Biogas production by anaerobic digestion of Eupatorium odoratum L.
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Biological Wastes 33 (1990) 67-70
Biogas Production by Anaerobic Digestion of Eupatorium odoratum L.
Eupatorium odoratum L. is a prolific producer of biomass among the weeds introduced into lndia and it can be used for energy production. Since freshly harvested biomass contains inhibitors of microorganisms involved in methanogenesis, the effects of leaching and partial aerobic decomposition of the weed before anaerobic digestion were studied (1.0 m 3 pilot-scale batch fermenters) in relation to biogas production. About 70% more biogas was produced by the pretreated waste, and it also gave a higher count of cellulolytic and methanogenic bacteria than the untreated material.
Eupatoriurn odoratum L. is a noxious perennial weed of the tropical plantations, introduced to India from the West Indies in the early part of this century. In the newly afforested areas and nearby cultivated fields it has become a serious menace in the Western Ghats and the north-east of India. It is reported to be an alternate host for pseudomosaic virus in Sumatra (Bennett & Rao, 1968). The abundantly available biomass was used for biogas production after pretreatment, to eliminate antimicrobial com- pounds, and this could contribute to its eradication.
E. odoratum was collected from the Forest Research Station (Prabhunagar) abutting the eastern fringe of the Western Ghats. The methanogenic
67 Biological Wastes 026%7483/90/$03"50 O 1990 Elsevier Science Publishers Ltd, England. Printed in Great Britain
68 K. S. Jagadeesh, G. S. Geeta, T. K. R. Reddy
inoculum ofcowdung was obtained from the livestock pens of the university. The weed was chopped (5 cm size) and steeped in slaked lime (1% w/w) for 24 h for softening and eliminating antimicrobials. The liquid was drained from the lime-soaked mass placed on a wire mesh and the solids were heaped. The heap was left for partial aerobic decomposition at ambient temperature for 4-6 days, until the material became brown. It was then mixed with cowdung (1:1) and charged into a 1.0m 3 pilot-scale batch fermenter at a total solid content of about 8%. An unleached control of Eupatorium-cowdung mixture as well as the conventional control of cowdung slurry were also maintained. The biogas produced was measured daily ('Inseref' gas-flow meter).
The pH of the fermentation substrate was monitored ('Digisun' digital pH meter), and its total solid content was determined by drying the sample in a hot air oven at 103-105C for 8 h. The anaerobic cellulolytic (Hungate, 1966) and methanogenic (Smith & Hungate, 1958) bacteria were also enumerated.
RESULTS AND DISCUSSION
E. odoratum is known to contain antibacterial tannins, phenols, 0c-pinene, cadinene, camphor and limonene (Inya Agha, 1987), which seem to inhibit methanogenesis in laboratory fermenters. They were leached off in the pretreatment process. The pH of the unleached fermentation mixture turned
TABLE 1 Effect of Leaching of Eupatorium on Biogas Production
Treatment combination Treatment TS of the Total digestion biogas mixture production
Gas produced Gas yield/kg per kg dry matter
dry matter per day (litres) (litres)
890kg cowdung (18% TS) Control 9.0 19917 + 890 litres tap water
240 kg Eupatorium (50% TS) Unleached 8.75 9 305 + 240 kg cowdung material + 1 440 litres tap water
325 kg PADCE (20% TS) Leached 7-50 11454 + 325 kg cowdung material + 975 litres tap water
Retention period: 90 days. Temperature (average): maximum, 30-3C; minimum, 15.9C. PADCE: partially aerobically decomposed chopped Eupatorium. TS: total solids.
Anaerobic biogas production
TABLE 2 Changes in Bacterial Populations during Fermentation of Eupatorium
Treatment Cellulolytic bacteria (cells/ml) Methanogenic bacteria (cells/ml)
Days after charging Days after charging
20 50 90 20 50 90
Leached Eupatorium 8'0 10 4 6"0 x 104 1'4 10 4 0"8 X l0 S 17"5 x 105 13"0 X 105
Unleached Eupatorium 1-6 104 0'19 x 104 0"17 x 104 0"26 x 10 ~ 15"5 x 105 11"0 x l0 s
acidic (pH = 6.3) during the first week of fermentation. Lime (1.0% w/w) was added to buffer it at near neutrality.
As seen in Table 1, about 70% more biogas was obtained from the pretreated biomass than from the unleached. Partial aerobic decomposition aids in tissue disintegration (Kovacs et al., 1985). Liming is known to cause swelling of tissues to increase the pore space, thus allowing greater microbial breakdown (Wise, 1981). Thus there was a higher bacterial population in the pretreated biomass (Table 2). Similar increases in biogas yields were obtained with lime-treated seaweed (Troiano et al., 1976).
The financial assistance received from the Indian Council of Agricultural Research, New Delhi, under the All India Coordinated Project on Renewable Energy Sources for Agricultural and Agro-based Industries, is gratefully acknowledged.
Bennett, E D. & Rao, V. P. (1968). Distribution of an introduced weed, Eupatorium odoratum, in Asia and Africa and possibilities of its biological control. PANS (C), IS, 277-81.
Hungate, R. E. (1966). The Rumen and its Microbes. Academic Press, New York, pp. 26-8.
Inya Agha (1987). Phytochemical and antibacterial studies in the essential oil of Eupatorium odoratum. Int. J. Crude Drug Res., 25, 49-52.
Kovacs, K., Vas, A. & Juhasz, J. (1985). Energy production by fermentation of bulk organic wastes. In Agricultural Waste Utilisation and Management--Proc. V Int. Syrup. Agric. Wastes. ASAE, MI, USA, pp. 346-53.
70 K. S. Jagadeesh, G. S. Geeta, T. K. R. Reddy
Smith, E H. & Hungate, R. E. (1958). Isolation and characterisation of Methanobacterium ruminantium n. sp. J. Bacteriol., 75, 713-18.
Troiano, R. A., Wise, D. L., Augenstein, D. C., Kispert, R. G. & Cooney, C. L. (1976). Fuel gas production by anaerobic digestion of kelp. Res. Recov. Conserv., 2, 171.
Wise, D. L. (1981). Fuel Gas Production from Biomass, Vol. II. CRC Press Inc., FL, USA, pp. 95-6.
K. S. Jagadeesh, G. S. Geeta & T. K. R. Reddy Department of Agricultural Microbiology, University of Agricultural Sciences, Dharwad--580005, India
(Received 17 July 1989; revised version received 1 October 1989; accepted 17 October 1989)