MBBR FOLLOWED BY MICROFILTRATION AND REVERSE OSMOSIS AS A COMPACT ALTERNATIVE FOR ADVANCED TREATMENT OF A PESTICIDE-PRODUCING INDUSTRY WASTEWATER TOWARDS REUSE

The treatment of a chemical industry wastewater with the goal of reuse was evaluated in a three-step process. First, the industrial waste stream underwent biological treatment in a two stage moving-bed biofilm reactor (MBBR) system, which allowed achieving average effluent chemical oxygen demand (COD), dissolved organic carbon (DOC), ammonium, total nitrogen (TN), and total suspended solids (TSS) concentrations of 45.5, 27.2, 11.0, 34.2, and 210 mg/L, respectively. Salt and TSS concentrations after the MBBR process were still not compatible with the requirements for effluent reuse and the silt density index (SDI15) was found to be > 6.5, making a direct reverse osmosis (RO) application impractical. By employing microfiltration (MF) downstream of the biological treatment, no salt removal was observed, but the SDI15 was reduced to around 2, enabling final RO application. Long-term RO experiments conducted at different pressures (1.5-3.0 MPa) showed that biofouling became more severe under higher pressures, leading to the enhancement of the permeate flux drop. Rejection of DOC, TN, and salt by RO corresponded to 97.8 %, 89 %, and 99 %, respectively. The combined MBBR/MF/RO process allowed the production of a high-quality effluent appropriate for direct reuse in the industry as feed water in cooling towers, steam boilers, and general industrial process activities.