Lindsay Soh

Fate of sucralose through environmental and water treatment processes and impact on plant indicator species.

The degradation and partitioning of sucralose during exposure to a variety of environmental and advanced treatment processes (ATP) and the effect of sucralose on indicator plant species were systematically assessed. Bench scale experiments were used to reproduce conditions from environmental processes (microbial degradation, hydrolysis, soil sorption) and ATPs (chlorination, ozonation, sorption to activated carbon, and UV radiation). Degradation only occurred to a limited extent during hydrolysis, ozonation, and microbial processes indicating that breakdown of sucralose will likely be slow and incomplete leading to accumulation in surface waters. Further, the persistence of sucralose was compared to suggested human tracer compounds, caffeine and acesulfame-K. In comparison sucralose exhibits similar or enhanced characteristics pertaining to persistence, prevalence, and facile detection and can therefore be considered an ideal tracer for anthropogenic activity. Ecological effects of sucralose were assessed by measuring sucrose uptake inhibition in plant cotelydons and aquatic plant growth impairment. Sucralose did not inhibit plant cotelydon sucrose uptake, nor did it effect frond number, wet weight, or growth rate in aquatic plant, Lemna gibba. Though sucralose does not appear toxic to plant growth, the peristent qualities of sucralose may lead to chronic low-dose exposure with largely unknown consequences for human and environmental health.

Biodiesel production: the potential of algal lipids extracted with supercritical carbon dioxide

Supercritical carbon dioxide (scCO2) was used to extract components of interest from Scenedesmus dimorphus, a microalgae species, under varied algal harvesting and extraction conditions. Liquid chromatography-mass spectrometry (LC-MS) was used to quantify the concentration of fatty acid methyl esters (FAME) and the FAME profile of transesterified lipids, phospholipids and pigments extracted under varied supercritical temperatures and pressures. The scCO2 extraction results are compared with conventional solvent extraction to evaluate differences in the efficiency and nature of the extracted materials. Algae harvested by centrifugation (vs.lyophilization) demonstrated a similar extraction efficiency in scCO2, indicating potential energy benefits by avoiding conventional algal mass dehydration prior to extraction. Centrifuged algae and optimized extraction conditions (6000 psi; 100 °C) resulted in comparable FAME yields to conventional processes, as well as increased selectivity, reflected in the decreased pigment, nitrogen and phospholipid contamination of the FAME. Cell pre-treatments—sonication, microwave, bead beating and lyophilization—showed an enhancement in extraction yield in both conventional solvent and scCO2 extraction, allowing for improved extraction efficiencies. This study suggests that scCO2, a green solvent, shows great potential for algal lipid extraction for the sustainable production of biodiesel.

Evaluating microalgal integrated biorefinery schemes: empirical controlled growth studies and life cycle assessment.

Two freshwater and two marine microalgae species were grown under nitrogen replete and deplete conditions evaluating the impact on total biomass yield and biomolecular fractions (i.e. starch, protein, and lipid). A life cycle assessment was performed to evaluate varying species/growth conditions considering each biomass fraction and final product substitution based on energy consumption, greenhouse gas emissions (GHG), and eutrophication potential. Lipid for biodiesel was assumed as the primary product. Protein and carbohydrate fractions were processed as co-products. Composition of the non-lipid fraction presented significant trade-offs among biogas production, animal feed substitution, nutrient recycling, and carbon sequestration. Maximizing total lipid productivity rather than lipid content yielded the least GHG emissions. A marine, N-deplete case with relatively low lipid productivity but effective nutrient recycling had the lowest eutrophication impacts. Tailoring algal species/growth conditions to optimize the mix of biomolecular fractions matched to desired products and co-products can enable a sustainable integrated microalgal biorefinery.