Assessing the Performance of Floating Biofilters for Oxidation of Methane from Dairy Effluent Ponds

Mitigating methane (CH) emissions from New Zealand dairy effluent ponds using volcanic pumice soil biofilters has been found to be a promising technology. Because the soil column biofilter prototype previously used was cumbersome, here we assess the effectiveness of volcanic pumice soil-perlite biofilter media in a floating system to remove high concentrations of CH emitted from a dairy effluent pond and simultaneously in a laboratory setting. We measured the CH removal over a period of 11 mo and determined methanotroph population dynamics using molecular techniques to understand the role of methanotroph population abundance and diversity in CH removal. Irrespective of the season, the pond-floating biofilters removed 66.7 ± 5.7% CH throughout the study period and removed up to 101.5 g CH m h. By contrast, the laboratory-based floating biofilters experienced more biological disturbances, with both low (∼34%) and high (∼99%) CH removal phases during the study period and an average of 58% of the CH oxidized. These disturbances could be attributed to the measured lower abundance of type II methanotroph population compared with the pond biofilters. Despite the acidity of the pond biofilters increasing significantly by the end of the study period, the biofilter encouraged the growth of both type I ( and ) and type II ( and ) methanotrophs. This study demonstrated the potential of the floating biofilters to mitigate dairy effluent ponds emissions efficiently and indicated methanotroph abundance as a key factor controlling CH oxidation in the biofilter.