2020-04-02_Science_Illustrated

The Pipe is a floating desalination plant, designed to remove both dirt and salt from ocean water in

a process known as electromagnetic filtering. An electromagnetic field will separate substances by

attracting ions. According to the creators, a Pipe can desalinate 4.5 billion litres of water annually.

Floating desalination plant aims to

supply cities with drinking water

ELECTROMAGNETS

PURIFY WATER

Under the Pipe’s surface,

ocean water circulates in

a pipe system in which electro-

magnets attract ions in dirt and

salt, separating them from water.

SURFACE MADE OF STEEL

AND SOLAR PANELS

The surface of the plant is

covered in panels made of

recycled steel and solar cells

that supply electricity to the

electromagnetic desalination.

DRINKING WATER SENT

DIRECTLY TO THE SHORE

A pipeline directs the

desalinated drinking

water to a water supply net-

work. The maximum length of

the Pipe is 428 x 60 metres.

LONG^ SHOT

are surrounded by a ‘shell’of water mole-

cules too large to pass through the pores of

the membrane. As scientists can control the

size of the pores very accurately, the

membrane is also more efficient at allowing

the water through, so the desalination does

not require so high a pressure (and power

consumption) as other desalination methods.

Electric grid captures vapour

Membranes must be either cleaned or

replaced over time, as dirt and bacteria accu-

mulate. But ocean water can be desalinated

without them. MIT scientists have devel-

oped a method which can separate salt, dirt

and pesticides from water during a process

known as shock electrodialysis. The ocean

water flows through a porous glass material

with electrodes on either side. By having an

electric current flow to make the electrodes

positively or negatively charged, the salt

water divides into a high-salt region near

one electrode and a salt-poor region around

the other. When the amperage reaches a

critical level, a kind of shock wave develops

through the liquid, resulting in the low-salt

region being purified of up to 99.99% of the

salt from the original water sample.

Electricity is also key to another MIT water

concept, in which the power extracts drinking

water from vapour, rather than ocean water.

The method can be used to harvest water

vapour from power plants, where today an

extraordinary 39% of US fresh water is used

to cool power plants during electricity gener-

ation, with much of the water emitted into

the atmosphere in the form of water vapour.

Huge quantities of drinking water are wasted

in this way.

The scientists behind the Infinite Cooling

concept aim to change that. They have devel-

oped a method by which a grid collects drops

from water vapour. Normally, this method

would capture some 1-3% of the water from

emitted vapour in the form of water drops,

but scientists have discovered that by

running a weak electric current through the

grid they can ionise the air so that it becomes

electrically charged. The grid then attracts

much more of the water vapour that would

otherwise speed by and disappear into the

atmosphere. The collected water can be

usefully recycled in the power plant cooling

system, or could form part of the water

supply for a nearby town.

The search to squeeze out still more

refreshing droplets does not stop here. Even

the moisture of human excrement can be

extracted and used as drinking water. In

2015, an omniprocessor prototype was built

in Senegal’s capital of Dakar. The city has

little organised sewage and suffers severe

problems with waste water and sludge from

primitive toilets. But thanks to the omni-

processor, faeces from 50-100,000 people is

now converted into pure drinking water.

Together with the other technical solutions,

quaffing down purified poo might ensure a

future in which no one needs be thirsty.

99.99

% of the salt in ocean water

can be removed by a

‘shock wave’ of electricity.

KHA

LILI

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48 | SCIENCE ILLUSTRATED

TECHNOLOGY WATER