Methane oxidation in water-spreading and compost biofilters.

This study evaluated two biofilter designs to mitigate methane emissions from landfill vents. Water-spreading biofilters were designed to use the capillarity of coarse sand overlain by a finer sand to increase the active depth for methane oxidation. Compost biofilters consisted of 238-L barrels containing a 1:1 mixture (by volume) of compost to expanded polystyrene pellets. Two replicates of each type of biofilter were tested at an outdoor facility. Gas inflow consisted of an approximately 1:1 mixture (by volume) of CH4 and CO2. Methane output rates (J(out); g m(-2) day(-1)) were measured using the static chamber technique and the Pedersen et al. (2001) diffusion model. Methane oxidation rate (J(ox); g m(-2) day(-1)) and fraction of methane oxidized (f(ox)) were determined by mass balance. For methane inflow rates (J(in)) between 250 and 500 g m(-2) day(-1), the compost biofilter J(ox), 242 g m(-2) day(-1), was not significantly different (P = 0.0647) than the water-spreading biofilter J(ox), 203 g m(-2) day(-1); and the compost f(ox), 69%, was not significantly different (P = 0.7354) than water-spreading f(ox), 63%. The water-spreading biofilter was shown to generally perform as well as the compost biofilter, and it may be easier to implement at a landfill and require less maintenance.     

Odour control at biowaste composting facilities

There are several options to effectively reduce odorous emissions at composting facilities depending on the type of composting system used. Some of the more relevant measures for open and enclosed composting facilities are presented in this article. Results from different investigations on odour reduction efficiencies of biological waste gas treatment systems at various scales are presented. Biofilter/bioscrubber combinations were used and different biofilter materials were tested. The more relevant odorous substances in the waste gas were identified, and their reduction in the different systems was measured. The biofilter proved to be mainly responsible for efficient odour degradation. The investigations presented in this article revealed that screened compost was very effective, and proved to be a low cost biofilter material for odour degradation purposes. Screened compost showed higher degradation rates than a coke-compost mixture newly developed by the University of Leipzig. Furthermore, it seems that enclosed systems have advantages when compared to conventional open single bed biofilters.     

Performance of a passively vented field-scale biofilter for the microbial oxidation of landfill methane

An upflow biofilter system was operated on a passively vented landfill for the treatment of residual landfill methane. Biofilter methane emissions as a basis for determining methane removal rates were assessed by manual and automated chamber measurements, by measuring methane concentrations in the top layer gaseous phase in combination with gas flow rates, and by evaluating the methane load in the reverse gas flow following the change of landfill gas flux direction as governed by the course of barometric pressure. Methane removal rates were very high with maximum values of 80 g h(-1) m(-3). For the observed cases, the limit of biofilter methane oxidation capacity was not reached and absolute removal rates were thus linearly correlated to the amount of methane entering the filter. The analysis of methane loads flowing back from the biofilter following phases of longer, continuous and non-oscillating landfill gas emission, however, revealed that in these situations biofilter performance is restricted by deficient oxygen supply. At the oxygen-restricted capacity limit, removal rates are influenced by temperature (positively), methane influx (negatively) and flow rate (negatively) as a measure for the displacement of oxygen. These situations, however, account for only 12% of all emission phases. The investigated biofilter capacity, as derived from laboratory analyses of methanotrophic activities, is sufficient to oxidise 62% of the methane load emitted annually. Field and laboratory data provide a stable basis for the dimensioning of filters in future applications.     

The effect of bed properties on methane removal in an aerated biofilter--model studies

The capacity of laboratory-scale aerated biofilters to oxidize methane was investigated. Four types of organic and mineral-organic materials were flushed with a mixture of CH₄, CO₂ and air (1:1:8 by volume) during a six-month period. The filter bed materials were as follows: (1) municipal waste compost, (2) an organic horticultural substrate, (3) a composite of expanded perlite and compost amended with zeolite, and (4) the same mixture of perlite and compost amended with bentonite. Methanotrophic capacity during the six months of the experiment reached maximum values of between 889 and 1036 g m⁻² d⁻¹. Batch incubation tests were carried out in order to determine the influence of methane and oxygen concentrations, as well as the addition of sewage sludge, on methanotrophic activity. Michaelis constants K_M for CH₄ and O₂ were 4.6-14.9%, and 0.7-12.3%, respectively. Maximum methanotrophic activities V_max were between 1.3 and 11.6 cm³ g⁻¹ d⁻¹. The activity significantly increased when sewage sludge was added. The main conclusion is that the type of filter bed material (differing significantly in organic matter content, water-holding capacity, or gas diffusion coefficient) was not an important factor in determining methanotrophic capacity when oxygen was supplied to the biofilter.     

