Practical Enrichment of Strains of Sulfur-oxidizing Bacteria and Economical Medium for Bacterial Leaching

For phosphorus recovery, we used the technique of bacterial leaching to elute phosphorus from night soil sludge incineration ash using sulfur-oxidizing bacteria. The purpose of this study was to obtain practically enriched strains of bacteria suitable for the local environment without a complicated isolation operation and to confirm a simple and economical medium composition. Three bacterial strains were enriched at night soil treatment facilities by using the medium for sulfur-oxidizing bacteria. Two enriched strains had a greater ability to generate sulfuric acid and elute phosphorus than Acidithiobacillus thiooxidans NBRC13701 （ NBRC ） which was used for comparison. Clone library analysis indicated that seven and five kinds of Acidithiobacillus spp. strain were included in these enriched strains, respectively. The ability of another enriched strain for sulfuric acid generation and phosphorus elution did not reach that of NBRC, but it was thought that this enriched strain included only A. caldus with a higher optimal growth temperature than those of the others. With regard to the medium composition, seven of the 11 original components could be omitted. For sulfur, an important substrate, inexpensive desulfurization sulfur could be used. The ability of sulfuric acid generation was unaffected by these changes, but the medium preparation cost was reduced to 1/18.