Interactions of Methanogens and Denitrifiers in Degradation of Phenols

Experiments were conducted at 37°C in an upflow anaerobic sludge blanket reactor treating wastewater containing phenol (200 mg/L), m-cresol (100 mg/L), and nitrate at various concentrations. Results show that anaerobic sludge was able to conduct denitrification without much acclimation. Denitrifiers outcompeted methanogens for substrates for carbon and electron supplies. They were able to use phenol and m-cresol as substrate without a carbohydrate cosubstrate. Denitrifying 1 g of NO3--N required 3.34 g of chemical oxygen demand. Methanogenesis occurred only at chemical oxygen demand/NO3--N ratios greater than 3.34. At the ratio of 5.23, over 98% of phenol but only 60% of m-cresol were degraded jointly by denitrifiers and methanogens with 1 day of hydraulic retention. At ratios less than 3.34, methanogenesis ceased to take place and denitrification became incomplete because of insufficient supply of substrate. Batch tests further confirmed that degradation of m-cresol was enhanced not only by the presence of nitrate, but also by the presence of either sucrose or phenol as cosubstrate.