Civil Engineering ETDs

Publication Date

Spring 5-7-2018

Abstract

Growth of algae in saline produced waters (wastewater) from oil and gas production is of interest for potential production of algal biofuels, wastewater treatment and potential reuse or disposal. The objectives of this study were to determine the effects of salt concentrations and nitrogen source (ammonia or nitrate) and concentration on algal growth, lipid production, and nutrient removal to help determine suitability for growth on saline produced waters. Dunaliella tertiolecta (a marine algae) and a polyculture (previously discovered growing in PW) were grown on produced water with a range of salinities and varying nitrogen source and concentration, in a series of experiments primarily using triplicate flasks reactors.

Illumina sequencing of 23s RNA genes determined the polyculture was composed largely of Cyanobacterium aponinumand Parachlorella kessleri. The Polyculture growth was highest from brackish to hypersaline conditions (15 – 60 g TDS/L) of 45 – 50 mg AFDW/L/D. Growth was inhibited in higher ranges and ceased by 120 g TDS/L. The highest polyculture lipid fraction of 40% was achieved at a salinity level of 90 g TDS/L after nutrient stress, while the highest lipid productivity at 60 g TDS/L (8.5 mg/L/D). Growth rates were higher with ammonium than with nitrate as a nitrogen source (at a 60 g TDS/L), with little ammonia inhibition up to levels of 200 mg NH4-N/L. The highest biomass productivity was achieved using initial concentrations of 13 mg NH4-N/L and 1.7 mg PO4-P/L with a single day increase in biomass of 99 mg AFDW/L. The fatty acid methyl ester (FAME) profile of the polyculture oil was dominated by palmitic and stearic acids, indicating its suitability for transesterification to biodiesel.

D. tertiolectadisplayed consistent growth in PW over a broad range of salinities from 30 -210 g TDS/L. A biomass productivity of 16-17 mg AFDW/L/D was maintained up to a salinity of 120 g TDS/L with nitrate as a nitrogen source. Ammonium at the same molar concentration in 120 g TDS/L produced water increased growth to 21.8 mg AFDW/L/D, with higher lipid productivity. D. tertiolectawas more susceptible to free ammonia inhibition than was the polyculture. However, free ammonia inhibition was lower at higher salinities, apparently because of a shift in the ammonium species equilibrium away from deprotonation. A higher initial phosphate condition (8 vs. 1.7 mg PO4-P/L) produced slightly lower growth and oil production. Both biomass and lipid productivity were highest in 120 g TDS/L PW media at concentrations of 13 mg NH4-N/L and 1.7 PO4-P/L (21.8 mg AFDW/L/D, 11.2 mg lipid/L/D, and peak lipid content of 44%). FAMEs in D. tertiolectawere dominated by palmitic acid and unsaturated C18 chains, with little variation by salinity.

Both cultures demonstrated growth in hypersaline PW at TDS levels not previously published. The reported mixotrophic capabilities of P. kesslerishould be explored for improving growth. D. tertiolectaand other species in the genus could allow algae cultivation at TDS concentrations in excess of 210 g /L. High carbonate and lower levels of ammonium and phosphate are likely key to optimizing hypersaline media biomass and lipid productivity. These nutrients are commonly already present in PW. Both cultures can uptake bicarbonate in an alkaline media which can be supplied from carbon capture technologies of fossil fuel emissions. The results of this study indicate that algae cultivation in hypersaline produced water is a viable method for biofuel production.

Keywords

algae, hypersaline, biofuel, produced water, Dunaliella, salinity

Sponsors

EPSCor

Document Type

Thesis

Language

English

Degree Name

Civil Engineering

Level of Degree

Masters

Department Name

Civil Engineering

First Committee Member (Chair)

Dr. Andrew Schuler

Second Committee Member

Dr. Jose Cerrito

Third Committee Member

Dr. Kerry Howe

Fourth Committee Member

Dr. Enid Sullivan Graham

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