Chicken waste not want not

Foster Agblevor, associate professor of biological systems engineering at Virginia Tech, is leading a team of researchers in the College of Agriculture and Life Sciences that is developing transportable pyrolysis units that will convert poultry litter into bio-oil.

Agblevor is working with poultry growers to test the technology that would convert poultry litter to three value-added byproducts – pyrodiesel (bio-oil), producer gas, and fertiliser. The pyrolysis unit heats the litter until it vaporises. The vapour is then condensed to produce the bio-oil, and a slow release fertiliser is recovered from the reactor. The gas can then be used to operate the pyrolysis unit, making it a self-sufficient system.

More than 5.6 million tons of poultry litter are produced each year in the US. The litter consists of a mixture of bedding, manure, feathers, and spilled feed. According to Agblevor, current disposal methods such as land application and feeding to cattle are under pressure because of pollution of water resources due to leaching and runoff and concern about mad cow disease contamination in the food chain. There are also concerns that poultry litter can harbour diseases such as avian influenza. While avian influenza is not harmful to humans, people can spread it on their shoes, with their vehicles, or through movement of litter.

‘The self-contained transportable pyrolysis unit will allow poultry producers to process the litter on site rather than having to haul the litter to a separate location,’ Agblevor said. ‘In addition, the thermochemical process destroys the microorganisms reducing the likelihood of the transmission of disease to other locations.’

According to Agblevor, bio-oil yields ranged from 30 to 50 percent by weight, depending on the age and the bedding content of the litter. Bedding material that was mostly hardwood shavings yielded bio-oil as high as 62 percent by weight. The higher heating value of the poultry litter bio-oil ranged from 26 to 29 mega joules per kilogram while bio-oil from bedding material was only 24 mega joules per kilogram.

The bio-oils had relatively high nitrogen content ranging from 4 percent to 7 percent by weight, very low sulphur content, below 1 percent by weight, and were very viscous. The char yield ranged from 30 percent to 50 percent by weight, depending on the source, age, and composition of the poultry litter. The char also had a high ash content, ranging from 30 percent to 60 percent by weight.

‘The type of poultry litter used will affect the amount and quality of the bio-oil produced and ultimately will impact the producer’s profitability,’ Agblevor said. ‘Finding the right set of conditions for the poultry litter is key to the adaptation of this technology.’