Review on ultrasonic technology enhanced biological treatment of wastewater

Acoustic black hole ultrasonic radiator for high-efficiency radiation

The utilization of conventional longitudinal transducers in the field of ultrasonic liquid processing is constrained by limitations in radiation area and directional characteristics. These limitations can be addressed through the implementation of mode conversion techniques. However, an expanded radiation area may also result in reduced acoustic radiation intensity. To mitigate this issue, this study proposes an Acoustic Black Hole Ultrasonic Radiator (ABHUR) designed to enhance ultrasound intensity and thereby achieve high-efficiency radiation. The proposed ABHUR comprises a Bolted Langevin-type Transducer (BLT) and a Curved Acoustic Black Hole (CABH) ring. A theoretical model, based on the transfer matrix method, is developed to analyze the in-plane vibrational behavior of the CABH ring, and its validity is confirmed through Finite Element Method (FEM) simulations. The underwater vibrational and sound field distribution properties of the ABHUR are investigated using FEM and compared with two alternative radiators employing longitudinal-bending (L-B) and longitudinal-radial (L-R) modes. Owing to the unique properties of the Acoustic Black Hole structure (ABHs), which amplify bending wave amplitudes and concentrate energy, the ABHUR operating in L-B mode demonstrates superior ultrasound intensity. Furthermore, a prototype of the ABHUR is fabricated, and a series of three experiments are conducted to validate the operational feasibility of the proposed system.

Ultrasonic cavitation treatment of o-cresol wastewater and long-term pilot-scale study

Acoustic cavitation is a cutting-edge and eco-friendly advanced oxidation technology with significant efficacy in removing organic pollutants from water. Despite its potential, research on the degradation of o-cresol, a common and challenging phenolic pollutant, is limited. This study systematically investigates the optimal conditions for degrading o-cresol via acoustic cavitation and evaluates its application potential through extensive pilot tests. Batch test results indicate that ultrasonic cavitation effectively treats high concentrations of o-cresol (300 mg L-1), with aeration and neutral pH conditions enhancing removal efficiency, while the initial concentration has minimal impact on the removal rate. Additionally, analyses of total organic carbon (TOC), degradation products, and volatile organic compounds (VOCs) reveal that the main intermediates of o-cresol degradation through ultrasonic cavitation are substituted phenols and alkanes, with a mineralization rate reaching 60%. To assess the practical application of ultrasonic cavitation devices for o-cresol wastewater treatment, long-term pilot tests were conducted. These tests confirmed the device's effectiveness in removing o-cresol and its operational stability over 180 days. Furthermore, the study established the relationship between the o-cresol removal rate, hydraulic retention time (HRT), and operational cost. Consequently, this study demonstrates the feasibility of ultrasonic cavitation technology in treating high-concentration o-cresol wastewater and its potential for use in the pretreatment stage of biochemical treatment processes.

A solar-powered electrocoagulation process with a novel CNT/silver nanowire coated basalt fabric cathode for effective oil/water separation: From fundamentals to application

Electrocoagulation (EC) has proven its high efficiency and environmental sustainability for treating several types of wastewaters. However, the primary drawbacks of the conventional EC process are the suitable electrode materials and the relatively high cost due to the requirement for electric energy. To overcome these practical challenges, this study investigated effective oil/water separation by a solar-powered electrocoagulation (SPEC) process using a novel highly conductive basalt fabric (BF) cathode. The BF cathode was fabricated using a simple approach: dip-coating in carbon nanotubes (CNT) dispersion, followed by a bath exhaustion coating in a silver nanowires (AgNws) solution, and its successful preparation was confirmed through several advanced characterization techniques. The effect of the CNT-AgNws coating on the electrical conductivity of the BF-CNT/AgNws was investigated using the four-probe tester. The BF-CNT/AgNws cathode exhibited a high conductivity of 1.66 × 104 S/m, which indicates its applicability in the SPEC system. Under the operating conditions of applied voltage (25 V), SPEC time (30 min), stirring rate (150 rpm), and NaCl concentration (1 g/L), the experiment's results showed a high COD removal of 90.2 ± 0.03 %, a low energy consumption of 1.28 ± 0.01 kWh/kgCOD, and electrode consumption of 0.35 ± 0.06 kg/m3. In addition, due to the use of solar-powered energy, the overall cost was reduced by eliminating the electricity fees. Moreover, the reusability test results proved that the BF cathode has potential reusability in successive SPEC experiments while maintaining its performance. In conclusion, the obtained findings are very encouraging in designing novel EC cathodes for effective oily wastewater treatment at an industrial scale.

Treatment of high concentration phenol wastewater by low-frequency ultrasonic cavitation and long-term pilot scale study

Acoustic cavitation is an advanced, eco-friendly oxidation technology effective in removing organic pollutants from water. However, research on its use for degrading phenol, a common and challenging phenolic pollutant, is limited. This study explores the optimal conditions for phenol degradation using acoustic cavitation and assesses its practical application through extensive pilot tests. Results from batch tests show that low-frequency (15 kHz) ultrasonic cavitation effectively treats high concentrations of phenol (1000 mg L-1). Aeration and acidic pH enhance removal efficiency, while alkaline conditions inhibit degradation. Analysis of total organic carbon (TOC), degradation products, and volatile organic compounds (VOCs) reveals that the primary intermediates are substituted benzenes and alkanes. Long-term pilot tests demonstrated the device's effectiveness in phenol removal and its operational stability over 180 days. The study also establishes a relationship between removal efficiency, hydraulic retention time (HRT), and operating costs, highlighting the feasibility of low-frequency ultrasonic cavitation for treating high-concentration phenolic wastewater and its potential role in the pretreatment stage of biochemical processes.

