Arsenic

We recently had a case in Barry County with high arsenic concentration 10 ppm and a non-optimal pH of 7.5. We decided the best approach was to shift away from standard Activated Alumina and use an alternative on the activity series of metals that thrives in the neutral pH range.

Our top choice for effective arsenic removal for 500 gpd at pH Target 7.5, listed from the easiest to implement to the most complex.

1. Best Adsorption Alternative: Iron-Based Media

The most common and effective alternative for pH 7.5 water is an adsorbent based on iron oxides, as they maintain a strong positive surface charge (and therefore high capacity) up to pH 8.0 and higher.

Technology

Description Performance at pH 7.5

Granular Ferric Oxide (GFO) Granular Ferric Hydroxide (GFH) A highly porous, amorphous iron oxide media (e.g., Bayoxide, Ferrolox). This is the gold standard replacement for Activated Alumina in pH-neutral applications. Excellent. Capacity remains very high at pH 7.5. Iron oxides strongly attract the negatively charged arsenic ions at this pH.

Arsenic-Selective Media / IEAA

Specialized hybrid media, often involving iron or titanium oxide coatings on alumina or polymer beads e.g., ResinTech ASM-10-HP, Ad Edge AD-33. Excellent. These products are specifically engineered to have a high capacity across the entire potable water pH range pH 6 - 9), making them ideal for pH 7.5.

On lesser concentrations we've used Standard Activated Alumina, however its capacity drops severely at pH > 6.5 because its surface charge becomes too neutral. Whereas I Iron-based adsorbents have a different surface chemistry that keeps them highly effective at 7.5.

2. High-Capacity Solution: Reverse Osmosis (RO)

For extremely high concentrations like 10 ppm 10,000 ppb, Reverse Osmosis is one of the most reliable methods, as it physically separates contaminants.

Technology

Description Performance at pH 7.5

Reverse Osmosis (RO) A membrane process that uses high pressure to push water through a semi-permeable membrane, rejecting dissolved solids, including arsenic. Excellent. RO is highly effective (typically >95% removal) regardless of pH. It removes arsenic along with other salts and minerals.

Note: For 500 gpd and high concentrations, you would need a small commercial or industrial RO system, not a typical residential unit.

3. Large-Scale Chemical Solution: Coagulation/Filtration

This process is highly effective for high-volume, high-concentration water but is more complex than simple adsorption columns.

Technology

Description Performance at

pH 7.5

Enhanced Coagulation/Filtration Iron or aluminum salts (coagulants) are added to the water, where they react to form an insoluble precipitate floc that binds to the arsenic. The floc is then removed by settling and filtration.

Good. Iron coagulants ferric sulfate or ferric chloride work well in the pH range of 6.5 - 8.5. The pH 7.5 is effective.