The arsenic standard for US public drinking water has dropped from 50 µg/L in 1975 to 10 µg/L in 2001 and, for New Hampshire utilities, to 5 µg/L last year. An estimated 30% of all bedrock wells in New Hampshire contain arsenic above the new standard.
The Process
Removing arsenic from well water requires filtration, and the solution for public water suppliers can vary. The four filtration options include:
- Oxidation and conventional gravity or pressure filtration when combined with iron either naturally occurring or added
- Iron- or titanium-based adsorption media which is replaced when exhausted
- Anion exchange media which often requires pre-oxidation and is regenerated regularly with a brine solution backwash
- Membrane filtration
All filter systems generate a waste product whether it’s spent media for off-site disposal or a liquid waste stream containing the contaminants removed (typically discharged to a wastewater treatment facility). Arsenic often is not the only contaminant to be removed, so the approach to filtration could involve multiple unit processes. Although PFAS, for example, is another anion that can potentially be removed with arsenic in the same process.
Once Arsenic is Isolated
After removing arsenic from drinking water, there is no economical means to recover it and put it to use. This is unfortunate, since arsenic is a critical manufacturing ingredient for semiconductors, solar cells, optical materials and certain biomedical applications. (China provides about 90% of the arsenic used in the US, so a domestic source would help.)
Arsenic is famous not only for its benefits, but also for its history. From the time of the Roman Empire to the Renaissance, arsenic was the poison of choice. There are indications it may have been used even earlier, but records are conflicting. Its reputation was perhaps improved in 1910 when Paul Ehrlich, the father of modern-day pharmacology, developed arsphenamine – an arsenic-based drug highly effective in treating syphilis which was wide-spread and incurable at the time. (Penicillin replaced it in the 1940s.) In addition to its important history in medicine, arsenic has a physical beauty: The next time you enjoy fireworks, think of the arsenic adding the blue color to the pyrotechnics.
How We can Help
Hoyle Tanner is assisting several New Hampshire water utilities to determine the most reliable, lowest cost solution for meeting the arsenic Maximum Contaminant Levels (MCLs). One system we’ve worked with was able to lower the arsenic by modifying their wellfield operation and compliance sampling protocol. For another system, we are investigating how to improve the performance of their existing filter system to achieve better results. Consideration of these options, along with others that have included outside water purchases and participation in regional water supply approaches, will depend on the specific aspects of each water system.
Of all the services provided by towns, cities and public and investor-owned utilities, drinking water is arguably the most critical. We drink it and are concerned with its quality and health effects. We rely on it for fire protection. Public confidence in and reliability of our drinking water systems are primary goals of public and private water suppliers across the US. Hoyle Tanner places the highest priority on helping our clients meet those goals. Reach out to me if your community needs expert engineers to improve water quality.
