Aerobic Anaerobic Conditions Research Articles

Aerobic–anaerobic DHS reactor for enhancing denitrification in municipal wastewater treatment

Providing anaerobic environments can enhance the denitrification capacity of wastewater treatment systems. This study developed an aerobic–anaerobic downflow hanging sponge (DHS) reactor to increase denitrification. A siphon tube was integrated with a conventional DHS to create anaerobic conditions by controlling a water column inside the reactor. The siphon heights were set in the middle of the reactor, representing 2/5 of the total volume. Anaerobic conditions were maintained at the bottom (1/5), whereas aerobic conditions were maintained at the top (2/5). The middle part experienced alternating aerobic–anaerobic conditions within a siphon cycle. The hydraulic retention time (HRT) was 3 h, and the temperature was maintained at 30 °C. The study was divided into the low-loading and standard phases based on the influent soluble chemical oxygen demand (sCOD) concentration. During the low-loading phase, the aerobic–anaerobic DHS exhibited a higher sCOD removal rate (53.6 ± 26.6 %) than the control aerobic DHS (35.6 ± 31.9). However, the removal efficiencies for NH₄+–N and total nitrogen (TN) were lower, averaging 37.1 ± 24.7 % and 31.5 ± 21 %, respectively. In the standard phase, the aerobic–anaerobic DHS achieved an sCOD removal rate of 69.3 ± 14.8 % and an NH₄+–N removal rate of 17.2 ± 11.4 %. The control aerobic DHS showed higher sCOD and NH₄+–N removal at 84.7 ± 10.8 % and 54.1 ± 12.8 %, respectively, possibly due to the reduced aerobic zone volume in the aerobic–anaerobic DHS. The TN removal rates were also lower in the aerobic–anaerobic DHS (17.1 ± 11.4 %) than in the control DHS (25 ± 12.3 %). However, based on the ratio of nitrification to TN removal, the aerobic–anaerobic DHS showed a high denitrification rate of 85 %–100 %. The highest number of denitrifiers was in the middle section of the aerobic–anaerobic DHS, with Rhodocyclaceae the most prominent, followed by Comamonadaceae. Maintaining an anaerobic zone improved the denitrification capacity, indicating the potential of the aerobic–anaerobic DHS for efficient municipal wastewater treatment.

Метано- и сульфидогенез в озерах полуострова Абрау (Краснодарский край)

The geographical position, tectonic and geological-hydrogeological structure of the basin of the Malyy Liman and Abrau lakes, their landscape features as natural monuments of regional importance located on the territory of the Abrau peninsula of the Krasnodar Territory are described. Using the example of the aquatic landscapes of the Malyy Liman and Abrau lakes and the river of the same name, water and bottom sediments were studied. Hydrochemical parameters, the content of methane and sulfide sulfur in bottom sediments and methane in water as components of aquatic landscapes were studied. The results of the determination of sulfides, as well as the characteristic odor and color of bottom sediments, indicate the presence of free H2S and hydrotroilite (FeS ∙ nH2O) in them. Electron microscopy revealed the presence of hollow spheres in the bottom sediments, which indicates their possible gas saturation. Microinclusions of biogenic pyrite (FeS2), which was formed on fragments of plant and organism residues, were found under an electron microscope. In aerobic-anaerobic conditions of the upper layer of bottom sediments of lakes, pyrite formation occurs both directly through a one-stage process of pyritization of reactive iron, but also through a multi-stage process of pyrite formation from iron monosulfide. It has been established that lakes are exposed to anthropogenic influences, which can increase many times during the holiday season. This leads to their eutrophication and increased meanogenesis, which in turn contributes to the activation of methane emissions into the atmosphere. Specific methane fluxes from the water surface of the Malyy Liman and Abrau lakes have been determined.

