ISSN 01476874, Moscow University Soil Science Bulletin, 2013, Vol. 68, No. 3, pp. 135–141. © Allerton Press, Inc., 2013. Original Russian Text © O.V. Lisovitskaya, Ya.I. LebedSharlevich, N.V. Mozharova, S.A. Kulachkova, M.V. Gorlenko, 2013, published in Vestnik Moskovskogo Universiteta. Pochvovedenie, 2013, No. 3, pp. 40–46.
ECOLOGY
Biofiltration of Methane by Soil and Soillike Constructions and Specifics of Their Functioning O. V. Lisovitskayaa, Ya. I. LebedSharlevichb, N. V. Mozharovab, S. A. Kulachkovab, and M. V. Gorlenkob a
Training and Experimental SoilEcological Center, Moscow State University, Moscow, Russia b Department of Soil Science, Moscow State University, Moscow, 119991 Russia email:
[email protected], jana
[email protected],
[email protected],
[email protected],
[email protected] Received July 1, 2013
Abstract—Methane consumption in constructions is driven by its intense biofiltration which differs by sea sons according to the general specifics of the functioning of methanotrophs. Three stages of methane biofil tration were identified—adaptation, optimum, and stress. It was established that methane biofiltration in soil construction is 1.5–2.0 times higher than in soillike constructions. The biofiltration process under intense methane inflow leads to filtrate acidity increase; the Eh value drops in the summer period in constructions and grows during the winter season; a significant increase in microbial community stability is observed. Keywords: methane, biofiltration, soil, peat, compost, soil constructions, seasonal dynamics, multisubstrate testing. DOI: 10.3103/S014768741303006X
INTRODUCTION Over the last 260 years of the industrial epoch, the concentration of methane in the atmosphere has increased by 146% [16]. The threat posed by this gas is determined by its high potential to contribute to the greenhouse effect as well as by the fact that it is highly explosive. Methane emission is linked to the degradation of organic matter under anaerobic conditions [6]. The anthropogenic transformation of natural ecosystems increasingly is leading to a rise in methane emission in urban landscapes and the formation of gasgenerating soils [11, 12]. Accumulation of organic matter in dumps, asphalting, the utilization of sewage wastes, and preparation of an area for building construction resulting in gully–ravine system covering are factors that lead to the formation of methane and drop of its natural flow. The intensification of these processes makes the search for pathways of methane utilization an important issue. One of the most efficient techniques for methane “collection” is the construction of gas extracting sys tems in sites of its generation [18], which permits sec ondary use of the gas collected. Nevertheless, this technology implies a specific design as early as at the stage of methane source organization and is only prof itable for sites with a high rate of its formation and emission. The majority of sites have slower rates of methane production but are distributed considerably more widely. A promising solution for these situations
is biofiltration, a process of biological conversion of pollutants by substrates that contain living microor ganisms [14]. For the first time, this technique was applied in Germany and the Netherlands in the 1980s [19]. Biological conversion was carried out by a com munity of methanotrophic microorganisms which uti lize methane as a carbon and energy source thereby oxidizing it to carbon dioxide and water or intermedi ate products (methanol, formaldehyde, and formic acid) [3, 8]. This mechanism underlies the basis for operation of biofilters, different organic–mineral con structions that create optimal conditions for the devel opment of methanotrophs [13, 17, 20]. Multiple stud ies have focused on the analysis of rates and efficien cies from methane oxidation in biofilters by different substrates and their mixtures; nevertheless, the major ities of biofilters undergo rapid mineralization and do not have longterm stability. In the search for stable systems, we explored the biofiltration potential of soil and soillike constructions. The aim of the present work is to study methane biofiltration by soil and soillike constructions and to analyze specifics of their functioning. MATERIALS AND METHODS The objects of study were three constructions— consisting of the following layers (the layers are indi cated from top down): the filter bed working layer for methane biofiltration (0.25 m); the fiber layer to hold mineral particles and accumulate biophilic elements
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LISOVITSKAYA et al. H2O Gas collection 1 2 3 Filtrate collection
Methane supply Fig. 1. Scheme of the experiment: 1—filter bed working layer, 2—fiber layer, 3—gas distribution layer.
