Biological Wastes 32 (1990) 155-158

Short Communication

Anaerobic Fermentation of Ageratum for Biogas Production

ABSTRA CT

Production of biogas from mixtures of fresh and partially-decomposed Ageratum with cattle dung were studied in batch digesters at 30 +_ I°C. Partially decomposed Ageratum produced 319.4 litres of gas per kg dry matter as compared to 222.4 litres of gas per kg dry matter from pure cattle dung. Fresh Ageratum supplemented with cattle dung in a ratio of 3:2 (wet weight basis) did not produce any gas, because of the accumulation of excess acids. In contrast, similar mixtures of partially decomposed Ageratum and cattle dung yielded about 9% more biogas than did pure cattle dung. The methane contents of the gas obtained from Ageratum mixtures were 62-77% as compared to 5 6 4 0 % from pure cattle dung.

INTRODUCTION

Terrestrial and aquatic weeds could play an important role in meeting the energy needs of rural areas of many developing countries if an appropriate technology was developed to properly use them for the generation of biogas. Various terrestrial weeds like Parthenium (Nallathambi Gunaseelan, 1987), Eupatorium (Devkota, 1985) and Lantana camara (Kalia, 1983; Dar & Tandon, 1987) have been tried for biomethanation. However, no attempt has been made to study the biogas production from Ageratum which is an obnoxious weed, widely spread in many regions of India. This weed has a high potential for growth and is available almost throughout the year. Therefore, the aim of this study was to demonstrate the feasibility of producing methane from Ageratum with or without cattle dung.

155 Biological Wastes 0269-7483/90/$03"50 © 1990 Elsevier Science Publishers Ltd, England. Printed in Great Britain

156 Anjan K. Kalia, Sarbjit S. Kanwar

METHODS

Collection of biomass

Fresh Ageratum plants were collected from the University farm during August and chopped to an average length of 10-15 mm. For predigestion, chopped Ageratum was allowed to decompose for 4-5 days under aerobic conditions by making heaps covered with PVC sheets. Fresh cattle dung was obtained from the University dairy and effluent slurry was obtained from a 3 m 3 anaerobic digester fed on pure cattle dung for use as the inoculum. The chemical characteristics of these substrates are depicted in Table 1. The C:N ratio of Ageratum was lower than that of cattle dung which further decreased on its predigestion for 4-5 days outside the digester. Predigestion of Ageratum also resulted in reducing the bulk of the material.

Experimental design

Three-litre capacity bottles with a facility for drawing samples of the digesting mixtures were used as anaerobic digesters. These digesters (D 1 to D4) were filled with different mixtures of cattle dung and Ageratum and maintained at 30+ I°C in a thermostatically controlled water-bath. The digester contents were stirred manually for 5 to 10 minutes twice a day. The digestion of the substrates was carried out for eight weeks as a retention time of 55 days is used in Indian biogas plants.

Analytical methods

Samples of digesting mixtures were analysed at various intervals for pH, Total Solids, Volatile Solids, carbon (Sharma et al., 1987), nitrogen (Bremner, 1965), Alkalinity and total volatile fatty acids (Ripley et al., 1986).

TABLE 1 Chemical Profiles of Cattle Dung, Fresh and Partially Decomposed Ageratum

Type of Cattle Fresh Partially analysis dung Ageratum decomposed

Ageratum

Carbon (%)a 45.60 50.44 45-61 Total solids (%) 18.10 10.21 11'50 Volatile solids (%)a 82.04 90.80 82'10 Nitrogen (%)a 1'20 1"96 2"04 C :N ratio 38.00 25'75 22-36

a Dry weight basis.

Anaerobic fermentation of Ageratum 157

The volume of biogas generated was measured at a fixed time daily by a saline displacement technique as described by Arora (1975) with an additional T joint for obtaining gas samples. The methane content was determined in an Aimi l -Nucon 5700 gas chromatograph with porapak Q column using a thermal conductivity detector and hydrogen as carrier at 40 ml/min flow-rate. Injector, detector and column temperatures were 70°C, 80°C and 60°C respectively.

