Bioethanol production via enzymatic hydrolysis of lignocellulosic bi?omass: Wheat straw, corn stalks and hazelnut husk

Wheat straw, corn stalks and hazelnut husks which are abundant agricultural waste products in Turkey, could be valuable raw materials for bioethanol production. After harvest, these raw materials are usually left in the fields and burned, which decreases the biological activity of the soil and causes air pollution. Through the use of innovative biotechnology, these waste materials may be valuable in generating economic benefits as well as environmental dividends. The main objective of this study was to examine the suitability of these wastes for bioethanol production and to compare pretreatment techniques with regard to their efficiencies. In this study, wheat straw, corn stalks and hazelnut husks were first steam exploded and then chemically treated to achieve efficient hydrolysis. The conventional chemicals of sodium hydroxide (NaOH), sulfuric acid (H2SO4), hydrogen peroxide (H2O2) and an alternative chemical, sodium borohydrate (NaBH4), were utilized for the first time ever in the chemical treatment procedure.The obtained results showed that NaOH and NaBH4 treated wheat straw resulted in 87.8% and 83.3% glucan conversion in enzymatic hydrolysis, but H2O2 (74.7%) and H2SO4 (71.7%) had lower glucan conversion. The highest ethanol yield (115 g/kg wheat straw) was observed for 4% NaBH4 pretreated sample (60 min) and the theoretical yield (86.9%) was also calculated to be highest for the sample.Results showed that the corn stalks treated with NaOH (83.9%) and NaBH4 (82.9%) gave higher glucan conversion in enzymatic hydrolysis compared to those treated with H2O2 (74.5%) and H2SO4 (56.6%). The highest ethanol yield (97.4 g/kg corn stalk) was obtained when the stalks were pretreated with 4% NaBH4 for 90 min; the theoretical ethanol yield was found to be 72.5%.On the other hand, 4% NaBH4 (90 min) delignified the highest amount of lignin (49.1%) from the hazelnut husks structure. Pretreatment with NaOH and NaBH4, compared to H2O2 and H2SO4, resulted in selective delignification. The highest glucan to glucose conversion (74.4%) and the highest ethanol yield (52.6 g/kg husks) were observed for hazelnut husks treated with 2% NaOH for 90 min.Among the raw materials, wheat straw was found to be the most suitable for bioethanol production. In addition, results indicated that, pretreatment chemical of NaBH4 was as effective as NaOH.