Natural covers: Is it a viable solution to manage biosolids temporary stockpiles?

Rajapaksha, N.S.S.1, Gedara, S.1, Mansfield, H.1 and Startin, C.1

1 Environmental Services, Wastewater Wholesale, United Utilities



Agriculture recycling of Biosolids is recognised as the Best Practicable Environmental Option for sludge management in most situations. However, field stockpile management over the rainy winter months is challenging since most digested Biosolids are vulnerable to wet weather. Such stockpiles may cause risks to the environment and impose an extra cost to sludge producer in addition to the reputational damage. The aim of this study was to investigate the possibility of using natural covers to manage the stability of Biosolids stockpiles. Preliminary field trials were conducted using straw and live-grass covers. Initial finding reveals that the Biosolids stockpiles with live-grass cover tend to retain the stability during severe winter periods. This study suggests that natural covers could be a practical, efficient and economical technique for Biosolids stockpile management. However, further studies are recommended to identify suitable grass varieties for live covers, other potential natural cover materials and possible post-spreading issues.

Keywords: Agriculture Recycling, Biosolids, Live covers, Natural Covers, Stockpile Stability


The UK produces approximately 1.4 million tonnes (Dry Solids) of sewage sludge per annum with volumes increasing annually. Currently 80% of the total production goes to agricultural recycling after suitable treatment while rest is mainly disposed through incineration and landfill (OFWAT 2015). Treated sewage sludge (Biosolids) which contain plant nutrients and organic matter has been recycled to agricultural land around the world for many decades.


Agriculture recycling of Biosolids is recognised as the Best Practicable Environmental Option (BPEO) in most circumstances and supported by the UK government and European Commission. However, Biosolids recycling process poses various environmental and technical challenges in addition to the social and economic pressures faced by Biosolids undertakers. One of the important logistical aspects of Biosolids recycling is safe stockpiling.


EU/UK regulations allows Biosolids to be stockpiled on the same field location up to 12 months, in practice, it is kept to a minimum. However, Biosolids stockpile management over the rainy winter months is always challenging. The stockpile stability is broadly determined by;

  1. Having a Biosolids product “fit for the purpose”,
  2. Selection of appropriate stockpile location, and
  3. Employing appropriate stockpiling technique.


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