The influence of biochar and compost mixtures, water content, and gas flow rate, on the continuous adsorption of methane in a fixed bed column.

Biofiltration is an excellent alternative for the treatment of diffuse emissions of methane (CH) that cannot be treated by physical/chemical means or recovered for energy. Despite the advances on CH biological treatment technologies, they are limited by the low aqueous solubility of CH into the biofilm where CH mineralization occurs. In this study, the CH adsorption kinetics, adsorption capacity and transport behavior of CH was studied in batch experiments and in a fixed-bed column by varying the biochar and compost mixtures under 5-levels, 3 different water contents (dry, 15% and 30% water holding capacity), and 2 inlet flow rates. Experimental results were formally tested using analysis of variance (ANOVA) in order to draw objective conclusions based on statistical inference. As CH biofiltration requires water addition to maintain microbial activity, these results indicate adsorption capacity is not lost with water addition if biochar content is the dominant packing material. The Langmuir isotherm described the data best (R = 0.99). Maximum adsorption capacity by monolayer adsorption, or q, is relatively similar with or without the addition of water as long as the biochar component is the dominant material at 3.5 mg CH/g medium for a 7:1 biochar: compost, v/v mixture. Empirical regression models for q, k, (Thomas model) and τ and K (Yoon-Nelson model) were developed for the break through curves of CH. The current work demonstrates the applicability of utilizing biochar, a relatively inexpensive adsorbent, can compensate for the low solubility of CH and overcome the rate-limiting step of mass transfer from the gas phase and into the methanotrophic biofilm. Further, biochar may be a reliable back-up system for CH storage especially for fluctuating inlet loads that may be encountered in industrial applications adsorbing up to 13 mg CH/g biochar under dry conditions.