Effect of humic acid on phenanthrene removal by constructed wetlands using birnessite as a substrate

Biotic/abiotic transformation mechanisms of phenanthrene in iron-rich constructed wetland under redox fluctuation

Iron-rich constructed wetlands (CWs) could promote phenanthrene bioremediation efficiently through biotic and abiotic pathways, which have gained increasing attention. However, the biotic/abiotic transformation mechanisms of trace organic contaminants in iron-rich CW are still ambiguous. Herein, three CWs (i.e., CW-A: Control; CW-B: Iron-rich CW, CW-C: Iron-rich CW + tidal flow) were constructed to investigate the transformation mechanisms of phenanthrene through Mössbauer spectroscopy and metagenomics. Results demonstrated CW-C achieved the highest phenanthrene removal (94.0 %) and bacterial toxicity reduction (92.1 %) due to the optimized degradation pathway, and subsequently achieved the safe transformation of phenanthrene. Surface-bound/low-crystalline iron regulated hydroxyl radical (·OH) production predominantly, and its utilization was promoted in CW-C, which also improved electron transfer capacity. The enhanced electron transfer capacity led to the enrichment of PAH-degrading microorganisms (e.g., Thauera) and keystone species (Sphingobacteriales bacterium 46-32) in CW-C. Additionally, the abundances of phenanthrene transformation (e.g., EC:1.14.12.-) and tricarboxylic-acid-cycle (e.g., EC:2.3.3.1) enzyme were up-regulated in CW-C. Further analysis indicated that the safe transformation of phenanthrene was mainly attributed to the combined effect of abiotic (·OH and surface-bound/low-crystalline iron) and biotic (microbial community and diversity) mechanisms in CW-C, which contributed similarly. Our study revealed the essential role of active iron in the safe transformation of phenanthrene, and was beneficial for enhanced performance of iron-rich CW.

Current progress on manganese in constructed wetlands: Bibliometrics, effects on wastewater treatment, and plant uptake

Constructed wetlands (CWs) are a pollutant treatment design inspired by natural wetlands and are widely utilized for the removal of common pollutants. The research focus lies in the circulation of manganese (Mn) in the environment to enhance pollutant removal within CWs. This paper provides a comprehensive review of recent advancements in understanding the role and effects of Mn in chemical weapons, based on literature retrieval from 2002 to 2021. Ecological risk assessment and heavy metals within CWs emerge as current areas of research interest. Mn sources within CWs primarily include natural deposition, heavy metal wastewater, and intentional addition. The cycling between Mn(II) and Mn(IV) facilitates enhanced wastewater treatment within CWs. Moreover, employing a Mn matrix proves effective in reducing ammonia nitrogen wastewater, organic pollutants, as well as heavy metals such as Cd and Pb, thereby addressing complex pollution challenges practically. To comprehensively analyze influencing factors on the system's performance, both internal factors (biological species, design parameters, pH levels, etc.) and external factors (seasonal climate variations, precipitation patterns, ultraviolet radiation exposure, etc.) were discussed. Among these factors, microorganisms, pollutants, and temperature are the most important influencing factors, which emphasizes the importance of these factors for wetland operation. Lastly, this paper delves into plant absorption of Mn along with coping strategies employed by plants when faced with Mn poisoning or deficiency scenarios. When utilizing Mn for the regulation of constructed wetlands, it is crucial to consider the tolerance levels of associated plant species. Furthermore, the study predicts future research hotspots encompass high-efficiency catalysis techniques, matrix-filling approaches, and preparation of resource utilization methods involving Mn nanomaterials.

Bioremediation of polycyclic aromatic hydrocarbons: An updated microbiological review

A class of organic priority pollutants known as PAHs is of critical public health and environmental concern due to its carcinogenic properties as well as its genotoxic, mutagenic, and cytotoxic properties. Research to eliminate PAHs from the environment has increased significantly due to awareness about their negative effects on the environment and human health. Various environmental factors, including nutrients, microorganisms present and their abundance, and the nature and chemical properties of the PAH affect the biodegradation of PAHs. A large spectrum of bacteria, fungi, and algae have ability to degrade PAHs with the biodegradation capacity of bacteria and fungi receiving the most attention. A considerable amount of research has been conducted in the last few decades on analyzing microbial communities for their genomic organization, enzymatic and biochemical properties capable of degrading PAH. While it is true that PAH degrading microorganisms offer potential for recovering damaged ecosystems in a cost-efficient way, new advances are needed to make these microbes more robust and successful at eliminating toxic chemicals. By optimizing some factors like adsorption, bioavailability and mass transfer of PAHs, microorganisms in their natural habitat could be greatly improved to biodegrade PAHs. This review aims to comprehensively discuss the latest findings and address the current wealth of knowledge in the microbial bioremediation of PAHs. Additionally, recent breakthroughs in PAH degradation are discussed in order to facilitate a broader understanding of the bioremediation of PAHs in the environment.

Biotransformation as a tool for remediation of polycyclic aromatic hydrocarbons from polluted environment - review on toxicity and treatment technologies

Polycyclic aromatic hydrocarbons, a prominent family of persistent organic molecules produced by both anthropogenic and natural processes, are widespread in terrestrial and aquatic environments owing to their hydrophobicity, electrochemical stability and low aqueous solubility. Phenanthrene and naphthalene belong to the group of polycyclic aromatic hydrocarbons whose occurrence are reported to be relatively higher. The bioremediation mode of removing the toxicities of these two compounds has been reported to be promising than other methods. Most of the microbial classes of bacterial, fungal and algal origin are reported to degrade the target pollutants into non-toxic compounds effectively. The review aims to give an overview on toxicological studies, identification and enrichment techniques of phenanthrene and naphthalene degrading microbes and the bioremediation technologies (microbial assisted reactors, microbial fuel cells and microbial assisted constructed wetlands) reported by various researchers. All the three modes of bioremediation techniques were proved to be promising on different perspectives. In the treatment of phenanthrene, a maximum recovery of 96% and 98% was achieved in an aerobic membrane reactor with Bacillus species and single chamber air cathode microbial fuel cell with Acidovorax and Aquamicrobium respectively were reported. With the constructed wetland configuration, 95.5% of removal was attained with manganese oxide based microbial constructed wetland. The maximum degradation efficiency reported for naphthalene are 99% in a reverse membrane bioreactor, 98.5% in a marine sediment microbial fuel cell and 92.8% with a low-cost sandy soil constructed wetland.