R E S U L T S A N D D I S C U S S I O N

The details of the different mixtures used, their initial and final pH and total accumulated biogas production from them are given in Table 2. In the case of D4, no gas was produced throughout the study period. The gas yield from D 2 and D 3 w a s 8"8% and 43"6% more than from D 1 where only pure cattle dung was used. The major part of gas production (70-75% of total gas) was obtained up to the 4th week of fermentation, thereafter, it declined and in the last two weeks the gas production rate was very low. The methane content of the gas obtained from Ageratum mixtures (D 2 and D 3 ) varied between 62-77% as compared to 50-60% obtained from pure cattle dung. In DI, D 2

and D 3 digesters, a decrease in pH was noticed till the 3rd week of digestion, thereafter there was an increase in pH which remained close to 7"0 for most of the digestion period. However, in case of D 4 where fresh Ageratum was used, the pH was drastically decreased from 6.6 to 5" 1. This drastic reduction in pH resulted in toxic conditions for methane-producing bacteria.

During the digestion period the alkalinity ofD~, D 2 D 3 and D4 was in the range of 1120-1510, 1100-2980, 1350-3575 and 600-1000 mg CaCO3/litre,

TABLE 2 Mixtures of Ageratum and Cattle Dung used along with Initial and Final pH, and Total

Accumulated Gas Production from Different Digesters

Digester Cattle Ageratum Total pH Total accumulated dung (g) solids gas production (g) (g) Initial Final (litres/kg

dry matter)

D 1 500 - - 90.5 6.85 6'8 222.4 D 2 200 300 a 70.7 6.87 7.3 241.0 D 3 - - 500 a 57"5 7" 1 7"5 319"4 D4 200 300 b 67"4 6"6 5" 1 - -

a Partially decomposed. 5 Fresh. Seed slurry 100ml in each digester.

158 Anjan K. Kalia, Sarbjit S. Kanwar

respectively. The values for total volatile acids were in the ranges 560-1275, 395-2505, 580-3000 and 2610-3760 mg/litre. In all cases except D 4 the acid concentrat ion decreased over the digestion period, but concentrations in D4 increased. Alkalinity values of D 1, D 2 and D 3 were almost within the optimum range of 1500-5000 mg CaCOa/litre required for successful opera- tion of digesters (Chawla, 1986). However, in D 4, alkalinity was not enough to safeguard against pH reduction by the high concentration of volatile fatty acids.

Ageratum can be used as a substrate, with and without cattle dung, for the generation of biogas, provided it is partially decomposed prior to use. Fresh Ageratum as a substrate leads to the accumulation of acids and the failure of anaerobic digestion.

R E F E R E N C E S

Arora, H. C. (1975). Treatment of vegetable tanning effluent by anaerobic contact filter process. Water Pollution Control, 74, 584-9.

Bremner, J. M. (1965). Inorganic forms of nitrogen. In Methods of Soil Analysis: Chemical and microbiological properties Vol. 2. ed. C. A. Black, American Society of Agronomy, Madison, Wisconsin, pp. 1179-237.

Chawla, O. P. (1986). Methane fermentation technology. In Advances in Biogas Technology, Publications and Information Division, Indian Council of Agricultural Research, New Delhi, pp. 19-57.

Dar, G. H. & Tandon, S. M. (1987). Biogas production from pretreated wheat straw, lantana residue, apple and peach leaf litter with cattle dung. Biological Wastes, 21, 75-83.

Devkota, G. P. (1985). Utilization of Eupatorium species as an alternative feedstock for producing biogas. In Alternative Energy Sources VI. Vol. 2. ed. T. N. Veziroglu, Hemisphere Publishing, Washington, pp. 429-36.

Kalia, A. (1983). Bioconversion of'Lantana-camara to biogas. Proceeding of National Solar Energy Convention, Jyoti Ltd., Vadodra, India, pp. 183-84.

Nallathambi Gunaseelan, V. (1987). Parthenium as an additive with cattle manure in biogas production. Biological Wastes, 21, 195-202.

Ripley, L. E., Boyle, W. C. & Converse, J. C. (1986). Improved alkalimetric monitoring for anaerobic digestion of high-strength wastes. J. Water Pollut. Control Fed., 58, 406-11.

Sharma, S. K., Saini, J. S., Mishra, I. M. & Sharma, M. P. (1987). Mirabilis leaves--a potential source of methane. Biomass, 13, 13-24.

Anjan K. Kalia & Sarbjit S. Kanwar Bioenergy Laboratory, Department of Agricultural Engineering, Himachal Pradesh Agriculture University, Palampur-176062, India.

(Received 29 May 1989; revised version received 1 August 1989; accepted 28 August 1989)