valorization of fractions of dissolved organic matter
VALORIZATION OF FRACTIONS OF DISSOLVED ORGANIC MATTER EXTRACTED FROM MUNICIPAL SOLID WASTE LEACHATE AS AGRICULTURAL SOIL ENRICHMENT: STUDY ON A SOIL FROM TOGO G. FEUILLADE-CATHALIFAUD*, V. PALLIER*, M. TCHA TOM*, C. BACCOT* * University of Limoges, Research Group on Water Soil and Environment (GRESE), ENSIL, Parc Ester Technopôle, 16 rue Atlantis, 87068 Limoges Cedex, France
SUMMARY: In this strudy, the fertilizing value of Municipal Solid Waste Leachates (MSWL) as a partially co-product for organic soil enrichment was evaluated. To overcome negative impacts of the global composition of MSWL, Hydrophobic-like compounds (HPO*) and Transphilic-like compounds (TPH*) were specificaly extracted from dissolved Organic Matter (OM) of MSWL using XAD fractionation. HPO* and TPH* fractions were then used to enrich a soil from Togo with low OM content (0.3%) in order to evaluate their impact on both the stock of organic carbon (Corg) and the biological activity. Batch and column experiments were performed to assess the proportion of Corg that can be mobilized and adsorbed by each horizon, and to simulate an amendment at soil-scale. HPO* and TPH* fractions, comparable with fractions extracted from natural OM, increased the Corg content of each horizon, and allowed the adsorption of Corg on reconstituted soil. Futhermore, hydrophobic-like molecules were preferentially adsorbed than transphilic-like compounds, whereas TPH* fraction enhanced the biological activity of the soil.
1 INTRODUCTION The management of Municipal Solid Waste Leachates (MSWL) is technically and economically restrictive. Considering this effluent no more as a waste but rather as a partially co-product for soil enrichment could represent an interesting and innovative way of valorization. Several studies already considered the fertilizing value of MSWL because of its huge content in Dissolved Organic Matter (DOM), especially Humic-like Substances (HS*) (Wong and Leung, 1989; Revel et al., 1999; Justin et al., 2010; Alaribe et al., 2016). However, the global composition of MSWL negatively affects both the cultures and the environment with accumulation of trace elements in vegetables and soils, vegetable stress, root growth inhibition and decrease of the wildlife diversity (Risso et al., 2015; Mor et al., 2013; Wang et al., 2012; Coyle et al., 2011). Extracting specific organic molecules from DOM can thus be relevant to better control the composition of the amendment and get free of mineral and organic pollutants. The concentrations and characteristics of DOM in MSWL highly depend on several in situ Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2 - 6 October 2017 S. Margherita di Pula, Cagliari, Italy / © 2017 by CISA Publisher, Italy
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
factors (Foo and Hameed, 2009) and evolve during the successive stages of waste degradation during landfilling (Kulikowska and Klimiuk, 2008): DOM content decreases and the aromaticity of the organic molecules increases. MSWL used to be classified according to the characteristics of their DOM (Table 1).
Table 1: Classification of MSWL depending on the characteristics of their DOM (Chian and DeWalle, 1976; Millot, 1986; Berthe et al., 2008; Feuillade et al., 2009) Young MSWL
Intermediate MSWL
Stabilized MSWL
Landfilling phase
Aerobic and acidic
-
Methanogenic
COD (gO2.L-1)
> 20
3-15
0.3)
Medium (0.1-0.3)
Low (< 0.1)
Organic compounds
80% VFA HA* < 10% HPI* > 50%
5-30% VFA HA* < 10% HPI* ≤ 50%
HA* > 30% HPI* < 20%
< 10
10-30
> 30
SUVA index (L.cm-1.gC-1)
During landfilling anaerobic process, the DOM of MSWL evolves toward molecules presenting more aromatic and hydrophobic characters (Kulikowska and Klimiuk, 2008; Feuillade et al., 2009). Specific Ultra-Violet Absorbance (SUVA) index and fractionation according to the hydrophobic character used to be defined as relevant indicators of waste degradation and DOM evolution in MSWL during landfilling (Weishaar et al., 2003; Croué, 2004; Berthe et al., 2008; Feuillade et al., 2009). The fractionation protocol allows separating the HS* in groups of molecules presenting the same properties but with varying aromaticity and hydrophobicity: Humic-like Acids (HA*), Hydrophobic-like compounds (HPO*), Transphilic-like compounds (TPH*) and Hydrophilic-like compounds (HPI*). However, during the extraction process, trace elements were precipitated with HA* fraction and HPI* compounds, the resulting fraction, was composed of various small molecules like salts, hydrocarbons… Thereby, only HPO* and TPH* fractions can be extracted with a purity of 100% and were thus considered in this study. Only few studies dealt with the valorization of extracted DOM from MSWL, whatever the extraction process. Tahiri et al. (2014 and 2016) extracted HS* from MSWL by difference of solubility and compared their performances to the ones of natural HS from leonardite. Anthropogenic and natural HS presented chemical and structural similarities suggesting that HS* from MSWL could be used as biofertilizer or biostimulant. Moreover, both HS positively correlated with the root growth. Baccot et al. (2016) tested the biochemical methane potential of HPO* and TPH* fractions extracted from MSWL by XAD fractionation, to assess the impact of the hydrophobic character on anaerobic digestion. TPH* fraction content in the initial digestate directly correlated with the volume of biogas produced whereas the methane percentage in biogas was anti-correlated with HPI* fraction content. This research study focused on evaluating the impact of an enrichment with HPO* or TPH* fraction extracted from MSWL according to the hydrophobic character, on a soil from Togo with a low organic matter content in order to evaluate their impact on both the stock of carbon and the biological activity of the soil. Batch and column experiments were respectively performed to assess the proportion of organic molecules that can be mobilized and adsorbed by each layer of the soil, and simulate an amendment at soil-scale to assess the effect on the whole system.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
2 MATERIALS AND METHODS 2.1 Substrates of the study: Sampling and characterization 2.1.1
Soil
The soil tested (St) was an agricultural soil sampled at Lama-Kara (N9° 32’ 41.7” / E1° 11’ 55.9”, La Kara, Togo) nearby the Kara River. It was depth (205 cm) and its pH was neutral (from 7.14 to 7.52) (Table 2). The organic carbon (Corg) content of top horizons (0.3% and 0.4%) and their C/N ratios lower than 5 were characteristics of a low microbial activity. An external input of OM is thus needed to promote agricultural activities. According to the World reference base for soil resources 2014 (IUSS Working Group WRB, 2015) and the textural triangle, the St was a vertisol and its texture was predominantly sandy. Table 2: Characteristics of the horizons of the soil from Togo Hz #1
Hz #2
Hz #3
Hz #4
Method
0 – 10
10 – 68
68 – 95
95 – 205
-
Clay (< 2 mm)
9.1
30.0
28.9
12.0
Silt (2 – 50 µm)
8.8
9.4
15.1
13.0
Sand (50 – 2000 µm)
82.1
60.6
55.9
75.0
Corg* (%)
0.3
0.4
0.2
0.1
NF ISO 14235
NT (%)
0.06
0.08
0.07
0.06
NF EN 13654-1
C/N
4.2
4.8
3.4
1.5
-
pH
7.14
7.14
7.07
7.52
NF ISO 10390
Total iron (g.100g-1)
0.451
1.52
6.69
1.45
Total aluminum (g.100g-1)
0.172
0.372
0.798
0.154
Depth (cm)
Granulometry (%)
NF X31-107
Method of Mehra and Jackson (1960)
* The Corg was assimilated to total carbon because no effervescence was observed with HCl 37% at room temperature on each horizon.
2.1.2
Municipal solid waste leachate characteristics
The MSWL was sampled in Noth landfill (north east from Limoges, France) where 30 tons.day-1 of MSW generated by 60.000 residents were landfilled without any pretreatment. The MSWL was stored at 4°C and characterized within four days. The MSWL used was 4 years old. Its characteristics are presented Table 3. It presented a neutral pH, a BOD5/COD between 0.1 and 0.3, a VFA content lower than 10 g.L-1, a low content in Volatile Suspended Solid (VSS) and a SUVA index lower than 30 L.cm.-1gC-1. The fractionation of DOM according to the hydrophobic character underlined a high content in soluble fulvic-like acids (TPH* + HPO* = 68.3%), characteristic of an intermediate MSWL.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Table 3: Characteristics of the MSWL MSWL 7.35 ± 0.09
References - Methods NF T90-008
10.31 ± 0.05
NF EN 27888
COD (mgO2.L )
1289 ± 64
BOD5 (mgO2.L-1)
213 ± 46 475 ± 10
NFT 90-101 OxiTop®, WTW Company Thermal oxidation
0.40 ± 0.04
Potentiometric titration
28 ± 3
NF EN 872
21 ± 1
Westerhoff et al. (1999)
10 ± 1
Malcolm et al. (1992)
pH Conductivity (mS.cm-1) -1
Physico-chemical and chemical parameters
DOC (mgC.L-1) -1
VFA (gCH3COOH.L ) -1
Specific characterization of organic matter
VSS (mg.L ) SUVA index (L.cm-1.gC-1) Fractionation %HA* according to %HPO* the %TPH* hydrophobic %HPI* character
45 ± 2 23 ± 1 22 ± 1
Aiken et al. (1992) Croué et al. (1993)
2.2 Dissolved organic matter of MSWL: Extraction and characterization 2.2.1
Extraction and purification
The fractionation according to the hydrophobic character allows the separation of DOM in four fractions of increasing aromaticity (Figure 1).
