Arsenic Removal Technologies Pros And Cons

Arsenic is one of the most pervasive water contaminants in the U.S. According to the Water Quality Research Foundation (WQRF), there are nearly 15,000 community water systems with median arsenic levels above the U.S. EPA maximum contaminant level (MCL) of 10 ppb. 

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The technologies needed to remove arsenic are well understood and most water treatment plants (WTPs) have little trouble keeping concentrations under the MCL. Even smaller water treatment systems, such as community wells, or those serving RV parks, schools, or other decentralized systems, find that there are many options available that can help remove arsenic from source water. This includes reverse osmosis (RO) systems, membrane filters, and binary mixed metal cartridges.

The real challenge is finding the right technology that fits the needs, knowledge level, and budget of the water management organization. This article examines the advantages and disadvantages of three prominent arsenic removal technologies in terms of cost, complexity, and waste considerations.

Pros and Cons of Various Arsenic Removal Technologies

1. ElectroChemical Arsenic Remediation (ECAR)

In ElectroChemical Arsenic Remediation (ECAR), electricity is used to continuously dissolve an iron electrode, forming a type of rust in the water. Arsenic in the water binds to the rust particles, which can then be removed. The rust particles are created electrochemically at the time of use, eliminating the need for a costly supply chain. In addition, electrochemical processes resulting from the use of electricity greatly enhance the arsenic removal capacity (i.e. arsenic removed per unit iron input) relative to the common chemical methods of arsenic removal.

The only inputs required for ECAR treatment are ordinary mild steel plate electrodes and low voltage (< 3 V) electricity. During the ECAR process, trivalent arsenite (As[III]) is oxidized to pentavalent arsenate (As[V]). This is a key reaction, as As[III] does not adsorb as strongly as As[V] to mineral surfaces in natural waters, making it difficult to remove without pre-oxidation to As[V].  Both forms of arsenic are present in appreciable quantities in contaminated groundwater.

ECAR has many advantages over other low-cost arsenic removal methods such as chemical co-precipitation with ferric salts and filtration through activated alumina or granular iron-based adsorbent media. These include:

• ECAR operates at low voltages (< 3V in real groundwater with steel plates spaced 2 cm apart), easing electrical safety issues.
• Power can be supplied using grid, battery, or solar photovoltaic sources.
• The semi-batch process allows for electricity interruptions, and the equipment can be made robust against voltage surges, sags, and spikes.
• Arsenic-remediated water can be pumped and stored into an elevated delivery tank, preventing water supply disruptions during electricity outages.

2. Comparison with Other Methods

Alternative arsenic removal technologies like co-precipitation and filtration often require more complex maintenance and incur higher operational costs. The upfront investment and the costs associated with chemical procurement (such as ferric salts) can make these methods less feasible for smaller water treatment systems.

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In addition, technologies addressing both arsenic and microbial contamination of groundwater are essential in areas where both are prevalent. ECAR efficiently addresses the primary concern of arsenic removal, making it a preferred choice for communities heavily impacted by contaminated groundwater.

Conclusion

The search for effective arsenic removal technologies is critical in ensuring safe drinking water for populations worldwide. While ECAR offers reliable and cost-effective solutions, it's important to consider the specific needs and circumstances of the affected communities. As research and development continue, we may see further advancements that enhance the efficacy and affordability of arsenic removal technologies in the future.

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