Effect of agricultural and other wastes on anaerobic digestion of water hyacinth-cattle dung
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JOURNAL OF FERMENTATION AND BIOENGINEERING VOI. 70, NO. 5, 343-344. 1990
Effect of Agricultural and Other Wastes on Anaerobic Digestion of Water Hyacinth-Cattle Dung DATTA MADAMWAR,* VIKRAM PATEL, AND ANAMI PATEL
Department of Biosciences, Sardar Patel University, Vallabh Vidyanagar 388120, Gujarat, India
Received 17 March 1990/Accepted 14 September 1990
In order to improve the anaerobic digestion of water hyacinth-cattle dung with enriched methane content, the effect of various easily available residues, such as Polyalthia longifolia (Sonn.) Thw. leaves, Azadirachta indica A. Juss. leaves, eucalyptus leaves, sugarcane bagasse, banana stem, poultry waste, cheese whey, algal powder (Enteromorpha sp.) and sugarcane filtercake have been studied. Among the residues tested, sugarcane bagasse, banana stem. poultry waste, cheese whey and algal powder showed more than 100% increase in gas production with 5 to 10% higher methane content.
Water hyacinth (WH) has a high productivity coupled with an excellent pollutant removal and methane genera- tion potential that makes it amenable to util ization in in- tegrated pollution-control and energy-conversion systems in rural areas. Cattle dung (CD) has so far been the major resource for biogas production (1-3). In recent years WH has come to be used as a replacement for CD, mainly due to the limited availability of the latter (4-6). In practice, however, a problem arises due to the nature of the organic content in this material; it has a reputation for poor process stability. Our studies have shown that WH : CD used in the ratio of 7 : 3 on a dry weight basis gives a high produc- tion of biogas with enriched methane content. However, if anaerobic digestion can be made still more efficient and therefore more economically attractive, farmers will be more apt to adopt this process. One possible approach would be to increase the availability of hydrogen donors from easily digestible volatile solids. This would divert more carboxylated intermediates into methane rather than CO2 (7). Therefore, in an effort to improve the gas produc- tion and its methane content so as to enrich its fuel value, the effect of various easily available residues have been studied.
Sugarcane filtercake from a sugar factory, Palaj, India; cheese whey from Amul, India; and CD, WH, agricultural and other wastes obtained from Vidyanagar, Gujarat, India were used in biogas production by anaerobic bio- conversion.
Several bench-scale anaerobic digesters were used. Each vessel consisted of a 10l glass reaction bottle, having a working volume of 6 l and containing 7%o of total solids (TS) (mixture of WH : CD, 7 : 3 w/w). The digesters were intermittently stirred (120 rpm) with a magnetic stirrer and maintained at 37_+ 1 C in a thermostat. Gas was collected and measured by displacement of an acidified saturated salt solution, making due corrections for atmospheric pressure and temperature. The digesters were fed on a semi-continuous basis: once per day with a mixture of WH (dried at 60C and powdered to 50 mesh) and CD in the ratio of 7 : 3 (w/w) and TS of 7O/oo (w/v), and a loading
rate of 8.75 g TS/I of digester/d, which our studies found to be most suitable. Prior to feeding, an equal quantity of sludge was withdrawn from the bottom of the digester. Residues were incorporated with feed sludge.
Fresh digester was always started by preparing a mixture of powdered WH and CD in the ratio of 7 : 3 (w/w) to give a final TS concentration 7O/oo (w/v), and using 10% in- oculum from a running biogas digester of the same type.
Feed and effluent slurry were routinely analysed for pH, volatile acids, BOD, COD, TS, volatile solids, lignin, cel- lulose and hemicellulose as per standard procedures (8- 11).
A trend of enhanced gas production with increased a- mount of algal powder (Enteromorpha sp.) is evident from Fig. 1. Maximum enhancement (of over 100~) was achieved with the addition of 30/00 (w/w) of TS. In addition to in- creasing total gas production, algal powder was responsi- ble for higher methane content in the digester gas, with as much as 70f00 methane being present in the total gas as com- pared to 64~00 in the control without algal powder.
Process stability, as evidenced by lower volatile acids, consistently increased with increased levels of algal powder (Fig. 1). Volatile acid concentration ranged from 1.3 g/l in the digester with no algae to 1.1 g/l in the algal-dosed digester. This indicates that volatile acids were consumed at a faster rate than in the control experiments where no algal powder was used. From Fig. l, it seems that the pres- ence of algal powder in a suitable proport ion along with WH-CD boosts the methane-forming step of the digestion process, by making the substrate easily utilizable. This may be because of a suitable carbon to nitrogen ratio and easily digestible materials, but further study is required to explain this phenomenon.
Process performance can also be judged by BOD and COD values. As shown in Fig. 1, addition of algal powder gave low values of BOD and COD, indicating greater bio- degradation. It was found that there was 81% COD re- moval in a 30~00 (w/w of TS) algal powder-dosed digester in comparison to the control without additive where the COD reduction was 62~ in 8 d.
Studies with other residues like sugarcane bagasse, banana stem, poultry waste, cheese whey and sugarcane
344 MADAMWAR ET AL. J. FERMENT. BIOENG.,
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o c: "~ l I I I I I i l L I l 1 I l
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FIG. 1. Enhancement of anaerobic digestion of water hyacinth-cattle dung in presence of (a) algal powder, (b) poultry waste, (c) banana stem, (d) cheese whey, (e) sugarcane bagasse, (f) sugarcane filter cake. Symbols: O, gas production;