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Abstract It is usual to extract hot water from a storage tank, using displacement by cold water from the mains; this causes the temperature of the outgoing hot water to decrease with time. In order to alleviate this undesirable feature a number of tanks in series may be employed. In this communication the effect of number of tanks on the outlet temperature of hot water, has been analytically investigated; it has been assumed that the only heat exchange, taking place in the tanks is on account of flow of water. The considerations in this analysis are similar to those made by Rabinovich and Fert [1] and Rabinovich [2], for a system of tanks in a solar collector loop without any outflow of water. Thus the analysis is best applicable when hot water is extracted at a fast rate, so that the gain or loss of heat by other mechanisms is negligible, compared to that due to the flow of water. The analysis should also be applicable to shallow solar ponds, Sodha et al. [3], and built in storage water heaters, Sodha et al. [4].

Abstract A simple transient analytical approach has been adopted for developing an explicit expression for the water temperature of an indoor swimmingpool coupled to a panel of collectors. For qualitative assessment of the analytical results, computations have been made for the winter climatic conditions of Sri Nagar, India. The effects of several parameters, viz. inlet temperature, heat removal factors, collector, etc. on the performance of the proposed systems have been studied in detail. It is observed that (i) the proposed model agrees with the experimental results of the Australian passive solar swimming pool and (ii) the desired temperature for the indoor swimming pool can be achieved by the active method.

Continuous long-term open column (> 1 year, during July 2014–July 2015) percolation leaching experiments were undertaken to assess leachability of important constituent elements from Linz–Donawitz slag of Rourkela, Bokaro and Tata steel plants. Leachates were continuously collected at an interval of 3–5 days from open column during 110 cycles of percolation leaching test and analysed for As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Se, V and Zn concentration by inductively coupled plasma optical emission spectrometry. Leachate concentration of different elements showed remarkable variation in terms of leachability from different slag samples. Linz–Donawitz slags cumulative concentration of the elements in the leachate (µg/kg) range showed Mn (16.13–57.73) > Fe (38.36–54.43) > As (8.06–19.66) > Cu (7.83–10.66) > Cr (5.2–6.53) > Ni (5.2–6.16) > Zn (BDL—5.76) > Se (BDL—5) > Co (BDL—3.66) decreasing trend. Among Linz–Donawitz slags, Cr, Ni, Se and Zn leachate concentrations were relatively higher for Tata, whereas As, Co and Fe were higher for Bokaro. Leachate concentration of Cd, V and Pb was below detection limit in all slag samples from the steel plants. During initial period of leaching experiments, concentration of many elements (As, Cu, Fe and Mn) showed increasing trend, which reaches a plateau afterwards. The experimental results estimate low cumulative leachate content of different elements from Linz–Donawitz slag and therefore has prospect for bulk utilization for reclamation of degraded land, mine void filling, road construction etc.

Stipulation of fresh water for domestic use without any microbial, organic and inorganic contaminants is of high need. Sustainable, efficient, cost-effective and robust water purification technologies is of high need and it can be achieved using nanomaterials and their composite. Nanostructured graphene has unique properties like high surface to volume ratio, higher absorbability, reusability with minimal chemical alterations, and low cytotoxicity. From the validation of these properties, we have developed PLLA-Ag@graphene sandwich structures as an effective adsorbate for water purification application. As the real water bodies have lot of bacterial contaminants, the material is also designed as efficient adsorbate with antibacterial efficacy. In view of achieving these objectives, we have synthesized PLLA fibre mats by electrospinning method, followed by PLLA-Graphene and Ag decorated PLLA-graphene mats. The crystallite size for graphite and Ag@graphene was calculated as 30.82 nm and 43.79 nm, respectively. Furthermore, the UV analysis of Ag@graphene shows two peaks corresponding to graphene and Ag NP at 285 nm and 407 nm respectively. The layers were assembled in the order of polymeric fibre, as-fired biomass graphite, Ag@graphene for methodical filtration process. The filtration efficacy of the filtrate was tested using sewage water and the results shows higher contamination removal percentage of 87 % with TDS values in the drinking water standards after filtration. The antibacterial efficacy results also evidence of the potentialities of the hybrid system towards water purification application.

AbstractContamination of agricultural soil with heavy metals has become a serious concern worldwide. In the present study, Cr6+ resistant plant growth promoting Pseudomonas sp. (strain CPSB21) was isolated from the tannery effluent contaminated agricultural soils and evaluated for the plant growth promoting activities, oxidative stress tolerance, and Cr6+ bioremediation. Assessment of different plant growth promotion traits, such as phosphate solubilization, indole-3-acetic acid production, siderophores, ammonia and hydrogen cyanide production, revealed that the strain CPSB21 served as an efficient plant growth promoter under laboratory conditions. A pot experiment was performed using sunflower (Helianthus annuus L.) and tomato (Solanum lycopersicum L.) as a test crop. Cr6+ toxicity reduced plant growth, pigment content, N and P uptake, and Fe accumulation. However, inoculation of strain CPSB21 alleviated the Cr6+ toxicity and enhanced the plant growth parameters and nutrient uptake. Moreover, Cr toxicity had varied response on oxidative stress tolerance at graded Cr6+ concentration on both plants. An increase in superoxide dismutase (SOD) and catalase (CAT) activity and reduction in malonialdehyde (MDA) was observed on inoculation of strain CPSB21. Additionally, inoculation of CPSB21 enhanced the uptake of Cr6+ in sunflower plant, while no substantial enhancement was observed on inoculation in tomato plant.

