2. High Rate Algal Ponds (HRAP): purification mechanisms and performance

Less expensive and more energy-efficient than activated sludge systems, but more intensive than lagoon-type ponds, microalgae-based wastewater treatment systems such as High Rate Algal Ponds (HRAPs) are seen as promising solutions for secondary wastewater treatment in the most remote areas. HRAPs are shallow (30 to 50 cm) artificial channels in single or series of raceway-type loops, combined with an impeller. The photographs in figure 3 show the Peterborough HRAP in Australia, a large-scale 5,000 m ² system.