The effect of steaming and soaking treatments on respirable dust content of hay and the potential environmental polluting impact of the waste water produced

Abstract

Soaking hay is a long established practice for the control of respiratory disease, shown to reduce dust particles by up to 90% (Moore-Colyer, 1996). The biological oxygen demand (BOD) of the waste water (effluent) from soaking is sufficiently high however to raise concerns regarding environmental pollution (Clements and Pirie, 2007). Chemical oxygen demand (COD) has not been measured in effluent from soaking hay, but should be considered as a useful indicator of polluting effect. Alternative ways of achieving the same benefits of soaking hay, whilst minimising environmental risks should therefore be explored. One such option is steaming. The aims of the present study were to directly compare respirable dust particle concentrations of steamed and soaked hay, and to assess the environmental impacts of each treatment. One kilogram samples extracted from three bales of hay were subjected to either soaking (n=15) and steaming (n=15) treatments for durations of 0, 10, 30, 60 and 80 minutes. A commercially available hay steamer, requiring seven litres of water for a full cycle, was used for the steaming treatment. The soaking treatments were conducted using 50 litres of cold (~10 °C) water (12.5 l/kg hay). Standard procedures of measuring BOD and COD were used to test the effluent during each treatment. Hay samples were then stored overnight in a temperature controlled environment (15 °C). Respirable particle extraction was carried out using a suction and filter unit (3 μm), on a mechanical shaker for six minutes. Particles were counted using a microscope at × 10 magnification. Significantly fewer respirable dust particles were found in steamed hay (P<0.05). The BOD and COD of effluent from steamed hay were significantly lower (P<0.001). Duration of treatment had no significant effect on BOD, COD or respirable dust particles. Results confirmed previous findings (Blackman and Moore-Colyer, 1998) that steaming is more effective at reducing respirable dust particles than soaking. Environmental benefits were highlighted with steaming, both through reduced polluting effects of the effluent, and the volume of water required for treatment.