Brown and Caldwell Home Page

Brown and Caldwell engineers and scientists are technical and thought leaders in the environmental sector. Meet the people who have been advancing innovation for more than 70 years.
Author      Title/Abstract      

Ultraviolet Disinfection of Reverse Osmosis Product Water for Groundwater Replenishment in California
Author: David S. Murray
Date: 1/102

The Orange County Water District operates a reclamation facility in Fountain Valley, California. The Groundwater Replenishment (GWR) Project will reclaim secondary effluent now discharged to the Pacific Ocean. Post-secondary treatment will include microfiltration, reverse osmosis, and ultraviolet (UV) disinfection prior to injection or percolation into the groundwater aquifer. The GWR Project will produce high-quality treated effluent for direct replenishment of a major groundwater basin used to supply up to 75 percent of the water consumed by more than 2 million people. A portion of the reclaimed water will be injected near the Pacific coast to prevent salt-water intrusion, while the remainder will be pumped 14 miles off site to spreading basins for aquifer recharge, diverting up to 100 mgd from ocean discharge. Information is provided on the evaluation and design of UV disinfection equipment under California Department of Health Services (DHS) Title 22 requirements. The impacts of the discovery of a trace contaminant, N-nitrosodimethylamine (NDMA), in the secondary effluent on the design of the disinfection facilities will be discussed. Selection of the optimum UV lamp technology and configuration is discussed and the basic system layout presented. Important design issues included selection of the disinfection UV dose, the energy dose (EEO) for NDMA photolysis, and the UV transmittance value. Related issues such as redundancy require-ments, numbers of lamp banks and parallel trains, emergency power provisions, lamp cleaning, and related support facilities is presented. Information will be presented on how the selected UV system fits into the overall GWR Project, including the microfiltration/reverse osmosis proc-esses, effluent pumping, and product water distribution facilities. The paper discusses the unique design requirements for the use of UV light to destroy NDMA by photolysis, and how this can be accomplished during the disinfection process. Data is presented on pilot testing of NDMA destruction. Cost information and design criteria for the various alternatives are presented in the supporting data. A process schematic is also provided showing how UV disinfection will be installed to achieve disinfection to meet the new NWRI guidelines, and, at the same time, provide destruction of NDMA to meet DHS requirements.

This library contains published materials for which copyrights may be owned by entities other than Brown and Caldwell, but which are stored for limited uses by BC employees. Technical papers authored by BC employees generally may be printed and shared electronically with clients and prospective clients outside BC. Technical papers cannot be sold, and technical papers shared outside BC must have proper attribution of the original sponsoring organization or conference where the paper was presented. This attribution is embedded in each technical paper file when it is loaded into this library. Published articles from magazines or trade journals which are stored in this library are FOR INTERNAL USE ONLY and SHOULD NOT be distributed to clients or others outside BC, without express permission of the copyright owner. For questions regarding copyrights associated with any document in this library, or questions regarding copyrights in general, contact the Legal Department.