Figure 1: Protocol of fractionation of the dissolved organic molecules according to their hydrophobic character
The MSWL was first filtered on 0.45 µm cellulose nitrate membrane to remove particulates and humins insoluble at any pH (Malcolm and Mac Carthy, 1992). The HA* were precipitated by acidifying the sample at pH 2 with HCl 37% and were removed by filtration on 0.45 µm cellulose nitrate membrane. The solution was then successively passed through non-ionic resins in series (DAX-8 and XAD-4) (Aiken et al., 1992; Croué et al., 1993). Hydrophobic-like compounds
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
(HPO*) and transphilic-like compounds (TPH*) were respectively adsorbed on DAX-8 and XAD4 resin whereas hydrophilic-like compounds (HPI*) were not retained like salts. The fractionation of DOM by XAD resins is based on an equilibrium between the DOM in solution and the resin. Leenheer (1981) and Thurman and Malcolm (1981) gave the relation between the capacity factor (k’) and the volume of sample used (1):
(1) where Vsample is the volume of sample to fractionate, V0 is the empty volume of the column (about 60% of the bed volume of resin). According to the Dissolved Organic Carbon (DOC) concentration of the MSWL (475 ± 10 mgC.L-1), the capacity factor k’ was fixed at 25 because it is better adapted for high organic load and minimizes the volume of sample used (Berthe et al., 2008). The volumes of resin and solution were thus 85 and 2652 mL respectively. Before desorption, only HPO* and TPH* fractions were purified with formic acid at pH 2 to eliminate ionic compounds (mainly Cl- due to the acidification of leachate) until the absence of chloride validated by a nitrate silver test. Then, fractions of DOM were desorbed from DAX-8 and XAD-4 resins with an acetonitrile-deionized water (75%-25%; v/v) solution at pH 6.0. A vacuum evaporation helped concentrating HPO* and TPH* fractions and removing residues of acetonitrile and formic acid. The liquid samples were frozen at -20°C and freeze-dried to recover powders of HPO* and TPH* fractions. The DOC of the MSWL used for the extraction (475 ± 10 mgC.L-1) was composed of 45% of HPO* and 23% of TPH*. 380 mg of HPO* and 217 mg of TPH* per liter of MSWL were thus extracted as DOM fractions are composed of around 50% (w/w) of carbon according to DOC measurements. It was respectively more than 40 and 70 times higher than an extraction from a surface water with 10 mgC.L-1 (Labanowski and Feuillade, 2009). MSWL was thus well adapted for extraction and concentration of HPO* and TPH* fractions.
2.2.2
Comparison with natural organic matter fractions
A comparison of the characteristics of HPO* and TPH* fractions extracted from MSWL to Natural Organic Matter (NOM) was performed by using elemental analysis, SUVA index and Apparent Molecular Weight (AMW). Elemental analysis were carried out by the Service Central des Analyses (CNRS unit, Villeurbanne, France) to determine the C, H, O, N and S contents within a standard deviation from 0.25% to 0.4%. SUVA index was calculated as the ratio of the ultraviolet absorbance measuring at 254 nm with a SHIMADZU spectrophotometer (model 1700 PharmasPec) and 1 cm long quartz cells, to the DOC content. Fractionation of the DOM by ultrafiltration was performed according to the protocol of Berthe et al. (2008) with a sample volume of 40 mL and cutoff thresholds of 0.5, 3 and 30 kDa.
2.2.3
Glocal characteristics of solutions of organic fraction extracted from MSWL
Characteristics of extracted organic fraction solutions are presented Table 4. The solutions presented a low conductivity because ions are not retained on XAD resins and remained in the hydrophilic fraction, and an acid pH because of the acidic conditions of the extraction protocol.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
As expected, HPO* fraction was more aromatic than TPH* fraction with higher SUVA index (22 ± 1 L.cm-1.gC-1) and C/N ratio (11.5 ± 0.4).
Table 4: Characterization of organic fraction solutions HPO* solution
TPH* solution
References - Methods
4.9 ± 0.4
3.7 ± 0.3
NF T90-008
36 ± 8
49 ± 5
NF EN 27888
22 ± 1
22 ± 1
Thermal oxidation
NT (mg.L )
1.87 ± 0.09
2.5 ± 0.1
NF EN ISO 7890-3
C/N
11.5 ± 0.4
9.4 ± 0.7
SUVA index (L.cm-1.gC-1)
22 ± 1
18 ± 1
Elemental analysis Westerhoff et al. (1999)
pH -1
Conductivity (µS.cm ) -1
DOC (mgC.L ) -1
2.3 Leaching experiments Batch and column experiments were performed to estimate the impact of HPO* and TPH* fractions as organic enrichement on the soil from Togo. Batch experiments allowed evaluating organic compounds that can be easily mobilized in solution or adsorbed by each layer of the soil whereas column experiments, more representative of in situ conditions, simulate an organic enrichement at soil-scale to assess the effect on the whole system. 2.3.1
Column experiments
The protocol used was adapted from the OCDE guidelines #312 (OCDE, 2004; Figure 2). HPO* or TPH* fraction dissolved in CaCl2 at 0.058 mM Humic balance of 500 kg OM.ha-1.year-1
Solution of CaCl2 at 0.058 mM
Hz1
Hz2
Hz3
Hz4
Column: - Height = 35 cm - Diameter = 4.5 cm - Material = Glass + Sintered glass at the bottom - Reconstituted soil (fraction < 2 mm)
Hz1
Hz2
Artificial rain: - Solution of CaCl2 at 0.058 mM - Average pluviometry of 1000 mm.year-1 - 2 wet seasons (April-June / September-October) è Repeated injection only during wet seasons - Postulate: 40% infiltration and 60% runoff
Hz3
Hz4
Conditions: - Darkness (Column covered with aluminum foil) - 18-25°C - Duplicate Leaching juices characterization Control
Test Injections
Jan.
Feb.
March
April
May
June
Jul.
Aug.
Sept.
Oct.
Nov.
Dec.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Figure 2: Protocol of experiments in column
The tested soil (St) was reconstituted according to the profile with each horizon previously dried and sieved to 2 mm in order to overcome the effects of soil structure. HPO* or TPH* fraction was amended on soil by respecting a humic balance of 500 kg of OM.hectare-1.year-1. An average pluviometry of 1000 mm.year-1 was simulated with an alternation of 2 wet seasons (April to June and September to October) and 2 dry seasons (July to August and November to March) according to the tropical climate of Togo. Moreover, a postulate was established: 40% of infiltration and 60% of runoff were considered to respect characteristics of St. A solution of CaCl2 at 0.058 mM was used as artificial rain, respecting an ionic strength of 0.173 mM (OCDE, 2004; Kay et al., 2005; Wehrhan et al., 2007). After a stabilization phase with artificial rain, the annual organic enrichment was divided up on the 2 wet seasons (5 inputs, Figure 2). Organic fractions were dissolved in CaCl2 solution to respect a homogenous input. A control was carried out with only CaCl2 at 0.058 mM, without any enrichment, in order to assess the mobilization of organic compounds from soil in the liquid phase. Fluorescence analyses were performed on leaching juices filtered on 0.45 μm nitrate cellulose membranes. A ionic strength between 0-1M KCl had no significant effect on the Excitation-Emission Matrix (EEM) spectra (Mobed et al., 1996). Thus, considering this condition and the values of conductivity in the range 15.9 - 191.6 μS.cm-1, samples ionic strength was not buffered. Dilutions of juices were performed in order to avoid saturation of the fluorescence detector and to limit inner-filtering effect. DOC concentration was then in the range 1-5 mgC.L-1 for each analyzed sample. Instrument stability was checked using the Raman peak of deionized water excited at 350 nm, with emission monitored at 395 nm. Water Raman intensities were consistent between each session, with values variation < 6%. Fluorescence EEM spectra were obtained by collecting series of emission scans between wavelengths 250-500 nm with 1 nm intervals and with a 5 nm excitation wavelength intervals between 220 and 500 nm. For each fraction, the Fluorescence Index (FI) was calculated according to the equation from McKnight et al., (2001) (2) at a fixed excitation wavelength of 370 nm, to estimate the bacterial activity in column tests.
