Municipal solid waste management in Kolkata,India – A review

Kolkata is one of four metropolitan cities in India. With an area of 187.33 sq km and a population of about 8 million, it generates around 3,000 t d^?1 of municipal solid waste (MSW) at a rate of 450–500 g 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 (3,350–4,200 kJ kg^?1) with high moisture and inert content. A 700 t d^?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.     

Linear stability of sand waves sheared by a turbulent flow

Environmental Fluid Mechanics - In this paper, the linear stability of sand waves sheared by a turbulent flow is analyzed. The velocity distribution in the streamwise direction is considered to...     

Kinetics of phenol biodegradation at high concentration by a metabolically versatile isolated yeast Candida tropicalis PHB5

A highly tolerant phenol-degrading yeast strain PHB5 was isolated from wastewater effluent of a coke oven plant and identified as Candida tropicalis based on phylogenetic analysis. Biodegradation experiments with C. tropicalis PHB5 showed that the strain was able to utilize 99.4 % of 2,400 mg l^?1 phenol as sole source of carbon and energy within 48 h. Strain PHB5 was also observed to grow on 18 various aromatic hydrocarbons. Haldane model was used to fit the exponential growth data and the following kinetic parameters were obtained: μ _max?=?0.3407 h^?1, K _S?=?15.81 mg l^?1, K _i?=?169.0 mg l^?1 (R ²?=?0.9886). The true specific growth rate, calculated from μ _max, was 0.2113. A volumetric phenol degradation rate (V _max) was calculated by fitting the phenol consumption data with Gompertz model and specific degradation rate (q) was calculated from V _max. The q values were fitted with Haldane model, yielding following parameters: q _max?=?0.2766 g g^?1 h^?1, K _S ′?=?2.819 mg l^?1, K _i ′?=?2,093 (R ²?=?0.8176). The yield factor (Y _X/S ) varied between 0.185 to 0.96 g g^?1 for different initial phenol concentrations. Phenol degradation by the strain proceeded through a pathway involving production of intermediates such as catechol and cis,cis-muconic acid which were identified by enzymatic assays and HPLC analysis.     

Fractionation and bioavailability of metals and their impacts on microbial properties in sewage irrigated soil

A study was conducted to evaluate the effect of long-term irrigation of sewage contaminated with heavy metals like Cd, Cr, Cu and Pb on microbial and biochemical parameters of soils of West Bengal, India. The microbial parameters included microbial biomass carbon (MBC), microbial metabolic quotient; the biochemical parameters included fluorescein diacetate hydrolyzing activity, beta-glucosidase, urease, phosphatase, and aryl sulphatase activities. A sequential extraction technique was used to quantify water soluble, exchangeable, carbonate bound, Fe/Mn-oxide bound, organically bound, and residual metal fractions. Metal concentrations in the two most labile fractions (i.e., water soluble and exchangeable fractions) were generally low. Total metal concentrations at each site seemed to be associated with soil amorphous Fe and Al minerals. The MBC and the enzymes studied were significantly and negatively correlated with water soluble and exchangeable metals but not significantly correlated with other forms, indicating that water soluble and exchangeable forms exerted a strong inhibitory effect on the soil microbial and biochemical parameters. It was concluded that irrigating soils with metal contaminated sewage seemed to damage soil quality in the long term.     

Photolysis of oxyfluorfen in aqueous methanol

Photolysis of oxyfluorfen, an herbicide of the nitrodiphenyl ether class, was studied in aqueous methanol under UV and sunlight. UV irradiation was carried out in a borosilicate glass photoreactor (containing 250 ppm oxyfluorfen in 50% aqueous methanol) equipped with a quartz filter and 125 watt mercury lamp (maximum output 254 nm) at 25 ± 1°C. Sunlight irradiation was conducted at 28 ± 1°C in borosilicate Erlenmeyer flasks containing 250 ppm oxyfluorfen in 50% aqueous methanol. The samples from both the irradiated conditions were withdrawn at a definite time interval and extracted to measure oxyfluorfen content by gas chromatography-flame ionization detector for rate study. The half-life values were 20 hours and 2.7 days under UV and sunlight exposure, respectively. Photolysis of oxyfluorfen yielded 13 photoproducts of which three were characterized by infrared spectrophotometer and ¹H NMR and ¹³C NMR spectroscopy. The rest of the photoproducts were identified by gas chromatography-mass spectrometry (GC-MS) and thin layer chromatography (TLC). An ionization potential 70 eV was used for electron impact-mass spectrometry (EI-MS) and methane was used as reagent gas for chemical ionization-mass spectrometry (CI-MS). Two of the photoproducts were also synthesized for comparison. The main phototransformation pathways of oxyfluorfen involved nitro reduction, dechlorination, and hydrolysis as well as nucleophiles displacement reaction.     

Self-preserving characteristics in wall-wake flow downstream of an isolated bedform

Environmental Fluid Mechanics - The results of an experimental study on the turbulence characteristics in flow over and downstream of an isolated bedform are presented. The vertical profiles of...     

Comparison of microbial indicators under two water regimes in a soil amended with combined paper mill sludge and decomposed cow manure

An incubation study was conducted under laboratory conditions to compare the effects of soil amendment of combined paper mill sludge (PS) and decomposed cow manure (DCM) on selected microbial indicators. A lateritic soil (Typic Haplustalf) was amended with 0 (control), 20 or 80tha(-1) (wet weight) of PS or DCM. The amended soils were then adjusted to 60% water holding capacity (WHC) or submerged conditions, and incubated at 27 degrees C in dark for up to 120days (d). The microbial biomass C (MBC), the basal soil respiration and the enzyme activities of the beta-glucosidase, acid phosphatase and sulphatase were analyzed at day 15, 30, 45, 60 and 120. Compared to the unamended soil (control), the MBC, the basal soil respiration and the enzyme activities increased with the rate of PS and DCM. At similar rate, the DCM treatment increased significantly the MBC, the soil respiration and the enzyme activities compared to the PS treatment. Also, the water regimes affected the microbial activities. At 60% WHC, the MBC and soil respiration increased during the first 30d and decreased thereafter. The enzyme activities showed similar trends, where they increased for the first 60d, and decreased thereafter. In contrast, under submerged condition, the MBC and enzymes activities declined during 120d, whereas the soil respiration increased. Compared to the control, the used of PS and DCM had no negative impact of the soil microbial parameters, even at the highest application rate. Long-term field experiments are required to confirm these laboratory results.     

Preface: special issue on the hydrodynamic and fluvial instabilities

Environmental Fluid Mechanics -