Pretreatment of hypersaline and high-organic wastewater with a three-dimensional electrocatalytic system: a pilot-scale study.

The three-dimensional electrocatalytic oxidation (3DEO) is a promising electrochemical system in the treatment of refractory wastewater, but still far from large-scale applications. In this work, we prepared 146.5 Kg Ti-Sn-Sb@γ-Al2O3 particle electrodes to construct a 3DEO system for the pretreatment of hypersaline and high-organic wastewater in an industrial park sewage plant, with activated carbon particle electrodes as a comparison. The average COD removal rates of Ti-Sn-Sb@γ-Al2O3 and activated carbon-based 3DEO systems were 24.43 and 48.73%, respectively, and the energy consumption of the two 3DEO systems were 102.8 and 31.4 kWh/Kg COD, respectively. However, compared to the negligible enhancement of wastewater biodegradability in the activated carbon 3DEO system, the Ti-Sn-Sb@γ-Al2O3 3DEO system greatly improved the biochemical index (B/C) from 0.021 to 0.166 (by 690.5%). Due to its superior catalytic capacity, Ti-Sn-Sb@γ-Al2O3 outperforms activated carbon in improving biodegradability as the latter relies mainly on adsorption. The results of this work provide a 3DEO engineering practice experience on the pretreatment of hypersaline and high-organic wastewater.

Self-endowed magnetic photocatalysts derived from iron-rich sludge and its recycling in photocatalytic process for tetracycline degradation.

The disposal of iron-rich sludge by landfill or incineration poses environmental risks and wastes resources. The utilization of iron-rich sludge for magnetic material preparation offers a sustainable and resource-efficient solution for its disposal. Herein, self-endowed magnetic photocatalysts were initially prepared by pyrolysis using iron-rich sludge without any additives. The photocatalysts performance were evaluated for tetracycline degradation, with the highest degradation rate of 95.3 % at a concentration of 10 mg·L-1 (pH = 7) within 5 h being achieved for the photocatalyst prepared at 800 °C. The reactive radical species in the photocatalysis process were confirmed to be •OH and O2•- activated by ferrous oxygen species under light irradiation. Furthermore, quinone-like structures induced bound persistent free radicals, which emerged as the predominant factors influencing 1O2 formation. The employed photocatalyst can be efficiently separated and recovered owing to its magnetism. This work presents an economic solution for antibiotic removal using waste iron-rich sludge.

Adsorption Performance and Mechanisms of Tetracycline on Clay Minerals in Estuaries and Nearby Coastal Areas.

Clay minerals in sediments have strong adsorption capacities for pollutants, but their role in the distribution of antibiotics in estuaries and nearby coastal areas is unclear. We evaluated the clay mineral montmorillonite (SWy-2) adsorption capacity for tetracycline (TC). We assessed the adsorption capacity of SWy-2 for TC by measuring the removal percentage of 30 mg/L TC over time. The effects of pH and ionic strength on the TC adsorption onto SWy-2 were investigated. We analyzed the kinetics of TC adsorption using a pseudo-second-order model and determined the adsorption isotherm using the Langmuir equation. SWy-2 particles were characterized using zeta potential, Fourier transform infrared (FTIR), and X-ray diffraction (XRD) analyses before and after TC adsorption. The removal percentage of 30 mg/L TC by SWy-2 reached 70.76% within 0.25 h and gradually increased to 78.64% at 6 h. TC adsorption was influenced by pH and ionic strength, where low pH enhanced and high ionic strength reduced the adsorption. The kinetics of TC adsorption followed a pseudo-second-order model, and the adsorption isotherm adhered to the Langmuir equation. The saturated adsorption capacity (qmax) of SWy-2 for TC was 227.27 mg/g. Zeta potential, FTIR, and XRD analyses confirmed that electrostatic interactions and chemical bonds played a significant role in the TC adsorption by SWy-2. SWy-2 clay mineral exhibits a substantial adsorption capacity for TC, indicating its potential as an effective sorbent to mitigate antibiotic contamination in estuaries and nearby coastal areas. The observed effects of pH and ionic strength on TC adsorption have implications for the environmental fate and transport of antibiotics. The pseudo-second-order kinetic model and Langmuir isotherm equation provide valuable insights into the adsorption behavior and capacity of TC on SWy-2. Characterization analyses support the involvement of electrostatic interactions and chemical bonds in the SWy-2-TC adsorption mechanism.