The Ultimate Fate of Reactive Dyes Absorbed onto Polymer Beads: Feasibility and Optimization of Sorbent Bio-Regeneration under Alternated Anaerobic–Aerobic Phases

Dyes employed in many production cycles are characterized by high toxicity and persistence in the environment, and conventional wastewater treatments often fail to reach high removal efficiencies. Consequently, there is an increasing research demand aimed at the development of more efficient and sustainable technologies. A two-step strategy consisting of dye sorption followed by sorbent bio-regeneration is proposed here, with a special focus on the regeneration step. The objective of this study was to establish the best operating conditions to achieve regeneration of dye-loaded polymers and concurrently the ultimate removal of the dyes. To this aim, the bio-regeneration of the Hytrel 8206 polymer, used as a sorbent material to remove Remazol Red dye from textile wastewater, was investigated in a two-phase partitioning bioreactor (TPPB) under alternated anaerobic–aerobic conditions. Comprehensive analysis of operational parameters, including sorbent load and initial contamination levels, was conducted to optimize bio-regeneration efficiency. Experimental data demonstrated high regeneration efficiencies (91–98%) with biodegradation efficiencies up to 89%. This study also examines the biodegradation process to investigate the fate of biodegradation intermediates; results confirmed the successful degradation of the dye without significant by-product accumulation. This research underscores the potential of TPPB-based bio-regeneration of polymeric sorbent material for sustainable wastewater treatment, offering a promising solution to the global challenge of dye pollution in water resources.

Carbon, nitrogen, and phosphorus release characteristics and underlying mechanisms in fish manure from recirculating aquaculture systems under alternating aerobic-anaerobic conditions

To mitigate the adverse environmental impacts of aquaculture operations, recirculating aquaculture systems (RASs) have emerged as promising alternatives to traditional aquaculture methods. Fish manure is the primary pollutant in RASs, and oxygen fluctuations significantly influencing the release of pollutants. However, the release characteristics and underlying mechanisms of carbon (C), nitrogen (N), and phosphorus (P) during alternating aerobic-anaerobic conditions in RASs remain poorly understood. This study conducted batch incubation experiments to examine the release dynamics of C, N, and P from fish manure under simulated alternating aerobic-anaerobic conditions. Results showed that the overlying water exhibited anaerobic and reductive conditions, with both COD and TOC concentrations decreasing over time. NH4+-N levels significantly decreased from days 1–9, while NO3--N concentrations peaked on day 16. Furthermore, the alternating aerobic-anaerobic conditions significantly increased TP concentration in the overlying water. Soluble microbial byproduct-like substances in the overlying water transformed into humic acid-like substances over time. The relative abundance of Proteobacteria and Firmicutes decreased by 13.6 % and 6 %, respectively, while the relative abundance of Actinobacteria, Bacteroidota, and Chloroflexi increased by 7 %, 12.8 %, and 1.4 %, respectively. Overall, both abiotic and biotic factors influenced the release of C, N, and P from fish manure. The coupled effects of abiotic factors, specific bacterial communities, and functional genes played a critical role in the release and transformation of these elements. These findings provide new insights into the release behaviours and mechanisms of pollutants in RASs, contributing to improved environmental risk management in RASs.

Degradation of Azo-dye (Disperse Red) Using Rhizosphere Bacterial Consortium

This study investigates the degradation of the azo dye (Disperse Red) using a rhizosphere bacterial consortium. Standard microbiological and molecular techniques were employed to isolate and identify organisms from rhizosphere soil. Degradation of azodye was carried out in a fabricated anoxic and oxic chambers with hydraulic retention time of 40hrs. Initial identification of the bacterial isolates through Gram’s reaction and biochemical tests revealed the presence of organisms belonging to the genera Pseudomonas, Lysinibacillus, and Citrobacter. Molecular and phylogenetic analyses confirmed the isolates as Pseudomonas aeruginosa, Lysinibacillus sphaericus, Pseudomonas chengduensis, and Citrobacter freundii. During the preliminary testing, the degradation efficiency was assessed under varying glucose concentrations. Higher decolorization rate of 56.17% was observed in the medium with 10% glucose after 72 hours, while the medium with 5% glucose achieved a 44.17% colour reduction. Notably, lower degradation rates recorded were 11.96% and 12.85% for the 5% and 10% dye enhance glucose mineral salt media, respectively. However, During the actual degradation testing in a double-chamber system enhanced with biochar, the first anaerobic cycle achieved a maximum decolorization of 71.95% after 94 hours, with the first aerobic cycle further enhancing degradation to 90.51%. The second anaerobic cycle increased degradation to 94.78%, and the final aerobic cycle achieved a decolorization of 98.47%. These results show that the rate of Disperse Red degradation is highly dependent on glucose levels and alternating anaerobic-aerobic conditions. This study demonstrates the potential of using rhizosphere bacterial consortia to bioremediate wastewater contaminated with azo dyes, offering an efficient and sustainable method of environmental management. The results underline the need of optimizing ambient conditions to increase microbial degradation processes.

