Regulatory of salinity on assembly of activated sludge microbial communities and nitrogen transformation potential in industrial plants of the lower Yangtze River basin.

This study aims to thoroughly investigate the impact mode of salinity carried by industrial wastewater on the anaerobic-anoxic-oxic (A2O) sludge in wastewater treatment plants (WWTPs). Through comprehensive investigation of the A2O stage activated sludge (AS) from 19 industrial WWTPs in the downstream area of the Yangtze River, China, A total of 38 samples of anaerobic sludge and oxic sludge were collected and analyzed. We found that salinity stress significantly inhibits the growth of the AS community, particularly evident in the anaerobic sludge community. Furthermore, the high-saline environment induces changes in the structure and functional patterns of the AS community, leading to intensive interactions and resource exchanges among microorganisms. Halophilic microorganisms may play a crucial role in this process, significantly impacting the overall community structure, especially in the oxic sludge community. Additionally, salinity stress not only suppresses the nitrogen transformation potential of the AS but also leads to the accumulation of nitrite, thereby increasing the emission potential of both NO and N2O, exacerbating the greenhouse effect of the A2O process in industrial WWTPs. The findings of this study provide necessary theoretical support for maintaining the long-term stable operation of the A2O sludge system in industrial WWTPs, reducing carbon footprint, and improving nitrogen removal efficiency.

Asynchronous characteristics of Feammox and iron reduction from paddy soils in Southern China.

Recently, the newly discovered anaerobic ammonium oxidation coupled with iron reduction (i.e., Feammox) has been proven to be a widespread nitrogen (N) loss pathway in ecosystems and has an essential contribution to gaseous N loss in paddy soil. However, the mechanism of iron-nitrogen coupling transformation and the role of iron-reducing bacteria (IRB) in Feammox were poorly understood. This study investigated the Feammox and iron reduction changes and microbial community evolution in a long-term anaerobic incubation by 15N isotope labeling combined with molecular biological techniques. The average rates of Feammox and iron reduction during the whole incubation were 0.25 ± 0.04 µg N g-1 d-1 and 40.58 ± 3.28 µg Fe g-1 d-1, respectively. High iron oxide content increased the Feammox rate, but decreased the proportion of Feammox-N2 in three Feammox pathways. RBG-13-54-9, Brevundimonas, and Pelomonas played a vital role in the evolution of microbial communities. The characteristics of asynchronous changes between Feammox and iron reduction were found through long-term incubation. IRB might not be the key species directly driving Feammox, and it is necessary to reevaluate the role of IRB in Feammox process.

Degradation of thiocyanate by Fe/Cu/C microelectrolysis: Role of pre-magnetization and enhancement mechanism.

Thiocyanate (SCN-), a non-volatile inorganic pollutant, is commonly found in various types of industrial wastewater, which is resistant to hydrolysis and has the potential to be toxic to organisms. Premagnetized iron-copper-carbon ternary micro-electrolytic filler (pre-Fe/Cu/C) was prepared to degrade SCN-. Pre-Fe/Cu/C exhibited the most significant enhancement effect on SCN- removal when magnetized for 5 min with an intensity of 100 mT, and the SCN- removal rate was the highest at an initial pH of 3.0 and an aeration rate of 1.6 L/min. The electrochemical corrosion and electron transfer in the pre-Fe/Cu/C system were confirmed through SEM, XPS, FTIR, XRD, and electrochemical tests. This resulted in the formation of more corrosion products and multiple cycles of Fe2+/Fe3+ and Cu0/Cu+/Cu2+. Additionally, density functional theory (DFT) calculations and electron paramagnetic resonance (EPR) were utilized to illustrate the oxygen adsorption properties of the materials and the participation of reactive oxygen species (1O2, ·O2-, and ·OH) in SCN- removal. The degradation products of SCN- were identified as SO42-, HCO3-, NH4+, and N2. This study introduced the use of permanent magnets for the first time to enhance Fe/Cu/C ternary micro-electrolytic fillers, offering a cost-effective, versatile, and stable approach that effectively effectively enhanced the degradation of SCN-.

