Screening of potential zooplankton control technologies for wastewater treatment High Rate Algal Ponds

Zooplankton taxa including cladocerans and rotifers are one of the greatest challenges for effectivemanagement of High Rate Algal Ponds (HRAPs) for wastewater treatment as they can establish and rapidly consume beneficial microalgae. Harmful zooplankton need to be controlled using cost effective treatments, and herewe tested under controlled laboratory conditions the efficacy of chemical CO2 asphyxiation, biological control of rotifers using competitor species expected to graze only moderately on colonial microalgae, and mechanical disruption using hydrodynamic shear stress. CO2 asphyxiation caused acute mortality of all zooplankton species (iota < 10 min). Increasing the cladoceran Moina tenuicornis to densities >2500 individuals/L was associated with a decrease in rotifer populations (similar to 23% of the population in the control). The ostracod Heterocypris incongruens at densities N1000 individuals/L were also associated with a decrease in rotifer densities that were similar to 27% of the population in the control. Hydrodynamic shear stress killed 100% of M. tenuicornis and similar to 80% of the rotifer Brachionus calyciflorus after a single pass. Furthermore, M. tenuicornis was concentrated in the upper 50 mm of a 300 mm deep water column using vertical migration induced by CO2 concentrations of between 25 and 180 mg/L. All of these treatments have potential for use to control zooplankton blooms inWWHRAPs. (C) 2016 Elsevier B. V. All rights reserved.