Aa. Carbonell-barrachina et al., Arsenic chemistry in municipal sewage sludge as affected by redox potential and pH, WATER RES, 34(1), 2000, pp. 216-224
This laboratory experiment systematically examines As speciation and solubi
lity in sewage sludge suspensions as affected by pH and redox potential (Eh
). Under oxidizing conditions, As solubility was low with the major portion
of soluble As present as organic species; dimethylarsinic acid (DMAA) was
always the dominant organic species. Under moderately reducing conditions (
0-100 mV), arsenite a as the major inorganic As species in solution and As
solubility significantly increased due to dissolution of iron oxyhydroxides
. Upon reduction to -250 mV, As solubility was controlled by the formation
of insoluble sulfides and as a result soluble As contents dramatically decr
eased as compared to levels measured at 0 mV. Speciation was drastically in
fluenced by pH. Soluble As was maximum at a neutral pH value and decreased
under both more acidic and alkaline concentrations. At pH 5.0, inorganic sp
ecies were the dominant forms in solution, however, at pH 6.5, organic spec
ies were the major soluble forms. Alkaline conditions (pH 8.0) resulted in
similar concentrations of soluble inorganic and organic As species. Arsenic
biomethylation was measured at pH 6.5 and 8.0, but was drastically restric
ted at pH 5.0. (C) 1999 Elsevier Science Ltd. Ail rights reserved.