Green gas-bagging – the false promise of anaerobic digestion
True story. In 2010/11 I became an anaerobic digester bore.
I was campaigning with Compassion in World Farming against the proposed Nocton Dairies in Lincolnshire.
There were any number of important reasons to object to the proposal, which initially wanted to raise 8000 cows indoors in disgraceful US-style mega-dairy conditions. But for me the key to stopping it was to strike at a particular weak point, the anaerobic digester – the feature the owners touted around as the ultimate green feather in their cap.
“Stop the digester and you stop the dairy.” I said to anyone who would listen. In fact, stop the digester and you stop any kind of mega-farm in the UK. Few people did actually listen. Mainstream journalists thought the story was too complex and not ‘sexy’ enough. In-house, there was fear of losing focus on the animal welfare message. And what if we were wrong about AD? What if it really was a green miracle? Decades of listening to tedious ‘greewash’ about energy miracles, however, made me smell a green, gas-bagging rat.
The pre-publicity for Nocton Dairies deftly tried to shift the focus away from animal welfare, and the devastating impact on the local environment, and onto so-called green credentials of anaerobic digestion (AD). And yet, the truth is, anaerobic digesters are only ever necessary on farms where there are too many animals are producing too much waste on too little land.
It’s a crucial issue because these kinds of expensive, unproven green bolt-ons are increasingly used to justify large intensive, industrial systems, which are hugely wasteful, powerfully polluting, and where animals are kept in unacceptable conditions.
Nevertheless a close look at AD, as the Soil Association and WSPA, as part of their objection to the Midland Pig Producers proposed mega-farm at Foston, in Derbyshire, have done over the holidays (see the report here) can only conclude that these units are expensive to build and expensive to maintain and their financial viability, rather like that of nuclear power, is dependent on massive government subsidies. In other words it depends on taxpayers’ money.
Evidence? What evidence?
The current government has thrown its weight behind plans to build many more anaerobic digesters for both on and off farm use throughout the UK. And yet there are no comprehensive studies on the energy efficiency of anaerobic digestion on the scale that we are currently contemplating.
Indeed there are no real world lifecycle analyses for instance which look at the total energy in versus the total energy out.
Estimates of the amount of so called ‘free’ energy created through anaerobic digestion do not take into account, for example, the energy required to build these massive units, or that required to hoover up and transport the waste that is used as feedstock, nor the energy required to transport and spread that waste on fields. Very often it doesn’t include a proper accounting of the energy required to keep these units running 24/7.
In my own trawling for facts I came across an estimate – not confirmed – that it would take 20,000 heavy lorry journeys a year to keep a typical off-farm plant provided with food crops, the food supermarkets throw away, slaughterhouse waste, factory farm waste, meat processing waste from various countries, diseased carcasses, animals which die on the farm, other ingredients and to take the processed remains away. If anyone can confirm this I’d love to hear from them.
The figures the government is working with are those created in optimal laboratory conditions rather than on the farm. Some of the data that we have seen suggest that under real world conditions the amount of energy produced is much lower than predicted and depends very much on the feedstock used. Slurry, as the Soil Association report notes, is not the best feedstock.
In addition, in order to kill the potential pathogens in slurry they need to be maintained at a particularly high temperature – this also takes energy. And even then complete kill of harmful bacteria and viruses is not guaranteed.
To get the most energy out you need to add crops and this of course raises an ethical question about potentially using food crops for energy generation. The public outcry against biofuels would suggest that this is a totally unacceptable situation in most people’s minds.
Ghost emissions
AD units are incredibly high maintenance and expensive to service. Because they are switched on 24/7, they are prone to lots of wear and tear. If not properly maintained they can leak and breakdown and produce emissions of nitrogen oxides as well as methane and sulphur leaks that are environmentally damaging and pose health risks.
From an environmental perspective there is almost no data on the ‘ghost emissions’ from AD units; that is, emissions of hydrogen sulphides and nitrogen oxides both of which can affect local air quality.
