Production of Lactic Acid from the Mixture of Softwood Pre-hydrolysate and Paper Mill Sludge by Simultaneous Saccharification and Fermentation

Abstract

Paper mill sludge is a solid waste material composed of pulp residues and ash generated from pulping and paper making process. The carbohydrate portion of the sludges from Kraft/Recycle paper mill has chemical and physical characteristics similar to those of commercial wood pulp. Because of its high carbohydrate content and well-dispersed structure, the sludge can be biologically converted to value-added products without pretreatment. In bioconversion of solid feedstock such as paper mill sludge, a certain amount of water must be present to attain fluidity. In this study, hemicellulose pre-hydrolysate, in place of water, was added to the sludge to increase the concentration of the final product. Pre-hydrolysate was obtained by hot-water treatment of pine wood in which the total sugar concentration reached 4 wt.%. The mixture was processed by simultaneous saccharification and fermentation (SSF) using enzymes (cellulase and pectinase) and Lactobacillus rhamnosus (ATCC-10863). Pectinase was added to hydrolyze mannose oligomers in the pre-hydrolysate to monomers. During the SSF of the mixture, calcium carbonate in the paper sludge acted as a buffer, yielding calcium lactate as the final product. External pH control was unnecessary due to the buffer action of calcium carbonate that maintained the pH near optimum for the SSF. The lactic acid yield in the range of 80-90 % of the theoretical maximum was obtained. Use of the mixed feed of pre-hydrolysate and pulp mill sludges in the SSF raised the product concentration to 60 g of lactate/L.

RETRACTED: Biodegradation of Endocrine-Disrupting Chemicals and Residual Organic Pollutants of Pulp and Paper Mill Effluent by Biostimulation

“…It might be produced due to softwood hydrolysis and fermentation of cellulose components of the wood. Several workers (Reddy and Yang, 2005; Shi et al, 2015) have reported the presence of lactic acid in pulp and paper mill effluents after bacterial degradation. Benzoic acid (benzoate) was also detected in biostimulated effluent after 3 and 6 days of bacterial growth.…”

Cellulase production from kraft hardwood pulp by Trichoderma reesei rut C‐30

“…The integrated ‘biorefinery’ process to produce biofuels and chemicals as a supplementary unit in kraft paper mills is an intriguing possibility . Our previous research found that the production of various chemicals could be integrated into the kraft process, while still preserving the main products ‐ paper and pulp . However, the biggest bottleneck in this biorefinery process is the high cost of the enzymes for the hydrolysis step .…”

Recombinant Lactococcus lactis for efficient conversion of cellodextrins into L‐lactic acid

“…Furthermore, few natural LAB can ferment inexpensive feedstocks such as starch, and no native cellulolytic and/or hemicellulolytic LAB has been isolated so far (Okano, Tanaka, et al, ). Fermentation of enzymatically hydrolyzed lignocellulosic feedstocks by LAB has been reported (Hu et al, ; Shi, Kang, & Lee, ). However, the high cost of commercial cellulases significantly reduces economic advantage of using cheap raw materials (Okano, Tanaka, et al, ; Olson, McBride, Shaw, & Lynd, ).…”