Belatedly perhaps but world leaders have at last woken up to two important issues about the future of our planet. Firstly, many human activities lead to the production of greenhouse gases that contribute to global warming on a scale and at a rate that threaten the next generations. Second, so-called 'non-renewable' energy sources are being used up at an alarming rate. One of the most frequently used buzzwords today is 'sustainability'.

On the first point, all aspects of human life are being scrutinised for the type and amount of greenhouse gases particularly methane and carbon dioxide ­ that they produce. Agriculture is known to be the source of a significant amount of methane, with ruminant animals being the main culprits' in this respect.

For the second point regarding the rapid depletion of non-renewable energy sources, such as oil, gas and coal, the remaining resources must be used with the highest efficiency and suitable renewable alternatives sought. As today's resources are being used up, they are becoming subject to rapid and unpredictable rises in prices that threaten the bottom line of any business. Some ideas of the most practical options for farmers were gathered at the special exhibition 'Bioenergy' at the EuroTier 2006 show in November last year.

One of the most frequently used buzzwords today is sustainability'. How can the world's poultry industry raise its sustainability?

Global warming and the poultry farmer

In October 2006, Sir Nicholas Stern published his report on the economic of climate change. Commissioned by the UK government but achieving headlines in the world's press, the report carried a clear warning that all is not well with our planet and that urgent action is needed to prevent a global catastrophe for future generations.

Agriculture did not receive particular attention in the Stern Report but it is well known that livestock production especially makes a significant contribution to the emission of greenhouse gases, particularly methane and carbon dioxide, which are responsible for global warming. A recent Food and Agriculture Organization (FAO) report indicates that livestock production generated 18% more greenhouse gas emissions than transport in terms of carbon dioxide equivalent. Whilst a high proportion of these emissions originate from ruminants, the poultry industry will sooner or later come under pressure to reduce its environmental impact too, and become more sustainable.

Making poultry production more sustainable

Poultry farmers should, like other industries and citizens, make the most efficient use of energy and other resources. Those who own or manage land in excess of their needs for food production now have increasing possibilities to grow crops suitable for biofuels, including biodiesel (bioethanol). This can be produced from a wide range of crops, including maize, oilseeds and even cereals, and it constitutes a promising renewable energy source, preserving mineral oil, gas and coal stocks.

Other renewable energy sources that fulfil the same aim include harnessing power from the sun (using photovoltaic cells), wind (wind turbines) and wood (as a source of heat and power). These were among the ideas on display at the special Bioenergy' exhibition at EuroTier 2006.

A concept that could fit well with a poultry enterprise is the production of bioenergy from the fermentation of waste materials from the farm. Not only does the system generate energy, it also disposes of waste materials and provides a valuable end-product in the form of liquid manure.

The economics of installing wind turbines or solar panels on poultry farms will depend on local climatic conditions, regulations and government subsidies and so their feasibility and the best option will differ widely. The availability of sustainably managed woodland or forest varies widely across the world, as does the level of technology, and so using wood as a fuel can be an environmental disaster or a realistic proposition. Under the right conditions, any or all of these possibilities can help producers to become less dependent on non-renewable energy sources, as well as make their business more sustainable.

Biogas generation on poultry farms

One option that received particular attention at the Hanover show was that of biogas generation. This offers two most attractive advantages: a hygienic and inexpensive method for disposing of a range of waste products and the generation of power. Poultry farms generate considerable quantities of solid waste products, including manure, litter, feathers, broken and cracked eggs and dead birds. All of these need to be disposed of hygienically yet cheaply. Incineration might be an option but it can be subject to a great deal of regulation and although incinerator design has advanced technologically in recent years, it is not the answer for all operations.

At EuroTier, Dr Kilian Hartmann (Business Project Manager at the Competence Centre of the DLG, the German Agricultural Society) explained how a biogas generation system works, and that biogas technology offers possibilities to poultry farmers either in the production of the biogas, or for a Combined Heat and Power (CHP) system. Biogas is formed by the activity of anaerobic bacteria breaking down an organic material. On poultry farms, manure, litter, feathers, broken eggs and carcasses of dead birds are all possible sources of organic material. Any biological material can be added, in fact, including maize, green materials, meat, fats and proteins providing the local regulations permit this method of disposal. The mix is known as the biomass.