I =450nm (2) FI = λem Iλem=500nm Fluorescence analyses were performed with a Shimadzu RF-5301 PC spectrofluorophotometer (Shimadzu Corp., Kyoto, Japan) with a 1-cm-long quartz cells, at room temperature (21 ± 2°C). DOC concentrations in leaching juices were performed to assess the transfer of organic compounds between soil and liquid phase. Measurements were realised by using a SHIMADZU carbon analyzer (model: TOC-L analyzer; precision: ± 50 µgC.L-1; detection limit: 4 µgC.L-1) according to the Non-Purgeable Organic Carbon measurement procedure. First, samples were acidified with HCl 1 mol.L-1 and sparged with high purity air to eliminate inorganic carbon and volatile organic compounds. Non-volatile organic carbon was then combusted in an oven at 720°C and the produced CO2 was quantified by infrared spectroscopy.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
2.3.2
Batch experiments
The protocol used was adapted from the standard NF EN 12457-2 (Figure 3). Batch experiments were performed on each horizon of the St previously dried and sieved to 2 mm. HPO* or TPH* fraction was dissolved in distilled water at a concentration of 50 mgC.L-1. This concentration allowed respecting the humic balance of 500 kg of OM.hectare-1.year-1 applied on column experiments when considering the density of St (1.41). Solutions were mixed with each horizon of soil by respecting a Liquid to Solid ratio (L/S) of 10. This ratio optimizes the transfer between liquid and solid phases (Yong et al., 1992; François et al., 2006) and promote the homogeneity of the system. To avoid bacterial activity, batch experiments were stopped after 48h. DOC of leaching juices were performed according to Section 2.3.1. A control with ultrapure water was carried out for each horizon in order to assess the mobilization of organic compounds from soil in the liquid phase. Distilled water
Horizon (fraction < 2 mm)
HPO* or TPH* (50 mg.L-1)
L/S = 10 [0.3L/30g] 100 rpm, 48h Triplicate
Control
Test
1h of decantation Separation of liquid and solid phases Centrifugation [4000 rpm, 10 min] Filtration at 0.45 µm (cellulose nitrate membrane)
Characterization of leaching juices
Figure 3: Protocol of the batch experiments
3 RESULTS AND DISCUSSION 3.1 Comparison of HPO* and TPH* fractions extracted from MSWL to NOM Whatever the hydrophobic fraction considered, distribution of AMW of DOM of both origins were comparable: the AMW increased with the hydrophobic character, and HPO fractions presented a higher percentage of compounds >30 kDa (17 ± 2%) than TPH fractions (7 ± 1%) (Table 5). Besides, anthropogenic and natural DOM presented comparable size: hydrophobic compounds were predominant between 0.5 and 3 kDa whereas transphilic molecules were equally distributed from 0 to 3 kDa. SUVA indexes confirmed the difference of aromaticity between HPO and TPH fractions with higher values for hydrophobic molecules. Moreover, SUVA indexes of DOM extracted from MSWL were in the range of the ones of NOM. Elemental composition of both fractions from MSWL and NOM were compable despite
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
differences due to the involved genesis processes (aerobic or anaerobic). NOM is composed of about 20% more oxygen than anthropogenic fractions, whereas these latter presented higher carbon and hydrogen percentages (respectively +11% and +21%). Whatever their origin, C/N ratios were comparable for each fraction: transphilic compounds presented a low C/N ratio (from 4 to 12) characteristic of a biologic reactivity, whereas hydrophobic molecules were less reactive with a C/N ratio around 20. However, both fractions were within the C/N ranges of conventional amendments: 8-24 for different manures (Kigozi et al., 2014), 10-23 for urban composts (Cellier et al., 2012) or 7.8-14.9 for MSW (Iglesias-Jimenez and Alvarez 1993, Hirai et al., 1986). Despite different origin and genesis process, HPO* and TPH* fractions extracted from MSWL were thus highly comparable to fractions extracted from NOM.
Table 5: Comparison of extracted DOM fractions from MSWL and NOM from surface water (Pernet-Coudrier et al., 2007; Labanowski and Feuillade, 2009) DOM from MSWL of Noth
NOM from surface water
HPO*
TPH*
HPO
TPH
22
18
18 - 34
13 - 21
C
56.3 ± 0.4
50.3 ± 0.4
49.2 ± 0.9
45.6 ± 0.9
O
30.8 ± 0.4
32.9 ± 0.4
38.7 ± 0.8
41.5 ± 0.8
H
6.7 ± 0.3
6.2 ± 0.3
5.2 ± 0.1
5.0 ± 0.1
N
2.7 ± 0.2
5.7 ± 0.2
2.7 ± 0.1
4.6 ± 0.1
S
1.9 ± 0.3
2.0 ± 0.3
nd
nd
20.7
8.8
18
10
Distribution of AMW
SUVA (L.cm-1.gC-1)
Elemental composition (% weight)
C/N nd: Not determined
3.2 Carbon adsorption on the soil 3.2.1
Batch experiments
Figure 4 presents the net Corg adsorption percentages on each horizon of St calculated after HPO* and TPH* tests. These results were compared to clay and initial Corg content of the horizons. No correlation between clay content and adsorption of Corg was highlighted. On the contrary, expect for the horizon #3, the higher the initial Corg content in the horizon, the lower the adsorption of Corg by this horizon. The horizon #3 of the St differed from the 3 others with the highest Corg adsorption percentage (72.4%). This capacity could be explained by its characteristics (Table 2). Indeed, its free iron and aluminum contents were 2 to 14 times higher than for the others horizons. Moreover, because of its neutral pH, aluminum exists as hydroxyaluminum ion, known for acting as a connection cation between clay minerals and OM (Baize,
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
2000). Connection between OM from HPO* or TPH* fraction and the abundant content of clay (28.9%) could thus be easily considered. Furthermore, interactions between OM and iron, extensively already highlighted in literature, could also explain the high Corg adsorption ability of this horizon #3 (Tipping and Woof, 1983; Gu et al., 1994; Porcal et al., 2009; Fink et al., 2016; Vindedahl et al., 2016). Moreover, both the high degradation of OM under tropical climate and the depth of this horizon (78 cm) disadvantage the Corg retention on this layer on in situ conditions. Despite better Corg retention, horizon #3 could thus not be relevant to retain carbon on St. Adsorption of Corg from HPO* fraction was systematically higher when compared to TPH* fraction in the same conditions. Hydrophobic compounds seemed thus to be better adsorbed by horizons of both soils. Enrichment with organic compounds extracted from MSWL allowed thus improving the Corg content of St. However, batch experiments were not representative of in situ conditions and column experiments were thus performed to identify mechanisms on a global scale. Corg content (g.100g-1)
Carbon adsorption – HPO* test Teneur en argile
Carbon – TPH* test Teneur enadsorption Corg
Adsorption du carbone - Essai HPO*
Adsorption du carbone - Essai TPH*
80%
4,5 4.5
72.4%
70%
4,0 4.0
69.7%
3,5 3.5
60%
3.0 3,0
50% 40%
2.5 2,5 2.0 2,0
30% 20%
40.2%
37.4%
34.0%
25.6% 24.0%
1.5 1,5 1.0 1,0
20.2%
10%
0.5 0,5
Organic carbon content (g.100g-1)
Clay content (%)
0.0 0,0
0% HzHzt #1 1
HzHzt #2 2
Hz Hzt #3 3
HzHzt #4 4
Figure 4: Net adsorption of Corg on each horizon of St after HPO* and TPH* batch experiments
3.2.2
Column experiments
Measurements of DOC concentrations in leaching juices allowed drawing net cumulative masses of Corg retained by the reconstituted soil from Togo during column experiments (squares, Figure 5). To better understand the organic enrichment impact, cumulative masses of HPO* and TPH* fractions brought (diamonds, Figure 5) were added on the same graph and translated in cumulative masses of carbon (crosses, Figure 5). As explained Section 2.3.1, inputs of organic fractions were provided in 5 times corresponding to the 2 wet seasons (arrows, Figure 5). Additions of HPO* or TPH* fractions (diamonds) increased in the same extent the cumulative masses of Corg added (crosses). The Corg brought by these organic fractions corresponded approximately to 50% of the cumulative masses of each fraction respectively, which was in accordance with the elemental composition (Table 5). Moreover, whatever the organic fraction,
