Aerobic Phase Research Articles

Biogeochemical process governing cadmium availability in sediments of typical coastal wetlands driven by drying-wetting alternation

Fluctuations in water levels within coastal wetlands can significantly affect cadmium (Cd) cycling and behavior in sediments. Understanding the effects of drying-wetting cycles on Cd availability and binding mechanisms is crucial. However, information regarding this subject remains limited. This study conducted incubation experiments employing chemical extraction, high-resolution mass spectrometry, and microbiological analysis to investigate the Cd behavior under these conditions. The results from a 40-day anaerobic incubation followed by a 20-day aerobic phase indicated that the drying-wetting cycles triggered fluctuations in physicochemical parameters (e.g., pH, EC, and reactive iron (Fed)), affecting Cd mobility. The mobility of Cd was closely linked to nanozyme activity (R2=0.63), exhibiting a strong correlation with Fed (R2=0.51). This suggested that the drying-wetting cycles induced Fed changes, which regulated the nanozyme activity, thereby affecting Cd availability. The changes in Cd availability were strongly linked to transformations in iron oxides and organic functional groups (carboxylic-OH and aliphatic C-H), whereas the bacterial community composition, particularly Bacilli and Clostridia, notably influenced Cd accessibility. These findings offer valuable insights into the geochemical dynamics of Cd in coastal wetland sediments under alternating drying-wetting cycles, enhancing our understanding of its biogeochemical cycling and potential risks.

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.

Pre-anoxic electro-stimulation enhanced simultaneous nitrification–denitrification in single-stage electrolysis-integrated sequencing batch biofilm reactor

Simultaneous nitrification–denitrification (SND) is a promising nitrogen removal process. However, total nitrogen (TN) removal is limited due to unsatisfactory denitrification. This study demonstrated that short-time (1 h) pre-anoxic electro-stimulation significantly enhanced SND efficiency in the aerobic phase by promoting the proliferation of mixotrophic and heterotrophic denitrifiers. SND and TN removal efficiencies at the optimal electric current (EC) (0.02 A) were 85.6 % and 93.9 %, which were 39.1 % and 17.2 % higher than control. Microbial community analysis indicated that the abundance of mixotrophic and heterotrophic denitrifiers significantly increased. H2 generated in the electro-stimulation process induced the proliferation of mixotrophic denitrifiers. The weak EC (0.02 A) promoted the activity and growth of heterotrophic denitrifiers by accelerating electron transfer. They concurrently mediated heterotrophic denitrification to enhance SND efficiency. PICRUSt2 analysis revealed that the abundance of denitrifying genes dramatically surged. This study provides new insights into applying electrolysis to achieve advanced SND while minimizing electricity consumption.

Sensor model fusion reveals the dynamics of lactobacillus fermentation with real time concentrations of lactic and acetic acids in ensiling of maize and ryegrass

Anaerobic lactobacillus (LAB) fermentation is key to production of silage. Tracking the dynamics of bacterial metabolism is important for the improvement of LAB fermentation and for evaluation of potential additives. This is currently limited by available ex situ analytical methods, while commercial sensors of lactic and acetic acid content remain unavailable. Here we validate an in situ pH sensor and devise a model-sensor package and a mini-fermenter system (1.5 L) for on-line analysis of LAB fermentation. By the fusion of the model based on mirror mapping principle and the time course of pH measured in situ, a general solution of the dynamic accumulation of organic acid (DAOA) and percentage yield of organic acid (PYOA, 0 ∼ 100 %) is obtained as a function of time. We link PYOA to the initial and final values of lactic and acetic concentrations analyzed ex situ to obtain specific solutions for the time courses of lactic and acetic acid production. We demonstrate the model-sensor system with fermentation of both maize and ryegrass, capturing the dynamic patterns of fermentation, including the rapid depletion of O2 in the initial aerobic phase (maize: ≈ 1.5 h, ryegrass: ≈ 9.2 h), the exponential decline of pH (R2 ≥ 0.99, RMSE ≤ 0.043) in the subsequent anaerobic phase, and metabolic feedbacks of pH on instantaneous acid production (ΔpH; inflection at pH 5), and on cumulative yields of total acidity and specific organic acids. These are all previously unavailable data streams.