Enhanced Adsorptive Removal of Tetracycline by Phosphomolybdic Acid-Modified Low-Temperature Sludge Biochar.

Increasing the adsorption capacity and reducing the energy consumption of sludge biochar during preparation is important. In this study, a new modification method was developed to prepare phosphomolybdic acid-modified sludge biochar through the low-temperature pyrolysis of sewage sludge using phosphomolybdic acid as a modifier. Tetracycline was used to assess the adsorption performance of sludge biochar, and phosphomolybdic acid-modified sludge biochar was prepared at different temperatures. The results showed that the adsorption capacity of sludge biochar improved from 84.49 to 120.86 mg/g through modification with phosphomolybdic acid at 200 °C. The maximum adsorption capacities of phosphomolybdic acid-modified sludge biochar (200 °C pyrolysis temperature) at 298, 308, and 318 K were 283.87, 421.39, and 545.48 mg/g, respectively. Both liquid film and intraparticle diffusion were the main rate-limiting steps of tetracycline adsorption by phosphomolybdic acid-modified sludge biochar. Furthermore, the adsorption of tetracycline by phosphomolybdic acid-modified sludge biochar was mainly attributed to π-π interactions, electrostatic interactions, hydrogen bonding, and pore filling.

Efficient photocatalytic degradation of tetracycline using magnetic biochar derived by iron-rich sludge.

Industrial wastewater treatment processes produce a large quantity of iron-rich sludge due to the extensive utilization of iron salt reagent. Reuse of iron-rich sludge is an attractive route for excess sludge disposal and management. In this study, sludge-derived magnetic photocatalyst was prepared using industrial iron-rich sludge as raw materials for the first time. The photocatalytic degradation system constructed by the sludge-derived photocatalysts were evaluated using tetracycline (TC) as the target contaminant, achieving a high degradation rate of 98.3% within 5 h under optimal conditions. Major reactive oxygen species in the photocatalytic systems were investigated using radical quenching experiments and electron paramagnetic resonance spectroscopy. The results suggested that •OH and O2•- were activated by photogenerated electrons and holes, respectively. Moreover, bound persistent free radicals induced by quinone-like structure in sludge-derived biochar were the predominant factors affecting radical 1O2 formation under the light irradiation. The reactive oxygen species of •OH, O2•-, and 1O2 played main roles in the degradation of TC. The used magnetic biochar can be effectively separated and recovered in aqueous solutions by the magnetism. This method provides a new cost-effective strategy for antibiotics removal from aqueous solution.

Ascorbic acid enhanced ferrous/persulfate system for degradation of tetracycline contaminated groundwater.

Persulfate (PS) activated by Fe(ii) has been widely investigated for degradation of contaminants. However, the Fe(ii)/PS systems used for actual contaminated groundwater remediation have been restricted by circulation of Fe(iii)/Fe(ii). Herein, an ascorbic acid (AA) enhanced Fe(ii)/PS system was developed for degradation of tetracycline (TC) contaminated groundwater. The influence of Fe(ii), AA, PS dosage and pH on degradation of TC was investigated, the free radicals produced in the reaction were identified and the reusability of Fe(ii) in the Fe(ii)/PS/AA system for degradation of TC was also evaluated. The results showed that AA significantly promoted the degradation of TC in the Fe(ii)/PS system, and a degradation rate of 86% for TC was achieved at 60 min. The dominant oxidant species for contaminant degradation in the Fe(ii)/PS/AA system is ˙OH. Appropriate Fe(ii), AA and PS dosage can improve the degradation rate of TC. Moreover, the degradation rate of TC in the Fe(ii)/PS/AA system under acidic conditions is higher than that under alkaline conditions. With the increase of reaction time, TC can also be completely degraded even with a little Fe(ii) or under alkaline conditions in the Fe(ii)/PS/AA system, and Fe(ii) showed a good reusability for the degradation of TC. Thus, the AA-enhanced Fe(ii)/PS system for the degradation of contaminants displays the advantages of less Fe(ii) consumption and a wide range of pH. This method provides a new strategy for in situ remediation of contaminated groundwater.

A virtual velocity-based integrated navigation method for strapdown inertial navigation system and Doppler velocity log coupled with unknown current.

