Exchange of polycyclic aromatic hydrocarbons across the air-water interface at the creek adjoining Mumbai harbour, India

Concentration levels of polycyclic aromatic hydrocarbons (PAHs) have been determined in air and water in order to estimate the magnitude and direction of gas flux across the air-water interface at the creek adjoining the Mumbai harbour, India. The range of total PAHs was found to be 4.1-30.4 ng/m3 in air and 84.3-377.5 ng/l in seawater, respectively. The lower molecular weight PAHs revealed positive values of the fluxes indicating the tendency for transfer of these contaminants from water to air. In contrast, fluxes of less volatile compounds like benzo(k)fluoranthene and benzo(a)pyrene were always from the atmosphere into the surface water of the creek at all locations and sampling periods. While the fugacity ratio ranged from 0.12 to 6.97, it was found greater than 1 for the lower molecular weight PAHs and less than 1 for higher molecular weight PAHs. The present study suggests the active transfer of lower molecular weight dissolved PAHs into the atmosphere due to volatilization and deposition of higher molecular weight gas-phase PAHs into the surface water.     

Groundwater potential zoning of a peri-urban wetland of south Bengal Basin, India

Demand for groundwater for drinking, agricultural, and industrial purposes has increased due to rapid increase in population. Therefore, it is imperative to assess the groundwater potential of different areas, especially in a fragile wetland ecosystem to select appropriate sites for developing well fields to minimize adverse environmental impacts of groundwater development. This study considers East Calcutta Wetlands (ECW)??a freshwater peri-urban inland wetland ecosystem located at the lower part of the deltaic alluvial plain of South Bengal Basin and east of Kolkata city. This wetland is well known over the world for its resource recovery systems developed by local people through ages, using wastewater of the city. The subsurface geology is completely blanketed by the Quaternary sediments comprising a succession of silty clay, sand of various grades, and sand mixed with occasional gravels and thin intercalations of silty clay. Groundwater occurs mostly under confined condition except in those places where the top aquitard has been obliterated due to scouring action of past channels. The groundwater in the study area is being over-extracted at the rate of 65 × 10³ m³/day. Overlay analysis in Geographic Information System platform using multiple criteria such as water quality index, hydraulic conductivity, groundwater velocity, and depth to piezometric surface reveals that in and around ECW, there are five groundwater potential zones. About 74% of the aquifer of this area shows very poor to medium groundwater potential. Management options such as minimization of groundwater abstraction by introducing the treated surface water supply system and the implementation of rainwater harvesting and artificial recharge in high-rise buildings and industries are suggested for different potential zones.     

Spatio-temporal variation in physicochemical properties of coastal waters off Kalpakkam, southeast coast of India, during summer, pre-monsoon and post-monsoon period

Seasonal observations on water-quality parameters and chlorophyll-a in the coastal waters off Kalpakkam, southeast coast of India, was carried out covering an area of about 30 km(2) to find out the variations in physicochemical properties during a monsoonal cycle of the year. Most of the parameters exhibited a significant spatial and seasonal variation. It revealed that the coastal water was significantly influenced by freshwater input from the nearby backwaters during North-east monsoon and post-monsoon periods. A marginal increase in pH from coast towards offshore was noticed during the observation. Relatively low salinity values were observed during pre and post monsoon when compared to summer. Bottom water was found to be highly turbid during summer and pre-monsoon conditions when compared to surface. This could be attributed to the strong northerly wind and northward current prior to the onset of southwest monsoon. N, P and Si based nutrients are relatively high in their concentration in the bottom water. Nitrate was significantly high during post-monsoon and contributed greatly towards total nitrogen as evident from the statistical correlation. Ammonia concentration was relatively high in the bottom samples during all the seasons except on a few occasions during post-monsoon. In general, phosphate and total phosphorous values remained low and particularly so in the surface water. Higher silicate concentration was observed in the bottom water, and there was a reducing trend towards offshore. High chlorophyll-a values were observed during summer and surface water was found to have higher pigment concentrations as compared to the bottom. Results show that phosphate acts as the limiting factor for phytoplankton production particularly during post-monsoon period whereas; none of the nutrients were found to be limiting the phytoplankton growth during other seasons.     

