Microalgal luxury uptake of phosphorus in waste stabilization ponds – frequency of occurrence and high performing genera

Microalgae commonly found in waste stabilization ponds (WSPs) are able to accumulate elevated phosphorus levels within their cells in a process known as luxury uptake. However, there are few studies focused on luxury uptake in full scale WSPs. In order to comprehensively quantify the occurrence of this phenomenon, eight different WSP sites comprising seven primary facultative, six maturation and two high rate algal ponds (HRAPs) spread over several climatic regions were monitored over four seasons. Of the 15 ponds studied, 13 of these exhibited elevated levels of biomass phosphorus content at some point; however, the occurrence in HRAPs was limited. More than half of the samples tested had elevated phosphorus contents and this occurred in all climatic zones surveyed. The phosphorus content of the biomass was significantly correlated to decreasing rainfall and increasing total dissolved phosphorus. Microscopic analysis revealed that nearly all the 17 microalgal and five cyanobacterial genera identified performed luxury uptake, but at varying frequencies. This is the first time that the genera of algae responsible for luxury uptake in full scale WSPs has been studied. Chlamydomonas/Cryptomonas, Micractinium/Microcystis and Scenedesmus were the only microalgal genera found to both commonly occur in WSPs and consistently perform luxury uptake.