The Alamitos Barrier Recycled Water Project

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Groundwater pumping in the Los Alamitos, California area over the last century has caused groundwater levels to drop, allowing seawater to intrude into the local groundwater aquifer. To prevent additional infiltration by seawater, a coastline barrier of wells injecting fresh water has been in place since 1965. Until recently, imported potable drinking water was injected into the aquifer. However, the Alamitos Barrier now utilizes highly-treated, recycled water for this application. One obstacle to the use of recycled water, however, is that it contains the contaminant N-nitrosodimethylamine (NDMA). Because the injected water mixes with potential drinking water in the aquifer, it must be of drinking water quality. The California Department of Health Services (DHS), in February, 2002, set a 10 part per trillion (ppt) drinking water action level for NDMA.

Due to its low affinity for carbon and its low volatility, NDMA resists removal by traditional VOC treatment technologies such as carbon adsorption and air stripping. In addition, due to its small molecular weight, NDMA passes through reverse osmosis (RO) membranes. However, NDMA degrades rapidly when exposed to ultraviolet light through the photochemical reaction known as UV-photolysis. This is cost-effectively performed using the TrojanUVPhox™ reactor. The spectral signature of the low-energy, high-output lamps have been uniquely selected to most efficiently treat NDMA and provide superior disinfection capabilities.

The Trojan Solution

To minimize footprint and energy consumption, Trojan’s patent-pending TrojanUVPhox™ reactor was selected. The TrojanUVPhox™ performs the final treatment step at Alamitos in what is considered to be the “gold standard” for advanced, recycled water treatment: micro-filtration, RO, and then UV with hydrogen peroxide (MF/RO/UV). MF and RO remove particulates and larger, molecular-weight dissolved constituents; while the TrojanUVPhox™, in conjunction with hydrogen peroxide, treats NDMA, disinfects, and acts as a final barrier to any other unregulated, organic contaminants. The reactor treats NDMA at a fraction of the operation and maintenance costs of traditional high-energy systems, in a very compact footprint. The system is currently treating NDMA to meet California's action level of 10 ppt, and is performing disinfection, as well.

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