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

Exploring the potential of biofiltration for mitigating harmful gaseous emissions from small or old landfills: a review

Landfills are widely employed as the primary means of solid waste disposal. However, this practice generates landfill gas (LFG) which contains methane (CH4), a potent greenhouse gas, as well as various volatile organic compounds and volatile inorganic compounds. These emissions from landfills contribute to approximately 25% of the total atmospheric CH4, indicating the imperative need to valorize or treat LFG prior to its release into the atmosphere. This review first aims to outline landfills, waste disposal and valorization, conventional gas treatment techniques commonly employed for LFG treatment, such as flares and thermal oxidation. Furthermore, it explores biotechnological approaches as more technically and economically feasible alternatives for mitigating LFG emissions, especially in the case of small and aged landfills where CH4 concentrations are often below 3% v/v. Finally, this review highlights biofilters as the most suitable biotechnological solution for LFG treatment and discusses several advantages and challenges associated with their implementation in the landfill environment.

Air biofilters for a mixture of organic gaseous pollutants: an approach for industrial applications

Hazardous airborne pollutants are frequently emitted to the atmosphere in the form of a gaseous mixture. Air biofilters as the primary biotechnological choice for waste gas treatment (low inlet concentration and high gas flow rate) should run properly when the feed contains multiple pollutants. Simultaneous removal of pollutants in biofilters has been extensively studied over the last 10 years. In this review, the results and findings of the mentioned studies including different groups of pollutants, such as methane (CH4) and volatile organic compounds (VOCs) are discussed. As the number of pollutants in a mixture increases, their elimination might become more complicated due to interactions between the pollutants. Parallel batch studies might be helpful to better understand these interaction effects in the absence of mass transfer limitations. Setting optimum operating conditions for removal of mixtures in biofilters is challenging because of opposing properties of pollutants. In biofilters, concerns, such as inlet gas composition variation and stability while dealing with abrupt inlet load and concentration changes, must be managed especially at industrial scales. Biofilters designed with multi-layer beds, allow tracking the fate of each pollutant as well as analyzing the diversity of microbial culture across the filter bed. Certain strategies are recommended to improve the performance of biofilters treating mixtures. For example, addition of (bio)surfactants as well as a second liquid phase in biotrickling filters might be considered for the elimination of multiple pollutants especially when hydrophobic pollutants are involved.

Simultaneous biodegradation of methane and styrene in biofilters packed with inorganic supports: Experimental and macrokinetic study

Four upflow 0.018 m³ biofilters (3 beds), B-ME, B-200, B-500 and B-700, all packed with inorganic materials, were operated at a constant air flow rate of 0.18 m³ h^-1 to eliminate methane (CH₄), a harmful greenhouse gas (GHG), and styrene (C₈H₈), a carcinogenic volatile organic compound (VOC). The biofilters were irrigated with 0.001 m³ of recycled nutrient solution (NS) every day (flow rate of 60 × 10^-3 m³ h^-1). Styrene inlet load (IL) was kept constant in each biofilter. Different CH₄-ILs varying in the range of 7-60 gCH₄ m^-3 h^-1 were examined in B-ME (IL of 0 gC₈H₈ m^-3 h^-1), B-200 (IL of 9 gC₈H₈ m^-3 h^-1), B-500 (IL of 22 gC₈H₈ m^-3 h^-1) and B-700 (IL of 32 gC₈H₈ m^-3 h^-1). Finally, the effect of C₈H₈ on the macrokinetic parameters of CH₄ biofiltration was studied based on the Michaelis-Menten model. Average C₈H₈ removal efficiencies (RE) varying between 64 and 100% were obtained at CH₄-ILs increasing from 7 to 60 gCH₄ m^-3 h^-1 and for C₈H₈-ILs range of 0-32 gC₈H₈ m^-3 h^-1. More than 90% of C₈H₈ was removed in the bottom and middle beds of the biofilters. By increasing C₈H₈-IL from 0 to 32 gC₈H₈ m^-3 h^-1, maximal EC in Michaelis-Menten model and macrokinetic saturation constant declined from 311 to 39 g m^-3 h^-1 and from 19 to 2.3 g m^-3, respectively, which confirmed that an uncompetitive inhibition occurred during CH₄ biofiltration in the presence of C₈H₈.