Parimal Pal

Removal of arsenic from contaminated groundwater by solar-driven membrane distillation using three different commercial membranes

Investigations on solar-driven membrane distillation (SDMD) were carried out for removal of arsenic from contaminated groundwater. Three different types of hydrophobic membranes made of polytetrafluoroethylene (PTFE) and polypropylene (PP) with surface area of 120 × 10(-4)m(2) were used as flat sheet in a direct contact membrane distillation (DCMD) set up in a cross flow module. Effects of initial arsenic concentration in the feed, feed velocity, feed temperature and distillate inlet temperature on arsenic removal efficiency and flux were studied where temperatures of feed and distillate were found to have significant effect on the flux. Almost 100% arsenic separation was achieved without wetting membrane pore even after 120 h of operation. The PTFE membrane with a flux of 49.80 kg/m(2)h was found to the best one out of the tested membranes. The study shows that solar-driven DCMD can effectively separate arsenic from groundwater using a cross flow membrane module with PTFE hydrophobic membrane.

Removal of arsenic from contaminated groundwater by solar-driven membrane distillation

Experimental investigations were carried out on removal of arsenic from contaminated groundwater by employing a new flat-sheet cross flow membrane module fitted with a hydrophobic polyvinylidenefluoride (PVDF) microfiltration membrane. The new design of the solar-driven membrane module in direct contact membrane distillation (DCMD) configuration successfully produced almost 100 per cent arsenic-free water from contaminated groundwater in a largely fouling-free operation while permitting high fluxes under reduced temperature polarization. For a feed flow rate of 0.120 m3/h, the 0.13 microm PVDF membrane yielded a high flux of 74 kg/(m2h) at a feed water temperature of 40 degrees C and, 95 kg/m2h at a feed water temperature of 60 degrees C. The encouraging results show that the design could be effectively exploited in the vast arsenic-affected rural areas of South-East Asian countries blessed with abundant sunlight particularly during the critical dry season.

Treatment of Coke Wastewater: A Critical Review for Developing Sustainable Management Strategies

The 1980–2011 literature on treatment of coke wastewater towards evolution of a sustainable management strategy is reviewed. Most conventional methods like physicochemical, biological along with recently studied membrane-based treatments have been captured with the purpose of finding out the reasons behind continued environmental pollution from coke oven operations. An extensive list of various methods of removal of cyanide, phenol, ammonia and chemical oxygen demand (COD) from coke wastewater has been compiled and their removal capacities under various conditions have been presented along with highlighting and discussing the key advancement on the application of membranes. It is evident from the literature survey that chemical or biological treatments followed by membrane separations have the potential for the removal of the hazardous components of coke wastewater. However, there are hardly any reported studies on development of integrated treatment schemes that can turn coke wastewater into usable recycled water. This technology gap needs to be addressed quickly, as such a scheme will not only save on consumption of freshwater but will also protect surface water bodies from contamination by hazardous coke wastewater in the backdrop of severe shortage of freshwater.

Removal of arsenic from drinking water by chemical precipitation - a modeling and simulation study of the physical-chemical processes

A dynamic mathematical model was developed for removal of arsenic from drinking water by chemical coagulation-precipitation and was validated experimentally in a bench-scale set-up. While examining arsenic removal efficiency of the scheme under different operating conditions, coagulant dose, pH and degree of oxidation were found to have pronounced impact. Removal efficiency of 91-92% was achieved for synthetic feed water spiked with 1 mg/L arsenic and pre-oxidized by potassium permanganate at optimum pH and coagulant dose. Model predictions corroborated well with the experimental findings (the overall correlation coefficient being 0.9895) indicating the capability of the model in predicting performance of such a treatment plant under different operating conditions. Menu-driven, user-friendly Visual Basic software developed in the study will be very handy in quick performance analysis. The simulation is expected to be very useful in full-scale design and operation of the treatment plants for removal of arsenic from drinking water.

