Chemical-Biological Stabilization Method for Treatment of Drilling Cuttings and Hydrocarbon Contaminated Soil ABSTRACT

Chemical-Biological Stabilization Method for Treatment of Drilling Cuttings and Hydrocarbon Contaminated Soil Dr. Randy H. Adams Juarez Autonomous Uni...
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Chemical-Biological Stabilization Method for Treatment of Drilling Cuttings and Hydrocarbon Contaminated Soil Dr. Randy H. Adams Juarez Autonomous University of Tabasco (UJAT), Academic Division of Biological Sciences Km 0.5 Carretera Villahermosa – Cárdenas, Villahermosa, Tabasco, México CP 86104 Tel.: (52-993) 391-6538, Fax: (52-993) 354-4308 e-mail: [email protected]

ABSTRACT A simple but effective treatment method was investigated. The original method consisted of mixing in sawdust, hydrated lime and organic rich river levee soil, extending it in a thin layer, and planting grasses, after which the material was allowed an extended maturation phase. Several modifications were made to the method consisting of: 1) altering the dosage of chemical reagent, 2) changing the order in which the chemical and organic materials are added, 3) avoiding addition of soil, 4) using alternative organic conditioners, and 5) modifying the dosage of organic conditioners. These changes resulted in material stabilization (reducing TCLP leachates to less than 1 ppm TPH), improved pH recovery (down to 7.7 in ten months), complete reduction in acute toxicity, and simplified logistics in terms of material additions. These modifications have been incorporated into a technological package ready for remediation scale implementation which is currently under application for patent.

INTRODUCTION Many of the soil remediation technologies internationally used and accepted today (such as land farming bioremediation) started out as simple methods developed by petroleum personnel trying to solve their environmental problems. These methods were derived by trial and error in field scale applications, long before the scientific basis for their use was understood (1). In many developing regions of the world, simple methods continue to be used, often with variable results. For the proper application of these methods, they need to be scientifically tested and optimized, and the physical, chemical and biological mechanisms employed therein better understood. In many tropical regions, this situation is further complicated by attempts to import remediation technology developed in temperate countries. Environmental conditions, such as high rainfall, often cause problems with reagent distribution and inadequate aeration. Furthermore, social and economic conditions vary greatly. In many tropical societies fine attention to detail is not part of the culture and technologies in which such attention is required frequently meet with questionable results. For these reasons it is necessary to develop remediation and treatment technologies applicable to developing regions and which consider these environmental and cultural differences (2). One simple method that has recently been developed in the Gulf of Mexico, especially in Veracruz, Tabasco and northern Chiapas states, is a chemical - biological stabilization method (3). Based on field observations, Pemex personnel in the Poza Rica (Veracruz) area, looked to develop a simple method for the treatment of waste pits. This method involved mixing together semisolid oily waste with lime, sawdust, and with organic rich river levee soil. These ingredients were thoroughly mixed and subsequently extended in a thin layer to a depth of roughly 20 – 40 cm (4). Finally, the material was planted with grass, or local weedy species were allowed to take root. In field applications, after roughly nine to twelve months, the material lost is oily appearance and the vegetation grew profusely, however, these treatments were not evaluated scientifically with respect to hydrocarbon mass reduction, toxicity, or soil leachates. Furthermore, the method had not been technically optimized prior to this study.

CHEMICAL REAGENT OPTIMIZATION We conducted a series of experiments in which the dosage of the chemical reagent, in this case hydrated lime, was evaluated for reductions in hydrocarbon mass (5). Previously, different reagent proportions of the components in the mixture had not been evaluated scientifically, and reductions had only been evaluated in terms of overall hydrocarbon concentration, not mass. However, environmental authorities questioned the reasonableness of this method, considering that the additions of the chemical and organic reagents, and river levee soil, were principally diluting the hydrocarbons in the mixture, rather than actually reducing the overall amount of hydrocarbons. Using drilling cuttings (TPH = 6.9 %), these experiments showed that at least four percent (w/w,

