Arsenic is among the most well-known, most feared drinking-water contaminants, and for a good reason. If consumed, it can cause several severe symptoms and, in extreme cases, even death. But before we get into a detailed conversation about the adverse effects it can have on the human body, let's discuss how it reaches our source water in the first place.
How does arsenic reach source water and contaminate it?
Arsenic occurs naturally in rocks and soil before being released into groundwater supplies. Inorganic arsenic compounds, such as those found in groundwater, are highly toxic. Industrial practices also have the potential for releasing arsenic into the environment. A byproduct of the industrial treatment process, arsenic is discharged into the groundwater during the production of paints and dyes, metals, soaps, drugs and wood preservatives. It can also be traced to deep-water brines produced from gas and oil well drilling.
Why is it challenging to remove arsenic from drinking water supplies?
Arsenic is highly soluble and has negative health consequences at low levels. The levels of arsenic are an order of magnitude lower than most other elements found in water, which means you need a solution that is highly selective to overcome any interferences from other salts.
What health threats does arsenic pose if consumed?
The International Agency for Research on Cancer (IARC) has classified arsenic and arsenic compounds as carcinogenic to humans. These effects can be quickly realized in high concentrations, but more than likely the effects are observed over chronic exposure at low levels. The World Health Organization recommends a level under 10 ppb in water to avoid these chronic health effects.
The immediate symptoms of acute arsenic poisoning include vomiting, abdominal pain and diarrhea. These are followed by numbness and tingling of the extremities, muscle cramping and, in extreme cases, death.
Long-term effects of ingestion of inorganic arsenic include developmental effects, neurotoxicity, diabetes, pulmonary disease and cardiovascular disease. Arsenic may also increase the risk of heart attacks in adults, as well as be associated with adverse pregnancy outcomes and infant mortality. There is some evidence of adverse effects on cognitive development.
How is arsenic removed from drinking water?
There are various options available for removing arsenic from drinking water. These methods range from ion exchange, activated alumina and reverse osmosis to coagulation/filtration and iron based adsorption. Of these methods, iron based adsorption seems to be particularly effective.
Adsorption is a continuous process where water flows through a vessel filled with an iron based adsorptive media. This media is able to bind arsenic and remove it from the water to safe levels.
What makes adsorption an ideal technology?
Adsorption is a simple, passive process with a relatively low cost. Very little operator interference is needed which is a key benefit for utilities without centralized treatment plants. Periodic backwashing is required, but the backwash frequency and water volume are much lower than other technologies such as coagulation/filtration. Compared to other similar processes using media filtration, like ion exchange or activated alumina, the iron based adsorptive media life is significantly longer which results in lower OPEX costs. Most importantly, arsenic is reliably removed to safe levels.
How does the SORB 33® process work? What types of media are involved?
The De Nora SORB 33® arsenic removal system is a fixed-bed adsorption system that uses a granular ferric oxide media, for the adsorption of dissolved arsenic. The system employs a simple “pump and treat” process that flows pressurized well or spring water through a fixed-bed pressure vessel containing the media where the arsenic removal occurs. Both arsenite (arsenic III) and arsenate (arsenic V) oxyanions are removed from water via a combination of oxidation, adsorption, occlusion (adhesion), or solid-solution formation by reaction with ferric oxide ions. The media used is disposed of as non-hazardous waste, and De Nora aftermarket services help you in determining changeout frequency and disposal requirements.
Source: Sean Kennedy, De Nora Water Technologies
What Can We Do to Prevent the Consumption of Arsenic?
Staying informed is the first step to preventing arsenic consumption via water sources. We offer a FREE guide on arsenic removal that discusses a couple of removal/treatment methods. Click below for more information.