4[2]Ann Ches Nut Hasbach,Putting Sludge to Work.Pollution Engineering,1991
5[4]Mac Nicol R D,Beckett P H,The disttibution of heavy metal between the principal components of digested sewage sludge,[J].Wat.Res,1989,23(2):199~206
6[6]Martinesz-Tarazona M R,Spears D A,Tascon M D,1992,Organic Affinity of Trace Elements in Asturian Bituminous Coals,Fuel,71(8)