Partitioning of wastewater treatment high rate algal pond biomass and particulate carbon

The partitioning of algae, bacteria, grazers and detritus in two wastewater treatment high rate algal ponds (HRAPs) was investigated in relation to particulate carbon (PC) over a year. Algae dominated the pond biomass accounting for similar to 61% of the PC. Changes in algal biomass correlated with changes in PC with both varying seasonally and having spring or summer maxima. The algal biomass itself was dominated by larger cells or colonies in the 20-200 mu m size fraction with Pediastrum sp. prominent. Bacterial biomass, in contrast, only accounted for similar to 13.5% of the PC and varied less seasonally. Grazer biomass was lowest at similar to 4% of the PC on average and was dominated by either zooplankton or microzooplankton. Grazer biomass however, varied the most and reached similar to 14% of the PC during a spring zooplankton bloom that markedly reduced algal biomass. The remaining similar to 21.5% of the PC was made up of dead algal, detrital matter, and mucilage that tended to aggregated into bio-floccs. The PC of an efficiently operating HRAP is shown to be driven by high algal biomass with low bacterial and grazer biomass. If this balance is lost grazers may grow to levels that enable them to reduce algal biomass and productivity compounding pond instability. (C) 2016 Elsevier B.V. All rights reserved.