Prolonged operation of a methane biofilter from acclimation to the failure stage.

Global warming needs immediate attention to reduce major greenhouse gas emissions such as methane (CH4). Bio-oxidation of dilute CH4 emissions in packed-bed bioreactors such as biofilters has been carried out over recent years at laboratory and large scales. However, a big challenge is to keep CH4 biofilters running for a long period. In this study, a packed-bed lab-scale bioreactor with a specialized inorganic-based filter bed was successfully operated over four years for CH4 elimination. The inoculation of the bioreactor was the active leachate of another CH4 biofilter which resulted in a fast acclimation and removal efficiency (RE) reached 80% after seven weeks of operation for CH4 inlet concentrations ranging from 700 to 800 ppmv and an empty bed residence time (EBRT) of 6 min. During four years of operation, the bioreactor often recorded REs higher than 65% for inlet concentrations in the range of 1900-2200 ppmv and an EBRT of 6 min. The rate and interval of the nutrient supply played an important role in maintaining the bioreactor's high performance over the long operation. Forced shutdowns were unavoidable during the 4-year operation and the bioreactor fully tolerated them with a partial recovery within one week and a progressive recovery over time. In the end, the bioreactor's filter bed started to deteriorate due to a long shutdown of twelve weeks and the extended operation of four years when the RE dropped to below 8% with no sign of returning to its earlier performance.

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.

Bioelimination of low methane concentrations emitted from wastewater treatment plants: a review.

Sewage from residents and industries is collected and transported to wastewater treatment plants (WWTPs) with sewer networks. The operation of WWTPs results in emissions of greenhouse gases, such as methane (CH4), mostly due to sludge anaerobic digestion. Amounts of emissions depend on the source of influent, i.e. municipal and industrial wastewater as well as sewer systems (gravity and rising). Wastewater is the fifth-largest source of anthropogenic CH4 emissions in the world and represents 7-9% of total global CH4 emissions into the atmosphere. Global wastewater CH4 emission grew by approximately 20% from 2005 to 2020 and is expected to grow by 8% between 2020 and 2030, which makes wastewater an important CH4 emitter worldwide. This review initially considers the emission of CH4 from WWTPs and sewer networks. In the second part, biotechniques available for biodegradation of low CH4 concentrations (<5% v/v) encountered in WWTPs have been studied. The paper reviews major bioreactor configurations for the treatment of polluted air, i.e. biotrickling filters, bioscrubbers, two-liquid phase bioreactors, biofilters, and hybrid reactor configurations, after which it focuses on CH4 biofiltration systems. Biofiltration represents a simple and efficient approach to bio-oxidize CH4 in waste gases from WWTPs. Major factors influencing a biofilter's performance along with knowledge gaps in relation to its application for treating gaseous emissions from WWTPs are discussed.

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.