Background Agaricus bisporus - better known as the white button mushroom - has become an important food source. A million tonnes are produced by European mushroom producers annually. Pasturised mushroom compost - produced from straw and horse and chicken manure - is the basis for agaricus bisporus growing. However, the production of mushroom compost involves the release of large quantities of ammonia into the atmosphere. Between 12,000 to 14,000 tonnes of ammonia are released in Europe every year from these processes. Objectives The project developed an environmentally sound clean technology for use in the composting agricultural sector. Presently, compost farms are aware of the urgency of addressing the ammonia emissions problem, but try to introduce solutions that have only a limited impact. Examples of these solutions include moving compost to other sites, using chimneys, and building bunkers or aerated floors. There is also a concern that compost quality will be affected if new technologies are introduced. The project will address these issues. Results The project developed an environmentally sound clean technology for composting in the agricultural sector. The new technology substantially reduces the emission of ammonia produced in the mushroom producing industry. In the closed system, air with a high ammonia content passes through the bio-washer and the bio-filter; the water used for bio-washer is used and recycled to produce the compost. After leaving the bio washer, ammonia concentrations are 100 PPM ammonia and after the bio-filter nearly all the ammonia is broken down to nitrite and nitrate. The project proposal foresaw a 90-95% ammonia and odour reduction. With the closed bio-washer and bio-filter, the air and odour pollution in the area was reduced by 95% without using any chemicals. The project also achieved its targeted 20-30% energy saving in a completely closed system. The quality of compost has also improved: the average yield has increased by 15-20%. In addition the following were constructed: three indoor tunnels, a covered wetting area, an exhaust system for the technological air produced in the indoor tunnels, a bio-filter and a bio-washer among other equipment and infrastructure.