Subhabrata Ray

Municipal solid waste management in Kolkata, India - a review.

Kolkata is one of four metropolitan cities in India. With an area of 187.33sqkm and a population of about 8 million, it generates around 3,000td(-1) of municipal solid waste (MSW) at a rate of 450-500g per capita per day. With rapid urbanization as a result of planned and unplanned growth and industrialization, the problems associated with handling MSW have increased at an alarming rate over the past few years. No source segregation arrangement exists; there is only limited (60%) house-to-house collection; and 50-55% open vats are used in the present collection system. The operational efficiency of the Kolkata Municipal Corporation (KMC) transport system is about 50%, with a fleet composed of about 30-35% old vehicles. The majority (80%) of these, particularly the hired vehicles, are more than 20 years old. The newly added areas covered by KMC have even lower collection efficiencies, and only an informal recycling system exists. The waste collected has a low energy value (3,350-4,200kJkg(-1)) with high moisture and inert content. A 700td(-1) compost plant set up in 2000 has not been functioning effectively since 2003. Open dumping (without liners and without a leachate management facility) and the threat of groundwater pollution, as well as saturation of an existing landfill site (Dhapa) are the most pressing problems for the city today. KMC spends 70-75% of its total expenditures on collection of solid waste, 25-30% on transportation, and less than 5% on final disposal arrangements. The Kolkata Environmental Improvement Project, funded by the Asian Development Bank, is seen as only a partial solution to the problem. A detailed plan should emphasize segregation at the source, investment in disposal arrangements (including the use of liners and leachate collection), and an optimized transport arrangement, among improvements.

Removal of Cr(VI) from Aqueous Solution: Electrocoagulation vs Chemical Coagulation

Abstract Hydrolyzed products of Al(III) have affinity below pHzpc for oppositely charged mono and bi‐nuclear species of hexavalent chromium. This study investigates the comparative performance of electrocoagulation (EC) and chemical coagulation (CC) for the removal of Cr(VI) from aqueous solution. The highest removal of Cr(VI) achieved with EC was about 42% with 4.36 mA/cm2 current density. Cathodic adsorption of chromium boosted up Cr(VI) removal during EC. Simultaneous electro‐ and chemical‐dissolution lead to high current efficiency of about 178%. Both the pH and the coagulant dosage have a significant impact on Cr(VI) removal in the pH ranges from 4.9 to 7.0. CC with alum and aluminum sulfate (AS) removed about 11% and 12% of Cr(VI). Co‐adsorption of divalent SO4 2− ions with Cr(VI) is responsible for the lower removal observed with chemical coagulants. About 0.061 and 0.099 mole of SO4 2− was adsorbed per mole Al in the precipitate in the pH range 4.9 to 7.0 with AS and alum. A higher coagulant dosage increases the removal of Cr(VI) but adversely affects the removal efficiency (Cr(VI) removed per unit of Al dosing). Cell current density (CD) has shown little effect on Cr(VI) removal and the pH elevation at the same charge density. Higher initial Cr(VI) concentration improves the removal efficiency as the species of Cr(VI) is acidic in solution and decreases the pH elevation rate.

Electro-Fenton treatment of synthetic organic dyes: Influence of operational parameters and kinetic study

This work investigates oxidative decolorization of two different dyes, Methylene blue and Titan yellow in aqueous solution using an environmentally friendly advanced electro-chemical oxidation (electro-Fenton) process. The effect of operating conditions like H2O2 concentration, current density, initial dye concentration was studied in a batch stirred cell. Individual decolorization decay kinetics for both dyes was investigated. The second-order absolute rate constants (L mol−1 s−1) between hydroxyl radical and dye have been calculated from experimental data by fitting it to the decolorization model. The apparent kinetic constants, kapp (s−1) for Methylene blue and Titan yellow dye decolorization were also determined. The experimental data showed a good fit to the theoretical model, which can predict data in a wide range of % dye decolorization. This process also reduces COD of the dye solution, and the unit energy demand (UED) in kWh/kg COD removed for different electrical current has been reported.

Oxidation kinetics of degradation of 1,4-dioxane in aqueous solution by H2O2/Fe(II) system

Kinetic studies of oxidative degradation of 1,4-dioxane present in aqueous solutions in the concentration range between 2.27 × 10−3 mol/L (200 ppm) and 5.68 × 10−3 mol/L (500 ppm) were conducted in batch rector. This analysis considers the hydroxyl radicals (·OH) produced by Fenton reagent as the main species responsible for the degradation process. 1,4-dioxane was degraded to the extent of 97 to 99% after 30 min of reaction time. The pH of the reaction medium decreased substantially during the experiment. In all cases, most of 1,4-dixane degradation occurred during the initial 5 min of reaction. A kinetic model is proposed for the oxidation of 1,4-dioxane by Fenton reagent and this model is applied to calculate the kinetic rate constant for the reaction between hydroxyl radicals and 1,4 dioxane. The reaction rate constant for the reaction of 1,4-dioxane with ·OH radicals was evaluated and the value is 2.25 × 108/M-s.

