Journal of Environmental Protection, 2013, 4, 1495-1501 Published Online December 2013 (http://www.scirp.org/journal/jep) http://dx.doi.org/10.4236/jep.2013.412171 Open Access JEP 1495 Surfactant-Enhanced Washing of Soils Contaminated with Wasted-Automotive Oils and the Quality of the Produced Wastewater Montserrat Zacarias-Salinas1, Mabel Vaca2, Miguel A. Flores2, Erick R. Bandala3, Luis G. Torres1* 1UPIBI-Instituto Politécnico Nacional. Av. Acueducto s.n. Colonia Barrio la Laguna Ticomán. México DF, México; 2Labor- atorio de Calidad de Agua y Residuos, Universidad Autónoma Metropolitana-Unidad Azcapotzalco México; 3Departamento de Ingeniería Civil y Ambiental Escuela de Ingeniería, Universidad de las Américas-Puebla. Sta. Catarina Mártir, Cholula, Puebla, México. Email: *LTorresBustillos@gmail.com Received February 16th, 2013; revised March 19th, 2013; accepted April 15th, 2013 Copyright © 2013 Montserrat Zacarias-Salinas et al. This is an open access article distributed under the Creative Commons Attribu- tion License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In accordance of the Creative Commons Attribution License all Copyrights © 2013 are reserved for SCIRP and the owner of the intellectual property Montserrat Zacarias-Salinas et al. All Copyright © 2013 are guarded by law and by SCIRP as a guardian. ABSTRACT An old automotive industrial site located at Mexico City with many years of operation and contaminated with heavy oil hydrocarbons, particularly spent oils, was assessed for restoration using the surfactant enhanced soil washing (SESW) process. The main goal of this study was to characterize the contaminated soil in terms of TPHs, BTEX, PAHs, and metals contents as well as microbiologically (total heterotrophs and specific degrading microorganisms). We also aimed to determine the surfactant type and concentration to be used in the SESW process for the automotive waste oil con- taminated soil. At the end, sixteen kg of contaminated soil were washed and the produced wastewater (approximately 40 L) was characterized in terms of COD, BOD; solids, and other physico-chemical parameters. The soil contained about 14,000 mg of TPH/kg soil (heavy fraction), 0.13 mg/kg of benzo (k) fluoranthene and 0.07 mg/kg of benzo (a) pyrene as well as traces of some metals. Metals concentrations were always under the maximum concentration levels suggested by Mexican regulations. 15 different surfactants were used to identify the one with the capability to achieve the highest TPH removal. Surfactants included 5 anionics, 2 zwitterionic, 5 nonionics and 3 natural gums. Sulfopon 30 at a concentration of 0.5% offered the best surfactant performance. The TPH removals employing the different surfac- tants were in the range from 38% to 68%, in comparison to the soil washing with water (10% of TPH removal). Once the surfactant was selected, 70 kg of soil were washed and the resulting water contained approximately 1300 mg/L of COD, 385 mg/L of BOD (BOD/COD = 0.29), 122 mg/L of MBAS, and 212 mg/L of oil and greases, among other con- taminants. Keywords: Wasted Automotive Oils; Surfactants; Soil Washing; Waste Water 1. Introduction The restoration of soil contaminated with hydrocarbons is often difficult and complex due, among other, to the adsorption on the soil matrix and the low solubility of these contaminants. It has been demonstrated that the more insoluble in water is the contaminant, the longer it remains in the soil matrix [1]. Many different techniques have been reported to re- store soils contaminated with hydrocarbons; among of them the surfactant-enhanced soil washing (SESW) have recently emerged as highly cost-effective [2-4]. Surfac- tants reduce surface tension and form aggregates (i.e. micelles in aqueous solution), changing surface tension as result of surfactant’s concentration on the solution’s surface. Contaminants present in soil are removed by means of two phenomena: 1) The solubilization of com- pounds due to the reduction of surface tension (bellow the surfactant’s critical micelle concentration (CMC) and 2) The mobilization of hydrophobic compounds due to the presence of the surfactant, at concentrations higher *Corresponding author.
