Methane biofiltration in the presence of ethanol vapor under steady and transient state conditions: an experimental study

Abstract

Methane (CH) removal in the presence of ethanol vapors was performed by a stone-based bed and a hybrid packing biofilter in parallel. In the absence of ethanol, a methane removal efficiency of 55 ± 1% was obtained for both biofilters under similar CH inlet load (IL) of 13 ± 0.5 g m h and an empty bed residence time (EBRT) of 6 min. The results proved the key role of the bottom section in both biofilters for simultaneous removal of CH and ethanol. Ethanol vapor was completely eliminated in the bottom sections for an ethanol IL variation between 1 and 11 g m h. Ethanol absorption and accumulation in the biofilm phase as well as ethanol conversion to CO contributed to ethanol removal efficiency of 100%. In the presence of ethanol vapor, CO productions in the bottom section increased almost fourfold in both biofilters. The ethanol concentration in the leachate of the biofilter exceeding 2200 g m in both biofilters demonstrated the excess accumulation of ethanol in the biofilm phase. The biofilters responded quickly to an ethanol shock load followed by a starvation with 20% decrease of their performance. The return to normal operations in both biofilters after the transient conditions took less than 5 days. Unlike the hybrid packing biofilter, excess pressure drop (up to 1.9 cmHO m) was an important concern for the stone bed biofilter. The biomass accumulation in the bottom section of the stone bed biofilter contributed to 80% of the total pressure drop. However, the 14-day starvation reduced the pressure drop to 0.25 cmHO m.

Moving from alcohol to methane biofilters: an experimental study on biofilter performance and carbon distribution

“…Nevertheless, with a lack of external C source (input C) or in the absence of a particular substrate, the microbial culture might survive by using extracellular polymeric substance (EPS) or other forms of accumulated biomass . For example, CO 2 production during starvation conditions, under the lack of external substrates, in biofilters has been reported in several studies . In the current study, the excess output C compared to input C might be the result of the same phenomena.…”

“…42 For example, CO 2 production during starvation conditions, under the lack of external substrates, in biofilters has been reported in several studies. 23,[43][44][45] In the current study, the excess output C compared to input C might be the result of the same phenomena. The biomass loss during gradual change of substrate from methanol to CH 4 was observed in the biofilter.…”

“…The biodegradation of CH 4 , methanol and ethanol happen through formation of intermediates. Methanol, formaldehyde and formic acid are the intermediates for CH 4 biodegradation ; methanol bioconversion is based on formaldehyde and formic acid production, 2 and intermediate compounds such as acetaldehyde, acetic acid and ethyl acetate contribute to ethanol bioxidation . Untreated intermediates usually can be found as output Cs in outlet gas stream or leachate of the biofilters if the pollutant inlet load is high (IL > 150 g m −3 h −1 ) .…”

“…Removal efficiency (RE), elimination capacity (EC), inlet load (IL) and CO 2 production rate (P CO2 ) were used to describe the performance of the biofilters. The mentioned parameters were defined earlier by Ferdowsi et al 23…”