Influence of Aeration, Introduction of Probiotics, and Supply of Water on Landfill Gas Production—Study of Models

When municipal solid waste (MSW) is placed in a landfill, it undergoes anaerobic decomposition, leading to the production of landfill gas, which primarily consists of methane (CH4) and carbon dioxide (CO2). Reducing methane emissions is essential in the fight against climate change. It must be implemented at global and European levels, as set out in 2030 in the impact assessment of the climate goal plan. This assessment states that to achieve the goal by 2030 and to reduce greenhouse gas emissions by at least 55%, the methane emissions must be reduced, considering the goals of the Paris Agreement. The Glasgow Climate Pact includes a global mitigation target of the year 2030: to reduce CO2 emissions by 45%, and the emissions of methane and other greenhouse gasses. For that purpose, looking for new, more advanced ways of managing such waste is necessary. The main objective of this experimental study was to evaluate the influence of aeration, probiotic introduction, and water supply on the production of landfill gasses (CO2, CH4, N2, H2, etc.) in five different landfill models during the management of MSW and to propose the best solutions for reducing environmental pollution. The results of the research showed that the first and second models of landfills, using only anaerobic conditions, can be used for the treatment of MSW for the production of biogas (CH4, CO2), as up to 40–60% of it was released during the 120-experiment period. The third landfill model can be applied in old, already closed landfills, where the rapid stabilization and aeration of MSW are required to minimize pollutant emissions (N2, etc.) and unwanted odors and shorten biodegradation processes. The results of the fourth and fifth landfill models, in which aerobic–anaerobic conditions were applied, showed that the developing nitrification–denitrification processes resulted in complete nitrogen removal (from 20% to 0%), and overall waste stabilization improved the biodegradation of the MSW. Later, relatively good (on average, 30%) results of biogas (CH4, CO2) emissions are achieved during anaerobic condition formation results. Summarizing all experiment results of all landfill models for the further evaluation of the processes, all models can be applied in real practice depending on where they will be used and what result they want to achieve.

Mechanistic investigation of azo dye removal from carbon-deficient dyeing wastewater using horizontal-vertical constructed wetlands

Azo dye degradation can be achieved by simulating a series of anaerobic and aerobic conditions within the constructed wetland (CW) system. The current investigation evaluated the effectiveness of a baffled horizontal-vertical CW system, planted with Typha angustifolia, simulating anaerobic-aerobic conditions to treat carbon-deficient synthetic dyeing wastewater containing 100 mg/L Reactive Yellow 145 (RY145) azo dye. In the absence of an available carbon source in dyeing wastewater, an optimum quantity of sodium acetate was supplemented as the substrate for microbial degradation of RY145. Influent dyeing wastewater characteristics were 5555 ADMI colour, 461 mg/L chemical oxygen demand (COD) and 39 mg/L total nitrogen (TN). During the operation period, the CW system achieved 97% colour, 87% COD, 95% ammonium nitrogen (NH4+-N) and 71% TN removals at 4 d hydraulic retention time (HRT). Favourable environmental conditions, such as low redox conditions and substrate availability in horizontal CW, contributed to a significant reduction in colour (96%). Most TN reduction (67%) happened in horizontal CW by denitrification and plant assimilation. The metagenomic study revealed that Proteobacteria, Bacteroidetes, Chloroflexi and Firmicutes were responsible for pollutant degradation within horizontal CW. The UV–visible spectra and high-resolution liquid chromatograph mass spectrometer (HR-LCMS) analysis confirmed that dye degradation intermediates generated from the breakage of azo bonds were eliminated in vertical CW with high redox conditions. The results of the phytotoxicity and fish toxicity experiments demonstrated a substantial toxicity reduction in the CW system-treated effluent.

