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The Devastating Effects Of Arsenic Poisoning And How To Remove The Threat

• 21.05.2020
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August 19, 2019

Source: Magna Imperio Systems Corporation

By Hrushikesh Joshi and Amanda Yoshino, Magna Imperio Systems Corp.

Arsenic (As) is a naturally occurring element that can be found at elevated concentrations in groundwater aquifers beneath Argentina, Bangladesh, Chile, China, India, Mexico, and the United States, per a 2018 World Health Organization (WHO) report (WHO, 2018). WHO estimates that at least 140 million people in 50 countries have been exposed to drinking water containing arsenic concentrations above the WHO recommended safe limit and U.S. Environmental Protection Agency (EPA) Maximum Contaminant Level (MCL) of 10 micrograms per liter (μg/L) (MassDEP, 2019). Above this limit, arsenic can cause significant health problems, including nausea, vomiting, diarrhea, skin disorders, endocrine disruption, decreased production of red and white blood cells, multiple types of cancer, cardiovascular issues, and neurological effects (Murphy et al., 1981; Federal Register, 2001; MassDEP, 2019).

Unfortunately, arsenic has no smell, taste, or color when dissolved in water – even in high concentrations – so laboratory analysis is required to detect its presence and concentration. One of the most damaging outcomes of this occurred in the 1970s, when arsenic-laden groundwater wells were installed in Bangladesh, leading to extensive poisoning of Bangladeshi people through ingestion and exposure to the contaminated well water (Smith A.H., et. al., 2000; Rammelt C., Boes J., 2004). While treatment methods currently exist to remove arsenic from drinking water, they often require the use of harsh chemicals, yield relatively low water recovery, or are energy intensive processes.

How Can Arsenic Be Removed?

Potential sources of arsenic contamination include, but are not limited to, leaching from geological deposits, wood preservatives, pesticides, liquid waste streams coming from industrial deposits, petroleum production, semiconductor manufacturing, and coal power plants.

Arsenic typically occurs in two forms: oxidized As⁵⁺ or reduced As³⁺, as shown in the arsenic oxidation half reaction:

At neutral pH and electrical potential, arsenite (As³⁺) is difficult to remove, as it can form uncharged arsenious acid (H₃AsO₃), as depicted in Figure 1. Arsenate (As⁵⁺) (anionic forms including H₂AsO₄^- and HAsO₄^2-) is easier to remove through ion exchange treatment methods, as it tends to remain ionized over a wide range of pH in oxidizing environments. Whereas As³⁺ is typically found in anaerobic groundwater, arsenate is most commonly present in surface waters due to oxidative conditions (WHO, 2011). In water treatment, As³⁺ is often oxidized to As⁵⁺ with the help of chlorine, hydrogen peroxide, or ozone prior to treatment.

Fig. 1 Pourbaix Diagram for arsenic. The As⁵⁺ form is more commonly present in oxidizing conditions, whereas As³⁺ is more likely to be found in reducing environments (WHO, 2011).

Treatment methods employed for arsenic removal include media – iron oxides/hydroxides, iron-based specialty media impregnated or coated with iron oxide/hydroxides, activated alumina media, ion exchange resins; membranes – reverse osmosis, electrodialysis; and distillation technologies. Common treatment methods and their respective drawbacks are summarized in Table 1.

Table 1. Summary of common treatment methods for arsenic (Water Quality Association, 2013).

An Electrochemical Solution to Arsenic Removal

Whereas existing arsenic removal technologies can require significant chemical usage or are limited to less than 90% water recovery, a typical END® system can achieve 95-98% water recovery with minimal chemical consumption. In a case study conducted for a customer wanting to decrease arsenic concentrations from 95 μg/L to less than 10 μg/L, the END® system demonstrated 98% removal of arsenic while simultaneously removing TDS and heavy metals, such as antimony, and contaminants of concern, such as fluoride, to below their respective drinking water MCLs. Removal for each constituent is shown in Figure 2. This system achieved 98% arsenic removal and 72% removal of TDS, with an SEC much lower than traditional technologies.

Fig. 2 Case study from customer with target TDS values for arsenic, antimony, and fluoride. Arsenic decreased from 95μg/L to 2μg/L.

The END® system overcomes many of the pitfalls associated with arsenic removal, including the use of harsh chemicals to regenerate media, low water recovery associated with pressure-driven membrane processes, and high energy consumption associated with distillation. The END® system operates continuously without the need for regeneration, yielding higher recoveries of 95%-98% compared to RO and removal of arsenic at a neutral pH. The energy consumption of the END® system is roughly one tenth that of traditional distillation methods. Finally, as an electrochemical process rather than media-based, END® does not require regeneration with strong base addition and acid neutralization, as required in ion exchange processes and other granular media processes.

References

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3. Massachusetts Department of Environmental Protection (MassDEP) (2019). “Arsenic in Private Well Water FAQs”, retrieved from https://www.mass.gov/service-details/arsenic-in-private-well-water-faqs
4. Murphy MJ, Lyon LW, Taylor JW (1981). Subacute arsenic neuropathy: clinical and electrophysiological observations. Journal of Neurology, Neurosurgery and Psychiatry, 44:896–900.
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