Micropollutant

It is estimated that there are currently around 235,000 individual chemical substances registered worldwide. A large number of these are released into wastewater by humans. If these are persistent, they remain during clarification in the wastewater and enter the environment. Some of them have ecotoxic relevant properties. In some cases, the chemical itself is not a concern, but its degradation products are. This has been known for a longer time. As early as 1976, a study was published in which salicylic acid and clofibric acid were detected in the effluent of a sewage treatment plant in Kansas City. We currently know that there are well over 1,000 substances in wastewater that pose a risk. Many others have not yet been sufficiently researched in this regard. == Effect ==

The influences of micropollutants are varied. The best known are those of hormones that enter the water through the contraceptive pill. Several studies have shown that feminization occurs in an unusually high number of fish below discharges from sewage treatment plants, which has a negative impact on the population. One in five male smallmouth bass in U.S. rivers has developed female sexual characteristics. Estrogen-like artificial compounds such as the plasticizer bisphenol A also have this effect. There is evidence that this also applies to humans. Such substances are called endocrine disruptors. Other substances, such as benzotriazole, which is added to dishwasher detergent as corrosion protection for silver cutlery, are suspected of being carcinogenic in addition to acting as an endocrine disruptor in the concentrations found. Another relevant factor is the danger posed by the spread of multi-resistant bacteria. There are two possible ways in which this can happen through wastewater. Firstly, by transporting already resistant strains into the receiving water due to inadequate treatment technology. The other possibility is the development of resistant cultures in the environment by introducing antibiotics into the water body. Preventing the entry of bacteria has long been used as a form of hygienic treatment using UV light or ozone, especially if the water is to be reused. Membrane systems such as membrane bioreactors or downstream ultrafiltration also serve this purpose. Depending on the intensity and technology, some micropollutants are also removed in addition to the bacteria. The extent to which membrane technologies with low energy consumption are able to deplete trace substances is being investigated. == Legislation ==

Techniques for elimination of micropollutants via a so called fourth treatment stage during sewage treatment are implemented in Germany, Switzerland, Sweden and the Netherlands and tests are ongoing in several other countries. In Switzerland it has been enshrined in law since 2016. Since 1 January 2025, there has been a recast of the Urban Waste Water Treatment Directive in the European Union, which requires the removal of a large proportion of micropollutants from wastewater. Due to the large number of amendments that have now been made, the directive was rewritten on November 27, 2024 as Directive (EU) 2024/3019, published in the EU Official Journal on December 12, and entered into force on January 1, 2025. The member states now have 31 months, i.e. until July 31, 2027, to adapt their national legislation to the new directive ("implementation of the directive"). The implementation of the framework guidelines is staggered until 2045, depending on the size of the sewage treatment plant and its population equivalents (PE). Sewage treatment plants with over 150,000 PE have priority and should be adapted immediately, as a significant proportion of the pollution comes from them followed by wastewater treatment plants with 10,000 to 150,000 PE that discharge into coastal waters or sensitive waters. The latter concerns waters with a low dilution ratio, waters from which drinking water is obtained and those that are coastal waters, or those used as bathing waters or used for mussel farming. Member States will be given the option not to apply fourth treatment in these areas if a risk assessment shows that there is no potential risk from micropollutants to human health and/or the environment. == Removal of micropollutants ==

Due to the large number of substances with very different chemical and physical properties, the removal of these substances is difficult. Three techniques and cominationes of them have been established so far. Two remove the contaminants with the help of activated carbon (PAC (Powdered Activated Carbon), GAC (Granulated Activated Carbon)) and one with ozone. In addition to that a large number of techniques are still in experimental stage. These include for example processes that work with plasma or ultrasound, so-called AOP processes, applications with zeolites and cyclodextrins, membrane processes or photocatalysis. == See also ==