Integrated aerobic-anaerobic digestion of highly solids-loaded corn stover and swine manure under dynamic aeration: Temperature rise, physicochemical characteristics, and methane production

This research aimed to design an integrated aerobic-anaerobic reactor with dynamic aeration that was automatically regulated based on real-time oxygen concentration and investigate the aerobic pretreatment and subsequent dry co-anaerobic digestion (co-AD) characteristics of highly solids-loaded corn stover and swine manure in terms of temperature rise, physiochemical characteristics, and methane production. The high-temperature feedstocks from the aerobic pretreatment phase rapidly entered the AD phase without transportation and effectively improved the start-up and methane production of the co-AD. Oxygen concentration range, aeration rate, and pretreatment time affected the cumulative aeration time, temperature rise, and organic matter removal interactively during aerobic pretreatment, and a low aeration rate was relatively preferable. Although the lignocellulose removal increased with the increase in pretreatment duration, the maximal lignin elimination efficiency only reached 1.30%. The inoculum injection in the transition phase from aerobic pretreatment to co-AD and the leachate reflux during co-AD were also critical for producing methane steadily apart from aerobic pretreatment. The cold air weakened the temperature rise of aerobic pretreatment, and the low-temperature leachate reduced the methane production in the co-AD process. An oxygen concentration range of 13%–17%, aeration rate of 0.10 m3/(min·m3), pretreatment time of 84 h, inoculum loading of 40%, leachate refluxing thrice per day, and double-layer inoculation were optimum for improving the integrated aerobic-anaerobic digestion system's ability to resist low temperatures and achieving high methane production. The maximal cumulative and volatile solids (VS) methane yields of corn stover and swine manure reached 444.58 L and 266.30 L/kg VS.

Reactive transport modelling of iron bentonite interaction in the FEBEX in situ experiment

The evolution of steel/bentonite interfaces in engineered barrier systems of radioactive waste disposal is governed by the corrosion of the steel and the interaction of corrosion products with the bentonite. In the early post-closure phase of the repository, the transition from aerobic to anaerobic corrosion in combination with evolving temperature conditions and chemical gradients due to the hydration of the bentonite take place. In situ tests in underground laboratories provide a high degree of representativeness for the early transient evolution of the interfaces. Complex Fe-bentonite interaction patterns have been observed, which include a concave Fe accumulation front and distinct coloured halos around the corroding steel. A reactive transport model for the FEBEX in situ test is presented, which describes the transition from aerobic to anaerobic corrosion, the transport of O2 in the gas and liquid phase and the chemical evolution of the steel/bentonite interface during the 18 years of the experiment. The model successfully reproduces the major steps of the interface evolution: an aerobic corrosion phase characterized by accumulation of goethite in the corrosion layer, and an anaerobic corrosion phase, where Fe(II) and Fe(II)/Fe(III) corrosion products form, including a gradual re-dissolution of the aerobic corrosion products. In the anaerobic corrosion phase, some of the Fe(II) diffuses into the bentonite, where it partly reacts with remaining O2 to form Fe(III) precipitates or interacts with the clay minerals via surface complexation or cation exchange. Two different approaches for the implementation of a potential electron transfer from sorbed Fe(II) to structural Fe(III) are presented, but the lack of experimental data does not allow evaluation of their representativeness for the FEBEX in situ experiment. The model calculations qualitatively reproduce the concave shape of the Fe accumulation front in the bentonite and a distinct zonation with an iron-oxide precipitation dominated zone adjacent to the steel and a Fe(II) sorption dominated zone further into the bentonite. Sensitivity cases with respect to the hydration of the bentonite and the transport parameters point to the importance of the fast O2 diffusion in the gas phase for the formation of these characteristic interface features. The calculated thickness of the Fe-bentonite interaction zone varies from 1 to 4 cm, which is smaller than observed in some areas of the experiment, where locally this zone extended >10 cm into the bentonite. It is possible that this difference is due to a more complex flow pattern in the in situ experiment that is not captured by the model or due to an additional decoupled electron transport across oxide rich layers.