Quantifying Stochastic Processes in Shaping Dissolved Organic Matter Pool with High-Resolution Mass Spectrometry.

Natural dissolved organic matter (DOM) represents a ubiquitous molecular mixture, progressively characterized by spatiotemporal resolution. However, an inadequate comprehension of DOM molecular dynamics, especially the stochastic processes involved, hinders carbon cycling predictions. This study employs ecological principles to introduce a neutral theory to elucidate the fundamental processes involving molecular generation, degradation, and migration. A neutral model is thus formulated to assess the probability distribution of DOM molecules, whose frequencies and abundances follow a ß-distribution relationship. The neutral model is subsequently validated with high-resolution mass spectrometry (HRMS) data from various waterbodies, including lakes, rivers, and seas. The model fitting highlights the prevalence of molecular neutral distribution and quantifies the stochasticity within DOM molecular dynamics. Furthermore, the model identifies deviations of HRMS observations from neutral expectations in photochemical and microbial experiments, revealing nonrandom molecular transformations. The ecological null model further validates the neutral modeling results, demonstrating that photodegradation reduces molecular stochastic dynamics at the surface of an acidic pit lake, while random distribution intensifies at the river surface compared with the porewater. Taken together, the DOM molecular neutral model emphasizes the significance of stochastic processes in shaping a natural DOM pool, offering a potential theoretical framework for DOM molecular dynamics in aquatic and other ecosystems.

The Stratified Distribution of Dissolved Organic Matter in an AMD Lake Revealed by Multi-sample Evaluation Procedure.

As a typical extreme environment, acid mine drainage (AMD) has been extensively studied for its biogeochemical cycle, but little is known about the quality of dissolved organic matter (DOM) in AMD. In this study, DOM molecules in an AMD lake were detected with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and the change of DOM molecules in the stratified water column was analyzed with a multi-sample evaluation procedure. The results demonstrate that DOM quality is highly stratified and can be linked with severe biogeochemical gradients. In the surface layer, DOM molecules can be distinguished by low quantities and intensities, as well as potential photodegradation products. Oxygen-poor and oxygen-rich molecules alternately dominate the chemocline, which can be explained by the redox-dependent adsorption/desorption of DOM on metastable secondary minerals. A rich and abundant DOM pool with a high proportion of heteroatoms exists at the bottom which can be significantly influenced by material exchange with sediments. These findings emphasize the active role of DOM in extreme AMD environments and expand the understanding of the carbon cycle in the hydrosphere.

Innovative recovery of matrix layered double hydroxide from simulated acid mine wastewater for the removal of copper and cadmium from wastewater.

This study innovatively added biochar to optimize regulation in the neutralization process of simulated acid mine drainage (AMD) and recovered a new type of matrix layered double hydroxides (MLDH), which can be used to remove copper (Cu(II)) and cadmium (Cd(II)) from wastewater. A series of batch experiments show that MLDH with strong selective removal ability of Cu(II) and Cd(II) can be successfully obtained by adding biochar (BC) at pH = 5 end in the neutralization process. Kinetic and isotherm modeling studies indicated that the removal of Cu(II) and Cd(II) by the MLDH was a chemical multilayer adsorption process. The removal mechanism of Cu(II) and Cd(II) was further analyzed through related characterization analysis with contribution rate calculation: the removal rates of Cu(II) and Cd(II) by ion exchange were 42.7% and 26%, while that by precipitation were 34.5% and 49.9%, respectively. This study can provide a theoretical reference and experimental basis for the recovery and utilization of valuable by-products in AMD and the treatment of heavy metal wastewater.

Temperature-Driven Activated Sludge Bacterial Community Assembly and Carbon Transformation Potential: A Case Study of Industrial Plants in the Yangtze River Delta.

