Amid drought, San Diego prepares to tap ocean $1b plant seen by some as key step; others foresee toll

Post date: Apr 12, 2015 2:41:10 PM

The technological approach being employed here, and in most recent plants, is called reverse osmosis. It involves forcing sea water through a membrane with holes so tiny that the water molecules can pass through but the larger salt molecules cannot.

$1b plant seen by some as key step; others foresee toll

GREGORY BULL/ASSOCIATED PRESS

Reverse-osmosis chambers towered over a worker at the Poseidon Water desalination plant being built in Carlsbad, Calif.

The technological approach being employed here, and in most recent plants, is called reverse osmosis. It involves forcing sea water through a membrane with holes so tiny that the water molecules can pass through but the larger salt molecules cannot.

A huge amount of energy is required to create enough pressure to shove the water through the membrane. But clever engineering has cut energy use of the plants in half over the last 20 years, as well as improving their reliability.

Future desalination plants also have the potential to blend well with the rising percentage of renewable power on the electric grids in California and Texas. Since treated water can be stored, the plants could be dialed up at times when electricity from wind or solar power is plentiful, and later dialed down to conserve energy.

However, as interest in desalination spreads, California and other states confront major decisions about the environmental rules for the new plants.

Both the intake of sea water and the disposal of excess salt into the ocean can harm sea life. Sucking in huge amounts of sea water, for instance, can kill fish eggs and larvae by the billions. Technical solutions exist, but they can drive up costs, and it is still unclear how strict California regulators will be with the plant developers.