Optimization of surface area loading rate for an anaerobic moving bed biofilm reactor treating brewery wastewater

Abstract

Three acclimated anaerobic moving bed biofilm reactors filled to 40% by volume with cubic AC920 media (protected surface area of 680 m2 m−3) were studied to treat brewery wastewater at hydraulic retention times of 6–24 h and mesophilic condition (35.0 ± 0.1 °C). The reactors were seeded with media that had developed mature anaerobic biofilm prior to the start of this study. Soluble chemical oxygen demand of the brewery wastewater was equal to 4.0 ± 1 kg m−3, total chemical oxygen demand 5.2 ± 2.1 kg-COD m−3, and the ratio of 5-day biological oxygen demand to chemical oxygen demand was equal to 0.77 ± 0.02. Dissolved oxygen concentration in the influent wastewater was below detection limit (0.1 mg-O2 L−1). This study focused on the assessment of optimal design surface area loading rates for an anaerobic moving bed biofilm process by varying the hydraulic retention times from 6 to 24 h. Volumetric removal rates of 3.0 ± 0.2, 4.2 ± 0.3, 7.2 ± 0.6, 12.4 ± 0.8, 13.4 ± 1.0, and 12.0 ± 1.1 g-sCOD d−1 were achieved at 24, 18, 12, 10, 8, and 6 h hydraulic retention times. Hydraulic retention time of 18 h exhibited the highest chemical oxygen demand removal, at 88 ± 2.5%, and the highest carbon conversion into methane at 0.34 ± 0.06 m3-CH4 kg-sCOD−1. At this hydraulic retention time the specific surface area activity was 13 ± 1 g-sCOD m−2d−1, considering that the organic loading rate was 4.0 ± 0.3 kg-sCOD m−3d−1. Biogas composition was 71 ± 2% methane and 26 ± 4% carbon dioxide. Media clogging and mass transfer limitations due to overgrowing biomass in the interior media channels was observed at surface area loading rates above 54 g-sCOD m−2 d−1. However, kinetic tests revealed that mass transfer limitation started at surface area loading rate of 44 g-sCOD m−2d−1. Anaerobic moving bed biofilm reactor has been shown to be a reliable treatment option for high-strength wastewaters and could be used in brewery wastewater management as a resource to comply with the discharge limit regulation.