Organic components contained in leachates resulting from decomposition of waste are difficult to degrade. They also contain inorganic components, as nitrogen compounds, phosphates, and chlorides, also Ca, Mg, K, and heavy metals. Leachate volume and its composition vary depending on biogeochemistry of type site of deposited residues, and age of sanitary landfill. In this study, it conducted a Heterogeneous Fenton, advanced oxidation process using lignitic activated carbon as solid matrix, with and without Fe 2+ impregnation, for the treatment of leachate (Le) obtained from a sanitary landfill located in the city of Mérida, Yucatan, Mexico. In this study was determined the efficiency of Heterogeneous Fenton process for to remove Chemical Oxygen Demand (COD) and Color from crude leachates using mesoporous activated carbon, previously treated with HCl, HNO 3, and a mixture of both acids and impregnated with Fe 2+ on actived carbon. It was studied of activated carbon behavior previously treated with each acid and the mixture, washed with hot water and impregnated with Fe 2+ using FeCl 2.4H 2O and FeSO 4·7H 2O salts. For leachate treatment by Heterogeneous Fenton reaction, it was selected carbon pretreatment with HCl acid and impregnation with FeSO 4·7H 2O. Treatment with HCl presented the advantage of not prematurely oxidize to Fe 2+. In order to select an optimal dose and achieve an adequate concentration of HO· radicals dosage tests was carried out H 2O 2. By selecting the indicated procedure, it was obtained more than 80% performance in removing COD and Color from crude leachate. The confidence level for the selected variables (acids and impregnation) was determined by a statistical analyzes using the Centurion XVII software. Finally, mesoporous lignitic carbon used in this study was found to be adequate for this oxidation process, and this method presented the advantage of not producing sludge as in traditional Fenton reaction.
Generation of solid waste is due to several factors, such as population growth, industrialization, changes in lifestyle, among others. The management of this waste, mainly its final disposal, is a complex work that has become a common problem in developing countries, where it represents not only an environmental but also a social problem [
Among the POA’s, Fenton process has been widely used for oxidation of many organic compounds due to their high efficiency to produce hydroxyl radicals from the decomposition of H2O2 in acidic medium through Fe salts. This is an attractive oxidation system because the iron is an abundant and non-toxic element, and H2O2 is easy to handle and environmentally safe [
In many Fenton systems, the rate-limiting constituent in formation of hydroxyl radicals (OH•) is the ferrous ions production. Ferrous ions formation of in GAC/H2O2/Fe system can be explained by GAC functions as an electron transfer catalyst (GAC and GAC+), for which it behaves like to a donor and capable of to reduce ferric ions to ferrous ions [
The objective was to determine the efficiency of Heterogeneous Fenton Process in the removal of COD and Color of crude leachates using lignitic GAC treated with acid and impregnated with Fe2+.
This research was carried out using leachate generated from a sanitary landfill of the Merida City, Yucatan; that began its operation 14 years ago. Samples were collected from leachates between September and December 2015 and were collected from evaporation ponds, where leachates of different ages are mixed, situation that makes treatment complex. For the sampling were used van Dorn samplers. A Granular Activated Carbon brand Carbotecnia Gamma L was used by being a lignitic granular carbon, which will be represented with acronym GAC, predominating a particle size of 9.7 ± 0.4135 mm, with 80% of mesopores and 20% macroporous, and this was characterized by chemical and spectroscopic analysis.
