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Wastewater Into Energy

michael posted more than 10 years ago | from the stand-upwind dept.

Science 54

fenimor writes "A lot of electric energy could be produced from a city's wastewater, researchers at University of Toronto have discovered. The research revealed that the wastewater contained enough organic material to potentially produce 113 megawatts of electricity - 5 times more than required to operate wastewater treatment plants."

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This first post... (1, Funny)

Anonymous Coward | more than 10 years ago | (#10313996)

belongs in waste water.

sad truth (1, Insightful)

BinLadenMyHero (688544) | more than 10 years ago | (#10314027)

So many cool techs.. great!
But if it doesn't turn out to make (or save) money, it will go nowhere.
Capitalism (and consumism) is ruining the planet.

Re:sad truth (1)

Marxist Hacker 42 (638312) | more than 10 years ago | (#10314060)

Actually, capitalism and consumerism aren't that bad- as long as you don't have the unholy union of government that is the corporation.

Re:sad truth (4, Interesting)

cpeterso (19082) | more than 10 years ago | (#10314145)


if it doesn't turn out to make (or save) money, it will go nowhere. Capitalism (and consumism) is ruining the planet.

Actually, capitalism will SAVE our planet. If people value living on a nice, clean planet, they will pay for such benefits. The problem is not capitalism. The problem is the environment is a market externality. It's the classic tragedy of the commons: everyone uses (up) the environment, but no one PAYS for it. This is usually because governments disallow or dismiss environmental class action lawsuits.

The Soviet Union was on of the world's worst polluters. Today, the US government is the worst polluter in the country. Why are they allowed to pollute? When you write the rules, they don't have to apply to you. For some reason, most environmental and endangered species protection laws DO NOT apply to the US government or military! >:(

Re:sad truth (2, Interesting)

MarsDefenseMinister (738128) | more than 10 years ago | (#10314367)

You're damn right that's capitalism. We all started out living on a nice clean planet. Then the capitalists got ahold of it and polluted parts of it up. And now, if we want to live on a clean planet, here's a capitalist right on schedule, promising to sell us one. And you know he's right, because the commies were terrible polluters. So what's wrong with this picture?

Re:sad truth (1)

smurf975 (632127) | more than 10 years ago | (#10314523)

No, he is saying that if you want a cleaner planet or just a cleaner country. You will have to pay for it (in dollars). Someone will have to pay for the cleaning crew, stricter laws and so higher prices.

However people tend to go for less environmental friendly products because they are cheaper. So in terms of capitalism it's their own fault for the messed up enverioment.

Re:sad truth (3, Insightful)

MarsDefenseMinister (738128) | more than 10 years ago | (#10314611)

I know what he's saying, but I'm offering another way to look at it. Every time someone asks us to cough up some money to clean up the environment, we have to ask ourselves who polluted it in the first place. We had a clean environment, and it was polluted because someone decided that the future could suffer so that a profit could be made today. This is a crime, and now to say that it's the natural order of things that we have to pay money to clean our environment is putting things backwards.

It's extortion. I'll stop polluting your environment and/or beating you up if you pay me some money. We shouldn't have to take it. You know who should have to pay for pollution? The capitalists. If they want to pollute, they should have to pay for it, not us.

Re:sad truth (1)

Scarblac (122480) | more than 9 years ago | (#10317336)

In short, using capitalism to fight pollution is fine, as long as the pollution becomes part of the equation.

Every polluter must pay for cleanup. Make the cost of removing pollution part of the cost of every product you use and buy. *Then* capitalism will have an effect, and people will choose to buy the cleaner things because they're cheaper.

If that doesn't happen, and producers get to pollute for free, capitalism has no mechanism to deal with it.

Re:sad truth (1)

CodeMonkey4Hire (773870) | more than 9 years ago | (#10318110)

Extorting the environment for short-term profits is akin to social security and the [US] national deficit. It is a tax on the youth (or unborn). We are shifting our problems to the future so our kids and their kids will have to fix them. Same as our parents did to us.