Temperature plays a critical role in the efficiency and stability of industrial wastewater treatment plants (WWTPs). This study focuses on the effects of temperature on activated sludge (AS) communities within the A2O process of 19 industrial WWTPs in the Yangtze River Delta, a key industrial region in China. The investigation aims to understand how temperature influences AS community composition, functional assembly, and carbon transformation processes, including CO2 emission potential. Our findings reveal that increased operating temperatures lead to a decrease in alpha diversity, simplifying community structure and increasing modularity. Dominant species become more prevalent, with significant decreases in the relative abundance of Chloroflexi and Actinobacteria, and increases in Bacteroidetes and Firmicutes. Moreover, higher temperatures enhance the overall carbon conversion potential of AS, particularly boosting CO2 absorption in anaerobic conditions as the potential for CO2 emission during glycolysis and TCA cycles grows and diminishes, respectively. The study highlights that temperature is a major factor affecting microbial community characteristics and CO2 fluxes, with more pronounced effects observed in anaerobic sludge. This study provides valuable insights for maintaining stable A2O system operations, understanding carbon footprints, and improving COD removal efficiency in industrial WWTPs.

Effect of hydrothermal carbonization on pyrolysis behavior, nutrients and metal species distribution in municipal sludge.

In this study, the effect of hydrothermal carbonation (HTC) on the pyrolysis behavior and the distribution of nutrients and metal species of waste-activated sludge (WAS) was investigated. Results showed that the pyrolysis activation energy range of WAS decreased from 11 to 57 kJ/mol to 10-36 kJ/mol when the hydrothermal carbonization was at 160 °C. As indicated by thermodynamic parameters, the hydrothermal carbonization process reduces the pyrolysis reaction activity of the hydrochar. The results of the chemical analysis indicate that hydrothermal carbonization significantly enhances the release of phosphorus and nitrogen, with maximum recovery at a temperature of 200 °C. The standard measurement and testing protocol revealed that hydrothermal carbonization increased the content of non-apatite inorganic P fraction in hydrochar and enhanced the availability of P. Heavy metal analysis shows that hydrothermal carbonization can strengthen the stability of heavy metals in WAS.

Interaction between acid-tolerant alga Graesiella sp. MA1 and schwertmannite under long-term acidic condition.

Schwertmannite (Sch), a typical Fe(III)-oxyhydroxysulphate mineral, is the precipitation reservoir of toxic elements in acid mine drainage (AMD). Acid-tolerant microbes in AMD can participate in the microbe-mediated transformation of Sch, while Sch affects the physiological characteristics of these acid-tolerant microbes. Based on our discovery of algae and Sch enrichment in a contaminated acid mine pit lake, we predicted the interaction between algae and Sch when incubated together. The acid-tolerant alga Graesiella sp. MA1 was isolated from the pit-lake surface water of an acidic mine and incubated with different contents of Sch. Sch was detected as the main product at the end of 81 d; however, there was a weak transformation. The presence of dissolved Fe(II) could be largely attributed to the photoreduction dissolution of Sch, which was promoted by Graesiella sp. MA1. The adaptation and growth phases of Graesiella sp. MA1 differed under Sch stress. The photosynthetic and metabolic activities increased and decreased at the adaptation and growth phases, respectively. The MDA contents and antioxidant activity of SOD, APX, and GSH in algal cells gradually enhanced as the Sch treatment content increased, indicating a defense strategy of Graesiella sp. MA1. Metabolomic analysis revealed that Sch affected the expression of significant differential metabolites in Graesiella sp. MA1. Organic carboxylic acid substances were essentially up-regulated in response to Sch stress. They were abundant in the medium-Sch system with the highest Fe(III) reduction, capable of complexing Fe(III), and underwent photochemical reactions via photo-induced charge transfer. The significant up-regulation of reducing sugars revealed the high energy requirement of Graesiella sp. MA1 under Sch stress. And first enriched KEGG pathway demonstrated the importance of sugar metabolism in Graesiella sp. MA1. Data acquired in this study provide novel insights into extreme acid stress adaptation of acid-tolerant algae and Sch, contributing to furthering understanding of AMD environments.

