Removal of Emerging Contaminants in Wastewater Treatment: Conventional Activated Sludge Treatment

Abstract

Persistent organic pollutants released from wastewater discharges into the environment can persist in the environment, bioaccumulate through the food web, enter drinking water production and pose a risk to human health and the environment. Conventional activated sludge (CAS) treatments are usually designed to remove or to decrease the concentrations of pathogens and the loads of the bulk organic but generally they are not designed to remove residues of trace organics.

In the present work the presence of pesticides, pharmaceuticals and personal care products, surfactants and other contaminants and their removal in CAS systems are presented and discussed.

The capacity to eliminate micropollutants in CAS depends on various factors, including physico-chemical properties, biological persistence of the individual compound and the technology and process conditions (e.g. temperature and seasonal variability, hydraulic and sludge retention time applied). Sludge retention time, though not exclusively, has been revealed as one of the most important process parameters. The relative importance of sorption, more relevant for lipophilic compounds and some hydrophilic compounds (e.g. surfactants), as compared to biodegradation can increase when the residence time in CAS is too short for implementing an efficient degradation. For high polar substances (e.g. most pharmaceuticals) the most important removal process is biological transformation or mineralization by microorganisms. Finally, present levels of knowledge about the degradation pathway in CAS is often not complete and formation of human and natural metabolites should be continuously and carefully monitored as they can be, occasionally, more toxic than the parental compounds.