Evaluation and optimization of a new microbial enhancement plug-flow ditch system for the pretreatment of acid mine drainage: semi-pilot test

Role of microbes in bioaccumulation of heavy metals in municipal solid waste: Impacts on plant and human being

The presence of heavy metals in municipal solid waste (MSW) is considered as prevalent global pollutants that cause serious risks to the environment and living organisms. Due to industrial and anthropogenic activities, the accumulation of heavy metals in the environmental matrices is increasing alarmingly. MSW causes several adverse environmental impacts, including greenhouse gas (GHG) emissions, river plastic accumulation, and other environmental pollution. Indigenous microorganisms (Pseudomonas, Flavobacterium, Bacillus, Nitrosomonas, etc.) with the help of new pathways and metabolic channels can offer the potential approaches for the treatment of pollutants. Microorganisms, that exhibit the ability of bioaccumulation and sequestration of metal ions in their intracellular spaces, can be utilized further for the cellular processes like enzyme signaling, catalysis, stabilizing charges on biomolecules, etc. Microbiological techniques for the treatment and remediation of heavy metals provide a new prospects for MSW management. This review provides the key insights on profiling of heavy metals in MSW, tolerance of microorganisms, and application of indigenous microorganisms in bioremediation. The literatures revealed that indigenous microbes can be exploited as potential agents for bioremediation.

The coupling reaction of Fe2+ bio-oxidation and resulting Fe3+ hydrolysis drastically improve the formation of iron hydroxysulfate minerals in AMD

The oxidation of Fe²⁺ by Acidithiobacillus ferrooxidans (A. ferrooxidans) in acid mine drainage (AMD) is often accompanied by formation of iron hydroxysulfate minerals, such as schwertmannite and jarosite. This study reported that 80 mmol L^-1 of Fe²⁺ could be completely oxidized by A. ferrooxidans LX5 within 48 h, but only 27.7% of the resultant Fe³⁺ precipitated to form schwertmannite. However, the conversion efficiency to jarosite was much higher (54.5%). The formation of jarosite lasted 120 h, while only 24 h when conversed to schwertmannite. By constructing a cyclic process of 'Cu-reducing coupled with bio-oxidization', the total Fe in AMD could be fully converted into mineral precipitates. The resultant mineral specie could be regulated simply by control the K⁺ concentration. Thermodynamically, Fe³⁺ cannot hydrolyze spontaneously to form schwertmannite due to the positive Gibbs free energy (ΔrGm∘ = 6.63 kJ mol^-1) of the reaction. However, if Fe²⁺ were biologically oxidized by A. ferrooxidans, the resultant Fe³⁺ could spontaneously form schwertmannite because the aforementioned coupling reaction has a negative Gibbs free energy (ΔrGm∘ = -34.12 kJ mol^-1). Even though Fe³⁺ itself could hydrolyze to form jarosite spontaneously with ΔrGm∘ = -22.20 kJ mol^-1, the coupling reaction of Fe²⁺ bio-oxidation followed by Fe³⁺ hydrolysis in the presence of K⁺ could easily promote the formation of jarosite, which exhibited a great negative Gibbs energy (ΔrGm∘ = -67.45 kJ mol^-1).

Advances in microbial remediation for heavy metal treatment: a mini review

Abstract

In recent years, microbiological treatment to remediate contamination by heavy metals has aroused public attention as such pollution has seriously threatens ecosystems and human health and impedes sustainable development. However, the aspect of actual industrial wastewater and solid waste remediation by microorganisms is not explored sufficiently. And what we focus on is technical field of microbial remediation. Therefore, in this review, we discuss and summarize heavy metal treatment via microbiological approaches in different media, including wastewater, solid waste from industrial factories and polluted sites. We also clarify the technical applicability from the perspective of biosorption, bioleaching, biominerization, etc. In particular, the exploration of the combination of microbiological approaches with chemical methods or phytoextraction are scrutinized in this review relative to real waste heavy metal remediation. Furthermore, we highlight the importance of hyperaccumulator endophytes.

Graphical abstract

Mine drainage: Treatment technologies and rare earth elements

The recent research and development on mine drainage published in 2018 was summarized in this annual review. In particular, this review was focused on two main aspects of mine drainage: (a) advances in treatment technologies and (b) rare earth elements in mine drainage and its recovery. The first section covers passive treatment technologies and active treatment options, including physiochemical treatment and biological treatment. The second section includes the characterization of rare earth elements in mine drainage and recovery technologies. Due to the importance of rare earth elements and the growing interest in their recovery from mine drainage, rare earth elements are reported as a separate section for the first time in this review. PRACTITIONER POINTS: Advances in treatment technologies for mine drainage are reviewed. Rare earth elements in mine drainage and its recovery are summarized. Reviewed technologies include passive, active, advanced and novel processes.

Comparison of the Biological and Chemical Synthesis of Schwertmannite at a Consistent Fe2+ Oxidation Efficiency and the Effect of Extracellular Polymeric Substances of Acidithiobacillus ferrooxidans on Biomineralization

Schwertmannite is an environmental mineral material that can promote the natural passivation of heavy metal elements, thereby reducing environmental pollution from toxic elements. However, the fundamental reason for the difference between the chemically (H₂O₂-FeSO₄) and biologically (Acidithiobacillus ferrooxidans-FeSO₄) synthesized schwertmannite is still unclear. In this study, X-ray diffraction, scanning electron microscopy, the Brunauer⁻Emmett⁻Teller method, and X-ray fluorescence spectrometry were used to compare the structure, specific surface area, and elemental composition of schwertmannite synthesized by biological and chemical methods. The removal capacity of As(III) by the two kinds of schwertmannite and the effects of extracellular polymeric substances (EPS) on biogenetic schwertmannite were also investigated. At a consistent Fe2+ oxidation efficiency, the chemical method synthesized more schwertmannite than the biological method over a 60-h period. The biosynthesized schwertmannite had a "chestnut shell" shape, with a larger particle size and specific surface than the chemically synthesized schwertmannite, which was relatively smooth. The saturated adsorption capacities of the biologically and chemically synthesized schwertmannite were 117.0 and 87.0 mg·g-1, respectively. After exfoliation of the EPS from A. ferrooxidans, the biosynthesized schwertmannite displayed a "wool ball" shape, with rough particle surfaces, many microporous structures, and a larger specific surface area. The schwertmannite yield also increased by about 45% compared with that before exfoliation, suggesting that the secretion of EPS by A. ferrooxidans can inhibit the formation of schwertmannite.