from the working layer (0.02 m); the gas distribution layer to allow homogeneous distribution of gas intro duced and drainage function (0.08 m) (Fig. 1). Natu ral sandyloam soil from the humic horizon of Albelu visol and prepared soillike organomineral substrates with compost and peat were used as filter bed working layers. The latter have a composition similar to soil (79% is washed river sand, 16% is clay (coalinit), and 5% is compost or peat). The physicochemical proper ties of the filter bed layer are given in Table 1. The fiber layer consisted of wood sawdust and a gas distribution layer of clayite. The last two layers are similar in all constructions. The functioning specifics of constructions was stud ied in the experiment. These layers were placed into plastic vessels with a diameter of 0.14 × 0.14 × 0.35 m equipped with hermetic tubes for gas supply and con trol of its content. From the bottom they are supplied with a screw lid for regular collection of moisture. Table 1. Physicochemical properties of the filter bed work ing layer of constructions Parameter Density, g/cm3 Granulometric composition The least mois ture capacity, % pH of filtrate Corg, % Ntotal, % C:N P2O5, mg/100 g K2O, mg/100 g
Humus horizon
Soil with compost
Soil with peat
1.40 1.33 1.36 sandyloam sandyloam sandyloam 26.9
32.0
32.7
6.9 1.60 0.13 12.3 10.1 0.4
6.0 1.51 0.12 12.6 14.7 12.6
6.7 2.06 0.10 20.6 21.7 7.6
The experiment was carried out under natural cli matic conditions in an open landscape of Moscow State University from June 2011 to March 2012. Irri gation was made according to the average monthly norm and frequency of precipitation in Moscow (Table 2) except for the period from January to March in the pres ence of natural snow cover on the surface of construc tions. Methane was introduced (50 mL 100 vol %) on each fourth day to make its content in the construc tions about 2.5 vol %. Before the introduction of methane, vessels were closed with hermetic lids from above to prevent gas leaks. The concentration of meth ane was measured in the vessel immediately after its introduction and then each day of the fourday cycle. This time period was used because the concentration of methane decreased to minimal values in this period. After the termination of the cycle, the vessel was opened, the oxidation–reduction potential of the sub strate was measured (Eh), and samples were collected for analysis of microbial biomass, potential bacterial oxidation, abiotic consumption of methane, and mul tisubstrate testing (MST). The filtrate was collected for determination of pH, and watering was performed. The cycle was then repeated. The physical, physicochemical, and chemical properties were analyzed using the following methods: density was determined by drilling, moisture was found by the weight method [1]; the pH and Eh values were assessed by potentiometry using an HI 8314 por tative ion meter (Hanna Instruments), mobile phos phorus compounds were measured by Kirsanov’s method, and mobile potassium compounds were found by photometry [2]. The total content of organic carbon and nitrogen was measured using a Vario III elemental analyzer (Elementar) during combustion in an oxygen medium at 1150°C. The content of gases (CH4 and CO2) was assessed using a Kristallyuks 4000M gas chromatograph equipped with a plasma ionization detector and thermal conductivity detector (the fidelity of determination is 10–5 %). The chro matograms were analyzed, and the concentration of methane was measured using the NetChrom program for Windows 2.0. The biomass of microorganisms was determined by the kinetic method based on the consumption of glu cose introduced [9]. The state of the microbial com munity was studied by the MST method according to a standard technique [5] which is based on analysis of specters of consumption of substrates by communities of microorganisms. The activity of biological oxida tion of methane and its abiotic consumption (sorp tion) was determined by the kinetic method according to the decrease in the methane concentration in closed bottles [9]. The results were statistically processed using the Excel and Statistica 6.01 programs.
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Temperature, °C
50 40 30 20 10 0 Ju ne Ju A ly Se ug pt us em t b O er ct N ob ov er e D mb ec er em b Ja er nu Fe ar br y ua M ry ar ch
Rate of consumption of CH4, g/m3 day
BIOFILTRATION OF METHANE BY SOIL AND SOILLIKE CONSTRUCTIONS
SC
CC
PC
40 30 20 10 0 −10 −20 −30
Temperature
Fig. 2. Dynamics of methane consumption by soil and soillike constructions.
RESULTS AND DISCUSSION Biofiltration of methane. Gas introduced into con structions may be consumed on its oxidation by microorganisms, abiotic absorption (sorption), partial dissolution in the liquid phase, and emission. During the experiment, emission was impossible (closed ves sels), in addition, methane is known to dissolve insig nificantly [1]; therefore, bacterial oxidation and sorp tion are the principal mechanisms of methane con sumption. During the experiment, different rates of methane biofiltration by the studied constructions were estab lished. A dominating trend was the differentiation of values between soil construction (SC) and soillike constructions with compost (CC) or with peat (PC), which have 1.5–2 times smaller rates of consumption than SC. The highest biological activity of methan otrophs is known to be at pH of 6.5–7.0, C:N = 15:1, oxygen availability of 10–20 vol %, and a temperature of 15–25°C [3, 15]. Different rates of methane biofil tration are likely to be associated with an initially higher pool of methanotrophic microorganisms in soil and more favorable physicochemical conditions for their development: pH values, balanced nutrient prop erties of the substrate expressed by the C:N ratio, a better enrichment with oxygen due to the presence of a structure in the soil (Table 1). This is confirmed by the results of potential oxidation of methane that dis play an increase in the rate of its bacterial oxidation from the beginning of the experiment to the middle of autumn from 10 to 70 ng/(g h) in the soil and from 5 to 20 ng/(g h) in soillike constructions. The curve of the actual consumption of methane corresponds to the pattern of its potential oxidation. The analysis per formed also allowed for detecting the presence of abi otic consumption (sorption) of gas that comprises about 30% of the total potential oxidation level. Nev ertheless, the sorptive potential has a certain satura tion; therefore, it likely cannot operate as stably as a bacterial filter. MOSCOW UNIVERSITY SOIL SCIENCE BULLETIN
