Integration of ozone with co-immobilized microalgae-activated sludge bacterial symbiosis for efficient on-site treatment of meat processing wastewater

Direct discharge of high concentration meat processing wastewater (MPW) into municipal sewage system will cause serious shock loading and reduce wastewater treatment efficiency, thus, efficient on-site pretreatment is usually required. Purpose of this study is to integrate ozone with microalgal biotreatment to achieve effective removal of both organic compounds and nutrients with one-step biodegradation and obtain high quality effluent dischargeable to municipal sewage system. Results showed that ozone pretreatment removed 35.0–90.2% color and inactivated 1.8–4.7 log CFU/mL bacteria in MPW. In post biotreatment using microalgae co-immobilized with activated sludge (ACS) bacteria, bacterial growth in ozone pretreated wastewater (7.1–8.1 log CFU/mL) were higher than non-pretreated control (6.0 log CFU/mL) due to enhanced biodegradability of wastewater pollutants. Algal biomass growth in wastewater pretreated with 0.5 (2489.3 mg/L) and 1 (2582.0 mg/L) minute's ozonation were improved and higher than control (2297.1 mg/L). Ozone pretreatment significantly improved nutrients removal. Following ozone pretreatment of 0.5 min, microalgal biotreatment removed 60.1% soluble chemical oxygen demand (sCOD), 79.5% total nitrogen (TN) and 91.9% total phosphate (PO₄³⁻) which were higher than control (34.4% sCOD, 63.4% TN, 77.6% total PO₄³⁻). Treated effluent contained 342.3 mg/L sCOD, 28.8 mg/L TN, 9.9 mg/L total PO₄³⁻ and could be discharged into municipal sewage system. However, excessive ozone pretreatment displayed adverse impact on algal growth and sCOD removal. Therefore, integration of 0.5 min's ozone pretreatment with microalgae-based biotreatment is an efficient on-site treatment to simultaneously remove organic compounds and nutrients with one-step biodegradation.