Algal biomass can be produced as a by-product of high rate algal ponds (HRAPs) running for waste water treatment (Park et al. 2011). The HRAPs are raceway-type open ponds with depths in the range of 0.2-0.5 m, retention times (HRT) ranging from 3 to 10 days (that depends on growth rate of test algae), and paddle wheel to provide mixing (Park and Craggs 2010; Craggs et al. 2012). In such systems algal photosynthesis releases oxygen which is required for degradation of organic matter by heterotrophic bacteria.

The concept of using HRAPs for waste water treatment and algal biomass pro­duction for purposes of energy production (biofuel) was presented by Rupert Craggs and his colleagues working at National Institute of Water and Atmospheric Research Ltd. (NIWA), New Zealand. The HRAPs keep the advantages of simplicity and economy, overcoming the disadvantages of other systems including poor effluent quality and limited nutrient and pathogen removal (Craggs et al. 2012).