Volume 35, Issue 1

Solid-liquid circulating fluidized beds (SLCFBs) offer several attractive features over conventional solid-liquid fluidized beds such as efficient liquid-solid contact, favorable mass and heat transfer, reduced back-mixing of phases, and integrated reactor and regenerator design. These unique features have stimulated theoretical and experimental investigations over the past two decades on transport phenomena in SLCFBs. However, there is a need to compile and analyze the published information with a coherent theme to design and develop SLCFB with sufficient degree of confidence for commercial application. Therefore, the present work reviews and analyzes the literature on hydrodynamic, mixing, heat transfer, and mass transfer characteristics of SLCFBs comprehensively. Suitable recommendations have also been made for future work in concise manner based on the knowledge gaps identified in the literature. Furthermore, a novel multistage SLCFB has been proposed to overcome the limitations of existing SLCFBs. The proposed model of SLCFB primarily consists of a single multistage column which is divided into two sections wherein both the steps of utilization viz. loading (adsorption, catalytic reaction, etc.) and regeneration of solid phase could be carried out simultaneously on a continuous mode.

Water-swellable elastomers (WSE) constitute a class of rubbery materials that have been widely studied both in academia and industry during the last 25 years. Market pull is the major driver for the exploration of these materials. The need of WSE in several sealing applications has driven the attention of many academic researchers toward the possibility to provide a rubber with water-swelling characteristics. As commercial rubbers are hydrophobic materials, making them swell in water presents an interesting and difficult challenge. This paper reviews the scientific and patent literature on the fundamental aspects of WSE: the various synthetic approaches, the properties of the corresponding polymers (not only the swelling performance but also the mechanical behavior), and some of their applications. Particular attention is paid to the chemical structure/performance relationships of WSE. Finally, the authors speculate on a great future for WSE that can be rationally designed for improved and/or new applications.

Hydrocarbon-containing oily wastewater generated by various industries creates a major environmental problem all over the world since petroleum products are commonly used as energy sources and raw materials in various industries. In case of offshore/coastal oil recovery operations, produced water is discharged through either shore side outfalls or coastal rim releases. In many cases, current disposal practices leads to severe environmental pollution by contamination of petroleum hydrocarbon to the surface, ground, and coastal waterways. Therefore, it is necessary to evaluate the performance of various processes for the recovery of petroleum hydrocarbons from wastewater. In this paper, a detailed review on the different separation/treatment processes of oily wastewater is presented. Previous and recent research works are reviewed in the area of oil-water separation from wastewater and also highlight the new developments in these areas. Various separation processes and technologies such as gravity separation, flotation process, membrane process, adsorption process, biological treatment, freeze/thaw process, and photocatalytic oxidation process (PoPs)/advanced oxidation processes (AoPs) are discussed and reviewed. The adsorption properties of a wide variety of porous sorbent materials in oily wastewater treatment, particularly in the area of oil spill cleanup, are also reviewed. The advantages and disadvantages of each process are critically discussed and compared.

Fluoride contamination of groundwater has become a major concern worldwide, resulting in serious medical conditions such as dental and skeletal fluorosis. Consequently, the WHO recommends that drinking water should not contain more than 1.5 mg/l of fluoride. Various defluoridation techniques such as coagulation, reverse osmosis, activated alumina adsorption, and biosorbent adsorption have been developed. Adsorption through the activated alumina and biosorbent process is not cost effective and has regeneration problems, and the reverse osmosis process has the high initial cost which makes it unacceptable for developing countries. Coagulation is a commonly employed field technology for defluoridation, which involves the addition of aluminum salts, lime, and bleaching powder followed by rapid mixing, flocculation, sedimentation, and filtration but suffers from a limitation of high residual aluminum in treated water. This paper critically reviews the recent developments in the coagulation technique for defluoridation along with its comparison to other defluoridation techniques. The review describes the pertinent gaps in the process and throws open suggestions for extending research by citing the recent studies which may lead to the revival of the process. The description about the suspension of alumino-fluoro complexes that constitute a substantial part of the residual aluminum after alum treatment has been narrated in the paper that helps in a deeper understanding of the defluoridation mechanism. To make the process highly suitable for communities, appropriate technological interventions, such as converting it to a continuous mode of operation, replacing alum with poly-aluminum chloride (PAC), and attaching a micro-filtration unit in series of the existing process, can be done. Also, using PAC as a coagulant with sand filtration has to be considered for making the process more efficient.