Phosphorus removal from fermented dairy manure concurrent with polyhydroxybutyrate-co-valerate synthesis under aerobic conditions

Wastewater phosphorus removal achieved biologically is associated with the process known as enhanced biological phosphorus removal (EBPR). In contrast with canonical EBPR operations that employ alternating anaerobic–aerobic conditions and achieve asynchronous carbon and phosphorus storage, research herein focused on phosphorus removal achieved under aerobic conditions synchronously with volatile fatty acid (VFA) storage as polyhydroxybutyrate-co-valerate (PHBV). 90.3 ± 3.4 % soluble phosphorus removal was achieved from dairy manure fermenter liquor; influent and effluent concentrations were 38.6 ± 9.5 and 3.7 ± 0.8 mgP/L, respectively. Concurrently, PHBV yield ranged from 0.17 to 0.64 mgCOD/mgCOD, yielding 147–535 mgCODPHBV/L. No evidence of EBPR mechanisms was observed, nor were canonical phosphorus accumulating organisms present; additionally, the polyphosphate kinase gene was not present in the microbial biomass. Phosphorus removal was primarily associated with biomass growth and secondarily with biomass complexation. Results demonstrate that concurrent PHBV synthesis and phosphorus recovery can be achieved microbially under aerobic dynamic feeding conditions when fed nutrient rich wastewater.

Comparison of benzotriazole ultraviolet stabilizers (BUVs) removal from wastewater after subsequent stages of sequencing batch reactor (SBR) treatment process

The research focused on benzotriazole ultraviolet stabilizers (BUVs) which are commonly used compounds despite being found dangerous, e.g. promoting breast cancer cell proliferation, damaging vital organs such as hearts, brains livers and kidneys. The aim of the study was to analyse the efficiency and removal rate of BUVs from wastewater depending on the quantity of tested compounds and SBR anaerobic-aerobic conditions. The study was conducted in sequencing batch reactors (SBRs - 17 L) with real flocculent activated sludge (8 L) and model wastewater (5 L) containing UV-326, UV-327, UV-328, UV-329 and UV-P from 50 to 600 μg∙L−1. The SBR were operated in 390 cycles of 7 h and 10 min over 130 days. The similarity of the technological parameters of the treatment process to those used in a real wastewater treatment plant was maintained. Efficiency removal of individual BUVs was strictly dependent on the dose of compounds introduced into wastewater and ranged from 68.2 to 97 %. Removal of UV-329 occurred with lowest efficiency (from 68.2 to 85.2 %) while UV-326 was most efficiently removed from the wastewater (from 94.1 to 97 %). UV-329 was removed from wastewater with the lowest (0.0968–0.9524 μg∙L−1∙min−1) average removal rate while UV-327 with the highest (0.16–1.3357 μg∙L−1∙min−1), irrespective of BUVs dose in the influent. Secondary release of BUVs into the wastewater occurred in SBR during the settling phase and was dependent on the type and concentration of the BUVs in the raw wastewater. This occurrence was noted for UV-326 ≥ 100; UV-327 = 600; UV-328 ≥ 200; UV-329 ≥ 50 and UV-P ≥ 100 μg∙L−1. The settling phase needs to be shortened to the required minimum. This is an important conclusion for WWTPs in regards to SBR cycle duration and technological parameters of the treatment process.

