Experimental Research on the Decontamination of Soils Polluted with Hydrocarbons

Transcription

1 Experimental Research on the Decontamination of Soils Polluted with Hydrocarbons MONICA EMANUELA STOICA*, LAZAR AVRAM, TUDORA CRISTESCU Petroleum - Gas University of Ploiesti, Drilling, Extraction and Transport of Hydrocarbons Department, 39 Bucuresti Blv., , Ploiesti, Romania Polluted soils decontamination with liquid petroleum products is one of the most complex environmental activities, both under theoretical and economical but also as organizational aspect. Choosing the right technology for an efficient decontamination of a soil polluted with oil products represents an important decision because of the large number of interactions that contributes on the final results. This paper presents the results obtained from the use of natural sorbents to decontaminate soils polluted with hydrocarbons. Keywords: depollution, contaminated site, sorption biodegradable products, hydrocarbons, decontamination efficiency Hydrocarbons extraction and transportation affects the environment both through the technological processes development themselves and also by some unwanted accidents that may occur [1, 8]. Physical methods of soil remediation are currently the most popular category for sites decontaminating. They consist in immobilizing of pollutants using adsorbents by encapsulation, by isolation, by stabilization or by inanimating and blocking of their migration, reducing the impact of pollution on the environment. These clean-up methods have been shown to be effective referring the degree that remediation is carried out. Currently, in Romania are mainly used, imported and also Enviropeat adsorbents, Nature Sorb or Sorb Spil based on dehydrated peat moss [2-5]. Composition and arrangement of soil components determine a number of qualities or properties that affect the retention and migration of pollutants, suggesting the possibility of decontamination. Nature Sorb absorbs and encapsulates oil products within the plant cells of the dehydrated peat moss that it contains. Also, there is taking place a biochemical process of breaking the chemical structures of the petroleum hydrocarbons by enzymes produced by the bacterial flora present in soil and water, humic acids playing the catalyst role. The adsorbent acts as a host to retain hydrocarbons and controls the biodegradation process. This process flows optimum in the presence of oxygen at temperatures of over 15 C, in the presence of the corresponding moisture and in the presence of nutrients like nitrogen, phosphorus and potassium [4]. The removal process of hydrocarbons from contaminated soils by using the natural biodegradable adsorbents is carried out by adsorption, through capillary action [6]. Petroleum products are retained within the peat pores by adsorption, peat acting as a sponge that collects the product by capillary phenomena and suction and allows the liquid to penetrate into its pores. In case of adsorbents for oil products, oleophilic walls (hydrophobic) of capillaries causes capillary rise of the pollutant and a capillary water leak. When the pollutant is in contact with the porous dry environment of the sorbent, it is adsorbed. Retention of the oil product pollutant is according to the size of pores, the superficial tension of the * monicastoica @yahoo.com liquid and the contact angle wetting of the surface in accordance with the law of Jurin [1]. (1) where: h represents the height of the liquid in the capillary, m σ - the interfacial tension between peat-oil phases, N / m θ - the contact angle r- the capillary radius, m ρ - the specific mass, kg/m 3 g - the gravity acceleration, m/s 2 Experimental part The experimental study was conducted in order to establish a method for remediation an area heavily polluted with hydrocarbons, situated in Prahova, near Ploieºti city using physical methods for decontamination. The experiments take into account to establish the optimum adsorbents quantities to be added in order to obtain the highest decontamination efficiency of removal of the hydrocarbons from the soil. The experiment lasted 90 days i.e. the first period (1-30), the second period (31-60) and the third period (61-90) Ṡampling was done according to law in force [9]. Samples have been taken from the contaminated soil situated in the vicinity of holes that were dug for extraction of fuel from pipelines, surface which lies between 1 and 3 m 2 around these holes, from two depths, namely from 5 cm to 30 cm. The number of samples was based on the contaminated areas. Were collected 10 contaminated soil samples and two blank assays, all sample denoted with S1, S12. Samples titles and collecting depths were recorded in table 1. Soil samples were collected with a sampling probe for agrochemicals. The amount of soil removal, of about 10 kg was transferred in polyethylene bags and bags were labeled. Transported to the laboratory, soil samples were prepared for analysis according to SR ISO 11464:1998, being dried in air, made mortar and sieved through at 2 mm grain size. 224

