Wave-powered buoys greatly reduce the ecological cost of desalination

This extraordinary desalination device, made from 170,000 recycled plastic bottles, works on the mechanical energy of waves as it floats in the ocean and creates up to 13,000 gallons (53,000 liters) of fresh water per day, discharging a much less concentrated brine than to other designs.

Only 3% of the Earth’s water is fresh water: take away the water locked up in frozen glaciers and you will only see 1%. So humanity finds itself on the wettest planet in the solar system, surrounded by water, yet still faces severe shortages of fresh water that are already affecting around half of the world’s population.

As the effects of climate change continue to unfold and global population rises to a projected peak of about eleven billion by the end of this century, water scarcity will get much worse and desalination technology will become ever more critical and ubiquitous.

Scaling up current desalination methods poses serious problems. First, it will require huge amounts of energy as it grows, and this occurs during the difficult transition from dirty to clean energy, when energy will be precious. Second, onshore industrial desalination plants take in huge amounts of salt water, then remove most of the water and pump a highly concentrated salt brine back into the ocean, often contaminated with chemicals used to pre-treat the water and keep the equipment clean. This heavy salty discharge tends to sink to the seabed, where it can cause ecological damage.

But there’s no way around it; humanity will need more and more desalination plants in the future. And that’s why Oneka’s wave-powered floating desalination buoys could prove to be such a valuable development.

Iceberg-class desalination buoys use local wave mechanical energy, as well as a few small solar arrays, to desalinate, test, and pump water ashore

Oneka

Oneka designed these things from the ground up to be eco-friendly. For starters, they’re built mostly from recycled plastic bottles; each “Iceberg” class buoy represents more than 170,000 bottles that will never go to landfill or join their people in the Great Pacific Garbage Patch.

They work entirely on wave energy. Anchored to the seabed anywhere with an average wave height of more than 1m (~3ft), they absorb energy from passing waves and convert it into mechanical pumping forces that pull seawater and push about a fourth through a reverse-osmosis desalination plant to create fresh, potable water, which is pumped ashore through high-density polyethylene piping, always using only wave-supplied energy.

The remaining three quarters are mixed again with the salty waste from the desalination process and released back into the sea. It is only 30% saltier than the water around it, a negligible change from the much more concentrated brine released by land-based desalination plants, and because these buoys are typically anchored at least a mile (1.6 km) from the sea , in large arrays with a lot of distance between the units, the brine disperses well and toxic ecological effects are minimized. Oneka says its own tests have found that within about 10 feet (3m) of each fixture, there is already no measurable increase in water salinity from baseline.

Just 10 feet from the buoy, Oneka says there is no measurable increase in water salinity
Just 10 feet from the buoy, Oneka says there is no measurable increase in water salinity

Oneka

To minimize the possibility of sucking up fish, eggs or other small aquatic animals that probably wouldn’t like to be desalinated, fine mesh filters protect water inlets and the pump cycle includes backwashing. Oneka claims that “there is no danger to fish, eggs or plants”.

Iceberg-class units are designed to generate between 30-50 cubic meters (8,000-13,000 gallons) of water per day, enough for the daily needs of 100-1,500 people, depending on lifestyle and consumption. On-board sensors, powered by small solar panels, continuously test the water produced, making sure it meets relevant standards. Oneka offers post-processing to adjust the taste of the water or to tune it for the benefit of agricultural users.

They do require some maintenance: three to seven visits a year to each unit for preventive and general maintenance. But with this care, each unit is designed to last between 15 and 20 years of service.

Clearly, the output of these relatively small machines is nowhere near that of the largest land-based desalination plants. In fact, it would take more than 20,000 iceberg-class buoys operating at full capacity to equal the clean water output of the world’s largest desalination plant, the Ras Al-Khair Desalination and Power Plant in Saudi Arabia.

Oneka says he’s working on “large-scale devices,” which could move the needle further in areas that need larger amounts. These “Glacier Class” machines, according to Just Have a Think, will produce about 10 times as much as Icebergs and, according to Saltwire, will be available in 2023 and begin demonstration trials off the coast of Barrington, a community of 4,000 people in Nova Scotia , Canada.

However, where they meet local requirements, existing machines appear to offer a cost-effective, scalable, and reliable way to generate clean water with no carbon dioxide emissions, no coastal space requirements, no discharge to the power grid, and a carefully limited effect on the ecology. of the oceans. It’s impressive technology, and we can think of few better ways to repurpose a couple hundred thousand old plastic bottles.

Source: Oneka via Just Have a Think

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