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
the St adsorbed all the Corg added by HPO* and TPH* fraction. A higher humic balance than 500 kg of OM.hectare-1.year-1 should be tested in the same conditions to assess if the tested soil could adsorb more Corg and to determine the optimal organic enrichement to apply. Masse cumulée de fraction HPO* amendée Cumulative mass of added HPO* Masse cumulée de C-HPO* amendé Cumulative mass of added CHPO* CHPO* Masse nette cumulée deof C adsorbed retenu Net cumulative mass Corg
80 70
Mass (mg)
60
Inputs of HPO* fraction
50 40 30 20 10 0 Sept
Oct
Nov
Dec Déc
Jan
Feb Fév
Mars March
April Avr
May Mai
June Juin
Juil July
Aug Août
(a)
70
Masse cumulée de fraction TPH* amendée Cumulative mass of added TPH* CTPH* Cumulative mass of added CTPH* Masse cumulée de C-TPH* amendé
60
Inputs of TPH* fraction
Masse (mg)
80
Net cumulative mass Corg Masse nette cumulée deofC adsorbed retenu
50 40 30 20 10
0 Sept
Oct
Nov
Déc Dec
Jan
Fév Feb
Mars March
Avr April
Mai May
Juin June
Juil July
Août Aug
(b)
Figure 5: Retained carbon by the St after addition of HPO* (a) or TPH* (b) fraction Analyses of leaching juices by 3D-fluorescence allowed estimating the impact of organic fractions on bacterial activity of soil from Togo by calculating the Fluorescence Index. Table 6 compares FI of each experiment between initial and final states. Control and HPO* tests presented a constant FI (1.69 and 1.70 respectively) in the range 1.6-1.9 characteristic of a persistent domination of microbially-derived organic matter. On the contrary, the FI of TPH* test increased by 20% from 1.79 to 2.24. The final value higher than 1.9 confirmed a material exclusively from bacterial origin. The TPH* fraction seemed thus to improve the bacterial activity.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Table 6: Evolution of the fluorescence index during column tests. Control test Initial state Fluorescenc e index
3.2.3
Final state
HPO* test Initial state
1.69 ± 0.02
TPH* test
Final state
1.70 ± 0.04
Initial state
Final state
1.79 ± 0.04
2.24 ± 0.05
Comparison of Corg adsorption capacities
Net Corg adsorption capacities were calculated for batch and column experiments (Table 7). They represented the adsorbed carbon mass brought by HPO* or TPH* fraction (expressed in mgCadsorbed) on the initial Corg content (expressed in mgChorizon). As underlined with batch experiments (Section 3.2.1), there was an anticorrelation between adsorption capacities and initial Corg content of each horizon: more Corg was retained on layer with low initial Corg content (Table 7). Moreover, the highest adsorption capacities were observed for the deepest horizons. HPO* and TPH* fractions extracted from MSWL allowed thus increasing the Corg content of horizons with low carbon. Batch experiments allowed calculating the Corg enrichment expected on column experiments considering the mass and the Corg of each layer used to reconstitute the soil. When compared to the initial Corg content of the whole reconstituted soil column, results were lower than the ones expected by batch experiments: Corg enrichment was only 3.5% for HPO* test and 2.9% for TPH* test (Table 7). Indeed, batch experiments did not simulate well the transfer mechanisms that occurr on the global soil, and they did not consider the different depths of each horizon as horizons #3 and #4 are more difficult to reach. They were thus less representative than column experiments. Nevertheless, same order of magnitude and same trend could be observed between batch and column experiments: hydrophobic compounds were better adsorbed than transphilic ones. Table 7: Corg enrichment (expressed in mgCadsorbed.mgChorizon-1) Adsorption capacities
Batch experiments
Column experiments
Initial Corg
HPO* test
TPH* test
Layer #1
3.1%
2.0%
0.3%
Layer #2
1.4%
1.1%
0.4%
Layer #3
6.7%
6.5%
0.2%
Layer #4
10.4%
8.8%
0.1%
4.5%
3.8%
-
3.5%
2.9%
-
Expected Corg enrichment on reconstituted soil Obtained Corg enrichment on reconstituted soil
4 CONCLUSIONS Batch and column experiments were performed to evaluate the potential Corg adsorption of HPO* and TPH* fractions extracted from MSWL on a soil from Togo with a low content in organic compounds. Despite different origin and genesis processes, HPO* and TPH* fractions presented global
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
and specific characteristics comparable with fractions extracted from natural organic matter. Moreover, their use as organic enrichments was relevant for a soil with low initial Corg as they increased the Corg content of each horizon (batch experiments) and they allowed the adsorption of Corg on a reconstituted soil (column experiments) when compared to controls. Futhermore, hydrophobic molecules were preferentially adsorbed than transphilic compounds, whereas TPH* fraction enhanced the biological activity of the soil. By calculating adsorption capacities, batch experiments allowed well simulating the results obtained in columns. Batch experiments can thus be considered as an interesting tool to easily and quickly evaluate adsorption capacities. It could now be interesting to repeat batch and column experiments with higher HPO* and TPH* concentrations (i) to estimate the evolution of the adsorption capacity with increasing HPO* or TPH* contents, (ii) to assess the maximum capacities of soils to adsorb Corg brought by these organic fractions extracted from MSWL, and (iii) to identify which fraction allows the best Corg retention.
AKNOWLEDGEMENTS First of all, the Authors would like to thank the Noth landfill for providing them the sample of MSWL. They would also thank Kwamivi SEGBAYA, Assistant Professor at the University of Lomé, for the sampling of soil in Togo. Finally, the Authors thank the Regional Council of Limousin for the financial support during this research project.
REFERENCES Aiken, G.R., Mcknight, D.M., Thorn, K.A., Thurman, E.M. (1992). Isolation of hydrophilic organic acids from water using non-ionic macroporous resins. Org. Geochem. 18, 567-573. Alaribe F.O., Agamuthu P. (2016). Fertigation of Brassica rapa L. using treated landfill leachate as a nutrient recycling option. S. Afr. J. Sci. 112 (3/4), 8 p. Baccot C., Pallier V., Feuillade-Cathalifaud G. (2016). Biochemical methane potential of fractions of organic matter extracted from a municipal solid waste leachate: impact of their hydrophobic character. Waste Management (in press). Baize D. (2000). Guide des analyses en pédologie, 2ème édition. Ed. INRA, 257 p. Berthe, C., Redon, E., Feuillade, G. (2008). Fractionation of the organic matter contained in leachate resulting from two modes of landfilling: An indicator of waste degradation. J. Hazard. Mater. 154, 262-271. Cellier A., Francou C., Houot S., Ballini C., Gauquelin T., Baldy V. (2012) Use of urban composts for the regeneration of a burnt Mediterranean soil: A laboratory approach. J. Environ. Manage. 95, 238-244. Chian, E.S.K. and DeWalle, P.B. (1976). Sanitary landfill leachates and their leachate treatment. J. Environ. Eng. Div. 102 (2), 411-431. Coyle D.R., Zalesny J.A., Zalesny Jr R.S., Wiese A.H. (2011). Irrigating Poplar Energy Crops with Landfill Leachate Negatively Affects Soil Micro- and Meso-Fauna. Int. J. Phytoremediation 13 (9), 845-858. Croué, J.P., Martin, B., Deguin, A., Legube, B. (1993). Isolation and characterization of dissolved hydrophobic and hydrophilic organic substances of a water reservoir. Proceeding of workshop on NOM in Drinking Water, Chamonix, France, Sept. 19-22. Croué, J.P. (2004). Isolation of humic and non-humic NOM fractions: structural characterization. Environ. Monit. Assess. 92, 193-207.
