Degradation of 4-chlorophenol by enriched mixed cultures utilizing phenol and glucose as added growth substrate

Abstract

Two mixed cultures, phenol-oxidizing (PO) and glucose-oxidizing (GO), were cultivated in two parallel chemostat reactors. The PO culture was enriched on phenol, and the GO culture was enriched on glucose. Batch biodegradation experiments were conducted to examine the degradation of 4-chlorophenol (4-CP) under various substrate conditions. The results indicate that in the absence of added growth substrate, 4-CP transformation by PO culture was complete at S ^o_c /X _o (initial 4-CP concentration/initial biomass concentration)  $\leqq$ 0.27 and that by GO culture was complete at S ^o_c /X _o = 0.09. In the presence of 5–500 mg phenol/l, the phenol dosage required to achieve the complete transformation of 4-CP was 60 mg/l at S ^o_c /X _o = 1, increasing to 120 mg/l at S ^o_c /X _o = 2, and to 180 mg/l at S ^o_c /X _o = 5. As glucose was added to the GO culture at a concentration of over 5–500 mg chemical oxygen demand (COD)/l, 4-CP was not completely transformed at S ^o_c /X _o = 5 [S ^o_c  = 50 mg/l, X _o  = 10 mg/l volatile suspended solids (VSS)]. These two cultures in utilizing added growth substrate were easily switched between glucose and phenol. Overall, the capacity of PO culture to degrade 4-CP, expressed as T _c (4-CP mass consumed /biomass inactivated, having unit of mg 4-CP/mg VSS), was 0.15–0.80, which compares with T _c values of 0.05–0.26 for GO culture. This work shows that adding phenol as a growth substrate is preferable over adding glucose, as it enhances 4-CP transformation, but a final choice should take into account both degradation efficiency and the risk of phenol toxicity.