The requirements for microalgal dewatering, nutrient recycling and control of effluent wastewater are becoming major challenges to producers (Borowitzka and Moheimani 2010; Charcosset 2009; Clarens et al. 2010; Wyman and Goodman 1993b; Xiong et al. 2008). It is crucial for industrial microalgae production to avoid becoming a net energy-intensive process generating effluent waste at risk of vari­able profitability (Borowitzka et al. 2010; Borowitzka and Moheimani 2010; Charcosset 2009; Clarens et al. 2010; Wyman and Goodman 1993b; Xiong et al.

2008) . As freshwater and energy are essential commodities, finding low-cost and high energy-efficient means to process water and utilise both waste energy and wastewater streams is important (Gude et al. 2010; McHenry 2013). As open pond microalgae production can become expensive due to variable capital, operational, and down-stream processing costs derived from the low microalgae cell densities (Lee 2001; McHenry 2010), and if not optimised, industrial microalgae production will consume large volumes of water through evaporative loss (Chisti 2007; Clarens et al. 2010), generate effluent and become an energy-intensive process (Borowitzka and Moheimani 2010; Charcosset 2009; Clarens et al. 2010; McHenry 2013; Wyman and Goodman 1993b; Xiong et al. 2008). In parallel, conventional industrial and mining process contaminated wastewater streams are also utilising desalination technologies to reduce environmental contamination and associated costs. With new methods of desalting and water processing, including reverse osmosis (RO), forward osmosis (FO) and membrane distillation (MD), desalination technologies are decreasing water processing costs markedly (Bennett 2011; Bourcier and Bruton 2009; Nicoll et al. 2011). This nascent area will require advances in technical performance, reliability and cost of water processing tech­nology to become commercially viable (Banat and Jwaied 2008).

The introduction of microalgae to water processing is a major potential field of exploration in water processing and efficiency circles. As microalgae species can maintain high growth rates in poor-quality or contaminated water and salinities higher than sea water (Amin 2009; Beer et al. 2009; Hightower 2009), they are able to expand the existing tranche of development possibilities and enable new inten­sive production options (Cantrell et al. 2008; Gross 2007; Hankamer et al. 2007). Industrial-scale microalgae production will likely require large and intensive water processing technologies for both culturing and biomass recovery. Yet, achieving energy-efficient and cost-effective microalgae dewatering and water management are major challenges. Progressive vertical integration of energy and water-intensive technologies (including large-scale algae) may enable higher aggregated net industrial efficiencies and potentially create new major resources as by-products including minerals, animal feeds, fertilisers, freshwater, electricity, and biofuel. The integration and colocation of industrial microalgae production (e. g. photobioreac­tors and open ponds) with desalination and other industrial operations are a growing potential area. The theoretical basis behind higher aggregated efficiencies is essentially vertical integration of infrastructure, energy and material flows, reducing total costs, net waste and associated potential environmental contamination. In particular, the judicial use of fast advancing technical capabilities to process water at high efficiency or using waste heat and wastewater through colocating with other industrial facilities may effectively cross-subsidise microalgae energy and water use (McHenry 2013).

1.4 Conclusion

There is no doubt that finding alternative renewable sources of food and energy for future generations is needed. Algae may be a promising answer for the future of biomass production and a carbon-neutral fuel source, considering that microalgae produce significantly higher areal biomass than traditional terrestrial crops. Still, it is unreasonable to think that there is a ‘silver-bullet’ answer to microalgae large-scale biomass production. The conventional (mixed and unmixed open ponds) microalgae to biomass production systems have only been economical for high-value products. The cost of production of microalgae in closed photobioreactors is also most likely to be to very high and not sustainable. Some alternative cultivation methods such as biofilm (see Chap. 2) and mixotrophic growth (see Chaps. 3 and 4), milking (Moheimani et al. 2013 a, b) and combining solar panels with microalgae cultivation system (see Chap. 15) can bring down the cost of production. Combining microalgae cultivation with CO2 bioremediation (see Chap. 7) and wastewater treatment (see Chaps. 5 and 6) can also add value to the whole algae biomass production. Fur­thermore, developing novel and economical dewatering systems will positively reduce the overall cost of production (see Chaps. 12, 13 and 14). Last but not least, modifying the algal species of interest can also reduce the cost of production (see Chaps. 8, 9, 10 and 11). Chapter 17 summarises the technoeconomics of the microalgae to biofuel production.