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Massachusetts Considering Desalination Plants
Iphtashu Fitz writes "Despite a reservoir system containing some 412 billion gallons of water for Boston and surrounding communities, some eastern Massachusetts towns are facing water shortages and are now considering water desalination plants as a new source of fresh drinking water. The city of Brockton, 20 miles south of Boston, has plans in the works to build a $40 million plant and could begin construction as soon as this September. Currently there are fewer than 100 desalination plants in the US and most of them are in smaller communities, but that seems to be changing. The largest desalination plant in the country is located in Tampa, FL, which expects it to provide 10% of the citys drinking water by 2008. California also has at least 10 large scale plants on the drawing board. Some environmental organizations like the Conservation Law Foundation dispute the need for desalination plants however. They argue that many water shortages could simply be solved by better conservation of existing supplies."
At the moment the biggest problem with desalination plants is not just their high build cost, but their high operational cost.
When using technologies such as reverse osmosis the energy costs for pushing high volumes of water at high pressures through the membranes is prohibitive, not to mention the wear on the equipment it's self. In a traditional water treatment plant most of the filtering is done with gravity.
Life is Short and Hard like a body building Elf
Probably the environmental impact of the plant itself - it will have to be sited near the coastline, away from already developed areas like harbors or bays, meaning that it will likely displace marshland or other undeveloped coastline. There will be waste discharge as a by-product of the desalianation process, which will increase local salinity. Desalination requires a pressure differential to overcome osmotic forces - the power for this will probably come from electricity. Electricity is in short supply in some places, which means that the water plant will require a coal, nuclear, gas-fired, or hydro plant to contribute part of its output to desalienate the water.
From a tax perspective, these plants will need to be built by somebody, probably with bond issues, and will require taxes to pay off. I'd be more pissed about that than the environmental impact.
The Quabbin Reservoir is big(412 billion gallons) and supplies Boston and some neighboring towns. The MWRA (Mass Water Resources Authority) also was responsible for building the outfall systems required to handle the use of this water. The problem isn't the existence of the water but the pipes and connections. Some towns see the MWRA as costly and are exploring other means. I doubt that 16 mile pipes and the costs of desalination are cheaper for Brockton than an MWRA hookup, but that doesn't figure sewer costs in. GIGO.....
They're even thinking of building a Nuclear Desalinization Plant in the Mideast. At an estimated cost of $200-300 million it will be able to provide enough water for 3 to 4 million people.
Add to that the fact that we are experiencing a building boom due to high house prices (think 900 square foot house for $250k) and we anticipate extensive demands on town water services.
That is why our water commissioner formally proposed a desalination plant for our town.
Despite the fact that the state has cut funding for just about everything, our kids are asked to bring paper, tissues and other basic supplies to school, and we had to shut off the town street lights and close a library to save money the town focus seems to be upon building our way out of this hole :(
At least elections are next tues.
Oh and on a related note, I took a vacation recently to the Carribean and the place we stayed had desalinated water....it tastes awful.
The main objection to desalination plants is that they are highly energy intensive. Purifying water from mountain spring water requires seven stages, most of which are chemical/physical:
Filtering of large solids (fish, leaves,twigs)
Removal of unpleasant odors and tastes using carbon filters
Chemical dosing with lime, ferrous sulfate and polymer to remove suspended particles.
Application of chlorine to kill off bacteria.
Application of fluoride to prevent tooth decay.
Filtering through anthracite coal and and sand to remove the last remaining suspended particles.
Desalination plants have the additional task of removing the salt from the water. There are two ways of achieving this. The first method is to boil the water until every last drop has been converted into steam and then recondensed again. Alternatively, membrane filtering can be used, which requires that the water is pumped at high pressure through a water but not salt permeable membrane. Both of these methods require large amounts of energy (Power stations are a good location for this).
More importantly, the areas that require desalination plants, are the same areas which are pouring/or have poured unprocessed sewage and toxic waste into ground water supplies. It would be more energy efficient and environmentally friendly to implement waste water purification, than to run a desalination plant in the first place.
