Oxidation-reduction Potential Research Articles

Nitrite manipulation in water by structure change of plasma electrolysis reactor

In this study, experimental reactors for cathodic nitrogen plasma electrolysis were designed by the composition of galvanic (voltaic) and electrolytic cells with wide and narrow connectors filled with tap water and agar solutions. The designed reactor can be used to simultaneously perform and manage nitrification in acidic and alkaline environments. According to the reactor’s performance, it can be installed on the irrigation system and used depending on the soil pH of the fields for delivering water and nitrogen species that are effective in growth. The nitrification process was investigated by choosing the optimal reactor with a wide connector based on different changes in oxidation-reduction potential and pH on the anode and cathode sides. The nitrite concentration changed directly with ammonium and nitrate concentrations on the cathode side. It changed inversely and directly with ammonium and nitrate concentrations on the anode side respectively. Nitrite concentration decreased from 5.387 ppm with water connector, to 0.326 ppm with 20% agar solution, and 0.314 ppm with 30% agar solution connectors on the anode side. It increased from 0 ppm to 0.191 ppm with a water connector, 0.405 ppm with 20% agar solution, and 7.454 ppm with 30% agar solution connectors on the cathode side.

Real-Time Monitoring of Seawater Quality Parameters in Ayia Napa, Cyprus

Real-time monitoring systems are crucial for the comprehensive management of operations and processes, as well as for assessing the impacts of coastal infrastructures on the marine environment. These systems not only support environmental protection and data-driven decision-making but also enable the early detection of adverse events and the issuance of timely warnings for prompt responses. Although water quality is a critical parameter in this monitoring framework, there are currently limited permanent systems in place dedicated to maintaining these objectives. Even fewer systems leverage their data for research purposes, leading to a gap in the literature regarding effective processing approaches for real-time water quality data. In this context, this study presents a real-time water quality monitoring system integrated into a broader in-field laboratory installed at a coastal area off the coast of Ayia Napa, Cyprus, as well as an initial measured data set of different qualitative quantities. It proposes a holistic approach for post-processing real-time seawater quality data, employing both time and frequency domain analyses, alongside filtering techniques. The study discusses the advantages of each method and emphasizes the importance of their combined use. Utilizing data collected from a three-month operational period, the study assesses the current state of marine seawater quality and examines both temporal and cyclic variations in various seawater quality parameters. The findings reveal that the examined seawater parameters are within reasonable values, indicating that the construction and operation of a nearby marina and the necessary infrastructures (e.g., breakwater) did not affect the seawater quality in the area. Additionally, the study identifies pronounced daily cyclic responses in different seawater quality parameters, including temperature, density, pH, dissolved oxygen, and turbidity. Finally, notable correlations are observed between temperature and dissolved oxygen, temperature and conductivity, oxidation–reduction potential (ORP) and salinity, ORP and dissolved oxygen, and ORP and TDS.

Understanding the interaction between soil ORP and enzyme activity: How does wetland type affect constructed wetland performance for the advanced treatment of swine wastewater?

Constructed wetlands (CWs) are widely used for the advanced treatment of swine wastewater. Wetland type is the most critical parameter for engineering applications; therefore, the performance of horizontal/vertical subsurface flow CWs (HSFCWs and VSFCWs) was explored over one year of operation. The effects of five antibiotics (40 μg/L each), copper (Cu, 1.0 mg/L), and their combination on CW performance and soil oxidation–reduction potential (ORP) and enzyme activity were investigated. The annual removal efficiencies of HSFCWs and VSFCWs for total organic carbon (TOC), nitrogen, and phosphorus were 72.03 %–84.49 % and 87.15 %–90.72 %, for antibiotics were 91.35 %–99.52 % and 87.33 %–99.57 %, and for Cu were 97.37 %–97.44 % and 95.52 %–96.85 %, respectively. The CWs removed antibiotics through substrate adsorption, plant absorption, and biodegradation. Total antibiotic residues in HSFCW and VSFCW soils ranged from 6.29 to 17.31 and 24.57 to 589.07 μg/kg, respectively, and enrofloxacin and roxithromycin posed medium and high risks in VSFCW non-rhizosphere soil. The amount of residual antibiotics in Phragmites australis parts was in the order of fibrous roots > rhizomes > aboveground. ORP and enzyme activities were greater in rhizosphere soil than in non-rhizosphere soil and greater in the VSFCWs than in the HSFCWs. CW performance and soil enzyme activities decreased under the stress of antibiotics and coexistence of antibiotics and Cu. These findings advance our knowledge of CW design, elucidate the unique advantages of CWs, and offer efficient operation strategies for swine wastewater advanced treatment, helping researchers recognize the adverse effects of antibiotics on CWs.

