A Step Farther Out (40 page)

Comes now the math: tons times energy/tons times a mess of constants I won't bother to give. The results are interesting: 1.6 x 10
²⁵
ergs, or 4.4 x 10
¹¹
kilowatt-hours. In other words, if we captured
all
the energy from our rubbish we could produce about 2% of the energy we used in 1974. Significant, yes. Important, perhaps. But it won't save us from Arab oil and sinking tankers.

Alas, things are worse than that. No industrial process is 100% efficient, and electrical generation is no exception. With present technology the best we've been able to do at burning rubbish is 27% efficiency, which means that if all our municipal waste were burned in the best boilers we know how to build, we'd get 1.2 x 10
¹¹
kW-hrs, or, coincidentally, some 2% of the electricity generated in 1974—and we have not counted in costs, the energy needed to process and dry, or indeed much of anything.

We could go another way. If we can persuade industries to build alongside the rubbish-disposal system, or take the rubbish to their plants, so that we can use the steam directly without turning it into electricity, we get 66% of the energy value, and that's a respectable 7% of all the process steam used in 1974; well worth trying for, if it doesn't cost too much.

So. What are the costs of all this? The ANNUAL REVIEW gives some figures, which I have recalculated to give Figure 37. (I recalculated because theirs were based on plants processing 275 tons unsorted refuse per day, an awkward figure at best.) They still don't mean very much; is this a low or a high cost? Well, one figure readily available is the capital cost per installed kilowatt of electrical power. That ranges from around $500 for a coal-fired plant to over $1000 for some kinds of nuclear.

Assuming 27% efficiency for a refuse-burning electrical plant, we find the capital cost per kW is $1103: much higher than other kinds of plant costs, which explains why electrical utilities aren't terribly interested. For $1100 a kW they can buy a nuclear
breeder
plant, whose operating costs will be lower than the value of the fuel produced. I suspect that my figures for nuclear power costs are a bit low; they're based on research done a couple of years ago, and the court and environmental impact statement costs of nuclear power are now about as high as the costs of the hardware; but even so, the refuse-plant generator is
expensive.

Or is it? After all, the cities have to get rid of the refuse
somehow.
If we subtract off the costs of sanitary land-fill, and a number of the other expenses of disposing of that growing mound of trash that gives mayors nightmares, our electrical plants begin to make sense after all: but only if we look at cities as a total system, and city budgets aren't prepared that way. Believe me, I know: I've been Executive Assistant to the Mayor of Los Angeles. The Department of Water and Power would scream bloody blue blazes if told they had to spend that kind of money; while many of DWP's senior administrators, people you can't do without, would go job-hunting if told their lordly department was to be combined with Sanitation. Moreover, the City Council would impeach anyone suggesting the kind of capital fundraising (and consequent increase in property taxes) a large-scale electricity-from-rubbish project would require.

Still, if we were starting over, if we could look at cities as total systems, rather than as a series of independent departments; it would make a great deal of sense to get rid of our refuse and extract the energy out of it at the same time. We could
not
run the city on its own garbage, nor is garbage a particularly efficient way to get electricity; but since you have to get rid of the
stuff anyway,
you might as well take out what you can, and the total system costs probably justify the initial capital expense.

Whether in this age, given what we've already spent, it makes much sense is not so obvious: you have to look at each city independently. I suspect that LA could sell the land set aside for sanitary land-fill (another department heard from: although Recreation and Parks knows it can't keep that land forever, right now they're not turning loose) for enough to build some good-sized plants; but I haven't done the numbers. In places where land values are not so high as here, it's more dubious.

Let's leave rubbish for a bit and get down in the sewers. If garbage can't provide more than a fraction of our energy needs, can sewage save us?

__________

Figure 37

THE COSTS OF GETTING POWER FROM WASTE

All figures in constant 1978 dollars per ton (2000 lbs) of unsorted refuse per day. Source: ANNUAL REVIEW OF ENERGY, Vol 1, 1976; Annual Reviews, Inc., Palo Alto, California.

__________

To begin with, sewage is valuable. That should be obvious: it is only the very wealthy western nation that can afford to throw
away
such a valuable resource. Indeed, we spend a lot of money and energy merely to throw it away, after which we burn a lot of valuable coal and oil to generate electricity in order to fix nitrogen to make fertilizer-fertilizer that's not as good as the high-nitrogen sewage we pollute rivers with.

Secondly, there's a long technological history of using sewage as a fuel source: begin with the Indian peasant, who uses buffalo chips to cook his food, and proceed to modern methane generators.

Finally, even if we don't use sewage as fertilizer—and thus by-pass the long series of inefficiencies involved in the generation and transmission of power, fixation of nitrogen, etc., culminating in commercial fertilizer—the stuff has a high energy content.

In other words, using sewage as an energy source has a lot going for it. There are several ways to go.

First, as agricultural nutrient, allowing the crop to be the actual energy-storage system. This is widely done in the Orient, with detrimental side effects: the honey-bucket is a pretty certain means of spreading epidemics. Surely we can do better than that.

Second, as methane source: shovel sewage into a tank, let ferment in the absence of air, and out comes methane. Methane is also known as natural gas, and is rather valuable; indeed, natural gas is the most critically short item in our energy budget. A pound of dry sewage solid will produce about 3 to 5 cubic feet of methane, which sells at $3.53 per 100 cubic meters. Now my source book, with a straight face, gives both those figures in the same paragraph. I'll translate: a ton of sewage produces some 225 cubic meters of methane, and the gas is worth about $80.00. The methane production pretty well sterilizes the residual, which can then be used as high-nitrogen fertilizer. (But we will have to use some of the methane as fuel for drying it before we can sell it.)

