Application of chitosan as an adsorbent to treat rice mill wastewater—Mechanism, modelling and optimization

•Application of chitosan for rice mill wastewater treatment.•Response surface methodology was applied to study the process.•Second order polynomial regression model was developed.•Experimental values showed good agreement with predicted values.•FT-IR was used to find out the process mechanism. The objectives of the present study is to investigate the chitosan as an adsorbent to treat rice mill wastewater under different process conditions such as agitation time (2–6min), initial pH (2.5–6.5), chitosan dose (400–800mg/l) and settling time (10–30min) in order to study the removal efficiency of chemical oxygen demand (COD) and total suspended solids (TSS). The results showed that, all process variables have significant effect on the removal efficiencies. The optimum process conditions were determined (agitation time of 4min, initial pH of 4.5, chitosan dose of 600mg/l and settling time of 20min) and showed high removal efficiencies (COD: 98% and TSS: 95%). FT-IR spectrophotometry was used to analyze and confirm the adsorption process. From the experimental data, Box–Behnken design (BBD) was used to develop the second order polynomial models with high coefficient of determination values (COD: 0.991 and TSS: 0.989).