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Highlights • Mixing conditions significantly influence the kinetic expression of NOD. • NOD continues to be expressed as long as permanganate is present. • There appears to be reduced species that react very slowly with permanganate. • The fast and slow reactions can also provide insight into the complex kinetics. • The level of mixing was shown to significantly increase the initial rate of NOD. Abstract Excess oxidant requirements are commonly observed during field applications of in situ chemical oxidation by permanganate for the remediation of groundwater. This excess oxidant, generally referred to as natural or soil oxidant demand, is a direct result of organic matter and other naturally occurring reduced species present in the subsurface. Since site conditions vary widely, laboratory scale experiments are often used to determine the natural oxidant demand of soil at hazardous waste sites. Though many researchers have reported values in the literature, experimental conditions often go unreported and few take these factors into consideration. This study provides a broader perspective of the issues and concerns related to determining the permanganate natural oxidant demand of soil while evaluating the effects that initial oxidant concentration, soil to water ratio, and mixing have on the rate and extent of permanganate consumption. It was found that mixing conditions significantly influenced the kinetic expression of permanganate natural oxidant demand while soil to water ratios were not shown to have a significant effect as long as initial permanganate concentrations were sufficient to overcome the oxidant demand of the soil (i.e., were not limiting). [ABSTRACT FROM AUTHOR]

Co-oxidation of trivalent chromium (Cr(III)) to hexavalent chromium (Cr(VI)) during ozonation of organic pollutants represents a common problem facing the implementation of in situ chemical oxidation (ISCO) for environmental remediation. A laboratory study was conducted by using groundwater and saturated soil samples from a field site in Sacramento, California, to determine optimal O 3 dosage to achieve satisfactory remediation of MTBE while minimizing co-oxidation of Cr(III) to Cr(VI). Total oxidant demand was determined (28.33 mg O 3 L −1 ) and used as the benchmark to establish a range of ozone dosages for the study. Concentration changes in MTBE and chromium were monitored at O 3 dosages less than and greater than the benchmark. The results indicate that MTBE is preferentially oxidized by ozone at and below the indicated benchmark dosage prior to the oxidation of Cr(III) to Cr(VI). The resultant O 3 dosage of 28.33 mg L −1 was applied in the field implementation, verifying that the O 3 can be applied in a controlled manner to remediate MTBE while minimizing the formation of Cr(VI). [ABSTRACT FROM AUTHOR]

Highlights: [•] Batch experiments were run to select an oxidant to degrade PAHs in an aged soil. [•] Modified Fenton's reaction, permanganate, persulfate and percarbonate were tested. [•] Permanganate was the most efficient: up to 70% degradation. [•] Increasing oxidant dose may not enhance PAH degradation; other effects are involved. [•] PAH degradation was limited because of low PAH availability. [ABSTRACT FROM AUTHOR]

The equilibrium model was developed to simulate the ozone breakthrough curve (BTC) during in situ ozonation of 2-chlorophenol (2-CP)-contaminated soil. Based on the model, the stoichiometric coefficient λ and the second-order rate constant k2 were determined by the non-linear least squares method. The model was found to fit well the experimental data obtained from one-dimensional columns. With the increase of gaseous ozone concentration, the stoichiometric coefficient λ would increase, while the second-order rate constant k2 would decrease. [ABSTRACT FROM AUTHOR]

• Degradation of AO7 by PDS activated from in situ electrochemically generated Cu+. • EC-Cu-PDS have higher degradation efficiency of 70% as compare to 56% of EC-Fe-PDS. • EE/O of the EC-Cu-PDS processes ranged from 0.008 to 2.42 kW h m−3. • Optimal operation condition was pH 2 with cathode to anode area of 4:1. • SO 4 − generated by both electrochemically at the anode and Cu+ activation of PDS. In this paper, the degradation of Acid Orange 7 (AO7), by persulfate activated from in situ electrochemically generated Cu+ (EC-Cu-PDS) was studied. The influence of key parameters such as pH, current density, copper concentration and electrode size were investigated, with the optimal operation condition being pH 2 with cathode to anode area of 4:1. The degradation efficiency of the EC-Cu-PDS after 30 min was compared to the efficiency of other electrocatalysis system using iron, cobalt or silver. The proposed EC-Cu-PDS process has a higher degradation efficiency of 70%, as compare to 56% of the EC-Fe-PDS process. Although the EC-Cu-PDS process has a lower degradation efficiency compared to 100% of Co-PMS and 80% of the EC-Ag-PDS processes, the EC-Cu-PDS process would be cheaper and safer to operate than the latter processes. The estimated electrical energy consumption of the EC-Cu-PDS processes was significantly lower than other electrocatalysis processes, ranging from 0.008 to 2.42 kW h m−3. The degradation of AO7 by the EC-Cu-PDS process was via oxidization of AO7 by both hydroxyl radicals generated at the anode and sulfate radicals generated by both electrochemically at the anode and Cu+ activation of PDS. [ABSTRACT FROM AUTHOR]

• Investigation of the factors limiting PAH degradation in soils during oxidation. • Permanganate was the most effective oxidant. • Permanganate oxidation: correlation between PAH degradation and availability. • Radical oxidation: sequential addition is better than single addition. • Type/age of soil organic matter and carbonate content influence PAH oxidation. In Situ Chemical Oxidation (ISCO) can be applied to soils contaminated by polyaromatic hydrocarbons (PAHs). PAH degradation yields are often rather low, because of different obstacles not clearly understood. These include the low availability of PAHs, the type and age of soil organic matter and the carbonate content of the soil. The aim of this work was to provide a better understanding of the influence of these limiting factors at a given oxidant dose. Batch experiments were performed on contrasted PAH-contaminated soils or matrices using permanganate, persulfate, modified Fenton's reagent and activated persulfate. PAH availability was estimated by a cyclodextrin-enhanced extraction method. Moderate amounts of oxidant were used in order to lower costs whilst minimizing environmental impacts. Results showed that chemical oxidation efficiency was mainly affected by PAH availability, particularly with low persistent oxidant. With permanganate, a correlation was found between PAH availability and degradation yield. With low persistent oxidants, degradation yields were significantly increased by sequential addition. The negative impacts of a high content of soil organic matter and/or carbonate were highlighted. For the aged contaminated soils, PAH degradation yields remained below 30% after most treatments except with permanganate (40–60%) and sequential addition of Fenton's reagent (40–70%). These results should have useful implications for the design of ISCO treatments. [ABSTRACT FROM AUTHOR]