Effects of different organic loading rates on acid phase of food waste anaerobic stabilization

January 2013

Journal of Applied Sciences Research;Jan2013, Vol. 9 Issue 1, p271

Academic Journal

Article

Anaerobic stabilization is a method of choice nowadays for food waste treatment. It does not only reduce the waste quantities but also generate biogas containing methane as a renewable energy source. Anaerobic stabilization proceeds in three stages: hydrolysis, acid fermentation, and methane generation. If an anaerobic process is overloaded with organic substrate as in a case of food waste, normal progress to the next stage may not occur and problems such as protracted acid period may arise. Long acid phase is a result of unbalanced organic input and utilizing ability of anaerobic system. While the pH is below 6.5, methane generation could not proceed effectively and, therefore, complete food waste stabilization was possible. This work attempted to investigate the food waste stabilization characteristics, focusing on acid phase, at different organic loading rates since this type of waste was capable of producing leachate with high organic content. Four bioreactors were set up. Approximately, 2.5 kg of food waste and 0.2 L of seed sludge was loaded to each reactor. The content of the reactors was mixed by leachate recirculation. Volatile fatty acid (VFA) and chemical oxygen demand (COD) was selected to indicate the organic concentration of leachate. Daily application of leachate with VFA mass loading rates of 0.0975, 0.195, 0.390, and 0.780 g VFA/L/d were applied on Day 6 for reactors 1, 2, 3 and 4, respectively. The leachate pH was adjusted and recycled on Day 40. After 160 days of experiment, reactor 4 that received the highest loading rate exhibited the shortest acid duration on Day 51 and the highest percent methane in the biogas. However, the system could not utilize organics in the leachate without pH adjustment before Day 40. Without buffering, reactor 3 seemed to outperform reactor 4 as indicated by percent methane before Day 40. Inversely linear relation between the duration of the acid phase and the buffered VFA loadings for all reactors was found with R²= 0.97. Therefore, daily VFA loading rate as high as 0.780 g VFA/L/d could be applied to enhance anaerobic food waste stabilization and shorten the acid period if the system pH is adequately buffered. The final leachate, however, required further treatment to reduce its COD and VFA contents.

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