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Using sludge on arable land - effect based levels and long-term accumulation for certain organic pollutants

image of Using sludge on arable land - effect based levels and long-term accumulation for certain organic pollutants

In the waste water treatment process in sewage treatment plants, sewage sludge is produced as a by-product. The sludge contains nitrogen and phosphorus that originate from the waste water. In addition to these nutrients, sludge also contains micronutrients and organic matter. Many of these substances are required for the production of food and they can be recycled by using sludge as a fertiliser on farm lands. Phosphorus is the nutrient that is of primary interest at present. This is due to the fact that phosphorus is a finite resource that is mined and has various levels of unwanted impurities. In the foreseeable future, there will be a shortage of phosphorus ore with low levels of impurities. Ores with higher levels of impurities may also be used in the production of mineral fertilisers in the future, but it may require that energy demanding cleaning techniques are used. Such a scenario will lead to higher market prices for phosphorus fertilisers, which may have social consequences on a global scale. It is therefore crucial that the available phosphorus is used efficiently, from an economic, environmental and social perspective.

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To control pollution from use of sludge

Limit values are used to protect human health and the environment, and are generally based on scientific principles. However, limit values may also be used as a driving force to obtain political or ethical principals. Limit values may well be an effective way to control soil contamination from sludge. However, limit values should be justified. Strict or liberal limitations can both cause criticism and give unexpected consequences regarding use of sludge as resource. Protection of soil and waters from contamination is important. It is also important to look at different soil usage, i.e. whether it concerns food production or parks, green areas, city gardens, urban areas, forests or land reclamation. This chapter contains a discussion on the suitability and constraints of risk based limit values for organic pollutants. Finally some aspects of monitoring programmes for organic pollutants in sludge are also discussed. An overview of the current Nordic regulations for use of sludge is given in appendice 5.

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