Activity and stability of biochar in hydrogen peroxide based oxidation system for degradation of naphthenic acid

High surface area biochar for the removal of naphthenic acids from environmental water and industrial wastewater

This study reports the production of biochar adsorbents from two major crop residues (i.e., rice and wheat straw) to remove naphthenic acids from water. The alkali treatment approach was used for biochar activation that resulted in a tremendous increase in their surface area, i.e., up to 2252 and 2314 m2/g, respectively, for rice and wheat straw biochars. Benzoic acid was used as a model compound to optimize critical adsorption parameters. Its maximum monolayer adsorption capacity of 459.55 and 357.64 mg/g was achieved for activated rice and wheat straw biochars. The adsorption of benzoic acid was exothermic (∆H° =  - 7.06 and - 3.89 kJ/mol) and identified possibly as physisorption (Gibbs free energy ranges 3.5-4.0 kJ/mol). The kinetic study suggested that adsorption follows pseudo-second-order kinetics with qe2 for rice straw and wheat straw-derived adsorbents at 200 and 194 mg/g, respectively. As adsorbent, the recyclability of activated biochars was noticed with no significant loss in their efficiency for up to ten successive regeneration cycles. The adsorption results were validated using a commercial naphthenic acid mixture-spiked river water and paper/pulp industrial effluent. The activated rice and wheat straw biochars exhibited excellent adsorption efficiency of 130.3 and 74.6 mg/g, respectively. The naphthenic acid adsorption on biochar surface was due to various interactions, i.e., weak van der Waal's, pore filling, π-π stacking, and ionic interactions. This study offers a cost-effective and eco-friendly approach to valorizing agricultural residues for pollutant removal from industrial wastewater, including petroleum refineries.

Enhanced adsorption of phosphate by rice straw-based biochar prepared via metal impregnation and bio-template technology

Phosphate removal from water through green, highly efficient technologies has received much attention. Biochar is an effective adsorbent for phosphate removal. However, adsorption capacity of phosphate on pristine rice straw-based biochar was not optimistic due to low anion exchange capacity. In this study, Fe-modified, Mg-modified and MgFe-modified rice straw-based biochar (Fe-BC, Mg-BC and MgFe-BC) were prepared by combining metal impregnation and biological template methods to improve the adsorption capacity of phosphate. The surface characteristics of biochar and the adsorption behavior of phosphate on biochar were investigated. The modified biochar had the specific surface area of 17.910-39.336 m2/g, and their surfaces were rich in a large number of functional groups and metal oxides. Phosphate release was observed on pristine rice straw-based biochar without metal impregnation. The maximum adsorption capacities of phosphate on MgFe-BC, Mg-BC and Fe-BC at 298 K were 6.93, 5.75 and 0.23 mg/g, respectively. Adsorption was a spontaneous endothermic process, while chemical adsorption dominated and electrostatic attraction and pores filling existed simultaneously. Based on the site energy distribution theory study, the standard deviation of MgFe-BC decreased from 6.96 to 4.64 kJ/mol with temperature increasing, which proved that the higher the temperature would cause the lower heterogeneity. Moreover, the effects of pH, humic acid, co-existing ions and ionic strength on phosphate adsorption of MgFe-BC were also discussed. MgFe-BC with fine pores and efficient adsorption sites is an ideal adsorbent for phosphate removal from water.

Sample preparation, analytical characterization, monitoring, risk assessment and treatment of naphthenic acids in industrial wastewater and surrounding water impacted by unconventional petroleum production

Industrial extraction of unconventional petroleum results in notable volumes of oil sands process water (OSPW), containing elevated concentrations of naphthenic acids (NAs). The presence of NAs represents an intricate amalgamation of dissolved organic constituents, thereby presenting a notable hurdle for the domain of environmental analytical chemistry. There is growing concern about monitoring the potential seepage of OSPW NAs into nearby groundwater and river water. This review summarizes recent studies on sample preparation, characterization, monitoring, risk assessment, and treatment of NAs in industrial wastewater and surrounding water. Sample preparation approaches, such as liquid-liquid extraction, solid phase microextraction, and solid phase extraction, are crucial in isolating chemical standards, performing molecular level analysis, assessing aquatic toxicity, monitoring, and treating OSPW. Instrument techniques for NAs analysis were reviewed to cover different injection modes, ionization sources, and mass analyzers. Recent studies of transfer and transformation of NAs provide insights to differentiate between anthropogenic and natural bitumen-derived sources of NAs. In addition, related risk assessment and treatment studies were also present for elucidation of environmental implication and reclamation strategies. The synthesis of the current state of scientific knowledge presented in this review targets government regulators, academic researchers, and industrial scientists with interests spanning analytical chemistry, toxicology, and wastewater management.

