Effect of biocover equipped with a novel passive air diffusion system on microbial methane oxidation and community of methanotrophs

A novel biocover with passive air diffusion system (PADS) was designed in this study. Its effect on landfill gas components in the macrocosms of simulated biocover systems was also investigated. The results show that O2 concentration increased in the whole profile of the macrocosms equipped with PADS. When simulated landfill gas (SLFG) flow rate was no more than 40 mL min(-1), the methane oxidation rate was 100%. The highest CH4 oxidation capacity reached to 31.34 mol m(-3) day(-1). Molecular microbiology analysis of the soil samples taken from the above macrocosm showed that the growth of type I methanotrophs was enhanced, attributable to enhanced air diffusion and distribution, whereas the microbial diversity and population density of type II methanotrophs were not so affected, as evidenced by the absence of any difference between the biocover equipped with PADS and that of the control. According to a phylogenic analysis, Methylobacter Methylosarcinafor type I, and Methylocystis, Methylosinus for type II, were the most prevalent species in the macrocosm with PADS.     

垃圾填埋场甲烷氧化菌及甲烷通量的研究

采用静态箱法、滚管计数法和气相色谱法,对6个不同封场时间填埋区的甲烷通量、覆土层甲烷氧化菌数量和甲烷氧化速率的变化趋势进行了测定,并分析了它们与封场时间、植被覆盖率等因素之间的相关性。结果发现6个填埋区甲烷通量的变化范围在-0.34～5.31 mg/(m2.h)之间;覆土层甲烷氧化菌的数量范围为3.10×107～20.77×107 cfu/g干土,甲烷氧化速率在1.65×10-8～4.34×10-8mol/(h.g)之间。覆土层甲烷氧化菌的数量与甲烷氧化速率呈正相关,但前者并不是后者的决定性因素;甲烷通量高时可刺激甲烷氧化菌数量及氧化速率的提高,且三者均与封场时间呈显著负相关,与植被覆盖率呈负相关;当含水率大于15%时,随着覆土层含水率的增加,甲烷氧化速率呈下降趋势;覆土pH、有机质和铵态氮与甲烷氧化速率等无明显相关性。提高覆土层的甲烷氧化速率可有效减少垃圾填埋场的甲烷排放。     

渗滤液耦合矿化垃圾制备甲烷氧化菌菌液

利用甲烷氧化菌菌液增加材料中甲烷氧化菌的数量,可以得到高甲烷氧化率的填埋场甲烷生物氧化覆盖材料。研究发现,渗滤液原水和渗滤液处理尾水均能促进甲烷氧化菌的生长,可利用渗滤液耦合矿化垃圾混合培养制备甲烷氧化菌菌液用于填埋场甲烷减排。填埋龄长的渗滤液原水有着较好的培养效果,得到的菌液在4 d内最高甲烷氧化速率达到2.68 mL/h,超过甲烷氧化菌培养液(nitrate minimal salt medium,NMS)的实验结果。渗滤液中总氮、无机碳、总有机碳和Ni元素的含量对甲烷氧化菌的培养过程影响较大,适用于甲烷氧化培养的渗滤液应满足:总氮1 400 mg/L,总有机碳55 mg/L,Ni元素0.4 mg/L,总磷含量较高。     

Illumina sequencing-based analysis of a microbial community enriched under anaerobic methane oxidation condition coupled to denitrification revealed coexistence of aerobic and anaerobic methanotrophs

Methane is produced in anaerobic environments, such as reactors used to treat wastewaters, and can be consumed by methanotrophs. The composition and structure of a microbial community enriched from anaerobic sewage sludge under methane-oxidation condition coupled to denitrification were investigated. Denaturing gradient gel electrophoresis (DGGE) analysis retrieved sequences of Methylocaldum and Chloroflexi. Deep sequencing analysis revealed a complex community that changed over time and was affected by methane concentration. Methylocaldum (8.2%), Methylosinus (2.3%), Methylomonas (0.02%), Methylacidiphilales (0.45%), Nitrospirales (0.18%), and Methanosarcinales (0.3%) were detected. Despite denitrifying conditions provided, Nitrospirales and Methanosarcinales, known to perform anaerobic methane oxidation coupled to denitrification (DAMO) process, were in very low abundance. Results demonstrated that aerobic and anaerobic methanotrophs coexisted in the reactor together with heterotrophic microorganisms, suggesting that a diverse microbial community was important to sustain methanotrophic activity. The methanogenic sludge was a good inoculum to enrich methanotrophs, and cultivation conditions play a selective role in determining community composition.     

