Bacterial pathogen indicators regrowth and reduced sulphur compounds’ emissions during storage of electro-dewatered biosolids

• Regrowth of coliforms not observed in all electro-dewatered biosolids after 7 d.
• Regrowth of total coliforms observed in inoculated heat-treated biosolids.
• Lower odour detection and recognition thresholds for electro-dewatered biosolids.
• Little volatile organic sulphur compounds above electro-dewatered biosolids.
• pH decrease, nutrient removal and inhibitor formation may explain observed effects.

Electro-dewatering (ED) increases biosolids dryness from 10–15 to 30–50%, which helps wastewater treatment facilities control disposal costs. Previous work showed that high temperatures due to Joule heating during ED inactivate total coliforms to meet USEPA Class A biosolids requirements. This allows biosolids land application if the requirements are still met after the storage period between production and application. In this study, we examined bacterial regrowth and odour emissions during the storage of ED biosolids. No regrowth of total coliforms was observed in ED biosolids over 7 d under aerobic or anaerobic incubations. To mimic on-site contamination during storage or transport, ED samples were seeded with untreated sludge. Total coliform counts decreased to detection limits after 4 d in inoculated samples. Olfactometric analysis of ED biosolids odours showed that odour concentrations were lower compared to the untreated and heat-treated control biosolids. Furthermore, under anaerobic conditions, odorous reduced sulphur compounds (methanethiol, dimethyl sulphide and dimethyl disulphide) were produced by untreated and heat-treated biosolids, but were not detected in the headspaces above ED samples. The data demonstrate that ED provides advantages not only as a dewatering technique, but also for producing biosolids with lower microbial counts and odour levels.

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