Passive landfill gas emission - Influence of atmospheric pressure and implications for the operation of methane-oxidising biofilters

A passively vented landfill site in Northern Germany was monitored for gas emission dynamics through high resolution measurements of landfill gas pressure, flow rate and composition as well as atmospheric pressure and temperature. Landfill gas emission could be directly related to atmospheric pressure changes on all scales as induced by the autooscillation of air, diurnal variations and the passage of pressure highs and lows. Gas flux reversed every 20 h on average, with 50% of emission phases lasting only 10h or less. During gas emission phases, methane loads fed to a connected methane oxidising biofiltration unit varied between near zero and 247 g CH4 h(-1)m(-3) filter material. Emission dynamics not only influenced the amount of methane fed to the biofilter but also the establishment of gas composition profiles within the biofilter, thus being of high relevance for biofilter operation. The duration of the gas emission phase emerged as most significant variable for the distribution of landfill gas components within the biofilter.     

Passive drainage and biofiltration of landfill gas: results of Australian field trial

A field scale trial was undertaken at a landfill site in Sydney, Australia (2004-2008), to investigate passive drainage and biofiltration of landfill gas as a means of managing landfill gas emissions from low to moderate gas generation landfill sites. The objective of the trial was to evaluate the effectiveness of a passive landfill gas drainage and biofiltration system at treating landfill gas under field conditions, and to identify and evaluate the factors that affect the behaviour and performance of the system.The trial results showed that passively aerated biofilters operating in a temperate climate can effectively oxidise methane in landfill gas, and demonstrated that maximum methane oxidation efficiencies greater than 90% and average oxidation efficiencies greater than 50% were achieved over the 4 years of operation. The trial results also showed that landfill gas loading was the primary factor that determined the behaviour and performance of the passively aerated biofilters. The landfill gas loading rate was found to control the diffusion of atmospheric oxygen into the biofilter media, limiting the microbial methane oxidation process. The temperature and moisture conditions within the biofilter were found to be affected by local climatic conditions and were also found to affect the behaviour and performance of the biofilter, but to a lesser degree than the landfill gas loading.     

Kinetics of microbial landfill methane oxidation in biofilters

A methane oxidizing biofilter system fitted to the passive venting system of a harbor sludge landfill in Germany was characterized with respect to the the methanotrophic population, methane oxidizing capacity, and reaction kinetics. Methanotrophic cell counts stabilized on a high level with 1.3 x 10(8) to 7.1 x 10(9) cells g dw(-1) about one year after first biofilter operation, and a maximum of 1.2 x 10(11) cells g dw(-1). Potential methane oxidizing activity varied between 5.3 and 10.7 microg h(-1) g dw(-1). Cell numbers correlated well with methane oxidation activities. Extrapolation of potential activities gave methane removal rates between 35 and 109 g CH4 h(-1) m(-3), calculated for 30 degrees C. Optimum temperature was 38 degrees C for freshly sampled biofilter material and 22 degrees C for a methanotrophic enrichment culture grown at 10 degrees C incubation temperature. Substrate kinetics revealed the presence of a low-affinity methane oxidizing community with a high Vmax of 1.78 micromol CH4 h(-1) g ww(-1) and a high K(M) of 15.1 microM. K(MO2) for methane oxidation was 58 microM. No substantial methane oxidizing activity was detected below 1.7-2.6 vol.-% O2 in the gaseous phase. Methane deprivation led to a decrease in methane oxidation activity within 5-9 weeks but could still be detected after 25 weeks of substrate deprivation and was fully restored within 3 weeks of continuous methane supply. Very high salt loads are leached from the novel biofilter material, expanded clay, yielding electric conductivity values of up to 15 mS cm(-1) in the leachate. Values > 6 mS cm(-1) were shown to depress methane consumption. Water retention characteristics of the material proved to be favourable for methane oxidizing systems with a gas permeable volume of 78% of bulk volume at field capacity water content. Correspondingly, no influence of water content on methane oxidation activity could be detected at water contents between 2.5 and 20 vol.-%.     