Biodegradation of undecylbenzenesulphonate by mixed methane-oxidizing culture

Biodegradation of undecylbenzenesulphonate (C(11)LAS) was performed in shake flasks at 21 degrees C by using a mixed methanotrophic-heterotrophic culture containing type II methanotrophs. Concentrations of C(11)LAS and aromatic intermediates were determined by reversed-phase high-performance liquid chromatography (RP-HPLC). Methane and carbon dioxide concentrations were measured in headspace samples by using gas chromatography. RP-HPLC analyses of aqueous samples show that the culture MM1 expresses the capability of C(11)LAS transformation in the presence or absence of methane. Simultaneous methane oxidation and C(11)LAS degradation, and the inhibition of both transformation processes by acetylene were observed. This suggests the possibility that C(11)LAS transformation is catalyzed by methane monooxygenase (MMO). Comparable affinity of culture MM1 for both methane and C(11)LAS ( [Formula: see text], respectively), and more than four times higher maximum transformation rate for methane than for C(11)LAS ( [Formula: see text] (dry weight) cells day(-1), respectively), were determined. This further supports the involvement of MMO enzyme system in transformation and suggests a pronounced competitive inhibition of C(11)LAS degradation by methane.     

Evaluation of gas emissions from coal stockpile

Gas emissions of carbon dioxide, methane, dimethylsulfide, carbon monoxide and oxygen from a coal stockpile in Velenje were determined. Gases from the coal stockpile were collected in Alltech Standard sampling bags and then analysed using a capillary gas chromatograph and electrochemical sensors. A flame ionisation detector equipped with a Zr/Ni catalytic reactor was used for the determination of methane and carbon dioxide. Dimethylsulfide was detected with a flame photometric detector, and the concentrations of carbon monoxide and oxygen were determined by use of electrochemical sensors. The results showed that the main influence on gas emissions is related to the ambient temperature. Emissions of carbon dioxide during summer 2001 (average temperature during sampling period was 24 degrees C) were approximately 30-times higher than during winter 2002 (average temperature during sampling period was -2 degrees C) and were also influenced by the oxygen concentration. Carbon dioxide is mainly formed by oxidation of coal. Methane and dimethylsulfide are desorbed from coal, and are present in higher concentrations in stockpile emissions when stockpiles are renewed. The dimethylsulfide concentration, in contrast to laboratory experiments in stockpile emissions, falls immediately due to photo-degradation.     

Specific resistance to filtration of biomass from membrane bioreactor reactor and activated sludge: effects of exocellular polymeric substances and dispersed microorganisms.

This study investigates the effect of dispersed microorganisms and exocellular polymeric substances on biomass dewaterability. Specific resistance to filtration (SRF) was measured for biomass from a membrane bioreactor and a completely mixed activated sludge system. Both laboratory-scale reactors were fed with synthetic wastewater and operated at a high food-to-microorganism ratio (F/M) (1 to 11 kilograms chemical oxygen demand per kilogram mixed liquor volatile suspended solids per day [kgCOD/(kg MLVSS.d)]) and short solids retention times (0.25 to 5 d). The SRF values were affected by strong interactions of three parameters: (1) the mixed liquor suspended solids concentration, (2) the amount of dispersed microorganisms, and (3) the exocellular polymeric substances (EPS) concentration. At F/M smaller than 2 kg COD/(kg MLSS.d) and mixed liquor suspended solids (MLSS) concentration higher than 2000 mg/L, increasing amount of dispersed microorganisms in the biomass yielded higher SRF values. However, at high F/M (> 5 kg COD/kg MLSS.d) and low MLSS concentrations (< 600 mg/L), lower EPS concentrations resulted in slightly smaller SRF values, even though the amount of dispersed microorganisms in the biomass was much higher. Thus, at low MLSS concentrations, EPS concentrations rather than the amount of dispersed microorganisms tend to control SRF.     