Far more wasteful a consumer of water is agriculture with "grandfather rights" to water supplies. Large areas of agriculture, particularly in the south west, are using vast quantities of water for high water consumption, relatively low added value crops such as alfalfa and rice. Tis water is delivered at prices set in the 1930s and guaranteed for ever. Those same water supplies would be fare better spent for the food of the community on providing for urban inhabitants, including - if they will - watering their laws.
If Mass is in trouble, watch out Arizona. Pheonix (I think it is) is taking most of its water from an aquifer which is about 40,000 years old, and dropping at 2 metres per year. It is going to run out. Then there is going to be Trouble.
Consciousness is an illusion caused by an excess of self consciousness.
it's _brockway_ not brockton!
You seem to be completely unfamiliar with all the techniques of water desalination. Saltwater Desalination: Chapter 1 will educate you. Of particular interest is http://www.coastal.ca.gov/desalrpt/dc1tbl1.gif this chart which shows that distillation consumes much less power than reverse osmosis
Even those who arrange and design shrubberies are under considerable economic stress at this period in history.
Some examples I recall, but since they are from my memory, take them with a grain of salt. I can have messed it up.
Berlin, Germany: The people there were so economical with their use of water, the sewers had not enough water to function properly.
In a quarter of Toyko a person built a tank to collect rain-water, to water his garden and WC. He ran into several problems with the administration, which (somewhere in summer last year, IRC) finally supports the idea.
Several neighbours were suprised by that idea and asked him to equip their homes with such a tank, too.
They do it mainly out of enviromental reasons. The savings on water can barely justify the investment.
So, how do you get people to save water?
Educate them
and make water more expensive
Later on, when you really need a de-salination plant, you could use the savings from the increased fees for water to build it. (Or, considering public spendings, you could use the reduction of increase of debt to build it.)
"Between strong and weak, between rich and poor [...], it is freedom which oppresses and the law which sets free"
Many people seem to be completely unfamiliar with all the techniques of water desalination. Saltwater Desalination: Chapter 1 will educate them. There are many techniques including Distillation and reverse osmosis Hopefully the flaming back and forth will cease. Of particular interest is this chart which shows that distillation consumes much less power than reverse osmosis.
Even those who arrange and design shrubberies are under considerable economic stress at this period in history.
Isn't New England is among the most water-rich areas of the country? I agree that conservation before increasing supply makes a lot of sense.
From Geology 101 - Seawater chemistry
The amount of salt in sea-water is measured in terms of salinity (the number of grams of salt in a kilogram of sea-water). Normal sea-water has a salinity of 35%, or around 35 grams. Thus, one metric ton (1000kg) of sea-water would give you 35,000 grams or 35 Kilograms of salt (35 x 1 Kilogram bags of salt).
Of this, the distribution is as follows:
Chloride: 55.04%
Sodium: 30.61%
Sulphate: 7.64%
Magnesium: 3.69%
Calcium: 1.16%
Potassium: 1.10%
Now, the average adult human need 2 litres of fresh water to drink just to survive each day (2 litres = 2 kilograms at 4.0 C). Although some of this can come from food such as meat, vegetables and fruit.
If a desalination plant is used, that's 70 grams of salt being produced per person/day.
At most an individual is only going to require 1 gram of each mineral (Eg. sodium).
So around 65 grams/day of salt is going to have to be placed somewhere.
Multiply this by 1,000 people for a small town (65kg salt produced per day) and
1 million for a large city (65 tonnes salt produced per day).
And that's not including the requirements for washing machines, dish-washers, garden sprinklers, and toilets.
Wow, a Lyndon Larouche link. Check out the circle-the-world MagLev train plan right next door.
Watch out Arizona? Woo Hoo! Five years of drought and counting.
Without a doubt, we here in Phoenix may already be living on borrowed time. Water here is pulled from 3 sources. Groundwater, as you mentioned, reservoirs on the Salt and Verde Rivers, and from the Colorado River via the Central Arizona Project.
