P.K. Tewari

Bio: P.K. Tewari is an academic researcher from Homi Bhabha National Institute. The author has contributed to research in topics: Desalination & Membrane. The author has an hindex of 16, co-authored 94 publications receiving 856 citations. Previous affiliations of P.K. Tewari include Indian Institute of Technology, Jodhpur & Bhabha Atomic Research Centre.

Carbon nanotube membranes for desalination and water purification: Challenges and opportunities

Abstract: Summary The importance as well as impact of application of carbon nanotube (CNT) membranes in the area of water technology development is tremendous. A substantial amount of work have been carried out with impregnation of CNTs (simply as one of the reinforcements for incorporation of better properties like antibiofouling and/or better strength, etc.) in polymer host matrix. However, the volume of work enabling CNTs as flow channels (in a membranous structure) is not significant and that is where the potential benefits of CNTs lie. Moreover, from impressive works carried out in this direction, it is quite obvious that still significant challenges have to be addressed to align the CNTs, to reinforce it in a suitable host matrix without disturbing the alignment and inhibiting the agglomeration (adoption of suitable nanocomposite fabrication route), to open the tips preferentially and to scale up favorably. It is believed that the innovative attributes put forth by CNTs and the application areas identified with CNTs are getting matured, while the area of development of CNT (based) membranes is far from being matured and it still needs to be looked into in the light of involvement of materials as well as process challenges.

Extraction of uranium from the concentrated brine rejected by integrated nuclear desalination plants

Abstract: This work was carried out under the specific collaboration agreement between the Bhabha Atomic Research Centre (BARC) from India and the Commissariat a l'Energie Atomique (CEA) from France. This paper summarises first results of review and research on the possible extraction of uranium from the concentrated brine rejected by integrated nuclear desalination systems, which both partners are currently developing in the two organisations. Three innovative and efficient methods of uranium extraction have been proposed: 1) Resin grafted with calixarene: this method has the advantage of very high selectivity. Its performances, especially for large-scale extraction, still need further RD 2) Magnetic separations: yet another method with high selectivity, easy separation and affording high degree of material recovery. The method, however, is in developmental stage; 3) Canal system with Braid adsorbents: high selectivity. Appears to be feasible in conjunction with existing technology. It would nonetheless require large amounts of adsorbents and adequate infrastructure.

Nano-ZnO impregnated inorganic–polymer hybrid thinfilm nanocomposite nanofiltration membranes: an investigation of variation in structure, morphology and transport properties

Abstract: Inorganic–polymer hybrid, thinfilm nanocomposite nanofiltration (TFN-NF) membranes prepared by in situ interfacial polymerization of branched polyethyleneimine and trimesoyl chloride, with simultaneous impregnation of as-synthesized hexagonal wurtzite ZnO nanocrystals (nano-ZnO), either through aqueous or organic phase, have been extensively characterized. XPS analysis revealed that there was no inter-atomic charge transfer between nano-ZnO and host polyamide matrix, indicating that no formation of chemical bonding occurred between them in the skin layers of the membranes. The type of interaction present within the nanocomposite polyamide matrices of the membranes was through formation of noncovalent type secondary chemical interactions with peripheral hydroxyl groups of nano-ZnO and polyamide network as substantiated through FTIR analysis. SEM revealed the formation of distinct patterns and coils, through multiple-point interactions between the nano-ZnO and the polyamide network in the membranes' skin surfaces when introduced through aqueous amine phase. However, when introduced through the organic phase, nanomaterials remained distributed as discrete clusters within the membranes' skin layers because of lack of polar environment around the reaction zone, further emphasizing the role of the medium in which the nanomaterials are incorporated. AFM showed variation of surface roughness features with change in the precursor medium of introduced nano-ZnO. Nanofiltration performance towards different solutes, providing differential rejections in the order of MgCl2 > NaCl ≥ Na2SO4, revealed that the membranes were distinctly positively charged. Solvent fluxes of the membranes were significantly higher when nanomaterials were introduced through the aqueous phase as compared to the organic phase.

Polyhydroxamic Acid Sorbents for Uranium Recovery

Abstract: Crosslinked polyacrylamides were synthesized by solution polymerization using benzoyl peroxide as the radical initiator. The water–insoluble polymer obtained was functionalized by reacting with hydroxylamine to convert the amide group into hydroxamic acid group. The resultant functionalized polymer was characterized in terms of moisture uptake, elemental composition, IR spectra, thermal stability, exchange capacity and heavy metal sorption. The sorbent, obtained in particulate form, was investigated for its sorption properties with respect to uranium from uranyl nitrate solutions under unstirred batch conditions. This paper will concentrate on preparation, characterization and performance evaluation with respect to uranium sorption as a function of concentration, time, solution pH and temperature. The potential of this sorbent for uranium and other heavy metal ion recovery from sea water is ascertained.

Development, Characterization and Performance Evaluation of Positively-Charged Thin Film-Composite Nanofiltration Membrane Containing Fixed Quaternary Ammonium Moieties

Abstract: Thin film composite (TFC) type positively-charged nanofiltration membranes, bearing fixed quaternary ammonium moieties, have been developed and studied. Branched polyethyleneimine (PEI) was functionalized by reaction with glycidyl trimethyl ammonium chloride (GTACl) to introduce quaternary ammonium chloride. Positively-charged TFC membranes were prepared by in situ interfacial polymerization of functionalized PEI and terephthaloyl chloride. The effects of variation of chemical compositions and other experimental conditions such as curing temperature and duration of curing on the performances of the membrane were studied. ATR FT-IR spectroscopy was done to establish the presence of charge-bearing groups in the membrane. The membranes were tested using single solute feed solutions of NaCl, Na2SO4, CaCl2, and MgSO4. Positive charges on the membranes were estimated in terms of their ion-exchange capacities (IEC). The values were also correlated to the solute-rejection properties of the membranes.