Evaluation of aerated biofilter systems for microbial methane oxidation of poor landfill gas

In the long-term, landfills are producing landfill gas (LFG) with low calorific values. Therefore, the utilization of LFG in combined heat and power plants (CHP) is limited to a certain period of time. A feasible method for LFG treatment is microbial CH(4) oxidation. Different materials were tested in actively aerated lab-scale bio-filter systems with a volume of 0.167 m(3). The required oxygen for the microbial CH(4) oxidation was provided through perforated probes, which distributed ambient air into the filter material. Three air input levels were installed along the height of the filter, each of them adjusted to a particular flow rate. During the tests, stable degradation rates of around 28 g/(m(3) h) in a fine-grained compost material were observed at a CH(4) inlet concentration of 30% over a period of 148 days. Compared with passive (not aerated) tests, the CH(4) oxidation rate increased by a factor of 5.5. Therefore, the enhancement of active aeration on the microbial CH(4) oxidation was confirmed. At a O(2)/CH(4) ratio of 2.5, nearly 100% of the CH(4) load was decomposed. By lowering the ratio from 2.5 to 2, the efficiency fell to values from 88% to 92%. By varying the distribution to the three air input levels, the CH(4) oxidation process was spread more evenly over the filter volume.     

Treatment of waste gas containing monomethylamine in a biofilter enriched with Pseudomonas mendocina

Waste gas containing monomethylamine (MMA) was treated in a biofilter packed with compost along with wood chips and enriched with Pseudomonas mendocina. The biofilter could remove MMA to the extent of more than 99% at a loading of 42.36 gm(-3)h(-1) with an empty bed retention time of 12s. At optimal operating conditions, the moisture content in the biofilter was maintained at around 45%. The biodegradative products of MMA were ammonia, nitrite, and nitrate.     

Performance of Trickle-Bed Air Biofilter: A Comparative Study of a Hydrophilic and a Hydrophobic Voc

Two lab-scale trickle-bed air biofilters were operated for investigating the difference in performance between a hydrophilic and a hydrophobic volatile organic compound (VOC). Methyl isobutyl ketone (MIBK) and styrene were selected as a model hydrophilic and hydrophobic VOCs, respectively. Effects of loading rates, biofilter re-acclimation, removal profile along biofilter depth, nitrogen consumption, and CO₂ production were compared under three operating conditions, namely, backwashing and two non-use periods (starvation and stagnant). Consistent over 99% removal efficiency up to loading rates of 3.26 kg COD/m³-day was obtained for the MIBK biofilter at 0.76 min empty bed retention time (EBRT) and 1.5 L/d nutrient flow. A similar performance for the styrene biofilter was obtained for loading rates up to 1.9kg COD/m³-day at 2.02 min EBRT and 2.4 L/d nutrient flow. The MIBK biofilter required only an initial acclimation period of 16 days while styrene biofilter required 46 days. Non-use periods can be used as another means of biomass control for both biofilters when the employed loading rate did not exceed 1.27 and 2.17 kg COD/m³-day for styrene and MIBK biofilters, respectively. The re-acclimation of both biofilter was delayed with increase of loading rate. MIBK biofilter re-acclimated in 90 min, while styrene biofilter re-acclimated in more than 600 min. Under similar loading rates, MIBK biofilter utilized less biofilter depth than styrene biofilter. Nitrogen consumption behaviors were apparently different between the two biofilters. Styrene biofilter had higher CO₂ production than MIBK biofilter and its CO₂ production was closely related to the theoretical complete chemical oxidation.     

