Detergent phosphates are hydrolysed in the wash water, sewerage system, sewage treatment, or surface waters, to simple natural phosphates, PO4. This is the same phosphate as comes from human metabolism, animals, food and other organic wastes, agricultural run-off … Because phosphate is essential for life, can act as fertiliser for plants and algae in surface waters, posing environmental problems termed “eutrophication” (which means “over feeding”).

Where phosphates are used in detergents, they only contribute around a quarter of the total phosphate in domestic wastewater, depending on lifestyle (population diet, detergent use …). Consequently, where eutrophication is a problem for lakes or rivers, stopping using detergent phosphates will not resolve the problem, and the only solution has to be to collect and treat municipal waste waters (nutrient removal). In rural areas, septic tank systems with appropriate soil infiltration, will also effectively prevent sewage phosphates from reaching surface waters

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Known and tested biological and chemical processes can remove phosphates in sewage treatment plants down to 0.1 or even 0.01 mgP/litre. In this case, the residual phosphate discharge will not depend on the treatment plant inflow concentration, but on the process used for nutrient removal. Nutrient removal in sewage works also improves treatment of organic pollution. The phosphates removed, along with nitrogen, potassium, magnesium and other minerals, can be recycled, directly into agriculture or biomass energy production by using sewage biosolids as fertiliser, or into industrial fertiliser or chemicals production.

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Eutrophication is a very complex process, and in many cases water bodies will not be negatively affected by sewage nutrient inputs:

· plant growth is limited by factors other than nutrients (water flow, temperature …) or by nutrients other than phosphate. Most marine environments, for example, are limited by nitrogen not phosphate

· increased algae production is consumed by natural grazers (zooplankton), which are in turn consumed by fish. In some cases, phosphate addition to lakes is carried out voluntarily to increase fish production

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· eutrophication problems can result from loss of such grazer populations, because of toxic pollution, which should be addressed by water treatment, or because of habitat loss

· the main source of phosphate is often agriculture (soil erosion, fertiliser run-off, animal manures …), industry, or natural background phosphates

If an ecosystem receives excessive inputs of nutrients from other sources such as agriculture, then removing nutrients from sewage will not prevent eutrophication, and reducing phosphates in detergents even less so (because detergents are only a minority contributor to sewage nutrients). Conversely, where ecosystems receive low nutrient levels (diffuse populations, extensive agriculture), then reducing sewage nutrients may also not be useful.

Because eutrophication is such a complex phenomenon, depending on many factors other than phosphates (other nutrients, water flow, climate, grazer populations …), and because detergents are only a relatively minor source of phosphates, relating eutrophication risk to detergent phosphate use is difficult. A methodology to achieve this however has now been developed by the Spanish national research institute INIA, with support from CEEP, and has been published by the European Union. This is based on probabilistic analysis of real water quality data, and concludes that use of phosphates in detergents typically increases the eutrophication risk only by around 0.5 - 3% in most of Europe.

© 2017 Global Phosphate Forum