Unfortunately, it will probably take a combination of government regulation and the pressures of capitalism to force us to clean up any of it. Until then, there are just too many people who don't seem to care. As long as people care more about their rights to own their automatic weapons (for hunting?) than the environment and the deficit we will continue to snowball downhill.

Re:sad truth (1)

MarsDefenseMinister (738128) | more than 9 years ago | (#10318369)

I'm not sure what you mean by the social security thing, but the national debt is caused by similar attitudes.

Re:sad truth (1)

CodeMonkey4Hire (773870) | more than 9 years ago | (#10318895)

Social security is basically* a way for your grandkids to help pay for your retirement. As long as the population was growing quickly (baby boom) the younger generation did not suffer greatly. However, now there is a great number of people reaching retirement age and the ratio of people collecting social security versus the people paying into social security is starting to/ about to crash.

So far the only actions that have been taken to "fix" this is to raise the age to collect retirement benefits. (I have heard this refered to derisively as the biggest pyramid scheme ever.) Now don't get me wrong, I lean a little in the liberal, socialist, and statist directions. I understand the need fot a social safety net for the poor and the old (and especially those who are both). It's just that this has become so broken and the people who get out to vote the best (the elderly and soon-to-be elderly) are the same ones who don't want to see any changes. They are effectively pushing the problem to successive generations (just like the enviroment, global warming, depletion of natural resources, extinction of fauna/flora, national debt, etc.).

*has turned into

Re:sad truth (1)

MarsDefenseMinister (738128) | more than 9 years ago | (#10319204)

OK, I understand what you are saying now. Offtopic, but it's interesting anyway. The date that Social Security is projected to run out of money is still very far off. So far off that I won't be around to see it, and I'm only 35! The articles that say SS will be bankrupt by 2029 are wrong. If you read closely, they are actually saying that SS will start to pay out more money than it takes in in 2029. The time for it to run out of money completely is much further off. And, even if we reach that point, everything can be brought back into balance again by paying out 75% benefits, or raising the retirement age.

This is not a problem that we are foisting off on our kids. It's chicken little type scare-mongering by people who want to see social security go away. They say that the system is bankrupt, as if it was bankrupt right now. They say 2029 is the dooms day, when 2029 is just the day that the very large trust begins to be tapped. They say the system cannot be fixed, as if today's situation is somehow holy, given to us by God, and cannot be altered to fit the situation.

Hogwash! A couple minutes of thinking about the situation should raise a lot of questions in people's minds about why some would be so dead-set against a program that works really well, and will continue to work well into the future.

Re:sad truth (1)

CodeMonkey4Hire (773870) | more than 9 years ago | (#10320369)

Yes, definitely offtopic (this is /., right?). I don't want to see it disappear, I just recognize that there are problems. I just hate that it has become one of the many 3rd rails in politics.

Re:sad truth (1)

cpeterso (19082) | more than 9 years ago | (#10322241)


Polluters would not be able to afford to pollute if consumers stopped buying the polluters' products. Consumers should stop financing polluters! I'm a vegetarian because I think meat production is wasteful and environmentally damaging. I am voting with my dollars. The market is greedy: it will follow the money. Look at all the hyped-up organic food markets and hybrid cars. The market is listening (albeit slowly).

Re:sad truth (1)

MarsDefenseMinister (738128) | more than 9 years ago | (#10322379)

Won't work, because the solution requires all consumers to act in unison, at the same time, consistently. In the end, the environment will still be trashed.

Re:sad truth (0)

Anonymous Coward | about 10 years ago | (#10325127)

EVERYONE POLLUTES. This includes every creature that produces carbon-dioxide, and produces solid-waste.

The problem with pollution is that "everybody blames everybody else" for the pollution, instead of having a little civic duty for your planet, while your children can still eat, and we can still grow things to eat. This won't be the case, if the pollution and carbon-dioxide levels reach 'x' point.

The sad truth is, we are running out of resources on this planet, and instead of offering solutions, we berate eachother.

That's like kicking your dog, while watching your planet hurl towards the star it orbits.

If we don't talk solutions, but push blame, then we don't know how to work together; To bad. Humans will die-off needlessly, but that's life; Maybe the NEXT species will encounter greatness. See you later you big-mouthed monkeys.

