Sankha Chakrabortty

A nanofiltration–coagulation integrated system for separation and stabilization of arsenic from groundwater

A membrane-integrated hybrid treatment system has been developed for continuous removal of arsenic from contaminated groundwater with simultaneous stabilization of arsenic rejects for safe disposal. Both trivalent and pentavalent arsenic could be removed by cross flow nanofiltration following a chemical pre-oxidation step for conversion of trivalent arsenic into pentavalent form. The very choice of the membrane module and its judicious integration with upstream oxidation and downstream stabilization resulted in continuous removal of more than 98% arsenic from water that contained around 190 mg L(-1) of total suspended solid, 205 mg L(-1) of total dissolved solid, 0.18 mg L(-1) of arsenic and 4.8 mg L(-1) of iron at a pH of 7.2. The used flat sheet cross flow membrane module yielded a high flux of 144-145 L m(-2) h(-1) at a transmembrane pressure of only 16 kgf·cm(-2) without the need for frequent replacement of the membranes. Transmembrane pressure, cross flow rate through the membrane module and oxidant dose were found to have pronounced effects on arsenic rejection and pure water flux. For the first time, an effective scheme for protection of the total environment has been ensured in this context where arsenic separated with high degree of efficiency has been stabilized in a solid matrix of iron and calcium under response surface optimized conditions. The study culminated in a total and sustainable solution to the problem of arsenic contamination of groundwater by offering arsenic-free water at a reasonably low price of only 1.41

Arsenic removal from contaminated groundwater by membrane-integrated hybrid plant: optimization and control using Visual Basic platform

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Performance analysis and optimization of an advanced pharmaceutical wastewater treatment plant through a visual basic software tool (PWWT.VB)

A simulation software (ARRPA) has been developed in Microsoft Visual Basic platform for optimization and control of a novel membrane-integrated arsenic separation plant in the backdrop of absence of such software. The user-friendly, menu-driven software is based on a dynamic linearized mathematical model, developed for the hybrid treatment scheme. The model captures the chemical kinetics in the pre-treating chemical reactor and the separation and transport phenomena involved in nanofiltration. The software has been validated through extensive experimental investigations. The agreement between the outputs from computer simulation program and the experimental findings are excellent and consistent under varying operating conditions reflecting high degree of accuracy and reliability of the software. High values of the overall correlation coefficient (R2 = 0.989) and Willmott d-index (0.989) are indicators of the capability of the software in analyzing performance of the plant. The software permits pre-analysis, manipulation of input data, helps in optimization and exhibits performance of an integrated plant visually on a graphical platform. Performance analysis of the whole system as well as the individual units is possible using the tool. The software first of its kind in its domain and in the well-known Microsoft Excel environment is likely to be very useful in successful design, optimization and operation of an advanced hybrid treatment plant for removal of arsenic from contaminated groundwater.

Removal of fluoride from contaminated groundwater by cross flow nanofiltration: Transport modeling and economic evaluation

A user-friendly, menu-driven simulation software tool has been developed for the first time to optimize and analyze the system performance of an advanced continuous membrane-integrated pharmaceutical wastewater treatment plant. The software allows pre-analysis and manipulation of input data which helps in optimization and shows the software performance visually on a graphical platform. Moreover, the software helps the user to “visualize” the effects of the operating parameters through its model-predicted output profiles. The software is based on a dynamic mathematical model, developed for a systematically integrated forward osmosis-nanofiltration process for removal of toxic organic compounds from pharmaceutical wastewater. The model-predicted values have been observed to corroborate well with the extensive experimental investigations which were found to be consistent under varying operating conditions like operating pressure, operating flow rate, and draw solute concentration. Low values of the relative error (RE = 0.09) and high values of Willmott-d-index (dwill = 0.981) reflected a high degree of accuracy and reliability of the software. This software is likely to be a very efficient tool for system design or simulation of an advanced membrane-integrated treatment plant for hazardous wastewater.