H2O2 activation and contaminants removal in heterogeneous Fenton-like systems

Emerging contaminants can be removed effectively in heterogeneous Fenton-like systems. Currently, catalyst activity and contaminant removal mechanisms have been studied extensively in Fenton-like systems. However, a systematic summary was lacking. This review summarized: 1) The effects of various heterogeneous catalysts on emerging contaminants degradation by activating H₂O₂; 2) The role of active sites in different catalysts during the activation of H₂O₂ and their contribution to the generation of active species; 3) The modulation of degradation pathways of emerging contaminants. This paper will help scholars to advance the controlled construction of active sites in heterogeneous Fenton-like systems. Suitable heterogeneous Fenton catalysts can be selected in practical water treatment processes.

Chemical modification of biochars as a method to improve its surface properties and efficiency in removing xenobiotics from aqueous media

Biochar (BC) is a carbonaceous material produced by pyrolysis of biomass, applied in various areas such as water purification, fuel production, soil amendment, etc. Many types of BC are characterized by insufficient textural parameters or poor surface chemistry, and hence by low adsorption capacity. This makes innovative chemical methods increasing BC ability to remove xenobiotics from aquatic environments highly needed. Many of them have already been described in the literature. This review presents them in detail and evaluates their effectiveness in improving textural parameters, surface chemistry, and adsorption capacity of BC.

Role of persistent free radicals and lewis acid sites in visible-light-driven wet peroxide activation by solid acid biochar catalysts - A mechanistic study

We report the synthesis of H₂SO₄-modified biochars (SBCs) as solid-acid catalysts to activate H₂O₂ at circumneutral pH under visible light radiation. Spent coffee grinds were pyrolyzed with TiO₂ at 300, 500 and 600 °C followed by steeping in 5 M H₂SO₄ and were used for the Fenton-like degradation of methyl orange (MO). The catalytic activity of SBC depended on the pyrolysis temperature and correlated well with the surface acidity and persistent free radical (PFR) concentration. Results showed that a complete MO removal and a TOC reduction of 70.2% can be achieved with SBC500 under photo-Fenton conditions. However, poisoning of the Lewis acid sites on SBC by PO₄^3- led to a dramatic decrease in the removal of MO with inhibition effects more pronounced than with radical scavengers, suggesting the key role played by acid-sites on the activation of H₂O₂. Finally, electron paramagnetic resonance (EPR) studies identified •OH as the key transient in the degradation followed by •O₂^- and ¹O₂. These findings suggest that H₂O₂ was likely adsorbed on the surface oxygenated functional groups before being decomposed by accepting electrons from the PFRs on the SBC surface.

Catalytic efficiency of raw and hydrolyzed eggshell in the oxidation of crystal violet and dye bathing wastewater by thermally activated peroxide oxidation method

In this study, hydrochar-based-eggshell was prepared via the subcritical water medium (SCWM) and used as a catalyst in the thermally activated peroxide oxidation (TAPO) approach for crystal violet and dye bathing wastewater degradation. The catalytic activities for the raw eggshell (RES) and hydrochar-based-eggshell (HES) were compared. RES and HES were characterized using a scanning electron microscope (SEM),energy-dispersive X-ray spectroscopy (SEM-EDX), and Fourier transforms infrared spectroscopy (FT-IR). The affecting parameters on the degradation process were optimized using response surface methodology (RSM). The effects of temperature (293-333 K), amount of catalyst (5-25 mg/50 mL), the concentration of H₂O₂ (0-8 mM), and treatment time (10-70 min) on the TAPO method were investigated using central composite design (CCD). For the crystal violet removal, two models were developed. Both models were significant and can be used to describe the design space. Also, the dye bathing wastewater degradation was described by another developed model, which had a high correlation coefficient (R² = 0.97). In general, catalytic activity for HES was higher than RES. The degradation of crystal violet reached 98.10% when a 20 mg HES catalyst and 6 mM H₂O₂ at 323 K for 55 min were used. While 97% of the color of dye bathing wastewater was removed in 55 min at 323 K using 25 mg of HES and 4 mM H₂O₂. This study showed that the hydrolyzed eggshells could be used in the oxidation of crystal violet and dye bathing wastewater by the thermally activated peroxide oxidation method.