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Feuillade, G., Parodi, A., Redon, E. (2009). Relation between organic matter properties in leachate and biogas production from MSW landfilling. Proceedings Sardinia 2009, 12th International Waste Management and Landfill Symposium, CISA publisher, Cagliari. Fink J.R., Inda A.V., Tiecher T., Barrón V. (2016). Iron oxides and organic matter on soil phosphorus availability. Ciencia e Agrotecnologia 40 (4), 369-379. Foo, K.Y. and Hameed, B.H. (2009). An overview of landfill leachate treatment via activated carbon adsorption process. J. Hazard. Mater. 171, 54-60. François V., Feuillade G., Skhiri N., Lagier T., Matejka G. (2006). Indicating the parameters of the state of degradation of municipal solid waste. J. Hazard. Mater. 137 (2), 1008-1015. Gu B., Schmitt J., Chen Z., Liang L., McCarthy J.F. (1994). Adsorption and desorption of natural organic matter on iron oxide: Mechanisms and models. Environ. Sci. Technol. 28 (1), 38-46. Hirai M.F., Katayama A., Kubota H. (1986). Effect of compost maturity on plant growth. BioCycle 27, 58-61. Iglesias-Jimenez A. and Alvarez C.E. (1993). Apparent avaibility of nitrogen in composted municipal refuse. Biol. Fertil. Soils 16, 313-318. IUSS Working Group WRB, 2015. World Reference Base for Soil Resources 2014, update 2015. International soil classification system for naming soils and creating legends for soil maps. World Soil Resources Reports No. 106. FAO, Rome. Justin M.Z., Pajk N., Zupanc V., Zupancic M. (2010). Phytoremediation of landfill leachate and compost wastewater by irrigation of Populus and Salix: Biomass and growth response. Waste Manage. 30, 1032-1042. Kay P., Blackwell P.A., Boxall A.B.A. (2005). Column studies to investigate the fate of veterinary antibiotics in clay soils following slurry application to agricultural land. Chemosphere 60, 497507. Kigozi R., Aboyade A.O., Muzenda E. (2014) Sizing of an Anaerobic Biodigester for the Organic Fraction of Municipal Solid Waste. in Proceedings of the World Congress on Engineering and Computer Science. Kulikowska, D., Klimiuk, E. (2008). The effect of landfill age on municipal leachate composition. Bioresource Technol. 99, 5981-5985. Labanowski J. and Feuillade G. (2009). Combination of biodegradable organic matter quantification and XAD-fractionation as effective working parameter for the study of biodegradability in environmental and anthropic samples. Chemosphere 74, 605-611. Labanowski J. and Feuillade G. (2011). Dissolved organic matter: Precautions for the study of hydrophilic substances using XAD resins. Water Res. 45, 315-327. Leenheer, J.A. (1981). Comprehensive approach to preparative isolation and fractionation of dissolved organic carbon from natural waters and wastewaters. Environ. Sci. Technol. 15, 578587. Malcolm, R.L. and Mac Carthy, P. (1992). Quantitative evaluation of XAD-8 and XAD-4 resins used in tandem for removing organic solutes from water. Environ. Int. 18, 597-607. McKnight D.M., Boyer E.W., Westerhoff P.K., Doran P.T., Kulbe T., Andersen D.T. (2001). Spectrofluorometric characterization of dissolved organic matter for indication of precursor organic material and aromaticity. Limnol. Ocean. 46, 38-48. Millot, N. (1986). Les lixiviats de décharges contrôlés, Caractérisation analytique et étude des filières de traitement. Ph.D. Thesis, University of Lyon. Mobed J.J., Hemmingsen S.L., Autry J.L., Mcgown L.B. (1996). Fluorescence characterization of IHSS humic substances: Total luminescence spectra with absorbance correction. Environ. Sci. Technol. 30, 3061-3065. Mor S., Kaur K., Khaiwal R. (2013). Growth behavior studies of bread wheat plant exposed to municipal landfill leachate. J. Environ. Biol. 34 (6), 1083-1087.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
OCDE. Essai n°312 : Lixiviation sur des colonnes de sol. Lignes directrices de l'OCDE pour les essais de produits chimiques, Section 3. Avril 2004. Pernet-Coudrier, B., Varrault, G, Clouzot, L., Rousselot, O., Tusseau-Vuillemin, M.-H., Mouchel, J.-M. (2007). Characterization of the dissolved organic waste materials of an important sewage treatment station and influence on the bioavailability of copper. Techniques - Sciences – Methodes 11, 35-42. Porcal P., Koprivnjak J.F., Molot L.A., Dillon P.J. (2009). Humic substances - Part 7: the biogeochemistry of dissolved organic carbon and its interactions with climate change. Environ. Sci. Pollut. Res. 16, 714-726. Revel J.C., Morard P., Bailly J.R., Labbé H., Berthout C., Kaemmerer M. (1999). Plants' use of leachate derived from municipal solid waste. J. Environ. Qual., vol. 28 (4), 1083-1089. Risso W.E., Kurokawa S.S.S., Andrade D.S., Hirooka E.Y. (2015). Organic production in corn: impact of fertilization with landfill leachate in chemical composition, productivity and concentration of metals in grain. Semina: Ciências Agrárias, Londrina 36 (5), 3101-3112. Tahiri A., Destain J., Thonart Ph., Druart Ph. (2014). Valorization and properties of landfill leachates humic substances. J. Mater. Environ. Sci. 5 (2), 2495-2498. Tahiri A., Richel A., Destain J., Druart P., Thonart P., Ongena M. (2016). Comprehensive comparison of the chemical and structural characterization of landfill leachate and leonardite humic fractions. Anal. Bioanal. Chem. 408, 1917-1928. Tipping E., Woof C. (1983). Elevated concentrations of humic substances in a seasonally anoxic hypolimnion: evidence for co-accumulation with iron. Arch. Hydrobiol. 98,137-145. Thurman, E.M. and Malcom, R.L. (1981). Preparative isolation of aquatic humic substances. Environ. Sci. Technol. 15, 463-466. Vindedahl A.M., Strehlau J.H., Arnold W.A., Penn R.L. (2016). Organic matter and iron oxide nanoparticles: Aggregation, interactions, and reactivity. Environ. Sci. Nano, 3 (3), 494-505. Wang S., Lai J., Zhao X. (2012). Effect of landfill leachate irrigation on soil physiochemical properties and the growth of two herbaceous flowers. Acta Ecologica Sinica 32 (19), 6128-6137. Weishaar, J.L., Aiken, G.R., Bergamashi, B.A., Farm, M.S., Fujii, R., Mopper, K. (2003). Evaluation of specific ultraviolet absorbance as an indicator of the chemical composition and reactivity of dissolved organic carbon. Environ. Sci. Technol. 37, 4702-4708. Wehrhan A., Kasteel R., Simunek J., Groeneweg J., Vereecken H. (2007). Transport of sulfadiazine in soil columns - Experiments and modelling approaches. J. Contam. Hydrol. 89, 107-135. Westerhoff P., Aiken G., Amy G., Debroux J. (1999). Relationships between the structure of natural organic matter and its reactivity towards molecular ozone and hydroxyl radicals. Water Res. 33 (10), 2265-2276 Wong M.H. and Leung C.K. (1989). Landfill leachate as irrigation water for tree and vegetable crops. Waste Manage. Res., vol. 7, 311-324. Yong R.N., Mohamed A.M.O., Warkentin B. (1992). Principles of contaminant transport in soils. Elsevier, Amsterdam, Netherlands. Dev. in geotech. Eng. 73, 327 pp.
SUMMARY: In this strudy, the fertilizing value of Municipal Solid Waste Leachates (MSWL) as a partially co-product for organic soil enrichment was evaluated. To overcome negative impacts of the global composition of MSWL, Hydrophobic-like compounds (HPO*) and Transphilic-like compounds (TPH*) were specificaly extracted from dissolved Organic Matter (OM) of MSWL using XAD fractionation. HPO* and TPH* fractions were then used to enrich a soil from Togo with low OM content (0.3%) in order to evaluate their impact on both the stock of organic carbon (Corg) and the biological activity. Batch and column experiments were performed to assess the proportion of Corg that can be mobilized and adsorbed by each horizon, and to simulate an amendment at soil-scale. HPO* and TPH* fractions, comparable with fractions extracted from natural OM, increased the Corg content of each horizon, and allowed the adsorption of Corg on reconstituted soil. Futhermore, hydrophobic-like molecules were preferentially adsorbed than transphilic-like compounds, whereas TPH* fraction enhanced the biological activity of the soil.
1 INTRODUCTION The management of Municipal Solid Waste Leachates (MSWL) is technically and economically restrictive. Considering this effluent no more as a waste but rather as a partially co-product for soil enrichment could represent an interesting and innovative way of valorization. Several studies already considered the fertilizing value of MSWL because of its huge content in Dissolved Organic Matter (DOM), especially Humic-like Substances (HS*) (Wong and Leung, 1989; Revel et al., 1999; Justin et al., 2010; Alaribe et al., 2016). However, the global composition of MSWL negatively affects both the cultures and the environment with accumulation of trace elements in vegetables and soils, vegetable stress, root growth inhibition and decrease of the wildlife diversity (Risso et al., 2015; Mor et al., 2013; Wang et al., 2012; Coyle et al., 2011). Extracting specific organic molecules from DOM can thus be relevant to better control the composition of the amendment and get free of mineral and organic pollutants. The concentrations and characteristics of DOM in MSWL highly depend on several in situ Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2 - 6 October 2017 S. Margherita di Pula, Cagliari, Italy / © 2017 by CISA Publisher, Italy
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
factors (Foo and Hameed, 2009) and evolve during the successive stages of waste degradation during landfilling (Kulikowska and Klimiuk, 2008): DOM content decreases and the aromaticity of the organic molecules increases. MSWL used to be classified according to the characteristics of their DOM (Table 1).
