Effect of oxygen injection in a reclaimed wastewater pipeline on the microbiological quality of water

Abstract

In this work the influence of oxygen injection on the inactivation of microbiological indicators during reclaimed wastewater transportation was studied. Experiments were carried out in a completely filled gravity pipe (62 km long), at two different periods of the year and with three different oxygen doses (7, 15 and 30 mg L⁻¹). Microbiological parameters studied were faecal coliforms, Escherichia coli, enterococci and somatic coliphages. As a consequence of the oxygen injection, a significant inactivation of the microbiological parameters was observed during the aerobic stretch of the pipe. Later, once the oxygen had been consumed, inactivation stopped and even a slight regrowth of the microbial population took place. Inactivations were within the range of 0.6–1.0 log₁₀ units, in most cases. No significant differences between inactivations for the different microbiological parameters were found, except for the somatic coliphages. A relationship between the inactivation degree and oxygen dose and organic matter content was observed. The biofilm played an important role in the inactivation process. The injection of oxygen contributes to improving the microbiological quality of reclaimed wastewater during its transport by pipelines, helping to diminish the subsequent on-site disinfection requirements.

Keywords:

• inactivation
• microbiological indicators
• oxygen injection
• water reuse
• water transport

Acknowledgements

This work was funded by the PROFIT programme, from the Science & Technology and Science & Education Ministries of Spain (Project Code numbers FIT-140100-2003-78 and FIT-310200-2004-97), by ‘Dirección General de Universidades del Gobierno de Canarias’ (Project Code number Pi 2003/058), and by the Science & Education Ministry of Spain, National Plan for Research and Development (2004–2007) (Code number CTM2006-11188/TECNO).