Mitigating aflatoxin B1 in high-moisture sorghum silage: Aspergillus flavus growth and aflatoxin B1 prediction

Aspergillus flavus (A. flavus), a frequent contaminant in silage, is a significant producer of aflatoxins, notably the potent carcinogen aflatoxin B1. This contaminant poses a potential risk during the initial aerobic phase of ensiling. The present work studied the impact of temperature on A. flavus growth and aflatoxin B1 production in laboratory-scale sorghum silos during the initial aerobic phase. Growth curves of A. flavus were generated at various temperatures and modeled with the Gompertz model. Results indicated that the optimal temperature range for the maximum growth rate in sorghum mini-silos is between 25 and 30°C. Mold biomass and aflatoxin B1 levels were quantified using qPCR and HPLC, respectively. A predictive model for aflatoxin B1 synthesis in the initial ensiling phase was established, in function of grain moisture, external temperature, and time. Within the studied range, A. flavus’s initial concentration did not significantly influence aflatoxin B1 production. According to the model maximum aflatoxin production is expected at 30% moisture and 25°C temperature, after 6 days in the aerobic phase. Aflatoxin B1 production in such conditions was corroborated experimentally. Growth curves and aflatoxin B1 production highlighted that at 48 h of incubation under optimal conditions, aflatoxin B1 concentrations in mini-silos exceeded national legislation limits, reaching values close to 100 ppb. These results underscore the risk associated with A. flavus presence in ensiling material, emphasizing the importance of controlling its development in sorghum silos.

Improvements in fermentation and nutritive quality of elephant grass [Cenchrus purpureus (Schumach.) Morrone] silages: a review.

Elephant grass [Pennisetum purpureum Schumach. syn. Cenchrus purpureus (Schumach.) Morrone], also known as Napier grass and King grass, includes varieties Taiwán, Gigante, Merkerón, Maralfalfa, and others. The grass achieves high biomass production in tropical-subtropical, temperate, and arid areas. The high-water concentration of elephant grass suggests that ensiling could offer an alternative way to preserve the nutritional quality of the grass during storage, however, some considerations should be addressed because of the particularities of the grass. Ensiling elephant grass may produce adequate fermentation but could suffer effluent losses and subsequent losses of nutrients due to leaching. To improve fermentation and nutrient characteristics of elephant grass silages, several studies were conducted with the inclusion of additives. Lactic acid bacteria inocula have reduced pH and increased crude protein content of elephant grass silage, but aerobic stability of silages could be affected by the bacterial inoculation. There is limited information, however, on the potential of different silage inoculants to reduce growth of spoilage microorganisms during the aerobic phase of silage prepared with elephant grass. Exogenous fibrolytic enzymes also may improve elephant grass silage quality by enhancing microbial fiber-degradation with subsequent increase in lactic acid and its associated pH reduction. Another study approach to improve fermentation and nutritional quality of elephant grass silages involved the addition of different feeds at ensiling, including conventional feeds such corn, wheat, rice bran, and molasses or alternative feeds such as different dehydrated by-products obtained from the food industries of juice and jelly. In the manuscript, the presented scientific information shows the great potential of the different manipulations to improve the quality of elephant grass silages and with possible enhance of the economic profit and sustainability of livestock farming in the tropical areas.

