Journal of Environmental Engineering

The Radke–Prausnitz model, a typical three-parameter model belonging to the Langmuir–Freundlich-type equation, is increasingly being used to correlate the equilibrium data of various adsorption processes. However, very few published works provide the correct information on (1) the nonlinear form of this model, (2) the units of its parameters, and (3) its original citation. This work provides a critical analysis of the Radke–Prausnitz model with special emphasis on promoting its proper application in adsorption research. The correct expression and citation of the models used in adsorption studies are provided. The correct units of its parameters $a_{\mathrm{RP}}$, $b_{\mathrm{RP}}$, and $\beta$ are $\mathrm{L}/\mathrm{kg}$, $({\mathrm{mol}/\mathrm{kg})/(\mathrm{mol}/\mathrm{L})}^{\beta }$, and unitless when the solution phase concentration $C_e$ is given in $\mathrm{mol}/\mathrm{L}$ and the adsorbed phase concentration $q_e$ is defined in $\mathrm{mol}/\mathrm{kg}$. The Radke–Prausnitz model can be reduced to the Henry, Freundlich, Langmuir, or Redlich–Peterson model in some special cases. The Radke—Prausnitz model is valid when the exponent $\beta$ is in the range of $0\le \beta \le 1$. A new adsorption equilibrium constant of this model is introduced. The feasibility of using the new equilibrium constant to calculate the thermodynamic parameters ($\mathrm{\Delta }G°$, $\mathrm{\Delta }H°$, and $\mathrm{\Delta }S°$) of adsorption processes is discussed herein.

Abstract

The increasing population growth, urbanization, climate change, mismanagement of water resources, and poorly planned water distribution systems with negligible integration with spatial planning are increasing water stress in many countries across the globe. Even though optimization of water distribution systems and integrated water management practices are being implemented in many cities and regions, there is a lack of an integrated study considering the urban water supply system, planning, and management. This paper identifies the various parameters and indicators to be considered along with the relevant tools and techniques for optimizing water resources, optimum water resource allocation, and integrated water supply and management. During the research, 116 indicators were identified through a literature review, followed by a three-round Delphi survey to attain consensus from 30 experts. At the end of the third round, 72 indicators achieved maximum consensus among the experts ($\mathrm{W}=0.741$). The identified indicators can be used for developing an integrated model for urban water supply systems, planning, and management.

Practical Applications

The changing climate, increasing urbanization, and rampant population growth are creating multiple challenges of water quality, water scarcity, floods, and droughts all over the globe. For present and future water security, it is essential to integrate the three aspects of urban waters, i.e., water supply systems or the different water resources like surface water, groundwater, recycled water, reclaimed water, and rainwater; water supply planning, which considers the planning for the present and future water demand, a contingency plan in case of emergency and water distribution system integrating the topography and spatial planning of a city or region; and water supply management, which addresses the allocation, distribution, and management of water resources along with recycling and reuse of wastewater. For the integration of these three aspects, an integrated model needs to be developed addressing all these together. In this paper, different indicators that should be considered for the integrated model have been derived through expert opinions followed by an empirical analysis to finalize the list of indicators.

The Xisha islands is a unique area where offshore structures can be utilized as exploration bases in the remote sea. Forecasting of sea state parameters is critical for the design and operation of offshore structures. The goal of this work is to establish an effective operational model to simulate wind waves in the Xisha Islands based on the third-generation wave model WAVEWATCH-III. During the process, two significant difficulties are highlighted and addressed: grid modeling optimization and physical source terms assessment. Typhoon-induced waves using different grid modeling techniques and physical parameterizations were modeled and evaluated using buoy measurements near islands and reefs. It was found that the unstructured triangular grid had a better performance than the other grid options in complex terrain environments like the Xisha Islands. The ST2 source-term package can provide efficient and accurate results in significant wave heights than the other source-term packages in the South China Sea.

