A team of researchers from CEAB-CSIC (Blanes Centre for Advanced Studies - Higher Council of Scientific Investigations) in Spain has discovered a potential solution that is sustainable, simple and low-cost to put an end to the excess of nitrate in Mediterranean rivers found in the effluent from sewage treatment plants, even if these comply with EU legislation.
According to the study, most waterways in the Mediterranean cannot dilute nitrates because of the low water levels. In fact, in summer, some rivers are nearly dry and the little water they contain is the discharge from wastewater treatment plants.
Although these wastewater treatment plants are very efficient at removing pollutants, such as phosphorus, nitrogen and organic matter, from faecal waters, it is impossible for them to eliminate them completely. In rivers with low water levels, this source of extra nutrients, together with fertilizers used in farming leads to an excess of nitrates.
Nitrates in freshwater and seawater proliferate microalgae and make lakes, lagoons, rivers and seas green-coloured. It also reduces oxygen levels, necessary for aquatic species.
Now, the team of scientists have found that by pouring brewery waste, or leaving the organic remains of the trimmings of aquatic plants used in the natural purification systems of wastewater treatment plants, it is possible to increase the rates of bacterial denitrification up to 40 per cent. Bacterial denitrification is responsible for removing nitrates from water in the natural environment. The researchers are optimistic about their study, saying the percentage of denitrification could even double in the future.
This new treatment method can be carried out immediately, according to Miquel Ribot, Technical Manager of the Urban River Lab at CEAB-CSIC and lead author of the study, and has already been implemented in ponds and lakes of urban parks in Barcelona.