Microeukaryotic communities diversity with a special emphasis on protozoa taxa in an integrated wastewater treatment system

This study developed an integrated wastewater treatment system that combines an upflow anaerobic sludge blanket (UASB), downflow hanging non-woven fabric (DHNW), and anaerobic baffled reactor (ABR) to explore the effect of treatment stages on the diversity of microeukaryotic communities. This study aimed to bridge the knowledge gap regarding the influence of integrated system stages on microeukaryotic community diversity. Through 18S rRNA amplicon sequencing, we identified unique microeukaryotic communities across different stages, with the aerobic phase hosting 35.77% of unique amplicon sequence variants (ASVs). The results of principal component analysis (PCA) and non-multidimensional scale analysis (nMDS) demonstrated the significant influence of wastewater treatment on both environmental factors and the microeukaryotic communities. Ciliophora was notably abundant in the effluent (42.09%) and sludge (17.11%). The aerobic stage was dominated by Ochrophyta, a diverse group of algae instrumental in nutrient removal, such as nitrogen and phosphorus, through biological processes. A redundancy analysis (RDA) revealed a positive correlation between chemical and biochemical oxygen demand and Cryptomycotina, highlighting its potential as a bioindicator for treatment efficacy. The detection of protozoan species, such as Acanthamoeba castellanii and Vermamoeba vermiformis, in the outlet stage poses health risks, whereas Cryptosporidium sp. was found in both the inlet and aerobic stages but not in the outlet. Our study reveals the complex nature of microeukaryotic diversity in the wastewater treatment system and its implications for treatment performance and public health.

Nutrient removal and emission of nitrous oxide and methane by a sequencing batch reactor treating wastewater with and without landfill leachate

Wastewater and landfill leachate treatment processes have the potential to generate nitrous oxide (N2O) and methane (CH4), both significant greenhouse gases (GHG). However, little is known about these emissions when a combined treatment approach (wastewater with leachate) is utilized. This study aimed to assess the emissions of these gases and nutrient removal in an anaerobic/aerobic/anoxic sequencing batch reactor (SBR) employed for treating wastewater with landfill leachate (1% v/v). Leachate contributes significantly to the removal of organic matter and nutrients, primarily phosphorus. The production and emission of N2O occurred during the aerobic phase, whereas CH4 was produced in the anaerobic and anoxic phases. This gas was emitted at the beginning of the aerobic phase and in the end of anoxic phase. The emission factors obtained in this work were 0.0108 and 0.0119 kg N2O-N per kg TNinfluent and 0.000225 and 0.000253 kg CH4-C per kg CODinfluent with and without landfill leachate, respectively. Regarding CO2-equivalent, the N2O was the major contributor, accounting for 99% of the emitted GHG by the process. Further studies are required; however, the main findings of this study suggest that this system may be appropriate when lower GHG emissions are required.

A comprehensive floc model for simulating simultaneous nitrification, denitrification, and phosphorus removal

A comprehensive floc model for simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) was designed, incorporating polyphosphate-accumulating organisms (PAOs), glycogen-accumulating organisms (GAOs), intrinsic half-saturation coefficients, and explicit external mass transfer terms. The calibrated model was able to effectively describe experimental data over a range of operating conditions. The estimated intrinsic half-saturation coefficients of oxygen values for ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, ordinary heterotrophic organisms (OHOs), PAOs, and GAOs were set at 0.08, 0.18, 0.03, 0.07, and 0.1 mg/L, respectively. Simulation suggested that low dissolved oxygen (DO) environments favor K-strategist nitrifying bacteria and PAOs. In SNDPR, virtually all influent and fermentation-generated volatile fatty acids were assimilated as polyhydroxyalkanoates by PAOs in the anaerobic phase. In the aerobic phase, PAOs absorbed 997 % and 171 % of the benchmark influent total phosphorus mass loading through aerobic growth and denitrification via nitrite. These high percentages were because they were calculated relative to the influent total phosphorus, rather than total phosphorus at the end of the anaerobic period. When considering simultaneous nitrification and denitrification, about 23.1 % of influent total Kjeldahl nitrogen was eliminated through denitrification by PAOs and OHOs via nitrite, which reduced the need for both oxygen and carbon in nitrogen removal. Moreover, the microbial and DO profiles within the floc indicated a distinct stratification, with decreasing DO and OHOs, and increasing PAOs towards the inner layer. This study demonstrates a successful floc model that can be used to investigate and design SNDPR for scientific and practical purposes.

