Groundwater pumping in the Los Alamitos, California area near Long Beach (pictured above) 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 2003, 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.
NDMA and Water Treatment
The California Division of Drinking Water has set a 10 part per trillion (ppt) drinking water notification level for NDMA. Due to its low affinity for carbon and its low volatility, NDMA resists removal by traditional 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 UV light through the photochemical reaction known as UV-photolysis.
System Design Parameters
|Flow Rate||8 Million Gallons Per Day|
|Influent NDMA Concentration||420 ppt|
|Effluent NDMA Concentration||<10 ppt|
|Contaminant Treatment||Combined UV-Photolysis and UV-Oxidation|
The TrojanUV Solution
To minimize footprint and energy consumption, the TrojanUVPhox™ was selected. The TrojanUVPhox performs the final treatment step at the Leo J. Vander Lans Water Treatment Facility in what is considered to be the gold standard for advanced recycled water treatment: microfiltration, RO, and then UV combined with hydrogen peroxide.
MF and RO remove particulates and larger molecular-weight contaminants, while the TrojanUVPhox in conjunction with hydrogen peroxide not only treats NDMA through UV-photolysis but also degrades additional contaminants including but not limited to 1,4-dioxane, through UV-oxidation. In addition, UV disinfection acts as a final disinfection barrier and is capable of inactivating multiple species of pathogenic bacteria, protozoa and viruses. The reactor treats NDMA at a fraction of the operation and maintenance costs of traditional high-energy systems, in a very compact footprint.
Three Treatment Processes in One System
|Description||Highly reactive hydroxyl radicals are formed when H2O2 is exposed to UV light. These radicals are capable of breaking down numerous chemical contaminants.||Chemical contaminants that absorb UV light are|
broken down into harmless constituents.
|Microorganisms are exposed to UV light which is absorbed by the genetic material (DNA) in a cell. The genetic material becomes extensively damaged resulting in the inability of the microorganism to replicate and cause infection.|
|Target Contaminant||1,4-Dioxane||NDMA||Spacies of bacteria, protozoa and viruses|
|Sources of Contaminant||Chemical stabilizer used with common volatile organic compounds such as PCE and TCE|
|By-product of drinking water and wastewater disinfection with chloramines|
|Natural leaching of wastes into groundwater
|Treatment Objective||0.5-Log Removal||2.14-Log Removal||>6-Log Removal of Virus|