Biodegradation of trace gases in simulated landfill soil cover systems

The attenuation of methane and seven volatile organic compounds (VOCs) was investigated in a dynamic methane and oxygen counter gradient system simulating a landfill soil cover. The VOCs investigated were: Tetrachloromethane (TeCM), trichloromethane (TCM), dichloromethane (DCM), trichloroethylene (TCE), vinyl chloride (VC), benzene, and toluene. Soil was sampled at Skellingsted landfill, Denmark. The soil columns showed a high capacity for methane oxidation, with oxidation rates up to 184 g/m2/d corresponding to a 77% reduction of inlet methane. Maximal methane oxidation occurred at 15-20 cm depth, in the upper part of the column where there were overlapping gradients of methane and oxygen. All the chlorinated hydrocarbons were degraded in the active soil columns with removal efficiencies higher than 57%. Soil gas concentration profiles indicated that the removal of the fully chlorinated compound TeCM was because of anaerobic degradation, whereas the degradation of lower chlorinated compounds like VC and DCM was located in the upper oxic part of the column. Benzene and toluene were also removed in the active column. This study demonstrates the complexity of landfill soil cover systems and shows that both anaerobic and aerobic bacteria may play an important role in reducing the emission of trace components into the atmosphere.     

Methane oxidation in compost-based landfill cover with vegetation during wet and dry conditions in the tropics

The effect of compost and vegetation on methane (CH4) oxidation was investigated during wet and dry conditions in a tropical region. A laboratory-scale experiment was conducted to examine the performance of nonvegetated and vegetated landfill cover systems in terms of CH4 oxidation efficiency. Two types of landfill cover materials (compost and sandy loam) and two species of tropical grasses (Sporobolus virginicus and Panicum repens) were studied for their effect on the CH4 oxidation reaction. It was found that the use of compost as cover material could maintain a high methane oxidation rate (MOR) of 12 mol CH4/m3 x day over a 250-day period. Leachate application showed a positive effect on promoting methanotrophic activity and increasing MOR. A high MOR of 12 mol CH4/m3 x day was achieved when using compost cover with P. repens during wet and dry seasons when leachate irrigation was practiced. In dry conditions, a lower MOR of 8 mol CH4/m3 x day was observed for 80 days.     

Biodegradation of Trace Gases in Simulated Landfill Soil

Abstract

The attenuation of methane and seven volatile organic compounds (VOCs) was investigated in a dynamic methane and oxygen counter gradient system simulating a landfill soil cover. The VOCs investigated were: Tetrachloromethane (TeCM), trichloromethane (TCM), dichloromethane (DCM), trichloroethylene (TCE), vinyl chlo-ride (VC), benzene, and toluene. Soil was sampled at Skellingsted landfill, Denmark. The soil columns showed a high capacity for methane oxidation, with oxidation rates up to 184 g/m²/d corresponding to a 77% reduction of inlet methane. Maximal methane oxidation occurred at 15–20 cm depth, in the upper part of the column where there were overlapping gradients of methane and oxygen. All the chlorinated hydrocarbons were degraded in the active soil columns with removal efficiencies higher than 57%. Soil gas concentration profiles indicated that the removal of the fully chlorinated compound TeCM was because of anaerobic degradation, whereas the degradation of lower chlorinated compounds like VC and DCM was located in the upper oxic part of the column. Benzene and toluene were also removed in the active column. This study demonstrates the complexity of landfill soil cover systems and shows that both anaerobic and aerobic bacteria may play an important role in reducing the emission of trace components into the atmosphere.     

