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Keywords:

  • poplar;
  • pretreatment;
  • adsorption;
  • Langmuir;
  • cellulase;
  • nitrogen factor;
  • inhibition;
  • delignification;
  • effectiveness;
  • desorption

Abstract

Adsorption of cellulase on solids resulting from pretreatment of poplar wood by ammonia fiber expansion (AFEX), ammonia recycled percolation (ARP), controlled pH, dilute acid (DA), flowthrough (FT), lime, and sulfur dioxide (SO2) and pure Avicel glucan was measured at 4°C, as were adsorption and desorption of cellulase and adsorption of β-glucosidase for lignin left after enzymatic digestion of the solids from these pretreatments. From this, Langmuir adsorption parameters, cellulose accessibility to cellulase, and the effectiveness of cellulase adsorbed on poplar solids were estimated, and the effect of delignification on cellulase effectiveness was determined. Furthermore, Avicel hydrolysis inhibition by enzymatic and acid lignin of poplar solids was studied. Flowthrough pretreated solids showed the highest maximum cellulase adsorption capacity (σsolids = 195 mg/g solid) followed by dilute acid (σsolids = 170.0 mg/g solid) and lime pretreated solids (σsolids = 150.8 mg/g solid), whereas controlled pH pretreated solids had the lowest (σsolids = 56 mg/g solid). Lime pretreated solids also had the highest cellulose accessibility (σcellulose = 241 mg/g cellulose) followed by FT and DA. AFEX lignin had the lowest cellulase adsorption capacity (σlignin = 57 mg/g lignin) followed by dilute acid lignin (σlignin = 74 mg/g lignin). AFEX lignin also had the lowest β-glucosidase capacity (σlignin = 66.6 mg/g lignin), while lignin from SO2lignin = 320 mg/g lignin) followed by dilute acid had the highest (301 mg/g lignin). Furthermore, SO2 followed by dilute acid pretreated solids gave the highest cellulase effectiveness, but delignification enhanced cellulase effectiveness more for high pH than low pH pretreatments, suggesting that lignin impedes access of enzymes to xylan more than to glucan, which in turn affects glucan accessibility. In addition, lignin from enzymatic digestion of AFEX and dilute acid pretreated solids inhibited Avicel hydrolysis less than ARP and flowthrough lignin, whereas acid lignin from unpretreated poplar inhibited enzymes the most. Irreversible binding of cellulase to lignin varied with pretreatment type and desorption method. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009