STINKING lagoons of pig manure created by thousands of animals in giant hog farms can pollute rivers, poison groundwater and pump out clouds of methane and carbon dioxide. So finding alternative uses for the slurry - to generate electricity, say - makes a lot of sense. The problem was that no one has been certain which way of doing it makes the most electricity for the least greenhouse gas production.
Now a Danish team has analysed the various ways in which firms in that country treat pig manure and use it to generate electricity in systems such as anaerobic digesters or incinerators. In anaerobic digestion, bacteria break down waste material by warming it in an oxygen-free vessel, releasing methane which is used in gas turbines. Incinerators burn material to boil water and drive a steam turbine.
The team, led by Trakarn Prapaspongsa at Aalborg University, found that for high-efficiency energy production, anaerobic digestion is the answer. But if minimising greenhouse gas emissions takes priority, the best option was to separate the solid from the liquid waste, dry the solids and incinerate them (Waste Management & Research, DOI: 10.1177/0734242x09338728).
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Have your say
Trying To Achieve Too Much?
Sun Oct 25 12:35:32 GMT 2009 by sciencebod
http://www.colinb-sciencebuzz.blogspot.com
Why worry about greenhouse gases if it's just pig poo? Pigs are carbon-neutral, are they not - assuming they are fed on pigswill that ultimately derives from green plants? So why not simply burn all the methane, and give the plants back their CO2? Are these Danes trying to be too virtuous here, and create a nett negative carbon balance?
It's that solids drying step that bothers me. What's the energy source for expelling water, which as we all know has an exceptionally high latent heat of evaporation? Fossil fuels? One hopes not. Or is some of the methane from anaerobic digesters being used to do that? Wouldn't the methane be better employed generating electricity for the National Grid. This article,scarcely more informative than the authors' lean abstract, would seem to raise more questions than it answers.
Some methane leaks out of the process anyways, and on a larger scale this can be much worse than a little CO2.
Trying To Achieve Too Much?
Mon Oct 26 14:04:57 GMT 2009 by Dennis
http://freetubetv.net
I don't really think that would lead to a disaster, it would just make the area highly flammable but I'm sure they could do something to relegate the effect - releasing some sort of nitrogen or oxygen to dillute it?
Ask, and you may get more than you ask for. The impact of commercial livestock farming:
(a) Most of the resulting sewage is discarded unutilised, some of it in waterways. It adds to the nitrite poisoning and oxygen deficiency of aquatic habitats, and releases 60% of all ammonia - which contributes to acid rain.
(b) Forests and grasslands are being cleared constantly. The total is now 30% of all land [FAO, '06]. 20% is for pasture [FAO db]. Many of these areas including old farms are in danger of reverting to desert through over-grazing. Wildlife that encroach on these vast human domains is eliminated as vermin.
(c) Food grain is diverted as fodder. The weight ratio of resulting food to feed (as measured in maize) is 8.4 for pork, 7.9 for cheese, 6.2 for beef, 3.8 for eggs and 3.4 for chicken [US DoA, '97].
(d) Fields for food crops are also diverted for pure fodder crops. Overall, a meat-based diet requires about 1.4 ha of land per person compared to 0.2 ha for a vegetarian one - based on grain, root crops or fruit.
(e) Meat requires up to 200 times as much water as for the same weight of wheat.
(f) GLOBAL WARMING: This industry produces 18% of all human GHG [FAO, '06] as methane from sewage and cattle breath. There is also CO2 from outdoor and indoor machinery, transport, slaughterhouses, the production of fertilizer for fodder, and the cultivation and processing of fodder. The industry at its current scale would not exist without refrigeration. It uses 10 - 20 times the energy needed for grain [Environment Cananda, '95].
(g) Immediate human impact: Mad cow disease arose from unnatural "scientific" feed. Misuse of antibiotics is producing outbreaks of lethal medicine-resistant versions of common pathogens; in some "pig" towns, red lesions have become common [IHT report on Dutch & US studies, 09]. Growth hormones, nitrite preservative, heavy metals and nuclear irradiation (to sterilize meat and milk) add to the danger. Explosive growth of common pathogens is a constant danger. There is a permanent stench in the neighbourhood of large pig farms. Feral pigs are an expanding new threat in USA.
You started well, but quickly veered off onto your vegetarian soapbox.
Yeah, it's a soap box, but it's an awfully comfortable one from a moral perspective.
HA! Nice point-by-point refutation -- NOT! Your comment can be translated thus: "I don't like hearing criticism about my carnivorous life-style, so I'll just say you "veered off"" and get the hell out of here."
Thanks for providing an excellent example of why the odds of humankind changing in time to avert catastrophe are slim to none.
Ammonia gas would make rainwater alkaline - not acidic. Learn some basic (no pun intended) chemistry.
See, for e.g.: http://library.witpress.com/pages/PaperInfo.asp?PaperID=11441
which says "... the ambient ammonia can neutralize the rain acidity... however... the total amount of the sulphur compound dissolved... is increased..."
So you get corrosion on the ground, on vegetation, buildings etc.
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it sounds incredible that pig poo can be turned in to electronic power, but it seems a good news for our earth. is it coming to real soon?
Why does it sound incredible? Pigs faeces are full of energy, it's just no one tapped it yet.
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