Effects of salinity and nitrogen source on growth and lipid production for a wild algal polyculture in produced water media

Abstract An algae polyculture (discovered in oil and gas produced water (PW) originating from a production facility in the Permian Basin of southwestern New Mexico) was composed primarily of Cyanobacterium aponinum , Parachlorella kessleri , with the remaining populations consisting of several species of halotolerant bacteria. The polyculture was tested in PW based media at a variety of different salinities and initial nutrient concentrations to determine the effects of these environmental conditions upon growth and lipid production. The polyculture exhibited growth rates of 46–51 mg ash free dry weight (AFDW)/L/D in PW over a salinity range from 15 to 60 g total dissolved solids (TDS)/L in PW containing nitrate as a nitrogen source. Growth was reduced at higher salinity. Biomass productivity in 60 g TDS/L PW was higher with ammonium as the nitrogen source (47.2–57 mg AFDW/L/D) than nitrate, with the highest growth observed using initial concentrations of 13 mg NH 4 -N and 1.7 PO 4 -P/L (single day growth of 99 mg AFDW/L/D). Of the conditions tested lipid productivity was greatest (around 12 mg lipids/L/D) at a salinity of 60 g TDS/L after phosphorus depletion (ammonium still present), and the maximum lipid content (48% of AFDW) after ammonium depletion (phosphate still present). Higher salinity, initial ammonium, and phosphate levels enriched for P. kessleri over C. aponinum , which also resulted in increased lipid content and productivity. Conversion of lipids to fatty acid methyl ester (FAME) created a profile dominated by palmitic (C16:0) and stearic (C18:0) acid and would produce a usable biodiesel. The results indicated that a mixed culture of C. aponinum , P. kessleri, and other micro fauna is a potential candidate for cultivation in brackish to hypersaline PW based media for the production of biomass and/or biofuels.