A comprehensive review of mathematical models developed for the estimation of organic disinfection byproducts.

In this review, we present comparative and comprehensive views on the foundations, potentials and limitations of the previously reported mathematical models for the estimation of the concentration of disinfection byproducts (DBPs) generated during the chlor(am)ination of water. To this end, DBPs models were divided into two major categories: static variable (SV) and dynamic variable (DV) or differential models. In SV models, variables remain in their original form throughout a chlor(am)ination modelling period while DV models consider the changes driven by a chlor(am)ination treatment as the variables. This classification and the comparative study of the two types of models led to a better understanding of the assumptions, potentials, and limitations of the existing DBP models. In opposition to several claims in the literature, certain DV models based on UV absorbance/fluorescence failed to selectively track the chromophores responsible for DBP formation. In this critical review, a conceptual model for the photophysics of dissolved organic matter (DOM) based on the theory of electron delocalization was proposed to explain some inconsistent spectroscopic properties of DOM following chlor(am)ination and several unique photophysical properties of DOM. New insights for the development and deployment of mathematical models were also provided to estimate DBPs in various settings.

Polyethyleneimine modification of activated fly ash and biochar for enhanced removal of natural organic matter from water via adsorption.

In this study, fly ash (FA) and biochar (BC), two common industrial byproducts, were activated and surface-modified with polyethyleneimine (PEI) to enhance their capacities to remove natural organic matter (NOM) from water via adsorption. Different fluorescent components were identified using fluorescence excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) to explore the individual adsorption behaviors of different organic constituents in a bulk NOM. The NOM adsorption was quantitatively examined via adsorption isotherm and kinetics models. Compared to the pristine adsorbents, the functionalized adsorbent with increased surface area and positive surface charge achieved higher NOM adsorption. By evaluating the adsorptive behaviors of UV-absorbing and fluorescent moieties, it was concluded that the operative mechanism of adsorption included electrostatic attraction, hydrogen bonding, and π-π interaction. At the optimal pH of 3, the surface-modified FA and BC (i.e., FA-PEI and BC-PEI) had adsorption capacities for NOM that were ∼3 times higher than the capacities of the pristine materials. Due to its aromatic features, π-π interaction may have enhanced BC and BC-PEI selective adsorption of aromatic NOM components compared to FA and FA-PEI. Kinetic modelling showed that the mesopores of FA-PEI were available for NOM adsorption and diffusion of NOM molecules into the mesoporous structures was rate-limiting. On the other hand, PEI-modification may have further reduced NOM diffusion through the narrow micropores in BC such that external adsorption primarily occurred on BC-PEI. The modified adsorbents showed a faster adsorption kinetics than the pristine counterparts and a high durability in repeated adsorption-desorption cycles.

Enhancing copper binding property of compost-derived humic substances by biochar amendment: Further insight from two-dimensional correlation spectroscopy.

Little is known about the environmental impacts of biochar (BC) amendment on the immobilization of heavy metals in compost-treated fields. In consequence, this study was designed to explore the effects of BC amendment on the copper (Cu) binding properties of compost-derived humic substances (HS). To this end, unamended and 4.7% (by wet weight) BC-amended compost were incubated in parallel with regular wetting for 6 months. The stability constants for Cu binding, calculated based on the fluorescence quenching technique, were higher for the compost-derived HS with versus without BC amendment. The result suggests that BC addition to compost may intensify the immobilization of heavy metals in a compost-treated field. Copper binding efficacy increased after the incubation with or without BC amendment. However, the enhanced Cu binding efficacy of the BC-amended HS was preserved even after the long-term incubation. Two-dimensional correlation spectroscopy revealed that the short wavelength fulvic-like fluorescence followed by humic-like fluorescence were preferentially associated with Cu binding. However, the range of wavelengths that tracked the binding of Cu were modified after BC amendment. This study evidenced beneficial and synergetic effects of BC amendment on the abatement of the potential environmental risk from heavy metal polluted field on a long-term basis.

Oxidation byproducts from the degradation of dissolved organic matter by advanced oxidation processes - A critical review.

