Use of the microalga Monoraphidium sp. grown in wastewater as a feedstock for biodiesel: Cultivation and fuel characteristics

The use of microalgae as feedstocks for biodiesel is potentially limited by climatic conditions with low light and temperature levels. Monoraphidium sp. Dek19 was identified by 18S rRNA gene sequencing. This is a species indigenous to the upper Midwestern USA which grows to high densities in wastewater with bioremediation resulting in a reduction of nitrate and phosphate levels. Mesocosm pool cultures (171L) were used to characterize growth of this species in larger volumes than typical of previous lab-based studies. The alga was shown to be cold-tolerant and to grow to workable density within 15 days at relatively low light intensities in sterilized treated effluent. It was harvested by FeCl3 flocculation and filtration, and lipid content was measured at 26% of dry weight. Pool cultures yielded enough biomass to extract lipids and transesterify them to biodiesel for testing in a stationary engine. GC analysis showed FAMEs produced from Monoraphidium sp. to have a similar fatty acid profile to soybean oil. Engine testing of this algal biodiesel in blends with petrodiesel showed a significant reduction in NOx emissions. The results of this study indicate in general that searching for species of algae adapted to local environments is a good strategy for developing biodiesel feedstocks, and specifically that Monoraphidium sp. Dek19 represents a species isolate that could be used to produce this fuel economically using wastewater in Northern locations with cool climates.