Reaewab/e Energy, Vol.5, Part II, pp. 791-795, 1994 Elsevier Scieace Ltd

P e r g R m o n Primed in Gre~ Bdtaln 0960-148,/94 $7.00-1.0.00

PRETREATMENT OF BAGASSE A N D C(K.'ONUT FIBRES FOR ENHANCED ANAEROBIC DEGRADATION BY RUMEN MICROORGANISMS

AMELIA K. KIVAISI AND S. ELIAPENDA

APPLIED MICROBIOLOGY UNIT, UNIVERSITY OF DAR ES SALAAM, P.O. BOX 35060, DAR ~S SALAAM, TANZANIA

ABSTRACT

The effect of chemical pretrea~em and particle size on anaerobic digestion of bagasse and coconut fibres by rumen microorganisms was studied. Both chemical wetreatmeut and particle size affected total fibre degradation and productions of methane and volatile fatty acids from these waste materials significantly (P < 0.05) compared to the untreated materials. Pretreatment of bagasse with sodium hydroxide, hydrochloric acid and ammonium hydroxide followe~ by incubations for 168 h increased fibre degradation by 11, 31 and 14 %, respectively. Pretreatment of c J ~ m t filges increased their extent of degradation by 55, 74 and 46 %, respectively. Methane yield from bagasse was increased by 44, 32, and 22 %, and that from coconut fibres was increased by 73, 76 and 46%, respectively. With the same pretreatment, amounts of ~olatile fatty acids produced from bagasse and coconut fibres increased by 42, 37 and 11%, and 40, 28, and I 1%, respectively.

By reducing particle sizes of bagasse and coconut fibres from 5 nun to less than 0.85 mm, the extent of total fibre degradation was increased by over 40%. The yields of methane woduced from these fibres increased bylan average of 30 %, and those of volatile fatty acids increased by almut the same order of magnitude. The suitability of using wetreated lignoceilulosic waste biomass as a substrate for methane production in a Rumen Derived Anaerobic Digestion -process is discussed.

Keyword Bagasse, coconut fibres, pretreatment, anaerobic digestiotl, romeo microorganisms

INTRODUCFION

In anaerobic degradation of lignocellulose, hydrolysis of cellulose is the major rate limiting step (Notice, et al, 1985). The low rate of hydrolysis is due to the ~ystallinity of cellulose, the association of cellulose and hemicellulose with lignin and the low celhilase activities present in conventional digesters.

In order to increase the rate of iignocellulose in anaerobic digesters, research has focused on improvement oi" cellulose hydrolysis by physical, chemical or biological pretreatments. Thermophilic treatment (55°C) is cmTently being applied to maximize enzyme activity for treating manure and household wgstes at large scales. In most cases economic analyses of pretreatment and thermophific digestion are ~flen discouramng. However, ~ are relatively cheap methods which include pretreatment with dilute alkalis and acids a~l reduction of particle size.

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In addition to pretreatment, research efforts are also directed to look for highly cellulolytic microorganisms from nature and through genetic engineering. So far in nature, microorganisms from forestomachs of ruminats and hind guts of termites and cockroaches are known to he efficient in degrading lignocellulose anaerobically. Therefore, this study examined the effects of combining the application of rumen microorganisms and cheap pretreatment methods on degradation of bagasse and coconut fibres.

MATF,~I.~2.~ AND METHODS

Substrates

Bagasse and coconut fibres were dried in the sun for five days, and were milled to desired particle sizes. All the materials were stored at room temperature (30°C) ready for use. On the dry weight basis, bagasse contained 93% volatile solids(VS), 6% ash, 82% neutral detergent fibre (NDF), 32% hemicellulose, 42% cellulose and 9% lignm. On same basis, coconut fil3res contained 93% VS, 6% ash, 73% NDF, 7% hc,~c¢l|u2os¢, 29S£ cellulose and 38% lignin.

Physical pretreatmonts

The substrate particles were reduced in size by chopping followed by milling. The desired sizes were obtained by sieving the milled materials through wire meshes of different sizes. The substrate samples used contained particle sizes in the range of 5 mm to less than 0.85 ram.

Chemical pretreatments

All chemical pretreatments were preceded by milling the substrates to pass through 2 mm mesh sieve. The substrates were then treated separately by immersion in the chemicals ( 1M NaOH, NH4OH and HCI) at room temperature for 30 days. The liquids were then decanted and the substrates were neutralised and dried.

Fermentation experiments

Batch culture incubations were performed as described previously(Kivaisi and Eliapenda, 1992). In order to be able to assess the effect of the pretreatment, untreated materials were fermented under the same conditions.

Analytical procedures.

VS, NDF, methane and VFA ~v¢.'c dc~em~e~ ~ dc.-~d~ed Freviougiy(IGv~/si :xnd Eliapenda, 1992).

Statistical analysis

The statistical differences in NDF degraded, mettane and VFA produced among various substrate pretreatments were tested by one way analysis of variance.

RESULTS AND DISCUSSION

The extent of degradation of NDF from the treated subsWates and the amounts of the fermentation products we,'¢ sigaificaafly diffecer, t (P< 0.05) and higher than those observed for the untreated substrates.

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The effect of substrate particle size on NDF degradation and on the amounts of fermentation products is shown in F!g 1. An increase of 47 and 43 % in NDF degradation was observed for bagasse and coconut fibres, respectively when particle size was reduced fwm 5 to less than 0.85ram. Within the same particle size range, methane production increased by 33 % for bagasse and 28 % for coconut fibres. The same decrease in particle size resulted into a significant increase in VFA production, with 29 % and 24 % for bagasse and coconut fibres, respectively. Shnilar results have been reported by Jerger et dl (1983) for woody biomass at particle sizes ranging between 0.003 and 8 ram. Conversion efficiencies of the materials used in this study were almost C,Taal!y i~fltle0cc~ b)' the pretreatment regardless of their lignin contents. This observation suggests that size redu~,'tion has more of a depolymerization effect than a delignification one.

