Development of a Batch Type Bio-Digester

Abstract

A bio-digester was designed, constructed and tested for the production of biogas. The digester was designed and constructed using a 32 liter – digester tank, an 18.5 liter water displacement tank and a 20liter temporary storage tank of 16 liter. Biogas was produced by charging the slurry into the digester through the inlet channel and then closing the inlet channel and a hose was used to connect the digester and the water displacement tank which was already filled with water to the bream, a second hose was also used to connect the water displacement tank to the temporary storage tank were the displaced water is channeled to and the volume of water displaced was measured and recorded daily for the two type of slurry. A digital thermometer was used to take the ambient temperature of the digester. The digester was tested with two types of slurry that is made up of poultry litters and water at the ratio of 1: 4 and 1: 2, one poultry litter was mixed with water in the ratio of five liter to twenty liters respectively and the other in the ratio of five liters to ten liters. On the first and second day after loading there was no significant production of gas. The third day a gas production of 1.53ml was noted and the volume continued to increase until the eight day with 7.52ml and the reduction continued from 7.34, 7.09, and 6.41 on the 9th, 10th, 11th day respectively. However with the reduction observed on the 8th day in which the average temperature was 33oC. The reduction in the volume of gas can be linked to the decrease in the amount of organic matter present in the slurry. The volume of the slurry retained in the digester tank was about nineteen liters which means that about five liters of slurry were converted to biogas. Change in the color of slurry evacuated was noticed with non offensive odour. From the result it can be deduced that the concentration of the slurry is directly proportional to the rate of gas production and also the ambient temperature of the digester is directly proportional to the production of biogas.