Surfactant-Enhanced Washing of Soils Contaminated with Wasted-Automotive Oils and the Quality of the Produced Wastewater Open Access JEP 1496 than surfactant’s CMC value [5]. SESW process has shown very good results, and also has been considered as an economic and easy technique, so its application has increased in interest [3,6-9] as shown the literature review. Iturbe et al. [6] reported TPH (Total Petroleum Hydrocarbons) removals over 92% for contaminated soil with an initial concentration up to 17,238 mg/kg, when washing contaminated soils using the surfactant Canarcel TW80 in concentrations of about 0.5%. In other studies with SDS (sodium dodecyl sulphate), TPH removals above 90% were reported when treating oil-hydrocarbons contaminated soils [10]. Chin-Chi et al. [11], when washing contaminated soil, showed high TPH removals, between 63% and 62%, respectively using biosurfactants (i.e. rhamnolopids and surfactin) for the SESW process in a soil contaminated with a 9000 mg/kg of hydrocarbons. These authors also used two synthetic surfactants (Triton X-100 and Tween 80) for the same washing process, finding that synthetic surfactants were clearly less efficient (40% and 35%, removal, respectively). Another experiment using a non- ionic surfactant Brij 35 showed removals of crude oil from soils of 93.54% in a surfactant-enhanced washing of soil contaminated with 50,000 mg/kg of crude oil [12]. In this work, an old automotive industrial site located at Mexico City was assessed for restoration using SESW. The site maintains operations for many years and pro- duced contamination with heavy oil hydrocarbons, in particular spent oils. Car service activities were carried out in the place, such as automotive oil change service, and wasted oils were stored in a submerged cement tank for many years. The company suspended its service more than 10 years ago and closed. The place was dismantled to become a residential zone. During the process of characterization the site, which was carried out by the UAM-Azcapotzalco (Mexico), it was noticed that the oil cement tank suffered spills caus- ing infiltration of the automotive oil waste in a large area of the old industry, contaminating the subsoil in an im- portant extent. The soil contained about 14,000 mg of TPH/kg soil referring to heavy fraction (The analysis of the TPHs present in the soil was made by the suggested methodology in Mexican standard using dry soil). The maximum permissible limit established by Mexican regulations concerning contaminated soil with heavy fraction petroleum hydrocarbons suggests reducing the concentration of the site up to 6000 mg/kg. The main goal of this study was to characterize the sub-soil of the old automotive industry, in terms of TPHs, BTEX (benzene, toluene, ethylbenzene and xylene), PAHs (polycyclic aromatic hydrocarbons), and a set of metals as well as microbiologically. To show the suit- ability of SESW process to remediate the site, including surfactant type selection and concentration to be used in the processes. Finally, the generated wastewater was characterized in terms of COD (chemical oxygen de- mand), BOD (biochemical oxygen demand), solids, and other parameters in order to determine the kind of proc- ess most suitable to treat the effluent to recycle the water into the soil washing process or to be disposed at the end of the soil remediation process. 2. Materials and Methods 2.1. Soil Sampling The soil samples were taken from the subsoil of the site using a 25 SCRS Giddings model hydraulic punch (Fig- ure 1), taking samples from 1.5 to 3.0 m deep, extracting about 70 kilograms of wet soil, which were stored in polypropylene black bags to avoid photo-degradation of pollutants and placed into pet boxes were they were maintained at room temperature during a period of 2 weeks before the experiments. Soil was thoroughly mixed to assure that concentrations of TPH as well as other organic and inorganic components were uniform for the whole batch of soil. 2.2. Soil Characterization The composed soil sample was dried at room tempera- ture for 3 days. The final moisture content in the soil was determined 10%, measured by mass difference. The physico-chemical characterization of the soil was carried out including texture, bulk and particle density, pore space, total and bioavailable nitrogen and phosphorus and conductivity measurements. TPH’s, the 16 PAH (Polycyclic aromatic hydrocarbons) normed by USEPA and BTEX were also determined. Finally, some metals and metalloids concentrations (Na, K, Ca, Mg, As, Cd, Zn, Cu, Cr, Pb, Ni, Hg and Fe), were determined in the soil sample. The analyses were performed based on EPA Figure 1. (a) Hydraulic punch employed at the sampling process; (b) Helicoidal drilling device.
