Controls of microalgal biomass and lipid production in municipal wastewater-fed bioreactors

Abstract

The use of wastewater as a nutrient source for algal growth as a biodiesel feedstock could increase the viability of this process and reduce wastewater discharge of nitrogen- and phosphorus-bearing compounds. In this study, four algal bioreactors were fed continuously with municipal wastewater effluent over a 6-month period; these were monitored weekly to determine algal biomass and lipid production, nutrient removal, and carbon and nutrient availability. Algal biomass production ranged from 0.78 to 15.9 g dry weight m⁻² d⁻¹ over the experimental period. Algal reactors removed 19% of dissolved nitrogen and 43% of dissolved phosphorus from wastewater effluent. A stoichiometric analysis of particulates revealed that algal biomass had far lower C:P ratios (67:1) and N:P ratios (6:1), but higher C:N ratios (17:1), than Redfield values. These data suggest that the algae produced were rich in phosphorus, and that nitrogen was likely to be growth-limiting in these systems. Nonetheless, numerous studies suggest that algal biomass can be enhanced by providing CO₂ in excess of normal atmospheric concentrations, and that algal biofuel production can contribute to CO₂ sequestration efforts. To optimize nutrient removal in wastewater-fed algal reactors, and to determine the potential for CO₂ sequestration, future reactor engineering research should continue to incorporate the expertise of ecological stoichiometry. © 2011 American Institute of Chemical Engineers Environ Prog, 2012