Dehalogenation of 2-chlorophenol (2-CP) in anaerobic batch cultures

The effects of seed materials from: anaerobically digested sewage sludge; sediment from a bleached kraft mill (BKM) aerated lagoon and an anaerobic bioreactor biomass treating BKM wastewater were investigated as to their potential for dehalogenation of 0.38 mM 2-chlorophenol. In batch cultures using a mineral medium containing 0.1% yeast extract under 20% CO2 + 80% N2 or 20% CO2 + 80% H2 atmosphere, dehalogenation was observed after extensive lag periods lasting from 97 to 250 days. Methane was detected in the head-space. Phenol was identified as an intermediate which further degraded via the benzoate pathway. The dehalogenation rates increased significantly in all cultures after re-spiking with 2-CP and yeast extract medium. Cultures with digested sewage sludge incubated under CO2/N2 head-space exhibited better dehalogenation rates of 2-CP compared to either the lagoon sediment or the bioreactor biomass. Higher dehalogenation rates were also observed over CO2/N2 head-space compared to CO2/H2 head-space for digested sludge. Digested sludge which was adapted to 2-CP over a one year period converted 0.38 mM 2-CP to phenol immediately. Degradation of 2-CP with various dilutions of adapted sludge indicated that dehalogenation activity did not increase linearly with biomass concentrations. The effect of four different organic electron donors on the dehalogenation of 2-CP by adapted sludge revealed that 0.1% yeast extract was preferred by the consortium compared to 10 mM each of acetate, propionate or ethanol.