REMOVAL AND RECOVERY OF HEAVY-METAL IONS FROM ANAEROBIC SLUDGE

The effective methods for extraction and removal of heavy metal ions f rom an anaerobic sludge were investigated. Extractability of heavy met al ions was increased by the conversion of the anaerobic sludge into a n aerobic sludge. By the addition of acid (pH 2) or ligands (pH 7), he avy metal ions such as Cu2+, Cd2+, Pb2+ and Zn2+ were extracted from t he aerobic sludge in a 50-100% yield and metals extracted wi acid were easily recovered by the adoption of neutralization method but less re covered with cation exchange resin. The electrolytic method can be fav orably used to remove metal ions in solution also when bath ligands an d suspended solid are present. In order to carry out extraction and re covery of metal ions at the same time, the aerobic sludge suspension w as electrolyzed at pH 2 and 6 in the presence of NTA. In this method, metal contents in aerobic sludge were reduced to below 15% except for pb(2+), at pH 2 after 7 days and recovery of metals on electrode was o ver 80% in the presence of NTA. When the anaerobic sludge suspension w as treated in a similar manner with forced aeration, metal contents we re reduced to below 25% except for Cd2+ and over 60% of metals were re covered.