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  • 1.
    Carlos-Pinedo, Sandra
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Environmental Science.
    Wang, Zhao
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Environmental Science.
    Eriksson, Ola
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Environmental Science.
    Methane yield from SS-AD: Experiences to learn by a full spectrum analysis at laboratory-, pilot- and full-scale2019In: Biomass and Bioenergy, ISSN 0961-9534, E-ISSN 1873-2909, Vol. 127, article id 105270Article, review/survey (Refereed)
    Abstract [en]

    Solid-state anaerobic digestion (SS-AD) takes place when solid content of the substrate is higher than 15%. Some advantages of this technology have been recognized as e.g., less required water added to raw feedstock and consequently minimized digester size and cost, higher volumetric organic loading rates (OLR) that may lead to higher efficiency methane yield and better acceptance of a wide range of feedstocks. However, scientific studies of SS-AD at pilot- and full-scale are very few and difficulties have been reported in operating SS-AD, especially when the system undergoes a scale-up, where methane production is the purpose. As a result, this review gives a summary of scientific studies for SS-AD processes at laboratory-, pilot- and full-scale, where a great diversity of substrate composition, reactor design and operational parameters have been categorized, and their performances in terms of methane yield have been analyzed. This, in turn, helps to identify that factors affecting methane yields at different scales arise mainly from operational conditions as well as the characteristic of feedstocks. This review even contributes to suggest several strategies for improvement of methane yield at full-scale.

  • 2.
    Guven, H.
    et al.
    Istanbul Technical University, Civil Engineering Faculty, Environmental Engineering Department, Istanbul, Turkey.
    Wang, Zhao
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Environmental Science.
    Eriksson, Ola
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Environmental Science.
    Evaluation of future food waste management alternatives in Istanbul from the life cycle assessment perspective2019In: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 239, article id 117999Article in journal (Refereed)
    Abstract [en]

    In developing countries like Turkey, food waste has the highest share compared to other municipal solid waste components. A detailed life cycle assessment has been performed to evaluate different food waste management options (i.e., landfilling, anaerobic digestion, thermal treatment, co-treatment with municipal wastewater) for Istanbul which is the largest city of Turkey and Europe. The current waste management has the worst environmental performance compared to proposed waste management scenarios as follows: Anaerobic digestion, thermal treatment and co-treatment with municipal wastewater. The thermal treatment scenario has been found to have the best environmental performance in most of the impact categories including climate change. The anaerobic digestion scenario ranks in the first place only in freshwater eutrophication, which is attributed to avoided fertilizer use in this scenario. A drastic improvement with 866% has been found in this category if the anaerobic digestion scenario was followed. Co-treatment with municipal wastewater refers to use of food waste disposers at households and provides improvements especially in marine eutrophication and ecotoxicity. Lower effluent emissions by means of biological wastewater treatment in the co-treatment scenario compared to other proposed scenarios lead to better performance in these categories. Various sub-scenarios have also been investigated such as using biogas as vehicle fuel, replacing a combined heat and power with a condensing plant and increasing food waste addition to sewer lines. Important improvements are not achievable in the first two sub-scenarios; however, increasing food waste addition to sewer lines reduces various environmental impact categories by −41% and −60%. © 2019 Elsevier Ltd

  • 3.
    Guven, Huseyin
    et al.
    Istanbul Technical University, Civil Engineering Faculty, Environmental Engineering Department, Ayazaga Campus, Maslak, Istanbul, Turkey.
    Eriksson, Ola
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Environmental engineering.
    Wang, Zhao
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Environmental engineering.
    Ozturk, Izzet
    Istanbul Technical University, Civil Engineering Faculty, Environmental Engineering Department, Ayazaga Campus, Maslak, Istanbul, Turkey.
    Life cycle assessment of upgrading options of a preliminary wastewater treatment plant including food waste addition2018In: Water Research, ISSN 0043-1354, E-ISSN 1879-2448, Vol. 145, p. 518-530, article id S0043-1354(18)30691-2Article in journal (Refereed)
    Abstract [en]

    Life cycle assessment (LCA) is a beneficial tool to evaluate the performance of wastewater treatment plants (WWTPs) and to compare different upgrading options. The main objective of this study is to investigate the environmental impact of upgrading options of a preliminary WWTP in Istanbul, Turkey. The preliminary plant currently consists of mechanical treatment units and various upgrading options including primary treatment and high-rate activated sludge system (HRAS) process as well as the addition of food waste to wastewater were compared. Results showed that the baseline scenario (S0) had worse performance than all future scenarios (S1-3) except for climate change. The scenario of adding food waste to wastewater (S3) has the best performance in climate change, terrestrial acidification, terrestrial ecotoxicity and fossil depletion. Increased addition of food waste was also tested in the sensitivity analysis, and major improvements were obtained especially in climate change and terrestrial ecotoxicity.

