The potential to improve pathogen removal in natural treatment systems with inclined planes

Author: Amy Hawley

Hawley, Amy, 2019 The potential to improve pathogen removal in natural treatment systems with inclined planes, Flinders University, College of Science and Engineering

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Water scarcity has increased the reliance on recycled wastewater to reduce the strain on global water supplies. High pathogen presence however, can be problematic with devastating impacts to public health a consequence. Reducing numbers are therefore essential.

Natural treatment ponds are becoming favourable using sunlight irradiance for microbial inactivation. Unfortunately in water light availability is restricted, lost through attenuation and non-microbial absorption. Increased exposure is exhibited in high rate algal ponds with shallow depths and paddlewheel rotation. To further improve removal strategies to enhance solar exposure are essential. Inclined planes have been proposed a possible solution with increased pathogen removal predicted when water is run down the sloped surface as a thin film. Pond walls are considered to be ideal inclined planes, formed with construction and often result with a large area of unused space. Utilising this redundant space can not only aid removal but assist in minimising costs.

In the current research the proposed theory was assessed is a series of laboratory and field based experiments. Examinations were performed using model and large scale high rate algal ponds with and without the addition of an inclined plane. MS2 and F-RNA phage were used as the test organism.

Results of the research demonstrated that phage inactivation rates could be improved with the inclusion of an inclined plane. In the model systems, the concept was proved in inclined planes of varying length under both optically clear and wastewaters when exposed to full sunlight or dark incubation and the inclined plane solely exposed. Operating the planes at the same hydraulic loading rate exhibited statistically similar removal rate. Results also confirmed water quality as an impacting factor as well as phage sensitivity towards sunlight irradiance. In the large scale system, mixed results were present with significantly improved inactivation only achieved once modifications to the system were performed. Nonetheless higher inactivation was observed whenever the inclined plane was in operation.

The current research has presented a novel and innovative approach to successfully improve pathogen removal in pond systems whilst maintaining the cost effectiveness of the system. The evaluations indicate the concept to be versatile with multiple disciplines with the water industry benefiting from the results. Furthermore, the concept paves a way for a more efficient treatment system to be realised. The research has also contributed to reducing the knowledge gap regarding phage removal in high rate algal ponds, which is currently lacking. This is the first time an inclined plane has been used for pathogen removal, with the concepts predicted adaptable to other pond systems.

Keywords: High rate algal ponds, inclined planes, pathogen removal, solar exposure, thin films, FRNA Phage

Subject: Water Management thesis

Thesis type: Doctor of Philosophy
Completed: 2019
School: College of Science and Engineering
Supervisor: Prof. Howard Fallowfield