An Integrated Approach to the Sustainable Remediation of Dairy Industry Effluents: Sequential Processes of Coagulation–Flocculation, Adsorption, and Photocatalysis

Abstract

Cheese whey wastewater (CWW) is a highly polluting effluent characterized by elevated organic load (COD ≈ 71,000 mg L–1) and turbidity (≈3250 NTU). In this study, a sequential treatment system combining coagulation/flocculation, adsorption, and heterogeneous photocatalysis was applied for CWW remediation. Coagulation/flocculation using an anionic polyacrylamide achieved removals of ∼22% COD, ∼37% BOD5, ∼30% turbidity, and >80% suspended solids. Subsequent adsorption with activated carbon increased removal efficiency to ∼65% COD, ∼55% BOD5, and ∼60% turbidity. Activated carbon characterization confirmed a porous structure and functional groups responsible for adsorption. The final TiO2-based photocatalysis stage further reduced COD to ∼5000 mg L–1 and BOD5 to ∼500 mg L–1, achieving overall removals of ∼95% COD and ∼90% BOD5, with turbidity below 200 NTU. Phytotoxicity assays indicated reduced toxicity after treatment, with a germination index of 90.04%. Techno-economic analysis showed improved profitability, with net income reaching 3.85 USD m–3 year–1, return on investment of 43.0%, payback period of 2.3 years, and net present value increasing from −0.15 to 18.57 USD m–3. These results demonstrate the efficiency and economic viability of the integrated system for dairy wastewater treatment.