Arsenic Overview Series - Part 2

Aug. 2, 2019

Current Solutions and Practices

Current Solutions and Practices

Current Solutions and Practices

EPA has indicated that the original compliance date of June 22, 2006, will be maintained, giving utilities up to five years to meet the final standard.

Consumers unwilling to drink arsenic contaminated water are demanding a more rapid implementation. Publicly owned utilities, however, will be held hostage from implementing a more rapid solution due to government approval cycles, annual budgets, required biding processes and slow implementation schedules. As a result, in-home treatment systems, which immediately can be installed, are a very popular treatment option for individual homeowners. Other advantages such as low implementation/operating costs and improved flexibility make the POU/POE approach option appealing.

For small communities with centrally treated water, the POU approach, also is growing in appeal. EPA’s most recent task force on implementation costs now estimates that for small communities with less than 5,000 homes, the POU option may be the most affordable approach. Disadvantages for the POU approach in compliance situations include unawareness of certain source water conditions, proper access into the home for installation and maintenance, effective performance monitoring, compliance sampling, and proper record keeping of compliance testing and certification.

For communities larger than this, centrally treated water remains the most economical approach.

POU/POE Treatment options

The top two POU/POE treatment technologies recognized by the industry are adsorption and reverse osmosis. The table below highlights the advantages and challenges faced by each technology.

Submit POU/POE Treatment Options

Treatment Technology

Technology Description

Advantages

Challenges

Adsorption

Filtration media that chemically binds the arsenic to the adsorbent.

Media types include:

· Activated Alumina

· Mixed Metal Oxides

· Granular Ferric Hydroxide

(See Glossary)

· No wasted water

· Removal of both As (III) and (V)

· Removal of other heavy metals such as flouride, copper, etc.

· Safe handling and disposal.

· Spent media meets EPA TCLP

· Low cost option

· No chemicals or regeneration required

· Requires certain contact time for optimal effectiveness

· Competing ions in water can reduce capacity

· Performance decreases with higher pH

Reverse Osmosis

Water is forced under pressure against a semipermeable membrane creating a barrier between the clean water and the contaminants of concern.



(See Glossary)

· Effectively reduces arsenic (V)

· Provides high quality drinking water, removing other dissolved contaminants

· Improves taste/odor, aesthetics

· Arsenic (V) removal efficiency

· Not effective for As (III) without preoxidation

· High cost if arsenic is primary target contaminant

· Not suitable for POE systems due to corrosion and affordability

· Requires proper attention and routine maintenance

· Wastes 3-5 gallons of water for every treated gallon

Immediate protection from contaminated water. An abundance of water treatment professionals are available to assist in selecting an appropriate system to meet specific treatment and maintenance needs.

Simple maintenance, usually performed by the homeowner through cartridge replacement. Waste disposal of adsorption technologies are non hazardous and can be disposed with household waste

Lower cost. At $0.10 to $0.20/gal., POU treated water is more than 50 percent less than the cost of bottled water, which ranges from $0.75 to $2/gal. Initial capital costs range between $250-500. Annual operating and maintenance costs will average $30-50. Annual costs are minimized because only the water needed for consumption is treated.

Customized flexibility. POU systems can be custom designed, allowing the consumer the opportunity to address a range of concerns based on budget and preferences. It also creates flexibility to cost effectively upgrade the system should new cartridge-based improvements be commercialized. The customer has the choice to decide which aspects of his water are most important to him and focus a solution towards improving the quality of his drinking water based on his needs and budget.

What level of arsenic is in the water? This factor will help determine the effectiveness of the system as well as the level of required maintenance.

What form of arsenic is in my water? Arsenic comes in both a pentavalent (AsV) and a trivalent (As III) state. Arsenic (III) is the harder to remove and more hazardous of the two. Not all treatment systems can remove both forms of arsenic and convert it to As (V) through oxidation with chemicals such as chlorine, potassium permanganate or ferric chloride, which can be dangerous to humans.

What is the water profile? Several characteristics of the water such as pH silicate level and temperature can effect the performance of a treatment system being considered, which may also make a pretreatment system necessary. This question is important for a small community system interested in using a POU solution for compliance.

How much water will be treated? Do I want to treat all of the water in my household or just my drinking water? This decision greatly will impact the cost of the treatment system. EPA data indicates that arsenic only is dangerous when ingested through consumption.

What type of waste is generated by the treatment system? Is there water waste? Is a hazardous material generated? Is disposal of the waste a problem?

How do I test for arsenic? There are several field test kit systems that can be used to determine the level of total arsenic present in the water. The use of these tests kits can help determine the level of treatment needed and ensure proper function of the treatment system once installed.

Treatment options for central treatment systems

For communities serving greater than 5,000 homes, central treatment has been identified as the most cost effective approach. Typical central treatment technologies used for arsenic reduction include coagulation/filtration, lime softening and ion exchange.

Submit Central Treatment System Options

Treatment Technology

Description

Advantages

Challenges

Coagulation / Filtration

Coagulants added to the influent water change the surface properties of suspended solids to allow agglomeration of particles into a flocculated precipitate that is filtered out.



(See Glossary)

· Easy modification of existing system can be performed to increase arsenic removal

· 95% removal of As (V)

· Not effective for As (III) without preoxidation

· Performance decreases with higher and lower pH

· Arsenic contaminated coagulation sludge may present a disposal issue

· Requires well-trained operators

Lime Softening

Cold Lime-softening: The process wherein lime is added to cold water, usually along with a small amount of coagulant and the reaction causes bicarbonate alkalinity to precipitate as calcium carbonate. Process used mainly in municipal systems for partial hardness reduction. See also Cold Lime-Soda Softening.



(See Glossary)

About the Author

Sherry Odom

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