ABSTRACT
Development of Contact Systems for Removal of Arsenic
from Drinking Water Using Synthesized Pyrite
The maximum contaminant level for arsenic in drinking water has recently been lowered, resulting in many more water supplies requiring treatment. Many of these systems are small groundwater supplies that have greater needs for simple and reliable treatment methods. Such groundwater systems often have arsenic that exists primarily as arsenite, which usually must be oxidized to arsenate to insure effective removal by most existing treatment methods. Furthermore, most existing treatment methods produce residuals that require additional treatment before they can be disposed and in some cases the residuals are not stable under typical disposal conditions.
An attractive alternative is to remove arsenic from contaminated groundwaters by adsorption onto pyrite, which is a solid consisting of iron and sulfur. This method does not require pre-oxidation and produces residuals that would be stable during typical land disposal. The keys to developing a competitive process for arsenic removal with pyrite are: 1) to develop reliable methods for producing pyrite with high adsorption capacity, 2) to develop an understanding of the process of removal of arsenic on synthesized pyrite and how it is affected by conditions expected in typical groundwater systems, and 3) to develop a simple and reliable method of contacting synthesized pyrite with water that can be applied at small water supplies. The first two requirements will be achieved by a companion project. Therefore the goal of this project will be to develop contacting methods for applying synthesized pyrite in treatment technologies for removal of arsenic from drinking water. Two approaches will be investigated for developing contactor systems. The first will develop a porous macro-sized adsorbent to be applied in packed beds. The second approach will develop methods for continuous production of pyrite and its removal by ultrafiltration/microfiltration membranes.
The work plan for this project will contain four tasks. The
first task includes preliminary work that must be accomplished before
subsequent tasks begin (preparing a project safety plan, demonstrating QA/QC
requirements for analytical procedures, and installing necessary equipment) The second task will focus on developing
porous adsorbents prepared with synthesized pyrite using four different
approaches. These adsorbents will be
made using synthesized pyrite particles of very small size so that they will
have high surface areas and high adsorption capacities. The adsorbents will be characterized in terms
of their ability to remove arsenic from water, their physical strength and
their ability to resist release of arsenic during leaching tests. The third research task will focus on
developing a contacting system based on continuous generation of pyrite and its
removal by membrane filtration. Similar
systems have been used with other adsorbents like activated carbon. Key areas of research will be techniques for
continuously generating pyrite of the desired size, characterization of the
rate of adsorption of arsenic on pyrite, the tendency of the membranes to
become clogged, the ability to clean the membranes, and the ability of the
removed pyrite to resist release of arsenic during leaching tests. The final task will es