Performance evaluation and optimization of field-scale bioscrubbers for intensive pig house exhaust air treatment in northern Germany

Abstract The treatment of exhaust air from three intensive pig houses in northern Germany by field-scale bioscrubbers (BS.1, BS.2, and BS.3) were evaluated monthly in 2015. The simultaneous removal of NH 3 and CH 4 was investigated by connecting a second bioscrubber (BS.2-2) to one of the three bioscrubbers (BS.2) to create a two-series connected bioscrubber (BS.2 + BS.2-2). Additionally, whether isolated methanotrophic bacterial inoculation in BS.2-2 intensified CH 4 removal was examined. Average NH 3 removal efficiencies of 86%, 80%, and 77% were observed for BS.1, BS.2, and BS.3, respectively, under fluctuate NH 3 inlet concentrations (variation of 22%–54%) throughout the study year. However, average CH 4 removal efficiencies were lower than 10% in the three bioscrubbers. The pH of the recirculation water, which ranged from 5.7 to 8.1, was demonstrated to be an important factor for NH 3 removal and negatively correlated with NH 3 removal and NH 4 + -N concentration in the recirculation water. The dominant NH 3 -oxidizing and methanotrophic bacteria in the bioscrubbers, analysed by transmission electron microscopy, were Nitrosomonas sp. and Type I methanotrophs, respectively. NH 3 removal efficiency reached 100% in the two-series connected bioscrubber, however, CH 4 removal was still low (average of 2%). After inoculating isolated methanotrophic bacteria into BS.2-2, the average CH 4 removal was enhanced to 35%, offering a great option for bioscrubbers application to intensify CH 4 removal. Therefore, a two-series connected bioscrubber inoculated with methanotrophic bacteria would be an option for simultaneous removal of NH 3 and CH 4 from the exhaust air of animal houses.