The integration of the strapdown inertial navigation system (SINS) and Doppler velocity log (DVL) has become a basic navigation solution for Autonomous Underwater Vehicles (AUVs). However, DVL cannot obtain the velocity relative to the ground when the distance between the AUV and seabed is over the operating range, which occurs often when AUVs are sailing in the middle layer of the ocean. When the DVL velocity relative to the current is used for an integrated filter, the unknown current velocity is coupled with the measured velocity error, which decreases the positioning accuracy. To address this problem, the effect of unknown coupled current velocity is analyzed from the perspective of filter observability, and an integrated SINS/DVL/virtual velocity navigation method is proposed. The virtual velocity based on the velocity variation extracted from the inertial measurement unit and DVL is constructed and used as an aided measurement for the Kalman filter. With the help of virtual velocity, the current velocity can be easily decoupled from measured SINS velocity error. The results of simulation and experiments demonstrated that the proposed method can effectively improve both the convergence speed and accuracy of velocity error compared with the classical method with SINS/DVL integration and, thus, significantly improve the positioning accuracy.

A self-alignment method for gravitational apparent acceleration identification and accelerometer bias estimation based on repeated navigation solution.

Estimating inertial measurement unit error without any external reference information has always been a difficult problem. The method based on the reconstruction of the gravitational apparent motion in the inertial frame can estimate the accelerometer bias, but a long identification time is needed to get high alignment accuracy. In order to reduce the convergence time and improve the accuracy of estimation, a fast estimation method based on repetitive navigation under the excitation of swing motion is proposed. Two data processing methods, the forward-forward loop and the backward-forward loop, are studied and compared in this paper. In addition, the influence of data length on the experiment result was analyzed. The simulation and experimental results show that the forward-forward loop calculation cannot solve the contradiction between speed and accuracy, while the backward-forward loop calculation can effectively estimate the accelerometer bias and realize self-alignment, with a short alignment time and high alignment accuracy.

Investigating the survey instrument for the underground pipeline with inertial sensor and dead reckoning method.

To survey deep-buried and non-metallic pipelines without excavation, a pipeline survey instrument composed of a data collection and data processing part is developed. The data collection part is composed of a walking machine, a nine-axis micro-electro-mechanical system inertial measurement unit (MEMS-IMU) installed on the walking machine, odometers based on Hall magnetic switches, and a control/data storage circuit, while data processing is executed on the personal computer, where the attitude and trajectory are acquired with the complementary filter and dead reckoning on the collected data. Key technologies include the following: (1) the gyro-bias is estimated with the parking mode when there is no angular motion excitation; (2) a magnetometer is introduced to assist MEMS-IMU tracking azimuth changes; (3) calibration based on ellipsoid fitting is designed for magnetometers and accelerometers without any references; (4) stretching and rotation on calculated trajectory are executed with position information of both pipeline ends. Test results on a pipeline of 104 m constructed on the ground show that the maximum error on the lateral direction is 0.13 m and the height is 0.06 m, while the mean errors are -0.04 m and -0.001 m, respectively.

A Newton iterative optimization combined with window loop calculation algorithm for estimating accelerometer bias based on gravitational apparent motion with excitation of swinging motion.

The initial alignment method, including the identification of inertial device error parameters, has always been a key issue in an inertial navigation system (INS). This study focuses on the error caused by the random noise of inertial devices that can be compensated by the reconstruction of gravitational apparent motion in an inertial frame under the condition of swinging motion. Attitude angles and accelerometer bias can also be estimated. However, the analysis and simulation results indicate that the existing methods cannot estimate the gyroscope bias. The accelerometer and the gyroscope bias will change over a long time, which will lead to long-term parameter identification accuracy decline or even failure. In this paper, a parameter identification algorithm based on Newton iterative optimization combined with a window loop calculation is designed to solve these problems. Simulation and turntable tests indicate that the proposed new algorithm can fulfill the initial alignment of strapdown INS under the swinging condition and estimate accelerometer bias effectively. Moreover, the new algorithm improves data utilization, which also has better time sensitivity, and the calculated alignment errors can nearly approach zero.

A novel Rauch-Tung-Streibel smoothing scheme based on the factor graph for autonomous underwater vehicles.