Study of Geochemical Association of Some Trace Metals in the Sediments of Chilika Lake: A Multivariate Statistical Approach

In order to establish the natural processes and geochemical factors responsible for enrichment of trace metal ions (Cu, Co, Ni, Zn and Cr) with respect to textural parameters (sand, silt and clay weight percentages) along with depth, multivariate statistical approach has been carried out for sediments in different water zones of Chilika lake, the largest brackish water lagoon in Asia. The rotated varimax factor results reveal that Cobalt enrichment is controlled by both textural parameters as well as adsorption mechanism. In fresh and saline water region, textural parameters and in mixed water, adsorption phenomenon predominates. Zn in fresh water is related to clay, whereas it is in adsorbed state in mixed water. Cu in fresh water sediments is in absorbed state and in mixed water it is related to depth and Co concentration. Cr does not show any specific association in fresh water, but in both mixed and saline water it is associated with clay minerals. Although both textural parameters and adsorption mechanism play an important role for the enrichment of trace metal ions in these lagoonal sediments, their relative importance varies with specific metal ions as well as the water quality. Sequential extraction technique was used to characterize the various forms of metals in the < 63μ size sediments of Chilika lake. The concentrations determined indicated selective accumulation of the various metals in the different phases with spatial variability in different water zones. Slightly higher availability of Co and Zn near Balugaon township in exchangeable phase may be related to anthropogenic activities. Among the non-lithogenous (NL) phases, reducible phase associated with higher concentration of Ni, Cu and Cr. Organic bound Zn and Co contributed highest percentages among NL fractions. Residual fraction contributed more than 50% in most of the cases, reflected the predominance of physical weathering, high erosion rate along the drainage basin.     

Autotrophic Biological Denitrification for Complete Removal of Nitrogen from Septic System Wastewater

The overall objective of this research was to develop a reliable, robust, and maintenance-free passive system for biological denitrification in on-site wastewater treatment systems. The process relies on sulfur oxidizing denitrifying bacteria in upflow packed bioreactors. Since this process consumes alkalinity, it is necessary to add a solid-phase buffer that can scavenge the H⁺ as it is generated by the biologically-mediated reaction and arrest the drop in the pH value. This study investigated the use of limestone, marble chips and crushed oyster shell as solid-phase buffers that provide alkalinity. Two bench-scale upflow column reactors and two field-scale bioreactors were constructed and packed with sulfur pellets and an alkalinity source. The pilot scale bioreactors (∼200 L each) were installed at the Massachusetts Alternative Septic System Test Center (MASSTC) in Sandwich, MA. The pilot-scale bioreactors performed better when oyster shell was used as the solid-phase buffer vis-à-vis marble chips. In both (pilot-scale and laboratory-scale) systems, denitrification rates were high with the effluent NO₃ ⁻ —N concentration consistently below 8 mg/L.     

Interparticle diffusion and thermodynamic modeling studies for the removal of heavy metals using mixed adsorbents in industrial effluents

Pollution of water, air, and soil by industrial effluents is a major problem nowadays. A variety of contaminants are too responsible for changing the physicochemical properties of the receiving body. There are practical treatment solutions available to clean up contaminants from various resources. The term “adsorption” refers to one of them. The purpose of the research work is to remove heavy metals from industrial effluent. Mixed adsorbents prepared from activated charcoal and bone charcoals were used to remove the copper and cadmium ions. The experiment carried out in a batch operation and modeling of these data for intraparticle diffusion and thermodynamic calculations were reported in this research work. At optimum operating condition pH 6; metal ion concentration 50 mg/L; dose 5 g/L; agitation 180 rpm and temperature 40°C maximum 99.41% copper ions and 88.12% cadmium ion removal was achieved. Cadmium ions were well fitted in the thermodynamic model compared to copper ions, as demonstrated by the higher correlation coefficient R² (0.9824) value. Intra particle diffusion demonstrated that film diffusion was a rate-limiting step at the start of the reaction, while microporous intraparticle diffusion was the rate-determining phase later on. A Fourier transformation infrared spectroscopy, X-ray diffraction, and scanning electron micrography analysis confirmed the suitability of mixed adsorbents for the removal of cadmium and copper metal ions.     