Three choices: (0)

Anonymous Coward | about 10 years ago | (#10328560)

  1. Put the government in charge of everything. They'll pollute like mad and do nothing about it. This has happened again, and again, and again. Meanwhile, you won't be able to get a decent pair of shoes or decent food or a roof that doesn't leak, because the government is in charge of everything and they can't do anything right. The country will be too poor to do anything about pollution anyway. This also has happened again, and again, and again.

  2. Leave things as they are. You'll have great shoes, a watertight roof, and a square meal. In fact, you and the rest of society will continue to be so wealthy that you can afford to clean up the pollution out of petty cash.

Think of it this way: You're telling me that you're being oppressed because, say, you've got $100 and you have to pay $5 to clean up somebody else's mess. Your solution is to fuck things up so you've only got $20, and you pay $0 to clean up the mess. Case A, you've got $95 to spend on beer and video games. Casae B, you've got $20 to spend on beer and video games. Oh, and in Case B the environment gets fucked up worse and stays fucked up forever. And you prefer Case B. HELLO?!

Re:sad truth (-1, Troll)

CamMac (140401) | more than 9 years ago | (#10314682)

Right, because it was the capitalist that first destroyed animals for his needs. It was the capitalist that first cut down trees to make her house. It was the capitalist who forced nature to only grow one kind of plant in an area, leeching nutrients from the soil. Of course, by capitalist you mean "Humanity trying its best to survive"

Whats your priority? Should we do our best to prevent damaging Mother Nature? Guess what. Mother Nature is out to kill you. And the only thing that lets us survivie is by beating her down. You say that damaging Mother Nature could be bad for us? Your right, in the long term. And no one cares for the long term. However, because the capitalist does care about his bottom line, the capitalist pig is willing to find cheap energy sources. The Capitalist pig is willing to find ways to make reintroduce nutrients into the soil. The capitalist pig is willing to do what he can to make sure that the resources he needs are there in the future and that his planet is clean.

Unlike the damn tree hugging hippies who can't take a bath for fear that the soap will harm the enviroment.

--Cam
PS To all the Treehuggers in Boulder with the "Save the Planet" type bumperstickers. If you paint your rust spots, and take you car in for regular maintance, it won't polute the enviroment half as much as it does now. Set the example.

Re:sad truth (1)

zymurgy_cat (627260) | more than 9 years ago | (#10316112)

cpeterso makes a good point about market externalities. An excellent book that points out how to capture market externalities and use market forces to protect the environment is "Costing the Earth" by Frances Cairncross (sp?), a former environmental editor for the Economist. Does a good job of showing how a carbon tax, eco-tourism, market-based pollution trading, etc. could work. Also does a good job showing why recycling can often be a counterproductive solution (ie, generating a lot of material that no one wants, thus depressing its value and creating even less of a reason to recycle.)

Re:sad truth (2, Insightful)

Yokaze (70883) | more than 9 years ago | (#10316682)

> If people value living on a nice, clean planet, they will pay for such benefits.

If they can afford to. The problem is, those people who don't care have more money to profit from, hence have an economical advantage, hence are more likely to decide, wether there will be a nice, clean planet.

Companies, which exploit land and its resources in an long term unsustainable way have a faster growth than companies, which don't.
This economical advantage will drive the latter companies into a fringe market, where only few idealist buy to a premium. Any criticism will be ignored by ostracising those people as tree-huggers, and the criticism as dooms-day prophecy. Sounds familiar?
Maybe because we already have a similar situation.

Are people buying from Fair Trade companies? How many people are building an enviromentally friendly home? How about clothes? Energy production?
Why? Why should I pay the premium, when others don't. Tragedy of the common indeed.

What is the difference between a "free market", and Manchester capitalism? Do you think, the then working people in the cities, which were coughing due to the exhausts from the factories, didn't wished for cleaner air, streets and water?

The point is, their voice counted nothing until they got the vote. Guess where the enviromental regulations come from.