Corrigendum: Biodegradation of 2-4-6 trichlorophenol by sequencing batch reactors (SBR) equipped with a rotating biological bed and operated in an anaerobic-aerobic condition

Corrigendum: Biodegradation of 2-4-6 trichlorophenol by sequencing batch reactors (SBR) equipped with a rotating biological bed and operated in an anaerobic-aerobic condition

Assessing the impact of increasing phenol loads on the performance and stability of an aerobic granular sludge system

This work evaluated the impact of phenol on the performance and stability of an aerobic granular sludge (AGS) sequencing batch reactor (SBR) operated under alternating anaerobic-aerobic conditions for simultaneous organic matter, nitrogen, and phosphorus removal. The reactor was fed with synthetic wastewater whose phenol concentration was gradually increased from 2 to 200 mg L−1, while the other carbon source (acetate) was reduced proportionally to keep the organic loading rate invariable. Up to 20 mg L−1 of phenol, the average COD removal was above 90%, while practically full ammonium, phosphorus, and phenol removal was achieved. However, at higher phenol concentrations, the activity of polyphosphate-accumulating organisms and nitrifiers was affected. Although the overall COD removal was only slightly affected by increasing phenol loads, replacing the main carbon source from acetate to phenol changed the organic matter removal profile over the cycle, with the latter being converted mainly within the aerated stage of the SBR. As a result, there was filamentous growth that deteriorated the settling properties of the granules. The establishment of an anaerobic feast-aerobic famine regime over the non-aerated and aerated phases of the AGS SBR and the presence of a readily biodegradable substrate (such as acetate) proved to be crucial for maintaining granules stability. Having phenol as the sole organic carbon source led to complete process failure regarding nutrient removal capability.

Microbial diversity, transformation and toxicity of azo dye biodegradation using thermo-alkaliphilic microbial consortia

In this research, the transformation and toxicity of Reactive Red 141 and 239 biodegraded under anaerobic-aerobic conditions as well as metagenomic analysis of Reactive Red 239 degrading microbial consortia collected from Shala Hot spring were investigated. Toxicity of dyes before treatment and after treatment on three plants, fish and microorganisms were done. A halotolerant and thermo-alkaliphilic bacterial consortia decolorizing azo dyes (>98% RR 141 and > 96% RR 239 in 7 h) under optimum conditions of salt concentration (0.5%), temperature (55 °C) and pH (9), were used. Toxicity effect of untreated dyes and treated dyes in Tomato > Beetroot > Cabbage plants, while the effect was Leuconostoc mesenteroides > Lactobacillus plantarum > Escherichia coli in microorganisms. Among fishes, the toxicity effect was highest in Oreochromis niloticus followed by Cyprinus carpio and Clarias gariepinus. The three most dominant phyla that could be in charge of decolorizing RR 239 under anaerobic-aerobic systems were Bacteroidota (22.6–29.0%), Proteobacteria (13.5–29.0%), and Chloroflexi (8.8–23.5%). At class level microbial community structure determination, Bacteroidia (18.9–27.2%), Gammaproteobacteria (11.0–15.8%), Alphaproteobacteria (2.5–5.0%) and Anaerolineae (17.0–21.9%) were dominant classes. The transformation of RR 141 and RR 239 into amine compounds were proposed via high performance liquid chromatography-mass spectroscopy (HPLC/MS) and fourier transform infrared spectroscopy (FT-IR). Overall, dye containing wastewaters treated under anaerobic-aerobic systems using thermo-alkaliphilic microbial consortia were found to be safe to agricultural (fishes and vegetables) purposes.

Fe/S Redox-Coupled Mercury Transformation Mediated by Acidithiobacillus ferrooxidans ATCC 23270 under Aerobic and/or Anaerobic Conditions.

Bioleaching processes or microbially mediated iron/sulfur redox processes in acid mine drainage (AMD) result in mineral dissolution and transformation, the release of mercury and other heavy metal ions, and changes in the occurrence forms and concentration of mercury. However, pertinent studies on these processes are scarce. Therefore, in this work, the Fe/S redox-coupled mercury transformation mediated by Acidithiobacillus ferrooxidans ATCC 23270 under aerobic and/or anaerobic conditions was studied by combining analyses of solution behavior (pH, redox potential, and Fe/S/Hg ion concentrations), the surface morphology and elemental composition of the solid substrate residue, the Fe/S/Hg speciation transformation, and bacterial transcriptomics. It was found that: (1) the presence of Hg2+ significantly inhibited the apparent iron/sulfur redox process; (2) the addition of Hg2+ caused a significant change in the composition of bacterial surface compounds and elements such as C, N, S, and Fe; (3) Hg mainly occurred in the form of Hg0, HgS, and HgSO4 in the solid substrate residues; and (4) the expression of mercury-resistant genes was higher in earlier stages of growth than in the later stages of growth. The results indicate that the addition of Hg2+ significantly affected the iron/sulfur redox process mediated by A. ferrooxidans ATCC 23270 under aerobic, anaerobic, and coupled aerobic-anaerobic conditions, which further promoted Hg transformation. This work is of great significance for the treatment and remediation of mercury pollution in heavy metal-polluted areas.

