Odour impact from farms with animal husbandry and biogas facilities.

Agricultural biogas facilities are usually combined with animal husbandry. Their siting near residential areas can lead to odour complaints by residents. The aim of this study was to identify relevant odour sources, to record odour impact, and to determine the main variables influencing odour impact. Therefore, a combined approach was designed to account for individual odour sources as well as the farms as a whole. On eight farms with cattle husbandry and biogas facilities, two of which kept pigs and poultry, the odour-relevant area sources ranged between 475 and 1810 m2. Solid manure from poultry, cattle and horses as well as grass cuttings, vegetable peelings, liquid-silage effluent and fermentation residues figured among the odour-intensive sources, in addition to biogas. Odour-plume inspections were performed at various distances from the farm, and assessors determined their odour perception and -intensities. The odour intensity in the downwind plume axis was explainable in a linear mixed-effects model by distance (p < 0.001), emitting surface area (p = 0.002) and wind speed (p = 0.018). As distance increased, odour intensity decreased by a factor of two per 50 m. Higher odour intensities resulted from larger surface areas in the animal enclosure, substrate storage, or especially odour-relevant sources. A mixture of odours was frequently perceived in the odour plume. If biogas escaped, an increase in odour impact was recognisable (p = 0.021). Biogas leakage should be avoided with a sufficiently large storage capacity, process optimisation, and regular servicing. In summary, animal husbandry and biogas facilities are to be viewed as an entire plant in terms of downwind odour perception. In planning processes for biogas facilities with animal husbandry, great care in the choice of site is called for, as are structural-technical and organisational measures for abatement.