Re:sad truth (2, Informative)

FooAtWFU (699187) | more than 10 years ago | (#10314181)

When I went to the local water treatment plant, they had a set of turbines to burn the gas which they could extract from the wastewater. They weren't using them. It was cheaper for them to just buy electricity as they needed.

Splashplop! (5, Funny)

contagious_d (807463) | more than 10 years ago | (#10314035)

According to the article, "Any recovery of potential energy above that can be returned to the grid.". I wonder if there is any way you could set this up so that you get credits on your power bill when you exceed a certain amount of waste. That would be awesome! Like getting paid for your hard work in the bathroom! Oh yeah, another thing... this is a story about poop. That is also awesome.

Brownouts... (2, Funny)

leonbrooks (8043) | more than 10 years ago | (#10314175)

...take on a whole new meaning.

"Citizens are advised to buy and eat more beans to ensure continuity of supply in coming weeks. Authorities are considering airing an updated version of War of the Worlds during the first season of peak demand."

Re:Splashplop! (3, Interesting)

TykeClone (668449) | more than 10 years ago | (#10314343)

The places with the most economies of scale to take advantage of this are cities (tax credits mean nothing to cities, unless they can sell them) or large livestock farms.

If you want to talk about poop - visit a hog confinement facility.

Methane gas (2, Interesting)

BrookHarty (9119) | more than 10 years ago | (#10314039)

Man I'm dense, I'm wondering how they turned shit into power, had to RTFA to find out its methane gas from microbe processed organic material. 1 More line on the Slashdot topic and I wouldnt have had to read the article, the article was that small....

Re:Methane gas (-1, Troll)

Anonymous Coward | more than 10 years ago | (#10314369)

Oh NO! You had to RTFA?! You poor bastard, that really sucks!

Fuck, man. I mean I know 99% of commenters don't bother to read the article before spewing their intellectual sewage, but I thought that was a bad thing.

Not shit. Energy! (1)

cryptochrome (303529) | more than 9 years ago | (#10315142)

Raggedy man.

Pretty old news (4, Informative)

HotNeedleOfInquiry (598897) | more than 10 years ago | (#10314049)

About 10 years ago I was elected to the board of directors of a wastewater district. We captured the methane from the digesters and used it to drive the aereation (sp) blowers. Saved about $30k/month in electricity. Most of the time surplus methane had to be flared off.

Now some places also dewater the sludge and burn it to generate energy. Quite a bit more messy and polluting than just using the methane.

All this technology has been around for about 20 years. It's just complicated and sometimes polluting. There's almost always regulatory issues about who can sell power to who, who can burn what where and so on.

At least it wasn't a repeat (2, Informative)

Engineer-Poet (795260) | more than 10 years ago | (#10314166)

When I saw this article I was afraid it was another "microbial fuel cell" thing.

I don't see any reason why dewatered sludge couldn't be fed through an anything-into-oil plant [changingworldtech.com] and converted to energy more cleanly than by incineration.

Re:At least it wasn't a repeat (1)

TykeClone (668449) | more than 10 years ago | (#10314361)

That would just make too much sense - how dare you!

This would also be a great opportunity for large livestock farmers - most of the time they have a surplus of "organic waste matter" and have to scramble to find a place to till it into the ground. If they could sell it for conversion into oil - that's just a good idea.

Sense and sensibility (1)

Engineer-Poet (795260) | more than 9 years ago | (#10320160)

That would just make too much sense - how dare you!
Engineer-Poet, confounding /. with logic since 2004.
This would also be a great opportunity for large livestock farmers - most of the time they have a surplus of "organic waste matter" and have to scramble to find a place to till it into the ground.
I'm not sure how useful it would be for livestock farmers. In a city, pretty much everything that goes to the sewage plant is quite a distance from where it originated. Unless you can reduce the bulk of the material by a large factor it's uneconomical to ship it very far to close the loop. A feedlot may be in a similar boat, but the livestock farmer who also grows grain and hay has a supply of nutrients (phosphorus, potassium, nitrogen) close to land that needs replacements for the nutrients removed to feed the livestock. Once the major amounts of carbon have been digested for methane, what remains looks like it would be more valuable for fertilizer than as a further feedstock; you certainly don't want to convert nitrate into ammonia (which seems to me what you'd get by putting nitrate into a reducing environment) if you can avoid it.

