Agricultural solid wastes either in natural or in modified forms have been successfully used for decades as non-conventional cost-effective adsorbents for removing metal ions and dyes from their aqueous phase and have been recognized as a sustainable solution for wastewater treatment. Therefore, this review article provides extensive literature information about heavy metals and dyes, their classifications and toxicity, various treatment methods with emphasis on adsorption characteristics by numerous agricultural solid wastes, or agricultural solid waste-derived adsorbents under various physicochemical process conditions. This review article not only provided an up-to-date information on the application of sustainable low-cost alternative adsorbents such as agricultural solid wastes, agricultural by-products, and biomass-based cost-effective activated carbon and various other natural materials in the batch adsorptive removal of heavy metal and dye from aqueous phase but also presented a comprehensive compilation of adsorptive pollutant removal information based on various reported continuous column operation studies which is one of the new aspect to this review article. The effectiveness of various batch and column operational process parameters on mechanistic adsorptive removal of both heavy metals and dyes by various agricultural solid waste-based adsorbents has been critically discussed here. Batch and column adsorption mechanism, batch kinetics, column dynamic modeling, and adsorptive behavior of adsorbents under various process parameters have also been critically analyzed and compared. Finally, literature information on recovery and regeneration through desorption techniques and cost comparison of various agricultural solid waste adsorbents with commercial activated carbons have also been reported here. Conclusions have been drawn from the literature reviewed, and few suggestions for future research direction are proposed.

Salt buildup is a global phenomenon in semiarid soils that leads to land degradation and water quality deterioration. These problems can be alleviated through the quantification of salt leaching from topsoil horizons. Delocalization of solid-phase salts and solution-phase leaching was evaluated within the topsoil layers of a semiarid farmland by utilizing a non-invasive electromagnetic sensing and stochastic modeling approach. The horizontal and vertical conductivity signals were strongly correlated (r = 0.988, P < 0.05) and characterized by high precision and low errors (0.12–0.18). Electrical conductivity across the field was highly variable within the 0.6-m profile with nearly all surveyed locations exhibiting values greater than 2 dS m⁻¹. Around 86% of the salinity data in 0.3-m depth ranged from 2 to 8 dS m⁻¹, and 56% data within 0.3–0.6 m surpassed 8 dS m⁻¹. Spatial depletion in salinity within the 0.3-m depth plausibly resulted from salt delocalization. The salinity values generally exceeded plant tolerance threshold limits and indicated that most crops would be adversely affected unless management practices were aimed at removing salts past the topsoil horizons. The leaching fraction levels ranged from 5 to 40% across the topsoil layers, and indicated the need for salt removal practices for most crops. Overall, salt delocalization analysis can benefit agronomic decisions for irrigation and soil quality management. The approach can be applied worldwide in locating impaired soil zones that need salt reclamation for developing best management practices pertaining to site-specific crop selection and agricultural water budgeting.

Biomass is a promising renewable energy source and its significance is escalating in the context of climate change and depletion of fossil foils. This study was conducted for two consecutive years 2016 and 2017, using five sorghum cultivars, i.e., JS-263, Jawar-2011, Hagari, JS-2002, and YS-2016, in order to determine the best cultivars in terms of dry matter yield, chemical composition, and biomethane yield grown under semi-arid conditions in Pakistan. The results revealed that sorghum cultivars responded differently in terms of growth, biomass yield, chemical composition, and methane yield. Cultivars Jawar-2011 produced maximum leaf area index, leaf area duration, crop growth rate, plant height, and leaves per plant, however, they were comparable with Sorghum-2016, whereas cultivar JS-2002 performed poorly among the tested cultivars. Similarly, cultivar Jawar-2011 produced maximum dry matter yield (16.37 t ha⁻¹) similar to that of YS-2016, further cultivar JS-2002 performed poorly and gave lower dry matter yield (12.87 t ha⁻¹). The maximum protein concentration (10.95), neutral detergent fibers (61.20), and lignin contents (5.55) found in Jawar-2011 were comparable with those in YS-2016, while the lowest neutral detergent fiber and lignin contents were found in JS-2002. Although JS-2002 produced the highest specific methane yield per kilogram of volatile solids, it was overcompensated by Jawar-2011 owing to higher dry matter yield per hectare. These results suggested that cultivar Jawar-2011 can be grown successfully in semi-arid conditions of Pakistan in order to get good biomass yield along with higher methane yield.

