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A Novel Adsorption Technology for Small-Scale Treatment of ArsenicEPA Grant Number: R831513
Title: A Novel Adsorption Technology for Small-Scale Treatment of Arsenic
Investigators: Assaf-Anid, Nada M. , Duby, Paul F.
Institution: Columbia University in the City of New York
EPA Project Officer: Richards, April
Project Period: December 15, 2003 through December 14, 2004 (Extended to April 30, 2006)
Project Amount: $49,794
RFA: Technology for a Sustainable Environment (2003) RFA Text | Recipients Lists
Research Category: Sustainability , Pollution Prevention/Sustainable Development
Surface modified activated carbons hold promise as effective sorbents in arsenic removal systems because they can be tailored to simultaneously remove inorganic and organic arsenic species as well as natural organic matter (NOM). This project aims at exploring the feasibility of novel iron-impregnated granular activated carbon materials for the treatment of both inorganic and organic arsenic by adsorption. The proposed technology will use fixed beds, a configuration that is well suited for small drinking water systems and for central use in homes or at the tap.
The Rapid Small-Scale Column Test (RSSCT) methodology, which has been proven to adequately simulate full-scale adsorbers, will be employed. Most importantly, the measured breakthrough curves in the RSSCT will be identical to those in the desired scaled-up systems (i.e., identical number of bed volumes at breakthrough), and they will reflect possible adsorption, complexation, redox, cooperative, and competitive interactions that can occur in those systems. The column breakthrough effluent concentration Ceffluent,b will be equal to the allowable concentration of 10 ppb total As. Over 90% removal levels were achieved in preliminary field and laboratory tests with mixed media including carbon and ferric hydroxide. Along with arsenic removal, removal of NOM is important because it can compete with arsenic for adsorption sites, form complexes with arsenic species in solution (through cation bridging), and cause leakage from a fixed bed. Although NOM is ubiquitous in all types of waters at concentrations ranging from 1 to 50 mg/L, its effect on arsenic adsorption is not fully understood. This project will study arsenic adsorption in NOM-containing water originating from geographically diverse ground water isolates, characterized for organic matter content and nature (acidity, molecular weight distribution, hydrophobicity),and spiked with a mixture of arsenic (III), (V), and monomethylarsonic acid (MMA). The influence of sulfate, pH, and calcium, on arsenic displacement and desorption will also be studied to evaluate sorbent selectivity. The insight gained from the proposed research will be important in risk predictions and performance considerations of this and other arsenic adsorption technologies.
Specific advantages of the proposed process include the design of a fixed bed adsorber that: 1) can reduce arsenic levels to below 10 ppb while reducing NOM; 2) can easily be scaled-up and rendered commercially viable; 3) contains a sorbent that exhibits good mechanical stability; 4) does not require feed water pre-oxidation because the sorbent will remove As(III), As(V) and organic arsenic; 5) does not require a sulfate source or anaerobic conditions; and 6) is expected to absorb variations in water chemistry and shock concentrations leading to arsenic toxicity peaks. The proposed system is expected to provide low capital and operating cost, to require minimal monitoring and maintenance, and to reduce waste generation. As with other fixed bed systems, process scale can be adjusted to usage rate. The capital cost of the proposed system (based on cost of sorbent) should be at least an order of magnitude lower than that of processes based on ion-exchange and iron-impregnated ion exchange resins. A more detailed cost estimate will be possible at the conclusion of this research, when carbon usage rates can be computed from fixed-bed breakthrough profiles.