Proceedings

The application of granulated biosolids for the production of grass silage

Smith G. 1, Chaney K.1 Murray, C.1, and Le, M.S.2, 1Harper Adams University College, UK, 2United Utilities, UK

(free)

The END-O-SLUDG project aims to identify and develop technologies to improve municipal waste management, whilst also lowering the Greenhouse gas emissions associated with the sewage sludge treatment process. Previous work from this project which is funded from the EU FP7, has focused mainly on arable crop production for the recycling of biosolids as a nutrient source. However, grassland systems provide a large potential for disposal to land with an area of 7.2 million hectares of improved grassland in the UK. This paper presents results from three years of experiments on grass cut for silage. Results suggest that biosolids can produce similar yields to conventional fertiliser in field experiments. Although some significant increases were recorded in PTEs assessments on the earthworm populations, where the trials were conducted, suggest that numbers were not affected by the applications of biosolids. This suggests that potentially toxic elements were not negatively impacting upon a key species that is an indicator of soil health.

Keywords: Biosolids, Earthworms, Grass silage, Potentially Toxic Elements.

Introduction Many arable systems today rely solely on inorganic (man-made) fertilisers for additional nutrients due to the greater understanding and better estimation of the nutrients available. However, the production of inorganic fertilisers relies heavily upon fossil fuels and other natural resources and as these become increasingly difficult to source, the price of fertilisers will increase. Thus, this has led to a renewed interest in alternative sources of nutrients.

Organic amendments such as biosolids are a bi-product from human sewage processing. In addition to providing key nutrients, they have many benefits, such as increasing soil organic matter and water holding capacity. More than 30 million tonnes of wet sewage sludge is produced in the UK each year (Davis, 1987). The constituents of sewage sludge can come from a wide range of sources. The majority of sewage sludge is comprised of human wastes; surface run-off and industrial wastes are other large contributors. The Code of Practice of Agricultural Sewage Sludge defines sewage sludge as “…the residue collected after treatment of the contents of urban drainage systems (DEFRA, 2006).”

The water treatment industry, like agriculture, is under increasing pressure to reduce its’ impact on the environment. The processing of sewage sludge into biosolids should allow the water industry to recycle their waste whilst providing agriculture with an effective fertiliser.

The END-O-SLUDG project is part of the seventh framework programme run by the European Commission (END-O-SLUDG, 2012), which aims to move sewage sludge from a waste product into an agricultural fertiliser. Research and development from 14 different partners is being integrated in order to change the use and perceptions of sewage sludge.

The overall aims of the project are;

  • The reduction of energy consumption when processing sewage sludge
  • Reduction in CO2 emissions
  • Develop novel techniques to process sludge globally in a more economic and environmental manner
  • Develop a range of fertiliser products with a range of applications

This paper will discuss the results from three consecutive years of harvest data from a grass silage system receiving Organo-Mineral Fertiliser in comparison to convention inorganic fertilisers. In addition to this, data regarding the heavy metal content of the soil and the possible impacts on the environment will also be discussed. The null hypothesis is that biosolid applications would have a detrimental effect on yield quantity and quality. Biosolid application would also result in detrimental effects to the soil in terms of heavy metal content and earthworm populations.

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