Maize fields near Mae Tao Creek in Pha Te Village, Tak Province, Thailand are contaminated with Zn, Cd, and Pb. This research studied the interaction between levels of the metals contaminating the soil and maize development, heavy metal accumulation in the seeds, and the soil bacterial community structure. Our field experiment was carried out in five plots with metal contents that gradually decreased from a high level near the creek to a lower level further into the land: Zn 380–4883 mg kg⁻¹, Cd 6–85 mg kg⁻¹, and Pb 34–154 mg kg⁻¹. Cultivation and isolation on nutrient agar (NA) was utilized to study the culturable bacterial community, and polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) was utilized for the unculturable bacterial communities. All statistical analyses clearly indicated that rainfall and irrigation were the main factors affecting total Zn concentration and bioavailable Zn, Cd, and Pb in the field. The variation in the contents of the heavy metals was weakly correlated with the culturable bacterial community indices (Shannon-Wiener, evenness and richness), but the contents resulted in a difference in the overall diversity of the bacteria in the soil. The richness, numbers of culturable rhizobacteria, and maize growth stage significantly affected the amount of Zn and Cd that accumulated in the roots. In addition, maize accumulated a high level of Zn in the seeds, while the low contents of Cd and Pb in the seeds were below our limit of detection. The results obtained could be informative for the management of maize cultivation in the area.

Rare earth elements (REEs) are a group of elements whose concentration in numerous environmental matrices continues to increase; therefore, the use of biological methods for their removal from soil would seem to be a safe and reasonable approach. The aim of this study was to estimate the phytoextraction efficiency and distribution of light and heavy (LREEs and HREEs) rare earth elements by three herbaceous plant species: Artemisia vulgaris L., Taraxacum officinale F.H. Wigg. and Trifolium repens L., growing at a distance of 1, 10, and 25 m from the edge of a frequented road in Poland. The concentration of REEs in soil and plants was highly correlated (r > 0.9300), which indicates the high potential of the studied plant species to phytoextraction of these elements. The largest proportion of REEs was from the group of LREEs, whereas HREEs comprised only an inconsiderable portion of the REEs group. The dominant elements in the group of LREEs were Nd and Ce, while Er was dominant in the HREEs group. Differences in the amounts of these elements influenced the total concentration of LREEs, HREEs, and finally REEs and their quantities which decreased with distance from the road. According to the Friedman rank sum test, significant differences in REEs concentration, mainly between A. vulgaris L., and T. repens L. were observed for plants growing at all three distances from the road. The same relation between A. vulgaris L. and T. officinale was observed. The efficiency of LREEs and REEs phytoextraction in the whole biomass of plants growing at all distances from the road was A. vulgaris L. > T. officinale L. > T. repens L. For HREEs, the same relationship was recorded only for plants growing at the distance 1 m from the road. Bioconcentration factor (BCF) values for LREEs and HREEs were respectively higher and lower than 1 for all studied plant species regardless of the distance from the road. The studied herbaceous plant species were able to effectively phytoextract LREEs only (BCF > 1); therefore, these plants, which are commonly present near roads, could be a useful tool for removing this group of REEs from contaminated soil.

The single and binary adsorptions of metronidazole (MNZ) and dimetridazole (DTZ) on activated carbon (F400) and activated carbon felt (ACF) were studied in this work. The adsorption capacities of both materials towards antibiotics were determined at pH = 7 and 25 °C. The π-π dispersive interactions controlled the adsorption mechanism of both antibiotics. The Prausnitz-Radke isotherm interpreted quite well the single adsorption equilibrium data of DTZ and MNZ on F400 and ACF. DTZ presented higher affinity for both adsorbents because the DTZ had higher electronic density and smaller molecular size than those of MNZ. The capacity of F400 for adsorbing DTZ or MNZ was higher than that of ACF because the ACF presented higher microporosity and surface area, which was unavailable for adsorbing DTZ and MNZ due to pore restriction. The binary equilibrium data on F400 and ACF were interpreted reasonably well with the extended Langmuir multicomponent isotherm and Sheindorf-Rebuhn-Sheintuch isotherm, respectively. The competitive adsorption of MNZ and DTZ was antagonistic, but not cooperative. In the binary adsorption, both antibiotics were adsorbed simultaneously, competed for the same adsorption sites, and both carbon materials presented higher selectivity towards DTZ than MNZ. Moreover, if one antibiotic was adsorbed first, then another antibiotic could be adsorbed on unoccupied sites or by displacing the antibiotic already adsorbed. The results revealed that the binary adsorption equilibrium was independent on the way of contacting the antibiotics.