Table 1: Classification of MSWL depending on the characteristics of their DOM (Chian and DeWalle, 1976; Millot, 1986; Berthe et al., 2008; Feuillade et al., 2009) Young MSWL
Intermediate MSWL
Stabilized MSWL
Landfilling phase
Aerobic and acidic
-
Methanogenic
COD (gO2.L-1)
> 20
3-15
0.3)
Medium (0.1-0.3)
Low (< 0.1)
Organic compounds
80% VFA HA* < 10% HPI* > 50%
5-30% VFA HA* < 10% HPI* ≤ 50%
HA* > 30% HPI* < 20%
< 10
10-30
> 30
SUVA index (L.cm-1.gC-1)
During landfilling anaerobic process, the DOM of MSWL evolves toward molecules presenting more aromatic and hydrophobic characters (Kulikowska and Klimiuk, 2008; Feuillade et al., 2009). Specific Ultra-Violet Absorbance (SUVA) index and fractionation according to the hydrophobic character used to be defined as relevant indicators of waste degradation and DOM evolution in MSWL during landfilling (Weishaar et al., 2003; Croué, 2004; Berthe et al., 2008; Feuillade et al., 2009). The fractionation protocol allows separating the HS* in groups of molecules presenting the same properties but with varying aromaticity and hydrophobicity: Humic-like Acids (HA*), Hydrophobic-like compounds (HPO*), Transphilic-like compounds (TPH*) and Hydrophilic-like compounds (HPI*). However, during the extraction process, trace elements were precipitated with HA* fraction and HPI* compounds, the resulting fraction, was composed of various small molecules like salts, hydrocarbons… Thereby, only HPO* and TPH* fractions can be extracted with a purity of 100% and were thus considered in this study. Only few studies dealt with the valorization of extracted DOM from MSWL, whatever the extraction process. Tahiri et al. (2014 and 2016) extracted HS* from MSWL by difference of solubility and compared their performances to the ones of natural HS from leonardite. Anthropogenic and natural HS presented chemical and structural similarities suggesting that HS* from MSWL could be used as biofertilizer or biostimulant. Moreover, both HS positively correlated with the root growth. Baccot et al. (2016) tested the biochemical methane potential of HPO* and TPH* fractions extracted from MSWL by XAD fractionation, to assess the impact of the hydrophobic character on anaerobic digestion. TPH* fraction content in the initial digestate directly correlated with the volume of biogas produced whereas the methane percentage in biogas was anti-correlated with HPI* fraction content. This research study focused on evaluating the impact of an enrichment with HPO* or TPH* fraction extracted from MSWL according to the hydrophobic character, on a soil from Togo with a low organic matter content in order to evaluate their impact on both the stock of carbon and the biological activity of the soil. Batch and column experiments were respectively performed to assess the proportion of organic molecules that can be mobilized and adsorbed by each layer of the soil, and simulate an amendment at soil-scale to assess the effect on the whole system.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
2 MATERIALS AND METHODS 2.1 Substrates of the study: Sampling and characterization 2.1.1
Soil
The soil tested (St) was an agricultural soil sampled at Lama-Kara (N9° 32’ 41.7” / E1° 11’ 55.9”, La Kara, Togo) nearby the Kara River. It was depth (205 cm) and its pH was neutral (from 7.14 to 7.52) (Table 2). The organic carbon (Corg) content of top horizons (0.3% and 0.4%) and their C/N ratios lower than 5 were characteristics of a low microbial activity. An external input of OM is thus needed to promote agricultural activities. According to the World reference base for soil resources 2014 (IUSS Working Group WRB, 2015) and the textural triangle, the St was a vertisol and its texture was predominantly sandy. Table 2: Characteristics of the horizons of the soil from Togo Hz #1
Hz #2
Hz #3
Hz #4
Method
0 – 10
10 – 68
68 – 95
95 – 205
-
Clay (< 2 mm)
9.1
30.0
28.9
12.0
Silt (2 – 50 µm)
8.8
9.4
15.1
13.0
Sand (50 – 2000 µm)
82.1
60.6
55.9
75.0
Corg* (%)
0.3
0.4
0.2
0.1
NF ISO 14235
NT (%)
0.06
0.08
0.07
0.06
NF EN 13654-1
C/N
4.2
4.8
3.4
1.5
-
pH
7.14
7.14
7.07
7.52
NF ISO 10390
Total iron (g.100g-1)
0.451
1.52
6.69
1.45
Total aluminum (g.100g-1)
0.172
0.372
0.798
0.154
Depth (cm)
Granulometry (%)
NF X31-107
Method of Mehra and Jackson (1960)
* The Corg was assimilated to total carbon because no effervescence was observed with HCl 37% at room temperature on each horizon.
2.1.2
Municipal solid waste leachate characteristics
The MSWL was sampled in Noth landfill (north east from Limoges, France) where 30 tons.day-1 of MSW generated by 60.000 residents were landfilled without any pretreatment. The MSWL was stored at 4°C and characterized within four days. The MSWL used was 4 years old. Its characteristics are presented Table 3. It presented a neutral pH, a BOD5/COD between 0.1 and 0.3, a VFA content lower than 10 g.L-1, a low content in Volatile Suspended Solid (VSS) and a SUVA index lower than 30 L.cm.-1gC-1. The fractionation of DOM according to the hydrophobic character underlined a high content in soluble fulvic-like acids (TPH* + HPO* = 68.3%), characteristic of an intermediate MSWL.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Table 3: Characteristics of the MSWL MSWL 7.35 ± 0.09
References - Methods NF T90-008
10.31 ± 0.05
NF EN 27888
COD (mgO2.L )
1289 ± 64
BOD5 (mgO2.L-1)
213 ± 46 475 ± 10
NFT 90-101 OxiTop®, WTW Company Thermal oxidation
0.40 ± 0.04
Potentiometric titration
28 ± 3
NF EN 872
21 ± 1
Westerhoff et al. (1999)
10 ± 1
Malcolm et al. (1992)
pH Conductivity (mS.cm-1) -1
Physico-chemical and chemical parameters
DOC (mgC.L-1) -1
VFA (gCH3COOH.L ) -1
Specific characterization of organic matter
VSS (mg.L ) SUVA index (L.cm-1.gC-1) Fractionation %HA* according to %HPO* the %TPH* hydrophobic %HPI* character
45 ± 2 23 ± 1 22 ± 1
Aiken et al. (1992) Croué et al. (1993)
2.2 Dissolved organic matter of MSWL: Extraction and characterization 2.2.1
Extraction and purification
The fractionation according to the hydrophobic character allows the separation of DOM in four fractions of increasing aromaticity (Figure 1).
Figure 1: Protocol of fractionation of the dissolved organic molecules according to their hydrophobic character
The MSWL was first filtered on 0.45 µm cellulose nitrate membrane to remove particulates and humins insoluble at any pH (Malcolm and Mac Carthy, 1992). The HA* were precipitated by acidifying the sample at pH 2 with HCl 37% and were removed by filtration on 0.45 µm cellulose nitrate membrane. The solution was then successively passed through non-ionic resins in series (DAX-8 and XAD-4) (Aiken et al., 1992; Croué et al., 1993). Hydrophobic-like compounds
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
(HPO*) and transphilic-like compounds (TPH*) were respectively adsorbed on DAX-8 and XAD4 resin whereas hydrophilic-like compounds (HPI*) were not retained like salts. The fractionation of DOM by XAD resins is based on an equilibrium between the DOM in solution and the resin. Leenheer (1981) and Thurman and Malcolm (1981) gave the relation between the capacity factor (k’) and the volume of sample used (1):
(1) where Vsample is the volume of sample to fractionate, V0 is the empty volume of the column (about 60% of the bed volume of resin). According to the Dissolved Organic Carbon (DOC) concentration of the MSWL (475 ± 10 mgC.L-1), the capacity factor k’ was fixed at 25 because it is better adapted for high organic load and minimizes the volume of sample used (Berthe et al., 2008). The volumes of resin and solution were thus 85 and 2652 mL respectively. Before desorption, only HPO* and TPH* fractions were purified with formic acid at pH 2 to eliminate ionic compounds (mainly Cl- due to the acidification of leachate) until the absence of chloride validated by a nitrate silver test. Then, fractions of DOM were desorbed from DAX-8 and XAD-4 resins with an acetonitrile-deionized water (75%-25%; v/v) solution at pH 6.0. A vacuum evaporation helped concentrating HPO* and TPH* fractions and removing residues of acetonitrile and formic acid. The liquid samples were frozen at -20°C and freeze-dried to recover powders of HPO* and TPH* fractions. The DOC of the MSWL used for the extraction (475 ± 10 mgC.L-1) was composed of 45% of HPO* and 23% of TPH*. 380 mg of HPO* and 217 mg of TPH* per liter of MSWL were thus extracted as DOM fractions are composed of around 50% (w/w) of carbon according to DOC measurements. It was respectively more than 40 and 70 times higher than an extraction from a surface water with 10 mgC.L-1 (Labanowski and Feuillade, 2009). MSWL was thus well adapted for extraction and concentration of HPO* and TPH* fractions.
2.2.2
Comparison with natural organic matter fractions
A comparison of the characteristics of HPO* and TPH* fractions extracted from MSWL to Natural Organic Matter (NOM) was performed by using elemental analysis, SUVA index and Apparent Molecular Weight (AMW). Elemental analysis were carried out by the Service Central des Analyses (CNRS unit, Villeurbanne, France) to determine the C, H, O, N and S contents within a standard deviation from 0.25% to 0.4%. SUVA index was calculated as the ratio of the ultraviolet absorbance measuring at 254 nm with a SHIMADZU spectrophotometer (model 1700 PharmasPec) and 1 cm long quartz cells, to the DOC content. Fractionation of the DOM by ultrafiltration was performed according to the protocol of Berthe et al. (2008) with a sample volume of 40 mL and cutoff thresholds of 0.5, 3 and 30 kDa.
2.2.3
Glocal characteristics of solutions of organic fraction extracted from MSWL
Characteristics of extracted organic fraction solutions are presented Table 4. The solutions presented a low conductivity because ions are not retained on XAD resins and remained in the hydrophilic fraction, and an acid pH because of the acidic conditions of the extraction protocol.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
As expected, HPO* fraction was more aromatic than TPH* fraction with higher SUVA index (22 ± 1 L.cm-1.gC-1) and C/N ratio (11.5 ± 0.4).
