Post-treatment of biologically treated wastewater of agrochemical industry by sulfated chitosan composite nanofiltration membrane

The objective of this study is to treat the biologically treated wastewater using sulfated chitosan/polyacrylonitrile (PAN) composite nanofiltration (NF) membrane to improve agrochemical industry wastewater quality for reuse. Although biological treatment is quite efficient, the wastewater does not meet the reuse criteria. Hence, further treatment to improve the water quality is investigated. Sulfated chitosan composite NF membranes, having a PAN ultrafiltration membrane as the substrate, are prepared by coating and cross-linking methods. The effects of membrane preparation conditions on the rejection and permeation performance of the membranes are studied. The new membranes are characterized by NMR and scanning electron micrograph. Wastewater from agrochemical industry contains high concentrations of organic matter, color, heavy metals and other toxic substances. The operating variables studied are applied pressure (3–15 atm) and feed flowrate (4–16 L/min). It is found that the observed rejection (R_o) increases with increase in feed pressure at constant feed flowrate. The rejection of cations follows the sequence: R_o(Zn²⁺) > R_o(Ni²⁺) > R_o(Cu²⁺) > R_o(Cd²⁺) for wastewater. It is observed that the order of solute rejection sequence is inversely proportional to the diffusion coefficients.