Reutilization of ferro-arsenic waste sludge for the development of concrete blocks through solidification: conservation of natural aggregates with policy suggestion

 In the present study, arsenic sludge and iron sludge extracted from a laboratory scale water treatment plant were aimed to reutilize for the development of concrete blocks. Three different grades (M15, M20 and M25) of concrete blocks were made by blending of arsenic sludge and improved iron sludge (50% sand and 40% iron sludge) in the range of density of 425 to 535 kg/m3 at an optimum ratio of 10:90 (arsenic: iron sludge) followed by mixing of designed quantity cement, coarse aggregates, water and additives. Concrete blocks developed based on this such combination exhibited 26 MPa, 32 MPa and 41 MPa compressive strengths, and 4.68 MPa, 5.92 MPa and 7.78 MPa tensile strengths for M15, M20 and M25, respectively. In comparison with the developed concrete blocks and the blocks made with 10% arsenic sludge and 90% fresh sand, the developed ones (employing 50% sand, 40% iron sludge and 10% arsenic sludge) showed more than 200% higher strength perseverance on average. Successful Toxicity Characteristic Leaching Procedure (TCLP) and compressive strength of the sludge-fixed concrete cubes classified it as a non-hazardous and completely safe to use value-added material. This process involves stabilization of arsenic-rich sludge generated from high-volume long-run laboratory-based arsenic-iron abatement set-up from contaminated water with successful fixation in solid matrix of concrete through complete substitution of natural fine aggregates (river sand) in cement mixture. Techno-economic assessment reveals such concrete block preparation at $0.09 each which is lesser than 1/2 of the present market price of same quality concrete block in India.

Conventional pyrolysis of Plastic waste for Product recovery and utilization of pyrolytic gases for carbon nanotubes production

Inevitably increase in plastic demand has resulted in an overgrowing production on a global scale. The utilization of plastics has been applied to a number of industries as it is a durable, moldable, and inexpensive material. High exploitation of plastic had resulted in a hefty amount of waste production, which is not easy to recycle due to its non-degradable nature and results in landfills. Nowadays, waste to energy processes such as pyrolysis has emerged as a superlative process for the management of plastic waste by converting it into useful products. On the other hand, the employment of carbon nanotubes (CNT's) has shown high growth in their production. CNT's were generally synthesized from conventional gases like methane, ethane, and ethylene. Plastic waste can be utilized to substitute the feed material for the CNT synthesis via pyrolysis method. In this study, a two-step pyrolysis process was investigated for product recovery and CNT's production. The first steps consisted of catalytic and non-catalytic degradation of mixed plastic waste in a vertical fixed bed reactor at 500 °C with a heating rate of 20 °C/min for the production of pyrolytic oil and gases and were analyzed. The second step consists of the employment of catalytic pyrolysis gases in a horizontal tube reactor maintained at a temperature of 800 °C over a bed of catalyst for the synthesis of CNT's via catalytic vapor deposition (CVD) technique. It was established that the use of catalyst decreases the oil phase production from 80.5 to 64%, char from 9 to 6.5% while an increase in gas phase production from 10.5 to 29.5% was reported. The alteration of hydrocarbons to CNT's was investigated via pre- and post-GC analysis of the gas samples. Post gas investigation indicates an increased concentration of hydrogen in the sample. Also, the decline of hydrocarbon gases concentration was observed in post sample analysis. Also, transmission electron microscopy (TEM) analysis confirms the synthesis of CNT's.