Ultrasound-induced structural changes in partial nitrification sludge: Unravelling the mechanism for improved nitrogen removal

Low-intensity ultrasound, as a form of biological enhancement technology, holds significant importance in the field of biological nitrogen removal. This study utilized low-intensity ultrasound (200 W, 6 min) to enhance partial nitrification and investigated its impact on sludge structure, as well as the internal relationship between structure and properties. The results demonstrated that ultrasound induced a higher concentration of nitrite in the effluent (40.16 > 24.48 mg/L), accompanied by a 67.76% increase in the activity of ammonia monooxygenase (AMO) and a 41.12% increase in the activity of hydroxylamine oxidoreductase (HAO), benefiting the partial nitrification. Based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theoretical analysis, ultrasonic treatment enhanced the electrostatic interaction energy (WR) between sludge flocs, raising the total interaction energy from 46.26 kT to 185.54 kT, thereby causing sludge dispersion. This structural alteration was primarily attributed to the fact that the tightly bonded extracellular polymer (TB-EPS) after ultrasound was found to increase hydrophilicity and negative charge, weakening the adsorption between sludge cells. In summary, this study elucidated that the change in sludge structure caused by ultrasonic treatment has the potential to enhance the nitrogen removal performance by partial nitrification.

Microplastics-biofilm interactions in biofilm-based wastewater treatment processes: A review

Microplastics, pervasive contaminants from plastic, present significant challenges to wastewater treatment processes. This review critically examines the interactions between microplastics and biofilm-based treatment technologies, specifically focusing on the concepts of "biofilm on microplastics" and "microplastics in biofilm". It discusses the implications of these interactions in contaminant removal and process performance. Advanced characterization techniques, including morphological characterization, chemical composition analysis, and bio-information analysis, are assessed to elucidate the complex interplay between microplastics and biofilms within biofilters, biological aerated filters (BAFs), rotating biological contactors (RBCs), and moving bed biofilm reactors (MBBRs). This review synthesizes current research findings, highlighting that microplastics can either hinder or enhance the treatment processes, contingent on their concentration, physicochemical properties, and the specific biofilm technology employed. The insights gained from this review are essential for developing strategies to mitigate the adverse effects of microplastics and for optimizing the design and operation of wastewater treatment.

Influences of different ultrasonic treatment intensities on the molecular chain conformation and interfacial behavior of sugar beet pectin

In this study, the effects of different ultrasonic treatment intensities (57, 170, and 283 W/cm2) on the chemical composition, molecular chain characteristics, crystal structure, micromorphology, interfacial adsorption behavior and emulsifying properties of sugar beet pectin (SBP) were investigated. Ultrasonic treatment did not change the types of SBP monosaccharides, but it had impacts on their various monosaccharide contents. Moreover, the feruloylated, acetyl, and methoxy groups of SBP also undergo varying degrees of changes. The increase in ultrasonic treatment intensity led to transition in the molecular chain conformation of SBP from rigid semi-flexible chains to flexible chains, accompanied by modification in its crystal structure. Microstructural analysis of SBP confirmed the significant change in molecular chain conformation. Modified SBP could form an elastic interfacial film with higher deformation resistance on the oil-water interface. The SBP sample modified with 170 W/cm2 exhibited better emulsifying properties owing to its better interfacial adsorption behavior. Moreover, the emulsions prepared with modified SBP exhibited better stability capability under different environmental stresses (pH value, salt ion concentration, heating temperature and freeze-thaw treatment). The results revealed that the ultrasonic technology is useful to improve the emulsifying properties of SBP.

Monitoring Pharmaceuticals and Personal Care Products in Healthcare Effluent Wastewater Samples and the Effectiveness of Drug Removal in Wastewater Treatment Plants Using the UHPLC-MS/MS Method

A multi-residue UHPLC-MS/MS analytical method, previously developed for monitoring 52 pharmaceuticals in drinking water, was used to analyse these pharmaceuticals in wastewater originating from healthcare facilities in the Czech Republic. Furthermore, the methodology was expanded to include the evaluation of the effectiveness of drug removal in Czech wastewater treatment plants (WWTPs). Of the 18 wastewater samples analysed by the validated UHPLC-MS/MS, each sample contained at least one quantifiable analyte. This study reveals the prevalence of several different drugs; mean concentrations of 702 μg L-1 of iomeprol, 48.8 μg L-1 of iopromide, 29.9 μg L-1 of gabapentin, 42.0 μg L-1 of caffeine and 82.5 μg L-1 of paracetamol were present. An analysis of 20 samples from ten WWTPs revealed different removal efficiencies for different analytes. Paracetamol was present in the inflow samples of all ten WWTPs and its removal efficiency was 100%. Analytes such as caffeine, ketoprofen, naproxen or atenolol showed high removal efficiencies exceeding 80%. On the other hand, pharmaceuticals like furosemide, metoprolol, iomeprol, zolpidem and tramadol showed lower removal efficiencies. Four pharmaceuticals exhibited higher concentrations in WWTP effluents than in the influents, resulting in negative removal efficiencies: warfarin at -9.5%, indomethacin at -53%, trimethoprim at -54% and metronidazole at -110%. These comprehensive findings contribute valuable insights to the pharmaceutical landscape of wastewater from healthcare facilities and the varied removal efficiencies of Czech WWTPs, which together with the already published literature, gives a more complete picture of the burden on the aquatic environment.