Gopinath Halder

Tannery wastewater is one of the most complex industrial effluents, which requires multiple stages of treatment due to its pollutant contents such as chromium (10–1000 mg/L), COD (7000–24,000 mg/L), TDS (3800–23,000 mg/L), and azo dyes (80–440 mg/L). This review critically analyses different membrane technologies for treating tannery wastewater generated during pre‐tanning, tanning, and post‐tanning operations, which include membrane modification mechanisms and permeate flux per unit pressure vs. energy trade‐offs toward industrial application potential. NF membranes achieve 90–95% chromium recovery and 85–95% sulfate rejection at 4–30 bar, enabling reuse of recovered chromium sulfate and reducing fresh chemical consumption by up to 40%. Integrated UF‐NF‐RO trains attain 95–99% COD removal at specific energy consumption of 1.5–6.0 kWh/m ³ , compared to 2–3 kWh/m ³ for standalone MBR systems and 3–5 kWh/m ³ for FO‐MD hybrids. Surface‐modified membranes reduce irreversible fouling by 30–60% and extend membrane service intervals by 25–40% compared with unmodified membranes. Techno‐economic analysis shows that membrane‐based chromium recovery reduces total treatment capital costs by 34% compared with conventional physicochemical systems at the 200 m ³ /day scale, with payback periods of 3–5 years. Critical limitations are identified: NF and RO flux declines by 30–50% within 72 h under real tannery feed variability; irreversible chromium‐organic scaling causes permanent 20–35% flux loss; and AI/IoT fouling prediction systems remain at industrial readiness levels 4–5 with unresolved model transferability challenges. The review identifies key research priorities: standardized long‐term performance testing under real tannery matrices, low‐cost robust ceramic membrane development, and validated techno‐economic frameworks for ZLD deployment in developing‐nation tanneries.