Pre-ozonation coupled with forward osmosis with fertilizer as draw solution for simultaneous wastewater treatment and agricultural irrigation

Membrane-based processes have emerged as effective solutions for treating tannery wastewater. Persistent membrane fouling remains a significant obstacle to long-term operational sustainability, and residual pollutants often persist in the treated effluent. To address these challenges, we investigated an integrated ozone-forward osmosis (O3-FO) process, with a focus on evaluating the efficacy of pre-ozonation in alleviating membrane fouling, as well as exploring the possibilities of this integrated process for the reuse of tannery wastewater. Fertilizer, specifically 2 M Ca(NO3)2, served as the draw solution (DS) in this process. The findings reveal that the integrated system demonstrated remarkable pollutant retention capabilities. Notably, no metal was detected in the fertilizer. Therefore, the integrated process not only dilutes the fertilizer but also minimizes the risk of heavy metal contamination to both crops and soil. Furthermore, pre-ozonation effectively mitigated membrane fouling, resulting in an increase in membrane flux with a maximum increase of 20.98 % at 0.6 L/min. Orthogonal partial least squares-discriminant analysis (OPLS-DA) revealed pre-ozonation has the most significant impact on four parameters: water flux (Jw), chemical oxygen demand (COD), fouling resistance (Rf) and oxidation reduction potential (ORP). Meanwhile, ammonium nitrogen (NH4-N) variation, dissolved organic carbon (DOC) variation and ORP played an important role in the four systems. Multi-criteria decision analysis (MCDA) showed that the 0.2 L/min O3-FO system achieved the highest score (0.66), followed by 0.6 L/min (0.53), 0.4 L/min (0.41) and 0 L/min (0.29). This research offers a theoretical framework for the synergistic integration of advanced oxidation and membrane technology in the treatment of industrial wastewater.

Virtual Sensing of Nitrite: A Novel Control for Safe Denitrification in Recirculating Aquaculture Systems (RASs)

Recirculating aquaculture system (RAS) technology is seen worldwide as a solution for sustainable fish production. However, there are still deficiencies in the process technology imperiling consistent operation and thus economic results. Drawbacks are linked to essential processes of the water treatment systems such as denitrification. Nitrogenous waste needs to be removed from RAS process water to maintain an adequate production environment for fish and to mitigate the environmental impact of discharged process water. At present, denitrification lacks reliable process control, especially regarding the organic carbon feed to heterotrophic denitrification processes. An investigation into heterotrophic denitrification in an experimental RAS resulted in the discovery of a virtual sensor based on measurements of the oxidation reduction potential (ORP). The virtual sensor responds to an insufficient carbon feed to denitrification. It is based on the oxidation of nitrite in an ozone-enhanced foam flotation installed downstream of the denitrification. The sensor essentially delivers a binary signal denoting either a complete or an incomplete denitrification process. The virtual sensor can be used for reliably controlling heterotrophic denitrification. It requires an upgraded process chain employing ozone-enhanced foam flotation (protein skimmer) downstream of the denitrification. However, the virtual sensor does not require any additional instrumentation.

Study on the response mechanisms and evolution prediction of groundwater microbial-toxicological indicators.