OptMSP: A toolbox for designing optimal multi-stage (bio)processes

One central goal of bioprocess engineering is to maximize the production of specific chemicals using microbial cell factories. Many bioprocesses are one-stage (batch) processes (OSPs), in which growth and product synthesis are coupled. However, OSPs often exhibit low volumetric productivities due to the competition for substrate for biomass and product synthesis implying trade-offs between biomass and product yields. Two-stage or, more generally, multi-stage processes (MSPs) offer the potential to tackle this trade-off for improved efficiency of bioprocesses, for example, by separating growth and production. MSPs have recently gained much attention, also because of a rapidly growing toolbox for the dynamic control of metabolic fluxes. Despite these promising advancements, computational tools specifically tailored for the optimal design of MSPs in the field of biotechnology are still lacking.Here, we present OptMSP, a new Python-based toolbox for identifying optimal MSPs maximizing a user-defined process metrics (such as volumetric productivity, yield, and titer or combinations thereof) under given constraints. In contrast to other methods, our framework starts with a set of well-defined modules representing relevant stages or sub-processes. Experimentally determined parameters (such as growth rates, substrate uptake and product formation rates) are used to build suitable ODE models describing the dynamic behavior of each module. OptMSP finds then the optimal combination of those modules, which, together with the optimal switching time points, maximize a given objective function. We demonstrate the applicability and relevance of the approach with three different case studies, including the example of lactate production by E. coli in a batch setup, where an aerobic growth phase can be combined with anaerobic production phases with or without growth and with or without enhanced ATP turnover.

Assessment of a Novel Real-Time Bio-Liquor Circulation System for Manure Management and Mitigation of Odor Potential in Swine Farming.

Recently, circulating biologically treated manure in slurry pits has been used as an odor reduction technology, but few successful results have been reported, due to the lack of proper control strategies for bioreactors. This study was conducted to investigate the performance of the developed real-time controlled bio-liquor circulation system (BCS) at farm scale. The BCS was operated sequentially as per swine manure inflow (anoxic, aerobic, and settling) circulation to the slurry pit. Each operational phase was self-adjusted in real-time using a novel algorithm for detecting the control point on the oxidation reduction potential (ORP) and pH (mV)-time profiles, the nitrogen break point (NBP), and the nitrate knee point (NKP) in the aerobic and anoxic phases, respectively. The NH4-N in the slurry manure was thoroughly removed (100%) in the bioreactor, optimizing the duration of each operational phase by accurately detecting real-time control points. The newly developed real-time BCS decreased the nitrogen and organic matter in the slurry pit by >70%, and the potential ammonia and methane emissions by 75% and 95%, respectively. This study highlights that improved BCS that utilizes ORP tracking and pH (mV)-time profiles can effectively optimize BCS operation, and thereby reduce malodor and GHG emissions from swine farms.

Enhancing biological dissolved organic nitrogen removal in landfill leachate wastewater: The role of sodium acetate co-metabolism

Dissolved organic nitrogen (DON) comprises approximately 25% of dissolved nitrogen in landfill leachate wastewater (LLW), posing potential risks such as stimulating algal growth and forming disinfection by-products if not treated properly. While DON characterization and removal by physicochemical methods in wastewater treatment systems have been examined, biological strategies for effective DON removal remain less developed. This study explores the influence of sodium acetate addition during denitrification process on LLW DON removal. With sodium acetate addition (Stage I), we achieved 99% ammonia removal, 94% total inorganic nitrogen (TIN) removal, and 45% DON removal. Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS) results suggested the majority of sulfur-containing DON molecules were eliminated in Stage I. Conversely, in the absence of sodium acetate (Stage II), while 99% ammonia removal was maintained, TIN removal dropped to around 10%, and DON concentrations (largely sulfur-containing DON) increased by approximately 22%. Cycle tests revealed similar DON reductions in the aerobic phase across both stages, whereas in the anoxic phase, DON concentrations decreased in Stage I but increased in Stage II. Functional gene prediction indicated higher expression of decarboxylase and deaminase genes in Stage I compared to Stage II. Consequently, this study posits that sodium acetate addition enhances DON removal, potentially via co-metabolism.

