Umudike Journal of Engineering and Technology

Biogas is a mixture of gaseous component generated from the decoposition of organic matter in the absence of oxygen. It consists of methane, carbondioxide, hydrogen and traces level of other gases which include carbon monoxide, hydrogen sulphide etc.Agricultural wastes are abundantly available and serve as one of the potential carbon sources for the production of biogas after biochemical conversion. This study focuses on digester design, fabrication and its utilizationin in the digestion of brewer spent grain and rice husk mixed with algae water. Three biogas digesters (A, B, C) with capacities 32litres, 30litres and 32litres respectively were designed and fabricated. The substrate (Rice Husk and Brewery Spent Grain) was first pre-treated for 21 days using Lake salt (Trona or Soduim carbonate or soda ash) locally known as “Akanwu” which aided to break down the lignin and cellulose in the feed. The substrate was mixed in the ratio 1:1 with algae water to substrate ratio 3:1 was used. The algae served as an inoculum to introduce micro organisms into the digester. The digester was stirred twice daily to avoid scum formation in the digester and allow for easy escape of the gas produced. The retention time used for this experiment was 47 days except for Digester C which was for 8 days. During this period the temperature readings for Digester A and B was taken in order to determine variation and its effect on production rate. The gas produced was measured using water displacement method, and at the end of the experiment the gas generated was further taken to the laboratory for analysis. The result obtained from the laboratory analysis showed that Digester A produced the highest methane content of 73.95% followed by the Digester B with 68.92% content and Digester C had the least methane content of 65.95 %.  Digester A had the highest cumulative biogas yield of 37.77litres over its PVC counterpart Digester B which had 22.66litres within the retention period. Result of this study showed that Digester A (Metallic Digester) was more efficient in biogas generation, which can be said to have resulted from its ability to retain heat and prevent air entrance or leakage.