An economical strategy towards the managing of selenium pollution from contaminated water: A current state-of-the-art review

During the last few decades, contamination of selenium (Se) in groundwater has turned out to be a major environmental concern to provide safe drinking water. The content of selenium in such contaminated water might range from 400 to 700 μg/L, where bringing it down to a safe level of 40 μg/L for municipal water supply employing appropriate methodologies is a major challenge for the global researcher communities. The current review focuses mostly on the governing selenium remediation technologies such as coagulation-flocculation, electrocoagulation, bioremediation, membrane-based approaches, adsorption, electro-kinetics, chemical precipitation, and reduction methods. This study emphasizes on the development of a variety of low-cost adsorbents and metal oxides for the selenium decontamination from groundwater as a cutting-edge technology development along with their applicability, and environmental concerns. Moreover, after the removal, the recovery methodologies using appropriate materials are analyzed which is the need of the hour for the reutilization of selenium in different processing industries for the generation of high valued products. From the literature survey, it has been found that hematite modified magnetic nanoparticles (MNP) efficiently adsorb Se (IV) (25.0 mg/g) from contaminated groundwater. MNP@hematite reduced Se (IV) concentration from 100 g/L to 10 g/L in 10 min at pH 4-9 using a dosage of 1 g/L. In 15 min, the magnetic adsorbent can be recycled and regenerated using a 10 mM NaOH solution. The adsorption and desorption efficiencies were over 97% and 82% for five consecutive cycles, respectively. To encourage the notion towards scale-up, a techno-economic evaluation with possible environmentally sensitive policy analysis has been introduced in this article to introspect the aspects of sustainability. This type of assessment is anticipated to be extremely encouraging to convey crucial recommendations to the scientific communities in order to produce high efficiency selenium elimination and further recovery from contaminated groundwater.

Strategic management of nitrate pollution from contaminated water using viable adsorbents: An economic assessment-based review with possible policy suggestions

Groundwater contaminated with nitrate has prompted a flurry of research studies around the world in the recent years to address this burning environmental issue. The common presence of nitrates in groundwater, wastewater, and surface waters has thrown an enormously critical challenge to the global research communities to provide safe and clean drinking water to municipalities. As per WHO, the maximum permissible limit of nitrate in drinking water is 10 mg/L and in groundwater is 50 mg/L; exceeding the limits, several human health problems are observed. Adsorption, ion-exchange processes, membrane-based approaches, electrochemical and chemical procedures, biological methods, filtration, nanoparticles, etc. have been well investigated and reviewed to reduce nitrate levels in water samples in the recent years. Process conditions, as well as the efficacy of various approaches, were discovered to influence different techniques for nitrate mitigation. But, because of low cost, simple operation, easy handling, and high removal effectiveness, adsorption has been found to be the most suitable and efficient approach. The main objectives of this review primarily focuses on the creation of a naturally abundant, cost-effective innovative abundant material, such as activated clay particles combined with iron oxide. Oxide-clay nanocomposite materials, effectively remove nitrate with higher removal efficiency along with recovery of nitrate concentrated sludge. Such methods stand out as flexible and economic ways for capturing stabilized nitrate in solid matrices to satisfy long-term operations. A techno-economic assessment along with suitable policy suggestions have been reported to justify the viability of the brighter processes. Indeed, this kind of analytical review appears ideal for municipal community recommendations on abatement of excess nitrate to supply of clean water.

Thermal degradation of waste plastics under non-sweeping atmosphere: Part 2: Effect of process temperature on product characteristics and their future applications

The current energy demand and diminishing conventional fuels have forced researchers to find an alternative source of energy. Waste to energy is the current trend for converting waste materials (plastic waste) into valuable fuels. This article mainly discussed the detailed characterization of the pyrolytic products, their comparative analysis and the reaction mechanism at varying operating temperature. This article is a successor of part 1, which primarily focused on the characterization of different waste plastics, their TG analysis, the effect of reactor temperature on yield analysis in a batch reactor and their detailed degradation mechanism. Furthermore, the results presented in this article report the characterization of products at three processing temperatures of 450, 500 and 550 °C. The pyrolytic oils from all wastes excluding PS show a very low density ranging from 0.71 to 0.76 kg/m³, whereas PS pyrolytic density is reported between 0.86 and 0.88 kg/m³. The viscosity of oils increases with an increase in the processing temperature and is similar to the conventional fuels. The FTIR analysis of the products (oil & gases) obtained from HDPE, PP and mixed plastic waste (MIX) shows a large presence of alkanes and a higher presence of aromatics. PS analysis reported a large presence of aromatics (~75%). The GC-MS analysis of all pyrolytic oils from waste plastics, simulated wastes (virgin plastics) and distilled fraction of MIX pyrolysis oil is compared. The GC analysis of non-condensable gases at all processing temperature reports that MIX produce the maximum H₂; HDPE, PS and MIX produces a high amounts of CH₄ too. The formation of lower hydrocarbons (C₅-C₁₂) in pyrolysis oil shows a trend as MIX > PP > PS > HDPE, while for the heavier hydrocarbons (>C₁₉) it is HDPE > PP > PS > MIX. The potential of the utilization of these products has been discussed in different sectors for future research.