Biogeochemical processes at the fringe of a landfill leachate pollution plume: potential for dissolved organic carbon, Fe(II), Mn(II), NH4, and CH4 oxidation

Various redox reactions may occur at the fringe of a landfill leachate plume, involving oxidation of dissolved organic carbon (DOC), CH4, Fe(II), Mn(II), and NH4 from leachate and reduction of O2, NO3 and SO4 from pristine groundwater. Knowledge on the relevance of these processes is essential for the simulation and evaluation of natural attenuation (NA) of pollution plumes. The occurrence of such biogeochemical processes was investigated at the top fringe of a landfill leachate plume (Banisveld, the Netherlands). Hydrochemical depth profiles of the top fringe were captured via installation of a series of multi-level samplers at 18, 39 and 58 m downstream from the landfill. Ten-centimeter vertical resolution was necessary to study NA within a fringe as thin as 0.5 m. Bromide appeared an equally well-conservative tracer as chloride to calculate dilution of landfill leachate, and its ratio to chloride was high compared to other possible sources of salt in groundwater. The plume fringe rose steadily from a depth of around 5 m towards the surface with a few meters in the period 1998-2003. The plume uplift may be caused by enhanced exfiltration to a brook downstream from the landfill, due to increased precipitation over this period and an artificial lowering of the water level of the brook. This rise invoked cation exchange including proton buffering, and triggered degassing of methane. The hydrochemical depth profile was simulated in a 1D vertical reactive transport model using PHREEQC-2. Optimization using the nonlinear optimization program PEST brought forward that solid organic carbon and not clay minerals controlled retardation of cations. Cation exchange resulted in spatial separation of Fe(II), Mn(II) and NH4 fronts from the fringe, and thereby prevented possible oxidation of these secondary redox species. Degradation of DOC may happen in the fringe zone. Re-dissolution of methane escaped from the plume and subsequent oxidation is an explanation for absence of previously present nitrate and anaerobic conditions in pristine groundwater above the plume. Stable carbon isotope (delta13C) values of methane confirm anaerobic methane oxidation immediately below the fringe zone, presumably coupled to reduction of sulfate, desorbed from iron oxide. Methane must be the principle reductant consuming soluble electron-acceptors in pristine groundwater, thereby limiting NA for other solutes including organic micro-pollutants at the fringe of this landfill leachate plume.     

Photocatalytic oxidation of methyl orange in a three-phase fluidized bed reactor

The photocatalytic oxidation of methyl orange under weak illumination conditions was carried out in two different types of fluidized bed reactors. TiO2 powder was employed as the photocatalysts and a 15 W low pressure mercury lamp was used as the light source and the reactor volume was 2.5 l. The parametric study of photocatalytic oxidation of methyl orange in two different types of fluidized beds was investigated; effect of catalyst loadings, pH, air flow rate, initial concentration and oxygen concentration on the oxidation reaction rate. The experimental results were analyzed in conjunction with the characteristics of fluidized bed and the reactor geometry effect on the reaction rate was analyzed.     

Characterization and reactivity of natural manganese ore catalysts in the selective catalytic oxidation of ammonia to nitrogen

Natural manganese ore (NMO) catalysts were characterized and tested in the selective catalytic oxidation of ammonia to nitrogen oxides under dilute conditions. Also, the oxidation of ammonia (NH(3)) was carried out using pure MnO(2), Mn(2)O(3) for comparing with the activity. It is found that the activity of NMO was similar to that of MnO(2) at low temperature below 150 degrees C but above this temperature, the activity of these catalysts showed the difference. In the course of NH(3) oxidation, N(2), NO, N(2)O and H(2)O were produced. But the quantity of NO(2) produced in this experiment was negligible. At temperature below 250 degrees C, selectivity into N(2) from NH(3) oxidation was in the order, NMO > MnO(2) > Mn(2)O(3). This is the reverse of activity of these manganese oxides. Also the characterization of NH(3) oxidation was proposed and supported by the effect of space velocity, inlet O(2) and NH(3) concentration. The increase of space velocity remarkably influenced not only the conversion but also selectivity into N(2). The higher the reaction temperature was, the higher the effect of inlet O(2) and NH(3) concentration on the reaction rate was. By introducing NO during NH(3) oxidation reaction, the possibility of NMO as selective catalytic reduction catalyst at low temperature was studied and showed positive results.     