The biomass is started using material from an existing plant. Almost any substrate or combination will break down and produce biogas eventually but getting the right conditions makes the process go most efficiently:


  • temperature should be 36-38°C. The heat can come from the CHP system itself
  • pH ideally 6.8-7.2
  • the correct balance of chemical components - carbohydrate (energy) to nitrogen (protein) in a ratio of 20-30:1 (C:N)
  • a dry matter content of 5-10%

The fermentation is actually a four-stage process: hydrolysis followed by acidification both rapid steps and then the slower stages of acetification and finally, methanation.

Today's sophisticated plants need to be monitored constantly to ensure that the various processes are in balance, which requires both monitoring equipment and training to use it to get an effective processing system.

Being high in nitrogen, the usual waste materials from poultry enterprises are not ideal sources of biomass. They also have too high a dry matter content. Unless mixed with a source of carbohydrate, the pH during fermentation can rise, and lead to the formation of ammonia, which slows down the activity of the bacteria and leads to the loss of nitrogen from the end product. Woody materials tend to break down slowly in fermentation systems, and so high levels of wood shavings as litter can be deleterious to the process. A solution to these problems would be to enter into an agreement with a local arable farmer or food processor for the supply of a high-carbohydrate waste to balance the fermentation system.

Once the process is complete, there remains an organic fertiliser, which is likely to have a commercial value locally for agricultural or horticultural crops.

Biogas production catches on fast in Germany

Mark Paterson of Fachagentur Nachwachsende Rohstoffe (FNR; expert agency on renewable raw materials, Gűlzow, Germany) explained the two options for biogas production as a wet' or a dry' process, with a moisture content of around 10-12% being the critical level for pumping. The options for fermentation are either a continuous process, which needs material to be fed into the system regularly, e.g. once an hour, or a batch process, which takes around 4-6 weeks to complete the fermentation. For wet fermentation, water can be added to the biomass to aid mixing and movement of the material but Mr Paterson recommended a closer look at a dry, batch fermentation as a possible option for poultry farmers interested in installing an energy-generating system.

Over recent years, many systems for the production of bioenergy have been installed in Germany, driven by the high concentration of livestock especially in the north of the country and financial support from the government. The number of biogas plants in Germany increased from 850 in 1999 to 3500 in 2006, and the amount of electric power rose from 49 to 1100 megawatts over the same period.

The Renewable Energy Source Act (EEG) of 2004 set a rate of 0.17/kWh of electricity fed into the national grid from renewable energy systems like this, as well as an EEG fee for waste heat utilisation.

A solution for the disposal of dry waste

Belgian company, OWS, has developed a vertical, dry fermentation system that could suit poultry farming situations. Since the technology was developed two decades ago to deal with municipal solid waste dumped in landfills, around 20 of the company's Dranco (Dry Anaerobic Composting) plants have been installed. Before the material goes into the digester, it is first screened to remove metals and other objects measuring more than 40mm that could damage the equipment.

Bert Dierick, Marketing Engineer with OWS, explained that the same technology is used for the farm version, known as Dranco-Farm. The first large-scale plant of this type has now started up in Germany. The system uses pure waste or pure energy crops, which means that the screening stage can be skipped. It is working well on dry materials minimum 30% dry matter such as maize and grass but it would also be effective on solid manures like that from poultry. Because of the high nitrogen content of poultry manure, a carbon-rich feedstock would be required to allow a balanced fermentation.

This system is a continuous process. Every tonne of fresh material is combined using a feeding pump with 6-8 tonnes of material exiting from the digester. The new mix is then fed into the digester and the biomass descends gradually through the digester by gravity.

Unlike the original Dranco systems that use steam, the Dranco-Farm system uses hot water to heat the outside of the screws under the digester. This has the advantage that no water is added to the fermenting mass. The temperature is about 48-55°C, i.e. thermophilic process. The retention time in the digester depends on the feedstock and varies from 25 days for biowaste up to 50 days for resistant substrates like maize silage. During this time, the high temperature kills many of the pathogens present.

Mr Dierick explained that when the residue leaves the digester, much of it is returned to the process. One such recycling takes about 2-3 days but multiple recycling raises the average retention time to the 25- to 50-day period quoted. A small part of the residue is sent to the residue storage. After an aerobic composting phase, a high quality compost is formed.

According to Mr Dierick, the latest results from the first farm system are well ahead of expectations. The current investment cost of 2.5 million for 500kW seems high but the system could become financially viable if waste disposal must be paid for, energy costs on the farm are reduced and/or payment is received for energy fed into the national grid.