Odour complaints are the single largest source of complaints with respect to intensive livestock operations. One method of odour reduction is the use of a biofilter. These low-cost filtration systems have been succssful in reducing hydrogen sulfide and odour emission levels from livestock operations.

This study set out to examine the impact of a manure-soaked straw cover, water-soaked straw cover and a dry-straw cover on the odour and hydrogen sulfide emissions generated from a manure storage unit. Two trails were completed to evaluate the biofilters, the first trail lasted from April 1 – May 4, 1998 and the second trial lasted from June 4 – July 23, 1998. All samples were analyzed for hydrogen sulfide and odour threshold levels.

Hydrogen sulfide levels were influenced by two factors: difussion of the odour through the biofilter and dilution by the fresh air flowing acress the surface of the biofilter. The average hydrogen sulfide reduction for the first trial (April 1 – May4) from the straw soaked with manure was 95% and the straw soaked with water realized a 91% reduction. During the second phase of the trial the dry straw cover was compared with the water-soaked straw cover. Average hydrogen sulfide concentrations at the surface ranged from 1,145 – 2,037 ppb at the manure surface and 110 – 115 at the outlet for the dry straw cover. Representing a 92% H2S reduction rate. The wet straw cover averaged 573 – 847 ppb at the manure surface and 101 – 153 ppb at the outlets, representing a 81% reduction in concentration levels. The average H2S reduction of the control, no straw cover was 50% between the manure surface and the outlet.

Odour reduction with the wet straw was 55% while the straw soaked with manure was 45%. The manure soaked cover odour reduction was not as high because the manure in the straw contributed to emitting odours. Odour reduction levels were reduced 59% with the dry straw cover. The hydrogen sulfide and odour concentrations were not as high in the second study. This can be explained by the summer testing period, in which the higher temperature would increase microbial activity and therefore increase the amount of hydrogen sulfide and odour being emitted from the manure.