Bacterial Communication Coordinated Behaviors of Whole Communities to Cope with Environmental Changes.

Bacterial communication plays an important role in coordinating microbial behaviors in a community. However, how bacterial communication organizes the entire community for anaerobes to cope with varied anaerobic-aerobic conditions remains unclear. We constructed a local bacterial communication gene (BCG) database comprising 19 BCG subtypes and 20279 protein sequences. BCGs in anammox-partial nitrification consortia coping with intermittent aerobic and anaerobic conditions as well as gene expressions of 19 species were inspected. We found that when suffering oxygen changes, intra- and interspecific communication by a diffusible signal factor (DSF) and bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) changed first, which in turn induced changes of autoinducer-2 (AI-2)-based interspecific and acyl homoserine lactone (AHLs)-based intraspecific communication. DSF and c-di-GMP-based communication regulated 455 genes, which covered 13.64% of the genomes and were mainly involved in antioxidation and metabolite residue degradation. For anammox bacteria, oxygen influenced DSF and c-di-GMP-based communication through RpfR to upregulate antioxidant proteins, oxidative damage-repairing proteins, peptidases, and carbohydrate-active enzymes, which benefited their adaptation to oxygen changes. Meanwhile, other bacteria also enhanced DSF and c-di-GMP-based communication by synthesizing DSF, which helped anammox bacteria survive at aerobic conditions. This study evidences the role of bacterial communication as an "organizer" within consortia to cope with environmental changes and sheds light on understanding bacterial behaviors from the perspective of sociomicrobiology.

Biodegradation of 2-4-6 trichlorophenol by sequencing batch reactors (SBR) equipped with a rotating biological bed and operated in an anaerobic-aerobic condition

2-4-6 Trichlorophenol (TCP) is toxic, carcinogenic, and resistant to biodegradation. In this study, a rotating biological bed (RBB) was used to improve the efficiency of Sequencing batch reactors (SBR), and it was operated in sequential anaerobic and aerobic conditions. Biofilm growth on media of rotating biological bed was also confirmed using Scanning Electron Microscope (SEM). In this study, the effect of 2-4-6 trichlorophenol concentration (5–430 mg/L), hydraulic retention time (HRT) (12–30 h), the number of operating cycles per day (6–12 cycles/d), the type of combination of anaerobic and aerobic processes and the presence of a rotating biological bed and its rotation were studied. SBR equipped with a rotating biological bed (SBR-RBB) with the sequential anaerobic-aerobic operation in optimal operating conditions (TCP: 430 mg/L, cycles/d: 8, and HRT: 6 h) can remove nearly 100% of TCP and more than 95% of TP and COD. The role of the presence of an RBB in removing TCP, TP, and COD was 7, 20, and 23%, respectively. The role of rotation of RBB also was 23%, 10, 21, and 62%, respectively. So, SBR-RBB, with the sequential anaerobic-aerobic operation, was able to remove higher concentrations of TCP (430 mg/L) in a shorter HRT (6 h) with higher efficiency (nearly 100%) compared to previous studies. Therefore, for the first time in this study, the biological treatment of 430 mg/L of TCP is reported by a biological process.

