A large number of individual processes are involved in the overall development of second-generation liquid biofuels via biochemical route. This leads to the possibil­ity of process integration that will lower the capital and operating cost and ensure that optimum production of high-value co-products is achieved. Although process integration has the benefit of cost reduction in most cases, it is not a universal strat­egy and may not be applicable to all the cases. Sometimes, there might involve large number of separate processes that should be linked to produce value-added products, and this increases the overall process cost.

Process integration can be done by several ways; for example, a two-stage fermentation process that can ferment glucose and xylose in separate ferment­ers. This would maximize sugar yields and also produce valuable products from separate fermentation process. Another possible approach to process integration could be application of thermophilic bacteria that can ferment both glucose and xylose (Bai et al. 2013; Ito et al. 2013; MacKenzie and Francis 2013). A single system can be developed that can hydrolyze and ferment sugars at the same time. Although this approach seems quite unrealistic at the moment, it can become true in the coming years by extensive research in the area. The integrated system of lignocellulose processing to liquid biofuels, if developed, can lower the bioethanol cost to 0.15 US$/l (IEA 2008). Therefore, process integration, although is a chal­lenging task, can significantly lower the biofuel cost and can pave the path toward an economical source of fuel for transportation in the coming years.