The effect of overliming on the toxicity of dilute acid pretreated lignocellulosics: the role of inorganics, uronic acids and ether-soluble organics

Although the treatment of dilute acid pretreated lignocellulosics with calc ium hydroxide or carbonate (overliming) is known to improve the fermentabil ity of carbohydrate-rich hydrolyzate streams, a firm understanding of the c hemistry behind the process is lacking. Quantitative evaluation of inorgani cs, uronic acids, and non-polar organics indicates that only a portion of t he improvement can be ascribed to these materials. Upon overliming. the con centrations of inorganics either increase (Ca, Mg), decrease (Fe, P, Zn, K) or remain relatively the same (Al. Na). Furthermore, organic compounds tha t are not extractable with tert-butyl methyl ether (MTBE) are toxic to Zymo monas,mobilis CP4(pZB5). Overliming and direct neutralization are somewhat effective in removing sulfate anions, although sulfate toxicity is consider ably less than that of acetic acid. Uronic acids were found to be non-toxic under pH controlled conditions. (C) 2000 Elsevier Science Inc. All rights reserved.