In the News

WATER DISTRICTS KICK OFF DESALINATION TESTING
PILOT PLANT HOPES TO PROVE VIABILITY OF FULL-SCALE FACILITY

By Aldwin Fajardo

Mid-County Post, 04/01/2008

Technician Harold Pepple, left, and CDM's Paul Meyerhofer.
Technician Harold Pepple, left, and CDM's Paul Meyerhofer.

In search of a viable answer to the county's looming water crisis, officials from the Soquel Creek Water District and the city of Santa Cruz gathered Thursday, Mar. 20, at UCSC's Long Marine Laboratory to officially open a pilot desalination facility that will extract drinkable water from Monterey Bay seawater.

Officials say that a drought in the year 2020, assuming modest population growth, would require curtailing consumer consumption by 60 percent in the city of Santa Cruz. Likewise, failure to address strained aquifers in the Soquel Creek District would leave the system's underground water reservoirs vulnerable to seawater intrusion that can permanently pollute water supplies.

Santa Cruz Water Department manager Bill Kocher said the testing plant simulates the full-scale desalination treatment process and will run for a year to determine how well the system handles seasonal changes and the Monterey Bay's unique water conditions. The system, which can process about 7,200 gallons of water per day, must be tailored to suit local currents, temperatures and the suspended matter that's fed to the ocean by local rivers.

Soquel Creek District manager Laura Brown said the pilot test program is required by the California Department of Public Health, which will test various desalination treatment processes over the 12-month period.

How Does Desalination Work?

The facility is testing several combinations of reverse osmosis (RO) membranes, including both seawater and low-pressure RO membranes, which remove sediment, marine minerals and salt. The plant is also testing different combinations of pre-treatment technologies.

In RO, seawater is pumped at high pressure through permeable membranes, separating salts from the water. The seawater is pre-treated to remove particles that would clog the membranes. The quality of the water produced depends on the pressure, the concentration of salts in the feedwater, and the salt permeation constant of the membranes.

Water extracted from the pilot plant will not be available for public consumption. Brown said pilot testing will ensure that a full-scale plant could meet environmental and water quality requirements.

After testing, the purified water and saline concentrate will be reblended and returned to the Long Marine Lab for use in their marine mammal pools. Treatment residuals will be discharged to the city's wastewater treatment plant.

Paul Meyerhofer, of the Walnut Creek engineering firm Camp, Dresser and McKee, said the plan is to test water samples from two locations initially every 12 days, and then conduct more frequent and varying sampling to eventually customize treatment results to the county's needs.

"Desalination is a proven process. We know it works but we are required to run a year-long testing due to the varying quality of sea water in different parts of the world. Also, we want to make sure we can meet water quality requirements and still be cost-effective," said Meyerhofer, whose company was contracted to build and run the pilot plant.

Environmental and Economic Challenges

The testing plant was initially projected to cost $3.3 million but increased to $4 million due to additional site improvements and watershed monitoring. It hopes to prove the viability of a full-scale desalination facility that could process 4.5 million gallons of water per day.

However, energy use requirements are high for desalination plants, and increased energy use may cause adverse environmental impacts. About 12kwh of energy is needed to desalinate 1,000 gallons of seawater — excluding any allowance for supply and distribution. This is equivalent to operating a dozen 100-watt light bulbs for 10 hours.

Soquel Creek's Bruce Daniels said they are looking at various energy-saving programs for the full-scale desalination plant which they hope to build by 2015. He mentioned the prospects of installing energy-efficient components and recovery devices to capture and re-use RO processing energy.

Daniels pointed out that they are exploring the possibility of solar and other renewable energy sources to power up the seawater treatment facility. Officials also have to be sure that concentrated saltwater is disposed of safely and that the plant doesn't harm marine life next door.

"This is only the beginning of an exciting process toward the construction of a full-scale treatment plant," said Heidi Luckenbach, desal program coordinator for the Santa Cruz Water Department.

Luckenbach added that additional studies will be conducted to investigate the location and design of the much larger facility's intake system.

The full-scale project concept is to retrofit an abandoned wastewater outfall with an intake structure and convey water to a location on the west-side of Santa Cruz, desalt the water, convey the concentrate to the wastewater treatment plant for blending with the advanced secondary treated wastewater effluent, and convey the permeate to the existing Bay Street Reservoir.

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