Abstract
Problem statement: Volatile Organic Compounds (VOCs) were widespread in groundwater of industrialized areas and in situ remediation intervents characterized by a high environmental compatibility were of main interest. The scope of this study was the evaluation of the potential of two innovative reagents (HRC and ORC from Regenesis) for the remediation of Volatile Organic Compounds (VOCs). The reagents respectively perform reduction and oxidation mechanisms, both effective in the degradation of VOCs. Approach: Hydrogen Release Compound (HRC) and Oxygen Release Compound (ORC) were tested about the degradation of Benzene, Toluene, Ethylbenzene and Xylene (BTEX) and some Chlorinated Aliphatic compounds (CAHs). Five series of batch tests were performed with an artificial polluted aqueous phase and some soil coming from a polluted site in which natural attenuation of VOCs occurs. Results: ORC exhibited a good efficiency in degradation of BTEX and zero order model was found as a reliable approximation of experimental data (with the exceptions of benzene and toluene, for which a first order kinetic model was trustworthy), while HRC showed a good efficiency in the degradation of CAHs and a first order model consistently estimated almost all experimental data. The experimental data were modeled by means of different mathematical equations, considering zero and first order kinetics and the results were discussed and compared. Conclusions: On the grounds of the performed tests, Oxygen Release Compound (ORC) is effective in BTEX degradation and Hydrogen Release Compound (HRC) in CAHs removal.
Highlights
Biodegradation of organic pollutants may happen by means of direct metabolic or co-metabolic processes: In the first the organic pollutant acts as a substrate for microorganisms, in the second the organic pollutant is degraded by microorganisms which are involved in other reactions and use other compounds as substrates
Oxygen Release Compound (ORC) exhibited a good efficiency in degradation of BTEX and zero order model was found as a reliable approximation of experimental data, while Hydrogen Release Compound (HRC) showed a good efficiency in the degradation of Cometabolic degradative processes usually involveChlorinated Aliphatic Hydrocarbons (CAHs) and a first order model consistently estimated almost all experimental data
The hydrogen/oxygen release compounds: Two reagents that may be employed in enhanced bioremediation processes are tested in this study towards BTEX and other Volatile Organic Compounds (VOCs), aromatic hydrocarbons and CAHs: Hydrogen Release Compound (HRC, a readily biodegradable organic substrate, mainly made of lactate, that acts as an indirect electron donor) and Oxygen Release Compound (ORC), containing magnesium peroxide
Summary
Biodegradation of organic pollutants may happen by means of direct metabolic or co-metabolic processes: In the first the organic pollutant acts as a substrate for microorganisms, in the second the organic pollutant is degraded by microorganisms which are involved in other reactions and use other compounds as substrates. The substrates concerned in these kind of co-metabolic processes are usually short chain aliphatic hydrocarbons and mono-cyclic aromatic hydrocarbons (McCarty, 1993; Hazen, 2009). Degradation processes based on the direct metabolism of pollutants generally concern hydrocarbons with less than 20-25 Carbon atoms in their molecule, Benzene, Toluene, Ethylbenzene and Xylene (BTEX) (Farhadian et al, 2008) and Polynuclear Aromatic Hydrocarbons (PAH). Aerobic cometabolism is effective in medium/low CAHs degradation (Frascari et al, 2006; 2007), for some of these pollutants (i.e., chlorobenzene, vinyl chloride) microbic species able to play a direct metabolic degradation are available. The aerobic cometabolisms of highly-chlorinated CAHs (i.e., perchloroethylene, PCE, carbon tetrachloride, hexachlorobenzene) is usually inhibited and it happens only with the support of a strong oxidant, the preferential degradation mechanism is anaerobic cometabolism (McCarty, 1993)
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