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Arsenic-contaminated water is a major concern in many areas worldwide, causing several diseases such as cancer. There is therefore a need for advanced methods to clean waters because conventional methods have drawbacks such as generation of hazardous sludge, heavy operation and high costs. Here we review arsenic sources, chemistry, toxicity and remediation methods. We discuss also sociological aspects of arsenic prevention. Sources include surface water, groundwater and seawater. Methods include bioremediation, phyto-remediation and biofilters. Sociological aspects are public awareness, sharing information on arsenic-free water sources, removing As at the household level, building a community plant and training facilitators.

Arsenic (As) contamination in soil–plant system is an important environmental, agricultural and health issue globally. The microbe- and sulfate-mediated As cycling in soil–plant system may depend on soil sulfate levels, and it can be used as a potential strategy to reduce plant As uptake and improve plant growth. Here, we investigated the role of soil microbes (SMs) to examine As phytoaccumulation using maize as a test plant, under varying sulfate levels (S-0, S-5, S-25 mmol kg−1) and As stress. The addition of sulfate and SMs promoted maize plant growth and reduced As concentration in shoots compared to sulfate-treated plants without SMs. Results revealed that the SMs-S-5 treatment proved to be the most promising in reducing As uptake by 27% and 48% in root and shoot of the maize plants, respectively. The SMs-S treatments, primarily with S-5, enhanced plant growth, shoot dry biomass, Chl a, b and total Chl (a + b) contents, and gas exchange attributes of maize plants. Similarly, the antioxidant defense in maize plants was increased significantly in SMs-S-treated plants, notably with SMs-S-5 treatment. Overall, the SMs-S-5-treated plants possessed improved plant growth, dry biomass, physiology and antioxidant defense system and decrease in plant shoot As concentration. The outcomes of this study suggest that sulfate supplementation in soil along with SMs could assist in reducing As accumulation by maize plants, thus providing a sustainable and eco-friendly bioremediation strategy in limiting As exposure.

Over recent decades, massive greenhouse gas (GHG) releases in the environment by anthropogenic activities have contributed to global warming. It is also important that additional pollutants are reduced, or emerging solutions are created to prevent repeated CO2 accumulations. Biological processes in nature can evaluate ambient CO2, but the biological mechanism cannot absorb and use all CO2 in metropolitan and commercial environments where a large concentration of CO2 production is observed. Specific chemicals and plastic goods with CO2 absorption properties are not environmentally friendly or rather pricey. The usage of CO2 as a raw material at an industrial level is less important than the excess. Mechanisms for the production, aggregation, and utilization of carbon have developed in nature. The photosynthetic and organic species assimilate and eventually transform CO2 into complex molecules. Over the last three decades, extensive work has been conducted to identify chemical and ecosystem transformations of CO2, over numerous biological and synthetic materials including lactones, exopolysaccharides, bioplastics, microbial alcohols, carboxylic acids, esters, and biodiesel polymers.

Arsenic is an extremely hazardous metalloid affecting the health of millions of people worldwide. Numerous technologies have been developed to remove As from drinking water/wastewater, of which adsorption is considered as the most effective technique. Nanoadsorbents such as nano-scale zero valent metals, carbon nanotubes (CNTs), and biochar/biomaterial-based nanocomposites are being widely used by the researchers for water treatment. In this chapter, recent developments in the nanoadsorbents to eliminate As from water/wastewater are discussed. Application of raw and engineered nanoparticles (NPs) such as iron oxide/hydroxide, alumina, copper oxide, titanium oxide, bi-metal oxides and carbonaceous NPs are primarily focused. Different techniques for the physico-chemical characterization of nanoadsorbents, including Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) have been discussed briefly. The influence of numerous factors (e.g., pH, synthesis method, initial concentration, particle size, competing ions, and contact medium) on As adsorption capacity by nanoadsorbents are deliberated. Furthermore, the chapter also discusses As adsorption mechanisms and regeneration and separation of nanoadsorbents from water/wastewater.

Nanotechnology is very ancient technology and its usage was first recorded in the 9th century. There are many cases of ancient objects utilizing nanocomposites; impressive examples are glass that alters color due to reflection of light and steel swords with incredible strength, crushing resistance, and extraordinarily sharp edges. Nanoparticles have a wide surface area and many particles per unit mass compared with microparticles. Initially, observations of nanoscale particles were gold-related. There are different synthetic methods for nanoparticle synthesis such as bottom-up, hydro/solvothermal, and top-down. The bottom-up methods include organic ligand-assisted growth, mediated synthesis of small molecules and ions, 2D template-confined growth, and seeded growth. The hydro methods include crystal phase transformation, biological synthesis, and nanoparticle assembly. The top-down methods include the mechanical compression method, exfoliation, and nanolithography.