2 Table 1 CODES AND DEPTHS OF SOIL SAMPLES Table 2 CODES OF USED SAMPLES AND ADSORBENTS After analysis the quality indicators of 10 samples taken, there were chosen for laboratory experiments, four samples of soil contaminated with petroleum products, that were in various stages of pollution, depending on the concentration of pollutants and on their location in order to pursue the influence of the concentration of pollutants on the bioremediation process, namely the samples with P3, P4, P8, P9 code, properly S3, S4, S8 and S12. The soil samples have been divided into three equal portions, maintaining a thickness of about 20 cm of the soil, a weight of 2.5 kg and were treated as follows: one part left as a blank assay, in order to determine the initial concentration of the pollutant - samples code P3a, P4a, P8A, P9a, one part treated with biodegradable sorbent, Sorb-Nature-type samples code P3b, P4b, P8b, P9b, one part treated with natural adsorbents, beech sawdust type - code samples P3c, P4C, P8c, P9c. Samples codes are listed in table 2. To ensure a uniform contact between the polluted soil and used adsorbents, respectively to maintain optimal conditions of humidity and aeration of the soil samples water has been periodically added. Experimental conditions were kept the same throughout the whole period of the experiments development, namely: ambient environment temperature between 25 C and aeration of samples at 2 days for their homogenization and maintaining contact between pollutants and adsorbents. The experiments have ben carried out as natural as possible, without the addition of any additional nutrients (nitrogen, phosphorus) in order to reflect as real as possible the natural bioremediation processes, as far as permitted by the processes of the degradation of the hydrocarbons from oil, where, the components are present in complex mixtures. For decontamination of polluted soil with petroleum products has been designed and applied an empirical model based on hydrocarbons concentration, exposure time, adsorbent column height and decontamination efficiency process. To remediation were used: Nature- Sorb biodegradable sorbent added in order to meet the concentration ratio oil products: adsorbent = 1:3 and beech sawdust was added of oil products concentration: sawdust = 1:5. This resulted in 12 experimental tests, for which were used the quantities of adsorbent shown in table 3. Table 3 THE USED QUANTITY OF ADSORBENTS To monitor the biodegradation process, were conducted periodical analysis of the quality indicators of the experimental samples, namely: ph, total organic carbon (TOC) and total petroleum hydrocarbons (TPH). Samples for periodical analysis were taken after homogenization, to give a significant value for the quality indicators monitored [7]. For determination of ph was used a Mettler Toledo ph meter, InLab Cool type, with an accuracy of ± 0.01 ph units, with automatic calibration. Measurements were performed in compliance with standard provisions SR ISO 10390:1999. For the analysis of total petroleum hydrocarbons (TPH) extraction method was used with a highly volatile solvent, followed by solvent recovery by distillation and gravimetric determination of the residue of the extract, according to SR ISO 14507:2000 and SR 7877/ Total organic carbon was determined using the Elementary VARIOTOC CUBE analyzer through the high temperature combustion method. The principle of the method consists in the oxidation of the carbon bound to the carbon dioxide. Solid samples were weighed and placed into the analyzer by means of a ball - valve in the REV. CHIM. (Bucharest) 65 No

3 Table 4 INITIAL QUALITY INDICATORS OF SOIL SAMPLES Table 5 QUALITY INDICATORS OF SELECTED EXPERIMENTAL SAMPLES BEFORE TREATMENT BEGINNING combustion tube at 900 C, in the presence of oxygen as a carrier gas. The gas formed by combustion is dried, stabilized in terms of flow rate and measured in a cell-ir. Depending on the detected signal of CO 2, shall be calculated the total organic carbon content from the sample (TOC). The result is expressed in percentage of dry matter (% d.m.). Setting the hydrocarbon composition of the soil samples was performed with AGILENT 6890N-MSD gas chromatography system consisting of: 6890N Agilent Technologies gas chromatograph (with a maximum programming speed of 120 o C/min., temperature range: o C, accuracy: ± 2 %, repeatability: ± 0.05 psi, flame ionization detector (FID) specifically optimized for capillary columns); mass detector (MSD) Agilent Technologies 5975 inert XL with electron impact, inert ionization source and scanning SIM / SCAN synchronously. Results and discussions The initial values of the quality indicators: ph, total organic carbon (TOC) and also total petroleum hydrocarbons content (TPH) determined for the soil samples collected prior to treatment beginning, are shown in table 4. Of the ten samples collected, four samples were selected, depending on the state of pollution, the concentration of pollutants and their location. 226 After analyzing the results obtained and presented in table 4, we can see the following: - the values for total petroleum hydrocarbons (TPH) in the analised samples exceed the alert threshold of 1000 mg / kg d.m. for samples with S1-S12 codes and exceed intervention threshold of 2000 mg / kg d.m. for samples with S10, S11, S12 codes; - a soil with a concentration of TPH greater than 1000 mg / kg d.m. or greater than 0.01% TPH is considered to be contaminated and needs remedial, so that, for the analised samples it is need to be made a treatment for decontamination; - TPH analysis from the soil indicates the contamination level, but does neither indicate the type of existing hydrocarbons nor the concentration of each of them; - establishing the existing hydrocarbons types and of their concentration in the collected samples was performed by the method of gas chromatography coupled with mass spectrometry method; - GC-MS analysis has demonstrated that in the taken soil exist in relevant concentrations diesel and mineral oils (C 20-C 40), heavy fractions, relatively stable, which migrate less than in the ground, both horizontally and vertically; - the values of ph are situated within the normal limits, neutral to slightly alkaline, i.e. between 6.5 and 8.5 ph units;

