Effect of the Ammonium ChlorideConcentration on the Mineral Medium Composition – Biodegradation of Phenol by a Microbial Consortium

Abstract

Phenol and its homologues are aromatics containing hydroxyl, methyl, amide and sulphonic groups attached to the benzene ring. These molecules are both anthropogenic and xenobiotics. Phenols are environmental pollutants discharged through wastewaters from various industries. Phenols are toxic to several biochemical reactions. However biological transformation of phenols to non-toxic entities exists in specialized microbes, owing to enzymatic potential involving enzymes of aromatic catabolic pathways. In this study, a series of experiments were performed to examine the effects of the mineral medium composition and the pH on phenol removal. In this purpose, phenol biodegradation was carried out in a batch reactor containing mixed bacteria; the temperature (30°C), the stirring velocity (200 r /min) and the phenol concentration (125 mg/L) were kept constants. The initial pH was varied in the range 5 – 9 and the mineral components were tested in the following concentration ranges: 0 – 2 g/L for NH4Cl, 0 – 4 g/L for KH2PO4, 0 – 4 g/L for NaH2PO4 and 0 – 0.2 g/L for MgSO4. Their effects on phenol biodegradation and specific growth rate were examined. All experiments were carried out at a given initial bacterial concentration of 0.08 g/L (based on optical density determination, 0.079). The shorter biodegradation time of phenol was 20.6 h for NaH2PO4, KH2PO4 and MgSO4 concentrations of 2 – 4, 3 and 0.2 g/L respectively. Maximum specific growth rate (0.65 h-1) and total phenol removal (99.99 %) were recorded for an optimal pH value of 8 and the following mineral medium concentrations (g/L): 1, 4, 3 and 0.1 for NH4Cl, KH2PO4, NaH2PO4 and MgSO4 respectively.