Assessment of phenol-degrading ability of Acinetobacter sp. B9 for its application in bioremediation of phenol-contaminated industrial effluents

Successful bioremediation of a phenol-contaminated environment requires application of those microbial strains that have acquired phenol tolerance and phenol-degrading abilities. A newly isolated strain B9 of Acinetobacter sp. was adapted to a high phenol concentration by growing sequentially from low- to high-strength phenol. The acclimatised strain was able to grow and completely degrade up to 14?mM of phenol in 136?h. The degradation rates were found to increase with an increase in the phenol concentration from 2.0 to 7.5?mM. The strain preferred neutral to alkaline pH range for growth and phenol degradation, with the optimum being pH 8.0. The optimum temperature for phenol degradation was found to be in the range of 30–35°C. Transmission electron micrographs showed a disorganised and convoluted cell membrane in the case of phenol-stressed cells, showing a major effect of phenol on the membrane. Enzymatic and gas chromatography-mass spectrometry studies show the presence of an ortho-cleavage pathway for phenol degradation. Efficient phenol degradation was observed even in the presence of pyridine and heavy metals as co-toxicants showing the potential of strain in bioremediation of industrial wastes. Application of strain B9 to real tannery wastewater showed 100% removal of initial 0.5?mM phenol within 48?h of treatment.     

Arsenic bioaccumulation in rice and edible plants and subsequent transmission through food chain in Bengal basin: a review of the perspectives for environmental health

Arsenic (As) is a metalloid that poses serious environmental threats due to its behemoth toxicity and wide abundance. The use of arsenic-contaminated groundwater for irrigation purpose in crop fields elevates arsenic concentration in surface soil and in the plants. In many arsenic-affected countries, including Bangladesh and India, rice is reported to be one of the major sources of arsenic contamination. Rice is much more efficient at accumulating arsenic into the grains than other staple cereal crops. Rice is generally grown in submerged flooded condition, where arsenic bioavailability is high in soil. As arsenic species are phytotoxic, they can also affect the overall production of rice, and can reduce the economic growth of a country. Once the foodstuffs are contaminated with arsenic, this local problem can gain further significance and may become a global problem, as many food products are exported to other countries. Large-scale use of rainwater in irrigation systems, bioremediation by arsenic-resistant organisms and hyperaccumulating plants, and the aerobic cultivation of rice are some possible ways to reduce the extent of bioaccumulation in rice. Investigation on a complete food chain is urgently needed in the arsenic-contaminated zones, which should be our priority in future researches.     

Arsenic uptake by plants and possible phytoremediation applications: a brief overview

This review focuses the behaviour of arsenic in plant?Csoil and plant?Cwater systems, arsenic?Cplant cell interactions, phytoremediation, and biosorption. Arsenate and arsenite uptake by plants varies in different environment conditions. An eco-friendly and low-cost method for arsenic removal from soil?Cwater system is phytoremediation, in which living plants are used to remove arsenic from the environment or to render it less toxic. Several factors such as soil redox conditions, arsenic speciation in soils, and the presence of phosphates play a major role. Translocation factor is the important feature for categorising plants for their remediation ability. Phytoremediation techniques often do not take into account the biosorption processes of living plants and plant litter. In biosorption techniques, contaminants can be removed by a biological substrate, as a sorbent, bacteria, fungi, algae, or vascular plants surfaces based on passive binding of arsenic or other contaminants on cell wall surfaces containing special active functional groups. Evaluation of the current literature suggests that understanding molecular level processes, and kinetic aspects in phytoremediation using advanced analytical techniques are essential for designing phytoremediation technologies with improved, predictable remedial success. Hence, more efforts are needed on addressing the molecular level behaviour of arsenic in plants, kinetics of uptake, and transfer of arsenic in plants with flowing waters, remobilisation through decay, possible methylation, and volatilisation.     

Targeting arsenic-safe aquifers for drinking water supplies

At present, 70 countries worldwide are affected by groundwater contamination by arsenic (As) released from predominantly geogenic sources. Consequently, the As problem is becoming a global issue. The option to target As-safe aquifers, which uses geological, geochemical, hydrogeological, morphological and climatic similarities to delimit As-safe aquifers, appears as a sustainable mitigation option. Two pilot areas, Meghna Flood Plain in Matlab Upazila, representative of Bengal Delta in Bangladesh, and Río Dulce Alluvial Cone, representing a typical aquifer setting in the Chaco-Pampean Plain in Argentina groundwater As occurrence, were compared. In rural Bangladesh, As removal techniques have been provided to the population, but with low social acceptance. In contrast, “targeting As-safe aquifers” was socially accepted in Bangladesh, where sediment color could be used to identify As-safe aquifer zones and to install safe wells. The investigation in Argentina is more complex because of very different conditions and sources of As. Targeting As-safe aquifers could be a sustainable option for many rural areas and isolated peri-urban areas.     