This study aims to investigate the response mechanisms of groundwater microbial-toxicological indicators, specifically total bacteria count (TBC) and total coliform count (TCC), to water quality indicators and environmental conditions. Using data from a water source in the western plateau of China, a predictive model focusing on TBC and TCC was developed. An orthogonal experimental design was employed to manipulate environmental conditions such as temperature, pH, and porosity, facilitating laboratory experiments. These experiments measured pH, chemical oxygen demand (COD), oxidation-reduction potential (ORP), TBC, and TCC at varying depths and environmental conditions. Principal component analysis elucidated the mechanisms by which water quality indicators and environmental conditions affect groundwater microbial-toxicological indicators. A prediction model for these indicators in plateau regions was established based on a backpropagation neural network (BP-NN), using TBC and TCC as target variables and the newly extracted principal components as influencing factors. The results demonstrate that environmental conditions and water quality indicators primarily influence the evolution of groundwater microbial-toxicological indicators by altering the ionic charge quantities, redox conditions, and temperature of the groundwater. The predictive model for groundwater microbial-toxicological indicators shows trends consistent with experimental outcomes, with an average relative error of less than 15%, meeting engineering requirements. PRACTITIONER POINTS: The values of total bacteria count (TBC) and total coliform count (TCC) under different conditions were obtained by column experiments. The influence mechanism of environmental conditions and groundwater indicators on TBC and TCC was elaborated by principal component analysis. TBC and TCC prediction models were established through the investigation of water sources in a plateau area and laboratory experiments.

Experimental Design, Statistical Analysis, and Modeling of the Reduction in Methane Emissions from Dam Lake Treatment Using Agro-Industrial Biochar: A New Methane Capture Index

This study aimed to reduce the methane (CH4) emissions originating from dam lake treatment using malt dust-derived biochar, which is an agro-industrial byproduct of the brewery industry. Optimum operating and water quality parameters for CH4 reduction were determined using statistical analyses based on the Box–Behnken design method. Also, a Monte Carlo simulation was performed to determine the correlation between CH4 emissions and operating parameters. According to the simulation, dissolved oxygen (DO) and the oxidation–reduction potential (ORP) had the highest correlation with CH4 emissions, with values of 92.03% and 94.57%, respectively. According to the Box–Behnken design methodology, the optimum operating parameters were 4 mg/L of dissolved oxygen, −359 mV of ORP, and 7.5 pH for the minimum CH4 emissions. There was a reported reduction of up to 19.4% in CH4 emissions for the dam lake treatment using malt dust-derived biochar. Finally, a new methane capture index, based on the biochar application (MCI), was developed and validated. The largest methane capture capacity was related to the malt dust-derived biochar produced at the lowest temperature (M1).

Impact of hydrophobic and hydrophilic surface properties on Pseudomonas aeruginosa adhesion in materials used in mineral water wells

Microbiologically contaminated water is a significant source of infections in humans and animals, with Pseudomonas aeruginosa (PSA) being particularly concerning due to its ability to thrive in water environments and its resistance to many disinfectants. Therefore, this study investigates the adhesion potential of PSA strains on various materials used in mineral water extraction wells, focusing on hydrophobic and hydrophilic properties. Mineral water samples were collected from three wells (P-01, P-07, and P-08) within the Guarani Aquifer System and Fractured Aquifer System (SAF) in Brazil. The physicochemical properties of the water, including concentrations of Sr (strontium), Fe (iron), Si (silicon), SO4 2− (sulfate ions), Cl− (chloride ions), and ORP (oxidation-reduction potential), were analyzed. Results indicated higher PSA adhesion on hydrophobic materials, particularly high-density polyethylene (HDPE) and geomechanically plasticized polyvinyl chloride (PVC). Multiple correlation analyses revealed positive correlations between PSA adhesion on hydrophilic materials and Sr, Fe, Si, SO4 2−, and Cl− concentrations. Conversely, ORP negatively correlated with bacterial adhesion on PVC surfaces, suggesting higher ORP values reduced PSA attachment. These findings highlight the importance of water composition and material properties in influencing bacterial adhesion and potential biofilm formation in mineral water extraction systems.

