TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: In (M1), the composting is repeated by using the obtained composted soil. In addition to the decomposition of the debris in the soil by the Lactobacillus microbes, the production of various enzymes during the lactic acid fermentation enables volume reduction of the debris and suppresses the foul smell generated during the degradation. EXAMPLE - Concrete manure board was installed and about 5 m3 if soil was laid over the board. Mixture of 2.4 m3 of octopus and internal organs of scallop, Lactobacillus and 100 kg of rice bran was prepared. A hole was dug in the soil and the prepared mixture was added and the soil was covered to the thickness of about 20 cm. The soil was compacted, covered with a sheet for preventing the permeation of rainwater and left. This allowed anaerobic fermentation of the debris by Lactobacillus and the generation of foul smell was suppressed. Partial degradation of the debris was carried out by lactic acid fermentation. The temperature of the soil during anaerobic fermentation was 15-20. After anaerobic fermentation for about 2-4 weeks, the soil was turned over for promoting aerobic fermentation. The temperature of the soil was rapidly raised to 15-60degreesC. By repeating the above operation several times, the volume of the debris was gradually reduced. The volume of manure was about 7.6 m3 immediately after the addition of debris and was finally decreased to about 5.8 m3. The C/N ratio was about 18. Dissolution test was performed, 0.01 mg/l or less of cadmium was contained in the composted soil. The amount of cadmium in the soil was measured. The cadmium content in the soil before and after composting was 0.3 mg/kg and 1.9 mg/l or less, respectively. About 5 m3 of the composted soil was obtained. The prepared mixture was added and composting was performed as above. The volume of manure was about 7.6 m3 immediately after the addition of debris and was finally decreased to about 5.9 m3. The C/N ratio was about 20. Dissolution test was performed, 0.01 mg/l or less of cadmium was contained in the composted soil. The amount of cadmium in the soil was measured. The cadmium content in the soil was 3.4 mg/kg. The composted soil was again obtained and the process was continued. The result showed that the debris of fish such as their internal organs can be effectively degraded by reducing their volume using Lactobacillus and heavy metal e.g. cadmium contained in their internal organs can be accumulated in the soil. The accumulated cadmium was separated by performing a neutralization process.