Mechanisms of manganese-tolerant Bacillus brevis MM2 mediated oxytetracycline biodegradation process.

Addressing the environmental threat of oxytetracycline (OTC) contamination, this study harnesses the bioremediation capabilities of Bacillus brevis MM2, a manganese-oxidizing bacterium from acid mine drainage. We demonstrate the strain's exceptional efficiency in degrading OTC under high manganese conditions, with complete removal achieved within 24 h. The degradation is facilitated by the production of Bio-MnOx, utilizing their high redox potential and large specific surface area, which significantly enhance the adsorption and oxidation of OTC. Advanced characterization techniques, including X-ray diffraction, scanning electron microscopy, High Resolution-Transmission Electronic Microscope and X-ray photoelectron spectroscopy, provide a detailed analysis of the structural and functional properties of Bio-MnOx. The study also reveals the crucial role of Mn(III) intermediates and reactive oxygen species in the OTC degradation process, with quenching experiments validating their substantial impact on efficiency. Laccase activity, a key manganese-oxidizing enzyme, is assessed spectrophotometrically, further highlighting the enzymatic contribution to Mn(II) oxidation and OTC breakdown. This research contributes valuable insights and approaches for the targeted bioremediation of OTC-contaminated aquatic environments, offering a promising strategy for combating pollution from antibiotics and analogous compounds.

Tailings particle size effects on pollution and ecological remediation: A case study of an iron tailings reservoir.

The particle size distribution in tailings notably influences their physical properties and behavior. Despite this, our understanding of how the distribution of tailings particle sizes impacts in situ pollution and ecological remediation in in-situ environment remains limited. In this study, an iron tailings reservoir was sampled along a particle flow path to compare the pollution characteristic and microbial communities across regions with different particle sizes. The results revealed a gradual reduction in tailings particle size along the flow direction. The predominant mineral composition shifts from minerals such as albite and quartz to layered minerals. Total nitrogen, total organic carbon, and total metal concentrations increased, whereas the acid-generating potential decreased. The region with the finest tailings particle size exhibited the highest microbial diversity, featuring metal-resistant microorganisms such as KD4-96, Micrococcaceae, and Acidimicrobiia. Significant discrepancies were observed in tailings pollution and ecological risks across different particle sizes. Consequently, it is necessary to assess tailings reservoirs pollution in the early stages of remediation before determining appropriate remediation methods. These findings underscore that tailings particle distribution is a critical factor in shaping geochemical characteristics. The responsive nature of the microbial community further validated these outcomes and offered novel insights into the ecological remediation of tailings.

Multi-omics insights into biogeochemical responses to organic matter addition in an acidic pit lake: Implications for bioremediation.

Acidic pit lakes (APLs) emerge as reservoirs of acid mine drainage in flooded open-pit mines, representing extreme ecosystems and environmental challenges worldwide. The bioremediation of these oligotrophic waters necessitates the addition of organic matter, but the biogeochemical response of APLs to exogenous organic matter remains inadequately comprehended. This study delves into the biogeochemical impacts and remediation effects of digestate-derived organic matter within an APL, employing a multi-omics approach encompassing geochemical analyses, amplicon and metagenome sequencing, and ultra-high resolution mass spectrometry. The results indicated that digestate addition first stimulated fungal proliferation, particularly Ascomycetes and Basidiomycetes, which generated organic acids through lignocellulosic hydrolysis and fermentation. These simple compounds further supported heterotrophic growth, including Acidiphilium, Acidithrix, and Clostridium, thereby facilitating nitrate, iron, and sulfate reduction linked with acidity consumption. Nutrients derived from digestate also promoted the macroscopic development of acidophilic algae. Notably, the increased sulfate reduction-related genes primarily originated from assimilatory metabolism, thus connecting sulfate decrease to organosulfur increase. Assimilatory and dissimilatory sulfate reduction collectively contributed to sulfate removal and metal fixation. These findings yield multi-omics insights into APL biogeochemical responses to organic matter addition, enhancing the understanding of carbon-centered biogeochemical cycling in extreme ecosystems and guiding organic amendment-based bioremediation in oligotrophic polluted environments.

