Since the inception of industrial revolution, metal refining plants using pyrometallurgical processes have generated the prodigious emissions of lead （Pb） and cadmium （Cd）. As the core target of such ...pollutants, a large number of soils are nowadays contaminated over widespread areas, posing a great threat to public health worldwide. Unlike organic pollutants, Pb and Cd do not undergo chemical or microbial breakdown and stay likely in site for longer duration after their release. Immobilization is an in-situ remediation technique that uses cost-effective soil amendments to reduce Pb and Cd availability in the contaminated soils. The Pb and Cd contamination in the soil environment is reviewed with focus on source enrichment, speciation and associated health risks, and immobilization options using various soil amendments. Commonly applied and emerging cost-effective soil amendments for Pb and Cd immobilization include phosphate compounds, liming, animal manure, biosolids, metal oxides, and biochar. These immobilizing agents could reduce the transfer of metal pollutants or residues to food web （plant uptake and leaching to subsurface water） and their long-term sustainability in heavy metal fixation needs further assessment.
Contamination of agricultural soil by heavy metals has become a global issue concerning food security and human health risk. In this study, a soil investigation was conducted to evaluate metals ...accumulation, potential ecological and health risks as well as to identify sources of metals in paddy soils in Hanzhong City, which is located in a sedimentary basin. Ninety-two (92) surface soil samples (bulk soil) and their corresponding rice samples, 21 irrigation water samples, and 18 fertilizer samples were collected from two typical counties and quantified for the heavy metals (i.e., As, Cd, Cu, Hg, Pb, and Zn) concentrations. The results showed that As, Cd, and Zn were the main contaminants in soils in the studied area. Additionally, elevated Hg content in soils might also pose risks to the local ecosystem. Cadmium and As demonstrated high mobility, and their average contents in rice grains were slightly higher than the permissible threshold (0.20 mg kg−1). Moreover, Pb, As, and Cd intake via rice consumption might result in potential risks to local residents. Metal distribution revealed that pollution in the studied area is non-homogeneous, and agricultural activities (As, Cu, and Cd), transportation emission (Cu and Pb), coal combustion (Hg and As), and smelting activities (Zn, Pb, and Cu) were ascertained as the potential sources based on the Positive matrix factorization (PMF) analysis results.
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•Metal contents in 92 soil and rice, 22 water, and 18 fertilizer samples were determined.•Cd and As were the main pollutants in soils, and soil Hg may pose risks to local ecosystem.•Average Cd and As contents in rice grains slightly exceeded the permissive limits.•Daily intake of Pb, As, and Cd might pose risks to local residents health.•Five sources were identified as main contributors to the elevated metals in paddy soils.
Mining operations, industrial production and domestic and agricultural use of metal and metal containing compound have resulted in the release of toxic metals into the environment. Metal pollution ...has serious implications for the human health and the environment. Few heavy metals are toxic and lethal in trace concentrations and can be teratogenic, mutagenic, endocrine disruptors while others can cause behavioral and neurological disorders among infants and children. Therefore, remediation of heavy metals contaminated soil could be the only effective option to reduce the negative effects on ecosystem health. Thus, keeping in view the above facts, an attempt has been made in this article to review the current status, challenges and opportunities in the phytoremediation for remediating heavy metals from contaminated soils. The prime focus is given to phytoextraction and phytostabilization as the most promising and alternative methods for soil reclamation.
•Soil heavy metals contamination is an alarming environmental fact.•Soil cleanup is a great challenge in most countries.•Hyperaccumulator plants provide an opportunity to remediate heavy metals.•Phytoextraction and phytostabilization are promising remediation approaches.•More research is required to test new hyperaccumulators for soil cleanup.
Biochar（BC）, known as the new black gold, is a stable, novel carbonaceous by-product that is synthesized through pyrolysis of biological materials in the absence of O_2.Recently, an emerging interest ...in the application of BC as a robust soil amendment has given rise to a broad research area in science and technology.It is considered a promising remediation option for heavy metal（HM）-contaminated soils to reduce HM bioavailability to plants.Remediation efficacy of BC depends on the porosity, composition,pyrolysis temperature, feedstock, and residence time of pyrolysis.This review article aimed to present an overview of BC use in the immobilization of HMs, i.e., Cd, As, Pb, Zn, Ni, Cu, Mn, Cr, and Sb, in contaminated soils.The remaining uncertain factors, including the specific soil HM immobilization mechanisms, long-term beneficial effects, and potential environmental risks associated with BC application are analyzed.Future research must be conducted to ensure that the management of environmental pollution is in accord with ecological sustainability and adaptation of the black gold biotechnology on a commercial basis for immobilization of HMs in contaminated soils.
