Final Report: Treatment of Arsenic in Small Drinking Water Systems Using Self-Assembled Monolayers on Mesoporous Supports, A High-Capacity Selective SorbentEPA Contract Number: 68D02092
Title: Treatment of Arsenic in Small Drinking Water Systems Using Self-Assembled Monolayers on Mesoporous Supports, A High-Capacity Selective Sorbent
Investigators: Usinowicz, Paul J.
Small Business: HydroPure Technologies LLC
EPA Contact: Richards, April
Project Period: October 1, 2002 through July 31, 2003
Project Amount: $99,970
RFA: Small Business Innovation Research (SBIR) - Phase I (2002) RFA Text | Recipients Lists
Research Category: Water and Watersheds , SBIR - Water and Wastewater , Small Business Innovation Research (SBIR)
HydroPure Technologies, L.L.C. (HPT), worked with Battelle Pacific Northwest Division to develop and test self-assembled monolayers on mesoporous supports (SAMMS) for removal of arsenic from potable water sources. SAMMS exhibits highly specific adsorption of oxometallate anions, and testing was performed to demonstrate the ability of SAMMS to effectively remove arsenic, which is present as either arsenite (As(III)) or arsenate (As(V)) in natural waters, from a test groundwater matrix. This project focused on optimizing the fundamental interfacial binding chemistry of these nanoporous hybrid materials to help develop superior arsenic sorbent materials.
The technical challenges for arsenic (As) removal are several-fold: (1) meet the U.S. Environmental Protection Agency's (EPA) new standard for a lower As concentration of 10 µg/L, (2) effectively and efficiently treat the newly included water supply systems (those with < 30 µg/L), and (3) provide a technology that can be readily installed as point-of-entry (POE) or point-of-use (POU) systems. An additional challenge for As treatment is removal of the As reduced form, As(III). As(III) generally requires oxidation to As(V) and subsequent removal by precipitation or sorption technologies. The ability to concurrently remove As(III) on a sorbent or precipitant is an attractive feature of a treatment technology.
Two forms of SAMMS were tested in laboratory kinetic and equilibrium experiments. A copper/ethylenediamine SAMMS (Cu-EDA SAMMS) was tested for As(V) removal from a low-level concentration groundwater matrix. A multifunctional SAMMS, incorporating chromate with the copper/ethylenediamine functionalization (Cu-EDA-CrO4 SAMMS) was tested for removal of As(III). Several sets of kinetic testing were performed to confirm As(V) removal in a low As concentration groundwater matrix and to determine the removal rates for As(III) by the multifunctional Cu-EDA-CrO4 SAMMS. Comparative kinetic testing of SAMMS versus several commercially available sorbents also was performed.
Preliminary engineering for developing conceptual POU/POE SAMMS systems for small drinking water applications was part of the research effort. The engineering evaluations included the configuration of a POU/POE unit, the ability to retrofit SAMMS to existing commercial units, the need for separate As(V) and As(III) units, and the operability of the POU/POE unit. In addition, a business model was developed and a commercialization evaluation was performed, independently and with input from Foresight Science and Technology.
Phase I project results have shown that Cu-EDA SAMMS can effectively remove As(V) from natural waters to produce potable water, meeting the new EPA drinking water standards. Testing with Cu-EDA-CrO4 SAMMS demonstrated that the multifunctional form of SAMMS can remove As(III) as well. The kinetics of As removal by SAMMS are highly favorable and it has been shown in preliminary testing to be more rapid than competing commercial sorbents. The testing also supported earlier research findings that the pore size of SAMMS needs to be > 50 Å to minimize molecular diffusion resistance. Capacities of SAMMS also are competitive with other sorbents. The major issues for the multifunctional form are in determining the proportion of functionalization for oxidation of the As(III) and the removal of the As(V).
The Phase I project identified application needs, specifically the development of the engineered form /engineered unit operation for POU/POE applications. At present, SAMMS is most readily available in small particle sizes, and these can be used in supported form or in combined systems, such as a carbon block. The MCM-41 substrate used in most of the Phase I testing has production limitations for larger particle size. Alternative substrates have been identified that are easier to produce and can be produced in "granular" form (e.g., 20/30 mesh U.S. Standard Sieve size). The larger particle evaluation will be pursued in Phase II, because such a particle can be readily implemented in POU/POE unit operations, and will have attractive hydraulic performance properties, vis-à-vis the powdered SAMMS.
SAMMS has good commercialization potential because of its fast kinetics and favorable capacities. SAMMS has the potential for direct retrofit into existing POU/POE unit operations, basically replacing sorption media. The ability of SAMMS to concurrently treat As(III) and As(V) also is advantageous, and, although there were limiting factors for the overall removal of As(III)—principally pore size of the substrate that limited kinetics—there are readily implemented improvements to overcome these limitations. Preliminary testing also has shown that the spent SAMMS can be disposed as non-hazardous waste, because the sorption of As species results in a stable end product.
The development needs have been identified to: (1) improve overall sorption performance of SAMMS, (2) provide effective concurrent As(III) and As(V) removal by SAMMS, (3) more efficiently and economically produce SAMMS, and (4) provide SAMMS-based engineered unit operations for As POU/POE units. The objective is to maximize capacities and kinetics of SAMMS for removal of As species, decrease SAMMS production costs, and provide a highly competitive POU/POE unit for producing drinking water that meets the As standard.
SAMMS technology offers a simple, single-unit process for the removal of As(III) and As(V) from potable water sources. The SAMMS process can be used for POE or POU installations, and also is applicable to larger installations. The benefits of rapid kinetics, good capacities, and simplicity of operations provide attractiveness for commercial implementation of the SAMMS technology. The potential for retrofit of existing commercial equipment offerings also is attractive from the commercial perspective.
With the appropriate functionalization, SAMMS has been shown to effectively remove As(V), and concurrently, As(III). The demonstrated performance of SAMMS from Phase I testing and the advantages of a flexible single unit for achieving required water quality provide an attractive technology for As POU/POE treatment units. The identification of readily implemented improvements that will enhance the performance and cost competitiveness of SAMMS is key to improving SAMMS’ cost competitiveness. Those improvements include faster and less labor-intensive functionalization using supercritical fluids, alternate backbone substrate materials, and incorporation of alternative functionalizations into the SAMMS product, which will be tested in the Phase II work.
SAMMS has good market penetration potential for POE and/or POU customers. The ability to compete in U.S. and foreign markets, and the ability to be incorporated into larger treatment systems presents an attractive investment and alternative technology to meet the needs for treating waters with As contamination.