Surfactant-Enhanced Washing of Soils Contaminated with Wasted-Automotive Oils and the Quality of the Produced Wastewater Open Access JEP 1497 standard methodology suggested in Mexican regulations, for TPH content the methods were EPA 9071B and EPA1664A. The microbiological assessments were applied to the contaminated soil in order to determine the amount of present microorganisms. Plate counts were carried out using nutritive agar Petri dishes for heterotrophic bacteria count and for hydrocarbon degrading bacteria, diesel, gasoline or automotive-oil waste was employed as car- bon source. The mineral medium used was as follows (in mg/L): KH2PO4, 8.5; K2HPO4, 21.75; Na2HPO4 * 7H2O, 33.4; NH4Cl, 1.7; MgSO4 * 7H2O, 22.5 CaCl2, 27.5; FeCl3 * 6H2O, 0.25. These mineral media was adapted from the one suggested in a Mexican standard employed to determine BOD (NMX-AA-028 in NOM-001-SE- MARNAT-1996). The bacteria were incubated at 30˚C over a period of 48 to 96 hours for heterotrophic and hy- drocarbon degrading bacteria. The quantities of bacteria were expressed as a CFU/g of dry soil. 2.3. Washing Solutions Five anionic surfactants were used: sodium dodecyl sulfate (SDS), sodium bencen-dodecyl sulfonate (SDBS), Texapon N40 (TN40), Sulfopon30 (S30) and Surfacpol A14104. The five nonionic surfactants employed along this work were Tween 80 (TW80), Tween 20 (TW20), Span 80 (SP80), Brij 35 (B35) and Emulgin W600 (EW). Two zwitterionic products were employed: Polafix CAPB and Polafix LO. Finally, three natural gums (ca- pable to act as a surfactants/emulsifiers) were employed, i.e., locust bean gum (LGB), guar gum (G) and mezquite seed gum (MZ). Distillated water was used as a blank for soil washing assessments. Some characteristics of the employed surfactants are shown in Table 1. Two sets of soil washing experiments were performed; the first set was carried out using synthetic surfactants (anionic, nonionic and zwitterionic) concentrations of 0.5% and 0.1% for natural gums. In the second set of assessments, different concentrations of surfactants were tested of 0.25%, 0.5% and 1% for the synthetics surfac- tants and 0.05%, 0.1% and 0.2% for natural gums. 2.4. Soil Washing The SESW experiments were carried out in 40 mL glass vials, where 6 g of contaminated soil dried at room tem- perature were added together with 20 mL of the washing solution or water. The vials were shaken at 200 rpm for a period of 23 hours and, then, they allowed to settle for an hour. 2.5. Measurement of TPH’s in Soil Washing After washing the soils, supernatant was separated and stored in the freezer until further analysis. The washed soil samples were placed in aluminum trays to be dried at room temperature (25˚C) for 3 days. Then TPH’s con- centration was determined by a gravimetric method after Soxhlet extraction using hexane as a solvent, described in Section 2.2. Soil humidity was determined and taken into account to report mg of heavy fraction/g of dry soil using the methodology suggested in Mexican standards. Table 1. Some characteristics of the employed syntetic surfactants. Surfactant Ionic natureChemical name Mol weight (g/gmol)HLB CMC (mg/L) Reference SDS Anionic Sodium dodecyl sulfate 288.4 40 400 [13] SDBS Anionic Sodium dodecyl-bencenesulfonate322.37 NR 1.5 [14] Texapon 40 Anionic Sodium lauryl ether sulphonate 442 NR 1458 [13] Sulfopon 30 Anionic Sodium lauryl sulphate 272 NR 150 This work Surfacpol A14104 Anionic NR NR NR NR [14] Tween 80 Non-ionic Sorbitan monoleate (Poe 20) 1308 15 65.4 [13] Tween 20 Non-ionic Sorbitan monolaurate 1226 16.7 60.74 [13] Span 80 Non-ionic Sorbitan monooleate 428 NR NR Brij 35 Non-ionic Lauric alcohol ether 1206 16.7 NR [14] Emulgin W600 Non-ionic Nonyl phenol 483 11 45.06 [13] Polafix CAPB ZwitterionicCocoamide-propyl Betaine NR NR 80 [14] Polafix LO ZwitterionicNR NR NR NR - HLB: Hydrophilic Lipophilic Balance; CMC: Critical Micelle Concentration; NR: Not Reported.
