Groundwater vs. farming - meeting the needs of both

Liquid manure obtained from animal husbandry is a nutrient medium used as a valuable natural fertiliser. However, inappropriate use of this manure is one of the reasons for increased concentrations of nitrates and phosphates in ground and surface water. A major problem arises from intensive animal husbandry, combined with a shortage of land that can be used for distributing liquid manure.

Because of the increasing strain imposed on groundwater as a result of excess use of fertilisers, the legislative authorities in The Netherlands and Belgium felt compelled to impose more stringent regulations on drinking water and soil protection. The resultant restrictions have led to surpluses of liquid manure in intensive farms, and in particular in pig-feeding operations.

The problem of how to spread the liquid manure on land without causing environmental problems has been solved by reducing phosphate and nitrogen levels. This task of solid-liquid separation is handled efficiently and cost-effectively by mechanical separation technology using decanters. The decanter removes 70%-90% of phosphate compounds and 30%-35% of nitrogen compounds. After separation, these substances remain in the crumbly solid phase, which can easily be transported with conveyer belts and stored. The liquid can then be spread on fields with less strain on the soil and groundwater. The farmer can use existing land for a larger number of animals.

Specific use of nutrients
A permanent liquid manure treatment installation consists primarily of a liquid manure collection tank with an agitator, a de-watering station, product pump, clarifying decanter and control unit as well as the tank for holding clarified liquid manure. Solid particles, are removed by centrifugal treatment, and de-watered to a trickling consistency. The solids discharged from the decanter are suitable for processing into fertiliser but must first be treated hygienically by drying or composting. The solids can then be filled into commercial packings and sold as valuable fertiliser. In the Netherlands, fertiliser obtained in this way may be spread on land that still has to be fertilised. However, in the Flemish part of Belgium, it has to be exported.

A Dutch company has ordered AD1220 decanters from Westfalia Separator which are fitted with a 2-gear drive for optimum dewatering, and are capable of processing up to 20 m3/h. The company operates the decanters, including the necessary installation components such as pumps and pumping technology, as a mobile installation on a truck. The power supply is obtained from a diesel generator, which is also on the mobile installation. This means that the decanter is a completely independent unit and can be moved from farm to farm for processing liquid manure.

The mechanical process of separating liquid manure into solids and a liquid suspension using decanters does not use any chemicals, e.g. flocculants and while most orders to date have been from Belgium and the Netherlands where regulations regarding groundwater and environmental protection are strict, the method is suitable for use worldwide.


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