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Brownsville and South Padre Lead The Way in Seawater Desalination
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0 Comments ::  :: South Padre Island, Economy |
 Several years ago Texas Governor Rick Perry announced an initiative to explore using the Gulf as an uninterruptible drought-proof supply. The Texas Water Development Board, the state agency charged with developing water supply, was tasked with putting out a request for proposal. Three sites were selected for a feasibility analysis: Brownsville, Corpus Christi, and Freeport. After a two-year period, results were turned in to the Texas Water Development Board. Based on the feasibility analyses, Brownsville clearly was the site ready to go forward.
The Corpus Christi and Freeport proposals also showed potential, but it was deemed premature to invest in pilot plant studies at these sites because they appeared less likely to be implemented in the near future. These sites will remain under consideration as possible candidates for future funding.
Why was Brownsville the best site candidate?
The South Texas Border continues to be one of the fastest growing areas in the State of Texas and the United States. Population in the Rio Grande Region is projected to more than double over the next 50 years fueling increased demand for municipal water supplies. By 2050, the Lower Rio Grande Valley will need 184,000 acre-feet of NEW water supplies.
The Brownsville Public Utilities Board had been working with Bill Norris to come up with an efficient project at a reasonable cost in a short amount of time. Bill Norris, a pioneer who helped develop reverse osmosis plants that convert brackish groundwater into good, clean drinking water, unveiled a $720,000 reverse osmosis plant that each day converts 250,000 gallons of brackish groundwater into drinking water in Rancho Viejo. Last year in Brownsville, he developed a $22 million plant that pumps 7.5 million gallons a day for the Southmost Regional Water Authority. This experience prepared his company, NRS Consulting Engineers, and gave Brownsville's Proposal a competitive advantage because they could build and run the reverse osmosis plant in less time.
Where is the study taking place?
A pilot plant on the Brownsville Ship Channel is now collecting and analyzing site-specific data to determine best methods and costs to turn seawater into drinking water.
 What is the study expected to obtain?
• A detailed assessment of the Brownsville Ship Channel site for installing the full-scale facility.
• Developing and implementing a process for identifying and selecting the water pretreatment and treatment equipment
• Installing a 52,000 gallons per day pilot plant at a site located in the Brownsville Ship Channel
• Collecting data on ocean water quality for modeling of concentrate discharges
• Conducting a 12-month testing of sand and membrane filtration as forms of pretreatment
• Evaluating two different types of reverse-osmosis membranes for the removal of dissolved solids from seawater
• Reassessing the cost of constructing a full-scale facility and evaluating available funding options to implement the project.
• Support the design, funding and construction of a large-scale seawater desalination plant capable of producing 25 million gallons per day (MGD) of water for municipal and industrial use in the region.
What has the project team accomplished so far?
• The project team has developed a pilot plant study protocol that has been approved by the Texas Commission on Environmental Quality
• Selected pretreatment and treatment equipment manufacturers
• Commissioned the construction of the pilot plant
• Started work on the permitting process with the U.S. Corps of Engineers and the U.S. Coast Guard
• Conducted an assessment of alternate (back-up) sites for the seawater desalination plant
• Developed a proposal for operating the full-scale plant at a lower energy cost than was projected in the feasibility study.
• Water production operations at the pilot plant were scheduled to begin by December 2006 and continue until December 2007.
How does a desalination plant work? 
First, water collects in an intake well (1) and then is pumped (2) from the Brownsville ship channel into a pipeline that feeds to one of four pretreatment units. These units remove particles suspended in the water: silt, solids, and contaminants. This pretreatment reduces the work required of the critical reverse osmosis (RO) unit that removes salts, significantly reducing costs.
The four pretreatment units differ from one another:
- two ultrafiltration membrane units (3 & 4) from different suppliers using different technologies;
- a microfiltration unit (5); and
- a conventional treatment unit (6) that uses clarification, sedimentation, and filtration to remove contaminants.
The pilot is testing the various technologies to determine which works most efficiently under the specific conditions existing at the site. For this reason, it also features two parallel trains of holding tanks (7) and RO units (8):
- The water produced from the filtration processes (the "filtrate") is pumped to a holding tank designated only for the UF and MF processes. From there, the filtrate is pumped to an RO unit.
- The water produced from the conventional treatment unit is pumped to a separate holding tank and from there to a separate RO unit.
The RO unit is the key to the desalination process. Here, the water is forced by means of high pressure through fine membranes that keep salt molecules out while allowing water molecules through.
The RO process produces two streams of water: the "product water," cleaned of impurities and salts, and the "concentrate" or "brine," which is the wastewater from the process. The product water is pumped into holding tanks (9). In an operational plant, the product water would be further treated to ensure good taste and then pumped to homes and businesses. Because this pilot is for testing only, the holding tank is not connected to pipes that carry water to users. Instead, water from this tank is pumped along with concentrate and other water used in operating the facility to a mixing tank (10).
From there, the waters flow to a holding lagoon (11). The water is analyzed to determine its pH (i.e., whether it is acidic or alkaline). The pH is balanced (or "neutralized") (12) and then discharged into a receiving ditch (13), which flows back into the ship channel.
Where else in Texas will there be desalination plants?
A smaller seawater desalination facility located on South Padre Island has been recommended. Due to the recommendation, Laguna Madre Water District solicited financial assistance from TWDB to update its regional water facility plan and to conduct a seawater desalination pilot plant study. On July 18, 2006, TWDB considered and approved the request for financial assistance and awarded $231,000 to implement its plan. The small plant will process 1-million gallons per day.
The Corpus Christi and Freeport projects are among the seawater desalination projects recommended in the 2007 State Water Plan to meet the state’s future water supply needs.
How much will it cost? Who is paying for it?
Cost:
- Estimated Capital Cost : $150 million
- Annual operation and Maintenance Costs: $6.6 to $12.5 million
Brownsville Public Utilities Board:
- $38 million of the capital cost
- $6.6 to $12.5 million in operation and maintenance costs
State of Texas:
- $70 million in grants
- $45 million in low interest loans
Opportunities and Challenges:
Opportunities
- Inexhaustable supply of source water from the Gulf of Mexico
- Source of water is relatively close to large water demand areas located within 100 miles of the coast
- Desalination technology is an attractive option:
- it is reliable and becoming cost-competitive
- desalination plants offer security because of their industrial setting
- the modular design of desalination plants make them relatively easy to upgrade
- Relatively short time required to develop and construct full-scale plants
| Challenges
- Successfully constructing the first large-scale seawater desalination plant in Texas by 2010
- Developing favorable funding mechanisms to support creation of new water supplies from seawater desalination
- Mitigating the relatively high energy use
- Vulnerability to increasing energy costs
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The South Padre Island - Laguna Madre Seawater Desalination Pilot Plant Study
Project Summary: Conduct a 12-month pilot plant study to collect source water quality data to determine the cost of a 1-MGD full-scale facility and to update a regional water facility plan.
- Funding Recipient: Laguna Madre Water District
- Project Administrator: Laguna Madre Water District
- Contractors: NRS Consulting Engineers
- Project Start Date: Fall 2006
- Project Completion Date: Fall 2007
- Total Project Cost: $779,000
- TWDB Share of Project Cost: $779,000
- Benefits: The study will provide reliable, site-specific source water data from an open ocean intake or beach wells to determine the cost of a 1-MGD seawater desalination plant.
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