In submarine surveying and mapping applications, a novel Rauch-Tung-Streibel smoothing (RTSS) scheme based on the factor graph for autonomous underwater vehicles is presented to gain a better offline navigation solution in this paper. The factor graph method is applied to optimally use observation information of multi-sensors with the asynchronous and short-term failure problems to overcome deficiencies of the federal Kalman filter in information fusion processing. Furthermore, the revised RTSS as a post-mission smoothing algorithm is performed by combining the results of the factor graph and one backward data processing through recursively updating the smoothed state and its covariance. From the simulation analysis, it is found that the factor graph mainly owns plug and play capability and contributes to the real-time navigation accuracy over the federal Kalman filtering. The RTSS provides better accuracy and smoothness for the position, velocity, and attitude at the same time compared to the corresponding real-time navigation solution, especially when signals are lost or sensors fail for a short time. With the best of both methods, a novel smoothing scheme combining the factor graph with the RTSS is built. Semi-physical experiment results verify the reliability and effectiveness of the proposed method.

Reduced nontronite-activated H2O2 for contaminants degradation: The beneficial role of clayed fractions in ISCO treatments.

Clayed fractions in aquifers are generally deemed to be detrimental for in situ chemical oxidation (ISCO) treatments due to the difficulty of oxidant injection/transport and the retention/rebound of contaminants. Using a model clay mineral nontronite and a real sediment, here we show that the component of structural Fe(II) in clay minerals is particularly effective in activating hydrogen peroxide (H2O2) to hydroxyl radicals (OH) for contaminants degradation under pH-neutral conditions. Using reduced nontronite (Fe(II)/Fetotal : 40 %) as a model Fe(II)-bearing clay mineral, 2 mg/L trichloroethylene (TCE) was degraded by 82.0 % and 95.3 %at 2.5 min and 30 min, respectively, under the condition of 0.6 g/L reduced nontronite, 0.5 mM H2O2and pH 7.5. Reactive structural Fe(II) in nontronite was responsible for the initial quick reaction. The degradation was also efficient for phenol, benzoic, toluene and naphthalene, but exhibited higher efficiencies for those with stronger sorption to nontronite. With similar concentrations of H2O2 and Fe(II), nontronite-activated H2O2 at pH 7.5 led to similar efficiencies of TCE degradation and H2O2 utilization to classic homogeneous Fenton at pH 3. A real clayed sediment showed similar performance in activating H2O2 for contaminant degradation. Our findings implicate that clayed fractions in aquifers may probably contribute to contaminants degradation in H2O2-based ISCO treatments.

Sulfide drives hydroxyl radicals production in oxic ferric oxyhydroxides environments.

Perturbation of Fe(III)-bearing oxic environments by reduced species such as sulfide occurs widely in natural and engineered systems. However, whether hydroxyl radicals (OH) can be produced in these environments remains unexplored. Here we show that sulfide drives OH production in Fe(III) oxyhydroxides suspensions under neutral and oxic conditions. For lepidocrocite, ferrihydrite and goethite suspensions at 11.2 mM Fe, the addition of 0.5 mM sulfide produced 14.2, 14.3 and 22.4 µM OH within 120 min, respectively. With addition of sulfide to lepidocrocite suspensions at 11.2 mM Fe, the cumulative OH concentration within 120 min increased from 0 to 14.2, 25.2, 52.6 and 63.1 µM when sulfide dosage increased from 0 to 0.5, 2.5, 5 and 7.5 mM, respectively. At a fixed sulfide dosage of 5 mM, the cumulative OH concentration increased with increasing the number of sulfide additions. The mechanisms of OH production were attributed to the generation of surface-bound Fe(II), most likely in the form of >FeIIOH2+, and Fe(II) in the solid phase or FeS from the reactions between sulfide and Fe(III), followed by O2 activation. OH production could take place until depletion of sulfide. Finally, we found that the generated OH could oxidize the coexisting redox-active substances like phenol under neutral and oxic conditions. Our findings reveal that sulfide perturbation of Fe(III)-bearing oxic environments is a new source of OH, and contaminants oxidation by OH necessitates consideration in these environments.

An iterative optimization method for estimating accelerometer bias based on gravitational apparent motion with excitation of swinging motion.