Infiltration of secondary treated wastewater into an oxic aquifer: Hydrochemical insights from a large-scale sand tank experiment

To mitigate groundwater level decline, managed aquifer recharge (MAR) with secondary treated wastewater (STWW) is increasingly considered and implemented. However, the effectiveness and potential risks of such systems need evaluation prior to implementation. In this study, we present a large-scale sand tank experiment to analyse processes related to the infiltration of real STWW through the vadose zone and subsequent mixing with oxic native groundwater. The varying composition of STWW from 15 infiltration cycles over six months of operation and the retention times were the main drivers of the observed processes, which were characterized by a wide range of analytical techniques such as in situ high-resolution oxidation–reduction potential (ORP) measurements, closed mass balances of solutes, characterization of dissolved organic carbon (DOC), stable nitrate isotopes analysis, as well as numerical flow and transport modelling. Depending on the composition and infiltration rates of the STWW, both nitrification and denitrification could be observed, even simultaneously at different locations in the tank. Furthermore, due to the variability of the real STWW we observed enhanced arsenic mobilisation during times of elevated phosphate concentrations of the infiltrating STWW. Additionally, uranium was mobilised in our experimental system via carbonate mineral dissolution caused by the infiltrating STWW which was undersaturated of calcite for all infiltration cycles. Overall, our results showed the importance of conducting studies with waters of complex matrix, such as real STWW, and considering mixing with groundwater to assess the full range of possible processes encountered at MAR field sites.

Electro-activation for efficient lactulose production: The impact of operational parameters, electrolyte types, and environmental conditions

The electro-activation (EA) process has been employed to convert lactose into lactulose, a potent prebiotic with numerous health benefits. The study identified optimal conditions for lactulose production, including a specific current density, the use of calcium chloride as an efficient electrolyte, and the superiority of a steel cathode over a graphite cathode. The formation of intermediates other than lactulose increased as the temperature increased. The changes in pH and oxidation-reduction potential during the isomerization process were observed, highlighting their vital role in the formation of an ideal alkaline environment for lactulose production. The resultant solution produced by the EA process has significant antioxidant characteristics, likely due to the formation of Maillard Reaction Products during lactulose production. In conclusion, the EA system, with optimal operating conditions, is an energy-efficient, reagent-free, and environmentally friendly alternative for lactulose production.

Oxygen-induced evolution of anammox granular sludge explains its unique responses during preservation

Anammox granular sludge (AnGS) preservation is indispensable for the application of anammox technology. Oxygen is a common and crucial factor for anammox, yet its long-term effects on AnGS during preservation remain incomplete clarification. This study investigated the effect of oxygen on AnGS in two simulated preservation systems with open and sealed conditions, and the mechanism was discussed. The results showed that the open system was in an oxidized state with an average dissolved oxygen (DO) concentration and oxidation-reduction potential (ORP) of (3.10 ± 1.36) mg·L-1 and (112.58 ± 46.78) mV, while a reduced state for the sealed system with no detected DO and a lower average ORP of (-153.96 ± 64.32) mV. Both systems showed declines in AnGS activity, while with different responses of AnGS demonstrated by the evolution in terms of granular morphology and structure, bacterial communities, bacteria survival, and bacteria antioxidation. In the open system, reactive oxygen species were generated and destroyed the unsaturated fatty acids in the cell membrane, further leading to the destructed cell structure and declined activity. However, in the sealed system, AnAOB tended to enter a dormant state after long-term preservation, contributing to better conditions in granular morphology and structure, higher AnAOB abundance, and higher live cell ratio. The findings of this study are expected to offer vital information and guidelines for the preservation technologies of AnGS.

Enhanced phosphorus removal from anoxic water using oxygen-carrying iron-rich biochar: Combined roles of adsorption and keystone taxa

Anthropogenic enrichment of phosphorus (P) in water environment can cause eutrophication, harmful algal blooms, and water quality deterioration. Adsorbents are often used for the removal and recovery of P from water, however, P is highly susceptible to re-release in anoxic benthic environments. As a response, this study prepared oxygen-carrying iron-rich biochar (O-Fe-BC) as an effective oxygen micro-nanobubble carrier (Q = 8.7024 cm³/g STP at 1.5 MPa) and P adsorbent (qm = 16.7097 mg P/g, q0.1 = 3.1974 mg P/g). Over the 90-day experimental period with O-Fe-BC, dissolved oxygen (DO) levels in the overlying water could maintain at ∼4 mg/L (peaking at ∼9.5 mg/L), and total phosphorus (TP) and soluble reactive phosphorus (SRP) levels decreased by over 96 %. The higher inorganic phosphorus content in the surface sediment-biochar mixture, along with the lower labile P and Fe concentration in the sediment pore water in the O-Fe-BC group compared to other groups, suggested the enhanced P immobilization. Further mechanism exploration revealed the combined roles of adsorption and microbial response, in which O-Fe-BC achieved efficient phosphate adsorption primarily through inner-sphere complexation via ligand exchange and keystone taxa (particularly Candidatus Electronema) played a crucial role in driving water chemistry divergence. Specially, these cable bacteria could provide large pools of Fe oxides in the surface sediment, binding with P to prevent its release, as supported by significant correlations between Ca. Electronema abundance and oxidation–reduction potential (ORP), TP, SRP, and sediment Fe-P variations. Additionally, a pot experiment with mung bean seedlings showed that the recovered O-Fe-BC significantly promoted the seed germination and growth, indicating its potential as a novel material for removing and recovering P from eutrophic waters. Taken together, our work provided a promising strategy for sustainable anoxia and P pollution mitigation, and also highlighted the indispensable roles of inner-sphere adsorption in P recovery and microbial keystone taxa in P cycling regulation.