Metabolomic and physiological changes of acid-tolerant Graesiella sp. MA1 during long-term acid stress.

Algae plays a significant role for the primary production in the oligotrophic ecosystems such as the acid mine pit lakes. Graesiella sp. MA1 was a new acid-tolerant photosynthetic protist isolated from an acid mine pit lake. To understand the acid responses of Graesiella sp. MA1, its physiological changes and metabolomics were studied during long-term acid stress. Photosynthetic pigments, soluble proteins, and antioxidant systems of Graesiella sp. MA1 cells displayed two phases, the adaptation phase and the growth phase. During the adaptation phase, both photosynthetic pigments and soluble proteins were inhibited, while antioxidant activity of SOD, APX, and GSH were promoted to response to the organism's damage. Metabolomics results revealed lipids and organic acids were abundant components in Graesiella sp. MA1 cells. In response to acid stress, the levels of acid-dependent resistant amino acids, including glutamate, aspartate, arginine, proline, lysine, and histidine, accumulated continuously to maintain orderly intracellular metabolic processes. In addition, fatty acids were mainly unsaturated, which could improve the fluidity of the cell membranes under acid stress. Metabolomic and physiological changes showed that Graesiella sp. MA1 had tolerance during long-term acid stress and the potential to be used as a bioremediation strain for the acidic wastewater.

Decadal evolution of an acidic pit lake: Insights into the biogeochemical impacts of microbial community succession.

Acidic pit lakes represent hydrological features resulting from the accumulation of acid mine drainage in mining operations. Long-term monitoring is essential for these extreme and contaminated environments, yet tracking investigations integrating microbial geochemical dynamics in acidic pit lakes have been lacking thus far. This study integrated historical data with field sampling to track decadal biogeochemical changes in an acidic pit lake. With limited artificial disturbance, significant and sustained biogeochemical changes were observed over the past decade. Surface water pH slowly increased from 2.8 to a maximum of 3.6, with a corresponding increase in bottom water pH to around 3.9, despite the accumulation of externally imported sulfate and metals. Elevated nutrient levels stimulated the macroscopic growth of Chlorophyta, resulting in a shift from reddish-brown to green water with floating algal bodies. Furthermore, microalgae-fixed organic carbon promoted the transition from the initial chemolithotrophy-based population dominated by Acidiphilium and Ferrovum to a heterotrophic community. The increase in heterotrophic iron- and sulfate-reducers may cause an elevation in ferrous levels and a decline in copper concentrations. However, most metals were not removed from the water column, potentially due to insufficient biosulfidogenesis or sulfide reoxidation. These findings offer novel insights into microbial succession in extreme ecosystem evolution and contribute to the management and remediation of acidic pit lakes.

Eukaryotic Community Structure and Interspecific Interactions in a Stratified Acidic Pit Lake Water in Anhui Province.

The stratified acidic pit lake formed by the confluence of acid mine drainage has a unique ecological niche and is a model system for extreme microbial studies. Eukaryotes are a component of the AMD community, with the main members including microalgae, fungi, and a small number of protozoa. In this study, we analyzed the structural traits and interactions of eukaryotes (primarily fungi and microalgae) in acidic pit lakes subjected to environmental gradients. Based on the findings, microalgae and fungi were found to dominate different water layers. Specifically, Chlorophyta showed dominance in the well-lit aerobic surface layer, whereas Basidiomycota was more abundant in the dark anoxic lower layer. Co-occurrence network analysis showed that reciprocal relationships between fungi and microalgae were prevalent in extremely acidic environments. Highly connected taxa within this network were Chlamydomonadaceae, Sporidiobolaceae, Filobasidiaceae, and unclassified Eukaryotes. Redundancy analysis (RDA) and random forest models revealed that Chlorophyta and Basidiomycota responded strongly to environmental gradients. Further analysis indicated that eukaryotic community structure was mainly determined by nutrient and metal concentrations. This study investigates the potential symbiosis between fungi and microalgae in the acidic pit lake, providing valuable insights for future eukaryotic biodiversity studies on AMD remediation.

