Characteristics of arsenic elution from sewage sludge

Characteristics of arsenic elution from sewage sludge were studied at different sludge pH values to develop a removal process for arsenic in sewage sludge. Forms of arsenic compounds (arsenious acid (As(III)), arsenic acid (As(V)), monomethylarsonic acid and dimethylarsinic acid) eluted from the sludge were analyzed using high-performance liquid chromatography-inductively, coupled plasma mass spectrometry. It was confirmed that four compounds of arsenic in the liquid phase separated from the sludge could be clearly classified and directly determined without being interfered with by coexistent matter dissolved from the sludge. An increase in sludge pH effectively increased the amount of arsenic eluted from the sludge, Although the sludge oxidation-reduction potential was increased by decreasing the sludge pH with sulfuric acid, the elution of arsenic was slight at pH 1. The predominant form of arsenic eluted from the sludge was arsenic acid at sludge pH 5, 7, 9 and 11, whereas it was arsenious acid at pH 1, Both monomethylarsonic and dimethylarsinic acids were insignificantly eluted at all of the pH values investigated. The form of arsenic dissolved from the sludge was found to almost correspond with that obtained from the Eh-pH diagram of arsenic in an aqueous system. It was concluded that elution of arsenic from sludge was promoted by increasing sludge pH and the dissolved arsenic existed mainly as arsenic acid at high pH. Copyright (C) 2001 John Wiley & Sons, Ltd.