The hydrocarbons can be chemically divided into aromatics and aliphatic families. The aromatic compounds consist of one or more benzene rings. Benzene
(C6H6) is a compound that consists of six carbon and six hydrogen atoms. The
simple aromatic environmental pollutants are benzene, ethyl benzene, toluene, and
xylene (ITRC 2003). The aliphatic can be further divided into the alkanes, the
alkenes, and the cycloalkanes groups. The constructed wetland can play a significant
role in the degradation of these hydrocarbons. Benzene is a primary component of
petroleum-based fuels and used in manufacturing processes. Benzene is toxic,
persistent, mobile, and soluble in surface water as well as in groundwater and less
biodegradable in the absence of oxygen (Coates et al. 2001).
The petroleum hydrocarbons extraction process consists of several steps such as
exploration, production, refining, storage, transportation, distribution, and utilization
which cause the contamination of water, sediments, and soil (Atlas and Cerniglia
1995). Energy play important role in economic growth and the increase use of
petroleum hydrocarbons can disturb the ecosystem including biotic and abiotic
components (Mueller et al. 1992). Although very low concentration of petroleum
hydrocarbons enter the aquifers, the soluble concentration exceeds the permissible
limits (Spence et al. 2005).
The information shared through various articles and symposia in 1995 shows that
various petroleum industries including refineries, oil and gas wells, and even
pumping stations seemed interested to use constructed wetlands to process the
wastewater and stormwater (Knight et al. 1999). The wastewaters releases from
petroleum hydrocarbon processes contain aromatic hydrocarbons such as benzene,
ethylbenzene toluene, and xylene, found in gasoline, and which is highly volatile
substances (Coates et al. 2002). The wastewater from petroleum hydrocarbons also
consists of other pollutants such as phosphorus, nitrogen, BOD, and COD (Knight
et al. 1999). The focus of petroleum industry is to assess the removal efficiency of
toxic hydrocarbons through constructed wetlands instead of the removal efficiency
of BOD and COD of treating wastewater (Knight et al. 1999; Ji et al. 2007). All of
the BTEX compounds including benzene due to its toxicity, high solubility, persistence, and carcinogenic nature represent a significant health risk in contaminated
environments. The thermodynamic stability of the benzene ring increases its persistence in the environment; therefore, many aromatic compounds are major environmental pollutants (Dagley 1986; Diaz 2004). The detail of hydrocarbons removal
mechanism is summarized in Table 6.4.
In the groundwater contaminated with gasoline, the BTEX fraction of total
volatile hydrocarbons is primarily responsible for most of the total toxicity, so it is
needed to target these compounds first to reduce the toxicity. Benzene concentrations in the natural gas range from about 0 to 1000 mg L
À1 and in crude oils from 0 to
10,000 mg L
À1 (Janks and Cadena 1991). Benzene solubility (1780 mg L
À1 ) in
water is very high; the contamination of water due to the oil exploration, process,
handling, production process, and underground tanks leakage is of great concern for
gas and oil industries. The three major mechanisms suggested for the removal of
hydrocarbons via constructed wetlands are biological, microbial degradation and
volatilization; other methods were chemical precipitation and filtration
6 Constructed Wetlands: A Clean-Green Technology for Degradation and. . .
153
(C6H6) is a compound that consists of six carbon and six hydrogen atoms. The
simple aromatic environmental pollutants are benzene, ethyl benzene, toluene, and
xylene (ITRC 2003). The aliphatic can be further divided into the alkanes, the
alkenes, and the cycloalkanes groups. The constructed wetland can play a significant
role in the degradation of these hydrocarbons. Benzene is a primary component of
petroleum-based fuels and used in manufacturing processes. Benzene is toxic,
persistent, mobile, and soluble in surface water as well as in groundwater and less
biodegradable in the absence of oxygen (Coates et al. 2001).
The petroleum hydrocarbons extraction process consists of several steps such as
exploration, production, refining, storage, transportation, distribution, and utilization
which cause the contamination of water, sediments, and soil (Atlas and Cerniglia
1995). Energy play important role in economic growth and the increase use of
petroleum hydrocarbons can disturb the ecosystem including biotic and abiotic
components (Mueller et al. 1992). Although very low concentration of petroleum
hydrocarbons enter the aquifers, the soluble concentration exceeds the permissible
limits (Spence et al. 2005).
The information shared through various articles and symposia in 1995 shows that
various petroleum industries including refineries, oil and gas wells, and even
pumping stations seemed interested to use constructed wetlands to process the
wastewater and stormwater (Knight et al. 1999). The wastewaters releases from
petroleum hydrocarbon processes contain aromatic hydrocarbons such as benzene,
ethylbenzene toluene, and xylene, found in gasoline, and which is highly volatile
substances (Coates et al. 2002). The wastewater from petroleum hydrocarbons also
consists of other pollutants such as phosphorus, nitrogen, BOD, and COD (Knight
et al. 1999). The focus of petroleum industry is to assess the removal efficiency of
toxic hydrocarbons through constructed wetlands instead of the removal efficiency
of BOD and COD of treating wastewater (Knight et al. 1999; Ji et al. 2007). All of
the BTEX compounds including benzene due to its toxicity, high solubility, persistence, and carcinogenic nature represent a significant health risk in contaminated
environments. The thermodynamic stability of the benzene ring increases its persistence in the environment; therefore, many aromatic compounds are major environmental pollutants (Dagley 1986; Diaz 2004). The detail of hydrocarbons removal
mechanism is summarized in Table 6.4.
In the groundwater contaminated with gasoline, the BTEX fraction of total
volatile hydrocarbons is primarily responsible for most of the total toxicity, so it is
needed to target these compounds first to reduce the toxicity. Benzene concentrations in the natural gas range from about 0 to 1000 mg L
À1 and in crude oils from 0 to
10,000 mg L
À1 (Janks and Cadena 1991). Benzene solubility (1780 mg L
À1 ) in
water is very high; the contamination of water due to the oil exploration, process,
handling, production process, and underground tanks leakage is of great concern for
gas and oil industries. The three major mechanisms suggested for the removal of
hydrocarbons via constructed wetlands are biological, microbial degradation and
volatilization; other methods were chemical precipitation and filtration
6 Constructed Wetlands: A Clean-Green Technology for Degradation and. . .
153