Metal oxide-biochar composites have been used for removing pollutants from aqueous systems. In this work, optimized MgO-impregnated porous biochar was prepared using an integrated ...adsorption-pyrolysis method for absorption of phosphate, ammonium and organic matter (humate). Results revealed that the MgO-biochar was comprised of nano-sized MgO flakes and nanotube-like porous carbon. Mg content had significant effects on the development of the nanotube-like porous carbon structure in MgO impregnated biochar and its adsorption capacity for phosphate, ammonium and humate. The adsorption isotherms fitted by Langmuir model illustrated that the optimized adsorbent, 20% Mg-biochar, exhibited maximum adsorption capabilities of more than 398 mg/g for phosphate, 22 mg/g for ammonium, and 247 mg/g for humate, respectively. The phosphate adsorption fitted the pseudo-second-order kinetic model, while ammonium and humate adsorption were best described by the intra-particle diffusion model. The existence of Cl−, NO3−, SO42−, K+, Na+ and Ca2+ ions had no significant impacts on humate adsorption, but the presence of SO42− and Ca2+ affected the phosphate adsorption, and the presence of K+, Na+ and Ca2+ ions inhibited ammonium adsorption. Characterization of adsorbents by X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) before and after treating swine wastewater revealed that struvite crystallization, electrostatic attraction, and π–π interactions contributed to the adsorption of phosphate, ammonium and humate. The results demonstrated that the optimized MgO-biochar could be employed as an effective adsorbent for the simultaneous removal and recovery of phosphate, ammonium and organic substances from nutrient-rich livestock wastewaters.
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•Mg introduction enhanced biochar’s affinities for phosphate and organic matter.•MgO-impregnated biochar was optimized at 20% Mg content for pollutant sorption.•More than 398 mg phosphate, 22 mg ammonium and 247 mg humate captured by per gram sorbent.•MgO-biochar decontamination of swine wastewater involved multi-mechanisms.
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•The challenges and opportunities for food waste (FW) composting were overviewed.•FW composting microbiological variations are explained.•Microbiology of FW composting has been ...studied with novel molecular tools.•Gaseous emissions reduction during FW composting were evaluated.•The global policy and legislation for food waste management were reviewed.
Increasing food waste (FW) generation has put significant pressure on the environment and has increased the global financial costs of its appropriate management. Among the traditional organic waste recycling technologies (i.e., incineration, landfilling and anaerobic digestion), composting is an economically feasible and reliable technology for FW recycling regardless of its technical flaws and social issues. The global scenario of FW generation, technical advancement in FW composting and essential nutrient recovery from organic waste with waste recycling are discussed in this article. Recent research on various strategies to improve FW composting, including co-composting, the addition of organic/inorganic additives, the mitigation of gaseous emission, and microbiological variations are comprehensively explained. Subsequently, it is shown that the performing FW composting in an existing mechanical facility can improve organic waste degradation and produce value-added mature compost to save on costs and increase the technological feasibility and viability of FW composting to some extent.
Biochar shows promise as a potential low–cost sorbent for removing oxyanions from wastewater. However, this generic material exhibits a very wide range in porosity, surface area and surface chemical ...properties that depend on the starting biomass composition and the conditions under which it is converted to char. Without dosing either reactant biomass or product biochar with certain metals (in elemental, oxide/hydroxide or layered double hydroxide form), the capacity of biochar to remove oxyanions is usually low. This review compiles the recent research on modifications of biochar to produce metal-biochar composites that exhibit high oxyanion removal capacities. The general effect of the added metal is first established and then an overview of the several syntheses used to make metal–biochar composites is presented. Effects of chemical activation and of the addition of single metallic elements, single and binary oxides/hydroxides, and layered double hydroxides on removal of AsO43–, AsO33–, CrO42–, NO3− and PO43– are next summarized. The effects of metal dosing and pyrolysis conditions on the surface chemistry and environmental stability of the composite are discussed. Finally, a summary of the research needed to maximize and/or target removal of specific oxyanions, address issues of long–term ecotoxicity of metal–biochar composites, and verify performance with field-testing is presented.
