3. Pollution and enhanced nutrient removal
In the 1960’s, movements, such as those in the U.S. associated with Rachel Carson’s Silent Spring, called for more attention to environmental causes, such as pollution of lakes, rivers and coastal waters. Incidents with lakes full of dead fish and smelly rivers, both in Europe and the US, made it apparent that something had to happen. Nutrients such as nitrogen and phosphorous were found to be a major problem in uncontrolled growth of algae and other water plants (eutrophication).
Regulations
As a result, regulations were set in place in the 70’s to regulate the discharge of wastewater from companies, industries and municipalities. In the US, following the 1970 creation of the U.S. Environmental Protection Agency, the Clean Water Act was introduced in 1972.
Early European water policy also began in the 1970s with the First Environmental Action Programme in 1973, followed by a first wave of legislation, starting with the 1975 Surface Water Directive, which allowed for funding for new and improved WWTPs.
BNR systems
From the 1990’s onwards, more and more countries started applying full Biological Nutrient Removal (BNR) systems. Nitrogen removal required the combination of nitrification (aerobic conditions) and denitrification (anoxic conditions). To remove phosphorus biologically, the biomass required exposure to anaerobic conditions (uptake of COD and release phosphate) and aerobic conditions (uptake of net phosphate). Thus, a complex, but effective system was developed comprising several compartments, internal recycle flows and (secondary) clarifiers to separate the treated effluent from the biological sludge.
However, along with this new technology, other challenges appeared, such as space availability and energy consumption.