Biological elimination of a high concentration of hydrogen sulfide from landfill biogas

Hydrogen sulfide (H2S) is one of the main contaminants found in biogas which is one of the end products of the anaerobic biodegradation of proteins and other sulfur-containing compounds in solid waste. The presence of H2S is one of the factors limiting the valorization of biogas. To valorize biogas, H2S and other contaminants must be removed. This study evaluated the performance of a pilot-scale biotrickling filter system on H2S removal from landfill biogas. The biotrickling filter system, which was packed with stainless-steel pall rings and inoculated with an H2S-oxidizing consortium, was designed to process 1 to 10 SCFM of biogas and used to determine the removal efficiency of a high concentration of hydrogen sulfide from landfill biogas. The biofiltration system consisted of two biotrickling filters connected in series. Results indicate that the biofiltration system reduced H2S concentration by 94–97% without reduction of the methane concentration in the outlet biogas. The inlet concentration of hydrogen sulfide, supplied to the two-phase bioreactor, was in the range of 900 to 1500 ppmv. The hydraulic retention times (HRT) of the two biotrickling filters were 3.9 and 0.9 min, respectively. Approximately 50 ppmv of H2S gas was detected in the outlet gas. The maximum elimination capacity of the biotrickling filter system was found to be 272 g H2S.m− 3.h− 1. During the biological process, the performance of biotrickling filter was not affected when the pH of the recirculated liquid decreased to 2–3. The overall performance of the biotrickling filter system was described using a modified Michaelis–Menten equation, and the Ks and Vm values for the biosystem were 34.7 ppmv and 200 mg H2S/L.h− 1, respectively.

Removal of H2S by vermicompost biofilter and analysis on bacterial community

The vermicompost collected from dewatered domestic sludge as packing material in biofilter was investigated for hydrogen sulfide (H2S) removal. No nutrients or microbial inoculation was added throughout the experiment. The corresponding bacterial community characteristics in the vermicompost biofilter of different spatial levels were evaluated by Miseq high-throughput sequencing technique. The results showed that the vermicompost biofilter performed well during operation. The H2S removal efficiency reached nearly 100% under condition of the inlet concentration <350 mg m−3 and 0.25−0.35 m3 h−1 gas flow rate. The maximum elimination capacity of 20.2 g m−3 h−1 was observed at a flow rate of 0.35 m3 h−1. Furthermore, the amounts of biodegraded products and pH varied accordingly. In addition, the results from high-throughput sequencing revealed pronouncedly spatial variation of the vermicompost, and the Rhodanobacter, Halothiobacillus, Mizugakiibacter as well as Thiobacillus, which can play an important role in removing H2S, were predominant in the final vermicompost. These results imply that the vermicompost with diverse microbial communities has a good potential for eliminating H2S.

A biofilter for treating toluene vapors: performance evaluation and microbial counts behavior

A lab-scale biofilter packed with mixed packing materials was used for degradation of the toluene. Different empty bed residence times, 148.3, 74.2 and 49.4 s, were tested for inlet concentration ranging from 0.2 to 1.2 g/m3. The maximum elimination capacity of 36.0 g/(m3h) occurred at an inlet loading rate of 45.9 g/(m3h). The contribution of the lower layer was higher than other layers and always had the highest elimination capacity. The carbon dioxide production rate and distribution of micro-organisms followed toluene elimination capacities. The results of this study indicated that mixed packing materials could be considered as a potential biofilter carrier, with low pressure drop (less than 84.9 Pa/m), for treating air streams containing VOCs.

Biofilter for treating toluene vapors: Performance evaluation and microbial counts behavior

A lab-scale biofilter packed with mixed packing materials was used for degradation of the toluene. Three gas flow rates, i.e. 0.1, 0.2 and 0.4 m3/h, were tested for inlet concentration ranging from 0.2 to 1.2 g/m3. Removal efficiencies ranging from 45.6 to 97.3% and elimination capacities ranging from 4.95 to 61.07 g/(m3 h) were observed depending on the inlet loading rates. Maximum elimination capacity of 35.95 g/(m3 h) occurred at inlet loading rate of 45.87 g/(m3 h). The lowest layer always had highest elimination capacity. Carbon dioxide concentrations and the microbial cell counts for bio-degraders followed toluene elimination capacities. Results of this study indicated that mixed packing materials could be considered as a potential biofilter carrier, with low pressure drop (less than 84.9 Pa/m), for treating air streams containing VOCs.

Biofilter for treating toluene vapors: Performance evaluation and microbial counts behavior

A lab-scale biofilter packed with mixed packing materials was used for degradation of the toluene. Three gas flow rates, i.e. 0.1, 0.2 and 0.4 m3/h, were tested for inlet concentration ranging from 0.2 to 1.2 g/m3. Removal efficiencies ranging from 45.6 to 97.3% and elimination capacities ranging from 4.95 to 61.07 g/(m3 h) were observed depending on the inlet loading rates. Maximum elimination capacity of 35.95 g/(m3 h) occurred at inlet loading rate of 45.87 g/(m3 h). The lowest layer always had highest elimination capacity. Carbon dioxide concentrations and the microbial cell counts for bio-degraders followed toluene elimination capacities. Results of this study indicated that mixed packing materials could be considered as a potential biofilter carrier, with low pressure drop (less than 84.9 Pa/m), for treating air streams containing VOCs.