Field calibration is an important method to guarantee the accuracy of a strapdown inertial navigation system. Zero velocity update based on the zero-velocity constraint when the carrier is without translational motion is a typical system-level calibration method. In zero velocity update, there is a coupling between biases and horizontal misalignment angles. The accuracy of horizontal misalignment angles is determined by the equivalent accelerometer biases in horizontal directions, which means that improving the accuracy of horizontal angles needs accurate calibration of accelerometer biases. Meanwhile, alignment with gravitational apparent motion is widely used taking advantages of its alignment ability in a swinging condition. But it is an analytical method and cannot calibrate sensor biases and is always dealt as a coarse alignment method. In order to calibrate accelerometer biases and utilize advantages of the alignment method with gravitational motion, a method to estimate accelerometer biases based on an iterative optimization method and gravitational apparent motion is presented in this paper. First, accelerometer biases are introduced to calculate apparent acceleration and an objective function is constructed. Then, Newton's iteration is applied to iteratively optimize the parameters describing gravitational apparent motion and accelerometer biases. As revealed by the theoretical analysis and experimental results, different patterns of gravity and accelerometer biases will be generated when the carrier exhibits a swinging motion; thus, the convergence of the proposed algorithm will be ensured. After accelerometer biases are removed, initial alignment performed with the gravitational apparent motion reconstructed by the estimated parameters gives nearly zero horizontal misalignment angles.

Robust data cleaning methodology using online support vector regression for ultra-short baseline positioning system.

Ultrashort baseline (USBL) acoustic positioning system is a significant navigation means for human occupied vehicle due its simple structure, convenient operation, and large-scale-maneuver capacity. In order to improve the quality of USBL raw data effectively and efficiently, a robust data cleaning methodology using Online Support Vector Regression (OSVR) is proposed to deal with measurement outliers and missing values. In this study, we applied sliding-window samples to train the OSVR model for online time series prediction and then utilized the obtained one-step ahead prediction to detect and replace outliers or supplement missing values. The experimental results of the online test show that the proposed methodology can satisfy the requirement of real-time navigation and acquire consecutive and consistent positioning data for USBL. In comparison with the raw data, the root mean square error results in longitude and latitude are reduced by 91.75% and 85.53%, respectively. In addition, such methodology outperforms other data cleaning algorithms based on Least Square (LS) and kernel recursive LS.

Oxidation of trichloroethylene by the hydroxyl radicals produced from oxygenation of reduced nontronite.

Reduction by Fe(II)-bearing silicate minerals has been proposed as an important mechanism for the attenuation of chlorinated hydrocarbons (CHCs) in anoxic subsurfaces. The redox condition of subsurface often changes from anoxic to oxic due to natural processes and human activities, but little is known about the transformation of CHCs induced by Fe(II)-bearing silicate minerals under oxic conditions. This study reveals that trichloroethylene (TCE) can be efficiently oxidized during the oxygenation of reduced nontronite at pH 7.5, whereas the reduction was negligible under anoxic conditions. The maximum oxidation of TCE (initially 1 mg/L) attained 89.6% for 3 h oxygenation of 2 g/L nontronite with 50% reduction extent. TCE oxidation is attributed to the strongly oxidizing hydroxyl radicals (OH) produced by the oxygenation of Fe(II) in nontronite. Fe(II) on the edges is preferentially oxygenated for OH production, and the interior Fe(II) serves as an electron pool to regenerate the Fe(II) on the edges. Oxidation of TCE could be sustainable through chemically or biologically reducing the oxidized silicate minerals. Our findings present a new mechanism for the transformation of CHCs and other redox-active substances in the redox-fluctuation environments.

Production of Hydroxyl radicals from oxygenation of simulated AMD due to CaCO3-induced pH increase.

