Summary and conclusions

Udvikling af standardiseret afprøvningsprocedure til dokumentation for BAT teknik i stalde -specielt luftrensning til landbrug.

The need to develop standardised procedures for testing technology is quite obvious. At present there are no common standardised procedures for the documentation of efficiency, economy and side effects. Thus the basis for evaluating techniques for BAT is very different in the different European countries.

The Danish Pig Production (DPP) has a long tradition of testing all types of techniques that can be used in pig farming including ammonia emission abatement techniques. The published tests from DPP are quite comprehensive and have been conducted in commercial farms in full scale and with high standards for statistical analysis. These can be used as a starting point to set up protocols for testing abatement techniques, for instance for air cleaners in housing for other animal species. But there is a need for a standard that ensures acceptance of the documentation in other European countries, which will give the producers of a technique access to a larger market and a quicker implementation of better technique. The study of literature, describing tests in Holland and Germany, shows quite big differences in the setup and evaluation. We have been informed that there are ongoing negotiations between the German "DLG-Testcentrum" and the Dutch research institute "Wageningen" to develop more standardized procedures. The German practice is to test air cleaning systems in commercial farms during one month in summer and during one month under winter conditions. These tests are not yet standard in all states of the German federation, but they are now compulsory for market access in Cloppenburg.

In Holland certification is divided into a theoretical test for air cleaner types that are stated to have a cleaning efficiency rate of at least 70 % towards ammonia, and a test in commercial farms or test farms that shows at least 90 % removal of ammonia in the exhaust air.

Even though there are standards for measurements of odour, there is still a difference in the way odour nuisance is evaluated. Some Dutch and German test institutes include the offensiveness of the odour (hedonic tone), and the German DLG-test puts a limit of maximum 300 OU_E in the exhaust air from the air cleaner combined with an indication of whether the original odour can be perceived or not. If both criteria are met the air cleaner has passed the test.

The Danish tests for odour are based on olfactometry alone, and hedonic tone questionnaires are not used in all cases. They are expensive to conduct and often only conducted in smaller panels than prescribed in the standard procedure for hedonic tone evaluation. Odour reduction is presented as a relative reduction (percent), and due to a large variation in emission from different farms it is difficult to compare the results from tests of different air cleaners.

A part of this project has been to test "Farm AirClean" from the company SKOV A/S. The cleaner is a decentralised air washer (spraying sulphuric acid into the air stream in the chimney) that was installed in a pilot scale setup in a container just outside a farm building with hens. The test showed a reduction in ammonia emission averaging 59 % in the summer period to 70-73 % during spring-summertime.

There was no significant reduction in odour (only four days of odour measurements, since no improvement was expected with this type of cleaner)

A comparative study of two different pieces of ON-line gas analysis equipment was conducted as a part of the test of Farm AirClean. The parallel setup with Innova Multigas Monitor (photo acoustic sensor) + multisampler and a Dräger (chemical sensor) combined in a Veng System multiplexer, showed that Innova was more stable in the low concentration area. Both pieces of equipment can be used to test aircleaners. However a standardisation of the use of equipment would be desirable, and up to now more published emission tests are made with Innova in Europe. The olfactometric test of Farm AirClean showed no significant reduction in odour concentration, but the test was stopped because no reduction was expected with further tests.

The variation in an olfactometric analysis of a single odour sample is fairly large. The Danish Meat Research Institute reports that a 95 percentile confidence interval can be from ÷37 % to +59 %. (Appendix A) The tests of air cleaning techniques at pig farms have shown that at least 6 repeated samples (before and after cleaner) are required to achieve statistical proof of a reduction of minimum 50 %.

The chemical odour components were measured using GCMS as part of the test of the Farm AirClean test. The test was only included in order to give the company extra information that might be used for optimization of the air cleaner, since there is not enough knowledge about the significance of a single chemical odour compound concentration for the air quality.

The energy and water consumption was measured, but these measurements can not be used in a final evaluation of the air cleaner, since the system was not ready to be marketed at the time when the test was conducted. It has been optimized since then. A full scale test of the system has to be conducted before a final evaluation can be made.