Anoxic Manganese Bioleaching – Investigation of Scale-up Parameters in a Stirred Bioreactor

Presently huge operation costs arising from aeration and high electron donor requirements accompanied by low metal recovery rates are some impediments to the large-scale application of bioleaching for low-grade ores. The current study investigates key parameters for scaling up anoxic bioleaching, which overcomes some of the above shortcomings, on polymetallic manganese nodules using soil-based manganese-reducing bacterial consortia in a stirred bioreactor. Operating conditions such as carbon source concentration and pulp density were optimized. Parameters like pH, oxidation–reduction potential (ORP), and microbial growth were monitored in the bioreactor in both stirred and non-stirred conditions. The Mn(IV) reduction and dissolution in the bioreactor was 27 (±2.8)% over 30 days, which significantly enhanced to 43 (±1.5)% and 42 (±0.35)% in the presence of humic acid and anthraquinone sulfonic acid, respectively, in 15 days. A maximum dissolution of 21 (±4.1)% Cu, 10 (±3.0)% Ni, 18 (±4.7)% Co and 7 (±3.9)% Fe were also obtained with 100 µM humic acid from the agitated bioreactor in 15 days. The corresponding specific glucose consumption rate per unit mass of ore was found to be 27 mg g−1 day−1, which is 10 times lower than the rates reported previously for aerobic bioleaching methods. The investigation shows that mild agitation can significantly improve the anoxic bioleaching, especially with added electron shuttles, to enable better ore-bacteria interaction and prevent ore compaction during scale-up. The pH and ORP of the system point toward a reductive dissolution of Mn by the organisms.

Two-dimensional distribution of arsenic species in the riparian zone regulated by As-Fe co-transformation under varying river water proportions and bicarbonate concentrations

Arsenic (As) contamination of groundwater is a major issue in global environmental health. In the riparian zone, mixing river water and groundwater with different substances is proposed to affect arsenic transformation and distribution. However, the distribution of arsenic species in the riparian zone and its co-transformation with iron under varying river water proportions and bicarbonate (HCO3–) concentrations remain unclear. The two-dimensional distributions of arsenic species, including exchangeable (Ex-As), carbonates-bounded (Carb-As), FeMn(hydr)oxide-bounded (Ox-As), organic-bounded (Om-As) and residual arsenic (Res-As), were investigated in three typical profiles of the riparian zone near the lower reaches of the Hanjiang River, China. The apparent enrichment of arsenic in the pore water, either As(III) and As(V), and in the sediment, mainly Carb-As and Ox-As, were observed in the profiles. The correlation analysis showed that the distributions of arsenic species in the riparian zone were primarily related to dissolved or total organic matter (DOC or TOC), Fe, HCO3–, dissolved oxygen (DO) and oxidation–reduction potential (Eh). Further batch experiments mixing simulated river water and groundwater with different proportions and HCO3– concentrations demonstrated that the forming of the arsenic-rich area in the riparian sediment was derived from the oxidation of Fe(II) and As(III) from groundwater, controlled by the varying DO from river water and HCO3– from organics degradation. These results provide more knowledge of the transforming process of arsenic in the riparian zone and a better understanding of the role of the riparian zone in arsenic restraint.

