Separation distances for broiler farms: Verifying methods and investigating the effects of thermal buoyancy

This report has two themes: thermal buoyancy of broiler odour plumes; and comparison of separation distance formulas and Calpuff modelling for determining separation distances to minimise odour impacts. The thermal environment in and around broiler sheds influences the dispersion of odour plumes; however, this environment is not well understood and it has been unclear how well odour dispersion models simulate the buoyancy (causing vertical rise) and subsequent dispersion of plumes. This work and report improves the understanding of thermal gradients between the usually warmer air exhausted from broiler sheds and ambient air; and demonstrates how exhausted air interacts with the surrounding environment. Separation distances are calculated using odour dispersion modelling or separation distance formulas. The formulas offer a low-cost, simple and more transparent method to estimate separation distances. A separation distance formula (for broiler farms) has been proposed for use in Queensland, but required additional testing to validate it and support its adoption. Separation distance formulas were compared against Calpuff modelling using a variety of broiler farm scenarios and the Queensland odour impact criteria. Information contained in this report challenges the current techniques for modelling broiler farm odours (with relation to emission temperatures) and calculating separation distances.