MWDOC Sea Water Pilot Desalination Study QA/QC and Peer Review
Project ID: 3879
Principal Investigator: Saied Delagah
Research Topic: Desalination and Water Treatment
Priority Area Assignments: 2012 (Advanced Water Treatment)
Funded Fiscal Years: 2012
Keywords: seawater ro desalination,
Municipal Water District of Orange County (MWDOC) is investigating seawater desalination for potable water production. There are multiple aspects to the study that include seawater intake, pretreatment, and reverse osmosis (RO) treatment. MWDOC has asked the Bureau of Reclamation (Reclamation) to participate in this study as a technical advisor. Bill Steele from Reclamation's Southern California Area Office has asked Denver's Technical Service Center (TSC) to provide technical support to MWDOC and provide peer review and quality assurance/quality control (QA/QC) into the various tasks that will be completed in this study. The pilot research at MWDOC is investigating slant beach wells for subsurface intake, followed by pretreatment for iron and manganese leached from the subsurface and subsequent RO treatment train. The goal of the study is to provide design data for the full-scale plant.
Need and Benefit
There is a significant need for this project. Unlike other desalination facilities that either have open intake structures or a submerged intake, MWDOC is using a novel slant well intake described in the above section. The intake, when proven successful, will diminish the effect of impingement and entrainment (I&E) issues associated with other intakes. It will also act as a first line filter at no additional cost since it will use the ocean floor as a media filter of sorts. Currently, the pilot study feed water from the well that is operating has a 0.1 NTU turbidity. This value has been consistent over the last 6 month of testing. Dealing with I&E issues is a large hurdle to overcome for successful coastal sea water desalination; therefore, it is a very important aspect of this pilot study.
A consequence of the slant well is that it is currently tapping inland aquifers and surface waters as well as seawater. When the initial pumping of the slant well started, the feed contained 2,500 parts per million (ppm) total dissolved solids (TDS). That value has since increased to 15,000 ppm over the last year. Modeling of the feed predicted this rise in the TDS due to seawater mixing with the brackish water that the well is drawing. It is predicted that a system at full capacity will be running primarily on seawater with little influence from aquifers and surface water; however, for the pilot study and the start of the full-scale system, the intake would be under the influence of the aquifer and surface water or brackish waters. This brackish water contains iron and manganese (Fe & Mn) that require removal prior to RO. MWDOC is currently studying a pilot system for Fe & Mn removal and has asked Reclamation to help peer review and provide QA/QC on the pretreatment. Iron concentrations started at about 1 ppm a year ago and now have leveled off at 10 ppm for the past 4 month. 10 ppm iron would cause irreversible damage to membrane and would have to be dealt with in a pretreatment system. Models are predicting that the influence of iron and brackish water will diminish for the full-scale system. However, operation of an RO plant would require dealing with the iron prior to RO feed when it is present in the feed at the start of the full-scale system.
It is an important and necessary aspect of the piloting to understand the slant wells operation and its effects on desalination systems. I&E issues in California as well as other coastal communities must be dealt with for successful commissioning of RO plants.
A technical bulletin will be created summerizing the findings of the pilot test study. News release for the Denver News will be prepared.
This information was last updated on September 15, 2014
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