Thursday, September 28, 2006



yesterday i got to go to a conference in monterey on desalination. i learned quite a bit, and since it's pretty interesting to me (and SHOULD be pretty interesting to anyone who plans on living in california for the next several decades), i thought i'd share some of my notes.

there are about 12 existing coastal desalination facilities in california, with a total production capacity of about 2.7 million gallons per day (mgd). they're used mostly for emergency backup, industrial supplies, and drought relief. at the moment, there are more than 20 new plants being proposed for california, and they're at all stages of the planning and environmental process. by one estimate i found, these proposed plants would add about 370 mgd of production capacity. [note: 2.7 mgd is peanuts. 370 mgd is definitely not peanuts.] the biggest plant in the world is on the order of 72 mgd. the biggest one in the uS is in tampa bay, and i believe it's about 25 mgd. the existing plants in california are all very smallish. some of the proposed california plants would be on a large scale. a bunch would be bigger than 10 mgd; two would be on the order of 50 mgd; and one would be 120 mgd. i got the impression that 10-25 mgd looks about reasonable and rational for a large plant in california right now. anything larger than that would probably be called 'big' by industry standards.

summary: a bunch of small pilot-y desal projects currently exist in california. lots of desal projects, some of them huge, are proposed for california.

desalination takes a LOT of energy. at the moment, the rate of energy usage to create desalinated water from normal oceanic saltwater is 6.81-8.90 kilowatt-hours per kilogallon (kwh/kgal). 20 years ago, though, that would've been about 30 kwh/kgal, so the technology's come a long way. and it's still improving. at $0.08/kwh (which is low in california, i believe), this comes to $2.37-2.80/kgal (about $3 per thousand gallons of desalinated water). (what's a typical price for water in california? i'm not sure...)

desalination plants cause a variety of impacts. the impacts can be divided roughly into these categories:

-construction – normal construction impacts; not a big deal; but note that pipeline construction is included in this category.
-intake – intake of water can cause impingement and entrainment (trapping and sucking in) of marine species; but some methods are way better than others, and technology is improving while research is being done on the impacts.
-discharge – the water that is returned to the ocean after the desal process is highly saline. this can affect all sorts of marine life. this is dealt with by co-locating the facility (see below) and by careful planning regarding the location of the outfall.
-energy use and emissions – very energy-intensive; using brackish water would be more efficient; emission problem could be solved with alt energy source.
-land use – coastal access issues; sensitive habitats are located in coastal zones; zoning is stricter; etc.
-socioeconomics – it's an expensive way to get water, so rates go up
-co-location issues – in california, plants are generally co-located with another facility, such as a power plant or wastewater plant, so that the brine byproduct can be disposed of into an already-existing plume of outfall water. this makes the salinity impact much lower. however, power plant outfall plumes are bad in and of themselves, environmentally, and california is trying to phase out once-through cooling systems at power plants. if the power plants are decommissioned, the desal plants will have to do much more to deal with their wastewater.

it is important to remember, however, that all these impacts must be balanced against the environmental impacts of all other ways to get water. habitat destruction, species destruction, overdraft, seawater creep, and the various socioeconomic impacts associated with water politics...

that's the gist of the basics, issues-wise. know too that the field is very regulated. one plant under discussion had to get 5 federal permits, 12 state permits, and 7 local permits. that is a LOT of permits.

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