Vertical profiling and modelling of Escherichia coli decay in a shallow maturation pond operating in a tropical climate

ABSTRACT

Maturation ponds are excellent natural treatment systems for disinfecting domestic wastewater from pathogenic bacteria because of their great sunlight exposure through depth and high pH and dissolved oxygen values – all considered important factors. Escherichia coli (E. coli) removal is higher at closer to the surface of the pond and proceeds to decrease due to the limited amount of sunlight at deeper depths. To quantify the decay coefficients (K _b) of E. coli in a shallow maturation pond, quartz vessels were used to create isolated batch experiments and submerged at different depths inside the pond during different periods of the day (morning and afternoon). K _b values ranged from 0.48 to 0.28 h⁻¹, considering different depths and both periods. A dark control vessel was also used to quantify dark decay rates (K _d) at the same depth and periods as the quartz vessels, and ranged from 0.14 to 0.04 h⁻¹. Environmental variables did not appear to influence overall disinfection. Two models for estimating final E. coli concentrations were proposed, considering the kinetic coefficients obtained in the batch experiments and the dispersed flow regime for continuous flow ponds, which resulted in very good fittings with monitoring data and demonstrated the vertical profiling of E. coli concentration.

KEYWORDS:

• E. coli
• depth profiling
• modelling decay rates
• sunlight-mediated disinfection
• shallow baffled maturation pond

Acknowledgements

The authors thank the Brazilian institutions CNPq, Capes, Fapemig, Finep and COPASA.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was part of an international programme financed by the Bill and Melinda Gates Foundation for the project ‘Stimulating local innovation on sanitation for the urban poor in Sub-Saharan Africa and South-East Asia – SaniUp’, under the coordination of UNESCO-IHE, Institute for Water Education, Delft, the Netherlands.