Cleaner and sustainable water production lead to the development of environmentally friendly adsorbent materials for energy-efficient, cost-effective, and cleaner water production. In this study, the biochar derived from the rice husk, wheat straw, and corncob has been used for the adsorptive removal of heavy metals, including the lead (Pb+2) and cadmium (Cd+2). The synthesised biochar was characterised by a different structural and analytical approach. The characterisation of biochar revealed the existence of the combined redox, i.e. reductive and oxidative surface functional groups along with some inert functional groups which play a significant role in donating or accepting an electron to degrade the pollutants in the wastewater. The biochar synthesised in this study was found to be amorphous, and some negligible disorders and defects have been observed in the structure of biochar. The biochar has been highly stable under harsh thermal conditions by sustaining significant weight over a temperature of 700 ​°C and also be hygroscopic. The biochar rice husk, wheat straw, and corncob demonstrated the lead (Pb+2) adsorption capacity of 96.41%, 95.38%, and 96.92%, while for cadmium (Cd+2), the uptake capacity was found to be 94.73%, 93.68%, and 95.78%. The reported biochar is a cleaner, environmentally friendly, economical, and sustainable alternative to conventional adsorbent materials.

The municipal solid waste (MSW) is widely considered as a heterogeneous source of energy, with numerous characteristics varying depending on its geographical region or origin from where it is collected. The development of correlations for the prediction of the higher heating value (HHV) of MSW is a sustainable and cleaner way based on data of specific region from where MSW is obtained. In this research, a new approach reported for the development of correlations to predict the energy content of MSW accurately. The developed correlations lie within the all parameter affecting the HHV of MSW. The models presented can predict the HHV of MSW accurately (R2 > 0.8) compared to other models reported in the literature. However, model 13 developed on the basis of ultimate analysis demonstrated maximum accuracy (R2 = 0.919) among all 7 developed models. The aim of developing the prediction model for the HHV of different MSW samples was to reliably predict using proximate or ultimate analytical data to save experimentation costs and provide theoretical foundations for modelling MSW combustion, pyrolysis processes and thermal conversion for the energy security.

Biochar is considered to be the cost-effective, environmentally-friendly and sustainable sorbent that has an extraordinary potential to efficiently remove toxic elements, including arsenic (As) from water. Until now, no review has focused to understand various important and intriguing aspects on biochar use as a sorbent for As removal from water, either pristine or modified. This review discusses various factors governing As removal potential of biochars (e.g., pH, biochar dose and physico-chemical properties of biochar), sequestration mechanisms, fate of sorbed As on biochar and the redox-mediated interactions between biochar and As. The significance of biochar-derived materials for the treatment of As-contaminated drinking water/wastewater and their potential regeneration ability is also critically discussed, which has not been previously elaborated. This comprehensive review article could be greatly valuable for scientists, policymakers, water treatment industries, environmentalists and graduate students, who are involved in biochar-As research. The review covers some new overarching and key scientific opportunities for the remediation of As-contaminated water using biochar-based materials, which is a potential health risk to millions of people worldwide.

Despite the significant potential of nanofluids in energy storage applications, the experimental determination of thermophysical properties is relatively costly and time-consuming. Therefore, the modeling techniques can be used for the accurate estimation of thermo-physical behavior. The predictive models are useful for the understanding of thermo-physical behavior. Due to restrictions on classical models, there is a need to develop more reliable models to simulate the thermophysical behavior of nanofluids. This paper deals with the synthesis and experimental thermal conductivity measurement of the multi-walled carbon nanotubes (MWCNTs)-Kapok seed oil nanofluid. Additionally, two new correlations based on multiple non-linear regression analysis along well as dimensionless analysis are proposed to estimate thermal conductivity with high precision compared to the classical models. Based on the statistical analysis, the prediction accuracy of the proposed model was ranked. Finally, the sensitivity analysis has been carried out in combination with the residual analysis to assure the accuracy of the model parameters of both proposed models and adequacy of estimated values of model parameters, respectively. The results revealed the global minimum values for all parameters at 0% perturbations indicating that the model parameters were estimated with high accuracy and adequacy.