Characterization of the biofiltration of methane emissions from municipal anaerobic effluents

Automatic control of water content in a polyurethane foam packed bed used in biotrickling filters for polluted air treatment

Biotrickling filters (BTF) have been applied to treat waste air. Controlling the water content (WC) of BTFs is fundamental to ensure an adequate interfacial mass transfer and the support of the biofilm activity. A sensor system based on electrical conductance measurement was developed for the online assessment of the WC in a bench scale polyurethane foam (PUF) packed bed. ON/OFF and rule-based control algorithms were applied to keep the water content in a biofilm-free PUF-packed bed within the optimal range of 70-90% through the activation of a hydraulic pump. The applied control algorithms activated the pump at various times, which yielded different energy and water savings even under similar WC conditions suitable for biotrickling filtration of waste air. It was estimated that using the ON/OFF and rule-based system control schemes reduced the electrical power consumption by 98% and 99.8%, respectively, compared to systems under continuous water irrigation.

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.

Approaches to mitigation of hydrogen sulfide during anaerobic digestion process - A review

Anaerobic digestion (AD) is the primary technology for energy production from wet biomass under a limited oxygen supply. Various wastes rich in organic content have been renowned for enhancing the process of biogas production. However, several other intermediate unwanted products such as hydrogen sulfide, ammonia, carbon dioxide, siloxanes and halogens have been generated during the process, which tends to lower the quality and quantity of the harvested biogas. The removal of hydrogen sulfide from wastewater, a potential substrate for anaerobic digestion, using various technologies is covered in this study. It is recommended that microaeration would increase the higher removal efficiency of hydrogen sulfide based on a number of benefits for the specific method. The process is primarily accomplished by dosing smaller amounts of oxygen in the digester, which increases the system's oxidizing capacity by rendering the sulfate reducing bacteria responsible for converting sulfate ions to hydrogen sulfide inactive. This paper reviews physicochemical and biological methods that have been in place to eliminate the effects of hydrogen sulfide from wastewater treated anaerobically and future direction to remove hydrogen sulfide from biogas produced.

Experimental analysis and modeling of the methane degradation in a three stage biofilter using composted sawdust as packing media

Methane gas is a very effective greenhouse gas and the second-largest contributor to global warming. Biofiltration is an effective technology that uses microorganisms to degrade the pollutant by oxidizing it. In this work, the performance of a biofilter with supporting filter media, consisting of composted sawdust, is evaluated at three different sampling ports. Furthermore, a transient model is developed to predict methane concentration at various heights and times. The developed model is validated with the experimental data and shows good agreement with the experimental data. The highest removal efficiency and elimination capacity was found to be 72% and 0.108 g m^-3 h^-1 respectively. The effect of parameters such as specific surface area, the reaction rate constant, biofilm thickness and airflow rate were studied on the outlet methane concentration. Under similar conditions, the simulations showed that the removal efficiency of 95% might be achieved for the height of 2 m.

Biological-based methods for the removal of volatile organic compounds (VOCs) and heavy metals

The current scenario of increased population and industrial advancement leads to the spoliation of freshwater and tapper of the quality of water. These results decrease in freshwater bodies near all of the areas. Besides, organic and inorganic compounds discharged from different sources into the available natural water bodies are the cause of pollution. The occurrence of heavy metals in water and volatile organic compounds (VOCs) in the air is responsible for a vast range of negative impacts on the atmosphere and human health. Nonetheless, high uses of heavy metals for human purposes may alter the biochemical and geochemical equilibrium. The major air contaminants which are released into the surroundings known as VOCs are produced through different kinds of sources, such as petrochemical and pharmaceutical industries. VOCs are known to cause various health hazards. VOCs are a pivotal group of chemicals that evaporate readily at room temperature. To get over this problem, biofiltration technology has been evolved for the treatment of heavy metals using biological entities such as plants, algae, fungi, and bacteria. Biofiltration technology is a beneficial and sustainable method for the elimination of toxic pollutants from the aquatic environment. Various types of biological technologies ranging from biotrickling filters to biofilters have been developed and they are cost-effective, simple to fabricate, and easy to perform. A significant advantage of this process is the pollutant that is transformed into biodegradable trashes which can decompose within an average time period, thus yielding no secondary pollutants. The aim of this article is to scrutinize the role of biofiltration in the removal of heavy metals in wastewater and VOCs and also to analyze the recent bioremediation technologies and methods.