Oxygen affinity and light intensity induced robust phosphorus removal and fragile ammonia removal in a non-aerated bacteria-algae system

Non-aerated bacteria-algae system gaining O2 through photosynthesis presents an alternative for costly mechanical aeration. This study investigated oxygen supply and performance of nutrients removal at low and high light intensity (LL and HL). The results showed that P removal was high and robust (LL 97 ± 1.8 %, HL 95 % ± 2.9 %), while NH4+-N removal fluctuated dramatically (LL 66 ± 14.7 %, HL 84 ± 8.6 %). Oxygen generated at illumination of 200 μmol m−2 s−1, 6 h was sufficient to sustain aerobic phase for 2.25 g/L MLSS. However, O2 produced by algae was preferentially captured in the order of heterotrophic bacteria (HB), ammonia oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB). Oxygen affinity coupled with light intensity led to NOB suppression with stable nitrite accumulation ratio of 57 %. Free nitrous acid (FNA) and light stimulated the abundance of denitrifying polyphosphate accumulating organism (DPAO) of Flavobacterium, but with declined P-accumulating metabolism (PAM) of P release, P/C, K/P and Mg/P ratios. Flavobacterium and cyanobacteria Leptolyngbya, along with biologically induced CaP in extracellular polymeric substances was the key to robust P removal. AOB of Ellin6067 and DPAO of Flavobacteria offer a promising scenario for partial nitrification-denitrifying phosphorus removal.

Performance Evaluation and Microbial Shift of Sequencing Batch Biofilm Reactor Treating Synthetic Mariculture Wastewater Under Different Dissolved Oxygen at Aerobic Phase

Performance Evaluation and Microbial Shift of Sequencing Batch Biofilm Reactor Treating Synthetic Mariculture Wastewater Under Different Dissolved Oxygen at Aerobic Phase

Polyethylene terephthalate cap‐based bioreactors for combined domestic and dye wastewater treatment

AbstractIn the current study, a sequencing batch reactor (SBR), a sequencing batch biofilm reactor (SBBR) and a moving bed biofilm reactor (MBBR) were designed and used to treat actual samples of combined domestic and dye (Congo red) wastewaters over a 10‐hour cycle. A new application of reusing plastic bottle caps in the SBBR and MBBR was examined. In the SBR, maximum chemical oxygen demand (COD) removal of up to 66% ± 3% was achieved after nine cycles of operation. In the SBBR, a rapid increase in COD removal efficiency was observed during the first cycle, with a noticeable improvement in performance in subsequent cycles, eventually reaching a maximum COD removal efficiency of 77% ± 3%. In the MBBR, maximum COD removal of up to 88% ± 3% was achieved after nine cycles of operation. The biodegradation occurred during two phases in the SBR and SBBR, as an anaerobic phase in the first 2 hours and then as an aerobic phase in the last 8 hours of operation; the MBBR operated in the fully saturated aerobic phase for 10 hours. Of the three reactors used, results for the MBBR in the fully aerobic condition by using polyethylene terephthalate caps as a biocarrier, demonstrated the optimum conditions under which to treat and biodegrade Congo red at all concentration in each cycle. The maximum removal efficiency, which equalled 99% ± 1%, was recorded at an optimal concentration of 50 mg/L. Additionally, five kinetic models were proposed to assess microbial growth activity, and the results demonstrated the elimination of toxic effects when using polyethylene terephthalate caps as biocarriers in the MBBR. The laboratory experiments were consistent with the Monod model.

