A new method to treat fumigant pesticides-spent granular activated carbon utilizing alkaline hydrolysis.

Groundwater treatment of recalcitrant fumigant pesticides (1,2-dibromo-3-chloropropane (DBCP), 1,2-dibromoethane (EDB), 1,2-dichloropropane (DCP), and 1,2,3-trichloropropane (TCP)) often involves a pump and treat system with granular activated carbon (GAC). A novel and promising method of treating the pesticide-spent GAC is based on alkaline hydrolysis, a well-understood abiotic transformation mechanism, that offers a potentially greener approach to conventional thermal regeneration. Here, alkaline hydrolysis of these pesticide chemicals was evaluated under homogeneous (aqueous), and heterogeneous (pesticide spent-GAC) conditions involving bituminous- and coconut-based GAC. Aqueous treatment occurred at elevated pH (pH 12.0-12.4) and the pesticide rate of hydrolysis transformation was first-order (DBCP â‰« TCP â‰« EDB â‰« DCP). Significant pesticide loss (94.95-99.98%) was achieved in both types of GAC (pH 12.0-12.4; 30 d). GAC suspensions held (5 d) at pH 11.0, 12.0, and 12.6, resulted in the DBCP loss of 74%, 89%, and 99%, respectively. The pH dependency of DBCP hydrolysis underscores the correlation between alkaline conditions, aggressive hydrolysis treatment, and reaction time for engineered systems. The estimated time (4-8 min) for full OH- intraparticle diffusion into the GAC from bulk solution was much less than the pesticide hydrolysis half-lives indicating that alkaline hydrolysis treatment of pesticides in GAC was reaction rate limited. Rapid small scale column tests demonstrated that the post-treatment (i.e., base hydrolysis) impact on adsorptive characteristics of the GAC was limited.

Contrasting hydrogen peroxide- and persulfate-driven oxidation systems: Impact of radical scavenging on treatment efficiency and cost.

For the first time, the fate of radicals generated in heterogeneous chemical oxidation treatment systems has been accounted for and used to assess treatment performance in three reaction compartments; reaction with the target compound, rhodamine B (RhB), the aqueous phase scavengers, and the solid phase scavengers. Radicals formed during the ultra-violet (UV) activation of hydrogen peroxide (H2O2) (UV-AHP) and persulfate (S2O8 2-) (UV-APS) include hydroxyl (•OH) and sulfate radicals (SO4 •-), respectively. •OH and SO4 •-, used in oxidation treatment systems to degrade a broad spectrum of environmental contaminants, may also react with non-target chemical species (scavengers) that limit treatment efficiency. UV-AHP and UV-APS treatment systems were amended with solid phase alumina to assess scavenging by solid surfaces. The overall rate of reaction and rate of radical scavenging was greater for •OH than SO4 •-. Scavenging by dissolved constituents was dominated by the oxidant used (H2O2, S2O8 2-); and the rate of radical scavenging by alumina was greater than the rate of RhB oxidation in all cases. Treatment efficiency was lower in the UV-AHP than in the UV-APS treatment system and was attributed to greater aqueous and solid phase scavenging rates. The cost of commercially available H2O2 ($0.031 mol-1) and PS ($0.24 mol-1) was used in conjunction with the overall treatment efficiency to assess specific cost of treatment. The specific cost to treat the probe compound with UV-AHP was greater than UV-APS and was attributed to the much lower treatment efficiency with UV-AHP. The much-desired high reaction rate constants between •OH and environmental contaminants, relative to SO4 •-, may come at the cost of greater combined scavenging rates, and consequently lower treatment efficiency.

Fenton-driven oxidation of contaminant-spent granular activated carbon (GAC): GAC selection and implications.

Raw materials, activation methods, and post-activation treatment used in manufacturing granular activated carbon (GAC) results in a spectrum of physicochemical characteristics that potentially impact the adsorption oxidation treatment process. A comprehensive study is lacking that assesses the effect of GAC characteristics on adsorption oxidation treatment of contaminant spent-GAC. Consequently, it is inherently assumed the treatment process is GAC-independent. Here, GACs (n = 31) were characterized and used in the hydrogen peroxide (H2O2)-based adsorption oxidation treatment of 2-chlorophenol (2CP)-spent GAC. The GACs exhibited a range in surface area, pore volume distribution, metals content, surface functionality, and H2O2 reaction. Chloride recovery, the treatment metric for 2CP oxidation, indicated a wide range in oxidation (0-49.2%) where bituminous- and wood-based GAC performed best. A selected subset of GACs (n = 12), amended with iron, methyl tert-butyl ether (MTBE), and H2O2, exhibited a range in oxidative treatment (1.1-57.9%). Correlations were established between GAC surface functionality, H2O2 reactivity, adsorption, and MTBE oxidation indicating multiple parameters play a collective and compounding role. The order of GACs successfully used in the treatment process is bituminous-based coal > wood > coconut > peat. Results showed adsorption oxidation treatment is GAC-dependent, and therefore, GAC selection is a key factor in the success of this technology.

Sulfate Radical Scavenging by Mineral Surfaces in Persulfate-Driven Oxidation Systems: Reaction Rate Constants and Implications.

Activated persulfate (PS) is a common method used to generate sulfate radicals (SO4•-), a powerful oxidant capable of degrading a broad array of environmental contaminants. The reaction of SO4•- with nontarget species (i.e., scavenging) contributes significantly to treatment inefficiency. Radical scavenging in this manner has been quantified for nontarget chemical species in the aqueous phase but has never been quantified for solid phase media. Kinetic analysis and laboratory methods were developed to quantify the SO4•- scavenging rate constant (k≡S) for alumina, a naturally occurring mineral in soil and aquifer materials. SO4•- were generated in UV and thermally activated persulfate (UV-APS, T-APS) batch systems, and the loss of rhodamine B (RhB) served as an indicator of SO4•- activity. k≡S for alumina was 2.42 × 104 and 2.03 × 104 m-2 s-1 for UV-APS and T-APS oxidative treatment systems, respectively. At [alumina] >5 g L-1, the reaction of SO4•- with solid phase media increased over the aqueous phase reactions with RhB and aqueous scavengers. SO4•- scavenging by solid surfaces was orders of magnitude greater than the reaction with the target compound and scavengers in the aqueous phase, underscoring the significant role of solid surfaces in scavenging SO4•-.