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

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