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Management of wastewater sludges to minimise risks from human pathogens

Gibbs, R., Hu, C., Ho, G.ORCID: 0000-0001-9190-8812 and Oliver, J. (1999) Management of wastewater sludges to minimise risks from human pathogens. In: Proceedings of the International Regional Conference on Environmental Technologies for Wastewater Management, December 1997, Perth, Western Australia pp. 113-212.

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Sludges that are produced from wastewater that has human faecal input are a potential risk to human health because of the possible presence of human pathogens. However, sludges that do not have a high industrial input have very good beneficial re-use properties as soil conditioners and slow release fertilisers. Sludge management should take into account both the risks and potential benefits of sludges. Sludges produced by settling contain high numbers of a range of pathogens. Further biological treatments such as anaerobic digestion and composting produce a more stabilised product that is referred to as biosolids. These treatments reduce pathogen concentrations but some pathogens appear able to survive. We have found that two pathogens of particular concern are salmonellae and Giardia. Salmonellae appear to survive composting in low numbers and can survive for long periods. They can also potentially regrow in biosolids. We found that salmonellae regrew in stored biosolids after one year of storage and in soil amended with biosolids. Giardia are also of concern because they survived sludge treatments and biosolids composting in high numbers. However we found that Giardia cysts were reduced to below detection limits by 3 months storage after composting. From our studies recommendations for sludge management are that biosolids should be composted and that biosolids should be stored after composting before becoming available for re-use options in which humans are likely to be exposed. Storage may result in regrowth of salmonellae so monitoring for salmonellae should be carried out.

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