How well do wastewater treatment plants remove pharmaceuticals?

A comprehensive analysis of pharmaceuticals in Spanish wastewater has indicated that they are widespread pollutants. The majority of pharmaceuticals present in incoming wastewater were still present in both treated water and in the river waters receiving the treated water.

The EU Urban Wastewater Treatment Directive1 (UWWTD) requires Member States to ensure that both discharges from urban wastewater treatment plants and receiving waters are monitored. In addition, the Water Framework Directive2 requires water to be maintained at a good ecological and chemical status. The objective of wastewater treatment under the UWWTD is to remove suspended solids (bigger than 5 micrometres) with primary treatment, and organic material with secondary treatment. If wastewater is discharged in sensitive areas (water bodies with risk of becoming eutrophic, or areas which include bathing waters, for instance, which require further treatment than secondary to fulfil other Directives), more stringent treatment will be applied that also involves nutrient removal (nitrates, phosphates) or disinfection.

The long-term research, carried out under the EU AquaTerra project3, was conducted in the Ebro river basin in North-East Spain. It assessed seven wastewater treatment plants (WWTPs) for the presence of 73 pharmaceuticals in both incoming water (influent) and treated water (effluent). It also assessed the river waters receiving the effluent.

The most prominent pharmaceuticals were non-steroidal anti-inflammatory drugs (NSAIDs) and analgesics in both influent and effluent water of the WWTPs. One of the most significant NSAIDs was ibuprofen.

Further examination revealed that for some pharmaceuticals there was poor or no elimination in all seven of the WWTPs. For example, macrolide antibiotics and benzodiazepines were sometimes at higher levels in effluent than in the influent. A tentative explanation is that pharmaceuticals are changed in the body when humans digest them, but they are converted back into the original pharmaceutical during wastewater treatment.

Moderately good treatment was observed for one large group of pharmaceuticals with removal of between 40 and 70 per cent of the substance. This group included lipid regulators and beta-blockers. Only NSAIDs and the antihypertensive enalapril were treated at a high-effectiveness, with removal rates of 81 to 98 per cent.

The research also investigated the impact of the hydraulic retention time (HRT) - the amount of time the liquid remains in the WWTP. The results indicated that a long HRT is influential when compounds take a long time to degrade, such as antibiotics.

The pharmaceuticals detected more frequently in river waters tended to be those that were not removed effectively during wastewater treatment, with the exception of analgesics and anti-inflammatories. Despite high removal rates these were present at high concentrations in river waters. This is because their concentration in the influent was so high that significant levels remain in the effluent and subsequently reach rivers.

The researchers evaluated the risks of pharmaceuticals that were in the rivers and the effluent towards algae, daphnids and fish. The results indicated that there are no significant risks in river waters, probably because the pharmaceuticals are highly diluted. However, the researchers pointed out that risk assessments only considered single pharmaceuticals, whereas pharmaceuticals are often present as mixtures which could have greater, unknown toxic effects on ecosystems.

1. See http://ec.europa.eu/environment/water/water-urbanwaste/directiveprinciples/index_en.htm#planning
2. See http://ec.europa.eu/environment/water/water-framework/info/intro_en.htm
3. AquaTerra was supported by the European Commission under the Sixth Framework Programme. See www.eu-aquaterra.de

Source: Gros, M., Petrovic, M, Ginebreda, A & Barceló, D. (2010). Removal of pharmaceuticals during wastewater treatment and environmental risk assessment using hazard indices. Environment International. 36:15-26.

Contact: mpeqam@cid.csic.es