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Biogas from solid waste originated during biscuit and chocolate production: A preliminary study
Biological Wastes 28 (1989) 157-161
Short Communication Biogas from Solid Waste Originated During Biscuit and Chocolate Production: A Preliminary Study
ABSTRACT The solid waste originated during the biscuit and chocolate production was subjected to anaerobic digestion in a 180-1itre capacity biogas plant of floating dome design. Three different hydraulic retention times ( HRT), viz. 20, 30 and 40 days, were studied with ~0% total solids in the influent slurry. The data collected showed that the waste is amenable to anaerobic digestion. The biogas produced was more at 40 days HRT, viz. 466 litres kg- x waste added per day with 57% methane and 65% degradation in volatile solids. The anaerobic digestion at lower HRT, viz. 20 and 30 days, resulted in high VFA concentration and low pH of the fermenting slurry.
INTRODUCTION Much solid waste is generated during the production of confectioneries like biscuits and chocolate. The solid waste collected from the mixing and packing unit is rich in carbohydrates and fats which are easily biodegradable and thus should be a good substrate for biogas production. At present the waste is disposed of by incineration. There are many reports describing anaerobic digestion as an appropriate mode of treatment for agricultural and industrial wastes with recovery of methane. Production of biogas from industrial canteen waste (Yeole et aL, 1984) and market waste (Ranade et al., 1987) have also been reported. The present paper describes preliminary laboratory work carried out on the anaerobic digestion of the waste from biscuit and chocolate production (BCP waste) at different HRT. 157 Biological Wastes 0269-7483]89/$03.50 © 1989 Elsevier Science Publishers Ltd, England. Printed in Great Britain
158
D. R. Ranade, T. Y. Yeole, K. K. Meher, R. V. Gadre, S. H. Godbole
METHODS The solid waste was obtained from Sathe Biscuit and Chocolate Company Ltd, Pune. The waste was collected from biscuit, chocolate and packing units of the company and mixed in the proportion 1:2:3 based on the quantities arising daily from each unit. The waste mainly consisted o f m a i d a (fine wheat flour), ghee (milk fat), pieces and powder of biscuit with chocolate paste. Pieces of packing paper were not included. The composite waste had 90% (w/w) total solids and 85% total volatile solids. Three 180-1itre capacity, non-stirred, anaerobic digesters of floating-dome design (Dayal, 1981) were initially charged with fermenting cattle dung slurry from a 3 m a d a y - ~ biogas plant. The plants were stabilized by daily addition of 6 litres cattle dung slurry having 10% total solids for 40 days. After stabilization of the plants for effective methanogenesis, they were charged daily with different volumes of BCP waste slurry (10% TS) to have 20, 30 and 40 days HRT, over a period of 80 days.
Analyses The daily biogas produced was measured by a wet meter (Toshniwal, Madras) and analyzed for its methane content by gas chromatography (Ranade et al., 1987). Temperature (minimum and maximum) and pH of the fermenting slurry were recorded daily. Total solids (TS) and volatile solids (VS) in the influent and effluent were determined, twice a week, during the last 40 days of the experiment by S t a n d a r d M e t h o d s (APHA, 1985). Volatile fatty acids (VFA) of the influent and effluent were analyzed once a week during the last 40 days of the experiment by gas chromatography (Ranade et al., 1987).
RESULTS A N D DISCUSSION The data on the average values of the last 40 days of the experiment are given in Table I and daily productions of biogas from the waste at different HRT are shown in Fig. 1. The anaerobic digestion of the waste was stable at 40 days HRT, as compared with 30 days HRT. The daily biogas production was also greater at 40 days H R T (261 litres d a y - t; 57% methane) than at 30 days H R T (140 litres d a y - ~; 42% methane). The pH of the fermenting slurry at 40 days H R T was 6.7 as against 5.3 at 30 days HRT. The VFA concentration of the fermenting mass at 40 days HRT was only 480 mg litre-x, whereas it was 9200mg litre- ~ at 30 days HRT. The initial VFA of
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D. R. Ranade, 7"., Y. Yeole, K. K. Meher, R. V. Gadre, S. H. Godbole
TABLE 1 P r o d u c t i o n o f Biogas f r o m B C P W a s t e at Different H R T (Averages o f last 40 days o f the Experiment)
HRT (days)
BCP fresh waste (kg
Biogas produced a
Methane content (litres kg- 1 (%) TS day- 1)
pH of the effluentb
VFA in Temperature effluent range (mg litre- 1) (oC)
day- x)
(litres day- 1)
30
0"75
140
275
42
5.3
9 200
40
0-56
261
518
57
6.7
480
20 to 40
Digester volume 180 litres. a Gas volume corrected to STP. b Influent pH 6'5 and VFA 195 mg litre- 1.
