Role of the reactor configuration in the biological detoxification of a dump site-polychlorobiphenyl-contaminated soil in lab-scale slurry phase conditions

The biotreatability of a xenobiotic contaminated soil is frequently determi ned through a bioslurry treatment usually performed in lab-scale shaken baf fled flasks. In this study, a 3-1 unconventional stirred tank reactor was d eveloped and tested in the slurry-phase treatment of a soil heavily contami nated by polychlorobiphenyls (PCBs) derived from an Italian dump site, in t he absence and in the presence of biphenyl and of the exogenous PCB aerobic ally dechlorinating co-culture ECO3. The data obtained were compared with t hose obtained on the same soil in experiments performed in parallel in 3-1 baffled shaken flask reactors. Considerably higher PCB removal and soil det oxification yields (determined through the Lepidium sativum germination tes t and the Collembola mortality test) were attained in the stirred tank reac tors? which generally displayed a higher slurry-phase homogeneity and a hig her availability of biphenyl- and chlorobenzoic acid-degrading bacteria com pared to the corresponding shaken flask reactors. Moreover, enhanced soil P CB biodegradation and detoxification yields were observed when the develope d reactor was supplemented with biphenyl and the exogenous ECO3 bacteria. I n conclusion, the results of the soil biotreatability experiments commonly performed in bioslurry lab-scale reactors are significantly influenced by t he reactor configuration; the use of the unconventional stirred tank reacto r system developed in this work is recommended.