Effect of Fenton Reagent Dose on Coexisting Chemical and Microbial Oxidation in Soil

Abstract

The ability of modified Fenton reactions to promote simultaneous chemical and biological oxidation in an artificially contaminated soil was studied in batch laboratory slurry reactors. Tetrachloroethene (PCE) and oxalate (OA) were used to distinguish chemical oxidation from aerobic heterotrophic metabolism. PCE was mineralized by Fenton reactions, but OA was not oxidized. Indigenous soil microorganisms did not degrade added PCE aerobically but readily assimilated OA. Fenton reactions were promoted at the natural soil pH (7.6) by adding H2O2 and Fe(III), with nitrilotriacetic acid (NTA) as a chelator, at a constant molar ratio of H2O2/Fe(III)/NTA of 50:1:1. The *OH-mediated mineralization of PCE was demonstrated by adding 2-propanol (an *OH scavenger), which inhibited PCE oxidation. In subsequent dosing studies, PCE oxidation served as an indicator of Fenton reactions, while OA assimilation, dissolved oxygen (DO) concentration, and heterotrophic plate counts were indicators of aerobic microbial activity. Increasing Fenton doses to 20 times that required to achieve 95% PCE oxidation only delayed OA assimilation by 500 min and reduced plate counts by 1.5 log units g(-1) soil. Results show that aerobic metabolism can coexist with Fenton oxidation in soils.

Calcium peroxide (CaO2) for use in modified Fenton chemistry

“…The final Cl − concentration was approximately 11 mM, resulting in a ratio of 3.7 mmol Cl − released/mmol PCE oxidized. This is similar to molar ratios observed by Ndjou'ou et al [26] for MF oxidation of PCE in soils using liquid H 2 O 2 . The amount of PCE oxidized (5.83 mmol, or 97%) was obtained by subtracting the mmol volatilized from the total mmol removed.…”

“…The dose of PCE in all three reactors was 6 mmol (3 mM, or 500 mg/L), and the dose of 2-propanol was 30 mM. Using 2-propanol was based on its effectiveness as a scavenger of • OH [26,28,29]. Analyses done at the end of the experiments (60 h) verified that no CaO 2 and no measurable amount of unreacted H 2 O 2 remained in the MF reactors.…”

“…It is also difficult to distinguish biological from chemical oxidation of contaminants since both are oxidative processes with the same products. This difficulty is exacerbated by recent findings that aerobic biodegradation co-exists with MF oxidation of contaminants in soils, even at high doses of liquid H 2 O 2 [26].…”

Efforts to improve coupled in situ chemical oxidation with bioremediation: a review of optimization strategies

“…The oxidative stress, increase or decrease in pH (persulfate and Fenton's reagent, respectively), and change in redox conditions caused by ISCO treatments significantly alter subsurface conditions and are toxic to microbial populations (Buyuksonmez et al 1998;Macbeth et al 2007;Miller et al 1996). However, recent work indicates that, although chemical oxidation can temporarily reduce microbial activity, bacterial populations do regenerate contaminant degradation ability both in the field (Jones et al 2009;Koch et al 2007;Ladaa et al 2008;Luhrs et al 2006;Macbeth et al 2005;Studer et al 2009) and in laboratory experiments (Aunola et al 2006;Hood et al 2006;Kao and Wu 2000;Kulik et al 2006;Ndjou'ou et al 2006). In many cases, it has been concluded that ISCO pretreatment appears to improve overall remediation by (1) decreasing the concentration of pollutants to levels less toxic for the soil biota (Chapelle et al 2005), (2) improving bioavailability of the parent compound (Kulik et al 2006;Miller et al 1996), (3) producing bioavailable and biodegradable oxidized daughter compounds (Lee and Hosomi 2001;Marley et al 2003;Miller et al 1996;Nam et al 2001), or (4) providing oxygen for aerobic biological transformation of contaminants (Kulik et al 2006).…”

Rapid probing of photocatalytic activity on titania-based self-cleaning materials using 7-hydroxycoumarin fluorescent probe

“…Due to strong oxidizing ability, the advanced oxidation processes (such as ultrasonic oxidation [1][2][3], photocatalytic oxidation [4][5][6][7], and Fenton oxidation [8,9]) are increasingly used for analysis and degradation removal of organic pollutants in concerns of environmental analysis and protection. Among these processes, the photocatalytic oxidation seems to be the most attractive.…”