More advanced WWTPs apply additional treatments to reduce nutrients, organic matter and metals in the sewage, and these wastewater discharges, despite being highly diluted, can exert minor effects if they continue for a long time.
"To study the effects of these plants properly, we designed an innovative experiment that allowed us to handle the entire ecosystem over several years," explained Ioar de Guzmán, a researcher in the UPV/EHU's Stream Ecology group. First, several variables were measured for one year in two selected reaches in an unpolluted stream, to see the difference between these reaches."That way we knew how these stream variables changed depending on time and place," she said.
"We believe that by adhering to the limits stipulated by the legislation, the problems are reduced, but impacts are nevertheless generated; we must bear in mind that for an optimal conservation of the trophic networks of the streams, these treatments have to be even more stringent," concluded the researcher from the Stream Ecology group.