Finally, we can produce the methane and then burn the residual. It has been calculated that doing that will let us build a system that operates at zero profit provided that we charge about $5.50 a ton dump fee: that is, those who wish to dispose of sewage must pay us.

Why is this? We're getting valuable fuel out of the system; surely we need not charge a dump fee? Ah, but the plant itself costs a lot of money, and that money isn't free. If the plant already existed, it would make a profit; but the "profit" is lower than current interest rates, and thus the dump fee. Another of the little points usually forgotten by those who are faddishly out to save the world.

On the other hand, technology improves, and one commercial utility, Southern California Edison, was at one time trying to find ways to use sewage as fuel: they contracted to take the entire sewage output of one of the smaller southern Calif. cities free and get rid of it by burning it in their boilers. They didn't quite know how to make that work, but they were doing the research, when along came the Public Utilities Commission to tell them to stop. It seems that wasn't a justifiable use of the rate-payers' money. Utilities shouldn't engage in fuel research, they should generate power. Thus we were all protected by our government, and now a government agency will have to do the necessary research if sewage is to be burned at a profit.

Still, just how much energy could we get from this source? Well, each of us produces about .25 pounds (yeah, I know, but all the other numbers I could find were in the English system and I give up) of
dry
solid each day. That's 11 million tons a year; if it all went into methane generation systems we'd get 90 billion cubic feet of methane annually, and at 994.7 Btu per cubic foot that's 9.6 x 10
²³
ergs or 0.19% (2 tenths of a percent) of the 1974 energy budget. Sigh. It's unlikely to save us, isn't it? However, don't despair. We can also add the animal wastes, which amount to some 25 million tons a year, and get up to 2000 billion cubic feet of methane, 2.1 x 10
²⁵
ergs, or 2.6% of all energy used in 1974. Better than that, it's just about 10% of the energy we obtained from natural gas in 1974—i.e., we could cut natural gas consumption by 10% a year. It's not the Earth, but it's something.

Of course it's also expensive, and technologically some time
away.
What I've given are some maximum theoretical figures, not what we could do tomorrow morning if we set our minds to it.

* * *

Let's see: 2% from human and animal sewage; another 2% from municipal refuse; add in another percentage point just in case: and we've come up with a grand total of 5% of the 1974 energy budget, provided that we can use ALL of the energy from our sewage and garbage and other trash. Since we cannot possibly capture 100% of that energy, I leave it to you to guess at the actual efficiencies; and I think you now see why engineers, as opposed to faddists, don't think we can run the United States on its own garbage heaps.

That doesn't mean the energies in our waste aren't worth recovering. It's particularly true in the case of animal wastes: methane generators aren't very sensitive to scale. Once you get up to a couple of tons a day, larger methane cookers don't cost much less per pound processed. Thus quite small operations could feasibly build them; and, like garbage, both animal and human wastes
must
be disposed of anyway, and dairies ought to be encouraged (through higher sewage fees and the like) to catch that energy and feed it into the national pipeline. Once again, though, each case must be examined individually: distance to pipeline; availability of water (methane cookers take lots of water); and other such factors enter here.

But having done it, we haven't saved ourselves.

* * *

If we got 5% of the 1974 energy budget from sewage and garbage (which we can't, because 5% comes only with 100% efficiency), we'd still have to depend on Arab oil. What else can we do?

Not too long ago there was in vogue a scheme to grow crops for alcohol and run much of our transport system on that. It was even worked out quite elaborately: take sewage and transport it (means not specified) out to marginal farmlands; take the urban poor off the welfare rolls and give them small holdings of that marginal land; and let them grow alcohol crops, thus relieving unemployment, getting people out of the cities, and solving the energy crisis—as well as dealing with sewage.

It sounds good. It sounds marvelous. Why don't we do it?

Well, alas, there are some problems. For one, many of those urban poor have just come to the city from marginal farms on which they couldn't make a living. It might require a larger police force and army than we have to make them go back But leave that. Let's assume we have the labor force or can get it.

What crops produce the most alcohol? You already know that: corn (maize, as they call it everywhere but in the USA); wheat; barley; in other words, cash crops. If they grow well they'll be grown: gone are the days of our big farm surpluses. They are also all crops which respond best to agro-business techniques: there are
enormous
economies of scale. It doesn't cost anywhere near a thousand times as much to keep 40,000 acres in cultivation as it does to keep 40 going.

Then there are the costs of collection. The alcohol must be transported and distributed: first, though, the crops themselves must be carried around to the fermenting vats (since the costs of providing each farm, or small community of farms, with its own generation facility would be colossal); then the resulting alcohol must be piped to where it will be used.

All this is in competition with food crops. True: the United States probably could, at hideous capital costs, grow enough alcohol to run its transport system, and thus be free or nearly so of imported petroleum. We could even afford to do it. It would have one monstrous side effect, though: as we are now one of the few food-exporting countries of this world, we would condemn a lot of people to starvation. I suspect that the very ones who now clamor for our energy-independence achieved through croplands growing alcohol would be the first to denounce such callous behavior.

But: it is in precisely this area that research can be made to pay off. Right now growing plants are very inefficient things. They don't really convert much (1% or so) of the sunlight falling on them into useful energy. Over the millennia man has selectively bred some plants (such as maize, wheat, barley, etc.) to do a much better job than most; now molecular biology may allow us to double that efficiency in a few years.