Arsenic release from microbial reduction of scorodite in the presence of electron shuttle in flooded soil

Manganese promotes stability of natural arsenic sinks in a groundwater system with arsenic-immobilization minerals: Natural remediation mechanism and environmental implications

Arsenic (As)-immobilizing iron (Fe)-manganese (Mn) minerals (AFMM) represent potential As sinks in As-enriched groundwater environments. The process and mechanisms governing As bio-leaching from AFMM through interaction with reducing bacteria, however, remain poorly delineated. This study examined the transformation and release of As from AFMM with varying Mn/Fe molar ratios (0:1, 1:5, 1:3, and 1:1) in the presence of As(V)-reducing bacteria specifically Shewanella putrefaciens CN32. Notably, strain CN32 significantly facilitated the bio-reduction of As(V), Fe(III), and Mn(IV) in AFMM. In systems with Mn/Fe molar ratios of 1:5, 1:3, and 1:1, As bio-reduction decreased by 28%, 34%, and 47%, respectively, compared to the system with a 0:1 ratio. This Mn-induced inhibition of Fe/As bio-reduction was linked to several concurrent factors: preferential Mn bio-reduction, reoxidation of resultant Fe(II)/As(III) due to Mn components, and As adsorption onto emergent Fe precipitates. Both the reductive dissolution of AFMM and the bio-reduction of As(V) predominantly controlled As bio-release. Structural equation models indicated that reducing bacteria destabilize natural As sinks more through As reduction than through Mn(II) release, Fe reduction, or Fe(II) release. Systems with Mn/Fe molar ratios of 1:5, 1:3, and 1:1 showed a decrease in As bio-release by 24%, 41%, and 59%, respectively, relative to the 0:1 system. The observed suppression of As bioleaching was ascribed to both the inhibition of As/Fe bio-reduction by Mn components and the immobilization of As by freshly generated Fe precipitates. These insights into the constraining effect of Mn on the biotransformation and bioleaching of As from AFMM are crucial for grasping the long-term stability of natural As sinks in groundwater, and enhance strategies for in-situ As stabilization in As-afflicted aquifers through Nature-Based Solutions.

Application of dirty-acid wastewater treatment technology in non-ferrous metal smelting industry: Retrospect and prospect

Dirty-acid wastewater (DW) originating from the non-ferrous metal smelting industry is characterized by a high concentration of H2SO4 and As. During the chemical precipitation treatment, a significant volume of arsenic-containing slag is generated, leading to elevated treatment expenses. The imperative to address DW with methods that are cost-effective, highly efficient, and safe is underscored. This paper conducts a comprehensive analysis of three typical methods to DW treatment, encompassing technical principles, industrial application flow charts, research advancements, arsenic residual treatment, and economic considerations. Notably, the sulfide method emerges as a focal point due to its minimal production of arsenic residue and the associated lowest overall treatment costs. Moreover, in response to increasingly stringent environmental protection policies targeting new pollutants and carbon emissions reduction, the paper explores the evolving trends in DW treatment. These trends encompass rare metal and sulfuric acid recycling, cost-effective H2S production methods, and strategies for reducing, safely disposing of, and harnessing resources from arsenic residue.

Contradictory Impacts of Nitrate on the Dissimilatory Arsenate-Respiring Prokaryotes-Induced Reductive Mobilization of Arsenic from Contaminated Sediments: Mechanism Insight from Metagenomic and Functional Analyses

Dissimilatory arsenate-respiring prokaryotes (DARPs) are considered to be a key impetus of the reductive dissolution of solid-phase arsenic. However, little is known about the interaction between nitrate and DARPs so far. In this study, we showed that nitrate either inhibited or promoted the DARP population-catalyzed reductive mobilization of As in sediments. Metagenomic analysis of the microbial communities in the microcosms after seven days of As release assays suggested that microbes mainly consisted of: Type-I DARPs having potential to reduce NO3- into NO2- and Type-II DARPs having potential to reduce NO3- to NH4+. We further isolated two cultivable DARPs, Neobacillus sp. A01 and Paenibacillus sp. A02, which represent Type-I and -II DARPs, respectively. We observed that nitrate suppressed A01-mediated release of As(III) but promoted A02-mediated release of As(III). Furthermore, we demonstrated that this observation was due to the fact that nitrite, the end product of incomplete denitrification by Type-I DARPs, suppressed the arrA gene expression per cell and growth of all DARPs, whereas ammonium, the end product of dissimilatory nitrate reduction to ammonium (DNRA) by Type-II DARPs, enhanced the arrA gene expression per cell and significantly promoted the growth of all DARPs. These findings suggest that the actual effects of nitrate on DARP population-catalyzed reductive mobilization of arsenic, largely depend on the ratio of Type-I to Type-II DARPs in sediments.

Effect of Micro-Nanobubbles on Arsenic Removal by Trichoderma atroviride for Bioscorodite Generation

The global environmental issue of arsenic (As) contamination in drinking water is a significant problem that requires attention. Therefore, the aim of this research was to address the application of a sustainable methodology for arsenic removal through mycoremediation aerated with micro-nanobubbles (MNBs), leading to bioscorodite (FeAsO4·2H2O) generation. To achieve this, the fungus Trichoderma atroviride was cultivated in a medium amended with 1 g/L of As(III) and 8.5 g/L of Fe(II) salts at 28 °C for 5 days in a tubular reactor equipped with an air MNBs diffuser (TR-MNBs). A control was performed using shaking flasks (SF) at 120 rpm. A reaction was conducted at 92 °C for 32 h for bioscorodite synthesis, followed by further characterization of crystals through Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and X-ray diffraction (XRD) analyses. At the end of the fungal growth in the TR-MNBs, the pH decreased to 2.7-3.0, and the oxidation-reduction potential (ORP) reached a value of 306 mV at 5 days. Arsenic decreased by 70%, attributed to possible adsorption through rapid complexation of oxidized As(V) with the exchangeable ferrihydrite ((Fe(III))4-5(OH,O)12), sites, and the fungal biomass. This mineral might be produced under oxidizing and acidic conditions, with a high iron concentration (As:Fe molar ratio = 0.14). The crystals produced in the reaction using the TR-MNBs culture broth and characterized by SEM, XRD, and FTIR revealed the morphology, pattern, and As-O-Fe vibration bands typical of bioscorodite and römerite (Fe(II)(Fe(III))2(SO4)4·14H2O). Arsenic reduction in SF was 30%, with slight characteristics of bioscorodite. Consequently, further research should include integrating the TR-MNBs system into a pilot plant for arsenic removal from contaminated water.

Review on arsenic environment behaviors in aqueous solution and soil

Arsenic pollution in environment has always been an important environmental problem that has attracted wide attention in recent years. Adsorption is one of the main methods of treatment for arsenic in the aqueous solution and soil because of the advantages of high efficiency, low cost and wide application. Firstly, this report summarizes the commonly and widely used adsorbent materials such as metal-organic frameworks, layered bimetallic hydroxides, chitosan, biochar and their derivatives. The adsorption effects and mechanisms of these materials are further discussed, and the application prospects of these adsorbents are considered. Meanwhile, the gaps and deficiencies in the study of adsorption mechanism was pointed out. Then, this study comprehensively evaluated the effects of various factors on arsenic transport, including (i) the effects of pH and redox potential on the existing form of As; (ii) complexation mechanism of dissolved organic matter and As; (iii) factors affecting the plant enrichment of As. Finally, the latest scientific researches on microbial remediation of arsenic and the mechanisms were summarized. The review finally enlightens the subsequent development of more efficient and practical adsorption material.