Anaerobic Removal of COD in Metal-Cutting-Fluid Wastewater

The treatment of metal-cutting-fluid wastewater was investigated using an anaerobic, granular activated carbon, fluidized-bed process. During 900 days of operation, three influent COD concentrations were tested: 1029, 3343, and 5324 mg/L. For each influent COD concentration, a series of influent flow rates was used to test a range of unexpanded empty-bed contact times from 0.9 to 7.5 hours. The findings include the following: (1) the reactor removed biodegradable COD effectively and efficiently at relatively high loading rates (more than 70${\rm kg}/{\rm m}^{3}\cdot {\rm d}$); (2) approximately 35% of the influent COD was nonbiodegradable-more than approximately 65% of the nonbiodegradable COD was aerobically biodegradable; (3) approximately 68% of the COD biodegraded was converted to methane, showing potential for energy recovery; (4) a relatively low biomass production (a yield coefficient of approximately 0.09 g biomass produced/g COD degraded) was observed; and (5) the overall removal rate of biodegradable COD followed first-order kinetics.