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Slurry sanitation using heat, a new, simple, low-energy method

Date:
December 7, 2010
Source:
Cemagref
Summary:
Livestock effluents have always been spread as fertiliser on fields. But they can also transmit diseases to humans and animals, for example, over 100 pathogenic micro-organisms (bacteria, viruses, parasites) have been identified in pig slurry. To destroy the main causes of illness and avoid epidemics, scientists use heat exchangers for thermal treatment of the slurry, a well known technique that they are trying to make more energy efficient.

Livestock effluents have always been spread as fertiliser on fields. But they can also transmit diseases to humans and animals, for example, over 100 pathogenic micro-organisms (bacteria, viruses, parasites) have been identified in pig slurry. To destroy the main causes of illness and avoid epidemics, Cemagref scientists use heat exchangers for thermal treatment of the slurry, a well known technique that they are trying to make more energy efficient.

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The higher the temperature, the more effectively the micro-organisms are destroyed, so an easy solution would be to set up sterilisation programmes, e.g. treatment at over 120C for at least 30 minutes. But the cost of such treatments would by much too high for most farmers. The initial goal of the research is therefore to create treatments that are less costly, but sufficient to meet sanitation targets. The slurry is heated to temperatures between 55C and 96C and maintained at a high temperature before cooling and storage. To determine treatment effectiveness, the researchers selected a set of seven bacterial and viral indicators, representing various levels of thermoresistance.

The results showed that heating to 60C for ten minutes is sufficient to make the slurry acceptable for spreading purposes. But none of the treatments up to 55C for three days or 70C for one hour (protocols based on those required for composting) were sufficient to destroy the most resistant pathogens. Heating to 96C for ten minutes is required to destroy some of them and temperatures over 100C would appear necessary to completely remove pathogens from the slurry.

These results induced the researchers to look for less costly solutions. For example, a second heat exchanger is used to recycle the calories from the hot slurry as it cools. This technique recovers between 55 and 70% of the energy used to heat the slurry. Another important factor is the progressive clogging of the system, which reduces heat exchange and thus augments the cost of the process. It will be necessary to determine the best treatment strategies for the future development of the process and the best cleaning techniques, whether mechanical or chemical. Finally, there are plans to couple the process with a methanisation system to produce biogas as an energy source.

This research is attempting to devise more than a simple process, but rather a general method applicable to all types of liquid waste. Reduced energy consumption will enable farmers, agri-food companies and local governments to comply with regulations and sanitation standards in the future.


Story Source:

The above story is based on materials provided by Cemagref. Note: Materials may be edited for content and length.


Cite This Page:

Cemagref. "Slurry sanitation using heat, a new, simple, low-energy method." ScienceDaily. ScienceDaily, 7 December 2010. <www.sciencedaily.com/releases/2010/12/101206093512.htm>.
Cemagref. (2010, December 7). Slurry sanitation using heat, a new, simple, low-energy method. ScienceDaily. Retrieved October 24, 2014 from www.sciencedaily.com/releases/2010/12/101206093512.htm
Cemagref. "Slurry sanitation using heat, a new, simple, low-energy method." ScienceDaily. www.sciencedaily.com/releases/2010/12/101206093512.htm (accessed October 24, 2014).

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