Achieving Optimal Conditions of Membrane Bioreactors for Dairy Industry Wastewater Treatment

The optimization of membrane bioreactor (MBR) equipped with a submerged flat-sheet polyethersulfone (PES) membrane for the wastewater treatment from dairy processing facilities was investigated. The effects of key parameters such as the hydraulic retention time (HRT, from 8 to 16 hr), mixed liquor suspended solids (MLSS, 3000 to 9000 mg/L), and rate of aeration (Qair: 1 and 2 L/min) on COD removal efficiency were systematically investigated. Through the response surface method (RSM), the maximum the COD removal efficiency of 92.67% was obtained under the optimal conditions of HRT: 13.83 hr, MLSS: 7239.84 mg/L, and Qair: 1.75 L/min. The statistical analysis identified MLSS as the most influential factor in the COD removal efficiency, accounting for 30% of the variation, followed by HRT with 16%, and the rate of aeration showing the least impact of 8%. A notable reduction in the UV absorbance of wastewater between 200 and 500 nm, after treatment using MBR under optimal conditions, signified successful targeting of toxic or colored pollutants. Finally, a mechanism for the wastewater treatment in MBRs, which included the biological degradation, adsorption on the surface of biomass and membrane, and separation through membrane filtration, was proposed.