Effects of acidifiers on soil greenhouse gas emissions in calcareous soils in a semi-arid area

Abstract In most agricultural fields, when soil pH is high, elemental sulfur or sulfuric acid are used to reduce soil pH and increase the availability of macro and micronutrients for optimum crop yield. However, how these inputs impact soil greenhouse gas emissions is unknown. This study aimed to measure the amount of greenhouse gas emissions and pH after the application of various doses of elemental sulfur (ES) and sulfuric acid (SA). Using static chambers, this study quantifies soil greenhouse gas emissions (CO2, N2O, and CH4) for 12 months after the application of ES (200, 400, 600, 800, and 1000 kg ha−1) and SA (20, 40, 60, 80 and 100 kg ha−1) to a calcareous soil (pH 8.1) in Zanjan, Iran. Also, in order to simulate rainfed and dryland farming which are common practices in this area, this study was conducted with and without sprinkler irrigation. Application of ES slowly decreased soil pH (more than half a unit) over the year whereas application of SA temporarily reduced the pH (less than a half unit) for a few weeks. CO2 and N2O emissions and CH4 uptake were maximum during summer and lowest in winter. Cumulative CO2 fluxes ranged from 1859.2 kg−1 CO2-C ha−1 year−1 in the control treatment to 2269.6 kg CO2-C ha−1 year−1 in the 1000 kg ha−1 ES treatment. Cumulative fluxes for N2O-N were 2.5 and 3.7 kg N2O-N ha−1 year−1 and cumulative CH4 uptakes were 0.2 and 2.3 kg CH4-C ha−1 year−1 in the same treatments. Irrigation significantly increased CO2 and N2O emissions and, depending on the amount of ES applied, decreased or increased CH4 uptake. SA application had a negligible effect on GHGs emissions in this experiment and only the highest amount of SA altered GHGs emissions

The Role of Microbes in Detoxification and Availability of Metalloids

This chapter tackles the metal(loid)s persistent in the nature that may pollute water resources and terrestrial ecosystems as a result of both naturally in geological mineralization areas resources and anthropogenic activities. "Bioremediation" refers to the process used for the treatment of contaminated media through neutralization, removal, or alteration of environmental variables to stimulate the growth of microorganisms that are responsible for the degradation of toxic chemicals. Microbes in nature may alter metalloids such as As, Se, Sb, and Te by reduction, oxidation, and methylation mechanisms, which is called the "biotransformation processes." Microbial enzymatic activities play a crucial rule in the efficacy of most of bioremediation-related techniques. Therefore, the identification of enzymes involved in the biotransformation of metalloids could help a better understanding of bioremediation processes and an improvement of the effectiveness of bioremediation strategies. In this chapter we review the existing literature and factors affecting bioremediation and the availability of metalloids which would help scientists and environmental policymakers gain a better understanding of the bioremediation technologies used for the remediation of contaminated environments

Phosphorus Removal from Wastewater: The Potential Use of Biochar and the Key Controlling Factors

In recent years, a large volume of literature has been published regarding the removal of phosphorus (P) from wastewater. Various sorbing materials, such as metal oxides and hydroxides, carbonates and hydroxides of calcium (Ca) and magnesium (Mg), hydrotalcite, activated carbon, anion exchange resins, industrial solid wastes and organic solid wastes, have been suggested for P removal. Many of these sorbents are expensive and/or may cause some environmental problems. In contrast, biochar, as an economical and environmentally friendly sorbing material, has received much attention in recent years and has been used as a novel sorbent for the removal of different organic and inorganic pollutants. Biochar is a type of sustainable carbonaceous material that is produced from the thermal treatment of agricultural organic residues and other organic waste streams under oxygen free conditions. This paper reviews the potential use of biochar and the key controlling factors affecting P removal from wastewater. The ability of biochar to remove P from wastewater depends on its physical and chemical properties. Some of the most important physicochemical properties of biochar (structural characteristics, electrical conductivity (EC), mineral composition, pH, zeta potential, cation exchange capacity (CEC) and anion exchange capacity (AEC)) are affected by the feedstock type as well as temperature of pyrolysis and the P sorption capacity is highly dependent on these properties. The P removal is also affected by the water matrix chemistry, such as the presence of competing ions and bulk pH conditions. Finally, several recommendations for future research have been proposed to facilitate and enhance the environmental efficiency of biochar application

Pb(II) Removal from Aqueous Solutions by Adsorption on Stabilized Zero-Valent Iron Nanoparticles—A Green Approach

Nano zero-valent iron particles (nZVFe) are known as one of the most effective materials for the treatment of contaminated water. However, a strong tendency to agglomerate has been reported as one of their major drawbacks. The present study describes a green approach to synthesizing stabilized nZVFe, using biomass as a porous support material. Therefore, in the first step, biomass-derived activated carbon was prepared by thermochemical procedure from rice straw (RSAC), and then the RSAC-supported nZVFe composite (nZVFe–RSAC) was employed to extract Pb(II) from aqueous solution and was successfully synthesized by the sodium borohydride reduction method. It was confirmed through scanning electron microscopy (SEM) and X-ray diffraction (XRD) characteristics that the nZVFe particles are uniformly dispersed. Results of the batch experiments showed that 6 (g L−1) of this nanocomposite could effectively remove about 97% of Pb(II) ions at pH = 6 from aqueous solution. The maximum adsorption capacities of the RS, RSAC, and nZVFe–RSAC were 23.3, 67.8, and 140.8 (mg g−1), respectively. Based on the results of the adsorption isotherm studies, the adsorption of Pb(II) on nZVFe–RSAC is consistent with the Langmuir–Freundlich isotherm model R2=0.996). The thermodynamic outcomes exhibited the endothermic, possible, and spontaneous nature of adsorption. Adsorption enthalpy and entropy values were determined as 32.2 kJ mol−1 and 216.9 J mol−1 K−1, respectively. Adsorption kinetics data showed that Pb(II) adsorption onto nZVFe–RSAC was fitted well according to a pseudo-second-order model. Most importantly, the investigation of the adsorption mechanism showed that nZVFe particles are involved in the removal of Pb(II) ions through two main processes, namely Pb adsorption on the surface of nZVFe particles and direct role in the redox reaction. Subsequently, all intermediates produced through the redox reaction between nZVFe and Pb(II) were adsorbed on the nZVFe–RSAC surface. According to the results of the NZVFe–RSAC recyclability experiments, even after five cycles of recovery, this nanocomposite can retain more than 60% of its initial removal efficiency. So, the nZVFe–RSAC nanocomposite could be a promising material for permeable reactive barriers given its potential for removing Pb(II) ions. Due to low-cost and wide availability of iron salts as well as rice biowaste, combined with the high adsorption capacity, make nZVFe–RSAC an appropriate choice for use in the field of Pb(II) removal from contaminated water