Thermal degradation of waste plastics under non-sweeping atmosphere: Part 1: Effect of temperature, product optimization, and degradation mechanism

Continuous generation of plastic waste has prompted substantial research efforts in its utilization as a feedstock for energy generation. Pyrolysis has emerged as one of the best waste management technique for energy extraction from the plastic waste. The objective of this work is to investigate the effect of operating temperature on the liquid product yields in the pyrolysis process by non-isothermal heating. Non-catalytic thermal pyrolysis of waste polyethylene (PE) [high density polyethylene (HDPE)], waste polypropene (PP), waste polystyrene (PS), waste polyethylene terephthalate (PET) and mixed plastic waste (MPW) was carried out in a non-sweeping atmosphere in a semi-batch reactor at four different temperatures 450, 500, 550, and 600 °C. The minimum degradation temperature of the mixed and individual plastics was obtained using a thermogravimetric apparatus (TGA) at a heating rate of 20^°C/min. The TGA results show that all plastics degrade in a single step and the degradation temperatures of PS > PET > PP > HDPE, while mixed plastic degradation indicates two distinct degradation steps. Further, a waste polymer shows a lower degradation temperature than the virgin polymer. The degradation of HDPE is found to produce the maximum oil yield with minimum solid residue. The degradation of PET results in the highest amount of solid and benzoic acid as crystals and gas with no oil. Degradation of mixed plastic causes oil yield in the intermediate range of pyrolysis of individual plastic wastes. Overall, 500 °C is observed to be an optimum temperature for the recovery of low-density pyrolytic oil with the highest liquid yield. The degradation of PE and PP is found to be caused by random chain scission followed by inter and intramolecular hydrogen transfer. The degradation of PS occurs by side elimination or end chain scission followed by β-scission mechanism. The degradation of mix plastics results from random chain scission followed by β-scission mechanism. The effect of temperature on oil and gas recovery as well as recovery time was also assessed.

Ambient air quality status in Raniganj-Asansol area, India

This investigation presents the assessment of ambient air quality with respect to suspended particulate matter (SPM), sulphur dioxide (SO2) and oxides of nitrogen (NOx) at four sites (RGC, SRS, BBC and BCC) in the Raniganj-Asansol area in West Bengal, India. Ambient air was monitored with a sampling frequency of twenty four hours (3 x 8 hours) at each site on every alternate day (3 days a week) covering a period of one year. A total of 429 samples were collected from RGC, 429 from SRS and 435 each from the BBC and BCC sites. Meteorological parameters such as temperature, relative humidity, wind-speed and wind-direction were also recorded simultaneously during the sampling period. Monthly and seasonal variation of these pollutants have been observed and recorded. The annual average and range values have also been calculated. Results of the investigation indicates that the 95th percentile values of SPM levels exceed the limits (200 microg m(-3)) at RGC, SRS and BBC sites and is within the limit of 500 microg m(-3) at the BCC sites. The 95th percentile values of SO2 levels did not exceed the reference level at any of the monitoring stations. The 95th percentile values of NOx are found to be exceeding the limit (80 microg m(-3)) at RGC, SRS and BBC sites but is within the prescribed limit of 120 microg m(-3) at the BCC site. Further, it has been observed that the concentrations of the pollutants are high in winter in comparison to the summer or the monsoon seasons. Results of the investigation indicates that industrial activities, indiscriminate open air burning of coal by the local inhabitants for cooking as well as coking purposes, vehicular traffic, etc. are responsible for the high concentration of pollutants in this area.