Activated carbon was pretreated with concentrated hydrochloric acid (Ultrex Baker), in a ratio of 100 g of carbon per 300 ml of HCl, for a period of 8h with stirring, at room temperature, in Orbital-Shaker equipment at 100rpm, decanted and washed with hot distilled water until a constant pH of 4 ± 0.51. Subsequently it was subjected for 24 h to 105˚C; after this stage, a heat treatment to GAC was carried out at 350˚C in a muffle, in order to improve the porosity of coal [
Treatment with HNO3 (Ultrex Baker) for GAC was important [
A procedure was followed as in the previous two cases using 30 mL of HNO3 and 90 mL of HCl, with the same pH conditions, drying and subsequent heat treatment
Leachate (Le) from a sanitary landfill in the city of Mérida was characterized, determining the following parameters, pH, temperature and conductivity, measured in situ with a Lab Quest field interface (Vernier, USA), according to Mexican standard: NMX-AA-008-SCFI-2011, NMX-AA-007-SCFI-2000 and NMX-AA-093-SCFI-2000, respectively. For determination of total and soluble COD, the samples were oxidized in a HI839800 reactor (HANNA Instruments, USA), according to Standard Methods 5520 C; Then a DR/2400 spectrophotometer (HACH, USA) was used, based on the Standard Methods 5520 D [
BOD was determined in a FOC225E Sensor System 10 (VELP, Italy) incubator, based on Standard Methods 5210. In addition, dissolved oxygen (DO), turbidity, color, alkalinity, ammonia nitrogen (N-NH3) phosphorus, total solids (ST), total volatile solids (STV), total suspended solids (SST), volatile suspended solids (SSV). Metals such as Ca, K, Fe and Cu were determined by atomic absorption spectrophotometry in a flame atomic absorption spectrometer (AA) SOLAAR M6 (Thermo Elemental, England), after microwave digestion in a model 5 (MARS, USA), according to NMX-AA-051-SCFI-200 standard.
The characterization of mesoporous GAC of lignitic origin was carried out by means of equipment ASAP 2020 Automatic Hydrocarbon-Resistant Micropore and Chemisorption Analyzer brand Micromeritics, to obtain the data of its structure, area and volume of pore. As far as characterization by scanning microscopy (SEM), it was performed in a JSM-6610 LV (JEOL, Ltd., USA) microscope. For this analysis N2 was used.
Manganese, nickel, zinc and iron metals present in the GAC were determined by atomic absorption spectrophotometry by flame method in (AA) SOLAAR M6 (Thermo Elemental) equipment, with a previous acidic digestion by microwave in equipment 5 (MARS, USA), also based on the NMX standard -AA-051-SCFI- 200. 1 g of GAC both HCl-treated and HNO3 were used independently and combined. Digestion process of samples was 20 min at 175˚C.
GAC’s previously treated with HCl, HNO3 and with combined acids were impregnated with ferrous chloride (Fe Cl2∙4H2O) and ferrous sulfate (FeSO4∙7H2O), both of Aldrich brand in a ratio of 100g of carbon per 25 ± 0.35 g of FeCl2∙4H2O and 35 ± 0.37 g of FeSO4∙7H2O respectively, these values were calculated stoichiometrically. It was stabilized by lyophilization in Virtis Benchtop equipment.
Experiments were carried out by Batch, taking place in 250 ml containers, suitable for 100 ml of Le and 5 g of impregnated GAC. As a control, GAC impregnated but without the pre-treatment of HCl was used, it was only washed with hot water and the procedure was followed. Leachate (Le) was adjusted to a value pH of 3 for its contact with different GAC’s for 2 h with stirring in an orbital shaker, brand Lab-Line Instruments, with controlled temperature at 150˚C and 200 rpm. Finally they were filtered in Whatman grade GF/B filters of 1 μm pore; five tests were made for each case.
Tests were carried out at room temperature using 100 mL of Le with 5 g of each GAC treated with different acids, mentioned in GAC treatment paragraph, with continuous agitation at 200 rpm during 4 h. The pH of Le was adjusted to 3 and 5 g of pre-treated activated carbon was added.
Doses with 3.2, 6.4 and 9.6 mg/L of 30% H2O2 (Merck) were tested to remove COD and color in Le, efficiencies of these removals also were determined.
