Abstract:

Currently, karst groundwater contaminated by petroleum hydrocarbons is increasingly common, but few researches focus on
such contamination especially in karst subterranean river. In such cases, perhaps biodegradation is a good way to remove contaminants. However, there is few experimental evidences to support this method. To better understand the biodegradation of BTEX compounds that are greatly concerned among petroleum contaminants, a microcosm experiment was performed to examine the BTEX biodegradability in limestone aqueous medium, using limestone and fresh karst groundwater. Four groups including control, nitrate amendment, sulfate amendment and free amendment cases were designed. In the control group (P0), concentrations of nitrate and sulfate had no change during the period from day 7 to day 77, but concentrations of dissolved oxygen had obvious changes due to incomplete sterilization. In nitrate-amended group (P1), the amendments of nitrate stimulated the BTEX attenuation in concentration from 2.085 mg/L to 0.129 mg/L. Nitrite as an intermediate was first accumulated and then disappeared. In sulfate-amended group (P2), concentrations of both sulfate and BTEX were basically stable, indicating that no enhancement occurred in the groups. In no addition group (P3), the removal rate of BTEX was 15% (excluding the value in P0 group). Our data shows that : (1) BTEX compounds have biodegradability in the presence of available electron acceptor like dissolved oxygen or nitrate; (2) amendment of nitrate can enhance the BTEX biodegradation to reach a removal rate of 74%; (3) amendment of sulfate has no effect on the BTEX biodegradation; (4) methylbenzene and xylene are readily biodegraded, but benzene is difficulty.

Key words: BTEX, biodegradability, limestone, karst groundwater