Advanced separation and anaerobic digestion technologies for value-added bioproducts and biofuel from pulp and paper mill wastes

Abstract

In the first research project, the extraction of hemicellulose from the process water and synthetic hydrolyzate using liquid-liquid extraction (LLE) was examined. Specifically, the effects of the main experimental variables (the type of solvent, hydrolyzate to solvent volume ratio, and pH) on extraction performance were explored. The tested solvents showed varying affinity and selectivity to recover hemicellulose. It was found that the hemicellulose extraction efficiency of n-hexane (71.03%) and tributyl phosphate (TBP) (72.34%) was higher than that of 1-butanol (62.36%), and toluene (67.03%) at a solvent: hydrolyzate volume ratio of 1:3. A pH value of 4.3, a phase ratio of 1:3 mL/mL, and an extraction time of 30 min were considered optimal conditions for hemicellulose extraction. In the second study, the thermophilic submerged anaerobic membrane bioreactor (ThSAnMBR) technology was used for pulp and paper primary sludge treatment, and both biological and membrane performance were evaluated. The biological performance was studied in terms of biogas production, solids reduction, chemical and structural changes of the digestate, and permeate quality under various operating conditions. While the effect of primary sludge on the membrane performance and fouling was systematically investigated. Several experimental parameters were investigated including solids retention time (SRT) (32- 55 days), hydraulic retention time (HRT) (3-8 days), organic loading rates (OLRs) (2.5-6.8 kg-COD/m3d), temperature (50±1°C), membrane fouling and cleaning frequency. Membrane performance was evaluated by monitoring its flux and corresponding transmembrane pressure as well as changes in its chemical and physical properties resulting from operating conditions using Fourier transform infrared (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray analyzer (EDX), contact angle, and pore size measurement. [...]