For goundwater, the aquifer is dropping. As a result, we are banking water from the Colorado River from the States allotment by pumping it back into the aquifer. Actually holding water for other States that are not talking their full allotment (Nevada and Utah if I remember). The point of that is to take our full amount of water every year so that California doesn't try and lay claim to the water. Of course, at some point the other States are going to want their water back.
We have also had a drought going on five years or so now. Roosevelt Lake on the salt River was running at 1/3 to 1/4 capacity lately, and Horseshoe Lake is about dry also. Saguaro, Canyon, and Apache Lakes on the Salt River are not drawn down, yet. On the Verde River, Horseshoe was drawn down but Bartlett is still full. We really need at least five or six really wet years to pull out of the drought. Most of this water comes from the Winter snowpack in Northern Arizona. If youu see news this Summer about large fires in North Central Az, then it was most likely a dry Winter.
The canals in Phoenix that were dug over 100 years ago were actually following canals that had been dug by a Indian tribe which we call the Hohokam (they used sharpened sticks to break up the ground before carrying it away). They had extensive irrigation in the Valley where Phoenix now sits for agriculture. They disappeared about 100 years before Coloumbus arrived in the New World. They may have disappeared because of drought or their crops failed (the Salt River is called that for a reason), we do not know why.
Phoenix might just dry up and blow away, soon!
Just picking nits, but if there are 1000g in 1kg, then 35% should be 350g of salt in 1000g of saltwater, or you should say 3.5% = 35g of salt in 1000g of salt water.
Likewise, 1 metric ton (1000kg) of sea-water at 35% (as you say) would be 350kg of salt, not 35kg.
They're planning to build the plant in Dighton, which means the source of water will be the Taunton River, which is more brackish than saline.
Boiling a pound of water at atmospheric pressure takes roughly 1000 BTU's, and there are 140,000 BTU's in a gallon of fuel oil. So a gallon of oil can boil 140 pounds of water or about 18 gallons. That is a lot of oil.
But if you boil a pound of water to remove the salt, condense it, you are throwing away all of that heat released when it condenses, almost as much as required to boil it. How can you recover that heat since you are going to boil at a slightly higher temp and condense at a lower temp and heat cannot move uphill?
One technique is multi-effect distillation. You boil and then condense at atmospheric pressure. The condensing at atmospheric pressure is hot enough to boil at some pressure below atmospheric. You condense and then use that heat to boil at an even lower pressure. You keep going until you are what ever vacuum pressure boils water at room temperature. The same 1000 BTU's to boil a pound of water is used several times to boil several pounds of water in several "effects" (stages of the still).
The other method is mechanical vapor compression. If you take the vapor from boiling and compress it in an centrifugal compressor, it can condense at a somewhat higher temperature, and you use that heat to boil the water feeding the compressor. While it seems like pulling yourself up from your bootstraps and violating a thermodynamic law, it is not that much different than a heat pump.
There is some minimum energy required to desalinate water, it is much less than 1000 BTU per pound, and if you know the osmotic pressure for that salt concentration, you take that pressure and the volume of water you want and use work = pressure times volume. That energy is not without consequence, and that is why you probably want to desalinate brackish (slightly salty -- often available from wells when pure water is not available) than going for sea water.
Also, there is some effort in approaching the thermodynamic "reversible" minimum energy of desalination. The multi-effect stills and the vapor compression still have to move large amounts of heat through heat exchangers at small temperature differentials. With reverse osmosis, you probably are pumping harder than the bare minimum to oppose the osmotic pressure so you get enough fluid through the membrane to make it worthwhile.
Multi-effect distillation is probably the way to go for big plants, vapor compression for mid-sized, and reverse osmosis is really probably only effective for small-scale stuff because the membranes are expensive and need replacement. Even with what I said, the energy needs are not trivial -- perhaps you want some kind of cogeneration where you run a multi-effect still from the waste heat stream of a gas turbine.
If construction was anything like programming, an incorrectly fitted lock would bring down the entire building...
Yes, that should read: 35 o/oo(parts per thousand), not % (parts per hundred).
