DEVELOPMENT OF STORAGE METHOD OF CRUSHED KITCHEN GARBAGE USING LACTIC ACID FERMENTATION IN JOHKASOU FOR METHANE FERMENTATION

Abstract

 Recently, the construction of resource recycling centers of excess sludge has been progressing nationwide when night soil treatment facilities are upgraded. Recycling of energy and resources by methane fermentation and composting of organic wastes, including night soil, johkasou sludge, and kitchen garbage, is being promoted. However, johkasou sludge and kitchen garbage are usually collected independently. In order to reduce the labor and environmental load, a process is developed in which garbage crushed by a disposer is stored in a johkasou, and both johkasou sludge and kitchen garbage are simultaneously and efficiently collected for methane fermentation. Assuming that solids in domestic wastewater and kitchen garbage accumulate in the solid-liquid separation tank of a johkasou, four-week storage experiments were conducted three times continuously using a reactor with a working volume of 0.2 L simulating a solid-liquid separation tank. Degradation behavior of simulated kitchen garbage inoculated with indigenous lactic acid bacteria at 13-25℃ was investigated.

 Lactic acid fermentation resulted in decreased pH of 3.5 and suppressed the solubilization of solids. A preservation ratio of suspended solids was 80%, which shows that decrease in biogas generation potential was suppressed.

 The life cycle CO₂ evaluation of the process revealed that the simultaneous collection of organic waste reduces approximately 140 kg-CO₂/(household • year) compared to the conventional process of independent collection of kitchen garbage and johkasou sludge. In addition, the introduction of the simultaneous collection process reduces the cost of municipal waste treatment by approximately 9,500 JPY/(household•year).