Feasibility study of increasing the rate of digestion in anaerobic digesters

Abstract

The anaerobic digestion of vegetable garbage, is quite slow, with retention times of 80- 100 days. Because of these slow rates of digestion, reaction vessels needed, are quite large. Research clearly needs to concentrate on increasing the rate of the process and decreasing the reactor volumes required. in commercial applications. In this study a literature survey was carried out to find out the possible ways of increasing the rate of anaerobic digestion and later some laboratory work was carried out in order to verify some of the findings of the literature survey. Literature survey showed that for the anaerobic digestion to be efficient the environment inside the reactor should be strictly anaerobic; the value of pH should be between 7 and 8. the feedstock should be biodegradable and should contain enough seed bacteria; the carbon to nitrogen ratio ( CIN) of the feed should be between 20 and 30. Furthermore literature shows that anaerobic digestion can occur in three different temperature ranges due to the activity made by three different groups of bacteria. Cryophylic range is between 10°C and 20°C: Mesophilic range is between 30°C to 40°C; and Thermophilic range is between 4SoC and 60°C According to the literature thermophilic bacteria are most efficient and they can digest vegetable garbage within a period of 10 days. Laboratory experiments also confirmed that within the thermophilic range, if the other environmental parameters are fulfilled. a mixture of vegetable garbage is anaerobically digested in a period of 10 days Laboratory experiments confirmed that application of enrichment culture also enhances the performance of anaerobic digesters.