LIFE02 ENV/E/000187 ENERWASTE - Implementation of an anaerobic digestion facility at a slaughterhouse

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Biological Conversion : LIFE Projects : Liquid Biofuels and Biogas

Type of Project	Demonstration
Contract No	LIFE02 ENV/E/000187
Total Cost	348 KEuro
EC Contribution	64 KEuro
Start Date	1-2-2002
Duration	18 Months

Abstract

Asturias in the northwest of Spain is traditionally a stockbreeding region, producing beef and spicy sausages. The success of its meat producing and processing industry, however, also means that vast quantities of waste, including the remains of animals, are generated. Until recently, these by-products were generally converted into animal fodder and fertiliser. The outbreak of BSE (bovine spongiform encephalopathy), led to the introduction of new EU regulations that greatly limit the possible uses of animal residues.

Those parts considered possibly harmful to health are either incinerated and subsequently deposited in landfills, or disposed of by sterilisation, which is a similarly costly and environmentally harmful process. Increasingly strict control by national authorities also makes it less easy for abattoirs to dispose of their liquid residues by discharge to the municipal wastewater treatment plants.

This project sought means to reduce electricity costs for powering machinery and refrigeration, and to lower costs for waste disposal, while at the same time improving environmental performance. This was achieved through the construction of a biogas plant to treat the animal by-products and produce energy.

Though animal waste (manure) is often used for anaerobic digestion, this was not the case for the remains of the animals themselves as, before the outbreak of BSE, these were sold at a profit. Consequently, the objective of the project was to show that abattoir waste, including animal remains, can be effectively and economically treated with anaerobic digestion. This means that rather than having to dispose of waste material, which is costly and wasteful, the remains can be transformed directly into biogas, electricity and fertiliser.

A pilot plant, that continues to run smoothly (with a capacity of around 180 tonnes of feedstock a year) produced biogas with a methane content of around 80%. This was used for tests, to obtain reliable data and to gain the experience necessary to design a large-scale industrial plant.

The feedstock used includes bovine and pig fat, intestines and intestinal contents, as well as plant and animal washing-waters. The incoming material is ground to fragments under 10 mm in size. This provides the bacteria with a larger surface area, enabling a faster digestion process. The material is mixed and pasteurised at 70ºC for an hour. Liquid waste is added to obtain the optimal mixture with which to feed the digester. The material then passes through the macerator, which further reduces the particle size to below 4 mm.The mixture is pumped into the hydrolysis tank, with a hydraulic retention time of 4-5 days. From there, it passes to an automatic mixer that sits on top of the digester and slowly mixes the incoming material, ensuring a continuous and homogenous feeding.The continuous digester works under mesophilic conditions at 38ºC, with a retention time of 25 days.

The plant has succeeded in demonstrating that even difficult to treat materials like slaughterhouse wastes can be processed through anaerobic digestion. Furthermore, it has served to determine the optimal operating conditions (organic loading rate, hydraulic retention time, temperature, etc.) for a full-scale plant that will treat 9,000 tonnes of waste a year, producing 600,000 Nm³ of biogas and 1,970 MWh of electricity annually, of which only around 10% will be destined for the plant's own consumption.

Beneficiary Matadero Frigorífico del NalónTotal, Spain

Contacts

Contact

• Marcos DIAZ / Matadero Frigorífico del NalónTotal SPAIN