Methane and carbon dioxide production from simulated anaerobic degradation of cattle carcasses

Approximately 2.2million cattle carcasses require disposal annually in the United States. Land burial is a convenient disposal method that has been widely used in animal production for disposal of both daily mortalities as well as during catastrophic mortality events. To date, greenhouse gas production after mortality burial has not been quantified, and this study represents the first attempt to quantify greenhouse gas emissions from land burial of animal carcasses. In this study, anaerobic decomposition of both homogenized and unhomogenized cattle carcass material was investigated using bench-scale reactors. Maximum yields of methane and carbon dioxide were 0.33 and 0.09m(3)/kg dry material, respectively, a higher methane yield than that previously reported for municipal solid waste. Variability in methane production rates were observed over time and between reactors. Based on our laboratory data, annual methane emissions from burial of cattle mortalities in the United States could total 1.6Tg CO(2) equivalents. Although this represents less than 1% of total emissions produced by the agricultural sector in 2009, greenhouse gas emissions from animal carcass burial may be significant if disposal of swine and poultry carcasses is also considered.     

Long-term behavior of passively aerated compost methanotrophic biofilter columns

The methane oxidation potential of several types of compost methanotrophic biofilter columns were compared in the laboratory over a period of 220 days. The results indicate an increase in methanotrophic activity over a period of about 100 days, up to a maximum of 400 g m(-2) day(-1), and a gradual decline to about 100 g m(-2) day(-1) within the next 120 days. High methane oxidation rates appear to be restricted to a small area of the column, 10-15 cm thick. Based on the laboratory investigations carried out to determine the cause for the decline in methane oxidation rate, it was concluded that the formation of exopolymeric substances (EPS), at the zones of maximum methane oxidation, was responsible for this decline. In monitoring methane oxidation in a column for up to 600 days, it was observed that mixing of the medium after formation of EPS enabled the column to temporarily recover high performance. The results suggest that stable, homogenous compost, with a low C/N and low ammonium content, mixed on a regular basis, could achieve and maintain high methane oxidation efficiencies.     

Elimination of Methanol and Ethanol by Biofiltration: An Experimental Study

This study presents the experimental results obtained during long-term operation of two biofilters treating two alcohols: methanol and ethanol. The biofilters used for this purpose were previously packed with a compost material made from tobacco processing residues. The alcohols concentrations tested lay between 0.40 and 3.20 g/m³ for methanol, and 0.55 and 5.05 g/m³ for ethanol. The empty bed residence time in each biofilter was 60 s. Biofilter inlet loads of less than 190 and 300 g/m³/h for the methanol and ethanol additions respectively, were thereafter evaluated. In addition, the concentrations of nutrient nitrogen were also varied, from 0.1 to 2.0 g-N/l and from 0.3 to 11.3 g-N/l for the ethanol and the methanol, respectively. The results thus obtained have made it possible to select the optimal nitrogen concentrations which, for the cases examined, turn out to be 0.3 g-N/l and between 2 and 3.8 g-N/l for the ethanol and methanol substrates, respectively. The maximum elimination capacities obtained in this study were 82 and 150 g/m³/h, respectively for the methanol and ethanol cases. It was therefore concluded that, for a readily biodegradable compound such as ethanol, the nitrogen requirement is substantially lower than that needed for the methanol degradation, the latter appearing to be more difficult to degrade biologically under similar operating conditions. The production rate of the co-product carbon dioxide during methanol and ethanol biofiltration was also investigated. Also, a good correlation was found to exist between the temperature and the conversion achieved in the biofilter.     

Performance evaluation of an anaerobic/aerobic landfill-based digester using yard waste for energy and compost production

The objective of this study was to evaluate a new alternative for yard waste management by constructing, operating and monitoring a landfill-based two-stage batch digester (anaerobic/aerobic) with the recovery of energy and compost. The system was initially operated under anaerobic conditions for 366 days, after which the yard waste was aerated for an additional 191 days. Off gas generated from the aerobic stage was treated by biofilters. Net energy recovery was 84.3MWh, or 46kWh per million metric tons of wet waste (as received), and the biochemical methane potential of the treated waste decreased by 83% during the two-stage operation. The average removal efficiencies of volatile organic compounds and non-methane organic compounds in the biofilters were 96-99% and 68-99%, respectively.     