  • 4.
    Wang, Zhao
    KTH.
    A weighted correlation approach of the density functional theory for an inhomogeneous fluid at an interface2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This doctoral thesis presents a newly developed density functional theory (DFT), i.e., the weighted correlation approach (WCA), to study the structural and thermodynamic properties of an inhomogeneous fluid at an interface. The WCA approach provides a generic formulation to evaluate the change of the single-particle direct correlation function in terms of a series of pair direct correlation functions weighted by different correlation-weight functions with adjustable correlation-weight factors. When applied practically, however, an approximation of the pair direct correlation function has to be made, together with appropriate definitions of the weighted densities and the choices of the correlation-weight functions. Despite this seeming complexity, it is shown that the WCA approach can be regarded as a generalization of the classic density functional approaches and this enables us to develop and apply DFT methods in different ways. For demonstration purposes, several implementations of the WCA approach are proposed and applied to predict the density distribution of an inhomogeneous fluid at an interface. The WCA approach is also employed with a novel pressure expression to investigate the inhomogeneous fluid-mediated interaction pressure for different cases. The WCA calculations from the above applications suggest that it is a successful approach for describing the structural and thermodynamic properties of an inhomogeneous fluid at an interface, as compared to the published results of the Monte Carlo simulations, density functional methods and experimental data.

  • 5.
    Wang, Zhao
    et al.
    KTH, Kemisk apparatteknik.
    Liu, Longcheng
    KTH, Kemisk apparatteknik.
    Hard-sphere fluid-mediated interaction: a novel pressure expression with application of the weighted correlation approachIn: Article in journal (Other academic)
  • 6.
    Wang, Zhao
    et al.
    KTH, Kemisk apparatteknik.
    Liu, Longcheng
    KTH, Kemisk apparatteknik.
    The swelling pressure of Na-bentonite: Study with a density functional approach2012In: Chemistry Letters, ISSN 0366-7022, E-ISSN 1348-0715, Vol. 41, no 10, p. 1346-1348Article in journal (Refereed)
    Abstract [en]

    The combination of the fundamental measure theory (FMT) and the weighted correlation approach (WCA) within the framework of the density functional theory, i.e., the FMT/ WCA approach, is applied to study the swelling pressure of Nabentonite at different salt conditions. Good agreement between the FMT/WCA simulations and the results from both experiments and a Donnan-equilibrium-based DLVO model suggests that the hydration repulsion between charged surfaces can be well accounted by the ionion correlations effect.

  • 7.
    Wang, Zhao
    et al.
    KTH, Kemisk apparatteknik.
    Liu, Longcheng
    KTH, Kemisk apparatteknik.
    Weighted correlation approach: An extended version with applications to the hard-sphere fluid2012In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 86, no 3, article id 031115Article in journal (Refereed)
    Abstract [en]

    The purpose of this study is to extend the weighted correlation approach (WCA) for inhomogeneous fluids. It now introduces a generic expression to evaluate the single-particle direct correlation function in terms of a series of pair direct correlation functions weighted by different correlation-weight functions and adjustable weight factors. When applied for practical use, however, approximations of the pair direct correlation functions have to be made, together with appropriate definitions of the weighted densities and the choices of the correlation-weight functions. The WCA approach would, then, not only help us to connect and compare different strategies and their underlying assumptions in the density functional approaches, but also enable us to propose and apply density functional theory methods to predict the density profile of, e. g., the hard-sphere fluid confined between a pair of parallel planar hard walls. Numerical results of the extended WCA approach, against the Monte Carlo (MC) simulations in a range of surface separations and bulk densities, suggest that it is capable of representing the fine features of the hard-sphere density distributions. The WCA results also agree well with the calculations from the fundamental measure theory. In addition, the thermodynamic self-consistency of the WCA approach is confirmed by its fairly good agreement with the MC fitted data for the surface tension of a hard-sphere fluid at a planar hard wall. All these tests show that a pure WCA approach can be constructed to investigate the states of ionic hard-sphere fluids.

