Packed bed reactors (PBRs) to treat chlorinated aliphatic hydrocarbons via aerobic cometabolism as pump & treat technology

Frequently, in CAH-contaminated sites the need to protect downstream targets and to prevent the widening of the plume determine the choice of a pump and treat remediation approach. In these cases, groundwater is treated on-site typically by means of adsorption, which concentrates the contaminants in the sorbing medium without destroying them. On the other hand, on-site AC in bioreactors represents an interesting alternative, thanks to its potential to complete transform CAHs into non-toxic end products. Numerous bioreactor solutions can be implemented. Among these, packed bed reactors (PBRs) present important advantages, such as the removal of the biomass settling step and a higher cell resistance in the presence of toxic compounds. In addition, they display a high tolerance versus very high and variable organic loads. In particular, they represent an interesting solution for the biodegradation of recalcitrant and toxic compounds, since biomass grown in the form of biofilm is partially protected against toxic substances and inhibition phenomena due to high substrate concentrations. In this respect, PBRs inoculated with selected pure cultures or mixed consortia have been shown to be very promising both for the metabolic and the cometabolic degradation of several recalcitrant and toxic compounds, such as polychlorinated biphenyls, polyethoxylated nonyl phenols, nitrophenols and chlorinated solvents.