Abstract
In this study, a theoretical model for the transport phenomena in a vacuum membrane distillation (VMD) unit used for desalination was developed. The model is based on the conservation equations for the mass, momentum, energy and species within the feed saline solution with coupled boundary conditions, as well as on the mass and energy balances on the membrane sides. The slip velocity and temperature jump boundary conditions due to the membrane's hydrophobicity were also taken into consideration. All combinations of effective thermal conductivity and tortuosity models, usually used in membrane distillation modeling are studied and discussed to show their adequacy with experimental data from the literature for PVDF, PTFE, and PP hydrophobic membranes used in VMD devices. It was found that neglecting slip velocity and temperature jump boundary conditions leads to an underestimation of the permeate flux. In addition, many effective thermal conductivity and tortuosity model combinations overestimate or underestimate the experimental data for pure water production, while others seem to fit it better.
Key Words
effective thermal conductivity; membrane distillation; slip flow; temperature jump; tortuosity
Address
Nizar Loussif: Laboratory for the Study of Thermal and Energy Systems LESTE-LR99ES31, ENIM, University of Monastir, Monastir, 5019, Tunisia/ Higher School of Sciences and Technology of Hammam Sousse (ESSTHS), Department of Physics,
University of Sousse, Sousse, 4011, Tunisia
Jamel Orfi: Mechanical Engineering Department, College of Engineering, King Saud University, P.O.Box 800, Riyadh 11421, Saudi Arabia
Abstract
This study aims to empirically derive a Nusselt number equation for predicting water flux in a direct contact membrane distillation (DCMD) system under varying cross flow velocities (CFV) and temperatures. The temperature of the bulk solution and the membrane surface differ due to the heat transfer coefficient. It is essential to determine the temperature of the membrane's surface using the heat transfer coefficient, which can be calculated using the Nusselt number, in order to predict the flux. The heat transfer coefficient varies due to various factors, which include membrane characteristics, operating conditions, module configurations, and overall system designs. The heat transfer coefficient varies depending on the characteristics of each system. Directly using previously reported Nusselt equations has limitations in predicting flux. It is necessary to derive an empirical equation for the system that was used in this study. One influential factor related to heat transfer is the CFV and temperature. Experiments were conducted under varying CFV (0.069–0.208 m/s) and temperatures (40–60
Key Words
cross flow velocity; heat transfer coefficient; membrane distillation; Nusselt number
Address
Bora Shin, Jaewon Shin, Yanuar Chandra Wirasembada and Jinwoo Cho: Department of Environment and Energy, Sejong University, 209 Neungdong-ro, Gwangin-gu, Seoul 05006, Republic of Korea
Abstract
In this work graphene oxide (GO) was synthesized and reduced to obtain reduced graphene oxide (rGO), which was further functionalized to obtain functionalized reduced graphene oxide (f-rGO). The performance of membranes was studied in terms of pure water flux and rejection of heavy metal. The resulting membranes showed improved water permeability, heavy metal rejection, and antifouling properties compared to pristine polyethersulfone membranes. These enhancements were attributed to increased hydrophilicity and smoother surfaces facilitated by the graphene derivatives which was analysed by contact angle analyser, atomic force microscopy and field emission scanning electron microscopy. Functionalized reduced graphene oxide containing polyethersulfone membrane gives increased water flux reaching a maximum of 257 LMH (L/m2.h) and higher metal removal nearly 86% rejection for Pb (II), 92% rejection for Cu (II) and 95% rejection for Cr (VI) as well as increased bovine serum albumin rejection of 94.2% along with 80.5% flux recovery ratio which is higher than reduced graphene oxide containing polyethersulfone and pristine polyethersulfone membranes. Overall, functionalized reduced graphene oxide containing polyethersulfone membranes exhibited the best performance, making them promising for various separation applications.
