Appl Microbiol Biotechnol (1988) 29:408--412 Applied Microbiology Biotechnology © Springer-Verlag 1988 Effects of lignin on the anaerobic degradation of (ligno) cellulosic wastes by rumen microorganisms Huub J. M. Op den Camp, Frank J. M. Verhagen, Amelia K. Kivaisi, Federico E. de Windt, Henk J. Lubberding, Huub J. Gijzen*, and Godfried D. Vogels Department of Microbiology, Faculty of Science, University of Nijmegen, Toernooiveld, NL-6525 ED Nijmegen, The Netherlands Summary. There appeared to be a clear correlation between the lignin content (% of TS) of several waste and natural materials and their degradabil- ity by rumen microorganisms. Materials with lig- nin contents higher than 25% were not degraded within 72 h. The effects of Kraft pine lignin and some lignin monomers on filter paper degrad- ation, methane production and CMCase activity were tested. Testing these compounds in concen- trations comparable to natural conditions showed minor effects. At higher concentrations p-cou- maric acid strongly inhibited cellulose degrada- tion and methane production in batch cultures. Influence of lignin compounds on degradation is discussed in relation to structural effects and en- zyme or growth inhibition. Introduction Lignocellulosic residues are produced as a solid waste product by agricultural and industrial activ- ities. Anaerobic digestion of this biomass could provide an attractive means of waste reduction and waste stabilization with the recovery of methane as an energy source. Hydrolysis of cellu- lose is generally considered as the rate-limiting step in the overall degradation. Recently we de- monstrated that the application of rumen micro- organisms, in combination with a high-rate UASB-type reactor (RUDAD-system) 1, resulted in an enhanced conversion of filter paper cellu- * Present address: Department of Microbiology, University of Dar-es-Salaam, Dar-es-Salaam, Tanzania Offprint requests to: H. J. M. Op den Camp UASB -- upflow anaerobic sludge blanket; RUDAD -- rumen derived anaerobic digestion lose into biogas (Gijzen et al. (1988b) Further- more, the potential application to the anaerobic degradation of lignocellulosic waste materials was tested (Gijzen et al. 1987; Gijzen et al. 1988c). From the latter results it was obvious that ligno- cellulosic wastes with a lignin content of about 10-15% were degraded with rather high efficien- cy, whereas spent mushroom compost (38% lig- nin) was much less degradable (Gijzen et al. 1987). Recently the inhibitory effects of phenolic monomers on pure cultures of ruminal bacteria were reported by several authors (Chesson et al. 1982; Varel and Jung 1986; Borneman et al. 1986). In contrast Chen et al. (1985, 1987) re- ported the conversion of lignin model compounds to volatile fatty acids by mixed rumen bacteria. In order to study the influence of the lignin content we determined the in vitro degradation of ligno- cellulosic wastes and model substrates, with lignin contents varying from 0%-34% of TS, in batch cultures. To elucidate whether the decrease in degradability with increasing lignin content is caused by structural effects, enzyme or growth in- hibition, we tested the influence of kraft pine lig- nin and lignin monomers on the in vitro degrada- tion of filter paper cellulose and on rumen cellu- lase activity. Materials and methods Materials Various lignocellulosic waste materials or model substrates were tested. The waste materials including hay, barley straw (Hordeum vulgare), bagasse, rye straw (Lolium sp.), reed (Phragmites communis), newspaper, saw dust and coconut fi- ber were dried (16 h, 70°C) and ground before use. In addi- tion to the waste materials, alfalfa hay (Medicago sativa), pur- chased from van Heeswijk (Veghel, The Netherlands), and ill-