Effects of nitrogen application rate and a nitrification inhibitor dicyandiamide on methanotroph abundance and methane uptake in a grazed pasture soil

Methane-oxidizing bacteria (methanotrophs) in the soil are a unique group of methylotrophic bacteria that utilize methane (CH₄) as their sole source of carbon and energy which limit the flux of methane to the atmosphere from soils and consume atmospheric methane. A field experiment was conducted to determine the effect of nitrogen application rates and the nitrification inhibitor dicyandiamide (DCD) on the abundance of methanotrophs and on methane flux in a grazed pasture soil. Nitrogen (N) was applied at four different rates, with urea applied at 50 and 100 kg N ha^?1 and animal urine at 300 and 600 kg N ha^?1. DCD was applied at 10 kg ha^?1. The results showed that both the DNA and selected mRNA copy numbers of the methanotroph pmoA gene were not affected by the application of urea, urine or DCD. The methanotroph DNA and mRNA pmoA gene copy numbers were low in this soil, below 7.13?×?10³ g^?1 soil and 3.75?×?10³ μg^?1 RNA, respectively. Daily CH₄ flux varied slightly among different treatments during the experimental period, ranging from ?12.89 g CH₄ ha^?1 day^?1 to ?0.83 g CH₄ ha^?1 day^?1, but no significant treatment effect was found. This study suggests that the application of urea fertilizer, animal urine returns and the use of the nitrification inhibitor DCD do not significantly affect soil methanotroph abundance or daily CH₄ fluxes in grazed grassland soils.     

Online oxygen control for sulfide oxidation in anaerobic treatment of high-sulfate wastewater.

A new technique for sulfide control was investigated in an upflow-anaerobic filter (UAF) treating high-strength, sulfate-rich wastewater. The technique used periodic oxygen injection using oxidation-reduction potential (ORP) as a controlling parameter to regulate oxygen injection. The UAF was operated at a constant influent total-organic carbon of 6740 mg/L but with different influent sulfates of 1000, 3000, and 6000 mg/L. At 1000 and 3000 mg/L influent sulfates, the produced sulfide did not impose any inhibition to methane-producing bacteria (MPB). However, at 6000 mg/L influent sulfate, the produced dissolved sulfide of 804 mg S/L (free sulfide = 280 mg S/L) severely inhibited the methanogenesis, but not the sulfidogenesis. Upon oxygen injection at elevated ORP of -265 mV, sulfides were almost completely eliminated with a concomitant improvement in methane yield by 46%. If oxygenation was excessive because of an oversetting of ORP, the excess oxygen could be used rapidly by facultative heterotrophs, thereby protecting the MPB from oxygen stress. Regarding online sulfide oxidation, it was found that the biogas and injected oxygen needed to pass through an aqueous layer containing trace metals, which were found to have a significant catalytic effect on abiotic sulfide oxidation.     

Immobilization of mercury by pyrite (FeS2)

Elemental mercury (Hg⁰) is a metal with a number of atypical properties, which has resulted in its use in myriad anthropogenic processes. However, these same properties have also led to severe local subsurface contamination at many places where it has been used. As such, we studied the influence of various parameters on Hg(II) sorption onto pyrite (pH, time, Hg(II) concentration), a potential subsurface reactive barrier. Batch sorption studies revealed that total Hg(II) removal increases with both pH and time. X-ray absorption spectroscopy analysis showed that a transformation in the coordination environment at low pH occurred during aging over 2 weeks, to form an ordered monolayer of monodentate Hg-Cl complexes on pyrite. In column studies packed with pure quartz sand, the transport of Hg(II) was significantly retarded by the presence of a thin pyrite-sand reactive barrier, although dissolved oxygen inhibited Hg(II) sorption onto pyrite in the column.     

