Despite the progress achieved so far in waste water treatment, diffuse and point-source pollution still threaten the status of EU waters, particularly in relation to micropollutants. Micropollutants are organic compounds that are present in the aquatic environment at concentrations in the range of a few n/l to μg/l. They comprise a wide range of organic compounds such as pesticides, biocides, pharmaceuticals, x-ray-contrast media and flame retardants.
These substances can cause risks to or via the aquatic environment, including risks to waters used for the abstraction of drinking water, and can have an impact on fundamental biochemical processes such as the endocrine system.
Municipal waste water treatment plants are a major source of micropollutants as they cannot sufficiently be eliminated by the commonly applied techniques (primary and biological treatment) via biological degradation and adsorption to activated sludge. Also, the possibilities of preventing the discharge of hundreds of micropollutants at source are limited, so end-of-pipe techniques must be applied.
Minimising the discharge of heavily or non-biodegradable organic compounds, especially micropollutants, involves:
- treating at least twice the dry weather waste water inflow (in case of rain or thawing)
- treating the waste water at nitrifying conditions and performing denitrification and phosphorous removal (see the best practice on energy efficient waste wate rtreatment achieving full nitrification)
- in the case of sensitive areas, removing suspended solids by sand filtration (or by submerged membranes) and significantly removing micropollutants by adequate techniques, such as adsorption to pulverised activated carbon or oxidation with chlorine-free oxidising agents (specifically ozone in a cascade reactor)
- monitoring online organic compounds (total organic carbon), ammonia, nitrate and phosphorous in the case of plant capacities of more than 100,000 population equivalents or a daily inflow BOD5-load of more than 6000 kg.