Table 4: Characterization of organic fraction solutions HPO* solution
TPH* solution
References - Methods
4.9 ± 0.4
3.7 ± 0.3
NF T90-008
36 ± 8
49 ± 5
NF EN 27888
22 ± 1
22 ± 1
Thermal oxidation
NT (mg.L )
1.87 ± 0.09
2.5 ± 0.1
NF EN ISO 7890-3
C/N
11.5 ± 0.4
9.4 ± 0.7
SUVA index (L.cm-1.gC-1)
22 ± 1
18 ± 1
Elemental analysis Westerhoff et al. (1999)
pH -1
Conductivity (µS.cm ) -1
DOC (mgC.L ) -1
2.3 Leaching experiments Batch and column experiments were performed to estimate the impact of HPO* and TPH* fractions as organic enrichement on the soil from Togo. Batch experiments allowed evaluating organic compounds that can be easily mobilized in solution or adsorbed by each layer of the soil whereas column experiments, more representative of in situ conditions, simulate an organic enrichement at soil-scale to assess the effect on the whole system. 2.3.1
Column experiments
The protocol used was adapted from the OCDE guidelines #312 (OCDE, 2004; Figure 2). HPO* or TPH* fraction dissolved in CaCl2 at 0.058 mM Humic balance of 500 kg OM.ha-1.year-1
Solution of CaCl2 at 0.058 mM
Hz1
Hz2
Hz3
Hz4
Column: - Height = 35 cm - Diameter = 4.5 cm - Material = Glass + Sintered glass at the bottom - Reconstituted soil (fraction < 2 mm)
Hz1
Hz2
Artificial rain: - Solution of CaCl2 at 0.058 mM - Average pluviometry of 1000 mm.year-1 - 2 wet seasons (April-June / September-October) è Repeated injection only during wet seasons - Postulate: 40% infiltration and 60% runoff
Hz3
Hz4
Conditions: - Darkness (Column covered with aluminum foil) - 18-25°C - Duplicate Leaching juices characterization Control
Test Injections
Jan.
Feb.
March
April
May
June
Jul.
Aug.
Sept.
Oct.
Nov.
Dec.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Figure 2: Protocol of experiments in column
The tested soil (St) was reconstituted according to the profile with each horizon previously dried and sieved to 2 mm in order to overcome the effects of soil structure. HPO* or TPH* fraction was amended on soil by respecting a humic balance of 500 kg of OM.hectare-1.year-1. An average pluviometry of 1000 mm.year-1 was simulated with an alternation of 2 wet seasons (April to June and September to October) and 2 dry seasons (July to August and November to March) according to the tropical climate of Togo. Moreover, a postulate was established: 40% of infiltration and 60% of runoff were considered to respect characteristics of St. A solution of CaCl2 at 0.058 mM was used as artificial rain, respecting an ionic strength of 0.173 mM (OCDE, 2004; Kay et al., 2005; Wehrhan et al., 2007). After a stabilization phase with artificial rain, the annual organic enrichment was divided up on the 2 wet seasons (5 inputs, Figure 2). Organic fractions were dissolved in CaCl2 solution to respect a homogenous input. A control was carried out with only CaCl2 at 0.058 mM, without any enrichment, in order to assess the mobilization of organic compounds from soil in the liquid phase. Fluorescence analyses were performed on leaching juices filtered on 0.45 μm nitrate cellulose membranes. A ionic strength between 0-1M KCl had no significant effect on the Excitation-Emission Matrix (EEM) spectra (Mobed et al., 1996). Thus, considering this condition and the values of conductivity in the range 15.9 - 191.6 μS.cm-1, samples ionic strength was not buffered. Dilutions of juices were performed in order to avoid saturation of the fluorescence detector and to limit inner-filtering effect. DOC concentration was then in the range 1-5 mgC.L-1 for each analyzed sample. Instrument stability was checked using the Raman peak of deionized water excited at 350 nm, with emission monitored at 395 nm. Water Raman intensities were consistent between each session, with values variation < 6%. Fluorescence EEM spectra were obtained by collecting series of emission scans between wavelengths 250-500 nm with 1 nm intervals and with a 5 nm excitation wavelength intervals between 220 and 500 nm. For each fraction, the Fluorescence Index (FI) was calculated according to the equation from McKnight et al., (2001) (2) at a fixed excitation wavelength of 370 nm, to estimate the bacterial activity in column tests.
I =450nm (2) FI = λem Iλem=500nm Fluorescence analyses were performed with a Shimadzu RF-5301 PC spectrofluorophotometer (Shimadzu Corp., Kyoto, Japan) with a 1-cm-long quartz cells, at room temperature (21 ± 2°C). DOC concentrations in leaching juices were performed to assess the transfer of organic compounds between soil and liquid phase. Measurements were realised by using a SHIMADZU carbon analyzer (model: TOC-L analyzer; precision: ± 50 µgC.L-1; detection limit: 4 µgC.L-1) according to the Non-Purgeable Organic Carbon measurement procedure. First, samples were acidified with HCl 1 mol.L-1 and sparged with high purity air to eliminate inorganic carbon and volatile organic compounds. Non-volatile organic carbon was then combusted in an oven at 720°C and the produced CO2 was quantified by infrared spectroscopy.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
2.3.2
Batch experiments
The protocol used was adapted from the standard NF EN 12457-2 (Figure 3). Batch experiments were performed on each horizon of the St previously dried and sieved to 2 mm. HPO* or TPH* fraction was dissolved in distilled water at a concentration of 50 mgC.L-1. This concentration allowed respecting the humic balance of 500 kg of OM.hectare-1.year-1 applied on column experiments when considering the density of St (1.41). Solutions were mixed with each horizon of soil by respecting a Liquid to Solid ratio (L/S) of 10. This ratio optimizes the transfer between liquid and solid phases (Yong et al., 1992; François et al., 2006) and promote the homogeneity of the system. To avoid bacterial activity, batch experiments were stopped after 48h. DOC of leaching juices were performed according to Section 2.3.1. A control with ultrapure water was carried out for each horizon in order to assess the mobilization of organic compounds from soil in the liquid phase. Distilled water
Horizon (fraction < 2 mm)
HPO* or TPH* (50 mg.L-1)
L/S = 10 [0.3L/30g] 100 rpm, 48h Triplicate
Control
Test
1h of decantation Separation of liquid and solid phases Centrifugation [4000 rpm, 10 min] Filtration at 0.45 µm (cellulose nitrate membrane)
Characterization of leaching juices
Figure 3: Protocol of the batch experiments
3 RESULTS AND DISCUSSION 3.1 Comparison of HPO* and TPH* fractions extracted from MSWL to NOM Whatever the hydrophobic fraction considered, distribution of AMW of DOM of both origins were comparable: the AMW increased with the hydrophobic character, and HPO fractions presented a higher percentage of compounds >30 kDa (17 ± 2%) than TPH fractions (7 ± 1%) (Table 5). Besides, anthropogenic and natural DOM presented comparable size: hydrophobic compounds were predominant between 0.5 and 3 kDa whereas transphilic molecules were equally distributed from 0 to 3 kDa. SUVA indexes confirmed the difference of aromaticity between HPO and TPH fractions with higher values for hydrophobic molecules. Moreover, SUVA indexes of DOM extracted from MSWL were in the range of the ones of NOM. Elemental composition of both fractions from MSWL and NOM were compable despite
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
differences due to the involved genesis processes (aerobic or anaerobic). NOM is composed of about 20% more oxygen than anthropogenic fractions, whereas these latter presented higher carbon and hydrogen percentages (respectively +11% and +21%). Whatever their origin, C/N ratios were comparable for each fraction: transphilic compounds presented a low C/N ratio (from 4 to 12) characteristic of a biologic reactivity, whereas hydrophobic molecules were less reactive with a C/N ratio around 20. However, both fractions were within the C/N ranges of conventional amendments: 8-24 for different manures (Kigozi et al., 2014), 10-23 for urban composts (Cellier et al., 2012) or 7.8-14.9 for MSW (Iglesias-Jimenez and Alvarez 1993, Hirai et al., 1986). Despite different origin and genesis process, HPO* and TPH* fractions extracted from MSWL were thus highly comparable to fractions extracted from NOM.