In California permits for digesters on dairy farms are now being restricted (see here and here) because the amount of nitrogen oxide emissions they produce contributes to ground level ozone – a threat to respiratory health. Similar concerns have surfaced in Wisconsin.
Respiratory health is already an issue for those living in close proximity to dairy farms. AD simply adds a layer of complexity to an already terrible problem.
Although UK proponents point to the US experience of AD, these units are not nearly as popular or prevalent in America as we are led to believe, probably because of the standoff between regulators and farmers and perhaps because the costs involved. There are about 65,000 dairy farms (and 75,000 hog farms) in the US but EPA estimates about 150 digesters are operating on American farms.
Furthermore Environmental groups are not universally enthusiastic. The Sierra Clubdoes not support the building of new digesters. The Energy Justice Network is also opposed to them.
In the US the EPA has recently issued new upper limits on the types of emissions from digesters and these stringent new limits have forced some of the units currently in operation to shut down. Yet in the UK Defra seems to be issuing environmental and air quality permits based more on wishful thinking than science.
What’s in a name?
As far as the digestsate is concerned it is important not to let the current language of anaerobic digestion obfuscate the facts.
AD produces what is classified in the UK as a waste product – digestate (which can be solid or liquid). Markets are currently being sought for this waste especially as a ‘soil conditioner’. It is only a matter of obtaining a government permit to reclassify AD waste as fertiliser. Indeed in March 2011 an AD plant in Devon became the first site in the UK to be granted a certificate, under the Biofertiliser Certification Scheme, allowing it to classify its digestate output as a sustainable fertiliser rather than a waste product.
However, when proponents talk about ‘soil conditioners’ or a ‘natural fertilisers’ that can replace NPK (nitrogen, phosphorous and potassium) fertilisers they are being somewhat economical with the truth.
The environmental issues with conventional fertilisers are: 1) that they depend on fossil fuel inputs to produce and 2) that the high levels of nitrogen, phosphorous and potassium which are detrimental to the natural living structure of the soil and also due to run off polluting to water ways.
Digstate of course depends on fossil fuels to produce – and although AD units can produce their own electricity they are generally still dependent on the grid for some of its supply. And really to get a proper accounting of the energy inputs you would require an analysis of the energy required to maintain the cows in the first place.
But the most important point is that digestate seems to be just as high in NPK as synthetic fertilisers and this means the risk of pollution and run off is also just as high. If our enthusiasm for AD runs amok – will we even have enough land on which to safely spread this new ‘soil conditioner’?
Anaerobic digestion doesn’t get rid of waste it simply changes its form somewhat. Before people fall over themselves to celebrate anaerobic digesters as the jewel in factory farming’s crown a lot more research is needed.
Pastures are greenest of all
Building anaerobic digesters is now government policy. We have an ‘Implementation Plan’ and everything. Lots of subsidies are being made available to build them and they are perceived as ‘good practice’ – BUT on what basis? Where is the research? Defra along with other agencies like WRAP has only recently begun long term studies into viability and pollution, the results of which, according to the Government’s AD ‘Strategy and Action Plan’ won’t be known until 2014.
Our lust for AD and the great lengths that proponents have gone to promote them as ‘green’ and ‘sustainable’ is a smokescreen. The fact is big farms can’t work without a digester. So the lack of digester is seen as the problem to be solved, when in fact the real problem is one of scale.
Small scale outfits that graze their animals do not have this problem. A cow pat in a field does not have the climate implications that a slurry lagoon does. The humble cow pat is part of a virtuous eco-circle that allows farmers to farm sustainably without reliance on increasingly expensive, complex and unreliable technology.
If we want a sustainable livestock industry in the UK then this is where our meditations and negotiations on the sustainable future of farming need to begin.
© Pat Thomas 2012. No reproduction without the author’s permission.
