Evaluation of stability of compost prepared with Korean food wastes

Abstract

Food wastes were composted with saw dust, dried paper mill sludge, and decayed wood dust to reduce the volume of wastes and to produce a stable organic soil amendment. To determine the stability for agricultural utilization, the compost maturity was evaluated using physical, chemical, and biological parameters. Temperature of the inner compost heap remained high at over 50°C during the 80 d of composting, but the chemical and physical parameters apparently changed between 30 and 50 piling d: pH was a weakly acidic of the initial stage and neutral after 30 d of composting. The C / N ratio decreased to less than 12 after 65 d of composting, but the C / N ratio of the products was less than 0.5 time that of the initial value after 35 d of composting. Reducing sugar contents changed significantly between 40 and 45 d of composting, and the Y value that indicated color changes of the water extracts decreased and became stabilized at around 3 after 50 d of composting. Ring types and color on circular paper chromatograms showed an apparent difference before and after 40 d of composting. The content of sodium (Na), which might be one of the most harmful elements in Korean food wastes for agricultural utilization, increased from 12 to 17 g kg⁻¹ with time and Na mostly occurred in a water-soluble form. Acetic acid was the main component of volatile organic acids, and total organic acids were produced at a very high rate (500–700 mg kg⁻¹) during the first 5–30 d of composting and then the rate decreased rapidly to below 300 mg kg⁻¹ after 35 d of compo sting. Germination index of Chinese cabbage in water extracts fluctuated with compost pile turning to a value below 50 by 40 d of composting, due to the effects of high contents of organic acids and Na. The value exceeded 50 after 45 d of compo sting but did not increase further with continuous composting, which might be due to the high content of Na. Lettuce, a sensitive species, was scarcely germinated in water extracts of the food compost. Consequently, the high content of Na in Korean food waste compost, in spite of maturity, could be a limiting factor for agricultural utilization. The effects of Korean food waste compost on plant growth and soil conditions should be evaluated further at the field level.