Culturing of Selenastrum on diluted composting fluids; conversion of waste to valuable algal biomass in presence of bacteria

Abstract

Growth and fatty acid production of microalga Selenastrum sp. with associated bacteria was studied in lab-scale experiments in three composting leachate liquids. Nutrient reduction in cultures was measured at different initial substrate strengths. A small, pilot-scale photobioreactor (PBR) was used to verify lab-scale results. Similar growth conditions supported growth of both Selenastrum and bacteria. CO feed enhanced the production of biomass and lipids in PBR (2.4gL and 17% DW) compared to lab-scale (0.1-1.6gL and 4.0-6.5% DW) experiments. Also prolonged cultivation time increased lipid content in PBR. At both scales, NH-N with an initial concentration of ca. 40mgL was completely removed from the biowaste leachate. In lab-scale, maximal COD reduction was over 2000mgL, indicating mixotrophic growth of Selenastrum. Co-cultures are efficient in composting leachate liquid treatment, and conversion of waste to biomass is a promising approach to improve the bioeconomy of composting plants.

Integrated utilization of microalgae cultured in aquaculture wastewater: wastewater treatment and production of valuable fatty acids and tocopherols

“…These conditions can induce wax ester synthesis in E. gracilis (Regnault et al 1995) resulting in undesirably high SAFA content. However, as shown here and elsewhere (Tossavainen et al 2017), the high biomass production results in a higher total lipid yield and thus, also higher LC-PUFA and tocopherol yields. In our algal cultures, EPA and DHA contents were close to or higher than in general required for fish feeds and exceeded the required proportions of ARA and α-tocopherol.…”

“…More efficient COD reduction in cultures grown in the sludge-amended medium may have been a consequence of higher bacterial concentrations originating from the added non-sterilized sludge. Fast COD removal in algal-bacterial co-cultures in AWW, as well as other wastewaters, has been shown earlier (Halfhide et al 2014;Tossavainen et al 2017). However, mixotrophic uptake of organic substrates in E. gracilis and green algae has also been reported (Yamane et al 2001;Kim et al 2013), which suggests that contingently E. gracilis and Selenastrum contributed to COD removal.…”

“…The maximum reported growth rate for Euglena sp., grown in municipal wastewater, is 0.79 day −1 (on dry weight (DW) basis) (Mahapatra et al 2013), whereas growth rates of several green algal strains grown in various synthetic wastewaters varied between 0.04 and 0.32 day −1 for Selenastrum capricornutum, 0.07 and 0.38 day −1 for Scenedesmus obliquus, and 0.04 and 0.52 day −1 for Chlorella vulgaris (Zhao et al 2016). In our previous study (Tossavainen et al 2017), the growth rate of Selenastrum sp., grown in various composting fluids, was 0.34-0.68 day −1 . Furthermore, euglenoids are producers of LC-PUFAs (Korn 1964;Schwarzhans et al 2015;Tossavainen et al 2018).…”

“…Among the microalgal genera, euglenoids and green algae (Chlorophyceae) are common in polluted environments and efficiently remove nutrients from wastewaters (Mustafa et al 2012;Mahapatra et al 2013;Tossavainen et al 2017Tossavainen et al , 2018. The maximum reported growth rate for Euglena sp., grown in municipal wastewater, is 0.79 day −1 (on dry weight (DW) basis) (Mahapatra et al 2013), whereas growth rates of several green algal strains grown in various synthetic wastewaters varied between 0.04 and 0.32 day −1 for Selenastrum capricornutum, 0.07 and 0.38 day −1 for Scenedesmus obliquus, and 0.04 and 0.52 day −1 for Chlorella vulgaris (Zhao et al 2016).…”

“…Furthermore, euglenoids are producers of LC-PUFAs (Korn 1964;Schwarzhans et al 2015;Tossavainen et al 2018). The most abundant FAs in green algae are palmitic acid (C16:0), oleic acid (C18:1), linoleic acid (C18:2(n-6), LA), and linolenic acid (C18:3(n-3), ALA), whereas green algae are not able to synthesize LC-PUFAs (Taipale et al 2013;Tossavainen et al 2017). Also, odd number FAs, not common in biological organisms are typical of euglenoids (Schwarzhans et al 2015).…”