Evaluation of manure drying tunnels to serve as dust filters in the exhaust of laying hen houses: Emissions of particulate matter, ammonia, and odour

Poultry houses are important emission sources of ammonia, odour, and particulate matter (PM). Manure drying tunnels (MDTs) might act as 'end of pipe' PM filters, but might also emit additional ammonia and odour. This study aimed to gain insight into this matter (parts A and B) and into the perspective of two strategies to reduce additional emissions: (1) by pre-drying the manure on the belts inside the house (part C), and (2) by reducing manure accumulation time (MAT) in the house to 24-h followed by rapid drying inside the MDT (part D). This study was set up as an emission survey at 16 laying hen farms with a MDT. Results from parts A through C showed that PM10 removal efficiency of the MDTs increases linearly with manure layer thickness: from about 35% at 4 cm to 84% at 17 cm. Ammonia and odour concentrations in the drying air increased substantially upon passing the manure layers, from on average 5.5 to 13.9 ppm ammonia and from 822 to 1178 OUE m−3. In part C, ammonia emission decreased with increasing DM content of the manure, but even at DM content levels beyond 50%, substantial ammonia emission remained. In part D, the emission rates of houses and MDTs together were 44% lower for PM10, 20% higher for ammonia, and 40% higher for odour compared with the theoretical situation of the houses without MDT. Further shortening MAT to 18, 12, or 6 h might be needed to reduce emissions from MDTs.