Arsenic Removal from Drinking Water by Adsorptive Media. U.S. EPA Demonstration Project at South Truckee Meadows General Improvement District (STMGID), NV. Final Performance Evaluation Report

摘要

This report documents the activities performed during and the results obtained from the operation of an arsenic and antimony removal technology demonstrated at the South Truckee Meadows General Improvement District (STMGID) in Washoe County, NV. The objectives of the project were to evaluate (1) the effectiveness of a Siemens granular ferric hydroxide (GFH) adsorptive media system in removing arsenic and antimony to meet the respective maximum contaminant levels (MCLs) of 10 and 6 ig/L, (2) the reliability of the treatment system, (3) the required system operation and maintenance (O&M) and operators skills, and 4) the capital and O&M cost of the technology. The project also characterizes the water in the distribution system and process residuals produced by the treatment system. The GFH system was a fixed-bed adsorption system that used GFH, an iron-based media, to adsorb dissolved arsenic and antimony in drinking water supplies. When the media reached its adsorption capacity, it was removed from the vessels and replaced with new media. Spent media was disposed of at a sanitary landfill after passing the Toxicity Characteristic Leaching Procedure (TCLP) test. GFH was produced by GEH Wasserchemie Gmbh and marketed by Siemens under an exclusive agreement. Designed to treat up to 350 gal/min (gpm) of water, the GFH system at the STMGID site consisted of three 66-in diameter, 72-in tall vertical carbon steel pressure vessels configured in parallel. Based on the total media volume of 240 ft3, the empty bed contact time (EBCT) in each vessel (and the entire system) was 5.1 min and the hydraulic loading rate was 4.9 gpm/ft2. During Run 1 extending from September 27, 2005 through May 3, 2006, the GFH system operated for a total of 943 hr. After it began normal daily operation on November 18, 2005, the system operated an average of 3.8 hr/day. The average flowrate during the 32-week study period was 275 gpm, which was 21% lower than the design flowrate. The lower average flowrate resulted in a higher average EBCT, i.e., 6.5 min. The system experienced little pressure buildup during operation. Major operational difficulties involved the system control and data acquisition (SCADA) and programmable logic controller (PLC) interface and a mechanical problem with the pneumatic butterfly valves for the backwash discharge line. Otherwise the system was relatively simple to operate, requiring little attention from the operator. The daily demand on the operator was typically 30 min for routine activities, including visual inspection of the system and recording of operational parameters.