With removal percentages of COD and color obtained in all experiments, and using statistical software package STATGRAPHICS CENTURION XVII and Fisher’s LSD method [
In
Iron (II) content in impregnated GAC’s, is presented in
Impregnations with different acids were compared in both figures, a better
Parameter | Result | Metal | Result |
---|---|---|---|
Temperature (˚C) | 26.14 ± 0.91 | Ca (mg/L) | 120.34 ± 5.14 |
Conductivity (uc/cm) | 18.95 ± 0.81 | K (mg/L) | 11.44 ± 0.383 |
Dissolved Oxygen (mg/L) | 2.46 ± 0.09 | Fe (mg/L) | 2.13 ± 0.077 |
Turbidity (NTU) | 160.41 ± 7.38 | Cu (mg/L) | 0.71 ± 0.026 |
Color (pTCo) | 10900.35 ± 346.17 | ||
Alkalinity (mg/L) | 3388.80 ± 113.45 | ||
Total Chemical Oxygen Demand (mg/L) | 4865.23 ± 178.33 | ||
Soluble Chemical Oxygen Demand (mg/L) | 4180.44 ± 165.16 | ||
BOD5 (mg/L) | 240.12 ± 7.51 | ||
Total Organic Carbon (mg/L) | 1515.84 57.12 | ||
Total Nitrogen (mg/L) | 100.57 ± 4.67 | ||
Chlorides (mg/L) | 3698.85 ± 154.09 | ||
Phosphorus (mg/L) | 31.74 ± 1.17 | ||
Total Solids (mg/L) | 1403 81 ± 57.08 | ||
Total Fixed Solids (mg/L) | 9643.62 ± 304.62 | ||
Total Volatile Solids (mg/L) | 4395.18 ± 146.60 | ||
Total Suspended Solids (mg/L) | 156.66 ± 5.85 | ||
Fixed Suspended Solids (mg/L) | 26.61 ± 1.14 | ||
Volatile Suspended Solids (mg/L) | 130.43 ± 4.95 |
impregnation of GAC’s were obtained considering five experiments in each case, when using only HCl with respect to HNO3 and acids mixtures.
Lowest concentrations of Fe2+ were the GAC’s treated with HNO3 and acid mixture. The fact that impregnation quality decreased with HNO3 and mixtures may be due to that HNO3 somehow affects carbon surface by a possible oxidation of Fe2+ to Fe3+ from iron present in each GAC. Comparing the graphs of
tion of iron; however, there was not a very significant difference, as can be seen in
It is probably that Fe(OH)3 is present in aqueous medium to beginning and becoming Fe2O3 after heat treatment and this oxide could be blocking active sites for Fe2+ of the salts during impregnation. In acid mixture, considering HNO3 case, it is this acid in mixture that must be affecting the impregnation. To understand Fe(OH)3 formations, a pE-pH diagram of iron in aqueous medium is presented in
In
Dose of H2O2 (mg/L) | Non-impregnated GAC | HCl-treated GAC | HNO3-treated GAC | HCl+HNO3?treated GAC |
---|---|---|---|---|
3.2 | 61.63 ± 1.79 63.25 ± 2.15 59.62 ± 2.92 | 85.3 ± 3.04 83.5 ± 2.86 86.1 ± 2.79 | 82.17 ± 2.84 81.61 ± 3.23 79.89 ± 2.62 | 80.22 ± 3.31 79.34 ± 2.51 77.84 ± 2.72 |
6.4 | 70.13 ± 3.58 69.32 ± 2.56 69.51 ± 2.71 | 89.22 ± 3.48 90.43 ± 2.86 89.61 ± 3.75 | 86.71 ± 3.81 85.68 ± 3.21 84.39 ± 3.17 | 81.82 ± 2.67 82.57 ± 2.71 80.59 ± 3.16 |
9.6 | 68.33 ± 2.90 66.82 ± 3.05 64.36 ± 2.57 | 89.45 ± 4.08 89.90 ± 3.04 88.72 ± 2.64 | 86.24 ± 3.58 84.64 ± 3.25 86.76 ± 2.95 | 80.89 ± 2.39 81.56 ± 2.16 79.67 ± 2.80 |
Dose of H2O2 (mg/L) | Non-impregnated GAC | HCl-treated GAC | HNO3-treated GAC | HCl+HNO3?treated GAC |
---|---|---|---|---|
3.2 | 49.37 ± 1.70 52.13 ± 1.95 50.82 ± 1.67 | 91.06 ± 2.82 89.83 ± 3.38 90.51 ± 3.04 | 85.32 ± 2.95 80.27 ± 2.72 84.48 ± 2.70 | 82.77 ± 3.78 79.18 ± 3.06 81.92 ± 3.23 |
6.4 | 56.4 ± 1.80 59.4 ± 2.06 57.6 ± 2.28 | 93.22 ± 2.78 95.16 ± 3.52 89.71 ± 2.85 | 87.92 ± 2.94 89.11 ± 3.53 86.73 ± 3.71 | 85.84 ± 3.67 86.55 ± 4.02 83.23 ± 2.77 |
9.6 | 58.8 ± 2.03 60.4 ± 2.25 54.2 ± 1.99 | 92.36 ± 2.91 93.25 ± 3.61 91.34 ± 2.71 | 86.29 ± 3.83 88.73 ± 3.32 82.46 ± 2.58 | 85.37 ± 3.21 87.62 ± 2.89 84.91 ± 3.70 |
FeCl2∙4H2O and FeSO4∙7H2O. As in COD removal case, the Color removal was carried out using same amounts of Le, equal contact time and the same dose of H2O2,
because it is more stable to humidity, since the State of Yucatan has a high atmospheric humidity.
