Aquatic biodegradation behavior of pentachlorophenol assessed through a battery of shake flask die-away tests

Abstract

The aerobic aquatic biodegradability of pentachlorophenol (PCP) was studied in standard Organization for Economic Cooperation and Development/International Organization for Standardization shake flask screening tests for ready biodegradability and in more environmentally realistic surface water die-away tests with low chemical concentrations. Screening tests were conducted with either activated sludge or supernatant from settled activated sludge. Concentrations of activated sludge were 30 and 0.3 mg suspended solids per liter. Sludges were either freshly collected or initially preexposed to PCP. With supernatant, only low inoculum levels were used (0.5 ml/L). Some surface water tests were carried out with sediment amendment. Added chemical concentrations ranged from 1 to 74,000 μg/L. At nontoxic concentrations, PCP was rapidly biodegradable after an adaptation period of about 10 to 20 d. At concentrations below about 10 μg/L, degradation rates decreased, and the shape of the degradation curves indicated a shift from growth-linked degradation to non-growth-linked degradation. Addition of sediment to surface water reduced the acclimation periods but did not influence the subsequent degradation rate. Preexposure of activated sludge to PCP drastically eliminated the acclimation period and increased the tolerance of the sludge to PCP toxicity. With PCP used as a model compound, the results show that a battery of simple shake flask tests is suitable for provision of a detailed characterization of the biodegradability chemical compounds.