dry) of lime was required to significantly reduce the apparent hydrocarbon mass in the mixture. Increased concentrations of lime (> 4 %) did not improve the process, but elevated the alkalinity drastically (pH > 10.2, see figure 1). During these tests, a control in which no sawdust was added proved superior in terms of hydrocarbon mass reduction, but the pH was extremely high (>12). These results suggested that: 1) the sawdust was important in mitigating the high alkalinity of the lime, but that 2) it may interfere in the chemical reaction between the lime and drilling cuttings. For this reason we repeated the experiment, using four percent lime and sawdust, but adding the sawdust three days after the lime, to allow for complete reaction between the lime and the drilling cuttings. This modification proved to provide the greatest reduction in hydrocarbon mass (up to about 44 %) which was repeatable at a pilot scale (49 %).

ORGANIC AMENDMENT SELECTION Originally, the only organic amendment employed in this method was sawdust, but we investigated the use of alternatives which may be more easily obtainable in tropical climates, especially agricultural waste that can be readily collected during processing. These alternative amendments were added to drilling cuttings at a pilot scale after applying lime using the optimal dosification regime outlined above. These treatments were monitored for hydrocarbon mass removal, pH, acute toxicity using the Microtox assay, EPA carcinogenic polyaromatic hydrocarbons (PAHs), and TCLP leachates (6). All three treatments lead to an apparent hydrocarbon mass reduction of approx. 2/3 within less than five months. However, the treatment using sawdust was not as stable and after eight months some of the sequestered hydrocarbons were more easily extracted, causing an apparent increase in hydrocarbon mass. Furthermore, this treatment (with sawdust) was inferior to the other treatments with respect to pH recovery. After eight months the pH in this treatment was greater than ten and native weeds and grasses grew poorly, whereas in the other two treatments the pH was 7.5 – 8.0 after eight months and grasses grew profusely. Furthermore, the acute toxicity was completely eliminated in these two treatments, and the material presented less than 1 ppm TPHs as TCLP leachates (7, 8). Upon treatment cell dismantling, the material presented a structure and earthy odor typical of organic rich soil. Based on these observations the material was considered stabilized and in compliance with Mexican environmental legislation (9, 10, 11; see Table 1).

ORGANIC AMENDMENT OPTIMIZATION The organic amendment most promising in terms of pH control, hydrocarbon sequestering, toxicity reduction and TCLP leachates (organic alternative 2) was studied in further detail to determine if a different dosing regime would be as effective for the stabilization of drilling cuttings and hydrocarbon contaminated soil. A mixture of mineral soils and drilling cuttings from previous diagnostic work was treated using the optimal chemical reagent dosage previously mentioned and

the organic amendment was added at 9 % (w/w, dry) and 4 % (w/w, dry). This test showed that the lower concentration was practically as effective in hydrocarbon sequestering, pH mitigation, and toxicity control (12, see Table 2).

SITE SPECIFIC APLICATIONS This method is currently being investigated for application at two sites in western Tabasco state and southern Veracruz state.

La Venta Gas Processing Complex The first site being studied is behind a former refinery, were inadequately treated waste water was discharged into a marshy area. Due to long term chronic contamination, approximately eleven hectares at this site became completely devoid of vegetation. The TPH concentrations at this site varied from levels in the low percent range, up to over 20 % in some places. Furthermore, the site had also become contaminated with salts in the process water. In some areas the salt (NaCl) concentration was in the four to eight percent range. The contaminated soil has a loamy texture and also high concentrations of naturally occurring organic material (approx. 20 – 60 %). Nearby vegetation consisted of salt marsh, cattail marsh, and white mangrove (13, 14; see figure 2). Soil was collected and treated first chemically, to reduce the overall salt levels and sodium levels (see figure 3). Subsequently, this material was stabilized, at a pilot scale, using the chemical – biological method. Initially, the treated material appeared to still produce slightly oily leachates. It is probable that the increased quantities of naturally occurring organic material in the soil partially interfered with the chemical stabilization. Therefore, a subsequent treatment was applied to the material, after which, no oily leachate was observed (see figure 4). The toxicity in this material was reduced to below background levels (15), and hydrocarbons levels in TCLP leachates were < 1 ppm TPH. The final pH of the treated material was 8.3, near local maximums (14, see Table 3). After treatment, a salt tolerant sedge (marsh fimbry), naturally occurring in the adjacent salt marsh was transplanted into the treated material (see figure 5). After an initial post-transplant stress, these plants became adapted to the medium and began generating shoots from the established roots (16, see figure 6).

