Potential use of feedlot cattle manure for bioethanol production

• Anaerobic digestion of cattle manure reduces glucan and xylan content in fibers.
• AD fibres are poor substrates for cellulase saccharification (12% sugars/ODM).
• Pretreatment of feedlot cattle manure with dilute sulphuric acid was investigated.
• Enzymatic saccharification of pretreated manures yield up to 79% sugars/ODM.
• Industrial yeast rapidly and efficiently fermented recovered glucose.

This paper reports on processing options for the conversion of feedlot cattle manures into composite sugars for ethanol fermentation. Small-scale anaerobic digestion trials revealed that the process significantly reduces the content of glucan and xylan (ca. 70%) without effecting lignin. Moreover, anaerobic digestate (AD) fibres were poor substrates for cellulase (Cellic® CTec 2) saccharification, generating a maximum combined sugar yield of ca. 12% per original dry weight. Dilute acid pretreatment and enzyme saccharification of raw manures significantly improved total sugar recoveries, totalling 264 mg/g (79% theoretical). This was attained when manures were pretreated with 2.5% H2SO4 for 90 min at 121 °C and saccharified with 50 FPU CTec 2/g glucan. Saccharomycescerevisiae efficiently fermented crude hydrolysates within 6 h, yielding 7.3 g/L ethanol, representing glucose to ethanol conversion rate of 70%. With further developments (i.e., fermentation of xylose), this process could deliver greater yields, reinforcing its potential as a biofuel feedstock.