Iron coagulation and direct microfiltration to remove arsenic from groundwater

Abstract

Arsenic (As) removal using ferric hydroxide coagulation followed by direct microfiltration without flocculation was investigated for an application in Albuquerque, N.M. Typically, the influent drinking water (unchlorinated) was contacted with ferric hydroxide for ≤20 s in a rapid mixer and passed through a membrane microfiltration unit with a nominal pore size of 0.2 μm. Variables investigated included pH, iron (Fe) dose, mixing time and energy, filtrate flux, and backwash interval. The pH and ferric dose were found to be the most important variables controlling As removal. As removal to low levels (<2 μg/L) was achieved using either a dose of 7 mg/L Fe without deliberate pH reduction or a smaller dose of 1.9 mg/L Fe after sulfuric acid addition to reduce pH to 6.4. Extended operation (three to five days) showed that consistent As removal was obtained without any membrane fouling. Both the backwash water and the dried sludge passed the toxicity characteristic leaching procedure test as a nonhazardous waste.

Effect of aluminum speciation on arsenic removal during coagulation process

“…Early bench, pilot, and demonstration scale studies have shown that As(V) can be efficiently removed during coagulation with ferric chloride and alum even when present at low or high concentration in influent waters [8,9]. Aluminum (Al) based salts, e.g., polyaluminum chloride (PACl), aluminum chloride (AlCl 3 ), and alum (traditional Al coagulants), are most commonly used in water treatment plant.…”

Effect of organic matter on arsenic removal during coagulation/flocculation treatment

“…Its removal was thus not favored when pH increased. Indeed, the pH increase led to the decrease of numbers of positively charged active sites on hydroxide ferric surfaces and to the increase in numbers of OH -ions competitive with arsenic for adsorption on hydroxide ferric surface [40]. This experiment thus confirmed sorption as the predominant As(V) removal mechanism.…”

“…The influence of coagulant dose on As(III) and As(V) removal was studied by using FeCl 3 as coagulant [16,39,40] at concentrations between 25 and 150 mg L À1 (9.2 6 [Fe 3+ ] (mg L À1 ) 6 55.0 or 165 6 [Fe 3+ ] (lmol L À1 ) 6 985). pH was fixed at different values (with NaOH 1 mol L À1 ), 6.0 ± 0.2, 6.9 ± 0.3, and 7.7 ± 0.1, to study its influence on arsenic removal under these specific coagulant conditions.…”

Waste Treatment and Remediation Technologies for Arsenic

“…Microfiltration after precipitation/coprecipitation with Fe(III) salts is one of the most effective and popular strategies for removing As(V) from water. Specifically, a combination of iron (oxy)(hydr)oxide coprecipitation using Fe(III) chloride followed by microfiltration can reduce As(V) concentrations in water from 40 to less than 2 μg L −1 (Shih, 2005, 93-94, Table 7.1;Ghurye, Clifford and Tripp, 2004).…”