Changing World Tech doesn't have anything on their site for the products available from municipal solid waste, but if a city could use one plant to convert both their MSW and sewage sludge into fuels and stable byproducts they'd eliminate a great many headaches.

Re:Sense and sensibility (1)

TykeClone (668449) | more than 9 years ago | (#10323880)

The problems with large scale livestock farming are that you need a pretty good chunk of land to "take the poop" from an operation. When you put too much manure of the fields, you end up with nitrate runoff which makes people downstream (and eventually the gulf of mexico) unhappy.

I think that I read somewhere that some hog operations produce the raw sewage of a city of 30,000 people. When you get that much manure, disposing of it by tilling it back into the land becomes problematic, and converting it into oil would be an interesting idea.

I'm not sure that the economics of it would work, but it would be a neat thing to do - converting corn into oil with a small "middle step" (just watch that step).

Re:Sense and sensibility (1)

Engineer-Poet (795260) | about 10 years ago | (#10329286)

The problems with large scale livestock farming are that you need a pretty good chunk of land to "take the poop" from an operation....

I think that I read somewhere that some hog operations produce the raw sewage of a city of 30,000 people.

They're called CAFOs [google.com] , Concentrated Animal Feeding Operations. I suspect that these are only economical because they are allowed to dump animal waste with minimal or no treatment; if they had to pay for the remediation required of municipal sewage plants, they would cease to exist and the work would be done in much smaller operations closer to the source of the feed. This would allow the waste to be used as fertilizer on the farms from which the feed came, closing the loop.

Yes, you probably could dispose of the waste using thermal depolymerization. I don't think that this is economical in an era of rising oil and gas prices; being able to cut transportation requirements and recycle gas-derived nitrates (nitrate fertilizers are made from ammonia, which is synthesized from nitrogen and natural-gas-derived hydrogen) is going to have a lower overall energy cost than an inefficient conversion of excrement to fuel, especially if the excrement can be digested for methane with little loss of nitrogen.

Re:Sense and sensibility (1)

TykeClone (668449) | about 10 years ago | (#10332185)

You could do the same with human waste if it was guaranteed not to have any non-organic nastiness (like other chemicals or heavy metals) in it. The trick is to have access to enough land to till it into. Too much manure can cause problems when it runs off during the spring.

How many sewers are you willing to install? (1)

Engineer-Poet (795260) | about 10 years ago | (#10333996)

You could do the same with human waste if it was guaranteed not to have any non-organic nastiness (like other chemicals or heavy metals) in it.
If your town has even one plating plant or other manufacturing operation in it, good luck. You'd need separate sewer systems for domestic and industrial, and guarantee that nobody dumps anything nasty down either a domestic sewer or a storm drain. I see this having two chances: slim and none.

This is one reason why I think thermal depolymerization has a bright future for cities. It reduces the inputs to water, combustible gas, hydrocarbon liquids and a solid fraction of carbon and ash. If you can guarantee that e.g. heavy metals will wind up in the solid fraction, you've reduced it to a compact and stable form which can be landfilled much more safely than most other possibilities.

Re:How many sewers are you willing to install? (1)

TykeClone (668449) | about 10 years ago | (#10334420)

That's what I was trying to get at, but didn't say it so well.

You could also set up a pretty good system for it by doing taking corn and making ethanol and feed stock. The feed stock can be given to cattle (and hogs? not sure about that) which will produce lots and lots of manure and meat. A portion of the manure can be tilled back into the surrounding land, the balance can be taking to the depolymerization plant. After slaughtered, the remnants of the cattle and hog carcasses (that which is not used in hot dogs) could be also taken to the depolymerization plant.

Re:At least it wasn't a repeat (1)

tzanger (1575) | more than 9 years ago | (#10315293)

I don't see any reason why dewatered sludge couldn't be fed through an anything-into-oil plant and converted to energy more cleanly than by incineration.

