UASB Treatment of Wastewater Containing Concentrated Benzoate

The upflow anaerobic sludge blanket (UASB) process removed 97–99% of soluble chemical oxygen demand (COD) from wastewater containing concentrated benzoate at 37°C, pH 7.5, a hydraulic retention time of 9.8 h, and loading rates up to 30.6 g-COD/(L$\dot{s}$day) based on the reactor volume. About 95.2% of the total COD removed was converted to methane; 0.034 g of volatile suspended solids (VSS) was yielded for each gram of COD removed. The highly settleable granules were 1–3 mm in size with a layered microstructure and were composed in abundance of bacteria resembling the benzoate-degrading Syntrophus buswellii . Two interesting observations have led to the postulation that the degradation of benzoate into acetate was probably conducted completely inside the cell of Syntrophus buswellii -like bacteria: (1) No fatty acids except acetate were found in the effluent; and (2) the granules showed very limited butyrate-degrading capability and could not degrade propionate. This study demonstrated the feasibility of removing aromatic pollutants in wastewater by anaerobic processes.