M. Esperanza

Reduction of endocrine disruptor emissions in the environment: the benefit of wastewater treatment.

The occurrence and fate of four estrogens and five alkylphenolic compounds were studied in thirteen plants with various treatment processes, sizes and countries. Complete load mass balance, including water and sludge phases, has shown a high reduction of the total load of hormones, around 90%. The removal of alkylphenols was more variable, due to the degradation of nonylphenol (NP) precursors - alkylphenol polyethoxylates (APnEO) - during the treatment, resulting in significant production of shorter and toxic alkylphenols (NP and short polyethoxylates) that concentrate in the sludges. Under anaerobic conditions, such as anaerobic digestion process, the load of NP was in most cases observed to increase. When considering the environmental impact, the high reduction of endocrine disrupting compounds (EDC) concentrations between raw wastewater and effluent enables to satisfy the requirements of the Water Framework Directive for NP except in very critical situations where the dilution factor of the effluent in the river would be lower than 7. For sludges, the pending European Directive on spreading of sludge on land would be complied with in all cases.

On-site evaluation of the efficiency of conventional and advanced secondary processes for the removal of 60 organic micropollutants.

The next challenge of wastewater treatment is to reliably remove micropollutants at the microgram per litre range in order to reduce the discharge for priority substances and to meet the environmental quality standards set by the European Water Framework Directive. The present work assessed the occurrence of 60 organic substances (priority substances and other relevant pollutants) in municipal wastewater and sludge. Their fate in the treatment processes and their removal efficiencies were quantified. Thorough on-site mass balances were carried out at 8 municipal wastewater treatment plants chosen among conventional and advanced secondary processes. It was found that 70% of the substances were quantified in raw wastewater and 50% in effluent, with a transfer without a limited degradation for most of them. Low loaded activated sludge (AS) process reduced the emission of more than half of micropollutants. At low sludge retention time (AS under high load), lower removal efficiencies were measured compared to low loaded AS. No influence of temperature of the biological reactor was shown. The membrane bioreactor process increased the removal efficiencies for one third of the substances that were partially removed with AS. Still, five substances were measured at concentrations exceeding the environmental quality standards at the outlet of the studied plants. In addition to efforts for source-reduction, complementary treatments need to be set-up.

Occurrence and fate of relevant substances in wastewater treatment plants regarding Water Framework Directive and future legislations.

The next challenge of wastewater treatment is to reliably remove micropollutants at the microgram per litre range. During the present work more than 100 substances were analysed through on-site mass balances over 19 municipal wastewater treatment lines. The most relevant substances according to their occurrence in raw wastewater, in treated wastewater and in sludge were identified, and their fate in wastewater treatment processes was assessed. About half of priority substances of WFD were found at concentrations higher than 0.1 μg/L in wastewater. For 26 substances, potential non-compliance with Environmental Quality Standard of Water Framework Directive has been identified in treated wastewater, depending on river flow. Main concerns are for Cd, DEHP, diuron, alkylphenols, and chloroform. Emerging substances of particular concern are by-products, organic chemicals (e.g. triclosan, benzothiazole) and pharmaceuticals (e.g. ketoprofen, diclofenac, sulfamethoxazole, carbamazepine). About 80% of the load of micropollutants was removed by conventional activated sludge plants, but about two-thirds of removed substances were mainly transferred to sludge.