Arsenic Removal from Drinking Water at Rose Hill Center, Michigan

ADI Limited

Category: Environment

Arsenic is a relatively common element in groundwater and occurs naturally. Because of the substance’s toxic and carcinogenic nature, the World Health Organization has established a maximum allowable concentration of 10 g/L (micrograms per litre, or parts per billion) in drinking water. In the United States, the Environmental Protection Agency recently revised its rules to limit concentrations to 5 g/L, while in Canada our allowable level is 25 g/L.

Existing technologies for removing arsenic from drinking water all suffer from drawbacks. Coagulation processes, for example, produce a large volume of sludge. Ion exchange media are often affected by high sulphate concentrations. The performance of activated alumina declines significantly with increasing pH or fluoride concentrations. Other treatments are complex and have high costs.

In trying to find a simple, effective and low-cost treatment for this world-wide problem, ADI Limited of Fredericton, New Brunswick realized the greatest potential lay in developing a filtration media for use in a standard pressure filter. They tested 14 different formulations and eventually developed a unique filter media that adsorbs arsenic from drinking water. The filter is known by its registered trademark Media G2.

Media G2 is a patent-pending material consisting of a natural mineral substrate, with an iron-based surface coating that is applied in a proprietary process. The media particles, with a size of 0.3 millimetres, are placed in an ordinary filter vessel. Water flows downward through the filter bed and arsenic bonds to the surface of the particles. The technology is highly effective, typically providing 99% reduction of arsenic.

Rose Hill application

One of the most recent applications of the technology is at the Rose Hill Center, a small, non-profit psychiatric rehabilitation centre in Holly, Michigan. Rose Hill’s drinking water source is groundwater that contains 35-40 g/L. The facility staff had been attempting to lower the concentration with activated carbon filters without success. When they heard of ADI’s Media G2, they sent in samples for tests, and after positive results decided to install a full-scale system.

The Rose Hill plant processes 40,000 litres of water a day, through six 900-mm filter units. The retrofit consisted of replacing the carbon filters in the units with Media G2. An automated pH control system was also installed to maintain the filter inlet pH at 6.7-6.9, a range at which the filter performed at its optimum according to mini-column testing.

Start-up was February 1999. The plant’s operation is simple. Water passes down through the filters at a rate of 11-13 cubic metres an hour, providing a 10-15 minute contact time for the arsenic to react with and bind to the media particles. A staff member at the centre who has no previous water treatment experience easily performs maintenance. He carries out backwashing of the filters, requiring approximately three hours every two or three weeks to prevent compaction of the filter media, and he replenishes the acid feed container as necessary.The project was completed on budget and has been in operation over 18 months. The plant is monitored by the U.S. Environmental Protection Agency and is providing treated water with an arsenic concentration below 5 g/L.

Based on the current rate of water use at Rose Hill, the Media G2 system should last at least three years before it becomes saturated with arsenic. At that point, the centre will have to decide whether the media should be regenerated or replaced. Regeneration involves rinsing it with a 1% sodium hydroxide solution to desorb the arsenic. The used sodium hydroxide solution is then pH adjusted to below pH 7.0 to cause precipitation of a thick ferric arsenate sludge. The sludge and the arsenic-saturated Media G2 can be disposed of in a landfill as non-hazardous waste.

The technology was developed totally in-house by ADI. Recognizing that arsenic in drinking water is a serious health threat, they conducted research over several years in order to find a simple, effective, low-cost treatment. A method has been developed for mass-producing Media G2 at low cost, and the technology has already been used commercially at several locations around the world. Typical capital costs for full-scale plants range from Cdn. $120 to $170 per m3/day plant capacity. The typical operating cost is approximately $0.06 per cubic metre.CCE

Project name: Arsenic Removal from Rehabilitation Centre Drinking Water

Award winner: ADI Group Inc., ADI Limited, Fredericton, New Brunswick (prime consultant/technology inventor)

Client/owner: Rose Hill Center, Holly, Michigan

Project team: Eric Winchester, P.Eng., Michael McMullin, P.Eng., Ron Berry, P.Eng.