Insight into synergies between Acinetobacter sp. AL-6 and pomelo peel biochar in a hybrid process for highly efficient manganese removal

Classification of additives and their influence mechanisms in improving the performance of biologically induced carbonate precipitation

Microbial/enzyme induced carbonate precipitation (MICP/EICP) is one of the hot topics in the field of civil engineering, environmental engineering in recent years, primarily attributed to its environmental friendliness and low energy consumption. However, how to enhance its economic and technical feasibility to ensure its stable and high-performance is still a significant challenge. This paper systematically explores the strategic incorporation of additives as a promising approach to enhance the efficiency and controllability of MICP/EICP process. An overview of MICP and EICP, including a comparison between them, is first compiled. According to the characteristics of various additives and the regulatory requirements, they are classified into the following categories: organic macromolecular additives, inorganic additives, biological additives and others. It then highlights the potential of additives to impact the mineralization dynamic process and the underlying mechanisms of their involvement in the reaction, such as providing nucleation sites, enhancing bioactivity, altering the properties of the calcium carbonate product, and reducing by-products. Whereas these additives either possess outstanding biocompatibility, specific functional groups, or particular viscosity, can work synergistically with MICP/EICP, they still have some intrinsic limits that need to be addressed. Therefore, future perspectives in additive-modified MICP/EICP systems are discussed in-depth. These insights establish a theoretical framework for additive selection tailored to specific MICP/EICP applications, making the incorporation of additives a powerful tool in the future to improve mineralization outcomes in different application scenarios.

Enhancement of Mn2+, Fe2+ and NH4+-N removal by biochar synergistic strains combined with activated sludge in real wastewater treatment

Acinetobacter sp. AL-6 combining with biochar was adapted in activated sludge (AS & co-system) to decontaminate Mn2+, Fe2+ and NH4+-N, and treat activated sludge (AS) for its activity and settling performance improvement. Specifically, the co-system promoted the growth of bacteria in the activated sludge, thus increasing its ability to nitrify and adsorb Mn2+ and Fe2+, resulting in the removal of high concentrations of NH4+-N, Mn2+, Fe2+ and COD in the reactor by 100%, 100%, 100%, and 96.8%, respectively. And the pH of wastewater was increased from 4 to 8.5 by co-system also facilitated the precipitation of Mn2+ and Fe2+. The MLVSS/MLSS ratio increased from 0.64 to 0.95 and SVI30 decreased from 92.54 to 1.54 after the addition of co-system, which indicated that biochar helped to improve the activity and settling performance of activated sludge and prevented it from being damaged by the compound Mn2+ and Fe2+. In addition, biochar promoted the increase of the tyrosine-like protein substance and humic acid-like organic matter in the sludge EPS, thus enhanced the ability of sludge to adsorb Mn2+ and Fe2+. Concretely, compared with AS group, the proteins content and polysaccharides content of the AS & co-system group were increased by 13.14 times and 6.30 times respectively. Further, microbial diversity analysis showed that more resistant bacteria and dominant bacteria Acinetobacter sp. AL-6 in sludge enhanced the nitrification and adsorption of manganese and iron under the promotion of biochar. Pre-eminently, the more effective AS & co-system were applied to the removal of actual electrolytic manganese slag leachate taken from the contaminated site, and the removal of NH4+-N, Mn2+, Fe2+ and COD remained high at 100%, 100%, 71.82% and 94.72%, respectively, revealing advanced value for high engineering applications of AS & co-system.

Enhancing the Mn-Removal Efficiency of Acid-Mine Bacterial Consortium: Performance Optimization and Mechanism Study

In this study, an acclimated manganese-oxidizing bacteria (MnOB) consortium, QBS-1, was enriched in an acid mine area; then, it was used to eliminate Mn(Ⅱ) in different types of wastewater. QBS-1 presented excellent Mn removal performance between pH 4.0 and 8.0, and the best Mn-removal efficiency was up to 99.86% after response surface methodology optimization. Unlike other MnOB consortia, the core bacteria of QBS-1 were Stenotrophomonas and Achromobacter, which might play vital roles in Mn removal. Besides that, adsorption, co-precipitation and electrostatic binding by biological manganese oxides could further promote Mn elimination. Finally, the performance of the Mn biofilter demonstrated that QBS-1 was an excellent inoculant, which indicates good potential for removing Mn contamination steadily and efficiently.