Surfactant-Enhanced Washing of Soils Contaminated with Wasted-Automotive Oils and the Quality of the Produced Wastewater Open Access JEP 1498 3. Results and Discussion 3.1. Soil Characterization Table 2 shows some of the physical and chemical char- acteristics of the soil employed in this study. As shown the content of organic matter, nitrogen and phosphorus; are interesting because suggest the possibility of applying biological treatment to the resulting waste water. The moisture content of the soil was 40%. The conductivity of the soil was normal in the case of a clayish soil (0.3058 μS/cm), as well as the pore space percentage (66%). The report suggests that pH is mildly basic. The organic matter content indicates a moderately rich soil. However, the nitrogen content in the soil is poor, con- trasting with the very high contents of phosphorus. Met- als and metalloids concentrations in soil (Table 2), were reported were below the limits set in Mexican regulation. Two bacteria count processes were applied to the con- taminated soil, heterotrophs and hydrocarbon degraders (diesel, petroleum and automotive oil waste). The results showed an heterotrophic microorganisms count of 4.1 × 107 CFU/g. Regarding the specific degraders, values of 1 × 108 CFU/g, 1.5 × 108 CFU/g and 1 × 108 CFU/g were found for diesel, petroleum and automotive waste oil degraders, respectively. The microbial count was similar to that reported by Iturbe et al. [6] for a soil contami- nated with PAHs where bacteria counts of 1.8 × 108 CFU/g for heterotrophic and 5.4 × 108 CFU/g, 1 × 108 CFU/g and 5.6 × 108 CFU/g for diesel, petroleum and spent oil bacteria were reported. These values are higher Table 2. Physicochemical characteristics of the contami- nated soils. Parameter Result Parameter Result Conductivity 0.3058 µS/cm Pb 19.32 mg/kg pH 8.5 Fe 4432.65 mg/kg Apparent density 1.02 g/cm3 Zn 13.60 mg/kg Bulk density 3.0 g/cm3 Na 652.22 mg/kg Void space 66% K 949.65 mg/kg Soil percentual composition 60% clay 30% silt 10% sand Ca Mg As 23855.82 mg/kg 14401.59 mg/kg 1.78 mg/kg Texture Clayey Cd 2.80 mg/kg Organic matter 2.12 % Cu 6.73 mg/kg Total phosphorus 605.60 mg/kg Cr <1.0 mg/kg Available phosphorus 18.80 mg/kg Ni 9.87 mg/kg Total nitrogen 0.058% Hg 0.11 mg/kg Avail. nitrogen 9.93 mg/kg than those reported by Bogardt and Hemmingsen [15] for soils contaminated with diesel and petroleum oil (1.9 × 107 CFU/g and 3.3 × 107 CFU/g, respectively). On the other hand, Hernández-Espriu et al. [16] reported a bac- terial count of 2 × 1011 FCU/g for an agricultural soil contaminated with diesel. The observed amounts of mi- croorganisms are higher than the minimum necessary for biodegradation process (104) stated by Fahnestock [6,16]. Regarding the analysis of PAHs, BTEX and TPHs, it was found that only the heavy fraction hydrocarbons ex- ceeded the permissible limits established by Mexican legislation (Table 3). No BTEX were determined over the method detection limit and only two PAHs were found from the 16 PAH’s regulated by USEPA. These PAHs, however, were found with concentrations below the maximum permissible limits established in the Me- xican standards (Tabl e 4 ). No light fraction oil content in the media was found indicating that the contamination was due solely to automotive waste-oil spills. Despite the good performance and applications of sur- factants for the transference of hydrocarbons into water, the removal efficiency depends also on several factors including nature, amount of surfactants, age of contami- nated soil, soil properties and surfactant/oil/soil system behavior [10]. The highest removals were observed for Table 3. Mexican standards for PAHs, BETEX and TPHs. Maximum concentrations (mg/kg dry soil) Parameter Agricultural soil Residential soil Industrial soil TPHs Light fraction 200 200 500 Median fraction 1200 1200 5000 Heavy fraction 3000 3000 6000 BTEX Benzene 6 6 15 Toluene 40 40 100 Ethylbenzene 10 10 25 Xylene 40 40 100 PAHs Benzo (a) pyrene 2 2 10 Dibenzo (a,h) antracene2 2 10 Benzo (a) antracene 2 2 10 Benzo (b) fluorantrene2 2 10 Benzo (k) fluorantrene8 8 80 Inden (1, 2, 3, cd) pyrene2 2 10
