Effect of Mixing Ratios of Sudachi Peel on the Stability of Anaerobic Co-digestion of Rural Sewage Sludge, Kitchen Garbage and Sudachi Peel

― Conditions leading to process failure and possible improvement by the addition of nitrogen ―

Abstract

Anaerobic co-digestion experiments were conducted under six conditions in which mixing ratios of rural sewage sludge was set at 50% by weight, and the ratio of kitchen garbage and sudachi peel, a food waste with a relatively high C/N ratio of 36.1, was varied to understand the effect of the mixing ratio of sudachi peel on the stability of digestion. As a result, digestion proceeded stably when the ratio of sudachi peel was low, but when the ratio of sudachi peel was larger than 20%, the pH and gas production rate gradually dropped, indicating process failure. When urea was added to the feedstock material, digestion proceeded stably, indicating that the cause of process failure was nitrogen deficiency. The method of adding urea at the feedstock material stage of digestion not only improves the stability of digestion, but also increases the fertilizer value of the digestate and the efficiency of digestate application to the field due to the increased nitrogen concentration in the digestate.