Biogeochemical cycling in paddy soils controls antimony transformation: Roles of iron (oxyhydr)oxides, organic matter and sulfate

In paddy fields, periodic flooding and drainage phases can significantly affect the availability of antimony (Sb), but the underlying mechanisms remain unclear. In this study, Sb-contaminated paddy soil was incubated under anaerobic (40 day) and subsequently aerobic (40–55 day) conditions. The Sb fractions was investigated and a kinetic model was established to quantitatively evaluate the main processes controlling Sb transformation. Under anaerobic conditions, the reductive dissolution of iron (Fe) (oxyhydr)oxides, the release of soil colloids, and dissolved organic carbon (DOC) could facilitate the release of Sb(V), while newly released Sb(V) were synchronously reduced to Sb(III) that could be incorporated into the solid phase (34.1%, 40 day) or precipitated as Sb2S3 (9.7%, 40 day). After soil aeration, a significant increase in dissolved and extracted Sb(V) (34.7%, 45 day) was observed due to the Sb(III) oxidization by the reactive oxygen species (ROS) generated from Fe(II) oxidization. The dissolved and extracted Sb(V) were simultaneously incorporated into the solid phase as the re-aggregation of soil colloids and DOC, and only contributed to 17.1% of the total Sb content at the end of aerobic phase (55 day). Our results elucidated the mechanisms about how biogeochemical Fe/S/C cycling jointly controlled Sb transformation in paddy systems.

Multisite photocatalytic depolymerization of lignin model compound utilizing full-spectrum light over magnetic microspheres

Photocatalytic depolymerization is a high value-added approach for utilization of lignin. In this study, magnetic microspheres of FeCoRu@SiO2-TiO2 were synthesized by a co-precipitation method. Doping with CoOx and RuOx was used to improve the response to visible light, and doping with TiO2 was used to improve the response to ultraviolet light (λ<380nm). The lignin model compound depolymerization rate was >90%. The electron paramagnetic resonance results showed that the reaction occurred in two steps (aerobic phase and oxygen-free phase). Most of the O2- was produced in the first step by cleavage of C-O bonds. The second step was inhibited in an oxygen-free atmosphere. This research provides a valid method for enhancing the photocatalytic properties using full-spectrum light and exploring the lignin photocatalytic depolymerization mechanism. Further research is required to develop the catalyst properties and performance to produce radicals.

Oxygen Uptake Rate as an Indicator of the Substrates Utilized by Candidatus Accumulibacter

Candidatus Accumulibacter belongs to phosphate-accumulating organisms (PAOs) which exhibit a cyclic metabolism and are capable of intracellular polyphosphate accumulation and their hydrolysis under feast-famine anaerobic-aerobic cycling. In consortia of activated sludge microorganisms, these bacteria are responsible for enhanced biological phosphorus removal (EBPR). The spectrum of the substrates used by Ca. Accumulibacter remains insufficiently studied. It was investigated by measuring the oxygen uptake rates (OUR) of Ca. Accumulibacter-enriched culture supplemented with 17 different organic substrates. The highest oxygen uptake rate values were observed in the presence of tryptone, volatile fatty acids (acetate, propionate, and butyrate), succinate, pyruvate, and amino acids (aspartate and glutamate). Phosphate dynamics in the medium under shifts from anaerobic to aerobic cultivation in batch experiments were studied for these compounds (except for tryptone). All tested substrates were shown to cause phosphate cycling (release in the anaerobic phase and uptake in the aerobic one), with OURs for the substrates correlating with the number of phosphates consumed during the aerobic phase. It was concluded that OUR may be used as an indicator of the monosubstrates used by Ca. Accumulibacter in the anaerobic/aerobic cycle. The possible pathways for substrate transport and metabolism by Ca. Accumulibacter are discussed using stoichiometric data and the results of metagenomic analysis.