Torrefaction, as a pretreatment of biomass coupled with pyrolysis process, has gathered significant attention in recent years to obtain higher quality bio-oil. Being an energy-intensive process, the application of byproducts such as biochar from the integrated process might offset the extra energy provided during the torrefaction process. With this hypothesis, present work aimed to investigate the performance of biochar (BC) obtained from pyrolysis of native (BC-raw) and torrefied biomass (BC-torrefied) towards the synthetic wastewater treatment containing methylene blue (MB) dye. Both biochars were characterized by their physicochemical properties. The impact of time, dose of adsorbent, pH, concentration of MB, and temperature were examined during batch adsorption process. Results showed that BC-torrefied (103.47 m2/g) has higher Brunauer–Emmett–Teller (BET) surface area than BC-raw (80.40 m2/g). Both biochars behave in similar fashion toward MB removal; however, BC-torrefied had greater adsorption capacity (158.13 mg/g from Sips isotherm at 50 mg/L MB concentration) because of higher BET surface area, pore volume, and complexation on surface as compared to BC-raw (85.68 mg/g from Sips isotherm at 50 mg/L MB concentration). The experimental data were in good agreement with Sips isotherm and pseudo-second-order kinetic model for both biochars. The MB adsorption was unprompted and endothermic. Further, it was observed that hydrogen bonding, electrostatic force of attraction, ion exchange, surface complexation, and $$\pi$$ - $$\pi$$ interaction between MB dye and adsorbent were primarily accountable for adsorption process. Thus, BC-torrefied could be novel adsorbent for water treatment, and its application will facilitate the integrated torrefaction-pyrolysis process.

Abstract In this paper, the effect of number of collectors on the life cycle conversion efficiency (LCCE) of a single slope solar desalination unit (SSSDU) coupled with N alike partly covered photovoltaic thermal compound parabolic concentrator collectors (PVTCPCs) has been communicated. The analysis has been carried out for an archetypal day of July and December for the atmospheric situation of New Delhi with the help of analytical program fed in MATLAB. The average value of energy output for type a weather condition has been taken to find the annual energy output. The input data required for the numerical computations have been taken from IMD, Pune, India. It has been observed that the value of LCCE increases with the raise in the value of number of collectors.

Arsenic contamination in drinking water is a matter of concern for many countries. An efficient and low-cost solution for this hazard is essentially needed on urgent basis. Therefore, in this study, banana pith (an agricultural waste) was used for biochar production and later it was modified with iron and applied for arsenic adsorption from aqueous solution. Produced biochar was characterized for proximate, ultimate, and surface analyses. Interestingly, after iron impregnation, the surface area of biochar increased (31.59 m2/g) by nearly 8 times. Morphological analysis showed that iron particles firmly held within the pores after impregnation. Arsenate (As(V)) adsorption behavior of iron-impregnated banana pith biochar was evaluated through a batch study by considering various parameters like dose, concentration, pH, temperature, and competing anions. Compared to impregnated biochar, raw biomass and its biochar showed a lesser affinity for arsenate in aqueous solution. The adsorption isotherm of As(V) on banana pith biochar was covered in the temperature range of 298 to 318 K, and kinetic data of adsorption was experimentally generated at 298 K. Langmuir model for the sorption isotherms and pseudo-second-order kinetic model for the sorption kinetics represented the experimental data. The thermodynamic study showed negative Gibb's free energy (- 46.88 kJ/mol at 298 K, - 48.58 kJ/mol at 308 K, - 50.73 kJ/mol at 318 K) that suggested spontaneity of the adsorption process. Negative enthalpy (ΔH° = - 10.55 kJ/mol) showed exothermic nature of adsorption of arsenic, while negative entropy (ΔS° = 0.123 kJ/mol.K) suggested enthalpy-driven adsorption process. Mechanism of arsenic adsorption onto iron-impregnated banana pith biochar has also been discussed in detail. Based on the experimental observation, a predictive model for arsenate removal has been developed in this study. The findings of the present study elucidated that iron-impregnated banana pith biochar can be used as a low-cost adsorbing material for As(V) from aqueous solutions.

The present study aims to investigate the applicability of γ-Al2O3 nanoparticles (NPs) adsorbent for removal of arsenite and arsenate from aqueous solution. The nano-adsorbent was characterized using zeta potential analysis, dynamic light scattering, field emission scanning microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and X-ray diffraction. Batch adsorption studies were carried out to optimize adsorption parameters such as contact time, stirring speed, initial arsenic concentration, adsorbent dose, pH and effect of different competing anions. Langmuir adsorption capacities obtained at 298 K are 769.23 µg/g and 1000 µg/g for As(III) and As(V) removal correspondingly. The adsorption mechanism was well established by pseudo-second-order kinetic model. Negative values of enthalpy (ΔH°) obtained during adsorption [− 29.12 kJ/mol and − 35.55 kJ/mol for As(III) and As(V), respectively] confirmed the process was exothermic in nature. The negative values of ΔG° [− 6.14 to − 3.86 kJ/mol for As(III) and − 9.32 to − 6.68 kJ/mol for As(V)] further affirmed that the adsorption process is spontaneous in nature. There was no requirement of additional external energy supply for the enhanced removal as the adsorption was less favoured at high temperature. Phosphate and sulphate had the profound effect on reduction in the removal efficiency. Good regenerating efficiency of γ-Al2O3 NPs up to fourth cycle implied economic feasibility of the adsorbent. The effectiveness of γ-Al2O3 was also proved for removal of arsenic from real arsenic-contaminated groundwater.