Table 5: Comparison of extracted DOM fractions from MSWL and NOM from surface water (Pernet-Coudrier et al., 2007; Labanowski and Feuillade, 2009) DOM from MSWL of Noth
NOM from surface water
HPO*
TPH*
HPO
TPH
22
18
18 - 34
13 - 21
C
56.3 ± 0.4
50.3 ± 0.4
49.2 ± 0.9
45.6 ± 0.9
O
30.8 ± 0.4
32.9 ± 0.4
38.7 ± 0.8
41.5 ± 0.8
H
6.7 ± 0.3
6.2 ± 0.3
5.2 ± 0.1
5.0 ± 0.1
N
2.7 ± 0.2
5.7 ± 0.2
2.7 ± 0.1
4.6 ± 0.1
S
1.9 ± 0.3
2.0 ± 0.3
nd
nd
20.7
8.8
18
10
Distribution of AMW
SUVA (L.cm-1.gC-1)
Elemental composition (% weight)
C/N nd: Not determined
3.2 Carbon adsorption on the soil 3.2.1
Batch experiments
Figure 4 presents the net Corg adsorption percentages on each horizon of St calculated after HPO* and TPH* tests. These results were compared to clay and initial Corg content of the horizons. No correlation between clay content and adsorption of Corg was highlighted. On the contrary, expect for the horizon #3, the higher the initial Corg content in the horizon, the lower the adsorption of Corg by this horizon. The horizon #3 of the St differed from the 3 others with the highest Corg adsorption percentage (72.4%). This capacity could be explained by its characteristics (Table 2). Indeed, its free iron and aluminum contents were 2 to 14 times higher than for the others horizons. Moreover, because of its neutral pH, aluminum exists as hydroxyaluminum ion, known for acting as a connection cation between clay minerals and OM (Baize,
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
2000). Connection between OM from HPO* or TPH* fraction and the abundant content of clay (28.9%) could thus be easily considered. Furthermore, interactions between OM and iron, extensively already highlighted in literature, could also explain the high Corg adsorption ability of this horizon #3 (Tipping and Woof, 1983; Gu et al., 1994; Porcal et al., 2009; Fink et al., 2016; Vindedahl et al., 2016). Moreover, both the high degradation of OM under tropical climate and the depth of this horizon (78 cm) disadvantage the Corg retention on this layer on in situ conditions. Despite better Corg retention, horizon #3 could thus not be relevant to retain carbon on St. Adsorption of Corg from HPO* fraction was systematically higher when compared to TPH* fraction in the same conditions. Hydrophobic compounds seemed thus to be better adsorbed by horizons of both soils. Enrichment with organic compounds extracted from MSWL allowed thus improving the Corg content of St. However, batch experiments were not representative of in situ conditions and column experiments were thus performed to identify mechanisms on a global scale. Corg content (g.100g-1)
Carbon adsorption – HPO* test Teneur en argile
Carbon – TPH* test Teneur enadsorption Corg
Adsorption du carbone - Essai HPO*
Adsorption du carbone - Essai TPH*
80%
4,5 4.5
72.4%
70%
4,0 4.0
69.7%
3,5 3.5
60%
3.0 3,0
50% 40%
2.5 2,5 2.0 2,0
30% 20%
40.2%
37.4%
34.0%
25.6% 24.0%
1.5 1,5 1.0 1,0
20.2%
10%
0.5 0,5
Organic carbon content (g.100g-1)
Clay content (%)
0.0 0,0
0% HzHzt #1 1
HzHzt #2 2
Hz Hzt #3 3
HzHzt #4 4
Figure 4: Net adsorption of Corg on each horizon of St after HPO* and TPH* batch experiments
3.2.2
Column experiments
Measurements of DOC concentrations in leaching juices allowed drawing net cumulative masses of Corg retained by the reconstituted soil from Togo during column experiments (squares, Figure 5). To better understand the organic enrichment impact, cumulative masses of HPO* and TPH* fractions brought (diamonds, Figure 5) were added on the same graph and translated in cumulative masses of carbon (crosses, Figure 5). As explained Section 2.3.1, inputs of organic fractions were provided in 5 times corresponding to the 2 wet seasons (arrows, Figure 5). Additions of HPO* or TPH* fractions (diamonds) increased in the same extent the cumulative masses of Corg added (crosses). The Corg brought by these organic fractions corresponded approximately to 50% of the cumulative masses of each fraction respectively, which was in accordance with the elemental composition (Table 5). Moreover, whatever the organic fraction,
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
the St adsorbed all the Corg added by HPO* and TPH* fraction. A higher humic balance than 500 kg of OM.hectare-1.year-1 should be tested in the same conditions to assess if the tested soil could adsorb more Corg and to determine the optimal organic enrichement to apply. Masse cumulée de fraction HPO* amendée Cumulative mass of added HPO* Masse cumulée de C-HPO* amendé Cumulative mass of added CHPO* CHPO* Masse nette cumulée deof C adsorbed retenu Net cumulative mass Corg
80 70
Mass (mg)
60
Inputs of HPO* fraction
50 40 30 20 10 0 Sept
Oct
Nov
Dec Déc
Jan
Feb Fév
Mars March
April Avr
May Mai
June Juin
Juil July
Aug Août
(a)
70
Masse cumulée de fraction TPH* amendée Cumulative mass of added TPH* CTPH* Cumulative mass of added CTPH* Masse cumulée de C-TPH* amendé
60
Inputs of TPH* fraction
Masse (mg)
80
Net cumulative mass Corg Masse nette cumulée deofC adsorbed retenu
50 40 30 20 10
0 Sept
Oct
Nov
Déc Dec
Jan
Fév Feb
Mars March
Avr April
Mai May
Juin June
Juil July
Août Aug
(b)
Figure 5: Retained carbon by the St after addition of HPO* (a) or TPH* (b) fraction Analyses of leaching juices by 3D-fluorescence allowed estimating the impact of organic fractions on bacterial activity of soil from Togo by calculating the Fluorescence Index. Table 6 compares FI of each experiment between initial and final states. Control and HPO* tests presented a constant FI (1.69 and 1.70 respectively) in the range 1.6-1.9 characteristic of a persistent domination of microbially-derived organic matter. On the contrary, the FI of TPH* test increased by 20% from 1.79 to 2.24. The final value higher than 1.9 confirmed a material exclusively from bacterial origin. The TPH* fraction seemed thus to improve the bacterial activity.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Table 6: Evolution of the fluorescence index during column tests. Control test Initial state Fluorescenc e index
3.2.3
Final state
HPO* test Initial state
1.69 ± 0.02
TPH* test
Final state
1.70 ± 0.04
Initial state
Final state
1.79 ± 0.04
2.24 ± 0.05
Comparison of Corg adsorption capacities
Net Corg adsorption capacities were calculated for batch and column experiments (Table 7). They represented the adsorbed carbon mass brought by HPO* or TPH* fraction (expressed in mgCadsorbed) on the initial Corg content (expressed in mgChorizon). As underlined with batch experiments (Section 3.2.1), there was an anticorrelation between adsorption capacities and initial Corg content of each horizon: more Corg was retained on layer with low initial Corg content (Table 7). Moreover, the highest adsorption capacities were observed for the deepest horizons. HPO* and TPH* fractions extracted from MSWL allowed thus increasing the Corg content of horizons with low carbon. Batch experiments allowed calculating the Corg enrichment expected on column experiments considering the mass and the Corg of each layer used to reconstitute the soil. When compared to the initial Corg content of the whole reconstituted soil column, results were lower than the ones expected by batch experiments: Corg enrichment was only 3.5% for HPO* test and 2.9% for TPH* test (Table 7). Indeed, batch experiments did not simulate well the transfer mechanisms that occurr on the global soil, and they did not consider the different depths of each horizon as horizons #3 and #4 are more difficult to reach. They were thus less representative than column experiments. Nevertheless, same order of magnitude and same trend could be observed between batch and column experiments: hydrophobic compounds were better adsorbed than transphilic ones. Table 7: Corg enrichment (expressed in mgCadsorbed.mgChorizon-1) Adsorption capacities
Batch experiments
Column experiments
Initial Corg
HPO* test
TPH* test
Layer #1
3.1%
2.0%
0.3%
Layer #2
1.4%
1.1%
0.4%
Layer #3
6.7%
6.5%
0.2%
Layer #4
10.4%
8.8%
0.1%
4.5%
3.8%
-
3.5%
2.9%
-
Expected Corg enrichment on reconstituted soil Obtained Corg enrichment on reconstituted soil
4 CONCLUSIONS Batch and column experiments were performed to evaluate the potential Corg adsorption of HPO* and TPH* fractions extracted from MSWL on a soil from Togo with a low content in organic compounds. Despite different origin and genesis processes, HPO* and TPH* fractions presented global
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
and specific characteristics comparable with fractions extracted from natural organic matter. Moreover, their use as organic enrichments was relevant for a soil with low initial Corg as they increased the Corg content of each horizon (batch experiments) and they allowed the adsorption of Corg on a reconstituted soil (column experiments) when compared to controls. Futhermore, hydrophobic molecules were preferentially adsorbed than transphilic compounds, whereas TPH* fraction enhanced the biological activity of the soil. By calculating adsorption capacities, batch experiments allowed well simulating the results obtained in columns. Batch experiments can thus be considered as an interesting tool to easily and quickly evaluate adsorption capacities. It could now be interesting to repeat batch and column experiments with higher HPO* and TPH* concentrations (i) to estimate the evolution of the adsorption capacity with increasing HPO* or TPH* contents, (ii) to assess the maximum capacities of soils to adsorb Corg brought by these organic fractions extracted from MSWL, and (iii) to identify which fraction allows the best Corg retention.
AKNOWLEDGEMENTS First of all, the Authors would like to thank the Noth landfill for providing them the sample of MSWL. They would also thank Kwamivi SEGBAYA, Assistant Professor at the University of Lomé, for the sampling of soil in Togo. Finally, the Authors thank the Regional Council of Limousin for the financial support during this research project.
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