Evaluating the potential of thermo-alkaliphilic microbial consortia for azo dye biodegradation under anaerobic-aerobic conditions: Optimization and microbial diversity analysis

Wastewaters in textile industry are mainly characterized by higher pH, color, salt and chemical oxygen demand (COD) values, which are environmentally undesirable. Among these textile effluent characteristics, color removal is the most challenging task. In this study, the potential of Rift Valley halotolerant and thermo-alkaliphilic microbial consortia (collected from Shala hot spring located in Ethiopia) for azo dye biodegradation under anaerobic-aerobic conditions were evaluated. Optimization and microbial diversity analysis were done using Reactive Red 141. Under optimum conditions of pH (9), temperature (55 °C), salinity (0.5%), and nutrients, microbial consortia can remove >98% color and 92.7 ± 7.3% COD under anaerobic and aerobic conditions, respectively. In addition, the consortia was capable of decolorizing initial dye concentrations of 100–1000 mg/L, and various dye types including Everzol Blue LX, RY 84, RR 239, RB 198 and RY 700. The 16S rRNA gene sequence results showed that Bacteroidetes (25.3%) > Proteobacteria (21.0%) > Chloroflexi (18.5%) > Halobacterota (6.2%) dominant phyla. Based on the findings, non-color effluent adapted Rift Valley halotolerant and thermo-alkaliphilic bacterial consortia can be a potential candidate for bioremediation of textile and other industries characterized by higher salinity, temperature and pH.

Investigation of metabolic crosstalk between host and pathogenic Clostridioides difficile via multiomics approaches.

Clostridioides difficile is a gram-positive anaerobic bacterium that causes antibiotic-associated infections in the gut. C. difficile infection develops in the intestine of a host with an imbalance of the intestinal microbiota and, in severe cases, can lead to toxic megacolon, intestinal perforation, and even death. Despite its severity and importance, however, the lack of a model to understand host-pathogen interactions and the lack of research results on host cell effects and response mechanisms under C. difficile infection remain limited. Here, we developed an in vitro anaerobic-aerobic C. difficile infection model that enables direct interaction between human gut epithelial cells and C. difficile through the Mimetic Intestinal Host–Microbe Interaction Coculture System. Additionally, an integrative multiomics approach was applied to investigate the biological changes and response mechanisms of host cells caused by C. difficile in the early stage of infection. The C. difficile infection model was validated through the induction of disaggregation of the actin filaments and disruption of the intestinal epithelial barrier as the toxin-mediated phenotypes following infection progression. In addition, an upregulation of stress-induced chaperones and an increase in the ubiquitin proteasomal pathway were identified in response to protein stress that occurred in the early stage of infection, and downregulation of proteins contained in the electron transfer chain and ATP synthase was observed. It has been demonstrated that host cell energy metabolism is inhibited through the glycolysis of Caco-2 cells and the reduction of metabolites belonging to the TCA cycle. Taken together, our C. difficile infection model suggests a new biological response pathway in the host cell induced by C. difficile during the early stage of infection at the molecular level under anaerobic-aerobic conditions. Therefore, this study has the potential to be applied to the development of future therapeutics through basic metabolic studies of C. difficile infection.

Treatment of saline wastewater amended with endocrine disruptors by aerobic granular sludge: Assessing performance and microbial community dynamics

An aerobic granular sludge (AGS) sequencing batch reactor (SBR) adapted to salinity (12 g L−1 NaCl) was operated under alternating anaerobic-aerobic conditions for the treatment of synthetic saline wastewater containing endocrine-disrupting chemicals (EDCs), namely 17β–estradiol (E2), 17α–ethinylestradiol (EE2) and bisphenol-A (BPA). The SBR was intermittently fed with the EDCs at 2 mg L−1 of each compound. E2 was completely biodegraded, with 60–80% removal attained anaerobically and the remaining quickly consumed under aeration. EE2 was sorbed onto the granular sludge biomass in the anaerobic period, but it was desorbed in subsequent cycles even when the compound was not supplied to the reactor. BPA removal was poor but improved after bioaugmentation with an EDCs degrading bacteria. EDCs shock loads did not significantly affect the COD removal nor the activity of ammonium- and nitrite-oxidizing bacteria (AOB and NOB, respectively). In contrast, the activity of phosphate-accumulating organisms (PAOs) was affected, implying a decrease in P removal within the aerobic phase. AGS core microbiome grouped most bacteria belonging to the phylum Proteobacteria, followed by Bacteroidetes. The microbial profile showed that the introduction of the EDCs mixture increased the relative abundance of Chryseobacterium and Flavobacterium. AOB and NOB species were detected in the AGS biomass, with the latter showing lower relative abundance. Different PAOs, such as Rhodocyclus, Tetrasphaera and Gemmatimonas, were also part of the microbial community, but the addition of EDCs decreased significantly the relative abundance of Rhodocyclus. High microbial diversity was sustained over reactor operation, with the main bacterial groups responsible for nutrients and EDCs removal preserved in the AGS system. The results pointed to the maintenance of a core microbiome over reactor operation that may be related to the stability of the AGS process during EDCs loading.

