Incorporation of wastewater harvested algae into three-phase compression ignition emulsion fuels

The purpose of this study was to assess the technical feasibility of incorporating wastewater harvested algae into three-phase, oil-in-water-in-oil compression ignition emulsion fuels for use in diesel engines. The use of three-phase, oil-in-water-in-oil emulsion fuels in diesel engines can extend fuel supplies while reducing emissions. Decreases in heating values caused by the introduction of water into emulsion fuels can be partially offset with the addition of algae. Algae in the Chlorella genus are ideal for use in emulsion fuels because their small size enables easy passage through fuel systems, and their potentially high lipid content increases heating values. Chlorella also effectively treats wastewater while providing natural aeration in oxidation pond systems. This study estimated that algal biomass, consisting mostly of Chlorella, comprised approximately 74% of solids contained within the Arcata, CA wastewater oxidation ponds between July 2006 and September 2006. An estimated range of 3,200 and 3,700 kilowatt-hours were contained within solids present in daily oxidation pond effluent during the study period. From July 2005 to September 2005, the Arcata wastewater treatment facility consumed an average of 3,100 kilowatt-hours of electricity per day, indicating that algae may have potential to offset operating costs if an adequate energy harnessing process is developed. The dilute nature of wastewater algae necessitates thickening prior to use as fuel. Results from this study indicated that suspended air flotation more efficiently removed algae from wastewater when compared to dissolved air flotation. Suspended air flotation required less flotation water, consumed less energy and provided significantly higher percent cake, solids loading rate and hydraulic loading rate when compared to dissolved air flotation (P0.001). Algae harvested from oxidation ponds with suspended air flotation were incorporated into three-phase oil-in-water-in-oil emulsion fuels. Heating values of algal emulsion fuels containing 0.1 gram, 1.0 gram and 5.0 grams of algae per liter of emulsion fuel were compared to traditional three-phase emulsion fuels. Both treatment and control fuels contained 20% and 30% water, and were produced with Tween 80 and Span 80 surfactants. While all algal emulsion fuels had significantly higher heating values than controls (P0.001), maximum increases were observed in emulsion fuels containing 5.0 grams of algae per liter of fuel. The increases were 4.9% and 6.6% for emulsion fuels containing 20% and 30% water, respectively. While these increases are notable, stratification and separation of algae within the fuel were observed within 24 hours, and decay of algae within emulsion fuels was detected within seven days of production. The short life span of emulsion fuels may limit the practicality of their use for applications where the fuel can be combusted immediately after production.