Arbejdsrapport fra Miljøstyrelsen 31/2006 – Luftrensning til stalde - Videreudvikling af biofiltre til eksisterendestaldanlæg med akutte lugtproblemer - pilottest ved svinestald

Luftrensning til stalde

Summary and conclusions

Biological air cleaning is under on going development. The aim of this project was further development of bio filters for existing Danish livestock facilities requiring immediate attention. The goal is to create a concept, which is economical sustainable for farmers, and with an additional focus upon the following aspects:

Less requirement for construction space
Less operation and maintenance costs
Optimised efficiency for cleaning of odour (e.g. cleaning of metylsulfides and mercaptanes have traditionally been difficult to reduce)
Analysis of N₂O and NO production from ammonia metabolism

In order to accommodate these aspects, a test plant was established in connection to a pig production facility. Several constructions were tested in the test plant during the project period e.g. the filter materials straw, LECA and Bioblock as well as different constructions of humidifiers. The filters were connected to the floor exhaustion and established as a four chamber unit, which separately were supplied with exhaust air from two pig production units. The construction was made of one layer of Bioblocks placed on a metal net. Subsequently, straw and LECA were established over the Bioblocks each in two chambers, respectively,.

As a consequence of continuous replacement of equipment during the project period, it has not been possible to relate the operation costs directly to the pig production and the subsequent production of exhausted air.

The reductions of odour over the LECA filters were measured to 68 % and 75 %, respectively, as an average during a summer period. The reductions of odour over the straw filters were 76 % and 72%, respectively. When compared to former studies the results showed high odour reductions indicating a potential for air cleaning using these materials.

Simultaneous measurements with MIMS (Membrane Inlet Mass Spectometry) showed that especially LECA filters were able to reduce the emission of organic sulfides, which notoriously have been difficult to remove in air cleaning facilities including other types of straw filters.

The ammonia reduction over the LECA filters was measured to 72 % and 45 %, respectively, as an average during a summer period. The reduction of ammonia over the straw filters was 34 % and 22%, respectively. Obviously, LECA filters showed a higher ammonia reduction than the tested straw filters

The results from the project indicate that Bioblocks optimises air cleaning in respect to odour. The effect may be a result of better dispersion of air before entering the LECA and straw. Also, that cleaning is obtained during water condensing at the surfaces of the Bioblocks.

Results and experiences from the project showed that an efficient humidification of the exhausted air from the stable is an important factor to consider in relation to both an efficient reduction of ammonia and odour emission. The construction of a humidification system with a water pressure of 7-8 bar was not sufficient to obtain a optimal humidification of the air. Previous results have shown, that a pressure of 40 – 50 bar is necessary in connection to nozzles with small holes. These experiences were confirmed during this investigation.

With respect to stability and work load, LECA is easier to handle than straw, as well as a more stable material. Therefore LECA seems to be a solution that brings less workload.

During a summer period, a possible production of N₂O and NO from metabolism of ammonia in the filters were investigated. The results showed an emission of N₂O and NO corresponding to 5,0 – 5,4 % and 1,5 – 1,9 % of the total ammonia load.

The estimated N₂O produced from the filter corresponds to a global warming effect of 3% of what could be expected from the global warming effect from the CO₂ produced from the livestock facility. However, it should be pointed out, that these calculations are based upon only one triplet measurement, and that further measurements are needed in order to confirm this.

Analysis of the reject water showed a rather high amount of nitrogen indicating that a part of the nitrogen load can be colleted and used as fertiliser. However, an amount of reject water to the manure tank must be expected.

The amount of nitrogen that could not be found in the mass balance calculation is presumable captured in the filter material. With respect to the straw filter, this nitrogen could be reused by spreading the straw on the fields. On the other hand, the nitrogen from the LECA.let filter would be difficult to reuse, and a nitrogen loss should be expected when the LECA.let is disposed. However, a part of the LECA.let is expected to be usable as cover on the manure storage tank or regenerated by combusting.

Overall the results of the project can lead to the conclusion that LECA seems to have a higher potential as filter material in comparison to straw. However, in order to use these filters, a further development of less area demanding filter is still recommended.