In this study, three different electrocoagulation (EC) sludges were studied as an adsorbent (removal of humic acids) and as a catalyst [catalytic wet peroxide oxidation (CWPO) of bisphenol A (BPA)]. The sludges originated from electrocoagulation process in which aluminum (Al) and iron (Fe) electrodes were used for the treatment of mining industry wastewater. All the materials were used as dried sludge and calcined material. The stability of these materials was studied in neutral and alkaline conditions with analysis of the leached iron content in solution. Based on the EC sludge characterization with X-ray fluorescence (XRF), X-ray diffractometer (XRD), and diffuse-reflectance infrared Fourier transform (DRIFT) spectroscopy different forms of Fe occurring in EC sludges were found. The Brunauer–Emmett–Teller (BET) method showed reduced surface area after calcination process. Stability of the sludges was studied in neutral conditions, and the amount of iron leaching was low ($<1.4\mathrm{ppm}$). Adsorption experiments showed that the removal of humic acids (measured as total organic carbon) was over 50% in all tested materials in the pH range of 3–9, and over 92% with the S3 calcined material in all studied pH range. The calcined samples were catalytically more active than raw material in CWPO of BPA. The highest removal of BPA was 85% over calcined sludge. Therefore, calcined EC sludges are suitable materials for catalyst and adsorbent use. The main novelty of this paper was the finding of sludge modification in the EC process of water treatment through different electrode material and current density. This modification can be made in EC water treatment process, and it may provide low-cost materials to different utilization of EC sludge.

Abstract

In this study, novel Z-scheme heterojunction photocatalyst ${\mathrm{CoWO}}_4/\mathrm{RGO}/\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ was successfully fabricated by a facial hydrothermal. Obtained morphology and topography studies indicated that deposition of reduced graphene oxide (RGO) and ${\mathrm{CoWO}}_4$ nanoparticles did not affect the structure of $\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ sheets. However, optical results showed that visible light absorption of the material was significantly improved. The synthesized heterojunction photocatalyst exhibited improved photocatalytic performance in the novel degradation of rhodamine B, even upon visible irradiation. The improved photocatalytic performance was ascribed to interfacial contact between $\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ and ${\mathrm{CoWO}}_4$ in a Z-scheme heterojunction in which RGO served as electron mediator accelerating its transfer between $\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ and ${\mathrm{CoWO}}_4$ to minimize recombination of photogenerated electron-hole pairs. Therefore, rhodamine B degradation by ${\mathrm{CoWO}}_4/\mathrm{RGO}/\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ was 1.87 times higher than pristine $\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$. The synthesized heterojunction was relatively stable with no distinct reduction in photocatalytic activity after three recycling runs. The fabrication of heterojunction ${\mathrm{CoWO}}_4/\mathrm{RGO}/\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ is an efficient strategy to develop high-performance photocatalysts for various photocatalytic applications.

Practical Applications

The process of rapid industrialization and modernization has led to a global population explosion and resulting severe environmental pollution of soil, water, and air. In the process of treating environmental pollutants, humans leave wastewater with a large amount of hazardous pollutants such as heavy metals, carcinogenic metals, pesticides, insecticides, herbicides, and dyes, which are discharged directly into ecosystem and the natural environment. There are many different methods and materials to remove these pollutants. Among the most optimal approaches to remove pollutants are photocatalysis and carbon nitride ($\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$)-based nanomaterials ($\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ is a nonmetallic semiconductor material with high thermal, chemical stability, low bandgap energy, and a layered structure similar to graphite). It is useful in reducing operating costs and the scale of the equipment system and increasing recovery of contaminants after reaction. Due to its advantage in specific surface area, which is a very important property for pollutant removal, $\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ materials are currently being used as advanced materials. It has the potential for future removal of pollutants compared with previous traditional materials. This study summarizes the potential use of this nanomaterial to remove contaminants in solution, and future directions for developing countries such as Vietnam.

Water in municipal sludge has an electric double layer (EDL), and can be rapidly removed via electroosmosis. However, the understanding of the physical mechanisms of electroosmosis is limited owing to the complex pore structure of sludge porous media, which may restrict the development of electric dewatering (EDW) technology. In this study, the sludge microstructure was measured using the computerized tomography technique and quantitatively characterized using fractal geometry. A new pore-scale physical model for the electroosmotic flow through sludge porous media was developed based on the EDL theory, and the analytical expressions for the electroosmotic flow rate and permeability coefficient were determined. The proposed fractal pore-scale model for electroosmotic flow was validated by comparing it with the measured electroosmotic flow rate using a self-designed EDW device for municipal sludge composed of a hydraulic system and applied electric field. The results show that the electroosmotic flow rate of sludge porous media depends not only on the applied electric field, but also on the sludge microstructure including porosity, maximum pore size, and pore and tortuosity fractal dimensions. However, the correlation between the electroosmotic flow rate and the voltage gradient was usually nonlinear, and became linear only if the tortuosity fractal dimension equaled to one (straight flow path). The electroosmotic permeability coefficient increases with an increase in porosity; however, it is lowered by the increased pore and tortuosity fractal dimensions under a certain porosity. The electroosmosis phenomenon can effectively remove part of the interstitial water and surface water in sludge porous media, and the proposed electroosmotic physical model provides a useful theoretical basis for the development of EDW technology for municipal sludge.