The integrated method of ethanol-methane fermentation has
been studied in recent years. As shown in Fig. 1, some of the
organic matter within thin stillage is converted to methane by
anaerobic digestion. After further treatment the digestate is reused
as part of the process water for ethanol fermentation, forming a
closed-circuit circulation process. The overall technology reduced
energy consumption and water consumption, reducing waste
water emissions. Zhang and co-works (2010b) studied a full recycling
process incorporating two-stage anaerobic treatment of distillery
wastewater from bioethanol production from cassava.
Furthermore, Zhang et al. (2010a) studied the effect on ethanol
production of utilizing waste anaerobic digestion distillate effluent
in an integrated ethanol-methane fermentation process. Wang and
co-workers (2013) established and assessed a novel cleaner production
process for corn-grain fuel ethanol. Subsequently, Wang
et al. (2014a) studied the reuse of a mixture of anaerobic digestion
effluent and thin stillage for cassava ethanol production. In this
novel integrated process, a portion of thin stillage is mixed with
the effluent from anaerobic digestion of residual thin stillage, producing
a ‘mixed’ water which is then reused as process water for
the following ethanol fermentation batch (Wang et al., 2014a). This
novel integrated process reduced both energy consumption and
wastewater production.