Surfactant-Enhanced Washing of Soils Contaminated with Wasted-Automotive Oils and the Quality of the Produced Wastewater Open Access JEP 1499 Table 4. TPH’s and some PAH’s present in the contami- nated soils. Parameter Results (mg/kg) TPH’s (heavy fraction) 14,705 Benzo (k) fluoranthene 0.1280 Benzo (a) pyrene 0.0682 Sulfopon 30, Tween 20, CAPB Polafix and mezquite seed gum with 59%, 54%, 52% and 55% of TPHs re- moval respectively. Zamudio-Pérez et al. [17] reported TPHs removals of 57.7% when washing an oil-con- taminated soil, employing Brij 35 (Figure 2). They also tested natural gum as washing solutions. The best TPHs removal for natural gums was obtained with locust bean gum (31%). The second set of washing assessments different sur- factant concentrations was carried out with the best of each type except mezquite seed gum. The last was re- placed by guar gum because mezquite seed gum is not a commercial surfactant and its production method is com- plex. Three concentrations for every surfactant were eva- luated in the second washing procedure. It was observ- ed that Sulfopon 30 (0.5%) achieved the highest per- centage of removal 60%. Tween 20 (TW20) rendered removal efficiencies of 20%, 54% and 55% with solutions of 0.25%, 0.5% and 1% respectively. CAPB showed similar behavior, in this case, removals of 53% and 54% were achieved using concentration of 0.5% and 1% (Figure 3). Regarding the TPHs removal efficiency using guar gum, it was observed that the concentration of 0.1% pro- duced the best result, reaching 54%. Same result as in the first wash. It is noteworthy that although it was not the highest removal percentage the experimental set showed the greatest amount of TPHs removal per gram of prod- uct (Figure 4), as the washing solutions used has lower concentration than synthetic ones. In experiments made before, the standard deviations were not over the 5%, in this experiment the analysis showed the same behavior. 3.2. Characterization of the Generated Wastewaters The scaling-up of the washing process were carried out at the best conditions. In order to do that 16 k of soil were washed with Sulfopon 30 at 0.5%. Approximately, 40 L of wastewater were produced and characterized in terms of COD, BOD5, turbidity, electrical conductivity, color, hardness, MABS (methylene blue active substances), oils and greases, as well as 4 selected metals. Results are de- picted in Table 5 . As shown COD value was above 1300 Figure 2. TPHs removals for the 15 washing solutions and water. Figure 3. TPH’s removals when using different surfactants concentrations for SP30, TW20 and guar gum. Figure 4. TPH’s removals per mg of surfactant employed. mg/L which is below the reported by Bandala et al. [18] for refinery wastewater. Measured of BOD concentration was 380 mg /L generating a BOD5/COD ratio of 0.29 rating the wastewater as poorly biodegradable. Torres et al. [19] reported a rate of biodegradation on 41.7% (moderately biodegradable) of soil washing waste water from a site contaminated with hydrocarbons. The higher COD and BOD values obtained are due to the oil content
Surfactant-Enhanced Washing of Soils Contaminated with Wasted-Automotive Oils and the Quality of the Produced Wastewater Open Access JEP 1500 Table 5. Characteristics of the produ ced waste wate r. Parameter Result Zamudio Perez et al. [17]* Torres et al. [3] COD 1329 mg/L 1468.0 mg/L 20,153 mg/L BOD5 385 mg/L 289.6 mg/L 8410 mg/L BOD5/COD 0.29 0.197 0.41 Turbidity 1540 FAU 525 UNT NR Conductivity 1107 µS 2580.0 µS 1,353 µS Color 92 Pt/Co 3625 Pt/Co NR Hardness as CaCO3 489 mg/L 22.50 mg/L 337.31 mg/L MBAS 122 mg/L 0.015 mg/L 3368.0 mg/L Oil and greases 212 mg/L 6.0 mg/L 94.5 mg/L Pb 0.401 mg/L 20.13 mg/L 1.11 mg/L Fe 19.05 mg/L 11.25 mg/L 289.64 mg/L Cr 0.07 mg/L 0.023 mg/L 1.25 mg/L Al 24.21 mg/L 23.62 mg/L 429 mg/L *When using TW80. in