Equipment I designed does the heavy lifting for the heater jackets used in that stuff. A year ago I was sent down to Carthage, MO to the first large-scale facility these guys built for Butterball... It was a mixed emotion trip... I was thrilled that I got to see this stuff up close and that something I'd designed was in it, but at the same time the reason I was there was because the stuff I built wasn't working right. :-)

Re:At least it wasn't a repeat (1)

Engineer-Poet (795260) | more than 9 years ago | (#10323569)

Speaking of repeats, do you have any news about how the plant there is working? I heard that it had serious issues with defective welds, but little beyond that.

Re:At least it wasn't a repeat (1)

AB3A (192265) | about 10 years ago | (#10329091)

I don't see any reason why dewatered sludge couldn't be fed through an anything-into-oil plant and converted to energy more cleanly than by incineration.


My employer is a water and sewer utility. Allow me to inject some ugly realities in to this beautiful theory.

First, while most of us think of toilet output when we think of sewage, the reality of most municipal wastewater is that it has loads of soap in it. In fact, the smells you encounter most often at a wastewater plant are really kind of a musty perfume-like smell of soap. Most of what we get is not manure-like as it might be if it came from a chicken farm.

Second, did anyone notice that little item on the technology and products part of the web site marked "organic vapor"? What is that? Is it recoverable? Can you burn it for fuel without incurring the wrath of the EPA? Who would want to live anywhere near that kind of thing?

Third, there needs to be a plan for what happens in case of a storm. The composition of the watewater can change dramatically in situations like that.

OK, so maybe this particular idea isn't so hot. What about other co-generation ideas? Well, in today's growing cities the wastewater doesn't spend enough time in the pipes for anerobic digestion to get a significant start. So, we'd need a storage facility somewhere. Reality check: A typical plant in our system processes around 20 to 30 Million Gallons per Day (MGD). We also support a large regional facility which can process 200 MGD. Where in the world are you going to find a holding tank to store that much sewage for any length of time? The beauty of aerobic processes is that most of the water is back in the river in about eight hours. Can the same be done with Anerobic digestion?

Also, what does one do in the winter when temperatures get low enough to inhibit or slow bacterial activity? Heating that much water is not cheap in anyone's book.

Believe me, for what we spend on sludge hauling contracts, if there were any better solution, we'd jump at it even if it were more expensive in the short term. The problem is that they all have serious flaws when you take a closer look. We all wish there were some sort of magic bullet here, but there really isn't.

Re:At least it wasn't a repeat (1)

Engineer-Poet (795260) | about 10 years ago | (#10330184)

First, while most of us think of toilet output when we think of sewage, the reality of most municipal wastewater is that it has loads of soap in it.
I was talking about sludge, which is quite a bit removed (and concentrated) from the state of raw sewage. As for the soap, if you can separate that and feed it through thermal depolymerization it would be good. Lauryl sulfate (derived from dodecanol) ought to be just the kind of thing that produces good hydrocarbons as output. Ditto stearates.
The beauty of aerobic processes is that most of the water is back in the river in about eight hours. Can the same be done with Anerobic digestion?
I doubt it. Anaerobes seem to require days (high-temperature) or even weeks (low-temperature). The literature I've seen on producing "gobar gas" from manure talks about cycles on the order of 60 days. On the other hand, you are not going to be feeding raw sewage through this process; it's going to take the settled solids and enough water to make a slurry, and that's pretty much it. What's your ratio of solids to total volume?
... did anyone notice that little item on the technology and products part of the web site marked "organic vapor"? What is that? Is it recoverable? Can you burn it for fuel without incurring the wrath of the EPA? Who would want to live anywhere near that kind of thing?
The CARB is already requiring afterburners on bakeries to destroy "organic vapor" produced by yeast, so I suspect that burning the vapor may be a requirement. As for what it is, who knows; do you have any idea what organic byproducts of methanogens have a high enough vapor pressure to come off with the gas? I don't. But if you burn them with the methane (and they don't contain sulfur) you ought to be just fine. The people living nearby would probably like it better than the current vapors.
Believe me, for what we spend on sludge hauling contracts, if there were any better solution, we'd jump at it even if it were more expensive in the short term.
The May 2003 article in Discover which broke the anything-into-oil story to the wider world is here [discover.com] , but it's now subscriber-only. I seem to recall that it quoted conversion products for a mixture of sewage sludge and grease-trap waste, but I can't tell you what they are without the article to cite. Even the Google cache has been purged.

