Excellent article about recycled wastewater in California where intensifying drought has meant the utilities are increasingly relying on sewage to generate the state’s water needs. Twenty years ago, Los Angeles County spent millions on a recycled wastewater plant only to shut it down within weeks of its opening after an outcry from residents who objected to the idea of drinking their own sewage. But after several years of intermittent droughts and the high demand for mains water (approx. 80%) for California farms, which grow more than half of all the fruits, nuts and vegetables produced in the U.S, the state is moving away from desalination as a solution to re-using sewage.
Both types of water are treated mechanically, pumped through a multi-step filtration process that culminates with reverse-osmosis membranes that pull out impurities — including not just visible particles, but viruses, pathogens, hormone-disrupting chemicals and salt. The most difficult impurity to remove is, in fact, salt (which isn’t suspended in water, but dissolved). Sewage is easier and cheaper (desalinated water costs about $3,000 per acre-foot, while recycled wastewater costs $1,800 per acre-foot) to filter than ocean brine because it has far lower salinity and therefore requires less energy to pump through the membranes. It’s also more universally available; not every farm or city is located next to an ocean, but everybody has sewage.