A circular economic approach to the phytoextraction of Zn from basic oxygen steelmaking filtercake using Lemna minor and CO2

Pyrolysis of biomass harvested from heavy-metal contaminated area: Characteristics of bio-oils and biochars from batch-wise one-stage and continuous two-stage pyrolysis

This study evaluates pyrolysis products obtained from biomasses (silver grass, pine, and acacia) harvested from heavy-metal-contaminated soil. To do so, we utilized two methods: a batch one-stage pyrolysis, and a continuous two-stage pyrolysis. The study results show that the yields and characteristics of bio-oils and biochars varied depending on the pyrolysis process and the type of biomass. The two-stage pyrolysis having two reactors (auger and fluidized bed reactors) appeared to be very suitable for specific chemicals production such as acetic acid, acetol, catechol, and levoglucosan. The biochar obtained from the fluidized-bed reactor of two-stage pyrolysis had high thermal stability, high crystallinity, high inorganic content, and a small number of functional groups. In contrast, the biochar obtained from the one-stage pyrolysis had low thermal stability, low crystallinity, a high carbon content, and a large number of functional groups. The biochar obtained from the two-stage pyrolysis appeared to be suitable as a material for catalyst support and as an adsorbent. The biochar obtained from one-stage pyrolysis appeared to be a suitable as a soil amendment, as an adsorbent, and as a precursor of activated carbon. All biochars showed a negative carbon footprint. In the end, this study, which was conducted using two different processes, was able to obtain the fact that products of pyrolysis biomass contaminated with heavy metals have different characteristics depending on the process characteristics and that their utilization plans are different accordingly. If the optimal utilization method proposed through this study is found, pyrolysis will be able to gain importance as an effective treatment method for biomass contaminated with heavy metals.

Application of duckweed (Lemna sp.) and water fern (Azolla sp.) in the removal of pharmaceutical residues in water: State of art focus on antibiotics

In recent decades, antibiotic residues in the environment have increased, affecting components of biological communities, from bacteria to plants and animals. Different methods have been used to remove these compounds, including phytoremediation with floating aquatic species such as duckweed and aquatic fern, with positive results. This study analyses information about the removal efficiency of drugs, with a focus on antibiotics, using Lemna and Azolla, which will allow a better understanding of phytoremediation processes from the perspective of plant physiology. The physiological processes of macrophytes in an environment with this type of pollutant and the phytotoxic effects on plants at high concentrations are also analysed. The metabolization of toxic compounds occurs in three phases: phase I begins with the absorption of antibiotics and the secretion of reactive oxygen species (ROS); in phase II, the effects of ROS are neutralized and minimized by conjugation with enzymes such as glutathione transferase or metabolites such as glutathione; and phase III culminates with the storage of the assimilated compounds in the vacuoles, apoplast and cell wall. In this way, plants contribute to the removal of toxic compounds. In summary, there is sufficient scientific evidence on the efficiency of the elimination of pharmaceutical compounds by these floating macrophytes at the laboratory scale, which indicates that their application under real conditions can have good results.

Circular Economy Framework for Energy Recovery in Phytoremediation of Domestic Wastewater

Circular economy (CE) strategy is crucial in developing towards sustainable growth. It was created to promote resource utilization and the elimination of waste production. This article aimed to study the possibilities of using the CE framework in wastewater bioremediation and energy recovery using hydroponic tanks. The integration of phytoremediation with bioenergy, construction and lifespan of hydroponic tanks in phytoremediation of wastewater, selection of aquatic plants and the expected challenges in the implementation of CE in phytoremediation of wastewater were discussed. The plant-based biomass harvested and the relative growth rate (RGR) of the selected plants from the phytoremediation process was evaluated. The findings obtained indicated that the selected plants tripled in weight after 14 days cultivation period at different retention times. E. crassipes recorded the highest growth with 2.5 ± 0.03 g g−1 d−1, followed by S. molesta with 1.33 ± 0.05 g g−1 d−1 and then P. stratiotes recorded 0.92 ± 0.27 g g−1 d−1 at the end of the cultivation period. Therefore, the selected plants have been identified as having the potential to be used in phytoremediation as well as a source of energy production. The outcome of our review suggested the adoption of a lifecycle assessment as the CE framework for the phytoremediation of wastewater.