the BCP influent slurry was 195mg litre -1. The low pH and high VFA content of the fermenting mass at 30 days HRT were indicative of impaired methanogenesis. Digestion of the waste was also tried at 20 days HRT but the digester became sour, with high VFA concentration and low pH (VFA 10200mg litre-1; pH 4.8) of the fermenting slurry. The experiment was terminated after 20 days (Fig. 1). Anderson et al. (1982) in the studies on anaerobic digestion of industrial waste have reported the ideal VFA content as 250-500 mg litre-1. In the present study, the VFA content at 30 days H R T was 9200 mg litre-1, indicating an unstable digestion. In the present tests a loading rate equivalent to 40 days HRT was suitable for anaerobic digestion of the BCP waste. Degradation of organic matter in terms of volatile solids was 65% at this HRT. The preliminary experiments thus show that the solid waste arising from biscuit and chocolate manufacture, excluding the paper cuttings, is amenable to anaerobic digestion. The digestion process is stable at a loading rate of 2.8 kg TS m - a d a y - 1 and the biogas production of 518 litres kg- 1 TS added per day could be used in the factory. In the present study, the plants were charged daily with 10% TS slurry and run at ambient temperature as is usually practised in this country. Further experiments are therefore necessary to find out the optimum conditions for anaerobic digestion of BCP waste.
ACKNOWLEDGEMENT Grateful thanks are due to Sathe Biscuit and Chocolate Company Ltd, Pune, India for providing financial assistance to carry out this work.
Biogas from confectionery waste
161
REFERENCES Anderson, K. G., Donnelly, T. & Meckeown, K. J. (1982). Identification and control of inhibition in the anaerobic treatment of industrial waste water. Process Biochemistry, 17(4), 28-32. APHA (1985). Standard Methods for the Examination of Water and Waste Water, 16th edn. APHA, AWWA, WPCF, Washington, DC, USA. Dayal, M. (ed.) (1981). Biogas Technology and Utilization--A Status Report. Department of Science and Technology, Government of India, New Delhi. Ranade, D. R., Yeole, T. Y. & Godbole, S. H. (1987). Production of biogas from market waste. Biomass, 13(3), 147-53. Yeole, T. Y., Gadre, R. V., Ranade, D. R. & Godbole, S. H. (1984). Biogas from canteen waste. Khadigramodyog (The Journal of Rural Economy), 39(9), 371-3.
D. R. Ranade, T. Y. Yeole, K. K. Meher, R. V. Gadre & S. H. Godbole Department of Microbiology, M.A.C.S. Research Institute, Law College Road, Pune 411 004, India (Received 6 March 1988; revised version received 29 August 1988; accepted 5 September 1988)
Short Communication Biogas from Solid Waste Originated During Biscuit and Chocolate Production: A Preliminary Study
ABSTRACT The solid waste originated during the biscuit and chocolate production was subjected to anaerobic digestion in a 180-1itre capacity biogas plant of floating dome design. Three different hydraulic retention times ( HRT), viz. 20, 30 and 40 days, were studied with ~0% total solids in the influent slurry. The data collected showed that the waste is amenable to anaerobic digestion. The biogas produced was more at 40 days HRT, viz. 466 litres kg- x waste added per day with 57% methane and 65% degradation in volatile solids. The anaerobic digestion at lower HRT, viz. 20 and 30 days, resulted in high VFA concentration and low pH of the fermenting slurry.
INTRODUCTION Much solid waste is generated during the production of confectioneries like biscuits and chocolate. The solid waste collected from the mixing and packing unit is rich in carbohydrates and fats which are easily biodegradable and thus should be a good substrate for biogas production. At present the waste is disposed of by incineration. There are many reports describing anaerobic digestion as an appropriate mode of treatment for agricultural and industrial wastes with recovery of methane. Production of biogas from industrial canteen waste (Yeole et aL, 1984) and market waste (Ranade et al., 1987) have also been reported. The present paper describes preliminary laboratory work carried out on the anaerobic digestion of the waste from biscuit and chocolate production (BCP waste) at different HRT. 157 Biological Wastes 0269-7483]89/$03.50 © 1989 Elsevier Science Publishers Ltd, England. Printed in Great Britain
158
D. R. Ranade, T. Y. Yeole, K. K. Meher, R. V. Gadre, S. H. Godbole
METHODS The solid waste was obtained from Sathe Biscuit and Chocolate Company Ltd, Pune. The waste was collected from biscuit, chocolate and packing units of the company and mixed in the proportion 1:2:3 based on the quantities arising daily from each unit. The waste mainly consisted o f m a i d a (fine wheat flour), ghee (milk fat), pieces and powder of biscuit with chocolate paste. Pieces of packing paper were not included. The composite waste had 90% (w/w) total solids and 85% total volatile solids. Three 180-1itre capacity, non-stirred, anaerobic digesters of floating-dome design (Dayal, 1981) were initially charged with fermenting cattle dung slurry from a 3 m a d a y - ~ biogas plant. The plants were stabilized by daily addition of 6 litres cattle dung slurry having 10% total solids for 40 days. After stabilization of the plants for effective methanogenesis, they were charged daily with different volumes of BCP waste slurry (10% TS) to have 20, 30 and 40 days HRT, over a period of 80 days.