More effective application of biochar-based immobilization technology in the environment: Understanding the role of biochar

In recent years, biochar-based immobilization technology (BIT) has been widely used to treat different environmental issues because of its cost-effectiveness and high removal performance. However, the complexity of the real environment is always ignored, which hinders the transfer of the BIT from lab-scale to commercial applications. Therefore, in this review, the analysis is performed separately on the internal side of the BIT (microbial fixation and growth) and on the external side of the BIT (function) to achieve effective BIT performance. Importantly, the internal two stages of BIT have been discussed concisely. Further, the usage of BIT in different areas is summarized precisely. Notably, the key impacts were systemically analyzed during BIT applications including environmental conditions and biochar types. Finally, the suggestions and perspectives are elucidated to solve current issues regarding BIT.

Manganese Pollution and Its Remediation: A Review of Biological Removal and Promising Combination Strategies

Manganese (Mn), as a cofactor of multiple enzymes, exhibits great significance to the human body, plants and animals. It is also a critical raw material and alloying element. However, extensive employment for industrial purposes leads to its excessive emission into the environment and turns into a significant threat to the ecosystem and public health. This review firstly introduces the essentiality, toxicity and regulation of Mn. Several traditional physicochemical methods and their problems are briefly discussed as well. Biological remediation, especially microorganism-mediated strategies, is a potential alternative for remediating Mn-polluted environments in a cost-efficient and eco-friendly manner. Among them, microbially induced carbonate precipitation (MICP), biosorption, bioaccumulation, bio-oxidation are discussed in detail, including their mechanisms, pivotal influencing factors along with strengths and limitations. In order to promote bioremediation efficiency, the combination of different techniques is preferable, and their research progress is also summarized. Finally, we propose the future directions of Mn bioremediation by microbes. Conclusively, this review provides a scientific basis for the microbial remediation performance for Mn pollution and guides the development of a comprehensive competent strategy towards practical Mn remediation.

Development of nitric acid-modified activated carbon electrode for removal of Co2+/Mn2+/Ni2+ by electrosorption

In this paper, nitric acid-modified activated carbon was used as an electrode in the electrosorption process for the removal of Co²⁺, Mn²⁺, and Ni²⁺ from wastewater. The effects of applied voltage, initial pH, and coexisting ions on removal efficiency were investigated. The adsorption process was evaluated by adsorption isotherm models. The results indicated that the electrosorption process was consistent with the Langmuir model, proving that the electrosorption process was a monolayer adsorption process. The maximum adsorption capacities of Co²⁺, Mn²⁺, and Ni²⁺ were 131.58 mg/g, 102.04 mg/g, and 103.09 mg/g. Electrochemical tests revealed that the specific capacitance of AC-HNO₃ was 54.11 F/g when the scanning rate was 5 mV/s, while the specific capacitance of AC was 36.51 F/g. The Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) confirmed that the content of oxygen groups on the surface of activated carbon increased after modification, which provided more adsorption sites for electrosorption. When the selected concentration of HCl was used as the eluent, the elution efficiency of Co²⁺, Mn²⁺, and Ni²⁺ could reach 94.23%, 93.65%, and 90.61%. The removal efficiency could reach more than 95% after three cycles. The results of the study can be used as a reference significance for the removal of cobalt, manganese, and nickel ions from heavy metal wastewater by electrosorption.

Screening the functions of modified rice straw biochar for adsorbing manganese from drinking water

The seasonal out-of-limit of manganese ions (Mn²⁺) in the drinking water reservoirs is an intractable problem to water supply, which can pose a threat to the human health. In this study, the removal of Mn²⁺ by using pristine (BC), pre-alkali (Pre-BC) and post-alkali (Post-BC) modified biochar originating from rice straw was investigated. The maximum adsorption capacities obtained for BC, Pre-BC, and Post-BC were 20.59, 28.37, and 8.06 mg g⁻¹, respectively. The Langmuir isotherm model and the pseudo-second-order kinetic model were suitable fitting models to describe the adsorption process. The investigation of adsorption functions was carried out that revealed that the predominant forces were precipitation and cation exchange with the proportions of 43.38–69.15% and 38.05–55.79%, respectively. With regard to precipitation, Mn(ii) particles (Al–Si–O–Mn and MnCO₃) and insignificantly oxidized insoluble Mn(iv) particles (MnO₂) were formed on the biochar surface. Alkali and alkaline earth metals facilitated the behavior of cation exchange, where the primary contributing ions for cation exchange were Na⁺, Mg²⁺ and Ca²⁺ during the adsorption process. These outcomes suggest that alkali pre-treated modification of biochar is practical for the application of manganese pollution control in lakes and reservoirs.

Modified biochar was used to remove Mn²⁺ from water with principal adsorption functions of precipitation and cation exchange. The MnCO₃ and Al–Si–O–Mn mainly driven precipitation and Na⁺, Mg²⁺ and Ca²⁺ primarily contributed to the cation exchange.