Higher pH and faster decomposition in biowaste composting by increased aeration

Composting of source separated municipal biowaste has at several plants in Scandinavia been hampered by low pH. In this study the hypothesis that increased aeration would improve the process was tested in full-scale experiments at two large composting plants. The O2 concentrations were high (>15%) even at the low aeration rates, so the prevailing low pH was not due to an anaerobic process environment. In spite of this, increased aeration rates at the start of the process resulted in higher microbial activity, increased pH and a more stable compost product. At one plant the decomposition rate varied in proportion to the aeration rate, to the extent that the temperatures and O2 concentrations were similar during the early processes even though aeration rates varied between 10 and 50 m3/(h, m3 compost). However, increased aeration caused severe drying of the compost, but at one plant the addition of water was adequate to prevent drying. In conclusion, by increasing the aeration rates and adding water to compensate for drying, it was possible to shorten the time needed to produce a stable compost product and thus to increase the efficiency of the composting plants.     

Impact of different plants on the gas profile of a landfill cover

Methane is an important greenhouse gas emitted from landfill sites and old waste dumps. Biological methane oxidation in landfill covers can help to reduce methane emissions. To determine the influence of different plant covers on this oxidation in a compost layer, we conducted a lysimeter study. We compared the effect of four different plant covers (grass, alfalfa + grass, miscanthus and black poplar) and of bare soil on the concentration of methane, carbon dioxide and oxygen in lysimeters filled with compost. Plants were essential for a sustainable reduction in methane concentrations, whereas in bare soil, methane oxidation declined already after 6 weeks. Enhanced microbial activity - expected in lysimeters with plants that were exposed to landfill gas - was supported by the increased temperature of the gas in the substrate and the higher methane oxidation potential. At the end of the first experimental year and from mid-April of the second experimental year, the methane concentration was most strongly reduced in the lysimeters containing alfalfa + grass, followed by poplar, miscanthus and grass. The observed differences probably reflect the different root morphology of the investigated plants, which influences oxygen transport to deeper compost layers and regulates the water content.     

Availability and properties of materials for the Fakse Landfill biocover

Methane produced in landfills can be oxidized in landfill covers made of compost; often called biocovers. Compost materials originating from seven different sources were characterized to determine their methane-oxidizing capacity and suitability for use in a full-scale biocover at Fakse Landfill in Denmark. Methane oxidation rates were determined in batch incubations. Based on material availability, characteristics, and the results of batch incubations, five of the seven materials were selected for further testing in column incubations. Three of the best performing materials showed comparable average methane oxidation rates: screened garden waste compost, sewage sludge compost, and an unscreened 4-year old garden waste compost (120, 112, and 108 g m⁻² d⁻¹, respectively). On the basis of these results, material availability and cost, the unscreened garden waste compost was determined to be the optimal material for the biocover. Comparing the results to criteria given in the literature it was found that the C/N ratio was the best indicator of the methane oxidation capacity of compost materials. The results of this work indicate that batch incubations measuring methane oxidation rates offer a low-cost and effective method for comparing compost sources for suitability of use in landfill biocovers.     

Supercritical water gasification of sewage sludge using bench-scale batch reactor: advantages and drawbacks

Sewage sludge, a byproduct of municipal wastewater treatment, was gasified by supercritical water using a bench-scale batch reactor. Configuration of bench-scale batch reactor and operation procedures are discussed in detail. Experience and challenges that arose during the experiment are also shared. Using the bench-scale reactor under the condition of 600 °C, 23 MPa, and a reaction time of 60 min without catalyst presence, a total gas yield of 9.8 mol/(kg-sewage sludge) was obtained. Furthermore, investigations on operational parameters were conducted. Extension of reaction time up to 60 min increased the gasification, reaching a plateau thereafter. Investigation on pressure indicated the superiority of supercritical pressure. The addition of Ni as a catalyst also promoted gasification, although inorganic salts and char seemed to cover the catalyst surface. With regard to the prospect of future operation at a municipal waste water treatment plant, the effect of operational parameters on heavy metal concentration in the liquid phase is also discussed.     

