Chemical oxidation for mitigation of UV-quenching substances (UVQS) from municipal landfill leachate: Fenton process versus ozonation.

UV-quenching substance (UVQS), as an emerging municipal solid waste (MSW)-derived leachate contaminant, has a potential to interfere with UV disinfection when leachate is disposed of at publicly owned treatment works (POTWs). The objective of this study was to evaluate and compare two chemical oxidation processes under different operational conditions, i.e. Fenton process and ozonation, for alleviation of UV254 absorbance of a biologically pre-treated landfill leachate. Results showed that leachate UV254 absorbance was reduced due to the UVQS decomposition by hydroxyl radicals (·OH) during Fenton treatment, or by ozone (O3) and ·OH during ozonation. Fenton process exhibited a better treatment performance than ozonation under their respective optimal conditions, because ·OH could effectively decompose both hydrophobic and hydrophilic dissolved organic matter (DOM), but O3 tended to selectively oxidize hydrophobic compounds alone. Different analytical techniques, including molecular weight (MW) fractionation, hydrophobic/hydrophilic isolation, UV spectra scanning, parallel factor (PARAFAC) analysis, and fluorescence excitation-emission matrix spectrophotometry, were used to characterize UVQS. After either oxidation treatment, residual UVQS was more hydrophilic with a higher fraction of low MW molecules. It should be noted that the removed UV254 absorbance (ΔUV254) was directly proportional to the removed COD (ΔCOD) for the both treatments (Fenton process: ΔUV254 = 0.011ΔCOD; ozonation: ΔUV254 = 0.016ΔCOD). A greater ΔUV254/ΔCOD was observed for ozonation, suggesting that oxidant was more efficiently utilized during ozonation than in Fenton treatment for mitigation of the UV absorbance.

Mitigation and degradation of natural organic matters (NOMs) during ferrate(VI) application for drinking water treatment.

Ferrate(VI), as an alternative for pre-oxidation in drinking water treatment, has recently captured renewed interest. However, the knowledge in ferrate(VI) chemistry remains largely undeveloped. The information regarding ferrate(VI) reactions with natural organic matters (NOMs), an important water matrix component affecting water treatment, is highly limited. In this study, bench scale tests were performed to study ferrate(VI) decay and reactions with NOMs in a typical surface water matrix. Results showed that ferrate(VI) decay exhibited a pseudo 2nd-order reaction pattern (kobs = 15.2-1.6 mM(-1) min(-1) and 36.3-4.0 mM(-1) min(-1) with 1.0-7.0 mg/L Fe(VI) at initial pH 7.8 and 5.8, respectively), suggesting that self-decomposition is principally responsible for ferrate(VI) consumption. Ferrate(VI) tended to attacked electron-rich moieties in NOM molecules, but had limited capability to mineralize NOMs. Consequently, ferrate(VI) effectively reduced UV254 and specific UV absorbance (SUVA254), but poorly removed dissolved organic carbon (DOC). Generally, lower pH and higher ferrate(VI) dose favored the NOM destruction. Fe(VI) (3.0 mg/L) could remove 16% of initial DOC (4.43 mg/L), 56% of initial UV254 (0.063 cm(-1)), and 48% of initial SUVA254 (0.033 cm(-1) (mg/L)(-1)) at pH 5.80. Further organics analyses indicate that ferrate(VI) readily degraded hydrophobic and transphilic NOM fractions, but scarcely decomposed hydrophilic fraction. Fluorescence excitation-emission matrix (EEM) and fluorescence regional integration (FRI) analyses revealed that ferrate(VI) preferentially reacted with fulvic-like (region III) and humic-like (region V) substances and certain aromatic proteins (region II), difficultly decomposed soluble microbial byproducts (region IV), and rarely oxidized aromatic proteins in region I.

Removal of humic and tannic acids by adsorption-coagulation combined systems with activated biochar.

Despite recent interest in transforming biomass into bio-oil and syngas, there is inadequate information on the compatibility of byproducts (e.g., biochar) with agriculture and water purification infrastructures. A pyrolysis at 300°C yields efficient production of biochar, and its physicochemical properties can be improved by chemical activation, resulting in a suitable adsorbent for the removal of natural organic matter (NOM), including hydrophobic and hydrophilic substances, such as humic acids (HA) and tannic acids (TA), respectively. In this study, the adsorption affinities of different HA and TA combinations in NOM solutions were evaluated, and higher adsorption affinity of TA onto activated biochar (AB) produced in the laboratory was observed due to its superior chemisorption tendencies and size-exclusion effects compared with that of HA, whereas hydrophobic interactions between adsorbent and adsorbate were deficient. Assessment of the AB role in an adsorption-coagulation hybrid system as nuclei for coagulation in the presence of aluminum sulfate (alum) showed a synergistic effect in a HA-dominated NOM solution. An AB-alum hybrid system with a high proportion of HA in the NOM solution may be applicable as an end-of-pipe solution.