Colour diminution and COD reduction in treatment of coloured effluent by Electrocoagulation

This work experimentally investigates the colour and Chemical Oxygen Demand (COD) removal of effluents containing: Trypan Blue (TB); Orange G (OG) dye using the two most common electrode materials – Mild Steel (MS) and Aluminium (Al). Effects of the time of electrotreatment, solution pH, electrode material, current density and initial dye concentration on decolourisation and COD reduction are reported. MS electrodes show better colour removal efficiency event at lower cell current efficiency compared with Al electrodes and are able to achieve up to 90–98% removal in less than 60 min. Removal efficiency is higher in the case of TB compared with OG irrespective of electrode material due to higher electrostatic attraction between TB molecules and metal hydroxide sludge. Higher current density enhances colour removal even though pH elevation (approaching close to zero point charge) rate is higher. COD reduction is found to be about 10-20% lower than colour diminution measured spectrophotometrically suggesting different mechanisms of dye removal involved during EC.

Use of GIS and remote sensing for crop diversification — a case study for Punjab state

In this study, an attempt has been made to suggest crop diversification based on soil and weather requirements of different crops. State level spatial databases of various agro-physical parameters such as rainfall, soil texture, physiography and problem soil along with the agricultural area derived from remote sensing data were integrated using GIS. A raster based modelling approach was followed to arrive at suitable zones for practicing different cropping systems. The results showed that the south-western Punjab is suitable for low water requiring crops such as desi cotton, pearl millet, gram etc., where as north-eastern Punjab with high rainfall and excess drainage should practice maize based cropping system. Rice can be substituted by maize and other crops in Central Punjab, where water table is going down fast. Using this approach the area of rice based cropping system can be reduced from present 24.7 lakh ha to 19.6 lakh ha, thereby reducing the degradation of valuable land and water resources.

Irreversibility analysis of a separation system using sieve tray distillation column

An attempt has been made (1) to develop an expression for evaluating irreversibility due to vapour-liquid contact on trays, and (2) to assess the effects of the following parameters on the irreversibility of the total process: (1) relative contribution of different components to the total process irreversibility, i.e. the relative effects of the column trays, condenser, reboiler and associated fluid handling system, (2) variation in column configuration parameters like feed plate location and heat removal from the trays using circulation flux, (3) variation of the major design parameters of the sieve trays, i.e. hole diameter and weir height, and thereby evolve a strategy for performance optimization based on process irreversibility

IMPACT OF SO 2 EMISSION LIMITS ON PETROLEUM REFINERY OPERATIONS II: MINIMIZING EMISSIONS

The first part of this article presented a general-purpose linear programming model and applied it to an existing petroleum refinery in India to evaluate the impact of imposed maximum SO2 emission limits on operations and profitability. The present study presents two-step solution methodology designed to minimize SO2 emission rates while preserving refinery profit. The proposed two-step procedure identifies an alternate solution of the LP model leading to an operating plan with maximized profit and minimized SO2 emission rates. The study also shows that the alternative of increasing low-sulfur crude processing for lowering the total SO2 emission rate may be effective only up to a certain proportion of the low-sulfur crude.

Environmental impact assessment and its minimization in a refinery for sustainable development

Refining industry economics is under pressures for compliance with new environmental regulations. Regulatory authorities impose specific limits for individual pollutant concentrations and rates of discharge and do not consider the combined effect of all the pollutants. The Waste reduction (WAR) algorithm combines impact of all pollutants to a Potential Environmental Impact (PEI) score. A refinery modelled using Linear Programming that relates refinery economics with its PEI score. Its solution generates the operation plan of the refinery for profit maximization, while at the same time minimizing the PEI. The study shows that the secondary processing units contribute more to environmental impact.

Draining phenomenon in closed narrow tubes pierced at the top: an experimental and theoretical analysis

The phenomenon of draining, although ubiquitous in nature, has received scant attention especially in the meso-scale. We observe that closed top tubes drain by the inception of an axisymmetric ‘Taylor finger’ while a minute pierce of the top closure results in an altogether different physics with air entry from the top pushing the liquid out. Again, a coupled mechanism comprising full bore followed by film draining is observed for “too small” a top pierce at “high enough” Eotvos number. Top pierce initiates draining in dimensions which would not drain otherwise and finger entry hastens the process of draining. The myriad of phenomena thus exhibited is depicted as phase diagrams in vertical and inclined conduits. A mechanistic model has been proposed to predict draining and the onset of finger entry in vertical tubes.