Preparation of biochar and biochar composites and their application in a Fenton-like process for wastewater decontamination: A review

Biochar is a carbon-rich material that can be obtained from pyrolysis of solid waste (e.g., agricultural solid waste and sludge from wastewater treatment plants). Biochar features low cost, large specific surface area, and strong adsorption capacity. New biochar composites can be produced via modification and loading of nano particles onto biochar. Biochar can contribute to the dispersion and stabilization of nano particles. In addition, nano particles can increase the number of surface-active sites, which improves the physicochemical properties of the material. Biochar and biochar composites have been applied widely in wastewater treatment, and have significantly enhanced the treatment performance of Fenton-like processes (activation of hydrogen peroxide and persulfate) as an advanced oxidation process for organics removal and wastewater decontamination. This paper reviews the preparation methods for biochar and biochar composites to systematically analyze the influential factors on the preparation process. The paper also comprehensively reviews the mechanisms by which biochar removes different organic pollutants. However, due to the vast number of different biochar feedstocks and their preparation methods, it is difficult to compare the properties of one biochar to another. Guidance if provided for the application of biochar and biochar composites for wastewater decontamination.

Study of polarized activated carbon filters as simultaneous adsorbent and 3D-type electrode materials for electro-Fenton reactors

Electro-Fenton (EF) based water treatment processes using activated carbon (AC) packed beds constitute an attractive approach for the development of competitive degradation technology of persistent pollutants in aqueous effluents. In this work, the results of a study aimed to assess the effect on the EF performance of different parameters of the reactor's operation are presented. By means of a factorial experimental design, the influence of the AC source (lignitic or vegetal), AC acid pre-treatment, particle size distribution and the amount of Fe loaded resin in the reactor were analyzed. From the resulting data it was found that the most influential parameter in the EF performance of the reactor is the AC source. Modest effects were observed for AC acid pre-treatment, which limits Fe ion adsorption on the AC substrate. The use of a wide particle distribution of AC particles was also found to improve inter-particle electrical contact, thus favoring the electrochemical processes that take place inside the reactor. An investigation on the effect of the amount of Fe in the reactor as well as its distribution dynamics, also revealed that an excess of Fe ions in the reactor decreases the EF performance of the system since Fe ions efficiently adsorb on the AC substrate, particularly in non- acid treated samples. The best operation conditions consisted on using un-meshed vegetable AC, without acid pretreatment in an EF reactor loaded with 0.25 g of Fe, which allowed to reach full color removal of bright blue FCP model dye in 70 min.

Effects of feedstock and inherent mineral components on oxidation resistance of biochars

Chemical stability assessment of biochar has been universally used to indicate its potential of long-term carbon sequestration. The comparative study on oxidation resistance of biochars from diverse series of feedstock is relatively limited, as well as the effects of endogenous minerals on biochar stability. Herein, oxidation resistance of biochars from peanut shell, bamboo, saw dust, reed stalk, furfural residues, seaweed degumming residues and Enteromorpha prolifera at 500 °C (PS500, BB500, SD500, RS500, FR500, SR500 and EP500) was examined by the treatments of H₂O₂, K₂Cr₂O₇ and thermogravimetric analysis (TGA). Under H₂O₂ or K₂Cr₂O₇ condition, C loss of algae-derived biochars (SR500 and EP500) was extremely greater than that of other biochars due to higher content of labile carbon components. PS500, BB500, SD500, RS500 and FR500 characterized with similar properties in carbon fraction, but they exhibited different ability to resist oxidation. The mineral fraction of biochars (e.g., content and species) varied with the feedstock, which played complex effects on the oxidation resistance. The mineral decomposition (e.g., CaCO₃) in EP500 and SR500 above 500 °C influenced the analysis of biochar stability by TGA. After acid-washing, EP500 and SR500 showed weaker thermal oxidation resistance, agreed with the results of H₂O₂ and K₂Cr₂O₇ oxidation. The oxidation resistance of biochars was correlated better with O/C ratio, implying that O/C ratio was more robust indicator than other indexes (e.g., H/C ratio and the ratio of D band to G band of Raman). The FTIR, Raman and XPS results further demonstrated the elimination of aliphatics and amorphous aromatics and/or the carboxylation/carbonylation of aromatic structures by H₂O₂ and K₂Cr₂O₇. These findings are useful for better understanding the impacts of feedstock and inherent minerals on the oxidation resistance of biochars.