Human micronutrient deficiencies are a widespread problem worldwide and mainly concern people whose diet (mainly of plant origin) consists of insufficient amounts of critical vitamins and minerals. Low levels of micronutrients in plants are linked to, i.e., their decreasing concentration in soils and/or low bioavailability and presence of abiotic stresses which disturb the proper growth and development of plants. Agronomic biofortification of crops is a very promising way to improve the concentration of micronutrients in edible parts of crops without compromising yield and is recognized as the cheapest strategy to alleviate hidden hunger worldwide. The review is focused on the factors influencing the effectiveness of biofortified crops (a type of application, form, and a dose of applied microelement, biofertilizers, and nanofertilizers). Also, the accumulation of zinc, selenium, and iron in edible parts of crops, their effects on metabolism, morphological and yield parameters, and an impact on plants’ defense mechanisms against abiotic stress like salt, high/low temperature, heavy metal, and drought was discussed. Finally, the directions of future agronomic biofortification studies are proposed.

The multi-elemental composition, surface texture and morphology of biochar, produced by pyrolysis at 300, 350, 400 and 450 °C from freshwater macroalga Cladophora glomerata, as a biosorbent of toxic metals was examined with Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), Scanning Electron Microscopy (SEM), and Fourier Transform Infrared Spectroscopy (FT-IR) techniques. It was found that the yield of pyrolysis was inversely proportional to temperature: for 300 °C it was 63%, whereas for 450 °C—47%. The proximate analysis revealed that also biochar’s moisture and volatile matter was inversely proportional to temperature. The content of ash increased with temperature. All biochars were characterized by a similar total pore area of about 20 m2 g−1. FT-IR analysis showed that all biochars peaked at 3500–3100 cm−1 which was attributed to O–H stretching of the hydroxyl groups, at 2850–2970 cm−1, stretching vibrations of C–H bonds in aliphatic CH2 and CH groups, at 1605 cm−1, stretching vibrations from C=C of aromatics, at 1420 cm−1, bending oscillations from CH2, at about 1111 cm−1, stretching vibrations of Si–O, at 618 cm−1, vibrations from Fe–O bonds, and at 475 cm−1—Si–O–Si deformation vibrations. The biosorption properties of biochar towards Cr(III) ions were examined in kinetic studies. The biosorption capacity of biochar increased with an increase of pyrolysis temperature: the highest was for biochar obtained at 450 °C—87.1 mg Cr(III) g−1 and the lowest at 300 °C—45.9 mg g−1. Cladophora biochar also demonstrated a good ability to simultaneously remove metal ions from a multi-metal system, e.g., wastewater. The removal efficiency for Cr(III) was 89.9%, for Cu(II) 97.1% and for Zn(II) 93.7%. The biochar derived from waste-freshwater macroalgae can be a potent and eco-friendly alternative adsorptive material.

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Two different aquatic biomass sources-freshwater hornwort (Ceratophyllum demersum L.) and macroalga (Cladophora glomerata L.)-were used to produce biochars, which were investigated as Cr(III) ion sorbents. Wide range of pyrolysis temperatures from 250 to 800°C was examined. Resultant biochars were characterized in detail by means of proximate analysis, ultimate analysis, FT-IR, SEM imaging, Boehm titration, and mercury porosimetry. The sorption capacities of the macroalga biochars varied from 104.2 to 163.9 mg g −1 , whereas for hornwort biochars from 37.6 to 60.2 mg g −1. Obtained results were compared with literature data, suggesting that pyrolysis temperature and mineral matter content have crucial impact on the sorption capacities of Cr(III) ions. Simple thermal valorization of invasive aquatic macrophytes, i.e., hornwort or macroalga, allows to produce efficient adsorbents for chromium(III) ion removal from water.

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Waste fly ash, with both low (with the addition of vermiculite) and high contents of unburned coal, were subjected to hydrothermal syntheses aiming to obtain zeolite composite materials—zeolite + vermiculite (NaX–Ver) and zeolite + unburned carbon (NaX–C). The composites were compared with parent zeolite obtained from waste fly ash with a low content of unburned carbon (NaX–FA). In this study, the physicochemical characteristics of the obtained materials were evaluated. The potential application of the investigated zeolites for the adsorption of ammonium ions from aqueous solutions was determined. Composite NaX–Ver and parent zeolite NaX–FA were characterized by comparable adsorption capacities toward ammonium ions of 38.46 and 40.00 mg (NH4+) g−1, respectively. The nearly 2-fold lower adsorption capacity of composite NaX–C (21.05 mg (NH4+) g−1) was probably a result of the lower availability of ion exchange sites within the material. Adsorbents were also regenerated using 1 M NaCl solution at a pH of 10 and subjected to 3 cycles of adsorption–desorption experiments, which proved only a small reduction in adsorption properties. This study follows the current trend of waste utilization (fly ash) and the removal of pollutants from aqueous solutions with respect to their reuse, which remains in line with the goals of the circular economy.

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