The predatory bacterium, Bdellovibrio bacteriovorus, was applied as a biological pre-treatment to solar disinfection and solar photocatalytic disinfection for rainwater treatment. The photocatalyst used was immobilised titanium-dioxide reduced graphene oxide. The pre-treatment followed by solar photocatalysis for 120 min under natural sunlight reduced the viable counts of Klebsiella pneumoniae from 2.00 × 10 9 colony forming units (CFU)/mL to below the detection limit (BDL) (<1 CFU/100 μL). Correspondingly, ethidium monoazide bromide quantitative PCR analysis indicated a high total log reduction in K. pneumoniae gene copies (GC)/mL (5.85 logs after solar photocatalysis for 240 min). In contrast, solar disinfection and solar photocatalysis without the biological pre-treatment were more effective for Enterococcus faecium disinfection as the viable counts of E. faecium were reduced by 8.00 logs (from 1.00 × 10 8 CFU/mL to BDL) and the gene copies were reduced by ∼3.39 logs (from 2.09 × 10 6 GC/mL to ∼9.00 × 10 2 GC/mL) after 240 min of treatment. Predatory bacteria can be applied as a pre-treatment to solar disinfection and solar photocatalytic treatment to enhance the removal efficiency of Gram-negative bacteria, which is crucial for the development of a targeted water treatment approach.
Bibliographical noteFunding Information:
The authors would like to acknowledge the following individuals and institutions for their contribution to this project: • The financial assistance of the Deutscher Akademischer Austauschdienst / National Research Foundation of South Africa and the Royal Society Newton Mobility Grant (Grant number: NI170184 ). Opinions expressed and conclusions arrived at, are those of the authors and are not necessarily to be attributed to the DAAD/NRF or the Royal Society Newton Mobility Grant. • Pilar Fernández-Ibáñez and John Anthony Byrne acknowledge funding from Global Challenges Research Fund – United Kingdom Research and Innovation (GCRF UKRI) for SAFEWATER (Grant Ref number EP/P032427/1 ). • Dr Jeremy Hamilton and Dr Preetam Sharma from the Nanotechnology and Integrated BioEngineering Centre (NIBEC) at Ulster University (Northern Ireland) for their guidance during the synthesis and immobilisation of the TiO 2 -rGO material. • Casper Brink from the Microbiology Department at Stellenbosch University for creating the drawings of the designed SODIS systems in AutoCAD® 2018. • Dr Pieter Neethling from the Physics Department at Stellenbosch University for measuring the reflectance of the stainless-steel sheets utilised for the construction of the compound parabolic collectors. Appendix A
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- Bdellovibrio bacteriovorus
- Biological pre-treatment
- Harvested rainwater
- Solar disinfection