Address
Dixita P. Prajapati and C.N. Murthy: Macromolecular Materials Laboratory, Applied Chemistry Department, Faculty of Technology and Engineering, The Maharaja Sayajirao University of Baroda, Vadodara, Gujarat, India, 390001
Abstract
Algal blooms due to global warming and eutrophication causes excessive algal organic matters (AOMs) which lead to operational problems in water treatment plant such as unpleasant tastes, odors, and precursors of disinfection by-products (DBPs). In this study, the effects of several environmental factors, including dissolved organic matter (DOM), pH, and suspended solids (SS), on the growth of three different algal species and their AOM production were investigated. The increase in DOM concentration accelerated the growth of all three algal species, including Anabaena sp., Oscillatoria sp., and Microcystis aeruginosa. Also, AOMs released by these species showed the increase with the DOM concentration. In the case of pH, the growth rates of all three algal species at pH 6.0 were lower than those at both pH 7.5 and 10. Additionally, all algal species under pH 6.0 condition entered the stationary phase earlier than the other pH conditions. An increase in SS concentration was found to negatively affect algal growth by blocking the light necessary for photosynthesis. These findings suggest that environmental factors such as pH, SS, and DOM influence algal-derived organic matters which can cause problems in the water treatment plants. Therefore, it is necessary to understand the physicochemical characteristics of aquatic ecosystem for effective AOM management.
Key Words
algal organic matter (AOM); DOM; pH; SS
Address
Se-Hyun Oh and Yunchul Cho: Department of Civil and Environmental Engineering, Daejeon University, 62 Daehak-ro, Dong-gu, Daejeon 34520, Republic of Korea
Jing Wang: Research and Development Department, CanFit Resource Technologies Inc., 65 Fushi-Ro, Haidian District, Beijing, China
Abstract
Reed bed treatment systems utilize natural processes involving wetland vegetation, soils and their associated microbial assemblages to enhance the water quality for recycling. Reed plants are cost effective method of remediating the wastewater. In order to prove the removal mechanism from sewage and paper mill effluents, four different reed plant species, viz, Canna indica (Indian Shot), Colocassia esculenta (Taro), Typha domingensis (Southern Cattail) and Xanthosoma sagittifolium (Tannia), were compared for their removal efficacy. Up to 7 days, the screening was done with the effluents in four different reeds. The result shows that the Canna indica and Colocassia esculenta could be the better option for pollutant removal from the sewage and paper mill effluent, respectively. Canna indica showed the higher Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) removal by reducing the organic pollutant load due to presence of microbes near the rhizosphere which use oxygen as the source produced from the root's respiration process. This removal percentage was positively related to Radial Oxygen Loss (ROL) and microflora in the rhizosphere of reed plants. The highest ROL and the microbial population were recorded by the rhizosphere of Canna indica followed by Colocasia esculenta and Typha domingensis. Because of the high cost and limited effects of present physicochemical treatments in the wastewater treatment plant, this reed bed system can act as a cheaper process essential to remove the organic pollutants, thus making them suitable for agricultural and irrigation purposes. Therefore, it was concluded that Canna indica can be used as the best biological treatment choice for both the sewage and paper mill effluents.
Key Words
biofouling and reed bed system; pollutant removal; sewage reclamation; sustainability; wastewater treatment
Address
Kanagaraj Blessy Monica, Muthunalliappan Maheswari, Periyasamy Dhevagi and Ganesan Karthikeyan: Department of Environmental Sciences, Tamil Nadu Agricultural University, Coimbatore – 641003, India
Eswaran Kokiladevi: Department of Plant Biotechnology, Tamil Nadu Agricultural University, Coimbatore – 641003, India
Thiyagarajan Chitdeshwari: Department of Soil Science and Agricultural Chemistry, Tamil Nadu Agricultural University, Coimbatore – 641003, India, Uthandi Sivakumar
Uthandi Sivakumar: Department of Agricultural Microbiology, Tamil Nadu Agricultural University, Coimbatore – 641003, India