Redox reactions in the Fe-As-O2 system

We have examined two redox reactions involving arsenic and iron at near-neutral pH: the reduction of As(V) by Fe(II) under anoxic conditions, and the co-oxidation of As(III) during Fe(II) oxygenation. We also considered the impact of goethite, pH buffers, and radical scavengers on these reactions. In a series of anoxic experiments, Fe(II) was found to reduce As(V) in the presence of goethite, but not in homogeneous solution. The reaction rate increased with increasing pH and Fe(II) concentration, but in all cases was relatively slow. In aerobic experiments, the kinetics of Fe(II) oxygenation at neutral pH, and the corresponding oxidation of As(III) were found to depend heavily on pH buffer type and concentration. The classic formulation of Fe(II) oxidation by oxygen, involving four single-electron transfers, was reviewed and found to be inadequate for explaining observed oxidation of Fe(II) and As(III). Widely cited rate constants for Fe(II) oxygenation originate from experiments conducted in carbonate buffer, and do not match observations made in phosphate, MES, or HEPES systems. In phosphate buffer, Fe(II) oxidation is rapid and dependent on phosphate concentration. In MES and HEPES buffers, Fe(II) oxidation is much slower due to the lack of labile ferrous iron species. Oxygenation of Fe(II) appears to proceed through different mechanisms in phosphate and MES or HEPES systems. In both cases, reactive intermediary species are produced which can oxidize As(III). These oxidants are not the hydroxyl radical, but may be Fe(IV) species.     

Methane emission from lakes

A physico-chemical model to describe methane and carbon dioxide emission from lakes was developed. The model describes the emission by diffusion, bubbles and plants. The intensity of the fluxes can be calculated either for total or particular emission in dependence on gas bubbles composition. It was found, that diffusional (Q) and bubble (J) fluxes depend on the methane molar ratio (X) in bubbles as follows: [formula: see text]. The model allows to estimate the role of the methane oxidation by atmospheric oxygen in the total methane flux. It was shown, that the methane oxidation does not influence much methane fluxes to the atmosphere for most of the experimentally observed situations.     

A biological loss of endosulfan and related chlorinated organic compounds from aqueous systems in the presence and absence of oxygen.

Endosulfan is a cyclodiene organochlorine currently widely used as an insecticide throughout the world. This study reports that the endosulfan isomers can be readily dissipated from aqueous systems at neutral pH in the absence of biological material or chemical catalysts, in the presence or absence of oxygen. The study showed that aldrin, dieldrin, and endosulfan exhibit bi-phasic loss from water in unsealed and butyl rubber sealed vessels. Half-lives are substantially increased for endosulfan I when oxygen is removed from the incubation vessel. The study conditions, where PTFE was used, were such that loss due to volatilization and alkaline chemical hydrolysis was eliminated. Half-lives determined from these data indicate that the parent isomers are much less persistent than the related cyclodienes, aldrin and dieldrin, confirming the findings of previous studies. The major oxidation product of endosulfans I and II, endosulfan sulfate, is less volatile and can persist longer than either of the parent isomers. Endosulfan sulfate was not formed in any of the treatments suggesting that it would not be formed in aerated waters in the absence of microbial activity or strong chemical oxidants. Since endosulfan sulfate is formed in many environments through biological oxidation, and is only slowly degraded (both chemically in sterile media and biologically), it represents a predominant residue of technical grade endosulfan, which finds its way into aerobic and anaerobic aquatic environments. The data obtained contributes to and confirms the existing body of half-life data on endosulfan I and II and its major oxidation product, endosulfan sulfate. The half-life data generated from the current study can be used in models for predicting the loss of chlorinated cyclodiene compounds from aqueous systems. The findings also highlight the importance of critically reviewing half-life data, to determine what the predominant processes are that are acting on the compounds under study.     

Catalytic combustion of methane over commercial catalysts in presence of ammonia and hydrogen sulphide

The performance of different commercially available catalysts (supported Pd, Pt, Rh, bimetallic Pd-Pt, and Cr-Cu-Ti oxide catalyst) for the oxidation of methane, alone and in presence of ammonia and hydrogen sulphide is studied in this work. Catalysts performance was evaluated both in terms of activity and resistance to poisoning. The main conclusions are that supported Pd and Rh, present the highest activities for methane oxidation, both alone and in presence of ammonia, whereas they are severely poisoned in presence of H2S. Pt and Cr-Cu-Ti are less active but more sulphur resistant, but their activity is lower than the residual activity of sulphur-deactivated Pd and Rh catalysts. The Pd-Pt catalyst exhibits low activity and it is quickly deactivated in presence of hydrogen sulphide.