Naturally occurring algae can be a nuisance, particularly when they proliferate rapidly (bloom) as a result of inorganic nutrient enrichment of surface waters. One of the problems associated with algae stems from the fact that during periods of darkness they can switch from photosynthetic to respiratory metabolism thereby removing dissolved oxygen from the water. Much of the effort in the removal of inorganics (nitrogen and phosphorus) from wastewaters has been aimed at the elimination of algal blooms.
