S. A. Tiwari

Bio: S. A. Tiwari is an academic researcher. The author has contributed to research in topics: Reverse osmosis & Desalination. The author has an hindex of 2, co-authored 2 publications receiving 13 citations.

Fouling and cleaning of seawater reverse osmosis membranes in Kalpakkam nuclear desalination plant

Abstract: A seawater reverse osmosis plant of 1800 m³/day capacity is part of the 6300 ³/day capacity nuclear desalination demonstration project at Kalpakkam. The plant was commissioned in October 2002 and is in continuous operation. This paper deals with types of foulants, membrane cleaning procedures and the improvement in the reverse osmosis system after cleaning. This paper also describes the analysis of foulants, which may consist of adsorbed organic compounds, particulate matter, micro-organisms and metallic oxides, and describes the chemical cleaning procedure to be adopted, which is specific the seawater used because the membrane foulants are very specific with respect to the seawater constituents. The cleaning of the membranes in the Kalpakkam nuclear desalination plant was taken up because the quality of the permeate had deteriorated and the differential pressure across the membrane had gone up. This paper essentially deals with the selection of cleaning chemicals, the experience gained with the cleaning procedure adopted and the effects of cleaning on the membrane system.

Assessment of an ultrafiltration pre-treatment system for a seawater reverse osmosis plant

Abstract: The seawater reverse osmosis system requires extensive pre-treatment in order to ensure reliable performance. The conventional pre-treatment system involves dosing of chemicals, which requires frequent monitoring of raw water quality, and also involves adjusting the dosage. Besides being cumbersome, there is a lot of time lag involved in carrying out these measures. This calls for pre-treatment systems based on physicochemical mechanisms. During the last few years, Ultrafiltration (UF) has emerged as a leading unit operation in order to render raw seawater compatible with reverse osmosis operations. In this context, the Desalination Division of BARC has already installed an operational UF pre-treatment system. In this paper, we examine the role of UF in the overall operations of the seawater reverse osmosis system.

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.

Radioactive decontamination of water by membrane processes - A review

Abstract: The recent accident at the Fukushima Daiichi Nuclear Power Plant caused by the Great East Japan Earthquake of March 11, 2012 reminded us vividly of the serious hazards of radioactive substances spread over a wide range of the affected region. Currently, there is a great concern over the effect of contaminated soil and water on the health and safety of the inhabitants of the region. Hence, the advancement in the technologies of nuclear waste treatment is of vital importance if we decide to live with nuclear power to maintain our modern civilization. Among various separation technologies used, membrane technologies have been chosen in this article since they are considered as one of the emerging technologies with many advantages over the conventional processes. In this review the membrane technology is classified into different processes and, for each process, progress made since the onset of this millennium in the radioactive decontamination of water is shown. The new directions are shown by considering the progress made in membrane manufacturing and membrane processes. Thus, the combined efforts of the researchers who are engaged in membrane and membrane process design with those who are engaged in nuclear waste treatment near the plant sites were highlighted.

Efficiency of ultrafiltration for the pre-treatment of dye-bath effluents

Abstract: Textile dyeing processes are among the most environmentally unfriendly industrial processes, because they produce coloured wastewaters that are heavily polluted with dyes, textile auxiliaries and chemicals. The ultrafiltration (UF) method was studied as a wastewater pre-treatment technique for the decolourization of residual dye-bath effluents after dyeing cotton/polyamide blends using reactive and acid dyes. Ultrafiltration was performed using a poly-ether-sulfone membrane with a molecular weight cut-off of 10 kDa and a pore size of approximately 10 nm. The transmembrane pressure of the UF system was 250 kPa. Colour and COD removals were evaluated in dyebaths as the difference between initial and effluent values. The quality of wastewater was improved in such way that the effluent enables the efficiency of further biological wastewater treatment.

Steady electro-osmotic flow of a micropolar fluid in a microchannel

Abstract: We have formulated and solved the boundary-value problem of steady, symmetric and one-dimensional electro-osmotic flow of a micropolar fluid in a uniform rectangular microchannel, under the action of a uniform applied electric field. The Helmholtz–Smoluchowski equation and velocity for micropolar fluids have also been formulated. Numerical solutions turn out to be virtually identical to the analytic solutions obtained after using the Debye–Huckel approximation, when the microchannel height exceeds the Debye length, provided that the zeta potential is sufficiently small in magnitude. For a fixed Debye length, the mid-channel fluid speed is linearly proportional to the microchannel height when the fluid is micropolar, but not when the fluid is simple Newtonian. The stress and the microrotation are dominant at and in the vicinity of the microchannel walls, regardless of the microchannel height. The mid-channel couple stress decreases, but the couple stress at the walls intensifies, as the microchannel height increases and the flow tends towards turbulence.

Non-steady electro-osmotic flow of a micropolar fluid in a microchannel

Abstract: We formulated the initial-boundary-value problem of non-steady electro-osmotic flow of a micropolar fluid in a rectangular microchannel of height much larger than the Debye length and length much larger the height. Solving the governing differential equations numerically when a spatially uniform electric field is applied as an impulse of finite magnitude, we found that the effect is instantaneous on the flow, just as for simple Newtonian fluids. The decay times of the fluid velocity and the microrotation, however, are smaller in micropolar fluids than in simple Newtonian fluids. The maximum magnitude of microrotation decreases as the micropolarity increases. The effect of microrotation on the stress tensor is more dominant than that of the fluid speed, and a threshold effect with respect to the magnitude of the zeta potential is evident in the spatial profile of the couple stress tensor. We expect similar trends even when the applied electric field varies over some finite interval of time.