AWWA WQTC58830

Research was done to evaluate the use of reverse osmosis water treatment technology to removearsenic from groundwater supplies for small communities in North Dakota. Point-of-use reverseosmosis (POU-RO) technology was evaluated. Twenty-one POU-RO units were installed inhomes and other buildings in Oakes, North Dakota for a pilot test. After installation, the unitswere monitored for arsenic removal for two years. In addition to evaluating arsenic removal,questions about the management, maintenance, monitoring, and cost of treatment were addressedby this research.The City of Oakes is a predominantly residential community located in southeast North Dakota.The city has a population of about 1,760. Oakes drinking water is supplied by three wellssituated in different parts of the city. Typical arsenic concentrations in raw water pumped fromthese wells range from 10 to 21 ppb. The water delivered to residences in Oakes is notdisinfected or treated in any way.Arsenic removal was evaluated by periodically collecting and analyzing samples of treated water(i.e., permeate) and untreated water from each of the units installed for the pilot test. A total of105 permeate samples and 115 untreated water samples were collected and analyzed over thetwo- year test period. The arsenic concentrations in the untreated drinking water ranged from 6to 40 ppb and the average arsenic concentration was 13.5 ppb. With one exception, the arsenicconcentrations in the permeate samples ranged from 0 to 4 ppb and the average arsenicconcentration was 0.25 ppb.Even though most of the permeate samples collected during the test period contained nomeasurable amounts of arsenic, a few of the units did exhibit signs of reduced membraneperformance over the course of the monitoring period. Reduced membrane performance wasindicated by a gradual increase in the conductivity of the permeate over time. However, evenwhen permeate conductivity exceeded one half of the untreated water conductivity, the unit stillproduced substantial arsenic removal.Although reverse osmosis was believed to be the main removal mechanism for arsenic, it maynot have been the only significant mechanism. The POU-RO units also contained two activatedcarbon cartridges. Since these were both carbon block cartridges, they also serve as filters.When the prefilters were changed after one year of service, it was observed that they were coatedwith iron. It is possible that adsorption of arsenic onto the iron may have been an additionalremoval mechanism. Includes 9 references, table, figures.

Product Details

Edition:

Vol. - No.

Published:

11/02/2003

Number of Pages:

18

File Size:

1 file , 510 KB