The Role of Heterotrophic Microalgae in Waste Conversion to Biofuels and Bioproducts

Abstract

In the last few decades, microalgae have attracted attention from the scientific community worldwide, being considered a promising feedstock for renewable energy production, as well as for a wide range of high value-added products such as pigments and poly-unsaturated fatty acids for pharmaceutical, nutraceutical, food, and cosmetic markets. Despite the investments in microalgae biotechnology to date, the major obstacle to its wide commercialization is the high cost of microalgal biomass production and expensive product extraction steps. One way to reduce the microalgae production costs is the use of low-cost feedstock for microalgae production. Some wastes contain organic and inorganic components that may serve as nutrients for algal growth, decreasing the culture media cost and, thus, the overall process costs. Most of the research studies on microalgae waste treatment use autotrophic and mixotrophic microalgae growth. Research on heterotrophic microalgae to treat wastes is still scarce, although this cultivation mode shows several benefits over the others, such as higher organic carbon load tolerance, intracellular products production, and stability in production all year round, regardless of the location and climate. In this review article, the use of heterotrophic microalgae to simultaneously treat wastes and produce high value-added bioproducts and biofuels will be discussed, critically analyzing the most recent research done in this area so far and envisioning the use of this approach to a commercial scale in the near future.

Optimization of Chlorella vulgaris cultivation grown in waste molasses syrup using mixture design

“…In many researches, it has been demonstrated that wastewater and by‐products obtained from industries contains particles or have dark color that prevents adequate light penetration necessary for microalgae growth (Silva et al, 2021). The positive effect of NaNO 3 was observed in Figure 2 where the lipid productivity increased as NaNO 3 concentration in the blends increased.…”

“…It roughly contains 40%–50% sugar such as sucrose and fructose and is rich in microelements (e.g., Ca 2+ , Mg 2+ , K + , and Fe 2+ ) (Caballero et al, 2003; Yan et al, 2011). So, it can provide large amounts of nutrients for microalgae growth (Silva et al, 2021; Yew, Puah, et al, 2020).…”

Trends in mitigation of industrial waste: Global health hazards, environmental implications and waste derived economy for environmental sustainability

“…A total nitrogen removal efficiency of 94.45%, 0.241 g/L lipid production and biomass production of 1.42 g/L was attained in synergistic microalgal-bacterial incorporation in wastewater remediation (Leong et al, 2019). It was estimated that glucose derived biodiesel costs USD $3.79/L whereas agriculture waste and food waste derived biodiesel costs USD $2.6-3.0/L and $0.6/L (Silva et al, 2021).…”

Microalgae Biomass as a New Potential Source of Sustainable Green Lubricants

“…Heterotrophic and mixotrophic conditions exhibit higher biomass yield, extended exponential phase of growth, and less biomass loss [96]. Under mixotrophic conditions, both inorganic and organic carbon can be assimilated under certain operational conditions to increase biomass productivity and other high-value byproducts [97,98]. For example, Kujawska et al, 2021 [99], demonstrated waste glycerol as a potential organic carbon source to reach a Schizochytrium sp.…”