Sustainable reuse of toxic spent granular activated carbon by heterogeneous fenton reaction intensified by temperature changes.

A common strategy for removing highly toxic organic compounds, such as chlorinated organic compounds, is their adsorption on granular activated carbon. Spent granular activated carbon results in a toxic residue to manage; therefore, the regeneration and reuse of granular activated carbon on the site would be advisable. This work studies the regeneration of a granular activated carbon saturated in 1,2,4-trichlorobenzene, chosen as the model chlorinated organic compounds, by heterogeneous Fenton, where iron was previously immobilised on the granular activated carbon surface. This methodology avoids the addition of iron to the aqueous phase at concentrations above the allowable limits and the need for acidification. Three successive cycles of adsorption-regeneration were carried out batchwise (5 gGAC·L-1) with a granular activated carbon saturated with 300 mg124-TCB·gGAC-1. The recovery of the adsorption capacity after regeneration was studied with H2O2 (166 mM, 1.5 the stoichiometric dosage), at different concentrations adsorbed with iron adsorbed concentrations (0-12 mgFe·gGAC-1) and temperatures (20-80 °C). Stable recovery of the adsorption capacity values of 65% were obtained at 180 min with 12 mgFe·gGAC-1 and 60 °C. The porosity and surface chemistry of the adsorbent remained very similar after different adsorption-regeneration cycles without iron leaching into the aqueous phase. The oxidant consumption was close to the stoichiometric value for the mineralization of 1,2,4-trichlorobenzene, with a low unproductive consumption of H2O2 with granular activated carbon. In addition, no aromatic or chlorinated by-products were detected in the aqueous solution obtained in the regeneration process. The negligible toxicity of the aqueous phase with the Microtox bioassay confirmed the absence of toxic oxidation by-products.

Regeneration of Granulated Spent Activated Carbon with 1,2,4-Trichlorobenzene Using Thermally Activated Persulfate.

Chlorinated organic compounds (COCs) are persistent organic pollutants often found in groundwater near industrial sites or in industrial wastewaters. Adsorption into activated carbon is a common strategy to remediate these waters, but spent activated carbon results in a toxic residue to manage. To avoid the transport of the chlorinated compounds out of the site, the in-situ regeneration of the spent activated carbon can be considered for reuse to implement a circular economy. In this work, the regeneration of a commercial granular activated carbon (GAC) has been carried out using thermally activated sodium persulfate (TAP). GAC was previously saturated in 1,2,4-trichlorobenzene (124-TCB) as the model compound. The initial adsorption value was 350 mg124-TCB·gGAC -1. First, the nonproductive consumption of sodium persulfate was studied at different temperatures using nonsaturated GAC. Then, the regeneration of the saturated GAC (5 g) was studied by an aqueous solution (166 mM) of TAP (1 L) at a temperature range from 20 to 80 °C. The possible recovery of the adsorption capacity was studied after 3 h of treatment in three successive adsorption-regeneration cycles at the selected temperature (60 °C). The physicochemical changes of the GAC were also investigated before and after the regeneration treatments. The results evidence the significant deposition of sulfate on the GAC after each treatment of regeneration, which avoids the recovery of the initial adsorption capacity. Therefore, each regeneration cycle was necessarily followed by a washing step at 60 °C to remove this sulfate. After that, the regeneration treatment achieved a stable and high recovery of the initial adsorption capacity of about 48.2%.

Porous SiO2 Nanospheres Modified with ZrO2 and Their Use in One-Pot Catalytic Processes to Obtain Value-Added Chemicals from Furfural.

Porous SiO2 nanospheres were modified with different loadings of ZrO2 to obtain catalysts with a Si/Zr molar ratio from 2.5 to 30. These materials were characterized by X-ray diffraction, transmission and scanning electron microscopies, N2 adsorption-desorption at -196 °C, X-ray photoelectron spectroscopy and pyridine and 2-6-dimethylpyridine thermoprogrammed desorption. The characterization of these catalysts has revealed that a high proportion of Zr favors the formation of Lewis acid sites, which are implied in catalytic transfer hydrogenation processes, whereas the low Brönsted acidity promotes a dehydration reaction, being possible to give rise to a large variety of products from furfural through consecutive reactions, such as furfuryl alcohol, i-propyl furfuryl ether, i-propyl levulinate, and γ-valerolactone, in a range of temperature of 110-170 °C and 1-6 h of reaction.

Remediation of a biodiesel blend-contaminated soil by using a modified Fenton process.

A soil contaminated with a B20 biodiesel blend (20 % biodiesel, 80 % diesel) has been treated by modified Fenton process with or without chelant addition. All experiments were conducted without pH adjustment. The reagents used were as follows: hydrogen peroxide as oxidant (400-4,000 mmol L(-1)), ferric ion as catalyst (5-20 mmol L(-1)), and trisodium citrate (50 mmol L(-1)) as chelating agent. Soil was spiked at two different pollutant concentrations (1,000-10,000 mg diesel kg(-1) soil). Higher total petroleum hydrocarbon (TPH) removal efficiencies were obtained (up to 75 %) after the treatment in the absence of the chelant due to the low pH obtained in this case. In the presence of chelant, the TPH conversion obtained was lower because both higher pH is obtained and chelant competes with diesel for the oxidant. On the other hand, at neutral pH, the lifetime of the oxidant was increased. Fatty acid methyl esters (FAMEs) are easier to remove than diesel aliphatic hydrocarbons from the blend. An important decrease of the aqueous phase toxicity was observed after the modified Fenton reaction, supporting that nontoxic by-products were released to the aqueous phase during the treatment.