Aquatic Plants, Landoltia punctata, and Azolla filiculoides as Bio-Converters of Wastewater to Biofuel

Abstract

The aquatic plants, Azolla filiculoides, and Landoltia punctate, were used as complementing phytoremediators of wastewater containing high levels of phosphate, which simulates the effluents from textile, dyeing, and laundry detergent industries. Their complementarities are based on differences in capacities to uptake nitrogen and phosphate components from wastewater. Sequential treatment by L. punctata followed by A. filiculoides led to complete removal of NH₄, NO₃, and up to 93% reduction of PO₄. In experiments where L. punctata treatment was followed by fresh L. punctata, PO₄ concentration was reduced by 65%. The toxicity of wastewater assessed by shrimps, Paratya australiensis, showed a four-fold reduction of their mortality (LC₅₀ value) after treatment. Collected dry biomass was used as an alternative carbon source for heterotrophic marine protists, thraustochytrids, which produced up to 35% dry weight of lipids rich in palmitic acid (50% of total fatty acids), the key fatty acid for biodiesel production. The fermentation of treated L. punctata biomass by Enterobacter cloacae yielded up to 2.14 mol H₂/mole of reduced sugar, which is comparable with leading terrestrial feedstocks. A. filiculoides and L. punctata can be used as a new generation of feedstock, which can treat different types of wastewater and represent renewable and sustainable feedstock for bioenergy production.

Keywords: duckweed; hydrogen; phytoremediation; wastewater treatment.

Figure 1

Reductions of concentrations of PO₄, NH₄, NO₃ and Se in 100% (A,C,E,G) and 50% (B,D,F,H) SeSW by L. punctata followed by sequential treatment with A. filiculoides or L. punctata. Data expressed as mean ± standard deviation, * Significance levels: p < 0.05.

Figure 2

Survival rates of P. australiensis in untreated and treated by L. punctata and A. filiculoides SeSW.

Figure 3

(A): Growth of MAN43 cells in YP media supplemented with different carbon sources. Glu: glucose; (B): Lipid yields in L. punctata, A. filiculoides and MAN43 cells grown on different carbon sources. Black boxes: total lipids extracted from L. punctata and A. filiculoides; grey boxes: lipid yields in MAN43 cells grown on different carbon sources. Glu: glucose; Gly: glycerol. (C): FAME composition of lipids extracted from L. punctata, A. filiculoides and MAN43 grown on glucose. * Significance levels: p < 0.05.

Figure 4

(A) Hydrogen production by E. cloacae DT-1 from different concentrations of acid-treated prehydrolysate and enzymatically saccharified duckweed biomass; (B) hydrogen production performance of E. cloacae DT-1 from optimum concentrations of acid-treated prehydrolysate and enzymatically saccharified hydrolysate of duckweed biomass, under decreased partial pressure.