Biodegradation of DCM Vapor in a Biofilter

Biofiltration of DCM vapor from air stream was discussed in this study. Experimental investigations were conducted on a laboratory scale biofilter, containing mixture of compost and polystyrene inert particles as the filter materials. Activated sludge was used as an inoculum. The continuous performance of biofilter for DCM removal was monitored for different concentrations and flow rates. The removal efficiencies decreased at higher concentrations and higher gas flow rates. A maximum elimination capacity of 8g/(m3·h) was achieved. The response of biofilter to upset loading operation showed that the biofilm in the biofilters was quite stable and quickly adapted to adverse operational conditions.

Biodegradation of Styrene Vapor in a Biofilter

Volatile organic compounds (VOCs) are a new class of air pollutants posing threat to the environment. Newer technologies are being developed for their control among which biofiltration seem to be most attractive. Biofiltration of styrene vapor from air stream was discussed in this study. Experimental investigations were conducted on a laboratory scale biofilter, containing mixture of compost and polystyrene inert particles as the filter materials. Mixed consortium of activated sludge was used as an inoculum. The continuous performance of biofilter for styrene removal was monitored for different concentrations and flow rates. The removal efficiencies decreased at higher concentrations and higher gas flow rates. A maximum elimination capacity of 85g/(m3•h) was achieved. The response of biofilter to upset loading operation showed that the biofilm in the biofilters was quite stable and quickly adapted to adverse operational conditions.

Experimental Determination of Kinetic Parameters for the Removal of Ethylacetate and Xylene in a Biofilter

The biofilter packed with pressmud and inoculated with activated sludge obtained from pharmaceutical industry wastewater treatment plant was employed for the removal of ethyl acetate and xylene in this study. The effect of process variables like gas flow rates (0.03, 0.06, 0.09 and 0.12 m3 h-1), inlet concentration of ethyl acetate (1.75, 3.0, 7.0 and 10.5 g.m-3) and xylene (0.2, 0.4, 0.6 and 1.2. g.m-3) on the performance of biofilters was validated. The removal efficiency exceeded 97% for ethyl acetate at inlet concentrations up to 3.0 g.m-3 and 95% for xylene at inlet concentrations up to 0.4 g m-3. The maximum elimination capacity of 165 g m-3 h-1 and 66 g m-3 h-1 for the mixture of ethyl acetate and xylene were obtained. A steady state mathematical model was tested and proved to adequately describe the experimental results at the two operating regimes for both ethyl acetate and xylene.

Removal of Ammonia from Waste Gases by a Biotrickling Filter

A laboratory-scale biotrickling filter was evaluated for its effectiveness in treating waste gases containing ammonia at different inlet loading rates. The inlet concentration of ammonia varied from 20～300mg/m3, and the air flow rates were 0.61m3/h, 0.85m3/h and 1.06m3/h, equivalent to empty bed residence time of 35s, 25s and 20s, respectively. The experimental results showed that the inlet ammonia can be efficiently removed in the biotrickling filter. The removal efficiency was nearly 100% when inlet ammonia loading rate was below 28.33g/m3·h, and the maximum elimination capacity for the biotrickling filter was determined to be about 33.99 g/m3·h. The results in microbial analyses had proven that the ammonia oxidizing bacteria and nitrite oxidizing bacteria were dominant in the biotrickling filter. These results show that the treatment system studied can be considered as a viable alternative for the treatment of gaseous emissions containing different concentrations of ammonia.

Influence of Water Content on Biofiltration Performance

In biofiltration, contaminants in a gas stream are transferred into a biofilm on the filter bed medium and are metabolized by the microorganisms. Water is essential for microbial growth/activity and for transport of nutrients. In both full-scale and laboratory-scale systems, the water content of the medium is difficult to control. In this study, a biofilter, with rigorous water content control and internal gas recycle, was used to determine the influence of the water content on the degradation of toluene. Soil was used as the medium for treating toluene-contaminated air at an average inlet concentration of 263 ppm and a flow rate of 21 ml min-1. Through a water retention curve, gravimetric water content was related to matric potential. Results showed that lowering the water content from 79 to 48% (dry weight) or -20 to -400 cm H2O matric potential decreased the elimination capacity (EC) by 42% (29.8 to 17.3 g m-3h-1). Wetting the medium by increasing the matric potential from -400 to -10 cm H2O increased the elimination capacity to 43.9 g m-3h-1. However, further increase of the matric potential from -10 to -5 cm H2O decreased the elimination capacity by 57% (43.9 to 19.0 g m-3 h-1). Thus, this study suggests the soil water content should be controlled at about 96% (dry weight) or a matric potential of -10 cm H2O and the maximum elimination capacity is restricted to a narrow water content/matric potential. This narrow range impacts on the operation of full-scale biofilters as traditional techniques for water content control would make maintaining this range difficult.