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•Reviewed resource recovery from organic solid waste towards bio-circular economy.•Aerobic and anaerobic digestion technology: a sustainable approach for biorefinery.•Organic solid waste: a potential ...biorefinery and bio-economy option.
With the inevitable rise in human population, resource recovery from waste stream is becoming important for a sustainable economy, conservation of the ecosystem as well as for reducing the dependence on the finite natural resources. In this regard, a bio-based circular economy considers organic wastes and residues as potential resources that can be utilized to supply chemicals, nutrients, and fuels needed by mankind. This review explored the role of aerobic and anaerobic digestion technologies for the advancement of a bio-based circular society. The developed routes within the anaerobic digestion domain, such as the production of biogas and other high-value chemicals (volatile fatty acids) were discussed. The potential to recover important nutrients, such as nitrogen through composting, was also addressed. An emphasis was made on the innovative models for improved economics and process performance, which include co-digestion of various organic solid wastes, recovery of multiple bio-products, and integrated bioprocesses.
Metal oxide-Carbon composites have been developed tailoring towards specific functionalities for removing pollutants from contaminated environmental systems. In this study, we synthesized a novel ...CaO-MgO hybrid carbon composite for removal of phosphate and humate by co-pyrolysis of dolomite and sawdust at various temperatures. Increasing of pyrolysis temperature to 900 °C generated a composite rich in carbon, CaO and MgO particles. Phosphate and humate can be removed efficiently by the synthesized composite with the initial solution in the range of pH 3.0–11.0. The phosphate adsorption was best fitted by pseudo-second-order kinetic model, while the humate adsorption followed the pseudo-second-order and the intra-particle diffusion kinetic models. The maximum adsorption capabilities quantified by the Langmuir isotherm model were up to 207 mg phosphorus (or 621 mg phosphate) and 469 mg humate per one-gram composite used, respectively. Characterization of composites after adsorption revealed the contributions of phosphate crystal deposition and electrostatic attraction on the phosphate uptake and involvement of π − π interaction in the humate adsorption. The prepared composite has great potential for recovering phosphorus from wastewater, and the phosphate sorbed composite can be employed as a promising phosphorus slow-releasing fertilizer for improving plant growth.
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•A MgO-CaO-Carbon composite was produced by co-pyrolysis of sawdust and dolomite.•The composite showed maximum adsorption of 207 mg/g phosphorus and 469 mg/g humate.•Phosphate-loaded composite as fertilizer significantly improved plant growth.
Livestock farming and its products provide a diverse range of benefits for our day-to-day life. However, the ever-increasing demand for farmed animals has raised concerns about waste management and ...its impact on the environment. Worldwide, cattle produce enormous amounts of manure, which is detrimental to soil properties if poorly managed. Waste management with insect larvae is considered one of the most efficient techniques for resource recovery from manure. In recent years, the use of black soldier fly larvae (BSFL) for resource recovery has emerged as an effective method. Using BSFL has several advantages over traditional methods, as the larvae produce a safe compost and extract trace elements like Cu and Zn. This paper is a comprehensive review of the potential of BSFL for recycling organic wastes from livestock farming, manure bioconversion, parameters affecting the BSFL application on organic farming, and process performance of biomolecule degradation. The last part discusses the economic feasibility, lifecycle assessment, and circular bioeconomy of the BSFL in manure recycling. Moreover, it discusses the future perspectives associated with the application of BSFL. Specifically, this review discusses BSFL cultivation and its impact on the larvae's physiology, gut biochemical physiology, gut microbes and metabolic pathways, nutrient conservation and global warming potential, microbial decomposition of organic nutrients, total and pathogenic microbial dynamics, and recycling of rearing residues as fertilizer.
Illustration of how black soldier fly larvae can be used to convert livestock manure into various value-added products. 1. Typical livestock species and their manure accumulating at farms. 2. Black soldier fly life cycle and treatment of animal manure in typical rearing containers, and 3. Harvest and processing of larvae and residues into value-added products. Display omitted
•Black soldier fly larvae (BSFL) were reviewed as an efficient tool for resource recovery from organic wastes.•Discussion of the potential of BSFL for organic manure recycling•Economic feasibility, lifecycle assessment, and circular bio economy related to the application of BSFL.•Future perspectives associated with BSFL application were evaluated.
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