4 Table 6 QUALITY INDICATORS ANALYSIS RESULTS FROM THE SAMPLES COLLECTED DURING THE I st PERIOD Table 7 QUALITY INDICATORS ANALYSIS RESULTS FROM THE SAMPLES COLLECTED DURING THE II nd PERIOD Table 8 QUALITY INDICATORS ANALYSIS RESULTS FROM THE SAMPLES COLLECTED DURING THE III rd PERIOD Quality indicators determined for experimental samples selected before treatment beginning, are presented in table 5. The analysis outcomes of quality indicators on samples taken during the three periods are presented in tables 6-8. Analyzing these results it appears that: ph values were maintained in the neutral to slightly alkaline domain throughout the course of the experiment, having values ranging between: 6.75 and 7.54, but they are higher for the samples treated with sawdust. Yields obtained in the decontamination process of the contaminated soil with hydrocarbons during the experiment development, are presented in table 9. Analysing the results in table 9 are found decreased concentration levels of the total petroleum hydrocarbons for all the 12 experimental samples; high efficiency to REV. CHIM. (Bucharest) 65 No

5 Table 9 DECONTAMINATION EFFICIENCY OBTAINED DURING THE DECONTAMINATION PROCESS OF THE OIL PETROLEUM PRODUCTS DURING THE EXPERIMENT DEVELOPMENT reduce the concentration of oil product was recorded for samples treated with biodegradable sorbent (code b). Lower efficiency decontamination is recorded regarding the samples treated with beech sawdust (code c). Conclusions As discussed above no single technology is appropriate for all contaminant types and the variety of site-specific conditions that exist at different contaminated sites. Site conditions, contaminant types, contaminant source, source control measures, and the potential impact of the possible remedial measure determine the choice of a remediation strategy and technology. Often more than one remediation technology is needed to effectively address most contaminated site problems. The selection of one or more particular remediation technologies for a contaminated site is crucial in decision making. Decontamination efficiency have been growing steadily during the 4 months of the experiment development. For the samples treated with biodegradable sorbent were registered decreases near to the alert threshold, which indicates either continued treatment or modification of the initial report. By using the type beech sawdust natural sorbent were decreased initial TPH concentrations to values of about mg / kg d.m., which is above the alert threshold imposed by the legislation, namely 1000 mg/kg d.m., but below intervention threshold of 2000 mg/kg d.m. for soils of less sensitive use. Decontamination efficiency have been growing steadily during the 3 periods of the experiment development, thus obtaning values ranging from 30 to 31% by using the biodegradable sorbent and by 20 to 25% upon using beech sawdust. 228 The technology can be further studied in detail for obtain a more effective decontamination. References 1. ONUÞU, I., JUGÃNARU, T., Petroleum and petrochemical pollutants, Petroleum- Gas University Ploiesti, 2010, p BOGZA, P., Study on the use of natural sorbents for remediation of soil contaminated with petroleum and petroleum products, Research project for young people, type At, 2004, p STOICA, M., contributions on effective methods of remediating soil and footers contaminated with hydrocarbons, PhD Theses, Petroleum- Gas University Ploiesti,, PÃTRAªCU, C., AVRAM, L., STOICA M., Characterization of adsorbents used in depollution technologies of soils and surface waters contaminated with petroleum products, International Symposium Mineral Resources and Environment Engineering, North University of Baia Mare, 2008, p PÃTRAªCU, C., AVRAM, L., STOICA M., The impact analysis of the oil and petroleum product transport through pipes on the environmental, International Symposium Mineral Resources and Environment Engineering, North University, Baia Mare, 2008, p ROCCO, F., PIN, M., New Bioremediation and phytoremediation for soil decontamination: Experiences and perspectives, In: Urban Technology Network Project. Iniziativa Communitaria Interreg II C CADSES, 2000, p RISER-ROBERTS E., Remediation of Petroleum Contaminated Soils, Lewis Publishers, London, 1998, p DUMITRAN, C., ONUÞU, I., Environmental Risk analysis for crude oil soil pollution, Carpathian Journal of Earth and Environmental Sciences, April 2010, Vol. 5, No. 1, p *** STAS 7184/ STAS 7184/1-84 Soluri. Recoltarea probelor pentru studii pedologice ºi agrochimice Manuscript received: