Screening of potential zooplankton control technologies for wastewater treatment High Rate Algal Ponds
2017
Montemezzani, Valerio | Duggan, Ian C. | Hogg, Ian D. | Craggs, Rupert J.
Zooplankton taxa including cladocerans and rotifers are one of the greatest challenges for effective management 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 here we 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 (t<10min). Increasing the cladoceran Moina tenuicornis to densities >2500individuals/L was associated with a decrease in rotifer populations (~23% of the population in the control). The ostracod Heterocypris incongruens at densities >1000 individuals/L were also associated with a decrease in rotifer densities that were ~27% of the population in the control. Hydrodynamic shear stress killed 100% of M. tenuicornis and ~80% of the rotifer Brachionus calyciflorus after a single pass. Furthermore, M. tenuicornis was concentrated in the upper 50mm of a 300mm deep water column using vertical migration induced by CO2 concentrations of between 25 and 180mg/L. All of these treatments have potential for use to control zooplankton blooms in WW HRAPs.
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