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Biogas Production at Different Concentrations of Cowdung

S.K. Bosu
Department of Civil Technology, Polytechnic Institute, Mymensingh, Bangladesh.

M.A. Rashid
Dept. of Farm Structure, Bangladesh Aqricutturat University, Mymensingh

M.H. Rahman
Dept. of Civil Engg., Bangladesh University of Engineering and Technology, Dhaka

Abstract/ Executive Summary:

This study investigates the production of biogas, in batch operation, at different concentrations of cowdung under mixing and non- mixing conditions. The digesters of mixing set were equipped with a manually operated stirrer capable of mixing slurry in full anaerobic condition. Mixing was done by revolving 12 blades mounted on a shaft through a handle located outside the digester. Three digester sets for each mixing and non-mixing operations were used for biogas generation. The cowdung concentrations were varied from 40-60% gobar with a 10% increase by weight. The results reveal that biogas production is directly related to dung concentration. Biogas generation is found to vary from 250 to 440 litre per kg gobar with a maximum at dung-water ratio of 1: 1 by weight. Mixing of slurry increases biogas generation appreciably irrespective of the amount of gobar. The overall increases are found from 20% to as high as 60% depending on gobar contents. The net volume of gas production was found between 0.15 and 0.26 cu m/cu m of digester volume.

Keywords: Biogas, Fermentation, Digestion, Cowdung

Location: Mymensingh

Start Date:

End Date:

Program Area: Resource Development and Management

Commodity: Manures

Objectives:

Particular emphasis is given on biogas production at different cowdung concentrations in the mother slurry under mixing and non-mixing operations.

Methodology:

Organic wastes such as, human feces. animal feed and manure, aquatic weeds. plants and the byproducts of farms and industries are used as raw mate- rials for anaerobic fermentation. Animal dung is the best feed for anaerobes from nutritional point of view. The over night cowdung of Bangladesh Agricultural University Dairy Farm was used as raw material for experimentation. The collected gobar was a fresh dung for which it was almost free from anaerobic bacteria. The initial properties of gobar were as follows: total nitrogen 0.36%, total solids 20%. volatile solids 11.2%, moisture content 79.8% .and Carbon content 6.22%. The commercial coconut oil barrel of diameter 58 cm and volume 235 litre was used as digester. The digesters for mixing operation are equipped with a manually operated mixing assemble. Twelve blades (B) of 2 different sizes were welded with a main shaft (MS) in 4 rows. Two ends of main shaft were connected to the air tightening arrangements (GP) fitted diametrically with the digester. Air seal was a composite unit of asbestos loop and bore piece compressed by a metal plate. A movable handle (H) with groove arrangement guided by a ball-bearing caging (BC) was used to rotate the blades. A separate gas holder made of MS sheet placed invertedly into another water filled barrel was used to store the gas in mixing set. While in non-mixing set, gas was collected into an inverted holder placed over the digester. The volume of gas holder was so chosen that it could hold the gas generated in a day. A cylindrical gas holder (GH) of capacity 150 litre was kept in position by 3 MS rod welded with either water barrel or digester. Each digester (DT) was charged with slurry, a mixture of gobar and water having dung concentrations of 40%, 50% and 60% by weight. The amount of gobar needed for 190 litre slurry at different go bar concentrations (weight basis). After thoroughly mixing the requisite amount of gobar for a particular concentration, the' mixed dung was transferred into a drum where the needed amount of water was added. The digester was then charged with 190 litre mixed slurry. It was a batch scale study without seeding. In mixing set, the slurry was stirred every day at about 10 am by revolving the blades 30 times through the handle. The blades mixed the slurry by rotating.

Source of Information: Bangladesh J. Agril. Sci. 21(1): 133-139, January, 1994

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

In batch operation, biogas generation by anaerobic digestion depends on cowdung concentration of the mother slurry and degree of mixing the slurry. The highlights of this study are: i. Biogas generation is directly related to gobar cocentration of the mother slurry ii. Biogas production per kg gobar is maximum at 50% of gobar concentration by weight and iii. Mixing operation increases biogas production significantly.

Knowledge Management: Journal