Brunauer-Emmett-Teller (BET) and Langmuir isotherms to determine surface areas for GAC’s, non-impregnated, acids-treated and FeSO4∙7H2O-impregnated; the isotherms indicated.
In
Surface Area (m²/g) | ||||||
---|---|---|---|---|---|---|
Non-treated GAC * | HCl Treatment* | HNO3 Treatment* | HNO3+HCl Treatment* | |||
BET Surface Area | 583.77 | 614.42 | 562.62 | 573.22 | ||
Langmuir Surface Area | 792.38 | 821.55 | 808.72 | 821.74 | ||
BJH** adsorption cumulative surface area of pores between 17.000 Å and 3000.000 Å diameter. | 221.6 | 228.72 | 224.23 | 225.44 | ||
BJH desorption cumulative surface area of pores | 323.2 | 342.11 | 337.55 | 339.65 | ||
Pore Volume (cm³/g) | ||||||
Single point adsorption total pore volume of pores | 0.621 | 0.643 | 0.632 | 0.640 | ||
Single point desorption total pore volume of pores | 0.648 | ´0.672 | 0.659 | 0.661 | ||
BJH adsorption cumulative surface area of pores | 0.488 | 0. 503 | 0.498 | 0.523 | ||
BJH desorption cumulative surface area of pores | 0.537 | 0.560 | 0.550 | 0.557 | ||
Pore Size ( Å) | ||||||
Adsorption average pore width (4V/A by BET): | 42.57 | 47.77 | 43.11 | 45.57 | ||
Desorption average pore width (4V/A by BET): | 44.42 | 51.51 | 46.82 | 48.92 | ||
BJH adsorption average pore diameter (4V/A): | 88.07 | 93.05 | 89.84 | 90.76 | ||
BJH desorption average pore diameter (4V/A): | 66.41 | 71.82 | 68.52 | 69.75 | ||
*Washed with hot water. ***Barrett-Joyner-Halenda (BJH) Analysis.
The GAC’s treated with HCl, gave the best surface area by BET and Langmuir, the higher pore volume and sizes, what was reflected in the higher impregnation capacity, as shown in
Surface Area (m²/g) | |||
---|---|---|---|
Impregnated GAC (HCl) | Impregnated GAC (HNO3) | Impregnated GAC (HNO3+HCl) | |
BET Surface Area | 423.62 | 435.13 | 431.69 |
Langmuir Surface Area | 573.14 | 589.32 | 578.87 |
BJH* adsorption cumulative surface area of pores between 17.000 Å and 3000.000 Å diameter | 204.03 | 211.45 | 209.31 |
BJH desorption cumulative surface area of pores | 276.43 | 262.84 | 269.72 |
Pore Volume (cm³/g) | |||
Single point adsorption total pore volume of pores | 0.541 | 0.499 | 0.516 |
Single point desorption total pore volume of pores | 0.557 | 0.509 | 0.557 |
BJH adsorption cumulative surface area of pores | 0.468 | 0.428 | 0.442 |
BJH desorption cumulative surface area of pores | 0.501 | 0.458 | 0.476 |
Pore Size ( Å) | |||
Adsorption average pore width (4V/A by BET): | 51.08 Å | 44.26 Å | 48.44 Å |
Desorption average pore width (4V/A by BET): | 52.61 Å | 43.82 Å | 47.99 Å |
BJH adsorption average pore diameter (4V/A): | 91.81 Å | 84.21 Å | 87.78 Å |
BJH desorption average pore diameter (4V/A): | 72.55 Å | 66.12 Å | 68.45 Å |
*Barrett-Joyner-Halenda (BJH) Analysis.
