Abstract
Microalgae are promising candidates for sustainable wastewater treatment coupled to the production of biofuel, bioplastic and/or bio-fertilizers. In Nordic countries, however, light is a limiting factor for photosynthesis and biomass production during the winter season. Compared to municipal wastewater, industrial wastewater streams from the pulp and paper industry contain lower amounts of nitrogen, but high concentrations of carbon sources, which could be utilized by microalgae to enhance biomass production in limiting light. This study focused on the utilization of methanol, glycerol and xylose by five different Nordic microalgae [Chlorella vulgaris (13–1), Coelastrella sp. (3–4), Desmodesmus sp. (2–6), Chlorococcum sp. (MC1) and Scotiellopsis reticulata (UFA-2)] grown under mixotrophic conditions. Two of these strains, i.e., Chlorococcum sp. (MC1) and Scotiellopsis reticulata (UFA-2) were able to grow in the presence of xylose or methanol at concentrations of 6 g L–1, or 3%, respectively, in a 12/12 h day/night cycle. HPLC analysis confirmed the consumption of those substrates. Glycerol (2.3 g L–1) was tolerated by all strains and increased growth for Chlorella vulgaris (13–1), while higher concentrations (20 g L–1) were only tolerated by Chlorococcum sp. (MC-1). Fourier-transform infrared spectroscopy, performed after growth in presence of the dedicated carbon source, indicated an increase in the fingerprint region of the carbohydrate fraction. This was particularly the case for Chlorococcum sp. (MC1), when grown in presence of glycerol, and Scotiellopsis reticulata (UFA-2), when grown in presence of xylose. Therefore, these strains could be potential candidates for the production of biofuels, e.g., bioethanol or biogas. We could show that Nordic microalgae are able to grow on various carbon sources; the actual uptake rates are low during a 12/12 h day/night cycle requesting additional optimization of the cultivation conditions. Nonetheless, their potential to use pulp and paper waste-streams for cheap and sustainable biomass production is high and will support the development of new technologies, turning waste-streams into resources in a circular economy concept.
Highlights
Waste streams from oil crop based biofuel production contain large amounts of carbon in form of crude glycerol that might be a cheap source of carbon for microalgal cultivation (Dobson et al, 2012)
Glycerol is the main by-product in the production of biodiesel and large amounts are present in the corresponding waste streams (Yang et al, 2012)
All strains were able to grow in presence of glycerol at a concentration of 2.3 g L−1 (Figure 1), but only Chlorella vulgaris (13–1) showed a significantly (p = 0.049) better growth compared to the glycerol-free control, and the glycerol concentration in its medium decreased significantly (p = 0.001)
Summary
The annual global water demand is about 4,600 km according to the World Water Development Report from 2019. About 20% (∼ 920 km3) of the water is used by industry other than agriculture (Boretti and Rosa, 2019). The production of cellulose-based products (pulp, paper, and paperboard) generates 870 million m3 of wastewater per year just in Sweden. Most of it is recovered and recycled roughly 37 million m3 of water remain to be cleaned (Munthe et al, 2011). These waste streams are rich in phosphorus and organic carbon, e.g., cellulose or hemicellulose, with xylose being one of the major compounds, turning them into potentially high valuable resources for microalgal growth. Waste streams from oil crop based biofuel production contain large amounts of carbon in form of crude glycerol that might be a cheap source of carbon for microalgal cultivation (Dobson et al, 2012)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