the soil and the surfactant used in the washing pro- cedure. Differences in organic content for the wastewaters produced in this work, and those reported by Torres et al. [19] are significant. Nevertheless, it is important to re- mark that the produced wastewater characteristics will derive from several factors, i.e., 1) the soil type (sandy, loamy, clayey); 2) the contaminant type (light, medium, or heavy fractions in the case of oil derivatives); 3) the history of the contaminated soil, subjected to aging proc- esses (young versus old spills); 4) the efficiency of the washing system (surfactant type and concentration, soil/ water ratio, energy input). As observed, similar values for conductivity, hardness, the four selected metals and even for oil and greases were found. Important differences can be observed be- tween the wastewaters generated in this work, and those reported by Torres et al. [19], when comparing COD (15 fold), BOD (21.8 fold) and the BOD/COD value (1.4 fold). It is interesting to note that MABS and oil and greases values were rather different (27.6 and 0.44 fold, respectively). There is very little information on quality of wastewa- ters produced during the washing of contaminated soils; however, the characterization of these effluents is rele- vant regarding its treatment [17,19,20]. 4. Conclusions In the selection of a surfactant for a washing soil, it could be helpful to propose different type of surfactants to identify the higher removal of the contaminant. Also it is necessary to establish the concentration of the surfactant at the greater removal. The removal of TPH’s by soil washing vary for each type of surfactant, in this case, the greater removals were observed after using the SP30, however when looking at the milligrams of TPH removed for each gram of sur- factant employed, the natural gum removed more TPH, because the concentrations required were five times lo- wer. The characterization of the resulting water is rele- vant due to the treatment as suggested of the high rates of removal of TPH’s also the containing of the surfactant used in the washing process. Our research group is working on the treatment of the generated wastewaters in a low-cost packaging material submerged biofilter inoculated with hydrocarbon-degra- der microorganisms isolated from the original conta- minated soil. Besides, the changes in the biofilter mi- cro-flora due to the system operation (i.e., residence time, wastewater COD initial concentration and surfactant con- centration) are being evaluated using DGGE technology. 5. Acknowledgements Authors thank to S. Martinez and C. Serrano (Laborato- rio de Calidad de Agua y Residuos UAM-Azcapotzalco) because their help in the soil sampling procedure. The help of C. Orozco (UPIBI-IPN) in the production of the wastewaters in an agitated tank is also acknowledged. This work was financially supported by SEP-CONACyT (Grant 084080). REFERENCES [1] S. Paria, “Surfactant-Enhanced Remediation of Organic Contaminated Soil and Water,” Advances in Colloid and Interface Science, Vol. 138, No. 1, 2007, pp. 24-58. [2] L. G. Torres, J. L. Orantes and R. Iturbe, “Three Surfac- tants CMC and Diesel Removal Efficiencies from Highly Contaminated Sandy Soils Environment,” Geoscience, Vol. 1, 2003, pp. 28-36. [3] L. G. Torres, J. Orantes and L. R. Iturbe, “Biodegradation of Two Nonionic Surfactants Used for in Situ Flushing of Oil-Contaminated Soils,” Environmental Chemistry, Vol. 43, No. 5, 2006, pp. 251-255. [4] E. R. Bandala, Y. Velasco and L. G. Torres, “Decon- tamination of Soil Washing Wastewater Using Solar Driven Advanced Oxidation Processes,” Hazardous Ma- terials, Vol. 160, No. 2, 2008, pp. 402-407. doi:10.1016/j.jhazmat.2008.03.011http://dx.doi.org/10.10 16/j.jhazmat.2008.03.011 [5] M. M. Parnian and S. Ayatollahi, “Surfactant Remedia- tion of LNAPL Contaminated Soil; Effects of Adding Alkaline and Foam Producing Substances,” Iranian Jour-
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