Analyses The daily biogas produced was measured by a wet meter (Toshniwal, Madras) and analyzed for its methane content by gas chromatography (Ranade et al., 1987). Temperature (minimum and maximum) and pH of the fermenting slurry were recorded daily. Total solids (TS) and volatile solids (VS) in the influent and effluent were determined, twice a week, during the last 40 days of the experiment by S t a n d a r d M e t h o d s (APHA, 1985). Volatile fatty acids (VFA) of the influent and effluent were analyzed once a week during the last 40 days of the experiment by gas chromatography (Ranade et al., 1987).
RESULTS A N D DISCUSSION The data on the average values of the last 40 days of the experiment are given in Table I and daily productions of biogas from the waste at different HRT are shown in Fig. 1. The anaerobic digestion of the waste was stable at 40 days HRT, as compared with 30 days HRT. The daily biogas production was also greater at 40 days H R T (261 litres d a y - t; 57% methane) than at 30 days H R T (140 litres d a y - ~; 42% methane). The pH of the fermenting slurry at 40 days H R T was 6.7 as against 5.3 at 30 days HRT. The VFA concentration of the fermenting mass at 40 days HRT was only 480 mg litre-x, whereas it was 9200mg litre- ~ at 30 days HRT. The initial VFA of
Biogas from confectionery waste
159
0%
•
I I
,
@
i
"o t" ¢",1
,'2
o
.:,
•~
~o
.~
glq
",:
0
,..T 0
A e o / sial~7
,
o
160
D. R. Ranade, 7"., Y. Yeole, K. K. Meher, R. V. Gadre, S. H. Godbole
TABLE 1 P r o d u c t i o n o f Biogas f r o m B C P W a s t e at Different H R T (Averages o f last 40 days o f the Experiment)
HRT (days)
BCP fresh waste (kg
Biogas produced a
Methane content (litres kg- 1 (%) TS day- 1)
pH of the effluentb
VFA in Temperature effluent range (mg litre- 1) (oC)
day- x)
(litres day- 1)
30
0"75
140
275
42
5.3
9 200
40
0-56
261
518
57
6.7
480
20 to 40
Digester volume 180 litres. a Gas volume corrected to STP. b Influent pH 6'5 and VFA 195 mg litre- 1.
the BCP influent slurry was 195mg litre -1. The low pH and high VFA content of the fermenting mass at 30 days HRT were indicative of impaired methanogenesis. Digestion of the waste was also tried at 20 days HRT but the digester became sour, with high VFA concentration and low pH (VFA 10200mg litre-1; pH 4.8) of the fermenting slurry. The experiment was terminated after 20 days (Fig. 1). Anderson et al. (1982) in the studies on anaerobic digestion of industrial waste have reported the ideal VFA content as 250-500 mg litre-1. In the present study, the VFA content at 30 days H R T was 9200 mg litre-1, indicating an unstable digestion. In the present tests a loading rate equivalent to 40 days HRT was suitable for anaerobic digestion of the BCP waste. Degradation of organic matter in terms of volatile solids was 65% at this HRT. The preliminary experiments thus show that the solid waste arising from biscuit and chocolate manufacture, excluding the paper cuttings, is amenable to anaerobic digestion. The digestion process is stable at a loading rate of 2.8 kg TS m - a d a y - 1 and the biogas production of 518 litres kg- 1 TS added per day could be used in the factory. In the present study, the plants were charged daily with 10% TS slurry and run at ambient temperature as is usually practised in this country. Further experiments are therefore necessary to find out the optimum conditions for anaerobic digestion of BCP waste.
ACKNOWLEDGEMENT Grateful thanks are due to Sathe Biscuit and Chocolate Company Ltd, Pune, India for providing financial assistance to carry out this work.
Biogas from confectionery waste
161
REFERENCES Anderson, K. G., Donnelly, T. & Meckeown, K. J. (1982). Identification and control of inhibition in the anaerobic treatment of industrial waste water. Process Biochemistry, 17(4), 28-32. APHA (1985). Standard Methods for the Examination of Water and Waste Water, 16th edn. APHA, AWWA, WPCF, Washington, DC, USA. Dayal, M. (ed.) (1981). Biogas Technology and Utilization--A Status Report. Department of Science and Technology, Government of India, New Delhi. Ranade, D. R., Yeole, T. Y. & Godbole, S. H. (1987). Production of biogas from market waste. Biomass, 13(3), 147-53. Yeole, T. Y., Gadre, R. V., Ranade, D. R. & Godbole, S. H. (1984). Biogas from canteen waste. Khadigramodyog (The Journal of Rural Economy), 39(9), 371-3.
D. R. Ranade, T. Y. Yeole, K. K. Meher, R. V. Gadre & S. H. Godbole Department of Microbiology, M.A.C.S. Research Institute, Law College Road, Pune 411 004, India (Received 6 March 1988; revised version received 29 August 1988; accepted 5 September 1988)