Placing microalgae on the biofuels priority list: a review of the technological challenges

Abstract

Microalgae provide various potential advantages for biofuel production when compared with 'traditional' crops. Specifically, large-scale microalgal culture need not compete for arable land, while in theory their productivity is greater. In consequence, there has been resurgence in interest and a proliferation of algae fuel projects. However, while on a theoretical basis, microalgae may produce between 10-and 100-fold more oil per acre, such capacities have not been validated on a commercial scale. We critically review current designs of algal culture facilities, including photobioreactors and open ponds, with regards to photosynthetic productivity and associated biomass and oil production and include an analysis of alternative approaches using models, balancing space needs, productivity and biomass concentrations, together with nutrient requirements. In the light of the current interest in synthetic genomics and genetic modifications, we also evaluate the options for potential metabolic engineering of the lipid biosynthesis pathways of microalgae. We conclude that although significant literature exists on microalgal growth and biochemistry, significantly more work needs to be undertaken to understand and potentially manipulate algal lipid metabolism. Furthermore, with regards to chemical upgrading of algal lipids and biomass, we describe alternative fuel synthesis routes, and discuss and evaluate the application of catalysts traditionally used for plant oils. Simulations that incorporate financial elements, along with fluid dynamics and algae growth models, are likely to be increasingly useful for predicting reactor design efficiency and life cycle analysis to determine the viability of the various options for largescale culture. The greatest potential for cost reduction and increased yields most probably lies within closed or hybrid closed -open production systems.

Cell disruption technologies

“…They are common in large-scale processes due to their nonspecific disruptive nature and high efficiencies (G€ unerken et al, 2015). Furthermore, they are most effective and energy efficient at cell concentrations of 100-200 g/L (Greenwell et al, 2010), which makes them suitable to treat concentrated algae streams without the need of a drying step. The most traditional mechanical microalgae pretreatments include bead milling, French press (high-pressure homogenization), ultrasonication, microwave techniques, and electric shock.…”

Química Sem Fronteiras: o desafio da energia

“…36,37 Porém, a produção de microalgas para produção de biocombustíveis ainda encontra gargalos tecnológicos dos quais depende a sua expansão à escala comercial, como: (a) dificuldades na logística de produção em larga escala; (b) dificuldades no uso de organismos geneticamente modificados em sistemas abertos; (c) alto custo na formulação do meio (micronutrientes); (d) complexidade no escalonamento industrial de fotobiorreatores; (e) alto custo de produção em sistemas heterotrófi-cos; (f) alta demanda energética para secagem e extração; e (g) alta acidez do material lipídico isolado. No entanto, é fato que muitos destes fatores não são limitantes quando o cultivo de microalgas está associado à produção de materiais de maior valor agregado, como pigmentos, antioxidantes, proteínas, ácidos graxos poli-insaturados, carboidratos funcionais e outras classes de substâncias biologicamente ativas.…”

“…No entanto, é fato que muitos destes fatores não são limitantes quando o cultivo de microalgas está associado à produção de materiais de maior valor agregado, como pigmentos, antioxidantes, proteínas, ácidos graxos poli-insaturados, carboidratos funcionais e outras classes de substâncias biologicamente ativas. 37,38 O desenvolvimento de biocombustíveis avançados tem inspirado grande entusiasmo e potencial inovador em todos os setores e/ou competências associadas ao desenvolvimento científico e tecnoló-gico de nossa sociedade. O planejamento estratégico de instituições como a Agência Internacional de Energia (EIA) indica que as plantas atuais de produção de biocombustíveis já são capazes de deslocar 175 milhões de litros de derivados de petróleo anualmente e que esta estimativa deverá ser aumentada em incontáveis 1,9 bilhões de litros por ano ao serem consideradas as unidades que se encontram em construção e as que estão em estado avançado de planejamento e execução orçamentária.…”

Methods of energy extraction from microalgal biomass: a review

“…There appears to be considerably less research on the production of bioethanol than biodiesel, but bioethanol has been suggested as one of three top targets for future microalgal biofuel production (Gouveia 2011). The fermentation of microalgae has the potential advantage of exploiting the entire biomass, if an economic method of producing fermentable sugars from complex organic material is found.…”

“…Intact cell walls hamper lipid recovery and the most effective methods of recovery are from disrupted microalgal cells (Greenwell et al 2010). Mechanical pressing is the industry standard for oil recovery from oilseeds for both food and biofuel production, but it is ineffective for microalgae (de Boer et al 2012).…”