Texistepec Mining Unit The second site where this technology is being tested is the shore area of an artificial lake, previously used to collect acid leachate from a tailings pile at a sulfur mine. Associated with residual sulfur in the tailings are weathered hydrocarbons, originating from the salt domes from which the sulfur was extracted. The lake was previously treated chemically to neutralize the acid, but approximately ten hectares of beach area are still contaminated with hydrocarbons (19, see figures 7 and 8) . This technology is being considered for sediments in the range of approx. 50,000 – 60,000 ppm TPH.

In treated material the toxicity was completely reduced and in some samples was even stimulatory to the test organisms used in the bioassay. TCLP leachates were completely eliminated from the material (see Table 4). Subsequently a tropical C4 grass was planted in the treated material from seed. This species (humidicola grass), is originally from Africa but now is commonly used in the American tropics for cattle ranching. After a few weeks this grass had taken root, and other plant species from the nearby environment had also colonized the treated material (see figure 9). Currently, this process continues to be monitored to determine vegetative regeneration and toxicity reduction during a phyto-restoration phase (20).

CONCLUSION This remediation technology originated with petroleum personnel trying to develop a simple method to treat oil contaminated waste pits, based solely on empirical observations. Under certain circumstances, this method in its original form, was probably sufficient for site cleanup. However, without proper testing, this could not be scientifically proven. Our studies have shown that this technology, with some modifications, works when evaluated as a stabilization method instead of a toxic substance reduction method. The strategy used in stabilization methods is to immobilize potential contaminants in the soil matrix, thereby reducing bioavailability (and hence toxicity) as well as possible leachates which may latter contaminate groundwater sources (21). Using these criteria, this method does indeed result in site remediation. It is a simple, economical and effective method applicable for site cleanup in humid tropical and subtropical areas.

ACKNOWLEDGEMENT I would like to thank José Abisenas Álvarez Rivera, Francisco Javier Guzmán Osorio and Elias Francisco Sigala Carduña for their valuable assistance with laboratory and pilot scale studies, and Verónica Isidra Domínguez Rodríguez for her constant support and encouragement. I would also like to thank Conrado Tinal Ortíz for his assistance with remediation experiments in soil from La Venta.

REFERENCES CITED 1.

King R. B., Long, G. M., and Sheldon, J. K. Practical Environmental Bioremediation. Boca Raton, Florida, Lewis Publishers (1992).

2.

Adams S., R. H., Domínguez R., V. I, García H., L., “Potencial de la Biorremediación de Petróleo en el Trópico Mexicano,” Terra, 17 (2), 159 – 174 (1999).

3.

PEMEX Exploración y Producción – SIPA, “Tratamiento de Residuos Aceitosos y Restauración de Áreas Afectadas por Hidrocarburos,” Distrito de Poza Rica, Veracruz, México, Petróleos Mexicanos, Seguridad Industrial y Protección Ambiental (SIPA) (1995).

4.

Arroyo A., L., “Saneamiento Ecológico en Presas de Terracerías Impactadas por Hidrocarburos y Desechos de Perforación (Alternativa),” Distrito Cárdenas, Tabasco, México, PEMEX Exploración y Producción - SIPA, Gaceta Ecológica, 12 –14 (1997).