Advanced oxidation processes (AOPs) have been increasingly used for the treatment of source waters and wastewaters. AOPs characteristically produce oxidation byproducts (OBPs) from the partial degradation of dissolved organic matter (DOM) and/or the transformation of inorganic ions (especially, halides) into highly toxic substances including bromate and halogenated organic OBPs (X-OBPs). However, despite the enormous health and environmental risks posed by X-OBPs, an integral understanding of the complex OBP formation mechanisms during AOPs is lacking, which limits the development of safe and effective AOP-based water treatment schemes. The present critical and comprehensive review was intended to fill in this important knowledge gap. The study shows, contrary to the hitherto prevailing opinion, that the direct incorporation of halide atoms (X•) into DOM makes an insignificant contribution to the formation of organic X-OBPs. The principal halogenating agent is hypohalous acid/hypohalite (HOX/XO-), whose control is, therefore, critical to the reduction of both organic and inorganic X-OBPs. Significant generation of X-OBPs has been observed during sulfate radical AOPs (SR-AOPs), which arises principally from the oxidizing effects of the unactivated oxidant and/or the applied catalytic activator rather than the sulfate radical as is commonly held. A high organic carbon/X- molar ratio (>5), an effective non-catalytic activator such as UV or Fe2+, a low oxidant concentration, and short treatment time are suggested to limit the accumulation of HOX/XO- and, thus, the generation of X-OBPs during SR-AOPs. At present, there are no established techniques to prevent the formation of X-OBPs during UV/chlor(am)ine AOPs because the maintenance of substantial amounts of active halogen is essential to these processes. The findings and conclusions reached in this review would advance the research and application of AOPs.

Synthetic magnetite, maghemite, and haematite activation of persulphate for orange G degradation.

Due to the widespread application of persulphate (PS) for in-situ chemical oxidation (ISCO), the PS activating role of naturally occurring minerals, such as iron oxides, has been the subject of a number of studies. However, major discrepancies remain as to the effectiveness, mode, and factors that influence iron oxides activation of PS. In this study, an attempt has been made to bridge this important knowledge gaps by a systematic study of PS activation, measured by orange G degradation, using commercial and self-synthesised magnetite, maghemite, and haematite particles. The results showed that the activation of PS by iron oxides does not depend on mineralogy, surface area or concentration of surface OH groups, but on crystalline inhomogeneities or structural irregularities. Significant dissolution of iron oxides accompanied PS activation, in a mainly homogeneous process, requiring a low pH environment to be effective. The activation of PS by iron oxides at neutral pH was found to be no better than dissolved iron activation contrary to some earlier publications. The results also suggest that under alkaline conditions, PS alone was more effective in degrading orange G than with iron oxides or dissolved iron activation. Phosphate buffer significantly retarded orange G degradation by iron-activated or unactivated PS with negative implication for ISCO in non-acidic, buffering environments. The results of this study contribute to enhancing the fundamental understanding of ISCO processes.

Effects of dissolution conditions on the properties of PVDF ultrafiltration membranes.

Poly (vinylidene fluoride) (PVDF) is an important membrane forming material for water treatment. Earlier works have shown that major morphological changes can be achieved when PVDF is dissolved under different conditions with practical applications in membrane distillation and protein attachment. However, no previous report has discussed the effects of dissolution conditions on the performance of PVDF under ultrafiltration, which is one of the most important applications of the polymer. In this work, four different PVDF ultrafiltration membranes were produced from dopes dissolved either by stirring at 24°C, 90°C, 120°C or by sonication. It is shown that dope sonication results in membrane with enhanced thermal and mechanical stability, improved permeate flux during oil emulsion filtration and high flux recovery of ∼63% after cleaning. As a comparison, flux recovery of only ∼26% was obtained for the membrane produced from dope dissolved at 24°C. The outstanding performance of the dope-sonicated membrane was linked to its slightly lower porosity, narrow distribution of small pores and relatively smooth skin layer. Performance parameters for all membranes showed good correlation to porosity suggesting a tool for membrane design achievable by simple variation in the mode of polymer dissolution. The polymer dissolution effect was related to the degree of unfolding of the polymer molecular chains and their entanglements.