Shallow, paddle-wheel mixed, raceway-type ponds (high rate oxidation ponds, HROP) are generally used in the treatment of wastewaters with algae. Recently however, several other types of algal culture systems have been developed which have potential application for the tertiary, or higher, treatment of wastewaters. These include hyperconcentrated algal cultures, immobilised cell systems, dialysis cultures, tubular photobioreactors and algal mats. Depending on the particular application of the algae to wastewater treatment and the ultimate use of the algal biomass, these systems may be much better suited than the 'standard' HROP pond system
