Analysis of Psychrophilic Alternatives for Production of Biogas at Low Temperature Range

Abstract

The use of biogas technology in Nepal has benefited the country in improving health, environment, and economy and energy conservation. However, the mesophilic temperature ranges in which it has succeeded offer a limitation for scaling up in colder regions of Nepal. Even in warmer areas, winter results in dramatic drops in gas formation in the digesters. This thesis has focused on experimental study of biogas production potential with psychrophilic inoculums.

Various research works throughout the world have suggested that use of psychrophilic methanogens boost the biogas production potential even in low temperatures. Psychrophiles or cryophiles are extremophilic organisms that are capable of growth and reproduction in cold temperatures, ranging from −20 °C to +10 °C. Many such organisms are bacteria, but psychrophiles also include eukaryotes such as lichens, snow algae, fungi, and wingless midges. It is suggestive in relevant research works that such bacteria are found in permafrost (frozen ground) soils and bottom of high altitude lakes.

The samples were collected based on location selection from NAST’s research on psychrophiles. Catalase test was considered the major deciding factor for characterization. Further tests were carried out for it and 14 different prototype biogas digesters were made. The digester was also tested adding only the organic wastes for comparative study. Lab tests at RIBB suggested samples from Syangboche to be the best option. The prototype digesters were kept at 5, 10, 15 and 25 degrees Celsius. The pressure reading and temperature of the samples were noted. After 60 days, the gas pressure and the gas composition were tested and for 3 sets of temperature ranges, a total of 5 months’ time was used for gas analysis. The results showed increased biogas production while using the sample compared to the digester without the sample at all controlled temperatures. Moreover, even though biogas formation did occur in low temperature ranges with methane content greater than 50%, it was still lower than gas formation in the mesophilic range. Cost benefit analysis for a case study in Chitwan gave a B/C ratio of 1.62, NPV of Rs. 128,113, IRR of 54% and a payback period of 2.75 years for a digester of 6m3 .