality decline. This study compares variation of seasons in the physicochemical quality of Ayad River water and investigated sunlight-driven TiO₂ photocatalysis as a supplementary treatment measure.

A pronounced seasonal increase in organic and nutrient pollution was depicted during summer, alongside a consistent upstream-to-downstream spatial gradient of anthropogenic impact. Photocatalytic treatment reduced BOD by approximately 35-61% and produced proportionally greater reductions in COD (33-60%), indicating oxidation of both biodegradable and recalcitrant organic fractions. Nitrate attenuation was most pronounced at high-load sites (up to 88% at Sukha Nala), while dissolved oxygen improved at every site (6-67% increase). Treatment efficiency scaled positively with initial pollutant concentration, whereas major inorganic ions and hardness constituents remained largely unchanged.Seasonal hydrology and cumulative urban discharge are the principal determinants of pollutant dynamics in the Ayad River. Although photocatalysis alone cannot ensure compliance with potable water standards, it represents a viable, low-energy, complementary intervention within an integrated river management strategy for semi-arid urban catchments.