AWWA ACE63120

This slide presentation outlines a study on the effect of pH, Phosphate, and vanadate on As(III/V) adsorption during coagulation-filtration with zirconium, titanium, and ferric salts. Specific objectives included: determining the feasibility of using zirconium andtitanium salts in comparison to ferric chloride ascoagulants for Arsenic removal;studying the individual and combined effects of pHand competing ions includingsilica (0, 20 mg/L, NSFI water w/wo PO₄), phosphate (0, 40 µg P/L, NSFI water w/wo SiO₂), andvanadate (0, 50 µg/L in NSFI water w/wo SiO₂ and PO₄); and,studying the toxicity characteristics of the sludgesusing TCLP and California WET tests. Conclusions for As(III) indicated that: As(V) removal was pH dependent, and theremoval increased with decreasing pH for allcoagulants;Fe(III) was a much better coagulant thanTi(III), Ti(IV), and Zr(IV) at pH 6.5 and 8.5 forAs(V) removal. At pH 8.5, Fe(III),Ti(III), andTi(IV) were similar; Ti(III) was superior to the othercoagulants at pH 6.5 and 7.5, but at8.5, the Fe and Ti coagulants weresimilar in performance; and,As(III) was oxidized to As(V) in thepresence of Ti(III). The oxidationcontinued for several hours due to theslow rate of formation of H₂O₂ andoxidation of As(III) by H₂O₂. Conclusions for competing ions indicated that: for As(V) and As(III), Silica competition significantlyreduced the adsorption, the detrimental effect of silicaincreased with increasing pH, the presence ofphosphate lessened the detrimental effect of silica at allpHs;in the absence of silica, phosphate significantly reducedthe adsorption of As(V) at all pHs, and had a minor effecton the adsorption of As(III) at pH 7.5 and 8.5, in thepresence of silica, phosphate significantly reduced As(V)adsorption at pH 6.5 and 7.5, phosphate had no effect onthe adsorption of As(III) at any pH when SiO₂ was pres.; and, in the absence of silica and phosphate, vanadatesignificantly reduced the adsorption of As(V) at all pHs,and had a minor effect on the adsorption of As(III) at pH7.5 and 8.5. But in the presence of silica and phosphate,vanadate did not have significant effect on theadsorption of As(V) or As(III) at any pH. General conclusions indicated that: in-situ formed hydroxides had significantlyhigher adsorption capacities comparedwith the granular media, probably due tohigh effective surface area of thecoagulants; and, the settled liquid wastes contained lessthan 0.5% dry solids and, defined asTCLP extracts, easily passed the TCLPand California WET tests. Includes figures.

Product Details

Edition:

Vol. - No.

Published:

06/01/2006

Number of Pages:

25

File Size:

1 file , 1.6 MB