Separating Cyanide from Coke Wastewater by Cross Flow Nanofiltration

Investigations on separation of cyanide from coke wastewater were carried out in a cross flow nanofiltration membrane module following microfiltration of real industrial wastewater. Different composite polyamide nanofiltration membranes were used in the system while studying their effectiveness in cyanide separation under different operating conditions. Transmembrane pressure, pH, and cross flow velocity exhibited strong influence on percentage removal of cyanide. 94% cyanide rejection with a permeate flux of 79 liters per hour at a transmembrane pressure of 13 kg/cm2 and at a volumetric cross flow rate of 700 liters per hour was achieved. The membrane module with a composite membrane having high negative charge was successfully operated without any significant loss in flux even after 72 hours operation. These encouraging results show that microfiltration and nanofiltration with properly selected membranes in an appropriate module could lead to a practical solution to a longstanding problem of cyanide removal from industrial wastewater.

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

Assessing the feasibility of N and P recovery by struvite precipitation from nutrient-rich wastewater: a review

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Arsenic Separation by a Membrane-Integrated Hybrid Treatment System: Modeling, Simulation, and Techno-Economic Evaluation

Literature on recovery of nitrogen and phosphorous from wastewater in the form of value-added struvite fertilizer has been critically reviewed towards the evolution of a sustainable management strategy. Presence of nitrogen and phosphorus is widespread in both domestic as well as industrial wastewater streams such as swine wastewater, landfill leachate, urine waste, dairy manure, coke wastewater, and beverage wastewater. Where these nitrogen and phosphorus compounds cause eutrophication of water bodies and considered as harmful discharges to the environment, they can be turned useful through simple chemical conversion into struvite (MgNH4PO4·6H2O). In extensive studies on wastewater treatment, aspects of recovery of valuable materials remain dispersed. In the present article, almost all relevant aspects of sources of raw materials, chemistry and technology of struvite production, and its detailed characterization have been captured in a systematic and classified way so as to help in planning and designing an integrated scheme of struvite production through conversion of nitrogen and phosphorus components of waste streams. The study will help in formulating a new waste management strategy in this context by shifting focus from removal to recovery of nutrients from waste streams.

Acetic Acid Production and Purification: Critical Review Towards Process Intensification

A modeling and simulation study along with economic analysis was carried out for arsenic separation by a membrane-integrated hybrid treatment system that consisted of an oxidation unit integrated with a cross flow nanofiltration membrane module. About 96–98% arsenic removal efficiency was achieved in the membrane module after pre-oxidation. When pH was increased from 3 to 10, arsenic rejections reached as high as 98.5%. The dynamic mathematical model developed for the system used Extended Nernst-Plank equation as the basis for the nanofiltration model. A linearized approach in modeling was adopted that reduced the computation time significantly. Model predictions were found to corroborate very well with the experimental findings as indicated in the small relative errors of the order of only 0.003 and Willmott d-index of 0.993 reflecting very good model performance. Thus the developed model is expected to be very useful in scale-up, design and optimization of the membrane-integrated hybrid treatment system for removal of arsenic from contaminated groundwater.

Contamination of groundwater by arsenic: a review of occurrence, causes, impacts, remedies and membrane-based purification

The 1980–2015 literature has been critically reviewed to examine how acetic acid manufacturing practice has progressed over these 35 years and whether this important organic acid manufacturing sector is on the right track to ensure sustainable business. Amidst growing environmental awareness and emerging regulations all over the world, a paradigm shift in production strategy in favor of green processes appears imminent. Literature reveals that despite huge worldwide demand, conventional manufacturing practices still largely revolve around multi-step and multi-phase unit operations that fail to ensure clean production environment. Production process is still dominated by a chemical synthesis route where multiple traditional unit operations like distillation, evaporation, absorption, filtration, crystallization, acid and alkali treatments are required involving huge energy, material, manpower, and capital consumption. On the other hand, prospects for process intensification through adoption of membrane technology in downstream separation and purification appear to have brightened. Emergence of tailor-made and highly selective membranes in fouling free modules has opened up new avenues towards green production that has the potential of ensuring sustainable business. This article directs further research towards process intensification.