Having operated desalination plants for 6 years while in the US Navy (we could produce 200,000 gallons of fresh water daily, so small scale), the idea that you boil of every drop of water is a little misleading.
Actually we would remove only about 10% of the water from the saltwater we pumped through the system. Any higher extraction than that increased scaling problems creating a maintenance nightmare. One poster asked what the communities planned to do with all the "extra" salt. It is pumped back into the ocean with the rest of the brine.
Also, to reduce energy costs and heat loss, all the production is done at partial vacuums to reduce the boiling point. If memory serves, the we reduced the boiling point to 165F, but it was 14 years ago, so my memory is a little fuzzy.
I am afraid you got to read the article as well, not just the charts... Latest distillation methods (MSF, MED) require less electricity, but after you add the extra heating requirement, the energy bill can still be higher than reverse osmosis (RO)...
An extract from Saltwater Desalination Chapter 1
For example, in addition to the 3,500 to 7,000 kWh/AF of energy required for electricity, the thermal energy needs for a MSF distillation plant is estimated at 270 million Btu/AF (about 26,000 kWh/AF);
c.f. the energy for 2 passes RO is 6500-12000 kWh/AF.
When did the terminology transition from desalinization to desalination? Too many people have a problem remembering how to spell the former? All through the eighties and nineties when everyone here in Florida was talking about the technology, the name was always desalinization. This new term is new to me.
I don't know if anyone's tried scaling it. I imagine that for densely populated places that demand very large amounts of drinkable water on a daily basis, it would require impossible amounts of evaporation surface.
According to this page, the low end of the scale is about 11kWhr per 1,000 gallons (3,785L) for reverse osmosis. The Tampa plant produces up to 111,000,000 gallons per day. So that comes to 1,221,000 kWhr per day. We can skip the electrical conversion and use solar heat to evaporate and distill the water, but that requires much more power than reverse osmosis. I'm going to have to say this means it won't scale well, except perhaps in desert locations where you can make a very very very large, shallow black resevoir to evaporate water in.
I once in my life took a shower under a 5 gallon/minute showhead, and it was wonderful! They don't make them like they used to. It is illegal in the US for a shower to use that much water. IIRC the most you are allowed in 3 gallons/minute, and likely less.
One of the nice features is that you can buy things like water and electricity from your neighboring cities for a price. This price tends to be higher per unit of supply than you could provide with a structure like a power plant or water pump, but requires far less up front cost. The not so nice thing is that your neighbors will occassionally renegotiate the price with you, meaning you'll pay more each month if you want to continue getting these supplies.
The joke in the previous post is based on the fact that you could import water (based on the bottled water comment) or that you could build a costly desalination plant (as the article suggests is happening). In sim-city you'll get shafted in time if you don't provide your own facilities, thus the neighbors raising the cost of bottled water is funny.
Now I feel like one of those people that analyzes a joke until it isn't funny. However, I went to the trouble of explaining for the poor non-sim-city player so I'm just going to post it... blah. The interesting thing is that bottled water seems to be pretty expensive anyway, and building one of these big plants is probably well worth the trouble in the long run.
If not now, when?
15 min shower = 600 gallons
60 gallon tub = 480 pounds
So, how many bottles of Disante water would it take to fill a bathtub? :)
Desalination sounds like a good idea to me. It's not like the Atlantic is going away any time soon and while expensive to start up and maintain, you'll provide proof against fresh water shortages and drought.
This doesn't mean that it will be cool to water your lawn when they kick in the desal units to make up for a lack of fresh water - and your bill undoubtedly will spike regardless.
However, more communities that invest in desal plants (those near bodies of water that make that feasible) will feel less impact once the big squeeze comes as companies like Enron finish gobbling up fresh water utilities.
Often there is a 'restrictor' in the shower head that you can easily remove. I put in a new shower head at the Townhouse I lived in last, and it was pitiful. Then I took the head off and noticed that there was an insert I could remove with a regular phillips screwdriver.
I think it's sort of an aptitude test. People who don't know how to use a screwdriver suffer. Also, I probably broke some sort of law by making my modification.
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