Biopulping process design and analysis

Biomechanical pulping, the pretreatment of wood chips with a white-rot fungus prior to mechanical pulping, saves energy during refining and produces stronger paper. Although this process has been performed successfully on a laboratory-scale, further research is required for scale-up. This work focuses on developing methods of relating operating conditions to biopulping performance with the goal of aiding scale-up. The specific goals were: to study the effect of temperature, sterility, and nutrient supplementation on the biopulping of aspen wood by Phanerochaete chrysosporium, to develop methods of monitoring fungal growth and metabolism during biopulping, and to increase understanding of the economic impact of biopulping.; Previous biopulping experiments used chips that had been autoclaved to avoid contamination and supplemented with nutrients to increase growth rate and to reduce cellulose degradation. Experimental results showed that P. chrysosporium can biopulp nonsterile, unsupplemented aspen chips. Moreover, unsupplemented chips were shown to give better biopulping results than nutrient-supplemented chips for all nutrients tested. Temperature had a strong effect on biopulping performance. Unsupplemented chips incubated at 39{dollar}spcirc{dollar}C gave the best biopulping results--20% energy savings for a two-week treatment. At 30{dollar}spcirc{dollar}C and 35{dollar}spcirc{dollar}C, 10% energy savings were obtained for a two-week treatment. Energy savings for unsupplemented chips were insignificant above 39{dollar}spcirc{dollar}C and below 30{dollar}spcirc{dollar}C.; The carbon dioxide evolution rate of both nutrient-supplemented and unsupplemented chips was measured during biopulping of aspen chips by P. chrysosporium. During the growth phase, carbon dioxide evolution rate was an exponential function of time for supplemented chips and a linear function of time for unsupplemented chips. At 39{dollar}spcirc{dollar}C, the specific growth rate of P. chrysosporium on supplemented chips was 0.013 hr{dollar}sp{lcub}-1{rcub}{dollar} and the linear carbon dioxide evolution rate was 1.62 {dollar}mu{dollar}g CO{dollar}sb2{dollar}/g dry wood{dollar}cdot{dollar}hr{dollar}sp2.{dollar} These results suggest that growth on unsupplemented chips may be limited by the extracellular hydrolysis of wood components.; A differential model of an isolated plug of wood chips expressing temperature, fungal concentration, moisture content, and yield as functions of time was developed. Fungal growth rate, heat evolution rate, and wood consumption rate were stoichiometrically related to the carbon dioxide evolution rate. The resulting system of five nonlinear differential equations was numerically integrated. Simulations suggest that some forced convection may be required to maintain chip temperature between 30{dollar}spcirc{dollar}C and 39{dollar}spcirc{dollar}C. The most efficient method of supplying aeration would be temperature feedback control of air flow rate.