Ipomoea dasysperma seed gum: an effective natural coagulant for the decolorization of textile dye solutions

An investigation of dye decolorization from synthetic dye solutions using the non-ionic, water-soluble, high molecular weight seed gums Ipomoea dasysperma and guar gum as coagulants was undertaken. The use of galactomannans derived from plants in this system presents a sustainable method of textile effluent treatment. These natural coagulants extracted from plants proved to be workable alternatives to conventional coagulants like polyaluminum chloride, as they are biodegradable, safe to human health, are cost effective when compared to imported chemicals and have a wider effective dosage range for flocculation of various colloidal suspensions. Coagulant dose and coagulation pH are important factors influencing the mechanism of coagulation. Also the type and chemical structure of the dye plays an important role in the coagulation process. The seed gums alone were found to be effective for decolorization of direct dye and in combination with PAC their coagulation efficiency was well extended even for reactive and acid dyes.     

Development and modification of permanent magnet brushed DC motor for hybrid photovoltaic-operated solar systems

A modified brushed permanent magnet DC (PMDC) motor has been developed and fabricated for a photovoltaic (PV)-operated solar systems. The conventional PMDC motor has been plagued with constraints, the most critical being ingestion of vapours of working fluid inside the rotor and stator, damaging the insulation of windings and forming a thin film of moisture between commutator and brushes. This flaw results into a very low mean time between failures of the motor. In the past, many attempts have been made where-in variety of seals to isolate the working fluid vapours from inner parts of motor have been tried out, but to no avail. Even Brushless DC motors have been designed in the past but their exorbitant cost makes the entire arrangement not viable economically. The modification attempted in this article overcomes the problem of working fluid ingestion inside the motor. It is found that mass flow rate of working fluid obtained at maximum peak sunshine hours is 17.5 l/min at 3030 rpm of motor driven by a PV module of 40 W at 16.20 V. This low-cost modified PMDC motor has been robust with high mean time between failures as no breakdown observed during 18 months of operation.     

Heavy metal uptake and its effect on macronutrients, chlorophyll, protein, and peroxidase activity of Paspalum distichum grown on sludge-dosed soils

This study assessed the heavy metal (Cr, Mn, Ni, Cu, Zn, and Pb) uptake and its effect on biochemical parameters in Paspalum distichum, a wetland plant. Sludge collected from Bhalswa waste dump, New Delhi, was used as heavy metal source and dosed in different proportions viz. 20%, 40%, 60%, and 80% to the garden soil. The plants accumulated metals mostly in belowground organs. The metal accumulation followed the order: Cr>Mn>Cu>Zn>Ni>Pb. The range of heavy metal concentration in tissue of belowground organs after 180 days of growth was 1,778.65–4,288.01 ppm Cr, 828.11–1,360 ppm Mn, 236.52–330.07 ppm Ni, 155.79–282.35 ppm Cu, 27.05–91.16 ppm Zn, and 27.09–50.87 ppm Pb. The biochemical parameters viz. chlorophyll and protein contents and peroxidase (POD) activity exhibited no considerable adverse effect indicating the plants’ tolerance towards heavy metals. The high POD activity and synthesis of new protein bands at high sludge-dosed plants were also in support of this fact.     

Hydrogeochemical comparison and effects of overlapping redox zones on groundwater arsenic near the Western (Bhagirathi sub-basin, India) and Eastern (Meghna sub-basin, Bangladesh) margins of the Bengal Basin

Although arsenic (As) contamination of groundwater in the Bengal Basin has received wide attention over the past decade, comparative studies of hydrogeochemistry in geologically different sub-basins within the basin have been lacking. Groundwater samples were collected from sub-basins in the western margin (River Bhagirathi sub-basin, Nadia, India; 90 samples) and eastern margin (River Meghna sub-basin; Brahmanbaria, Bangladesh; 35 samples) of the Bengal Basin. Groundwater in the western site (Nadia) has mostly Ca-HCO(3) water while that in the eastern site (Brahmanbaria) is much more variable consisting of at least six different facies. The two sites show differences in major and minor solute trends indicating varying pathways of hydrogeochemical evolution However, both sites have similar reducing, postoxic environments (p(e): +5 to -2) with high concentrations of dissolved organic carbon, indicating dominantly metal-reducing processes and similarity in As mobilization mechanism. The trends of various redox-sensitive solutes (e.g. As, CH(4), Fe, Mn, NO(3)(-), NH(4)(+), SO(4)(2-)) indicate overlapping redox zones, leading to partial redox equilibrium conditions where As, once liberated from source minerals, would tend to remain in solution because of the complex interplay among the electron acceptors.