Evaluation of a hybrid physicochemical/biological technology to remove toxic H2S from air with elemental sulfur recovery

The removal of toxic hydrogen sulfide (H₂S) from the air at pilot-scale with elemental sulfur recovery was evaluated using Fe-EDTA chelate as a single treatment at a pH of about 8.5. This was later combined with a compost biofiltration process for polishing the pre-treated air. Experiments were performed in a unique container system that allowed deploying either Fe-EDTA chelate or Fe-EDTA chelate/biofiltration treatment (hybrid system). The results showed the feasibility of H₂S removal at concentrations between 200 and 5300 ppmv (H₂S loading rates of 7-190 g m^-3 h^-1) present in fouled air. The Fe-EDTA chelate as a single treatment was able to remove nearly 99.99% of the H₂S at inlet concentrations ≤ 2400 ppmv (107 g m^-3 h^-1), while the hybrid system archived undetectable outlet H₂S concentrations (<1 ppmv) at inlet levels of 4000 and 5300 ppmv. At 5300 ppmv, the Fe-EDTA chelate process H₂S removal efficiency decreased to 99.20% due to the limitation of oxygen mass transfer in the Fe(III) regeneration reaction. Under the previous conditions, the pH was required to be controlled by the addition of NaOH, due to the likely occurrence of undesirable parallel reactions. The elemental sulfur yield attained in the physicochemical module was 75-93% with around 80% recovered efficiently as a solid.

Biofiltration of methane

The on-going annual increase in global methane (CH₄) emissions can be largely attributed to anthropogenic activities. However, as more than half of these emissions are diffuse and possess a concentration less than 3% (v/v), physical-chemical treatments are inefficient as an abatement technology. In this regard, biotechnologies, such as biofiltration using methane-oxidizing bacteria, or methanotrophs, are a cost-effective and efficient means of combating diffuse CH₄ emissions. In this review, a number of abiotic factors including temperature, pH, water content, packing material, empty-bed residence time, inlet gas flow rate, CH₄ concentration, as well biotic factors, such as biomass development, are reviewed based on empirical findings on CH₄ biofiltration studies that have been performed in the last decades.

Biofiltration of methane from cow barns: Effects of climatic conditions and packing bed media acclimatization

The performance of biofiltration to mitigate CH₄ emissions from cow barns was investigated in the laboratory using two flow-through columns constructed with an acclimatized packed bed media composed of inexpensive materials and readily available in an agricultural context. The biofilters were fed with artificial exhaust gas at a constant rate of 0.036 m³ h^-1 and low inlet CH₄ concentration (0.22 g m^-3 = 300 ppm). The empty-bed residence time (EBRT) was equal to 0.21 h. Additionally, in order to simulate temperature changes under natural conditions and determine the influence of such cycles on CH₄ removal efficiency, the upper part of the biofilters were submitted to temperature oscillations over time. The maximum oxidation rate (1.68 μg _CH4 g_dw^-1h^-1) was obtained with the commercial compost mixed with straw. Accordingly, it was considered as packing bed media for the biofilters. The CH₄ removal efficiency was affected by the temperature prevailing within the biofilters, by the way in which the cooling-warming cycles were applied and by the acclimatization process. The shorter the cooling-warming cycles, the more oxidation rates varied. With longer cycles, CH₄ removal rates stabilized and CH₄ removal efficiencies attained nearly 100% in both biofilters, and remained at this level for more than 100 days, irrespective of the temperature at the top of the biofilter, which was - at times - adverse for microbiological activity. The first order rate constant for CH₄ oxidation kinetics of the entire system was estimated at 15 h^-1. If such rate could be transposed to real field conditions in Canada, home to nearly 945,000 dairy cows, biofiltration may be applied to efficiently abate between 2 × 10⁶ and 3 × 10⁶ t yr^-1 of CO₂ equivalent (depending on how estimates are performed) from bovine enteric fermentation alone.