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Composting of wastewater biosolids: Potential for regrowth of pathogens

Ho, G.E.ORCID: 0000-0001-9190-8812, Sidhu, J. and Gibbs, R.A. (2000) Composting of wastewater biosolids: Potential for regrowth of pathogens. In: International Workshop on Biosolid Management and Utilization, 10 - 13 September 2000, Nanjing Agricultural University, China

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Composting is commonly used as an effective means of stabilising wastewater biosolids and reducing pathogen concentrations to very low levels. However, under certain conditions enteric bacteria can regrow in previously composted biosolids. Regrowth of Salmonella in composted biosolids can pose a potential threat to public health. A study was carried out to find out whether regrowth of pathogens in composted biosolids could be prevented or controlled. The role of bio-available nutrients and indigenous microorganisms in inhibition of Salmonella regrowth was investigated.

A full-scale windrow composting process was found to be effective in reducing Salmonella concentrations to below the detection limit. However, Salmonella regrowth in stored biosolids after 26 weeks, coinciding with a rainfall after a dry spell, was observed. This suggests that Salmonella can survive the composting process in low numbers and regrowth can take place in the presence of favourable growth conditions.

The antagonistic activity of indigenous microorganisms was found to be the most significant factor in suppression of Salmonella regrowth in composted biosolids. The inactivation rate of Salmonella was found to be significantly greater in non-sterilised compost as compared to sterilised compost. Maximum inhibition of Salmonella growth was observed in biosolids that had been composting for two weeks.

The specific growth rate of Salmonella was found to have a strong negative correlation (- 0.85) with the maturity of the compost. However, a decline in bio-available nutrients was not sufficient to prevent the regrowth of Salmonella in composted biosolids stored for two years. The antagonistic effect of indigenous microorganisms towards Salmonella declined with the storage of compost. Consequently, it can be concluded that all composted biosolids had a Salmonella regrowth potential.

However, the presence of biologically active indigenous microflora significantly reduced this regrowth potential. As a result of a decline in the antagonistic activity of indigenous microflora with storage, longer Salmonella survival time could be expected in stored compost as compared to freshly composted biosolids. Consequently, long term storage of compost is not recommended as this may lead to an increased Salmonella regrowth potential and longer survival time.

Item Type: Conference Paper
Murdoch Affiliation(s): School of Environmental Science
United Nations SDGs: Goal 6: Clean Water and Sanitation
Goal 13: Climate Action
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