Persistence of Clostridium difficile in wastewater treatment-derived biosolids during land application or windrow...

To determine the persistence of Clostridium difficile spores in biosolids during composting or when amended into soil and held under natural environmental climatic conditions.

Five log CFU g(-1) Cl. difficile spores (ribotypes 027 or 078) were inoculated into agricultural soils (sandy loam or loam) amended with 10% w/w anaerobically digested biosolids. The inoculated soil : biosolids mixture was then placed into sentinel vials which were introduced at a depth of 15 cm within the field plot consisting of the corresponding soil type. Two trials were performed, the first of which started in late spring (May 2013 through to August 2014) and second from November 2013 through to October 2014 (fall trial). Ribotype 078 endospores in loam or sandy loam soil decreased during the summer but then increased in numbers towards the fall. At the end of the trial, levels of ribotype 078 spores had decreased by 1·5 log CFU g(-1) , with 027 spores decreasing by <1 log CFU g(-1) over the same time period. Windrow composting of biosolids decreased Cl. difficile levels from 3·7 log CFU g(-1) down to 0·3 log CFU g(-1) with the greater reduction occurring during the curing phase. In comparison, Cl. perfringens decreased from 6·3 log CFU g(-1) down to 2·4 log CFU g(-1) but mainly in the thermal phase of the composting process.

Composting of biosolids is a more effective means of inactivating Cl. difficile compared to land application.

Windrow composting represents an effective method to reduce the environmental burden of Cl. difficile associated with biosolids.