The impacts of intermittent mixing on High Rate Algal Pond performance

Author: Naomi Semi

Semi, Naomi, 2020 The impacts of intermittent mixing on High Rate Algal Pond performance, Flinders University, College of Science and Engineering

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High rate algal ponds (HRAP) are a sustainable wastewater treatment system that is suitable for rural and remote communities. They use less land area, less energy for operation/solar voltaic with battery storage, have shorter retention times compared to conventional waste stabilisation ponds (WSPs) and most importantly achieve treatment results that are comparable to WSPs. The key features of a HRAP include a shallow raceway pond system, continuously yet gently mixed by a paddlewheel and in the presence of sunlight and algal photosynthesis wastewater is treated. However, there is the likelihood of the mixing being interrupted either due to failure/outages of the electricity supply or as part of managing the operational costs. Therefore, the aim of this study was to assess the performance of a HRAP when subjected to different intermittent mixing conditions.

The project was conducted at the Kingston on Murray HRAP facility studying two intermittent mixing regimes to assess treatment performance. In Regime 1, to illustrate an instance where there could be a power failure to operate the paddle wheel or if there was a mechanical failure in the system, the mixing was intermittently turned on than off for 5 days over a 15-day period to determine if treatment changed within the periods and or recovered to its initial stage when mixing restarted. In Regime 2, the second intermittent mixing condition, compared the operation of two HRAPs where the experimental HRAP was turned off for 12 hours daily in the evenings to depict a situation where this could be done to save electrical energy consumption and HRAP 2 was kept in continuous operation for comparison.

Parameters studied included nutrients, carbon content, suspended solids (SS) and chlorophyll a. The seasons in which the study was conducted were considered as well as they have an impact on the performance of HRAPs. In Regime 1 the results of SS, chlorophyll a, the carbon content and nutrients between the on and off phases were statistically insignificant to conclude that the performance between the on, off and on phases were different. In Regime 2, chlorophyll a, inorganic carbon content as well and PO4 – P were comparable. Particulate organic carbon (POC) content was over 60% in both seasons and HRAP conditions studied in this regime indicated an ample organic carbon pool and the algal biomass was maintained. Despite some differences, the HRAP performances were comparable and maintained overall.

These results can contribute towards seeking amendments for the operational guidelines for HRAP systems in South Australia.

Keywords: High rate algal pond, intermittent mixing, nutrients, suspended solids, chlorophyll a, TOC, on, off,

Subject: Environmental management thesis

Thesis type: Masters
Completed: 2020
School: College of Science and Engineering
Supervisor: Professor Howard Fallowfield