Re:At least it wasn't a repeat (1)

AB3A (192265) | about 10 years ago | (#10332553)

I was talking about sludge, which is quite a bit removed (and concentrated) from the state of raw sewage. As for the soap, if you can separate that and feed it through thermal depolymerization it would be good. Lauryl sulfate (derived from dodecanol) ought to be just the kind of thing that produces good hydrocarbons as output. Ditto stearates.


Uhh, what about bleach? What about phosphates? Yeah, I know, the really widespread uses of phosphates has been banned, but you'll still see some evidence of it here and there.

Anaerobes seem to require days (high-temperature) or even weeks (low-temperature). The literature I've seen on producing "gobar gas" from manure talks about cycles on the order of 60 days. On the other hand, you are not going to be feeding raw sewage through this process; it's going to take the settled solids and enough water to make a slurry, and that's pretty much it. What's your ratio of solids to total volume?


Even if you were talking about sludge, we can manage to get enough storage together for a few days. It might be feasible to hang on to about a week's worth of that stuff if there were a motive to do so --but not a month or more.

I don't have typical solids to total volume number handy, but it is normally only a few percent of the total volume of water. Even then, if you have to accumulate this stuff over weeks for it to produce much energy, you're still looking at an extremely large and potentially dangerous storage problem (from the explosive gas it would produce).

The CARB is already requiring afterburners on bakeries to destroy "organic vapor" produced by yeast, so I suspect that burning the vapor may be a requirement. As for what it is, who knows; do you have any idea what organic byproducts of methanogens have a high enough vapor pressure to come off with the gas? I don't. But if you burn them with the methane (and they don't contain sulfur) you ought to be just fine. The people living nearby would probably like it better than the current vapors.


Most neighbors don't even know what those sewage smells are. They expect to smell decaying feces and they don't. So they're happy.

As for burning this stuff, we have one plant with a sludge furnace. We try to dewater the sludge enough so that we don't incur ridiculous transportation costs. This one plant was requried to install several afterburner rings to help get rid of the organic vapors.

If that's the sort of organic vapor these folks are talking about, it's going to cost an awful lot of that energy they produce to safely get rid of these things. Afterburners don't run cheap.

Sludge disposal and methane generation (1)

Engineer-Poet (795260) | about 10 years ago | (#10334517)

Uhh, what about bleach? What about phosphates?
I'll bet that hypochlorite winds up as chloride just from reacting with organic stuff. Dunno what you are asking about phosphates, and I will be the first to admit that I don't know what happens to them in the thermal depolymerization process. The articles I've seen would appear to suggest that they wind up among the solids.

Anaerobic digestion doesn't like bleach (kills the bugs) and will pass the phosphate through the system. You'll still have to dispose of it, but letting bugs convert the organics into methane will reduce the bulk and make it more concentrated.

Based on what you've said, I suspect that the most economical scheme for municipalities dealing with sewage sludge is thermal depolymerization; the market for sludge-derived products is small, contaminants such as heavy metals strongly indicate its disposal other than on cropland, and the processing time for TDP is much shorter than any bacterial process. The flip side of the coin is that digestion is a simpler process than TDP with lower capital costs and no patent barriers.

Even if you were talking about sludge, we can manage to get enough storage together for a few days.
Even if you arrange it vertically? If your solids fraction is 3% and your current residence time is 8 hours, adding the same volume again in methane digesters would allow you to hold the material for about 11 days. That may be enough for the thermophilic bugs to run the reaction close to completion and get rid of most of the BOD of the material.
... you're still looking at an extremely large and potentially dangerous storage problem (from the explosive gas it would produce).
You're storing the slurry. The gas is not explosive unless mixed with air, and you neither allow that to happen nor have more than small amount on hand at any time (the "head space" in the digester tanks). If I were designing such a plant (I'm not a civil engineer, so take with a truckload of salt) I'd use as much gas on-site as was required to run the plant and heat the digester tanks, and any excess would either be burned for additional power or sold to nearby industrial customers to help displace the need for natural gas.
If that's the sort of organic vapor these folks are talking about, it's going to cost an awful lot of that energy they produce to safely get rid of these things.
In the case of anaerobic digestion, the organic vapors are part of the fuel gas; they don't have to be "afterburned" because they're burned the first time. In the case of thermal depolymerization, any combustible gases go to provide process heat.

