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What are High Rate Algal Ponds?

Have you heard of the term 'high rate algal ponds'? You'd be excused if you hadn't but, since you are here and reading this post, you'd obviously like to know more.

Keep reading to learn the ins and outs of high-rate algal pools and, if you'd like some further info regarding wastewater, give Express Wastewater a call at 1300 722 517 and we can help.

What are HRAPs?

High-rate algal ponds, also called HRAPs, are shallow raceway ponds that move wastewater via a low-power paddle wheel. They are typically used in two scenarios:

  1. To treat high-strength wastewater
  2. To grow algal biomass for biofuel production.
Algal pond
Photo courtesy of the Local Government Association of South Australia. https://www.lga.sa.gov.au/page.aspx?u=7654

How do HRAPs work?

HRAPs are designed to boost the breakdown of organic waste via algal and bacterial growth and inactivate pathogens via exposure to sunlight. The organic breakdown and pathogen reduction are sped up, which results in smaller retention times in comparison to standard lagoon systems. The residence time is generally between 4-10 days and the depth of ponds is typically between 30cm and 50cm.

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What benefits do HRAPs offer?

High-rate algal ponds are sustainable, low-energy and low-cost alternative wastewater treatment options. They also take only 4-10 days to treat wastewater, compared to a conventional system that requires 66 days to treat wastewater to a similar level of treatment. It is also worth noting that:

  • HRAP's ability to remove pathogens is equal to, or better than, existing wastewater systems.
  • Cost about 40% less to construct compared with conventional lagoon systems.
  • Better public health outcomes.
  • The paddle wheel means low power consumption and a lower carbon footprint.
  • Shorter retention times of between 4-10 days for effective treatment result in a smaller carbon footprint and reduced evaporation by approximately 12-30%.
  • Minimal operator intervention is needed when instrumentation and alarms are installed.

Who uses HRAPs?

HRAPs are being found to benefit more and more people, including rural communities and areas that create high-strength wastewater. In South Australia they are having great success with HRAPs in rural communities - the below table shows a few places where HRAPs can be used for comparisons:

HRAP comparisons table
Table courtesy of Local Government Association of South Australia. lga.sa.gov.au
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If you would like some further information regarding wastewater solutions, give Express Wastewater a call at 1300 722 517 and we can discuss your needs today.


Local Government Association of South Australia (High Rate Algal Ponds): https://www.lga.sa.gov.au/about-lga/what-we-do/community-wastewater-management-systems/high-rate-algal-ponds-hrap

In Daily (A better model for sewage systems – and the Murray): https://indaily.com.au/news/sponsored-content/2019/03/07/a-better-model-for-sewage-systems-and-the-murray/