Volume 44 Number 6
World Spotlight: A European Approach to Arsenic -- The Globe’s Largest Municipal Reduction Program Under Way in the U.K.
As a naturally occurring chemical found in the Earth’s crust, arsenic (As) is released into drinking water supplies when rocks, minerals and soil erode. Historically, arsenic has been used in metallic form to create alloys (i.e., different metal mixtures) with lead and copper. Plus, arsenic compounds can be used in and to manufacture a range of products such as glass, wood preservatives, metal plating and electronics. Lastly, it’s present as an impurity in coal and oil-based products such as gas, diesel fuel and motor oil. Industrial use of arsenic has declined and its use in agricultural and household pesticides in the United Kingdom is no longer approved.
Arsenic in the UK
Typically, about 10 percent of total arsenic at a water utility is removed from the final effluent before discharge. The largest contributor of arsenic to sewage -- about 40 percent -- is dust and ash washed into street drains from roads and pavement. The total weight of arsenic discharged from houses and businesses in wastewater is about 20 percent of the total. About 30 percent comes from businesses discharging effluent to sewers from processes such as timber treatment using arsenic containing wood preservatives.
The most common forms of arsenic found in drinking water supplies are trivalent arsenite (As III) and pentavalent arsenate (As V). Drinking water contaminated with either form of arsenic is the most common medium for human exposure to this dangerous chemical. Studies have linked long-term exposure to arsenic contamination with cancer of the bladder, lungs, skin, kidney, nasal passages, liver and prostate. Non-cancerous effects of arsenic contamination include cardiovascular, pulmonary, immunological, neurological and endocrine effects.
Since 1958, the World Health Organization (WHO) has been involved in offering guidelines for setting drinking water standards. During that initial year, the WHO put forth the International Standards for Drinking Water establishing 200 micrograms per liter (mg/L) as an allowable concentration for arsenic levels. Having re-evaluated the standard in 1963 and reducing the allowable concentration to 50 mg/L in 1984, the WHO settled on a final provisional guideline of 10 mg/L in 1993. During a revision to the European Union (EU) Drinking Water Directive in 1998, the WHO provisional guideline was accepted by the EU. The 10 mg/L maximum contaminant level will become a statutory requirement in the United Kingdom on Dec. 25, 2003.
The largest independent water company in the UK, with headquarters in Birmingham, England, is responsible for supplying 8 million customers with drinking water, primarily in the central area of England. By the end of summer 2003, months before the deadline, it will have undertaken the largest municipal arsenic removal program in the world.
Meeting the demands
A variety of processes were studied to remove As from water including ion exchange, coagulation/filtration, reverse osmosis and various adsorbents. The best separation mechanism for As removal was determined to be irreversible adsorption onto a solid metal oxide that has a high As adsorption capacity. The media, a granular ferric oxide (GFO), was developed by Bayer AG specifically for groundwater source drinking water adsorption. When placed into a specially designed arsenic removal system, the media adsorbs As onto a solid granular media. With a high capacity for As, the media is long-lasting and can be disposed of in a non-hazardous landfill when it becomes exhausted. Plus, the exhausted media is in a solid waste form that requires no processing prior to disposal. Another advantage of this process is the small amount -- approximately 0.1 percent of treated water -- of residuals, or wastewater, generated in the process.
Capital and operating costs for this particular arsenic removal system are low, with the average processing costs at 10-25 cents per thousand gallons of water treated, depending upon system size and influent water As levels. The process, which will remove As to less than 4 mg/L, is simple to operate and can be remotely monitored along with well pump and disinfection operation. Very little operator intervention is required.
Putting it to work
About the authors