Evaluating β-chitosan's concentration-dependent performance in treating domestic laundry effluent – A case study in a South Indian metropolis

Laundry wastewater comprises a complex mixture of organic and inorganic pollutants posing significant threats to aquatic ecosystems and public health. This study investigates the performance of β-chitosan derived from squid pen waste as a sustainable biopolymer for the remediation of domestic laundry effluent collected from high-density residential areas within the Chennai metropolitan region, India. The treatment efficacy of β-chitosan was evaluated at three concentrations (2 %, 4 %, and 6 % w/v) through systematic assessment of Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) reductions across ten sites. The 4 % β-chitosan concentration consistently achieved optimal removal efficiencies, reducing BOD by 52.1–69.5 % and COD by 57.8–62.9 %, outperforming both lower and higher dosages. The reduced effectiveness at 6 % was attributed to molecular aggregation that limited available binding sites, while 2 % was insufficient to address pollutant loads. These findings demonstrate β-chitosan’s potential as an effective, biodegradable coagulant for wastewater treatment, contributing to circular economy approaches by valorizing marine biowaste. The robust and consistent treatment performance across diverse pollutant loads supports its applicability in sustainable urban wastewater management, offering an environmentally friendly alternative to conventional chemical treatments.