Achieving a Green Solution: Limitations and Focus Points for Sustainable Algal Fuels

Abstract

Abstract:Research investigating the potential of producing biofuels from algae has been enjoying a recent revival due to heightened oil prices, uncertain fossil fuel sources and legislative targets aimed at reducing our contribution to climate change. If the concept is to become a reality however, many obstacles need to be overcome. Recent studies have suggested that open ponds provide the most sustainable means of cultivation infrastructure due to their low energy inputs compared to more energy intensive photobioreactors. Most studies have focused on strains of algae which are capable of yielding high oil concentrations combined with high productivity. Yet it is very difficult to cultivate such strains in open ponds as a result of microbial competition and limited radiation-use efficiency. To improve viability, the use of wastewater has been considered by many researchers as a potential source of nutrients with the added benefit of tertiary water treatment however productivity rates are affected and optimal conditions can be difficult to maintain year round. This paper investigates the process streams which are likely to provide the most viable methods of energy recovery from cultivating and processing algal biomass. The key findings are the importance of a flexible approach which depends upon location of the cultivation ponds and the industry targeted. Additionally this study recommends moving towards technologies producing higher energy recoveries such as pyrolysis or anaerobic digestion as opposed to other studies which focused upon biodiesel production.

Environmental sustainability analysis of a protein-rich livestock feed ingredient in The Netherlands: Microalgae production versus soybean import

“…Probably the best way to reach a low environmental footprint is to switch from a linear economy to an integrated biorefinery concept in which algae are produced close to an industrial facility, which delivers its own products, and where waste heat, waste water and flue gases are used to stimulate the algal growth (Aitken and Antizar-Ladislao, 2012). This concept is beneficial for the joining industries: on the one hand, the required products are made, and on the other hand, sustainability-related issues such as land occupation, fossil fuel use and greenhouse gas emissions can be mitigated.…”

“…For the drying and extraction step, data are used from the literature and/or databases because these processes are not operational yet. According to a study of Aitken and Antizar-Ladislao (2012), it is stated that it is more efficient to dry the algae before extracting the oil. A natural gas-fired dryer is used to dehydrate the algae stream to 89% DW, which is a good percentage for a stable conservation.…”

“…The most well-known methods are centrifugation, filtration, flocculation, flotation, gravity sedimentation and electrophoresis (Wang et al, 2015). Most of these methods are very energy-intensive and/or have high capital costs (Aitken and Antizar-Ladislao, 2012). Often, multiple separation steps are used to concentrate the biomass, e.g., first microfiltration to retain the biomass followed by centrifugation (Weschler et al, 2014).…”

Assessing hydrothermal liquefaction for the production of bio-oil and enhanced metal recovery from microalgae cultivated on acid mine drainage

“…To create an economical biorefinery it is necessary to consider upstream factors, as well as final product quality. Despite the advantages conferred by HTL, cultivation of algal biomass is still a relatively energy-intensive process, and requires high inputs of water, nutrients and CO 2 [27]. As well as optimising bio-oil yields; maximising carbon efficiency, efficient water / nutrient recycling and ensuring an inexpensive source of CO 2 are crucial to the success of algal biofuel production [28].…”

Life cycle assessment of algae‐to‐biodiesel shallow pond production systems in the Mediterranean: influence of species, pond type, by(co)‐product valorisation and electricity mix

“…They are complex systems where appropriate handling is required to avoid oxygen accumulation, biofouling and cell damage by shear stress . As a result, PBRs are more commonly used for growing algae for high‐value commodities or for experimental work on a small scale . Shallow ponds are therefore more likely to operate on a commercial scale in the future …”