Assessment of risk to public health posed by persistent organochlorine pesticide residues in milk and milk products in Mumbai, India

The risk posed by the presence of organochlorine pesticides in milk and milk products was estimated for the population of Mumbai. To determine the levels of organochlorine pesticides in milk and milk products, a monitoring study was carried out in and around Mumbai City. 520 samples of milk and milk products of different brands were considered in this study. A survey was also conducted to determine the mean daily consumption of milk and milk products by different age groups and this data was used to evaluate the daily exposure to the public. Non-cancer effects were evaluated by comparing the predicted exposure distributions to the published guidance values. For chemicals identified as potential human carcinogens, cancer risk was evaluated using standard methodology. The majority of the chlorinated pesticides identified in the milk and milk product samples studied were found to be at levels which do not pose unacceptable risks to the public, with the exception of alpha-HCH. The cancer risk estimated for this chemical slightly exceeds the US EPA guidance value.     

Rapid adsorption of toxic Pb(Ⅱ) ions from aqueous solution using multiwall carbon nanotubes synthesized by microwave chemical vapor deposition technique

Multiwall carbon nanotubes(MWCNTs) were synthesized using a tubular microwave chemical vapor deposition technique, using acetylene and hydrogen as the precursor gases and ferrocene as catalyst. The novel MWCNT samples were tested for their performance in terms of Pb(Ⅱ)binding. The synthesized MWCNT samples were characterized using Fourier Transform Infrared(FT-IR), Brunauer, Emmett and Teller(BET), Field Emission Scanning Electron Microscopy(FESEM) analysis, and the adsorption of Pb(Ⅱ) was studied as a function of p H,initial Pb(Ⅱ) concentration, MWCNT dosage, agitation speed, and adsorption time, and process parameters were optimized. The adsorption data followed both Freundlich and Langmuir isotherms. On the basis of the Langmuir model, Qmaxwas calculated to be 104.2 mg/g for the microwave-synthesized MWCNTs. In order to investigate the dynamic behavior of MWCNTs as an adsorbent, the kinetic data were modeled using pseudo first-order and pseudo second-order equations. Different thermodynamic parameters, viz., ΔH0, ΔS0and ΔG0were evaluated and it was found that the adsorption was feasible, spontaneous and endothermic in nature. The statistical analysis revealed that the optimum conditions for the highest removal(99.9%) of Pb(Ⅱ) are at p H 5, MWCNT dosage 0.1 g, agitation speed 160 r/min and time of 22.5 min with the initial concentration of 10 mg/L. Our results proved that microwave-synthesized MWCNTs can be used as an effective Pb(Ⅱ) adsorbent due to their high adsorption capacity as well as the short adsorption time needed to achieve equilibrium.     

Distribution and fate of persistent organochlorine pesticides in coastal marine environment of Mumbai

Multi-compartment monitoring of residue levels of OCPs in coastal marine environment of Mumbai has been studied. The concentration of total HCHs in seawater varied from 0.16 to 15.92 ng/L and concentrations of total DDT varied from 3.01 to 33.21 ng/L. The total HCH concentration in the sediment samples was in the range of 3.8 to 16.2 ng/g. Gamma-HCH contributed almost 55% to the total HCH. In sediment samples the DDT has higher mean concentration in comparison to its metabolite DDE and DDD. The concentration of total HCHs in different marine species varied from 0.87 to 33.73 ng/g and concentrations of total DDT varied from 0.38 to 34.1 ng/g. The variation in the beta-HCH in different compartments is not significant and this could be due to the high persistence and metabolically inactive nature of this isomer. The alpha-HCH is found to be more dominant in fish samples whereas the gamma-HCH is major contributor in the sediment samples.     

Microalgae growth using high-strength wastewater followed by anaerobic co-digestion

Integration of algal biofuel production to wastewater anaerobic digestion infrastructure has the potential to increase biogas production, decrease high and variable internal nitrogen loads, and improve sludge digestibility and dewaterability. In this research, two species of microalgae, Spirulina platensis and Chlorella sp., were grown on sludge centrate and a centrate and nitrified wastewater effluent mixture. Harvested algae were co-digested with waste activated sludge (WAS) at varying ratios. High-growth (6.8 g m(-2) x d(-1)), nitrogen (36.5 g m(-3) x d(-1)), and phosphorus (6.5 g m(-3) x d(-1)) uptake rates were achieved with Chlorella on centrate. No growth was observed with S. platensis under the same conditions; however, both organisms grew well on the centrate and effluent mixture. Co-digestion of algae with WAS improved volatile solids reduction. Although co-digestion with S. platensis improved biosolids dewaterability, Chlorella had a slight negative effect on dewaterability compared to WAS alone. The efficiency of energy conversion from photons to biogas generated from Chlorella was estimated at 1.4%.