Factors affecting aerobic biodegradation of 2-chlorophenol in sequencing batch reactors

The feasibility of treating a synthetic wastewater containing 30 mg L(-1) of a-Chlorophenol (2-CP) in the presence or absence of dextrose or phenol as two different supplemental substrates by adapted activated sludge was investigated in 2 litre sequencing batch reactors (SBR's). Three parallel reactors received either no supplement or 20 - 200 mg L(-1) of either dextrose or phenol respectively as soluble organic carbon (SOC). Biomass concentrations in the reactors were maintained around 2 g L(-1) as volatile suspended solids (VSS). The specific biodegradation rates of 2-CP increased from 3.96 mg 2-CP g(-1) VSS hr(-1) in the absence of any supplements to 5.15 and 8.19 mg 2-CP g(-1) VSS hr(-1) when 20 mg SOC L(-1) of dextrose and phenol respectively were present. The biodegradation rates increased with an increase in the concentration of supplemental substrates to 40 mg SOC L(-1) accounting for a specific 2-CP removal of 7.94 and 11.54 mg 2-CP g(-1) VSS hr(-1) in presence of dextrose and phenol, respectively. A further increase in the concentration of supplements to 60, 80 and 200 mg SOC L(-1) decreased the specific 2-CP rates to 5.91, 5.27 and 4.45 mg 2-CP g(-1) VSS hr(-1) respectively in the presence of dextrose. For phenol, the rates initially increased to 14.94 mg 2-CP g(-1) VSS hr(-1) at 60 mg SOC L(-1), remained around 14.83 mg 2-CP g(-1) VSS hr(-1) at 80 mg SOC L(-1) and sharply fell to 7.56 mg 2-CP g(-1) VSS hr(-1) when the phenol concentration was raised finally to 200 mg SOC L(-1). The results indicate that the presence, nature and concentration of supplemental substrates are important factors influencing biodegradation rates of toxic compounds like 2-CP by a mixed microbial population of activated sludge.