Project Background 

The City has suffered water reliability concerns in recent years during the severe droughts California has endured. In response, the City installed portable, containerized desalination units to treat the brackish or saline waters at a diversion point approximately 4.5 miles upriver from the Noyo River mouth. To avert future challenges, the City has sought out new, reliable water supply alternatives. One promising technology is the Oneka Technologies (Oneka) wave-powered desalination system. The Oneka units convert seawater into freshwater through reverse osmosis (RO), using only the power of ocean waves. The Oneka design will be the first of its kind in California and would therefore benefit from a pilot study to demonstrate its effectiveness and refine its operational parameters to inform a future utility-scale deployment.

In September 2023 Oneka Technologies presented to the City Council about wave powered sustainable desalination.

View the presentation here. 

In consultation with the City, Oneka identified their Iceberg class unit as the most appropriate to pilot test off the coast of the City. The Iceberg unit is the 9th generation of this technology developed over seven years in the ocean environment. The pilot study will deploy a single Iceberg class unit that will produce on average 13,200 gal/day or 0.013 million gallon/day (MGD) for a period of 12 months. Over the course of the pilot study, the operational parameters and environmental impact of the Iceberg’s operation will be monitored to support permitting of a future array of Iceberg units to provide a utility-scale water supply.

Grant information 

In May 2023 the City was awarded a grant for $1,490,000.00 from the California Department of Water Resources

Location

The ideal distance from shore for the Iceberg is less than one mile. Positioning the Iceberg requires careful consideration of pumping efficiency, ambient wave energy, water depth for brine dispersion, and visual impacts. The preferred site is located 0.5 miles offshore. At this distance, the system’s pumping capacity to deliver the permeate to shore is not exceeded and would not require supplemental pumping that would require energy beyond the wave power available in the existing design. The distance minimizes the visual impact of the Iceberg in comparison to maintaining a position closer to shore. The low profile of the Iceberg will make it difficult to see from shore. Lastly, the water depth is optimal to tap into the natural wave energy without being in the dominant surf zone where the breaking waves could damage the Iceberg.

The preferred site minimizes the impact to all forms of marine life by preferentially placing the mooring system within an area dominated by soft-bottom habitat, minimizing the permeate pipeline distance to shore to maximize the efficiency of the wave-powered system to pump the water to shore without supplemental energy requirements, and the pipeline alignment can follow the existing, previously disturbed habitat created by the installation of the wastewater treatment plant’s ocean outfall.

The Iceberg minimizes impacts to all forms of marine life, water quality, and the marine environment through the use of its 60-micron mesh intake screen, shallow intake point, low through-screen velocity, and low intake volume. Passive discharge of the brine through the intake structure also minimizes impacts to all forms of marine life, water quality, and the marine environment. The passive diffusion of brine does not generate shearing forces as would occur with a multiport diffuser. Discharging low volumes of brine near the ocean’s surface allows the brine to mix as it falls through the water column until it has diluted to near-ambient salinity within 50 ft of the discharge. The Iceberg will be moored along the 80-ft, or deeper, isobath allowing for sufficient water depth for the brine to fall and mix well before contacting the seafloor. The near-surface passive discharge also eliminates the chance of suspending any seafloor sediments.

How it works 

The buoy is a fully self-contained desalination system powered exclusively by mechanical wave energy and uses no chemicals in the treatment process. Using the point absorber principle, the buoy gathers energy with every wave. The patented Power Take Off (PTO) mechanism drives a water pump which has a self-cleaning, 60-micron mesh, cylindrical intake screen at a nominal depth of four ft below the ocean surface. All material, including nearly all forms of marine life, are passively excluded by the 60-micron mesh intake screen at the point of withdrawal.
Once into the system, the pressurized water is filtered through 5-micron mesh cartridge filters before entering the RO membranes to remove all salts, pathogens, and contaminants of emerging concern in the source seawater. Before discharging back to the ocean, the high-pressure brine is used to power an energy recovery device for maximum efficiency. The resulting permeate remains pressurized as it is conveyed to shore through a three-in diameter HDPE pipe. Sufficient wave energy is required to pressurize the seawater enough to force the water through the reverse osmosis membranes and travel to the permeate receiving point at the seaward fenceline of the City’s wastewater treatment plant. The City will extend the permeate pipeline inside the wastewater treatment plant to an in-plant discharge point where the permeate will be routed back to the ocean via the existing ocean outfall. The City’s permeate pipeline within the wastewater treatment plant will include valving to allow permeate to be drawn from the line for testing and potentially for alternative, non-potable uses at the City’s determination.

Operation & Maintenance 

For operations and maintenance activities throughout the project period, the City will contract with Oneka for technical support in the operation and maintenance of the Iceberg. The Iceberg is a new technology that does not incorporate standard water plant operator criteria as certified under the Drinking Water Operator Certification Program. To support the City, Oneka intends to maintain a project staff of three operations personnel on site in Fort Bragg. This team will include the following:
● Operator/Technician
● Field Service Engineer
● Operations Coordinator
The operations team will be based in the the Noyo Harbor area to facilitate rapid response to the Iceberg if needed.

The Iceberg desalination buoy is designed to operate continuously throughout the 12-month pilot test period, producing permeate constantly unless planned maintenance activities and/or extreme sea conditions (hurricanes, typhoons, tsunamis, etc) trigger a temporary removal of the device. Once maintenance is completed or extreme sea conditions have subsided, the Iceberg buoy will be moved back into position to resume permeate production. The permeate pumped to shore will have multiple potential uses, but none of them potable at this time. Before any use by the City, the permeate will be tested in accordance with California Division of Drinking Water standards. During this time, the permeate will be directly routed to the wastewater treatment plant outfall as part of the City’s normal discharge. After testing, the City will evaluate the results and determine if the water is suitable for non-potable uses, and thereby replace the potential use of some potable water, such as watering City-owned vegetation, washing down surfaces and equipment at the wastewater treatment plant, and other instances where the small-volume, non-potable water could replace other water sources in the course of existing City operations without altering the City’s operations.

Learn more information about Oneka Technologies at their website here.