5.

Adams, R. H., “Chemical – Biological Stabilization of Hydrocarbon Contaminated Soil and Drilling Cuttings in Tropical Mexico,” Land Contam. Reclam., 12 (11) in review (2004).

6.

Adams S., R. H., “Validación y Optimización de la Técnica “Química-Biológica para el Tratamiento de Desechos Aceitosos” Informe Final, Proyecto 99-06-005-T, Villahermosa, Tabasco, Sistema Regional de Investigación SIGOLFO-CONACYT/Universidad Juárez Autónoma de Tabasco (2001).

7.

Secretaría de Comercio y Fomento Industrial (SECOFI), “Norma Mexicana NMX-AA112-1995-SCFI, Análisis de Agua y Sedimento - Evaluación de Toxicidad Aguda con Photobacterium phosphoreum - Método de Prueba,” México, D.F. (1995).

8.

Secretaría de Desarrollo Social, “Norma Oficial Mexicana NOM-053-ECOL-1993, Que Establece el Procedimiento para Llevar a Cabo la Prueba de Extracción para Determinar los Constituyentes que Hacen a un Residuo Peligroso por su Toxicidad al Ambiente,” México D.F., Diario Oficial de la Federación de fecha 22 de octubre de (1993).

9.

Secretaría de Medio Ambiente, Recursos Naturales y Pesca (SEMARNAP), “Ley General de Equilibrio Ecológico y Protección al Ambiente,” México, D.F., Diario Oficial de la Federación de fecha 28 de enero de (1988).

10.

Secretaría de Medio Ambiente, Recursos Naturales (SEMARNAT), “Ley General para la Prevención y Gestión Integral de los Residuos,” México, D.F., Diario Oficial de la Federación de fecha 8 de octubre de (2003).

11.

Secretaria de Medio Ambiente, Recursos Naturales y Pesca (SEMARNAP), “Norma Oficial Mexicana NOM-001-ECOL-1996, Que Establece los Límites Máximos Permisibles de Contaminantes en las Descargas de Aguas Residuales en Aguas y Bienes Nacionales,” México, D.F., Diario Oficial de la Federación de fecha 6 de enero de (1997).

12.

Adams, R. H. and Alvarez R., J. A. “Improved Stabilization Method for Hydrocarbon Contaminated Soil and Drilling Waste Using Lime and Cachasse,” Land Contam. Reclam., 13, in prep. (2005).

13.

Adams S., R. H. y Domínguez R., V.I. “Estudio de Riesgo Toxicológico”, En: “Caracterización de Suelo, Subsuelo y Mantos Freáticos Contaminados en el CPG La Venta,” No. Cto.:SPGRAFCS312/00, Villahermosa, Tabasco, Corporación en Ingeniería Ambiental/Pemex Gas y Petroquímica Básica (2000).

14.

Adams S., R.H., Castillo A., O., Zavala C., J., Palma-López, J. D. “Recuperación con Mangle Blanco (Laguncularia racemosa) de Áreas Impactadas por Hidrocarburos y su Manejo como Agrosilvoecosistema en la Zona Costera de Huimanguillo y Cárdenas, Tabasco,” Proyecto No. M076. México, D.F., Comisión Nacional para el Conocimiento y Uso de la Biodiversidad y The John T. and Catherine D. MacArthur Foundation (1999).

15.

Adams S., R. H., y Ricalde Z., S. Del C., “Determinación de Toxicidad en Suelos Representativos del Activo de Producción Petrolera Cinco Presidentes, Veracruz y Tabasco,” Rev. Inter. Contam. Ambient., en revisión (2004).

16.

Adams S., R. H., Álvarez R., J. A. y Tinal O., C. “Remediación de Suelo Pantanoso Contaminado con Agua Congénita y Petróleo de la Venta, Tabasco” presentado en el XXXV Congreso Anual de la Sociedad Mexicana de la Ciencia del Suelo, León, Guanajuato, México (Noviembre 8-10, 2004).

