Liquid Addition Techniques to Enhance Methane Biotrickling Filters at Dairy Barn Concentrations

Dilute methane (CH4) emissions from dairy barns (<500 ppm) are a challenging agricultural greenhouse-gas source to abate via biofiltration because its poor solubility makes gas–liquid mass transfer a primary limitation in biotrickling filters (BTFs). Here, we evaluated lab-scale BTFs for treating dairy-relevant CH4 concentrations and tested two enhancement strategies: (1) aerosolised nutrient delivery to improve liquid distribution and (2) reduced liquid addition rates to increase gas–liquid mass-transfer efficiency. Liquid-fed BTFs and aerosol-fed BTFs (ABTFs) packed with scoria or glass beads were compared. Aerosolised nutrients reduced the elimination capacity (EC) compared to biotrickling delivery. Switching from liquid to aerosol decreased an initial EC of ~30 g m−3 h−1 by 35% at 2500 ppm CH4, and the original EC was not recoverable. Slower liquid addition consistently improved CH4 removal for both delivery techniques. In a glass bead ABTF at 2500 ppm CH4, the EC increased from 5.5 to 12.4 g m−3 h−1 when the liquid coalescence rate decreased from 0.79 to 0.006 cm h−1. In a scoria ABTF, a 1.5-fold increase in EC was observed as the rate decreased from 2.36 to 0.15 cm h−1. Below a threshold liquid addition rate in the scoria BTF, the EC dropped ~33%, likely due to uneven wetting or high pH conditions. Therefore, optimising liquid delivery can significantly enhance BTF performance for agricultural CH4 mitigation.