Biodegradation of phenols in a sandstone aquifer under aerobic conditions and mixed nitrate and iron reducing conditions

Ammonia liquor with very high concentrations of phenol and alkylated phenol s is known to have leaked into the subsurface at a former coal carbonizatio n plant in the UK, giving high concentrations of ammonium in the groundwate r. In spite of this, no significant concentrations of phenols were found in the groundwater. The potential for biodegradation of the phenols in the sa ndstone aquifer at the site has been investigated in laboratory microcosms under aerobic (oxygen amended) and mixed nitrate and iron reducing (nitrate enriched and unamended) anaerobic conditions, at a range of concentrations (low: similar to 5 mg 1(-1): high: similar to 60 mg 1(-1), and very high: similar to 600 mg 1(-1)) and in the presence of other organic coal-tar comp ounds (mono- and polyaromatic hydrocarbons (BTEXs and PAHs) and heterocycli c compounds (NSOs)) and ammonia liquor. Sandstone cores and groundwater for the microcosms were collected from within the anaerobic ammonium plume at the field site. Fast and complete degradation of phenol, o- and p-cresol, 2,5- and 3,4-xyle nol with no or very short initial lag-phases was observed under aerobic con ditions at low concentrations. 2,6- and 3,5-Xylenol were degraded more slow ly and 3,5-xylenol degradation was only just complete after about 1 year. T he maximum rates of total phenols degradation in duplicate aerobic microcos ms were 1.06 and 1.76 mg 1(-1) day(-1). The degradation of phenols in nitrate enriched and unamended anaerobic micr ocosms was similar. Fast and complete biodegradation of phenol, cresols, 3, 4-xylenol and 3,5-xylenol was observed after short lag-phases in the anaero bic microcosms. 2,5-xylenol was partially degraded after a longer lag-phase and 2,6-xylenol persisted throughout the 3 month long experiments. The max imum rates of total phenols degradation in duplicate nitrate enriched and u namended anaerobic microcosms were 0.30-0.38 and 0.79-0.31 mg 1(-1) day(-1) , respectively. The highest phenols concentrations in the anaerobic microco sms apparently required very long adaptation periods or inhibited biodegrad ation of the phenols. For the intermediate concentration level. degradation occurred after comparable lag-phases and at comparable rates to those obse rved at low concentration. However, after a while degradation of phenols su ddenly decreased drastically and then stopped. Dilution by addition of anae robic groundwater resulted in continued but slow degradation of phenols in unamended microcosms. The effect of other organic coal-tar compounds (BTEXs, PAWs, NSOs) on the d egradation of the phenols under unamended conditions was limited to slightl y longer lag-phases fur some of the phenols. Other constituents of the ammo nia liquor did not appear to significantly affect the degradation of the ph enols. Fast and complete degradation of 2,3- and 2,4-xylenol was indicated. These experiments were continued for a longer period of time and revealed complete degradation of 2.5-xylenol and, after an approximately 6-month-lon g lag-phase partial degradation of 2,6-xylenol. The potential for natural attenuation of phenols from process effluents fro m coal carbonization under aerobic conditions and mixed nitrate and iron re ducing conditions appears promising. (C) 2000 Elsevier Science B.V. All rig hts reserved.