Impacts of oyster farms on sediment-associated mercury and methylmercury concentrations and health risks in an estuarine, mangrove forest, Zhanjiang Bay, China

Estuarine sediments serve as significant reservoirs for mercury (Hg) and methylmercury(MeHg), which can also interconvert in the external environment. The release of Hg in response to human activities raises concerns about its potential ecological and human health effects. Sediment samples were collected in December 2021 from four locations (sites), and Hg cycling by measuring the concentrations of, and controls on, the spatial distribution of total Hg (THg) and methylmercury (MeHg) in high-tidal zone (HTZ) and mid-tidal zone (MTZ) sediments of a mangrove forest (MF) and oyster farm (OF) was examined in northwestern Zhanjiang Bay, including simultaneous determination of sediment particle size, oxidation-reduction potential (Eh), pH, total organic carbon (TOC), sulfide concentration (S2-), and sulfate reducing bacteria (SRB). The research results indicated that concentrations of both THg and MeHg ranged between 20.0–104.0 ng/g and 0.011–0.277 ng/g in the sediments, respectively. The highest methylation potentials within the MF and OF were in sediments located approximately 10–15 cm below the surface. MeHg in the HTZ of the OF was likely derived from exogenous inputs as Hg methylation appears limited, and the formation of MeHg depended not only on the amount of inorganic mercury available for methylation in SRB, but also on the TOC, pH, Eh and S2- content in the sediment. A risk assessment of MeHg during the anthropogenic disturbance of this estuaries conducted on individuals eating oysters demonstrated that health risks are low.

Enhancing nitrogen removal from digested swine wastewater by anammox with aeration optimization coupling real-time control strategy

The nitrogen removal of anaerobically digested swine wastewater (ADSW) through partial nitritation and anammox is hindered by the challenge of balancing aeration between ammonia oxidizing bacteria (AOB) and anammox bacteria (AnAOB). This study focused on optimizing aeration through a real-time control strategy in an integrated fixed-film activated sludge reactor for treating ADSW. The system implemented a dual aeration mode that included both low dissolved oxygen (DO) (< 0.4 mg/L) and short-term high DO (0.6–1.2 mg/L), with pH, oxidation–reduction potential, and NH4+-N electrode values as real-time control parameters. NH4+-N removal rate increased from 3.37 to 12.82 mgN/(gVSS·h), and total nitrogen (TN) removal rate enhanced from 0.14 to 0.25 kgN/(m3·d). Increasing DO stimulated AOB activity by 31 % and provided sufficient NO2−-N for AnAOB. The r-strategist AnAOB (Candidatus Kuenenia) proliferated well in the biofilm (0.25 % in flocs vs. 1.86 % in biofilm). The enrichment of denitrifiers improved organic matter and TN removal.

Efficient butanol production from sweet sorghum stem juice by a co-culture system at an optimum temperature: Insights from oxidation-reduction potential monitoring and pilot scale validation

A two-stage co-culture approach was employed in an acetone-butanol-ethanol (ABE) fermentation. An obligate aerobic bacterium, Arthrobacter sp., was first grown for 6 h at 30 °C to create anaerobic conditions. Subsequently, Clostridium beijerinckii TISTR 1461 was inoculated and a fermentation was performed at 37 °C. To identify an intermediate temperature suitable for both microorganisms, their growth was examined at 30, 34, and 37 °C. C.beijerinckii exhibited the highest specific growth rate at 37 °C, while Arthrobacter sp. displayed similar growth rates at all tested temperatures. Butanol production from a synthetic medium (P2 medium) by C. beijerinckii at different temperatures using oxygen-free nitrogen (OFN) gas flushing as a control treatment revealed that fermentation at 37 °C gave the highest butanol concentration (PB, 9.98 g/L). Consequently, 37 °C was chosen for butanol production from sweet sorghum stem juice (SSJ) by co-culture of these two microorganisms in 1-L screw–capped bottles. Compared to the control treatment, higher PB (11.38 g/L), yield (YB/S, 0.37 g/g) and productivity (QB, 0.24 g/L∙h) were achieved using the co-culture system. These results were further confirmed by monitoring the oxidation–reduction potential (ORP) during ABE fermentation in a 2-L stirred-tank bioreactor (STR). Moreover, when the co-culture fermentation at 37 °C was scaled up in a 30-L STR, the PB, YB/S and QB values were comparable to those obtained in the 2-L STR. Therefore, co-culture fermentation of Arthrobacter sp. and C.beijerinckii TISTR 1461 at 37 °C represents a promising method for large-scale butanol production.

