Sugar production from cellulosic biosludges generated in a water treatment plant of a Kraft pulp mill

Abstract

A study on the enzymatic hydrolysis of cellulosic biosludges generated in a water treatment plant of a Kraft pulp mill was carried out. The effect of the operational conditions (cellulase to solid ratio (CSR), liquid to solid ratio (LSR), surfactant concentration (SC) and reaction time), on the hydrolysate composition was evaluated and a set of mathematical models able to predict the glucose and xylose concentrations in the reaction media was proposed. Using low cellulase charges (8 FPU/g) and high liquid to solid ratios (28–30 g/g), a quantitative conversion of the glucan fraction can be reached in 48 h, although diluted solutions are produced. However, operating at a cellulase to solid ratio of 12.5 FPU/g, a liquid to solid ratio of 12 g/g and a surfactant concentration of 0 g/L, 74% of the glucan fraction and 67% of the xylan fraction can be saccharified in 34 h, leading to solutions containing up to 27.8 g/L of glucose and 5.4 g/L of xylose. The results demonstrated that this solid residue shows high enzymatic digestibility and that no pretreatments are needed to enhance the saccharification step. These advantages, along with its negative price, make this solid a valuable raw material for lactic acid production.