Odour impact of an agricultural biogas facility combined with animal husbandry

Mostly, agricultural biogas facilities on farms in Switzerland exist in combination with animal husbandry. The proximity of these facilities to residential areas can lead to odour complaints from residents. Animal housing and outdoor exercise areas, feed and farmyard manure stores, as well as substrate and fermentation residue stores all figure among the diffuse emission sources. This paper presents odour investigations conducted on three days during the summer and transition season on a dairy farm with a biogas facility. Six assessors recorded their odour perception at different distances to the farm. At the positions near the farm, the assessors identified a high percentage of time with odour as well as with high odour intensities. The distances from the farm at which assessors were able to recognise a decrease both in the percentage of time with odour and in the high intensity levels were determined. Frequently, a mixture of odours was perceived in the odour plume. In situations with leaking biogas, odour impact was higher. Biogas odour was rated by the assessors as definitely unpleasant. Biogas leakage from facilities must be prevented by a sufficiently large gas storage volume, process optimisation, and regular maintenance. For new biogas facilities, great care in the choice of site must be exercised.