HCl, hot water-washed, and FeSO4∙7H2O impregnated.
By means of a multiple comparison procedure, means values were determined
COD/Dose of H2O2 | Cases | LS mean | LS sigma | Homogeneous groups | |
---|---|---|---|---|---|
3.2 mg/L | 12 | 76.817 | 0.384 | X | |
9.6 mg/L | 12 | 80.522 | 0.384 | X | |
6.4 mg/L | 12 | 81.617 | 0.384 | X | |
Color/Dose of H2O2 | Cases | LS mean | LS sigma | Homogeneous groups | |
3.2 mg/L | 12 | 76.400 | 0.618 | X | |
9.6 mg/L | 12 | 80.442 | 0.618 | X | |
6.4 mg/L | 12 | 80.875 | 0.618 | X |
*Fisher LSD (Least Significant Difference) method, 95% confidence interval.
COD/treatment Type | Cases | LS mean | LS sigma | Homogeneous groups | |||||
---|---|---|---|---|---|---|---|---|---|
No treatment | 9 | 65.856 | 0.445 | X | |||||
HCl +HNO3 | 9 | 80.418 | 0.444 | X | |||||
HNO3 | 9 | 84.400 | 0.444 | X | |||||
HCl | 9 | 87.933 | 0.444 | X | |||||
Color/treatment Type | Cases | LS mean | LS sigma | Homogeneous groups | |||||
No treatment | 9 | 55.466 | 0.714 | X | |||||
HCl +HNO3 | 9 | 84.111 | 0.714 | X | |||||
HNO3 | 9 | 85.656 | 0.714 | X | |||||
HCl | 9 | 91.722 | 0.714 | X | |||||
*Fisher LSD (Least Significant Difference) method, 95% confidence interval.
which are significantly different from each other. Homogeneous groups are identified by the alignment of the sign X in each column. Within each column, the levels that have sign X form a group of means values between which there are no statistically significant differences. The method used to discern between means values was the procedure of least significant differences of Fisher (LSD).
One X was assigned in each column for differentiate the homogeneous groups. Percentages of removal of COD and Color (these are independent variables) were related to the doses of H2O2. In the same way, the percentage of removal of these independent variables was analyzed, but considering as variables for GAC, without treatment and treatment with different acid.
In
In
These statistical analyses supported both the selection of H2O2 dose for the heterogeneous Fenton process and the choice of acid treatment.
After analyzing all the variables proposed in this paper, it is important to note that lignite carbon (GAC), due to its adsorbent properties, provided good chemical surface stability for Heterogeneous Fenton.
The acids pretreatments had a positive effect on the removal efficiency, particularly HCl, which presented the best efficiencies with respect to the other acids, since it does not present Fe2+ oxidation, as in the case of HNO3.
Regarding the salts, both FeSO4∙7H2O and FeCl2∙4H2O showed impregnation efficiencies above 80%, with similar reaction rates in the formation of OH• radi-
cals. However, FeSO4∙7H2O was selected because it showed the best stability against environmental humidity.
The pH with 4 values resulted in more efficient value during the impregnation on the surface of coal. Lyophilization for stability treatment by impregnation was fundamental to not alter the impregnated surface.
By means of statistical analysis a good certainty of the selection of H2O2 dose for treatment by Heterogeneous Fenton of leachate, also the best acid treatment for GAC was obtained.
To National Council for Sciences and Technology (CONACYT) which supports the PhD Graduates in Environmental Sciences and Engineering. To PhD. Sergio Gómez-Salazar researcher of the University Center in Sciences and Engineering of the University of Guadalajara by measurements specific areas to GAC’s. To PhD. Pedro Avila-Pérez, researcher of the National Institute of Nuclear Research by the analysis of scanning microscopy (SEM)
May-Marrufo, A.A., Mendez-Novelo, R.I., Barceló- Quintal, I.D., Solís-Correa, H.E. and Giacoman- Vallejos, G. (2017) Leachate Treatment by Heterogeneous Fenton on an Activated Carbon Substrate with Fe(II) Impregnated. Journal of Environmental Protection, 8, 524-539. https://doi.org/10.4236/jep.2017.84036