Like many Southwestern communities, Los Lunas, New Mexico, found itself out of compliance with the new US EPA standard for arsenic in drinking water regulation, and in need of a treatment solution. The city chose Tonka Water to help develop an arsenic removal process to meet their specific goals and unique requirements. Water conservation was critical to the community and played an integral role in equipment selection.
The method of arsenic co-precipitation with iron, followed by media filtration, was employed for arsenic removal. In this process the arsenic adsorbs to oxidized iron in the water, which agglomerates into filterable solids. In some parts of the country, this occurs naturally while removing iron from the water; however, in this case, there was no naturally occurring iron in the well water of Los Lunas, so it needed to be added in the form of ferric chloride.
The specific arsenic levels of Los Lunas are such that it is possible to treat a percentage of the raw water, while bypassing the remaining and blending to a finished water quality goal that is below the maximum contaminant limit (MCL) of 10 parts per billion.
A pilot study verified that the addition of ferric chloride, sodium hypochlorite for arsenic oxidation, and hydrochloric acid for pH depression would successfully remove arsenic to less than one part per billion. A higher hydraulic loading rate through the media filter also verified that with the ability to bypass water would significantly decrease the size of the equipment.
In total, four water treatment plants were constructed, ranging between 875 and 1500 gpm of production capacity, included OptaCell™ horizontal pressure filters with IMAR™ media, treating two thirds of the flow with co-precipitation and the other third of raw water bypassed the system. Each filter consists of four isolated cells, allowing for one or more to be taken out of service while the remaining cells operate under pressure.
The treatment process has been highly effective in bringing the water treatment Los Lunas into compliance with the US EPA standard for arsenic in drinking water and in providing quality water for the community.
|Arsenic (As)||15-24 μg/L||< 5 μg/L|