Air treatment techniques for abatement of emissions from intensive livestock production

Keywords: Air treatment; Scrubber; Bioscrubber; Biofilter; Biotrickling filter; Ammonia; NH3; Odour; Livestock production; Animal husbandry; Pig; Poultry. Intensive livestock production is connected with a number of environmental effects, including emissions of ammonia (NH3), greenhouse gases (CH4 and N2O), odour, and particulate matter (PM10 and PM2.5). Possible strategies for emission reduction from animal houses include feed management, adaptation of housing design, and the application of end-of-pipe air treatment, viz acid scrubbers and bioscrubbers. In order to comply with current and future regulations the implementation of air scrubbers is expected to expand in intensive livestock production areas across Europe. The aim of this thesis is to better understand and improve the performance of air scrubber systems in livestock operations. The objectives are to determine (1) how air scrubbers are performing at livestock farms with regard to ammonia and odour removal; (2) how the cost-efficiency of air scrubbers can be increased by applying a different treatment strategy; (3) if methane can be removed by biological air treatment systems; and (4) to discuss the drawbacks of current air scrubbing practices and make recommendations for improvement. It was found that ammonia removal efficiency by scrubbers is relatively high (on average 96% for acid scrubbers and 70% for bioscrubbers), that odour removal is relatively low (on average 31% for acid scrubbers and 44% for bioscrubbers), and that especially bioscrubbers often show a large variation in odour removal efficiency. Furthermore, it was found that bioscrubbers often experience operational problems. Next a partial air cleaning approach has been presented in which air is bypassed at occasionally occurring high air flow rates. Model calculations show that a reduction of scrubber volume by 50% still enables treatment of 80 - 90% of the ammonia load. This strategy reduces investment and operational costs but hardly affects average ammonia emission levels. Furthermore, it was demonstrated that biological oxidation of methane is possible, although the low water solubility of methane limits the practical application of biofilters or bioscrubbers for methane removal. Finally, it is concluded that scrubbers applied at animal houses can still be improved and optimized. For example the process control and performance of bioscrubbers might be enhanced by measurement of electrical conductivity (EC) as a control parameter for water discharge.