title: The effects of CO₂ addition along a pH gradient on wastewater microalgal photo-physiology, biomass production and nutrient removal.
abstract: Carbon limitation in domestic wastewater high rate algal ponds is thought to constrain microalgal photo-physiology and productivity, particularly in summer. This paper investigates the effects of CO₂ addition along a pH gradient on the performance of wastewater microalgae in high rate algal mesocosms. Performance was measured in terms of light absorption, electron transport rate, photosynthetic efficiency, biomass production and nutrient removal efficiency. Light absorption by the microalgae increased by up to 128% with increasing CO₂ supply, while a reduction in the package effect meant that there was less internal self-shading thereby increasing the efficiency of light absorption. CO₂ augmentation increased the maximum rate of both electron transport and photosynthesis by up to 256%. This led to increased biomass, with the highest yield occurring at the highest dissolved inorganic carbon/lowest pH combination tested (pH 6.5), with a doubling of chlorophyll-a (Chl-a) biomass while total microalgal biovolume increased by 660% in Micractinium bornhemiense and by 260% in Pediastrum boryanum dominated cultures. Increased microalgal biomass did not off-set the reduction in ammonia volatilisation in the control and overall nutrient removal was lower with CO₂ than without. Microalgal nutrient removal efficiency decreased as pH decreased and may have been related to decreased Chl-a per cell. This experiment demonstrated that CO₂ augmentation increased microalgal biomass in two distinct communities, however, care must be taken when interpreting results from standard biomass measurements with respect to CO₂ augmentation.
authors.affiliation: National Institute of Water and Atmospheric Research Ltd. (NIWA), PO Box 8602, Christchurch, New Zealand; Centre for Integrative Ecology, School of Biological Sciences, University of Canterbury, Christchurch, New Zealand. Electronic address: Donna.Sutherland@niwa.co.nz.
authors.forename: Donna L
authors.initials: DL
authors.lastname: Sutherland
authors.affiliation: National Institute of Water and Atmospheric Research Ltd. (NIWA), PO Box 8602, Christchurch, New Zealand. Electronic address: Clive.Howard-Williams@niwa.co.nz.
authors.forename: Clive
authors.initials: C
authors.lastname: Howard-Williams
authors.affiliation: Centre for Integrative Ecology, School of Biological Sciences, University of Canterbury, Christchurch, New Zealand. Electronic address: Matthew.Turnbull@canterbury.ac.nz.
authors.forename: Matthew H
authors.initials: MH
authors.lastname: Turnbull
authors.affiliation: Centre for Integrative Ecology, School of Biological Sciences, University of Canterbury, Christchurch, New Zealand. Electronic address: Paul.Broady@canterbury.ac.nz.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Broady
authors.affiliation: National Institute of Water and Atmospheric Research Ltd. (NIWA), PO Box 11-115, Hamilton 3200, New Zealand. Electronic address: Rupert.Craggs@niwa.co.nz.
authors.forename: Rupert J
authors.initials: RJ
authors.lastname: Craggs
mesh_terms: D018533:Biomass; D002245:Carbon Dioxide / Q000008:administration & dosage*; D006863:Hydrogen-Ion Concentration; D008027:Light; D058086:Microalgae / Q000378:metabolism / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis; D013045:Species Specificity; D062065:Wastewater
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen; D062065:Wastewater
keywords: Biomass enhancement; Carbon dioxide addition; High rate algal ponds; Light absorption; PAM; Photosynthesis