Key Targets for Improving Algal Biofuel Production

Abstract

A number of technological challenges need to be overcome if algae are to be utilized for commercial fuel production. Current economic assessment is largely based on laboratory scale up or commercial systems geared to the production of high value products, since no industrial scale plant exits that are dedicated to algal biofuel. For macroalgae (‘seaweeds’), the most promising processes are anaerobic digestion for biomethane production and fermentation for bioethanol, the latter with levels exceeding those from sugar cane. Currently, both processes could be enhanced by increasing the rate of degradation of the complex polysaccharide cell walls to generate fermentable sugars using specifically tailored hydrolytic enzymes. For microalgal biofuel production, open raceway ponds are more cost-effective than photobioreactors, with CO2 and harvesting/dewatering costs estimated to be ~50% and up to 15% of total costs, respectively. These costs need to be reduced by an order of magnitude if algal biodiesel is to compete with petroleum. Improved economics could be achieved by using a low-cost water supply supplemented with high glucose and nutrients from food grade industrial wastewater and using more efficient flocculation methods and CO2 from power plants. Solar radiation of not <3000 h·yr−1 favours production sites 30° north or south of the equator and should use marginal land with flat topography near oceans. Possible geographical sites are discussed. In terms of biomass conversion, advances in wet technologies such as hydrothermal liquefaction, anaerobic digestion, and transesterification for algal biodiesel are presented and how these can be integrated into a biorefinery are discussed.

Genetic engineering for biohydrogen production from microalgae

“… 25 Pretreatment of algal biomass to degrade cell walls enhances fermentative H 2 productivity by 50–70%. 45 Because microalgae lack lignin and hemicellulose, only simple pretreatment is required greatly reducing costs. 46 Biohydrogen is mainly obtained from the conversion of carbohydrates, so the best pretreatment strategies aim to release more carbohydrates.…”

“… 129 The advantage of this method is that it allows a reduction in oxygen concentration without impacting the photosynthetic rate, enabling the production of more hydrogen. 45 Similarly, genetic manipulation of microalgae using genes from methanotrophs to increase oxygen tolerance and enhance hydrogen production may also be effective. 129 …”

Humic Substances as Microalgal Biostimulants—Implications for Microalgal Biotechnology

“…Efficient harvesting and dewatering represent a major bottleneck for all microalgae-based biotechnologies, including those focused on more profitable products, such as carotenoids [ 194 ]. The dilute nature of microalgae in suspension requires high energy consumption for this initial step in microalgae processing [ 195 ].…”

Photoautotrophic and Mixotrophic Cultivation of Polyhydroxyalkanoate-Accumulating Microalgae Consortia Selected under Nitrogen and Phosphate Limitation

“…Applying open raceway ponds and using waste streams (wastewater and industrial exhaust gas) as nutrient and carbon sources has been proposed as a cost-effective approach for largescale microalgae production. However, suitable sites where nearby substrate sources and infrastructure, have suitable climate conditions, and do not compete with arable land need to be identified to locate large-scale production systems [25,26]. Improving the flocculation and filtration methods for microalgae harvesting and identifying low-cost, environmentally friendly, and reusable solvents for PHA extraction would make the process economically feasible.…”