Preparation of biologically activated lignite immobilized SRB particles and their AMD treatment characteristics

Ferrous sulfide nanoparticles can be biosynthesized by sulfate-reducing bacteria: Synthesis, characterization and removal of heavy metals from acid mine drainage

Ferrous sulfide nanoparticles (nFeS) have proven to be effective in removing heavy metals (HMs) from wastewater. One such approach, which has garnered much attention as a sustainable technology, is via the in situ microbial synthesis of nFeS. Here, a sulfate-reducing bacteria (SRB) strain, Geobacter sulfurreducens, was used to initially biosynthesize ferrous sulfide nanoparticles (SRB-nFeS) and thereafter remove HMs from acid mine drainage (AMD). SRB-nFeS was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) coupled to an energy dispersive spectrometer (EDS), three-dimensional excitation-emission matrix (3D-EEM) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Such characterization showed that SRB mediated the reduction of SO42- to S2- to form nFeS, where the metabolized substances functioned as complexing agents which coordinated with nFeS to form biofunctional SRB-nFeS with improved stability. One advantage of this synthetic route was that the attachment of nFeS to the bacterial surface protected SRB cells from HM toxicity. Furthermore, due to a synergistic effect between nFeS and SRB, HM removal from both solution and AMD by SRB-nFeS was enhanced relative to the constituent components. Thus, after 5 consecutive cycles of HM removal, SRB-nFeS removed, Pb(Ⅱ) (92.6%), Cd(Ⅱ) (78.7%), Cu(Ⅱ) (76.0%), Ni(Ⅱ) (62.5%), Mn(Ⅱ) (62.2%), and Zn(Ⅱ) (88.5%) from AMD This study thus provides new insights into the biosynthesis of SRB-nFeS and its subsequent practical application in the removal of HMs from AMD.

Adsorption mechanism of phosphorus on biomass ash modified with lanthanum immobilized by chitosan

The immobilized lanthanum-modified biomass ash gel ball (CS-La-BA) was prepared with lanthanum chloride, biomass ash, and chitosan to remove phosphorus from water. CS-La-BA was characterized by several analytical techniques. SEM-EDS results showed that CS-La-BA has a well-developed pore structure and abundant adsorption sites. The surface area of BET is 75.46 m²/g and the pore size is mostly at 1.84 nm, indicating that it is a composite porous material with abundant microporous structure. The presence of La on biomass ash and the charge property of CS-La-BA were determined by XRD and zeta potential, and the adsorption mechanism of CS-La-BA on phosphate, including precipitation, electrostatic adsorption, ligand exchange, and complexation mechanism, was revealed by FTIR and XPS. The effects of pH, temperature, adsorbent dosage, initial phosphorus concentration, adsorption time, and coexisting ions on the phosphorus uptake performance of CS-La-BA were discussed. The adsorption experiment results show that the phosphorus removal rate of CS-La-BA can reach 95.6%. Even after six desorption and regeneration experiments, the phosphorus removal rate still reaches 68.13%, which indicates that CS-La-BA has good phosphorus adsorption performance and desorption and regeneration capacity. The phosphorus adsorption process of CS-La-BA conforms to the Freundlich isotherm adsorption equation and general-order kinetic model. The internal diffusion of the adsorption process is dominant, and the maximum adsorption capacity is 31.73 mg/g (25 ℃). Thermodynamic experiments show that the adsorption process of phosphorus by CS-La-BA is a spontaneous entropy increase process.

Algae, biochar and bacteria for acid mine drainage (AMD) remediation: A review

Acid mine drainage (AMD) is a global issue and causes harmful environmental impacts. AMD has high acidity and contains a high concentration of heavy metals and metalloids, making it toxic to plants, animals, and humans. Traditional treatments for AMD have been widely used for a long time. Nevertheless, some limitations, such as low efficacy and secondary contamination, have led them to be replaced by other methods such as bio-based AMD treatments. This study reviewed three bio-based treatment methods using algae, biochar, and bacteria that can be used separately and potentially in combination for effective and sustainable AMD treatment to identify the removal mechanisms and essential parameters affecting AMD treatment. All bio-based methods, when applied as a single process and in combination (e.g. algae-biochar and algae-bacteria), were identified as effective treatments for AMD. Also, all these bio-based methods were found to be affected by some parameters (e.g. pH, temperature, biomass concentration and initial metal concentration) when removing heavy metals from AMD. However, we did not identify any research focusing on the combination of algae-biochar-bacteria as a consortium for AMD treatment. Therefore, due to the excellent performance in AMD treatment of algae, biochar and bacteria and the potential synergism among them, this review provides new insight and discusses the feasibility of a combination of algae-biochar-bacteria for AMD treatment.