Results of chemical prelreatment on NDF degradation and amounts of the fermentation products are presented in Table 1. Total fibre degradation for bagasse preffeatod with HCI, NH4OH and NaOH increased by 3 i, 14 and 11%, respectively. Coconut fibres p~eh-eated with the same chemicals were degra¢~ more than me onutmeo fibres by 74, 46 and 55 5$, respectively. Metlmne yields were increased by 22-44 • for' bagasse and by 49-76 % for coconut fibres. Production of VFA was increased by 11-42 % for bagasse and by 11-40 % for the coconut fibres by the chemical pretreatments.

All the three chemical pretreatments enhanced the degradation of coconut fibres more than that of bagasse. Since the latter was more lignified, these results suggest that the improved conversions were mote a result of the ability of the chemicals to break the li~,nin seal surrounding the fibres than a result of deerystal!iTation. However, the highest 04%) overall conversion efficiency obtained for the coconut fibres is relatively low compared to 68% obtained f(rc bagasse. The low degradation for the former was probably due to the relatively high liLmin content (38%) as compared to the 9% fignin content in the latter. Previously, a correlation was found between lignin content and degradability of substrates with lit~nin content varying between 0-34% by. tureen microorganisms (op den Camp et al. 1988). However, the degradation efficiency obtained in this study for the coconut fibres was markedly higher than the values reported eafier (op den Camp et al, 1988), who obtained virtually no degradation of substrates with litmin contents higher than 25 %.

This study has demonstrated that by combining grinding to small particle sizes and treatment with dilute acids or alkalis, overall conversion of highly li~ified residues by tureen microorganisms can be increase by over 40 ~ in batch cultures. Kolankaya et al (1985) observed similar results with Ammoniated straw with pure cultures of tureen bacteria.. A much higher conversion efficiency of the prelreat~ materials is anticipated in a Rumon Derived Anaerobic Dig~Rion process which applies mixed populations of mmen microorganisms. This is because m¢ tn'ocess is high t~tv (Gijzen ¢t al, 1988) and is therefore, biotechnologically attractive 1~" convel'sion of aighly ligailied bior~.~ residues into methane.

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l~ig. I. Effect of pva'ticI¢ ~ize on fibre degi-ddatio~i(A), a~d on production of VFA (B) and methane (C) for bagasse (i~iiiiil) and coconut fibres ::::::::::::::::::::::::::::::::::.9 after 168 h of incubation.

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Table 1. Effect of chemical pretreatment on NDF degradation and on amounts of fermentation products (means~ SD ").

Substrate Pretreatment Mean values after 168 h of incubation NDF VFA CH4

% mmol. 1" i .1-1 fv b

Bagasse Not treated 52.11 :~. I.~ 10g.12 ± 1.0 0.7± 0.006

NaOH 58.00 :~. 2.7 145.29 ± 2.0 1.0 ± 0.004

NH4OH 59.22 + 3.0 119.74 + 1.8 0.9 ± 0.003

HC1 68.04 ± 3.3 153.33 ± 2.5 0.9 ± 0.004

Co~,'onu', fibres No~. treated 19.82 + 1.4 33.10 + 1.1 0.2 ± 0.002

NaOH 30.73 + 2.7 46.34 ± 2.1 0.3 ± 0.002

NI-I4OH 28.94 _+ 2.1 36.67 ± 2.4 0.3 + 0.005

HCI 34.52 ± 1.9 42.33 ± 2.2 0.4 ± 0.004

*:n = 4 b: fermenter volume

R E F E R E N C E S

Gijzen, H.J., K.B. Zwart, F.J. Verhagen and G.D. Vogels(1988). High-rate two phase process for the anaerobic degradation of cellulose, employing rumen microorganisms for an efficient acidogenesis. Biotechnol Bioeneg. 31:418-425.

Jerger, D.E., D.A. Dolenc and D.P. Chynoweth (1983). Biogasification of woody biomass following physical and chemical pretreatment. Paper presented at 7th Symposium on energy from biomass and wastes, Orlando.

Kivaisi, A.K. and S. Eiiapenda (H;")2). Con vc~rsioa of agro-mdusti;'~l residues into volatile fatty acids and m e ~ e by rumen mictoorgatxisms. In Sayigh, A.A.M. (ed). ,'lenewat~le Energy: Biomass Technology and Wind Energy 3: 1468-1473.

Kolankaya, N., C.S. Stewart, S.H. Duncan, K.J. Cheng and J.W. Costerton (1985). The effect of ammonia treatment on the solubilization of straw and the growth of cellulolytic rumen bacteria. Y. AppL ltacteriol. 58: 371-379.

Noike, T.. E. Ginro, J.E. Chung, Jun-lchi and J.l. Matsumoto (1985). Characteristics of carbohydrate degradation and the rate-limiting step in anaerobic digestion. BiotechnoL Bioeng. 27: 1482-1489.

Opden Camp, H.J.M., F.J.M. Vcrhagen, A.K. Kivaisi, F.E. de Win~, H.J. Lubberding, H.J. Gijzen and G.D. V0g..,els (1988). Eft~t~ ot'!igni~ on the, at~e.~i¢ 0gra0~tion of lignocellulosic wastes by rumen ~croorgarfiSms. Appl. Microbiol. Biotechnol. 29. 408-412