Effect of sludge age on aerobic granular sludge: Addressing nutrient removal performance and biomass stability

The effect of the sludge retention time (SRT) on the stability and performance of an aerobic granular sludge (AGS) sequencing-batch reactor (SBR) on the simultaneous organic matter, nitrogen and phosphorus removal from simulated domestic wastewater was assessed in a long-term study (392 days). Operated under alternating anaerobic-aerobic conditions, the reactor was subjected to four experimental conditions: uncontrolled SRT (run I), SRT of 30 (run II), 20 (run III) and 15 days (run IV). The results showed that COD removal was kept stable and over 90 % throughout the SBR operation, regardless of the SRT. On the other hand, by allowing the sludge age to be dependent on natural solids washout by effluent withdrawal (SRT of 47–61 days), phosphate removal was substantially low (15 %), as also observed at an SRT of 30 days. Filamentous bacteria overgrowth was noticed at the later conditions, which affected the stability of the granular biomass, leading to a deterioration of its settling properties. The ratio between the sludge volume index after 30 and 5 min of settling (SVI30/SVI5) was around 0.70. Biological phosphate removal started to thrive at the sludge age of 20 days (35 %), reaching around 100 % at SRT of 15 days, at which the highest P-release/COD uptake ratio (0.14 mg P/mgCOD) and specific phosphate uptake (11.4 mgPO43−-P/(gVSS h)) were observed. Under the lowest SRT applied, the granules exhibited better structural and settling properties, with the SVI30/SVI5 ratio reaching almost 1.0. Moreover, nitrification was kept stable, and, even though nitrite build-up occurred during the SBR cycle, nitrate was the main oxidized nitrogen form in the effluent. Average COD, ammonium and total nitrogen removal amounted to 93 %, 97 % and 58 %. Cycle tests under normal and special conditions were carried out to assess specific nitrification, denitrification and phosphate uptake rates, and elucidate the key players in the biological conversions processes taking place in the AGS reactor. No phosphate uptake coupled to nitrate reduction was noticed, implying that P removal was not driven by denitrifying dephosphatation activity. To track the dynamics of important microbial functional groups, fluorescence in situ hybridization analysis was conducted.

The effect of different operational strategies on polyhydroxyalkanoates (PHAs) production at short-term biomass enrichment

In this study, polyhydroxyalkanoates (PHA) production under different short- time biomass enrichment strategies were investigated. Three strategies were applied in a sequencing batch reactor (SBR) including complete aerobic condition under the feast-famine regime, uncoupled carbon and nitrogen feeding regime and alternating anaerobic-aerobic conditions. Also, the effect of two different carbon sources comprising acetate and soft drink wastewaters on PHA production over the accumulation stage was evaluated. From the results, uncoupled carbon and nitrogen feeding regime showed a better performance to accumulate PHA rather than the other strategies. Besides, the accumulated PHA with acetate as a carbon source was significantly higher than soft drink wastewater. PHA production was obtained to be 79% and 25% mg-PHA/mg-TSS under uncoupled carbon and nitrogen feeding regime fed by acetate and soft drink wastewater, respectively. However, PHA production was less than 50% and 20% for other strategies with acetate and soft drink wastewater, respectively.