Contrasting prokaryotic and eukaryotic community assembly and species coexistence in acid mine drainage-polluted waters.

Acid mine drainage (AMD) is characterized by high acidity and high-concentration metals and sulfate, representing an extreme environment to life as well as environmental challenge worldwide. Microorganisms thriving in AMD habitats have evolved with distinct mechanisms in response to multiple stresses. Compared with microbial prokaryotes, our understanding regarding eukaryotic occurrence and role in AMD habitats remain limited. Here we examined microbial diversity and co-occurrence pattern within all domains of life in five lakes with varying degrees of AMD contamination ranging from extremely acidic to neutral. We demonstrated that AMD pollution reduced both eukaryotic and prokaryotic diversity in the lakes. In lakes with serious AMD pollution, chemoautotrophs including Ferrovum, Acidithiobacillus, and Leptospirillum showed significantly higher abundance, whereas with the macroscopic growths of photosynthetic microalgae (e.g., Coccomyxa and Chlamydomonas), heterotrophic or mixotrophic prokaryotes (e.g., Acidiphilium, Thiomonas, and Alicyclobacillus) increased in less polluted lakes. In the further improved ecosystems, Ochromonas, Rotifer, Ciliophora and other microeukaryotes appeared. Combined with a public dataset focusing on the microbes along an AMD-contaminated stream, we further demonstrated that acidity-dominated environmental selection served as the primary driver of both eukaryotic and prokaryotic community assemblies, and to a greater extent for eukaryotes. Furthermore, specific prokaryotic and eukaryotic taxa (e.g., Proteobacteria and Chlorophyta) exhibited wide taxonomic and functional associations in these AMD-polluted waters. These findings expand our knowledge on the eukaryotic diversity in AMD habitats, and provide insights into the ecological processes underlying microbial communities in response to AMD contamination.

[Characteristics of Bacterial Community Structure in the Sediment of Rural Black and Odorous Water Bodies].

Sediment microorganisms are the main drivers of the material circulation and organic matter degradation processes in rural black and odorous water bodies(RBOWB), and the community structure of sediment microorganisms follows the changes in the external environment. Here, the pollutant indicators, including nitrogen, phosphorus, and heavy metals in the overlying water and sediment of 29 RBOWB in Dongming County of Heze City were measured, respectively. Combined with Illumina sequencing results, the composition and diversity characteristics of sediment bacterial communities in RBOWB and their correlation with environmental factors were further analyzed. The experimental results showed a wide distribution of pollutants in both of the overlying water and sediment in the RBOWB of this region. Compared with agricultural non-point source pollution, the concentrations of nitrogen and phosphorus pollutants in the overlying water with domestic sewage as the main source of pollution were 3.1 and 1.5 times higher than those of agricultural non-point source pollution, respectively. In addition, the contents of heavy metals in the sediments of RBOWB were generally lower than the soil element background value in Heze City. The dominant bacteria phyla in the sediments of the RBOWB were Proteobacteria, Actinobacteria, Chloroflexi, Firmicutes, and Acidobacteria, and the total abundance of these five dominant phyla accounted for 70.3%-83.6% of all sequences. The dominant classes were γ-Proteobacteria, α-Proteobacteria, Anaerolineae, and Actinobacteria. The dominant genera were Thiobacillus and Pseudarthrobacter. Moreover, Spearman correlation analysis showed that the environmental factors of DO, COD, TN, TP, and organic matter exerted significant effects(P<0.05) on sediment bacterial genera in RBOWB, and sediment bacterial community richness was significantly influenced by TN(P<0.05). The above results provided the microbiological knowledge for treating RBOWB.

Molecular insights into the impacts of acid mine drainage on dissolved organic matter dynamics in pit lakes.