Many karst areas are impacted by acid mine drainage (AMD) which is characterized by low pH, high concentrations of dissolved Fe(II) and toxic contaminants. During the flow of AMD in karst areas, the increase in pH facilitates the oxygenation of Fe(II). Whereas, the oxidizing capacity for Fe(II) oxygenation in AMD is poorly understood. In light of the recent finding that hydroxyl radicals (OH) can be produced from Fe(II) oxygenation, this study experimentally measured the cumulative concentrations of OH produced from oxygenation of simulated AMD (8.93 mM Fe2+, pH 3) in the presence of limestone (CaCO3). With the increase in CaCO3 dosages from 0.67 to 2.78 g/L, Fe(II) oxidation rate increased accordingly, but the maximum concentration of cumulative OH appeared at the CaCO3 dosage of 1.39 g/L, being 59.3 µM within 24 h. The production of OH was mainly attributed to the rise of AMD pH due to dissolution of limestone, rendering the appearance of adsorbed Fe(II) on the newly formed lepidocrocite and ferrihydrite and complexed Fe2+ by carbonate (i.e., siderite). Oxygenation of these Fe(II) species was accountable for the production of OH. An appropriate pH (i.e., 5-6) was required for the moderate rate of Fe(II) oxidation, corresponding to the maximum production of OH. The OH produced from AMD oxygenation can concurrently oxidize the contaminants of arsenic and p-aminobenzenesulfonamide. Findings from this study suggest that the oxidizing impact of OH on contaminants transformation as well as organic carbon mineralization should be concerned for the oxygenation of AMD in karst areas.

A Novel Slope Method for Measurement of Fluid Density with a Micro-cantilever under Flexural and Torsional Vibrations.

A novel method, which was called a slope method, has been proposed to measure fluid density by the micro-cantilever sensing chip. The theoretical formulas of the slope method were discussed and established when the micro-cantilever sensing chip was under flexural and torsional vibrations. The slope was calculated based on the fitted curve between the excitation and output voltages of sensing chip under the nonresonant status. This measuring method need not sweep frequency to find the accurate resonant frequency. Therefore, the fluid density was measured easily based on the calculated slope. In addition, the micro-cantilver was drived by double sided excitation and free end excitation to oscillate under flexural and torsional vibrations, respectively. The corresponding experiments were carried out to measure the fluid density by the slope method. The measurement results were also analyzed when the sensing chip was under flexural and torsional nonresonant vibrations separately. The measurement accuracies under these vibrations were all better than 1.5%, and the density measuring sensitivity under torsional nonresonant vibration was about two times higher than that under flexural nonresonant vibration.

A MEMS Resonant Sensor to Measure Fluid Density and Viscosity under Flexural and Torsional Vibrating Modes.

Methods to calculate fluid density and viscosity using a micro-cantilever and based on the resonance principle were put forward. Their measuring mechanisms were analyzed and the theoretical equations to calculate the density and viscosity were deduced. The fluid-solid coupling simulations were completed for the micro-cantilevers with different shapes. The sensing chips with micro-cantilevers were designed based on the simulation results and fabricated using the micro electromechanical systems (MEMS) technology. Finally, the MEMS resonant sensor was packaged with the sensing chip to measure the densities and viscosities of eight different fluids under the flexural and torsional vibrating modes separately. The relative errors of the measured densities from 600 kg/m³ to 900 kg/m³ and viscosities from 200 µPa·s to 1000 µPa·s were calculated and analyzed with different microcantilevers under various vibrating modes. The experimental results showed that the effects of the shape and vibrating mode of micro-cantilever on the measurement accuracies of fluid density and viscosity were analyzed in detail.

Production of Abundant Hydroxyl Radicals from Oxygenation of Subsurface Sediments.

Hydroxyl radicals (•OH) play a crucial role in the fate of redox-active substances in the environment. Studies of the •OH production in nature has been constrained to surface environments exposed to light irradiation, but is overlooked in the subsurface under dark. Results of this study demonstrate that abundant •OH is produced when subsurface sediments are oxygenated under fluctuating redox conditions at neutral pH values. The cumulative concentrations of •OH produced within 24 h upon oxygenation of 33 sediments sampled from different redox conditions are 2-670 µmol •OH per kg dry sediment or 6.7-2521 µM •OH in sediment pore water. Fe(II)-containing minerals, particularly phyllosilicates, are the predominant contributor to •OH production. This production could be sustainable when sediment Fe(II) is regenerated by the biological reduction of Fe(III) during redox cycles. Production of •OH is further evident in a field injection-extraction test through injecting oxygenated water into a 23-m depth aquifer. The •OH produced can oxidize pollutants such as arsenic and tetracycline and contribute to CO2 emissions at levels that are comparable with soil respiration. These findings indicate that oxygenation of subsurface sediments is an important source of •OH in nature that has not been previously identified, and •OH-mediated oxidation represents an overlooked process for substance transformations at the oxic/anoxic interface.