17.

Cornelio G., Y de J., “Evaluación Preliminar de Toxicidad por Plaguicidas (Mancozeb) en Agua y Sedimentos en la Zona Platanera del Río Teapa, Tabasco, México,” Tesis de Licenciatura en Ingeniería Ambiental. Villahermosa, Tabasco, México, División Académica de Ciencias Biológicas, Universidad Juárez Autónoma de Tabasco (2001).

18.

Sigala C., E.F. “Evaluación y Refinación del Método ECOTEC-SPB para el Tratamiento de Recortes de Perforación y Remediación de Suelos Contaminados con Hidrocarburos,” Tesis de Licenciatura en Ecología. Villahermosa, Tabasco, México, División Académica de Ciencias Biológicas, Universidad Juárez Autónoma de Tabasco (2004).

19.

Universidad Nacional de México, Instituto de Ingeniería, “Diagnóstico de las Presas Existentes en la Unidad Minera Industrial Texistepec,” México, D.F., UNAM/Pemex Gas y Petroquímica Básica (2002).

20.

Guzmán O., F. J., Adams, R. H., and Avila G., J., “Comparison of Biostimulation, Bioaugmentation and Chemical-Biological Stabilization for Remediation of Hydrocarbon Contaminated Sediments,” presented at the 11th International Environmental Petroleum Conference, Albuquerque, N.M., USA (October 11-15, 2004).

21.

Al-Tabbaa, A. and Evans, C., “Deep Soil Mixing in the UK: Geoenvironmental Research and Recent Applications,” Land Contam. Reclam. 11 (1), 1 – 14, (2003) .

Table 1. Hydrocarbon stabilization with alternative organic amendments.

Amendment

% TPH reduction mass basis (final TPH conc.)

Final pH

Toxicity

TCLP Leachates (TPH, ppm in leachate)

Leachate Characteristic

Sawdust

41 % (final = 20,900 ppm)

10.3

Non toxic

< 0.3

Organic Alternative 1

56 % (final = 15,500 ppm)

8.0

Stimulatory*

Average = 0.6



Organic Alternative 2

56 % (final = 15,600 ppm)

7.7

Stimulatory*

Average = 0.6



No o ily f lavor , slight clayey flavor due to bentonite in drilling mu d s

* the test organism used in the bioassay (Microtox) was not only not affected by the treated material, but its activity was greater in the presence of the treated material than in tests blanks.

Table 2. Hydrocarbon stabilization with different organic amendment concentrations. Amendment concentration

% TPH reduction (mass basis)

Final % TPH

Final pH

Final Toxicity

Treatment period

9%

49

1.23

7.7

Non toxic

170 days

4%

52

1.24

7.7

Non toxic

170 days

Table 3. Hydrocarbon stabilization in soil from La Venta. Lot number

% organic material

Toxicity RTI-10*

Final pH

TCLP leachates (TPH, ppm)

1

21

~5 (non toxic)

8.3

non detect

2

56

9.8 (non toxic)

8.3

background

18 - 68

6.6 - 7.8 10 – 11.2 (regional soils)

non detect – 0.9

---------

* Relative Toxicity Index – 10. Index of toxicity normalized to background for regional soils. A value of 10 = non toxic, 5 ≈ ½ background toxicity, 20 = 2 x background toxicity. Source: refs. 17 and 18. Treatment: • • • •

Chemical pretreatment to reduce salinity Stabilization treatment to immobilize hydrocarbons and reduce toxicity Material required repeat treatment due to high concentrations of organic material Treated material planted with marsh sedge

Table 4. Hydrocarbon stabilization in soil from Texistepec.

Lot number

Treatment

Toxicity

1

Stabilization treatment to immobilize hydrocarbons and reduce toxicity

Non toxic, stimulatory

Treated material planted with humidicola grass

RTI-10 ≈ 2- 5

none

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