Adsorption characteristics of diclofenac and sulfamethoxazole to graphene oxide in aqueous solution.

The adsorptive properties of graphene oxide (GO) were characterized, and the binding energies of diclofenac (DCF) and sulfamethoxazole (SMX) on GO adsorption were predicted using molecular modeling. The adsorption behaviors of DCF and SMX were investigated in terms of GO dosage, contact time, and pH. Additionally, the effects of sonication on GO adsorption were examined. GO adsorption involves "oxygen-containing functional groups" (OCFGs) such as COOH, which exhibit negative charges over a wide range of pH values (pH 3-11). DCF (-18.8 kcal mol(-1)) had a more favorable binding energy on the GO surface than SMX (-15.9 kcal mol(-1)). Both DCF and SMX were removed from solution (adsorbed to GO), up to 35% and 12%, respectively, within 6h, and an increase in GO dosage enhanced the removal of DCF. Electrostatic repulsion occurred between dissociated DCF/SMX and the more negatively charged GO at basic pH (>pKa). The sonication of GO significantly improved the removal of DCF (75%) and SMX (30%) due to dispersion of exfoliated GO particles and the reduction of OCFGs on the GO surface. Both DCF and SMX in the adsorption isotherm were explained well by the Freundlich model. The results of this study can be used to maximize the adsorption capacities of micropollutants using GO in water treatment processes.

Removal of acetaminophen and naproxen by combined coagulation and adsorption using biochar: influence of combined sewer overflow components.

The combined coagulation and adsorption of targeted acetaminophen and naproxen using activated biochar and aluminum sulfate were studied under various synthetic "combined sewer overflow" (CSO) conditions. The biochar demonstrated better adsorption performance for both acetaminophen and naproxen (removal, 94.1 and 97.7%, respectively) than that of commercially available powdered activated carbon (removal, 81.6 and 94.1%, respectively) due to superior carbonaceous structure and surface properties examined by nuclear magnetic resonance analysis. The adsorption of naproxen was more favorable, occupying active adsorption sites on the adsorbents by naproxen due to its higher adsorption affinity compared to acetaminophen. Three classified CSO components (i.e., representing hydrophobic organics, hydrophilic organics, and inorganics) played different roles in the adsorption of both adsorbates, resulted in inhibition by humic acid complexation or metal ligands and negative electrostatic repulsion under adsorption and coagulation combined system. Adsorption alone with biochar was determined to be the most effective adsorptive condition for the removal of both acetaminophen and naproxen under various CSO conditions, while both coagulation alone and combined adsorption and coagulation failed to remove the acetaminophen and naproxen adequately due to an increase in ionic strength in the presence of spiked aluminum species derived from the coagulant.

Adsorption of selected endocrine disrupting compounds and pharmaceuticals on activated biochars.

Chemically activated biochar produced under oxygenated (O-biochar) and oxygen-free (N-biochar) conditions were characterized and the adsorption of endocrine disrupting compounds (EDCs): bisphenol A (BPA), atrazine (ATR), 17 α-ethinylestradiol (EE2), and pharmaceutical active compounds (PhACs); sulfamethoxazole (SMX), carbamazepine (CBM), diclofenac (DCF), ibuprofen (IBP) on both biochars and commercialized powdered activated carbon (PAC) were investigated. Characteristic analysis of adsorbents by solid-state nuclear magnetic resonance (NMR) was conducted to determine better understanding about the EDCs/PhACs adsorption. N-biochar consisted of higher polarity moieties with more alkyl (0-45 ppm), methoxyl (45-63 ppm), O-alkyl (63-108 ppm), and carboxyl carbon (165-187 ppm) content than other adsorbents, while aromaticity of O-biochar was higher than that of N-biochar. O-biochar was composed mostly of aromatic moieties, with low H/C and O/C ratios compared to the highly polarized N-biochar that contained diverse polar functional groups. The higher surface area and pore volume of N-biochar resulted in higher adsorption capacity toward EDCs/PhACs along with atomic-level molecular structural property than O-biochar and PAC. N-biochar had a highest adsorption capacity of all chemicals, suggesting that N-biochar derived from loblolly pine chip is a promising sorbent for agricultural and environmental applications. The adsorption of pH-sensitive dissociable SMX, DCF, IBP, and BPA varied and the order of adsorption capacity was correlated with the hydrophobicity (Kow) of adsorbates throughout the all adsorbents, whereas adsorption of non-ionizable CBM, ATR, and EE2 in varied pH allowed adsorbents to interact with hydrophobic property of adsorbates steadily throughout the study.