Elsevier

Bioresource Technology

Volume 105, February 2012, Pages 31-39
Bioresource Technology

Environmental strategies to remove volatile aromatic fractions (BTEX) from petroleum industry wastewater using biomass

https://doi.org/10.1016/j.biortech.2011.11.096Get rights and content

Abstract

This work investigates the potentials of peat and angico hardwood sawdust to remove BTEX (benzene, toluene, ethylbenzene, and isomers of xylene) from the produced water discharged into aquatic systems during petroleum extraction. Peat and angico sawdust samples were pyrolyzed at 500 °C, and found to contain n-alkenes, n-alkanes and pentacyclic triterpenes (peat), and 4-methoxyphenol, 1,4-dimethoxyphenol and 1,3,4-trimethoxyphenol (angico sawdust). In batch experiments, the removal capacities using peat were 32.4%, 50.0%, 63.0%, 67.8%, and 61.8% for benzene, toluene, ethylbenzene, m,p-xylenes and o-xylene, respectively. This compared with removal capacities using angico sawdust of 20.2%, 36.4%, 52.8%, 57.8%, and 53.7% for these compounds respectively, demonstrating the superior performance of the peat.

Highlights

► Environmental strategies to remove BTEX from petroleum industry wastewater. ► Use of natural material and an industrial byproduct for wastewater treatment. ► Use of off-line pyrolysis analysis is a useful tool for the characterization of adsorbent composition. ► Peat and angico sawdust samples were effective for removal of BTEX from produced water.

Introduction

Oil and gas extraction is a potential source of contamination of the air, water, and soil. Distribution networks can also be a source of pollution, notably from leaking underground storage tanks at gasoline stations and other distribution points, industries and domestic residences (Namkoong et al., 2003). This can result in the contamination of groundwater by hazardous volatile organic compounds, including benzene, toluene, ethylbenzene, and the xylene isomers (commonly termed BTEX). These compounds account for 20–40% of the total concentration of volatile organic compounds (VOCs) present in outdoor urban environments, and are the organic compounds most commonly monitored in the European Union countries (Zalel et al., 2008).

According to the Organization of Petroleum Exporting Countries (OPEC, 2011), demand for energy has increased from 55 million barrels of oil equivalent/day (mboe/day) in 1960 to 227 mboe/day in 2008. Energy demand will continue to increase as economies expand, the world population grows, and living conditions improve. In Brazil, substantial new petroleum reserves have been discovered in the deep water of the Santos Basin. These so-called “pre-salt” oil reservoirs cover an extensive area, are up to 300 m thick, and comprise limestone and shale formations underlying a substantial layer of salt (Agência Nacional do Petróleo, 2010). There are clear environmental concerns related to the exploitation of new reserves, both here and elsewhere, given the global background of increasing petroleum production and demand.

In addition to potential contamination due to oil, the extraction of petroleum and gas is usually accompanied by the generation of large quantities of wastewater (produced water), which is the principal waste material involved in the extraction process. This is exacerbated by the fact that many oil deposits lie near groundwater aquifers. During the lifetime of the oilfield, the volume of produced water generated can be 7–10-fold the volume of oil produced (Stephenson, 1992).

The chemical composition of this wastewater is influenced by the nature of the geological formation. Produced water can contain various toxic compounds of natural origin, such as volatile aromatic fractions of the oil (including BTEX), polycyclic aromatic hydrocarbons (PAHs), organic acids, phenols and alkylated phenols, metals and radionuclides, as well as a very high salt concentration (Dórea et al., 2007).

Aromatic compounds, including monoaromatic hydrocarbons such as BTEX, are amongst the principal contaminants of produced water. Human exposure to these compounds can lead to health problems ranging from irritation of the eyes, mucous membranes and skin, to weakened nervous systems, reduced bone marrow function and cancers. Benzene in particular is highly toxic, and is classified by the World Health Organization as a strong carcinogen, occupying sixth place in the list of dangerous substances (Mathur et al., 2007).

The United States Environmental Protection Agency has established maximum permissible levels of these contaminants in water destined for public supply of 0.005 mg L−1 (benzene), 1.0 mg L−1 (toluene), 0.7 mg L−1 (ethylbenzene) and 10 mg L−1 (total xylenes). In Brazil, the maximum values established by the Brazilian National Environment Council for discharges into water bodies are 5 μg L−1 (benzene), 2 μg L−1 (toluene), 90 μg L−1 (ethylbenzene) and 300 μg L−1 (xylenes) (CONAMA, 2000).

There is a general lack of cost-effective methods for the removal of organic contaminants from water. Biosorption offers an alternative removal technique, and the use of natural materials as well as industrial or agricultural byproducts has shown promising results for both organic and inorganic pollutants (Namkoong et al., 2003, Batista et al., 2009, Cunha et al., 2010, Jesus et al., 2011). Advantages of these materials include their abundance and low cost (since they have little aggregate value, compared to synthetic adsorbents).

Previous work has detected BTEX in produced water from oilfields in the State of Sergipe (Dórea et al., 2007). The present paper presents methodologies for the removal of BTEX present in produced water, using peat (an organic soil formed during the decomposition and humification of plant residues by microbiological oxidation in flooded environments) and an industrial byproduct (angico hardwood sawdust). The method was validated and optimized in batch adsorption experiments, and off-line pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was used to elucidate the chemical composition of the adsorbent materials.

Section snippets

Sample collection and preparation

The peat sample was collected from a peat bog in Santo Amaro das Brotas, Sergipe State, Brazil. The sample was air-dried, ground using a pestle and mortar, and sieved first through a 9-mesh grid to remove roots and twigs, and then through a 48-mesh grid to obtain a uniform particle size. White angico (Anadenanthera colubrina) sawdust was collected from a sawmill in the city of São Cristóvão, Sergipe State. The samples were washed and then dried at room temperature. The samples used in the

BTEX determination

Different purge-and-trap system and gas chromatography parameters were investigated in order to identify the best conditions for peak separation and identification. These included the purge time and temperature, the dry purge time, desorption time and temperature, transfer line temperature, carrier gas flow rate, column temperature program and detector temperature. Once these parameters had been optimized, it was possible to measure the retention times and peak areas corresponding to all of the

Conclusions

The adsorption capacities and removal rates indicated that the peat was more effective than the sawdust for removal of BTEX from aqueous media. This suggests that peat might also be the preferred adsorbent for the removal of other organic compounds. Nonetheless, both of the adsorbents investigated were effective for removal of BTEX from produced water. This is an important finding, since neither of the adsorbents were subjected to any form of chemical pretreatment.

Acknowledgements

The authors are grateful to CNPq (Process N° 556665/2009-0) and PRH ANP 45 for the provision of grants.

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