Abstract:
The low biodegradability and high persistence in environment of PCBs (polychlorinated biphenyls) make their
removal difficult and incomplete in conventional (chemical-biological) wastewater treatment plants (WWTP), and
frequent oversteps (5-250 ng/L) of the admissible limits in effluents (1 ng/L) are reported worldwide. In general,
accidental discharges of low loads might not be so critical, due to the fast pollutant dispersion over a short river-section
downstream the release point. In contrast, this problem can turn into a serious one if the pollutant is a POP (persistent
organic pollutants, as the PCBs), even for small concentrations in the WWTP effluent, due to its known high
bioaccumulation capacity in the environment. The paper illustrates, for the case of a low-level but frequent PCB-52
discharge from a WWTP, the high pollution potential for the river. By using a combined advective-dispersive dynamic
model, including the phase-exchange and bioaccumulation terms in biota and sediments, it is proved how a small but
quasi-continuous release of PCB can become dangerous on a long term. The model allows predicting the “moving
pollution front” effect propagated downstream the river, as soon as the aquatic phase-exchange equilibrium tends to be
reached in the critical discharge section.