The only drawback (1, Funny)

Anonymous Coward | more than 10 years ago | (#10314074)

The energy produced is pretty shitty.

Re:The only drawback (0)

Anonymous Coward | more than 9 years ago | (#10318135)

What's that smell?
Oh, that's just my electricity.

And when you're done with the methane (1, Insightful)

Marxist Hacker 42 (638312) | more than 10 years ago | (#10314110)

Use the deorderized sludge in your tabletop nanofactory to make steak- after all, the atoms are the same, it's just the arrangement that is different.

Re:And when you're done with the methane (0)

Anonymous Coward | more than 10 years ago | (#10314154)

I want to mod you disgusting, but I'll settle for insightful.

Energy? From organic material? (1)

perrin5 (38802) | more than 10 years ago | (#10314192)

Really!

All they did was see what the caloric content of the sewage was, and said "If we can turn 20% of this into energy, we have a profit".

where have I seen this before?

Been done for garbage (3, Interesting)

cft_128 (650084) | more than 10 years ago | (#10314318)

They are already doing this for dumps. They have been doing this in Michigan [solutions.ca] using Toronto's imported garbage, and it looks like another one is being developed near Montreal [canoe.ca] . It looks like the Montreal facility will power a paper plant, and if memory serves me correctly -- I can't actually find a link now -- the Michigan dump(s) are selling the power to the grid.

Problems with the Process (3, Informative)

EnergyEfficient (797153) | more than 9 years ago | (#10317244)

Anerobic decomposition makes things beyond A carbon and some hydrogen. You get a few Nitrogen/Hydrogens and more Sulfur/Hydrogens. Both of these gasses when oxidized will make acids that will eat up the equipment. You can ruin an internal combustion engine in less than a day, and a boiler in a week if you don't have the boiler lined. Alot of energy is imbedded in our sewage, from the machines in the field that prep and harvest the food we eat, to the trucks that move that food to the pumps that move the water then the sewage to be processed. With good engineering, some of that energy can be reclaimed, but the researchers make it sound like the process is 'simple' when it is not.

Re:Problems with the Process (1)

oerlikon (198562) | more than 9 years ago | (#10323065)

There may be technical issues, but it IS doable. The cities of Arcata, Chico, Eureka, and Merced in California all run methane co-generation plants at their waste water facilities.

http://www.energy.ca.gov/development/biomass/anaer obic.html [ca.gov]

http://www.biogasworks.com/ [biogasworks.com]

A lot of water research in Toronto (1)

Baron Eekman (713784) | more than 9 years ago | (#10318265)

Some moths ago, there were reports [slashdot.org] of using water from Lake Ontario for cooling. Maybe they can think of a combined solution.

They are already producing methane in TO (1)

rolfpal (28193) | more than 9 years ago | (#10318386)

The plant at ashbridges bay already uses anaerobic processes (on the sludge) to produce methane that is used in heating the plant.

The article was a little simplistic. The reason that sewage treatment plants use aerobic processes for water treatment is that they are efficient ( 1 day residence time comapared to 30 day residence time) Anaerobic digestion can be used when you have seperated the solids from the liquids since they are a very small fraction of the total, and this is what is quite often done. The gas can be used but must be cleaned up if you want to use it for power generation.

Sewage vs. wastewater (0)

Anonymous Coward | about 10 years ago | (#10327431)

what's the difference?

Re:Sewage vs. wastewater (1)

AB3A (192265) | about 10 years ago | (#10328553)

Sewage is usually the term used for the wastewater that comes from homes. Wastewater is more generic and it can include industrial wastes as well.
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