Design of top covers supporting aerobic in situ stabilization of old landfills – An experimental simulation in lysimeters

Landfill aeration by means of low pressure air injection is a promising tool to reduce long term emissions from organic waste fractions through accelerated biological stabilization. Top covers that enhance methane oxidation could provide a simple and economic way to mitigate residual greenhouse gas emissions from in situ aerated landfills, and may replace off-gas extraction and treatment, particularly at smaller and older sites. In this respect the installation of a landfill cover system adjusted to the forced-aerated landfill body is of great significance. Investigations into large scale lysimeters (2 × 2 × 3 m) under field conditions have been carried out using different top covers including compost materials and natural soils as a surrogate to gas extraction during active low pressure aeration. In the present study, the emission behaviour as well as the water balance performance of the lysimeters has been investigated, both prior to and during the first months of in situ aeration. Results reveal that mature sewage sludge compost (SSC) placed in one lysimeter exhibits in principle optimal ambient conditions for methanotrophic bacteria to enhance methane oxidation. Under laboratory conditions the mature compost mitigated CH₄ loadings up to 300 l CH₄/m² d. In addition, the compost material provided high air permeability even at 100% water holding capacity (WHC). In contrast, the more cohesive, mineral soil cover was expected to cause a notably uniform distribution of the injected air within the waste layer. Laboratory results also revealed sufficient air permeability of the soil materials (TS-F and SS-Z) placed in lysimeter C. However, at higher compaction density SS-Z became impermeable at 100% WHC.Methane emissions from the reference lysimeter with the smaller substrate cover (12–52 g CH₄/m² d) were significantly higher than fluxes from the other lysimeters (0–19 g CH₄/m² d) during in situ aeration. Regarding water balance, lysimeters covered with compost and compost-sand mixture, showed the lowest leachate rate (18–26% of the precipitation) due to the high water holding capacity and more favourable plant growth conditions compared to the lysimeters with mineral, more cohesive, soil covers (27–45% of the precipitation).On the basis of these results, the authors suggest a layered top cover system using both compost material as well as mineral soil in order to support active low-pressure aeration. Conventional soil materials with lower permeability may be used on top of the landfill body for a more uniform aeration of the waste due to an increased resistance to vertical gas flow. A compost cover may be built on top of the soil cover underlain by a gas distribution layer to improve methane oxidation rates and minimise water infiltration. By planting vegetation with a high transpiration rate, the leachate amount emanating from the landfill could be further minimised. The suggested design may be particularly suitable in combination with intermittent in situ aeration, in the later stage of an aeration measure, or at very small sites and shallow deposits. The top cover system could further regulate water infiltration into the landfill and mitigate residual CH₄ emissions, even beyond the time of active aeration.     

Biofiltration treatment of odors from municipal solid waste treatment plants

An in situ compost biofilter was established for the treatment of odors from biostabilization processing of municipal solid waste. The concentrations of total volatile organic compounds (VOCs) in odors and their components were measured. Biofilter media was characterized in terms of total carbon (TC), total nitrogen (TN), total phosphorus (TP), organic matter (OM), pH value and determination of bacterial colony structure. Gas chromatography–mass spectrometry (GC–MS) analysis showed that the main components of the produced gas were benzene, toluene, ethylbenzene and xylene (BTEX) along with other alkanes, alkenes, terpenes, and sulphur compounds. The compost biofilter had remarkable removal ability for alkylated benzenes (>80%), but poor removal for terpenes (～30%). Total VOC concentrations in odors during the biostabilization process period ranged from 0.7 to 87 ppmv, and the VOC removal efficiency of the biofilter varied from 20% to 95%. After about 140 days operation, TN, TC, TP and OM in compost were kept almost stable, but the dissolved N, NH₄–N and NO₃–N experienced an increase of 44.5%, 56.2% and 76.3%, respectively. Dissolved P decreased by 27.3%. The pH value experienced an increase in the early period and finally varied from 7.38 to 8.08. Results of bacterial colony in packing material indicated that bacteria and mold colony counts increased, but yeasts and actinomyces decreased along with biofilter operation, which were respectively, 3.7, 3.4, 0.04 and 0.07 times of their initial values.