Reverse osmosis desalination: Water sources, technology, and today's challenges

Abstract: Reverse osmosis membrane technology has developed over the past 40 years to a 44% share in world desalting production capacity, and an 80% share in the total number of desalination plants installed worldwide. The use of membrane desalination has increased as materials have improved and costs have decreased. Today, reverse osmosis membranes are the leading technology for new desalination installations, and they are applied to a variety of salt water resources using tailored pretreatment and membrane system design. Two distinct branches of reverse osmosis desalination have emerged: seawater reverse osmosis and brackish water reverse osmosis. Differences between the two water sources, including foulants, salinity, waste brine (concentrate) disposal options, and plant location, have created significant differences in process development, implementation, and key technical problems. Pretreatment options are similar for both types of reverse osmosis and depend on the specific components of the water source. Both brackish water and seawater reverse osmosis (RO) will continue to be used worldwide; new technology in energy recovery and renewable energy, as well as innovative plant design, will allow greater use of desalination for inland and rural communities, while providing more affordable water for large coastal cities. A wide variety of research and general information on RO desalination is available; however, a direct comparison of seawater and brackish water RO systems is necessary to highlight similarities and differences in process development. This article brings to light key parameters of an RO process and process modifications due to feed water characteristics.

Polymer-matrix nanocomposite membranes for water treatment

Abstract: One of the grand challenges to sustain the modern society is to secure adequate water resources of desirable quality for various designated uses. To address this challenge, membrane water treatment is expected to play an increasingly important role in areas such as drinking water treatment, brackish and seawater desalination, and wastewater treatment and reuse. Existing membranes for water treatment, typically polymeric in nature, are still restricted by several challenges including the trade-off relationship between permeability and selectivity (also called Robeson upper boundary in membrane gas separation), and low resistance to fouling. Nanocomposite membranes, a new class of membranes fabricated by combining polymeric materials with nanomaterials, are emerging as a promising solution to these challenges. The advanced nanocomposite membranes could be designed to meet specific water treatment applications by tuning their structure and physicochemical properties (e.g. hydrophilicity, porosity, charge density, and thermal and mechanical stability) and introducing unique functionalities (e.g. antibacterial, photocatalytic or adsorptive capabilities). This review is to summarize the recent scientific and technological advances in the development of nanocomposite membranes for water treatment. The nanocomposite membranes were classified into (1) conventional nanocomposite, (2) thin-film nanocomposite (TFN), (3) thin-film composite (TFC) with nanocomposite substrate, and (4) surface located nanocomposite, based on the membrane structure and location of nanomaterial. Challenges and future research directions in developing high performance nanocomposite membranes were also discussed.

Advances in heat pump systems: A review

Abstract: Heat pump systems offer economical alternatives of recovering heat from different sources for use in various industrial, commercial and residential applications. As the cost of energy continues to rise, it becomes imperative to save energy and improve overall energy efficiency. In this light, the heat pump becomes a key component in an energy recovery system with great potential for energy saving. Improving heat pump performance, reliability, and its environmental impact has been an ongoing concern. Recent progresses in heat pump systems have centred upon advanced cycle designs for both heat- and work-actuated systems, improved cycle components (including choice of working fluid), and exploiting utilisation in a wider range of applications. For the heat pump to be an economical proposition, continuous efforts need to be devoted to improving its performance and reliability while discovering novel applications. Some recent research efforts have markedly improved the energy efficiency of heat pump. For example, the incorporation of a heat-driven ejector to the heat pump has improved system efficiency by more than 20%. Additionally, the development of better compressor technology has the potential to reduce energy consumption of heat pump systems by as much as 80%. The evolution of new hybrid systems has also enabled the heat pump to perform efficiently with wider applications. For example, incorporating a desiccant to a heat pump cycle allowed better humidity and temperature controls with achievable COP as high as 6. This review paper provides an update on recent developments in heat pump systems, and is intended to be a “one-stop” archive of known practical heat pump solutions. The paper, broadly divided into three main sections, begins with a review of the various methods of enhancing the performance of heat pumps. This is followed by a review of the major hybrid heat pump systems suitable for application with various heat sources. Lastly, the paper presents novel applications of heat pump systems used in select industries.

Carbon nanotube membranes for water purification: A bright future in water desalination

Abstract: Water pollutants have huge impacts on the entire living systems including terrestrial, aquatic, and aerial flora and fauna. In addition to conventional priority, and newly emerging micro/nano-pollutants, increasing global warming and consequent climate changes are posing major threats to the fresh water availability. Global warming and climate change are constantly increasing the salinity level of both land and sea water, dwindling the availability of existing fresh water for household, agriculture and industry. This has made it urgent to invent an appropriate water treatment technology that not only removes macro-, micro- and nano-pollutants but also desalinates water to a significant extent. Tip-functionalized nonpolar interior home of carbon nanotubes (CNTs) provides strong invitation to polar water molecules and rejects salts and pollutants. Low energy consumption, antifouling and self-cleaning functions have made CNT membranes extraordinary over the conventional ones. We comprehensively reviewed here molecular modeling and experimental aspects of CNT-membrane fabrication and functionalization for the desalination of both sea and brackish water. We present here the current problems and future challenges in water treatments. The article is potentially important for the hydrologists, membrane technologists, environmentalists and industrialists working in the field of water purification technologies to eradicate fresh water crisis in near future.