Pit lakes are artificial hydrological features created by mining operations that typically suffer from acid mine drainage (AMD), which not only endangers water quality but also exacerbates carbon loss. However, the impacts of AMD on the fate and role of dissolved organic matter (DOM) in pit lakes remain unclear. This study employed negative electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) combined with biogeochemical analysis to examine DOM molecular variations and environmental controls across the AMD-induced acidic and metalliferous gradients in five pit lakes. The results demonstrated distinct DOM pools in pit lakes characterized by the prevalence of smaller aliphatic compounds compared to other waterbodies. AMD-induced geochemical gradients promoted DOM heterogeneity among pit lakes, with acidic pit lakes containing more lipid-like compounds. Acidity and metals enhanced DOM photodegradation, reducing the content, chemo-diversity and aromaticity. Organic sulfur was detected in high abundance, potentially from sulfate photo-esterification and mineral flotation agent. Furthermore, microbial involvements in carbon cycling were revealed by DOM-microbe correlation network, but microbial contributions to the DOM pools decreased under acidic and metal stresses. These findings highlight abnormal carbon dynamics caused by AMD pollution and integrate DOM fate into pit lake biogeochemistry, thereby contributing to management and remediation.

Simultaneous removal of COD and NH4+-N from domestic sewage by a single-stage up-flow anaerobic biological filter based on Feammox.

In recent years, Feammox has made it possible to remove NH4+-N under anaerobic conditions; however, its application in practical wastewater treatment processes has not been extensively reported. In this study, an up-flow anaerobic biological filter based on limonite (Lim-UAF) was developed to facilitate long-term and stable treatment of domestic sewage. Lim-UAF achieved the highest removal efficiency of chemical oxygen demand (COD) and NH4+-N at a hydraulic retention time (HRT) of 24 h (Stage II). Specifically, the COD and NH4+-N content decreased from 240.8 and 30.0 mg/L to about 7.5 and 0.35 mg/L, respectively. To analyze the potential nitrogen removal mechanism, the Lim-UAF was divided into three layers according to the height of the reactor. The results showed that COD and NH4+-N removal had remarkable characteristics in Lim-UAF. More than 55.0% of influent COD was removed in the lower layer (0-30 cm) of Lim-UAF, while 60.2% of NH4+-N was removed in the middle layer (30-60 cm). Microbial community analysis showed that the community structure in the middle and upper layers (60-90 cm) was relatively similar, but quite different from that of the lower layer. Heterotrophic bacteria were dominant in the lower layer, whereas iron-reducing and iron-oxidizing bacteria were enriched in the upper and middle layers. The formation of secondary minerals (siderite and Fe(OH)3) indicated that the Fe(III)/Fe(II) redox cycle occurred in Lim-UAF, which was triggered by the Feammox and NDFO processes. In summary, limonite was used to develop a single-stage wastewater treatment process for simultaneously removing organic matter and NH4+-N, which has excellent application prospects in domestic sewage treatment.

Roasting mechanism of lightweight low-aluminum-silicon ceramisite derived from municipal solid waste incineration fly ash and electrolytic manganese residue.

Municipal solid waste incineration (MSWI) fly ash and electrolytic manganese residue (EMR) belong to hazardous waste, and must be disposed of before processing. It was found that the low content of silicon and aluminum at low roasting temperature can meet the expansion mechanism of lightweight aggregates. A low-aluminum-silicon lightweight ceramisite was successfully prepared from MSWI fly and EMR, the formation mechanism of which was that the viscosity of molten stuffs in pellet was the function of temperature and chemical composition and had enough capacity of capturing the emerged gas over roasting. The resulting ceramisite met with the requirement of Lytag commercial lightweight aggregate. The content of heavy metal in ceramisite accorded with the requirement of soil environmental quality for development GB 36600-2018 Class I, and PCDD/Fs in ceramisite was 2.0 ng I-TEQ/kg, which was safe. The collaboration of thermal simulation and characterization (SEM-EDS, FTIR and XRD) elaborated the formation mechanism of ceramisite, with six stages provided.