An anaerobic ammonium oxidation (anammox) process was employed to remove nitrogen from wastewater generated from a coffee brewing facility. The effects of caffeine and chemical oxygen demand (COD) in coffee wastewater on anammox activity were investigated. The anammox activity was inhibited in synthetic wastewater with a caffeine concentration greater than 350 mg/L. Daily additions of caffeine at 2.5 mg/L for 28 days to the same substrate did not inhibit anammox activity. However, daily additions of coffee wastewater with COD of ≥387 mg/L and caffeine at 2.5 mg/L significantly inhibited anammox activity. Because the pH was increased in the system, resulting in an increase in free ammonia (FA) concentration, one could postulate that FA is an inhibitor of anammox activity. Quantitative polymerase chain reaction (qPCR) analysis was employed to determine the populations of anammox and denitrifying bacteria. Coffee wastewater with bacterial COD to total nitrogen (bCOD:TN) ratios of 0.3–0.6:1 did not have any effect on the abundances of anammox and denitrifying bacteria. The results from this work suggest that biodegradable COD (bCOD) rather than total COD (TCOD) should be used for calculating the COD:TN ratio during the study of the effects of nitrogen removal from real wastewaters using the anammox process. A not-competitive model could fit the anammox inhibition with caffeine concentrations at 50–500 mg/L with maximum specific anammox activity (SAAmax) of 0.594 mg-N/mg-volatile suspended solids (VSS)/d and inhibitory constant (Ki) of 480.97 mg/L.
