AEROBIC TRANSFORMATION OF SHORT-CHAIN ALKYLPHENOL POLYETHOXYLATES BY MIXED BACTERIAL CULTURES

Various aerobic mixed bacterial cultures, isolated from wastewater, river water, and from a forest soil, were applied for the biotransformation of short-chain alkylphenol polyethoxylates (APnEO; nEO = 1-3) using the shake culture technique. Almost complete transformation of both nonylphenol- and octylphenol polyethoxylate mixtures, added to a synthetic sewage at total concentrations in the range of 0.5-2.5 mg/L, was achieved within 6-23 days. The duration of the adaptation period (lag phase) and the transformation rate in exponential phase varied significantly, depending on the origin of the bacterial culture and structural characteristics of the APnEO molecules (number of EO groups per molecule and the size of the alkyl chain). Experiments conducted in a mineral medium showed that short-chain APnEO can be transformed even if they represented the only source of organic carbon, though at a rate significantly lower than that in the synthetic sewage. Autochthonous bacterial cultures originating from a polluted river and a secondary sewage effluent were also able to transform short-chain APnEO, the transformation rate being strongly dependent on temperature. The analyses of shake culture at the end of the exponential phase revealed a significant presence of alkylphenoxy carboxylic acids which accounted for up to 90% of APnEO originally added to the growth-media. This suggested that carboxylation of the terminal alcohol group was the most important transformation process involved.