Determination of biodegradability of phenolic compounds, characteristic to wastewater of the oil-shale chemical industry, on activated sludge by oxygen uptake measurement

Abstract

The aim of this study was to investigate the biodegradation of phenol, o-cresol and p-cresol individually and as bi-substrate mixtures at low initial substrate concentrations. Activated sludge was taken from the Kohtla-Järve wastewater treatment plant, Estonia, which is also treating phenolic wastewater from the oil-shale chemical industry and is considered to be acclimated to the phenolic compounds. Respirometric data have been used for evaluation of the kinetic parameters describing the bio-oxidation of substrates. Activated sludge was able to degrade phenol and p-cresol faster than o-cresol, showing better affinity to p-cresol. However, at higher concentrations, phenol and p-cresol exhibited also an inhibitory effect to the microorganisms. The highest values for maximum rate of oxygen uptake () were obtained for the bi-substrate system of phenol–p-cresol among the mixtures containing both substrates at equal concentrations from 0.005 mM to 0.050 mM. Concerning the systems containing one substrate at 0.1 mM and the other substrate varied in the abovementioned range, the highest values were found for phenol–o-cresol(0.1 mM). The interaction parameters indicated that phenol had a stronger inhibition effect on the biodegradation of p-cresol than p-cresol had on the biodegradation of phenol. However, the obtained interaction parameters for systems of phenol–o-cresol indicated that o-cresol had a stronger inhibition effect on the biodegradation of phenol, which in turn had a mild inhibition or even enhancing effect on the biodegradation of o-cresol. In the case of a 1:1 mixture, phenol and o-cresol had a similar mild inhibition effect on each other's biodegradation.