Microbial degradation of aromatic and polyaromatic toxic compounds adsorbed on powdered activated carbon

The microbial degradation of phenol (300–1300 mg l−1), p-nitrophenol (50–500 mg l−1), and phenanthrene (50–300 mg l−1) adsorbed on powdered activated carbon (PAC) was studied. The combination of physical sorption and biological degradation on PAC, which serves as adsorbent carrier, was compared with the degradation performance of suspended cells and cultures attached to sand, which serves as an example of an inert support. Almost similar profiles of degradation were obtained in the cultures with PAC for the three compounds studied, over the entire concentration range. However, at the higher concentrations, degradation was dramatically inhibited, or even ceased completely, in suspended or sand-attached cultures, even though specialized mixed bacterial cultures adapted to high toxicant concentrations were used in each case. Degradation with PAC assumes an intrinsic relationship between the activated carbon and bacteria in the same environment, thus regenerating the surface of the adsorbent/ carrier as diffusion and degradation proceed. The adsorbed material desorbs, diffuses out of the carbon and can then be metabolized. Our results highlight the applicability of activated carbon, in either powdered or granular form, to achieve a steady-state operation in continuous process, for the treatment of toxic chemicals, even with specialized bacteria.