  • 8.
    Wang, Zhao
    et al.
    KTH.
    Liu, Longcheng
    KTH, Kemisk apparatteknik.
    Neretnieks, Ivars
    KTH, Kemisk apparatteknik.
    A novel method to describe the interaction pressure between charged plates with application of the weighted correlation approach2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 135, no 24, p. 244107-Article in journal (Refereed)
    Abstract [en]

    Based on the Euler-Lagrange equation for ion density distribution in an inhomogeneous, charged, and hard-sphere fluid, a novel method is proposed to determine the interaction pressure between charged plates. The resulting expression is a sum of distinct physical contributions to the pressure, which involves different contributions to the single-particle direct correlation function. It can, therefore, be conveniently used in any density functional approach to facilitate analysis of the pressure components. In this study, the so-called fundamental measure theory (FMT)/weighted correlation approach (WCA) approach is applied to estimate both the hard-sphere and the electric residual contributions to the single-particle direct correlation function, upon the calculation of the ionic density profiles between charged plates. The results, against the Monte Carlo simulations, show that the FMT/WCA approach is superior to the typical FMT/mean spherical approximation approach of the density functional theory in predicting the interaction pressure between charged plates immersed in an electrolyte solution upon various conditions in the primitive model. The FMT/WCA approach can well capture the fine features of the pressure-separation dependence, to reproduce not only the shoulder shape and the weak attractions in monovalent electrolytes but also the strongly oscillatory behavior of pressure in divalent electrolytes where pronounced attractions are observed. In addition, it is found that the FMT/WCA approach even has an advantage over the anisotropic, hyper-netted chain approach in that it agrees with the Monte Carlo results to a very good extent with, however, much less computational effort.

  • 9.
    Wang, Zhao
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Environmental engineering.
    Liu, Longcheng
    Department of Chemical Engineering and Technology, Royal Institute of Technology, Stockholm, Sweden.
    Neretnieks, Ivars
    Department of Chemical Engineering and Technology, Royal Institute of Technology, Stockholm, Sweden.
    Hard-sphere fluid mediated interaction: a pressure expression with application of the weighted correlation approach2016In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 114, no 5, p. 599-607Article in journal (Refereed)
    Abstract [en]

    By using a so-called differential-integral method on the chemical potential of a hard-sphere fluid, a special variant of our previously developed expression that describes the interaction between charged plates immersed in an electrolyte, is introduced to examine the hard-sphere fluid mediated pressure in a slit. The resulting expression consists of a kinetic contribution and a hard-sphere contribution, and it is formulated as a function of the single-particle direct correlation function and the density distribution of a hard-sphere fluid. It allows us to conveniently apply the classic density functional theory to explicitly investigate the influence of the hard-sphere excluded-volume effect on the interaction pressure between surfaces. In this study, a newly proposed weighted correlation approach (WCA)-Denton and Ashcroft (DA) method is employed to predict the interaction pressure as well as its pressure components for a hard-sphere fluid inside a slit pore. Comparisons with the results from the Monte Carlo simulations and the fundamental measure theory suggest that the WCA-DA method is able to accurately capture the detailed characteristic pattern of the pressure-separation curves at different fluid densities. It is also found, both qualitatively and quantitatively, that the hard-sphere pressure contribution dominates over the kinetic pressure contribution in determining the oscillatory behaviour of the interaction pressure curves, especially when a hard-sphere fluid of high density is concerned.

  • 10.
    Wang, Zhao
    et al.
    KTH.
    Liu, Longcheng
    KTH, Kemisk apparatteknik.
    Neretnieks, Ivars
    KTH, Kemisk apparatteknik.
    The weighted correlation approach for density functional theory: a study on the structure of the electric double layer2011In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, no 17, article id 175002Article in journal (Refereed)
    Abstract [en]

    Within the framework of density functional theory, a weighted correlation approach is developed in order to obtain the density distributions of an inhomogeneous fluid. It results in a formally exact expression, by means of the concept of a weighted pair correlation function, used to evaluate the change of the single-particle direct correlation function of the system relative to that of a reference state. When applying the approach for practical use, however, an approximation of the pair correlation function has to be made, along with an appropriate definition of a weight function. Noticeably, combining this approach with fundamental measure theory gives rise to a new method, which we call the FMT/WCA-k(2) approach, for studying the structural and thermodynamic properties of a charged hard-sphere fluid subjected to a spatially varying external potential. Application of the FMT/WCA-k(2) approach in a range of electrolyte concentrations and surface charge densities, against the Monte Carlo simulations, shows that it is superior to the typical approaches of density functional theory in predicting the ionic density profiles of both counter-ions and co-ions near a highly charged surface. It is capable of capturing the fine features of the structural properties of the electric double layers, to well reproduce the layering effect and the charge inversion phenomenon, also in strongly coupled cases where divalent counter-ions are involved. In addition, it is found that the FMT/WCA-k(2) approach even has an advantage over the anisotropic, hyper-netted chain approaches in giving better agreement with the Monte Carlo results.

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