Anthropogenic activities, such as ore mining and processing, nuclear power generation, and weapon tests, have generated uranium (U) contamination to soils and waters. The mobility and bioavailability of U are influenced by its sources, speciation, and plant species. Phytoremediation has emerged as an environmentally friendly, cost-effective green technology to remediate radioisotope- and metal-contaminated soils. The main objective of this study was to explore the feasibility using sunflower (Helianthus annuus) and Indian mustard (Brassica juncea) in cleaning up soils with UO₂, UO₃, and UO₂(NO₃)₂. Uranium was found to be bioaccumulated in plant roots more than plant shoots. Uranium uptake by both plant species was significantly higher from the UO₃- and uranyl-contaminated soils than from UO₂-contaminated soils. UO₃- and UO₂(NO₃)₂-contaminated soils showed higher exchangeable, weak acid extractable, and labile U than the UO₂-contaminated soils. After a growing season, three U forms decreased as redistribution/transformation of U resulted in U species with lower extractability. This study indicates the importance of U speciation in soil with regard to the potential use of sunflower and Indian mustard for phytoremediation of U-contaminated soils.

Ni/Fe bimetallic nanoparticles have been widely used as strong reductants to degrade organic pollutants. Synthesis parameters of Ni/Fe nanoparticles can directly affect their characteristics and reactivity. In this study, Ni/Fe nanoparticles were prepared at different synthesis conditions, namely, synthesizing temperature, stirring rate, washing solutions, and preparation methods (post-coated and co-reducted Ni/Fe nanoparticles), and investigated their effectiveness of decabrominated diphenyl ether (BDE209) degradation. The results showed that the successive order of factors affecting the kinetics constant of Ni/Fe nanoparticles for the removal of decabrominated diphenyl ether (BDE209) were preparation methods, washing solutions, stirring rate, and synthesis temperature. It should be noted that the kinetics constants of post-coated Ni/Fe nanoparticles for removal of BDE209 was 0.049 min⁻¹, which was 14 times higher than that of co-reducted Ni/Fe nanoparticles. Moreover, the most remarkable influence on the particle size of Ni/Fe nanoparticles was the stirring rate, others synthesis conditions are mentioned in the following order: washing solutions > preparation methods > synthesis temperature. Interestingly, the effects of synthesis condition on the crystalline structure of Ni/Fe were weak. The results may facilitate more effective application of Ni/Fe nanoparticles for degradation of BDE209.

The use of plants for ecological remediation is an important method of controlling heavy metals in polluted land. Cotinus coggygria is a landscape plant that is used extensively in landscaping and afforestation. In this study, the cadmium tolerance level of C. coggygria was evaluated using electrical impedance spectroscopy (EIS) to lay a theoretical foundation for broad applications of this species in Cd-polluted areas and provide theoretical support to broaden the application range of the EIS technique. Two-year-old potted seedlings of C. coggygria were placed in a greenhouse to analyse the changes in the growth, water content and EIS parameters of the roots following treatment with different Cd concentrations (50, 100, 200, 500, 1000 and 1500 mg kg⁻¹), and soil without added Cd was used as the control. The roots grew well following Cd treatments of 50 and 100 mg kg⁻¹. The Cd contents increased with the increase in Cd concentration in the soil. However, the lowest root Cd content was found at 4 months of treatment. The extracellular resistance rₑ and the intracellular resistance rᵢ increased first overall and then decreased with the increasing Cd concentration, and both parameters increased with a longer treatment duration. The water content had a significant negative correlation with the Cd content (P < 0.01) and the rₑ (P < 0.05). C. coggygria could tolerate a soil Cd concentration of 100 mg kg⁻¹. There was a turning point in the growth, water content and EIS parameters of the C. coggygria roots when the soil Cd concentration reached 200 mg kg⁻¹. The root water content and rₑ could reflect the level of Cd tolerance in C. coggygria.

The nanoporous carbon using waste straw as carbon source was well prepared for effective dye removal from aqueous solution. The structure and surface properties of nanoporous carbon were characterized by X-ray diffraction, Raman spectroscopy, N₂ adsorption–desorption, and X-ray photoelectron spectroscopy. The results revealed that the nanoporous carbon exhibited large specific surface area and porous structure with abundant functional groups on the surface. In the adsorption experiments, the nanoporous carbon showed high dye adsorption capacity and rapid removal rate under higher pH value, initial dye concentration, and dosage of adsorbents. Moreover, the adsorption isotherm data fitted well to the Langmuir model, suggesting the monolayer adsorption. The maximum adsorption capacity could reach 555.56 mg/g, much higher than the recent reports. Besides, the adsorption kinetics fitted well to the pseudo-second-order model and the correlation coefficients were greater than 0.999. Thermodynamic study results indicated that dye adsorption onto the hierarchical nanoporous carbon was spontaneous and thermodynamically favorable. Therefore, with larger specific surface area and porous structure, the nanoporous carbon showed great potential as efficient adsorbents for dye in the aqueous environment.