A lime-augmented electro-coagulation (LATEC) process for treatment of sulfate-bearing wastewater with simultaneous recovery of commercially relevant end-product

Abstract

Treatment of industrial effluents bearing high dissolved sulfate concentration presents a major environmental challenge. A resource recovery-based approach was adopted in the present study. A two-stage electro-coagulation process developed using aluminum anode and stainless-steel cathode to treat a real industrial wastewater containing about 18,000 mg/L dissolved sulfate. EC process operating parameters like electrode arrangement, electrode-spacing, current density, and lime dosing were optimized. The treatment resulted in nearly 99 % overall sulfate removal efficiency with a final concentration of 191 mg/L meeting the maximum acceptable limit of 200 mg/L prevalent in India. Advanced analysis techniques like Field-Emission Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis, Brunauer-Emmett-Teller surface area, X-Ray Diffraction Analysis, thermal analysis, and X-Ray Photoelectron Spectroscopy were applied to characterize the end product to ascertain the presence and purity of ettringite. Further, setting time analysis, compressive strength test, and heat of hydration analysis were performed to evaluate the performance of the EC residue in ordinary portlandite cement as a seed-based hardening accelerator. A dose of 10 % ECEP by weight of concrete reduced the setting time significantly. The heat of hydration test showed that ECEP was rich in ettringite which reduced the induction period for the setting of concrete. Addition of the ECEP to concrete showed about 15 % and 5 % higher strength than the normal concrete after 1 and 3 days, respectively. Therefore, the process provides an EC-based treatment scheme with end product valorization potential in the precast concrete industry as a seed-based hardening accelerator for the early setting of concrete.