Enhancement in enzymatic hydrolysis by mechanical refining associated with metal ions for autohydrolysis pretreated Miscanthus

The production of sugars from lignocellulosic biomass is still an expensive process, mainly due to high enzyme cost. Recently, a few strategies have been suggested to produce low-cost sugars from biomass by mechanical refining of the pretreated biomass and the addition of metal ions at the hydrolysis. Mechanical refining modifies fiber properties and enhance the carbohydrate conversion, which also can reduce the enzyme dosage. Some metals, such as Ca²⁺ and Mg²⁺, have been reported to increase the yields of enzymatic hydrolysis, by reducing non-productive enzyme adsorption by the formation of a lignin-metal complex. The objective of this study is to investigate the synergistic effect of these processes (mechanical refining and metal ions) on the production of low-cost sugars from biomass. The autohydrolysis pretreated Miscanthus was submitted to mechanical refining of 2 k, 6 k and 10 k rotation in PFI refiner, and to Ca²⁺, Mg⁺² and Fe²⁺ 5 mM solutions (during and after refining), then followed by enzymatic hydrolysis. Iron seemed to inhibit enzymatic hydrolysis, especially if the biomass is refined, decreasing digestibility of cellulose by 25%. The highest yields for cellulose conversion were achieved by the addiction of magnesium (71.1%) and calcium (69.0%) after refining (6 k). Calcium and magnesium presented similar results when supplied during the refining, enhancing digestibility about 25%, where 15% improvement was observed when supplied after the refining. We will discuss the synergistic effect of this combination process and the optimization strategy to produce low-cost sugars from biomass.