Behaviour and fate of metals in urban wastewater treatment plants: a review|
Cantinho, P.; Matos, M.; Trancoso, M.A. & Correia dos Santos, M.M.
The concerns on metals in urban wastewater
treatment plants (WWTPs) are mainly related to its contents
in discharges to environment, namely in the final effluent and
in the sludge produced. In the near future, more restrictive
limits will be imposed to final effluents, due to the recent
guidelines of the European Water Framework Directive
(EUWFD). Concerning the sludge, at least seven metals (Cd,
Cr, Cu, Hg, Ni, Pb and Zn) have been regulated in different
countries, four of which were classified by EUWFD as priority
substances and two of which were also classified as
hazardous substances. Although WWTPs are not designed to
remove metals, the study of metals behaviour in these systems
is a crucial issue to develop predictive models that can
help more effectively the regulation of pre-treatment
requirements and contribute to optimize the systems to get
more acceptable metal concentrations in its discharges.
Relevant data have been published in the literature in recent
decades concerning the occurrence/fate/behaviour of metals
in WWTPs. However, the information is dispersed and not
standardized in terms of parameters for comparing results.
This work provides a critical review on this issue through a
careful systematization, in tables and graphs, of the results
reported in the literature, which allows its comparison and so
its analysis, in order to conclude about the state of the art in
this field. A summary of the main consensus, divergences
and constraints found, as well as some recommendations, is
presented as conclusions, aiming to contribute to a more
concerted action of future research.
Metals removal mechanisms; Metals mass balances; Metals behaviour models; Priority pollutants; Sewage sludge metals content; Urban wastewater metals sources