Medidas de control de olores para un tanque homogeneizador de una planta de tratamiento de aguas residuales en Costa Rica

[Objective] This study aimed to evaluate the short-term response of four different odor control measures in a homogenization tank of a university Wastewater Treatment Plant (WWTP). [Methodology] The following were implemented: aeration, adding lime, adding iron sulfate, and adding the commercial product BiOWiSH® Odor over four hydraulic retention times. The effluent and the unit were monitored during each period, using a baseline to compare the measures. Hydrogen potential, oxidation-reduction potential, dissolved oxygen, and dissolved sulfide concentration were measured in triplicate every 30 minutes. An odor perception survey was administered to WWTP visitors to evaluate intensity, offensiveness, and character (15 surveys per monitoring period). Differences were determined between control measures and the baseline using Student’s t-tests (quantitative data) and Mood’s median tests (qualitative data). Minitab 2019 was used with a 95% confidence level. [Results] All control measures significantly reduced the dissolved sulfide concentration in the unit. Aeration prevented oxygen depletion, reductive regime, and acid fermentation, which favored the oxidation of odorants. Aeration was also the only studied control measure that reduced odor intensity and offensiveness. [Conclusions] Applying aeration changed unit behavior and odor perception, which confirms its effectiveness, while adding iron sulfate, lime, and BiOWiSH® did not significantly change odor perception.

Enhanced multiferroic properties of Co-doped BiFeO3 nanoparticles via structural changes

The present study demonstrates a rhombohedral-to-orthorhombic phase transition of BiFe1-XCoXO3 (BFCXO, x = 0, 0.01, 0.03, and 0.05) nanoparticles induced by Co ion doping. With increasing concentration of Co dopant, XRD, Raman and IR patterns exhibit lattice shrinkage and increased lattice strain; SEM and TEM images reveal a corresponding reduction in grain size; XPS spectra indicate that the Fe2+ ions are readily oxidized by Co3+ to Fe3+ ions because to the greater oxidation–reduction potential of Fe3+/Fe2+ (1.3 eV) than that of Co3+/Co2+ (0.55 eV). Effective regulation of crystal structure and microstructure significantly alters the multiferroic properties of BFCXO samples. The Co-doped samples gradually transition from antiferromagnetism to ferromagnetism. Among them, BFC0.03O reaches its maximum values at Ms ~ 0.956 emu/g for magnetization saturation and Mr ~ 0.054 emu/g for remanent magnetization. Meanwhile, BFC0.03O exhibits better ferroelectric properties compared to its pure counterpart. This study presents an effective approach for controlling the structure and characteristics of BFO-based nanomaterials for multifunctional device applications.

Quantitative expression of LNAPL pollutant concentrations in capillary zone by coupling multiple environmental factors based on random forest algorithm

The capillary zone plays a crucial role in migration and transformation of pollutants. Light nonaqueous liquids (LNAPLs) have become the main organic pollutant in soil and groundwater environments. However, few studies have focused on the concentration distribution characteristics and quantitative expression of LNAPL pollutants within capillary zone. In this study, we conducted a sandbox-migration experiment using diesel oil as a typical LNAPL pollutant, with the capillary zone of silty sand as the research object. The variation characteristics of LNAPL pollutants (total petroleum hydrocarbon) concentration and environmental factors (moisture content, electrical conductivity, pH, and oxidationreduction potential) were essentially consistent at different locations with the same height. These characteristics differed within range of 10.0–50.0 cm and above 60.0 cm from groundwater. A model for quantitative expression of concentrations was constructed by coupling multiple environmental factors of 968 sets-7744 data via random forest algorithm. The goodness of fit (R2) for both training and test sets was greater than 0.90, and the mean absolute percentage error (MAPE) was less than 16.00 %. The absolute values of relative errors in predicting concentrations at characteristic points were less than 15.00 %. The constructed model can accurately and quantitatively express and predict concentrations in capillary zone.