The seasonal dynamics of methane oxidation in the biofilter has a unique pattern for all studied substrates and depends on the general specifics of microorgan ism development [7], and it differs according to tem perature conditions. From the beginning of the exper iment, three states of biofiltration are found: adapta tion (June–July) characterized by a certain decrease in the rates of methane consumption as compared to the beginning of the experiment; optimum (August– November) during which the rates of methane con sumption are demonstrated to be the highest, and the stress period (November–March) with minimal values of biofiltration. We relate the decreased rates of meth ane consumption during the period of adaptation to the rearrangement of the microbial community struc ture under the action of the gas introduced. It should be noted that in SC this rearrangement is quicker than in CC and PC, which is expressed in a smaller drop in the biofiltration rates. It is likely that soil has a higher buffer capacity in relation to external exposures due to the sta bility of the microbial community. We relate the opti mum stage to the maturity of the methanotrophic community and the optimal external conditions for its functioning. The stage of stress corresponds to the sea sonal temperature drop to negative values during the winter period, which suppresses functioning of meth anotrophic microorganisms. It is of interest that zero air temperature is a pecu liar critical point as the rate of methane consumption under these conditions sharply drops (November). Nevertheless, further decrease in temperature no longer affects the intensity of biofiltration—over the entire winter period methane is consumed with approximately the same rate. It is important that its consumption be continued despite the extremely unfavorable conditions for methanotrophic microor ganisms. We relate this phenomenon to the abiotic mechanism of methane consumption, i.e., sorption. The application of materials with high sorptive prop erties in constructions could enhance the consump Vol. 68
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Table 2. Characterization of climatic conditions of the experiment (according to [21]) Parameter Temperature, °C average monthly maximum minimum Mean sum of pre cipitates Number of days with precipitates
Septem Novem Decem October January ber ber ber
June
July
August
+23.1 +30 +17 75
+27.6 +33 +20 94
+23.3 +31 +13 77
+14.7 +18 +9 65
+8.0 +21 +2 59
+1.0 +8 –5 58
+0.2 +5 –5 56
11
12
10
11
10
12
12
tion of methane and increase the efficiency of con structions during the winter period. The content of carbon dioxide. Two stages are clearly distinguished in the dynamics of CO2 content in constructions: intense formation during the sum mer–autumn period linked to active functioning of microbial communities and its minimal formation during the winter period when the vital activities of microorganisms are suppressed by negative tempera tures. It is of interest to note that a community of microorganisms in PC and CC is more sensitive to low temperatures as compared to SC; therefore, the con tent of CO2 in these constructions drops to zero values a month earlier than in SCs. The maximal concentra tions of gas are revealed for CC (on average about 4.5% vol), which may be accounted for by the easily available type of organic substrate (compost) for microorganisms and its intense mineralization. In addition, the concen trations of nutrient substances are high in CC (Table 1). Dynamics of the Eh value. The analysis of the Eh value change indicates that systems function under dominating oxidative conditions optimal for methan otrophs. During the summer period, when the con centration of carbon dioxide is minimal, the Eh value drops in constructions with compost in which its con tent is twofold higher, on average, than in other con structions characterized by stable Eh values. During the winter period, the Eh rises sharply due to the decrease in CO2 and intensification of aeration. Table 3. Dynamics of microbial biomass in constructions SC (soil con struction)
CC (con PC (con struction struction with compost) with peat)
June (initial) 1347.8 ± 213.0
83.1 ± 11.5 108.4 ± 5.7
Sample
September
1057.1 ± 67.5
626.5 ± 66.9
78.3 ± 14.5
December
1311.3 ± 35.4
574.7 ± 33.8 567.1 ± 43.1
Febru ary
March
–5.5 +3 –16 42
–9.6 +1 –23 36
–0.7 +5 –8 34
11
8
8
pH dynamics of the filtrate. The main trend in the course of the experiment is the increase in the filtrate acidity that is collected from constructions; this is clearly observed during the summer–autumn period, when pH decreases by 0.5 units as compared to the beginning of the experiment in all constructions. The decreased pH correlates with the period of the maxi mal content of carbon dioxide in substrates and is likely determined by its dissolution in the liquid phase. At the end of autumn, an insignificant rise in pH is observed as a result of the CO2 content drop in con structions. Bacterial formation of methane. In addition to the methane introduced, an additional source in con structions may be the process of bacterial formation associated with activity of methanogenic bacteria which produce methane from carbon dioxide and hydrogen. As a rule, the process of methanogenesis proceeds under anaerobic conditions and is typical for soils that suffer from frequent underflooding and stag nant water. Nevertheless, it may also occur inside soil aggregates in which under anaerobic conditions the development of methanogenic bacteria is possible [10]. Therefore, the process of natural methanogene sis cannot be excluded in the experiment. The results of determination of bacterial methane formation show that in SC and PC this parameter cor responds to automorphic soils (
