Improvement of sewage sludge dewatering by piezoelectric effect driven directly with pressure from pressure filtration: Towards understanding piezo-dewatering mechanism

Synergetic conditioning via oxalic acid enhanced Fe2+/CaO2 and skeleton construct to achieve deep dewatering of sewage sludge

Extracellular polymeric substance (EPS) with highly hydrophilic groups and sludge with high compressibility are determined sludge dewaterability. Herein, Fe2+ catalyzed calcium peroxide (CaO2) assisted by oxalic acid (OA) Fenton-like process combined with coal slime was applied to improve sludge dewaterability. Results demonstrated that the sludge treated by 0.45/1/1.1-OA/Fe2+/CaO2 mM/g DS, the water content (WC), specific resistance to filtration and capillary suction time dropped to 53.01%, 24.3 s and 1.2 × 1012 m/kg, respectively. Under coal slime ratio as 0.6, WC and compressibility were further reduced to 42.72% and 0.66, respectively. The hydroxyl radicals generated by OA/Fe2+/CaO2 under near-neutral pH layer by layer collapsed EPS, resulting in the degradation and migration of inner releasing components and the exposure of inner sludge flocs skeleton. The hydrophilic tryptophan-like protein of TB-EPS were degraded into aromatic protein of S-EPS and exposed inner hydrophobic sites. The protein secondary structures were transformed by destroying hydrophilic functional groups, which were attributed to the reducing α-helix ratio and reconstructing β-sheet. Moreover, coal slime as the skeleton builder lowered compressibility and formed more macropores to increase the filterability of pre-oxidized sludge for the higher intensity of rigid substances. This study deepened the understanding of OA enhanced Fenton-like system effects on sludge dewaterability and proposed a cost-effective and synergistic waste treatment strategy in sludge dewatering.

Piezocatalysis for Chemical-Mechanical Polishing of SiC: Dual Roles of t-BaTiO3 as a Piezocatalyst and an Abrasive

Chemical mechanical polishing (CMP) offers a promising pathway to smooth third-generation semiconductors. However, it is still a challenge to reduce the use of additional oxidants or/and energy in current CMP processes. Here, a new and green atomically smoothing method: Piezocatalytic-CMP (Piezo-CMP) is reported. Investigation shows that the Piezo-CMP based on tetragonal BaTiO3 (t-BT) can polish the rough surface of a reaction sintering SiC (RS-SiC) to the ultra-smooth surface with an average surface roughness (Ra) of 0.45 nm and the rough surface of a single-crystal 4H-SiC to the atomic planarization Si and C surfaces with Ra of 0.120 and 0.157 nm, respectively. In these processes, t-BT plays a dual role of piezocatalyst and abrasive. That is, it piezo-catalytically generates in-situ active oxygen species to selectively oxidize protruding sites of SiC surface, yielding soft SiO2, and subsequently, it acts as a usual abrasive to mechanically remove these SiO2. This mechanism is further confirmed by density functional theory (DFT) calculation and molecular simulation. In this process, piezocatalytic oxidation is driven only by the original pressure and friction force of a conventional polishing process, thus, the piezo-CMP process do not require any additional oxidant and energy, being a green and effective polishing method.

Water flow promoted charge separation in piezoelectric Bi4Ti3O12 for the enhanced photocatalytic degradation of antibiotic

Addressing the issue of antibiotic residues in the environment is key to improving the quality of aquatic environments and reducing human health risks. In this study, piezoelectric bismuth titanate (Bi4Ti3O12) nanosheets are synthesized and employed to conduct antibiotic degradation. The piezoelectric potential induced by the water flow shear force is utilized to facilitate charge separation and migration in the photocatalytic process and enhance the catalytic degradation of antibiotic wastewater. As a result, 85% of tetracycline hydrochloride (TC) is degraded within 90 min. The piezo-photocatalytic process exhibits a 2.4 times faster reaction rate and a 15% higher mineralization rate than photocatalysis. Different environmental factors are investigated for their effects on the catalytic activity in piezo-photocatalysis. In situ electrochemical measurement and photoluminescence (PL) spectroscopy under stress demonstrated that the piezoelectric potential shifted the energy band of Bi4Ti3O12 and promoted the charge migration and separation, which produce more active species that favor the efficient catalytic degradation. Finally, the intermediate products of the tetracycline hydrochloride degradation process are analyzed and possible degradation pathways are suggested. This study elucidates the degradation mechanism of Bi4Ti3O12 as a piezo-photocatalyst for antibiotic pollutants, and meticulously investigates the charge transfer mechanism of the catalyst material in response to micro-stress. Hence, it provides an efficient solution for organic wastewater treatment and can potentially provide theoretical support for the development and performance optimization of catalyst materials applied in natural environments.

Effect of KMnO4/pH adjustment of extracellular polymeric substances under waste activated sludge on sludge dewatering

In this study, we examine the dewaterability of sludge after treatment by KMnO4 at various pH levels, with the goal of understanding the dewaterability of strong oxidizers to waste activated sludge. Good dewatering performance is observed, with capillary suction times (CST) reduced from 263.4 to 30.1 s, and specific resistance to filtration (SRF) falling by 19.6%. Proteins and polysaccharides in tightly bound extracellular polymeric substances (EPS) were also significantly reduced. Based on spectroscopic and electrochemical analysis, we propose mechanisms for the improved dewatering in terms of changes to the sludge's physicochemical properties and EPS. Under strong oxidation, the structure surrounding the bound water is oxidized and bound water is released, so the dewaterability of the sludge is improved.Weiliang Pan and Jiaoni Li contributed equally to this work.

Annealing and Plasma Effects on the Structural and Photocatalytic Properties of TiO2 Fibers Produced by Electrospinning

In this study, a combined method of heat treatment and plasma surface modification was used to improve the nanostructures and photocatalytic activity of electrospun TiO2 fibers. Based on the tuning effect of the annealing temperature from 500 to 800 °C, further improvements via the generation of H2 radiofrequency plasma reactions on the fiber’s surface were investigated. It was found that the anatase–rutile phase transition starts to occur at around 700 °C, which is higher than the common temperature for TiO2. The interfacial effect is generated by the symbiosis relationship between these two phases in the fibers, which can enhance photocatalytic activity since the anatase–rutile heterojunction in mixed-phase TiO2 is formed. The dramatic rise in oxygen vacancies on the fiber’s surface is created by the H2 plasma; this leads to the number of trapped electrons increasing and results in an accelerated separation between the photogenerated electrons and holes. Therefore, the photocatalytic mechanism, including the anatase–rutile heterojunction and the TiO2 fiber band structure containing oxygen vacancies, is predicted. The degradation rate was significantly enhanced (1.5 times) by increasing the annealing temperature up to 700 °C, which can be further improved upon after treatment with surface H2 plasma.

Enhancing the dewaterability of waste activated sludge by the combined ascorbic acid and zero-valent iron/persulfate system

In this work, a reducing/chelating agent, ascorbic acid (H₂A) was introduced to the traditional zero-valent iron (Fe⁰)/persulfate (PS) process for waste activated sludge dewatering. The experimental data indicated that H₂A-Fe⁰/PS process significantly enhanced the dewatering performance of sludge and enhanced the oxidation efficiency of Fe⁰-PS treatment. Under optimal conditions, the capillary suction time ratio before and after treatment (CST₀/CST) of H₂A-Fe⁰/PS treated sludge increased by 118% and 31.3% compared with untreated sludge and Fe⁰-PS treated sludge, respectively. The mechanism investigations revealed that the H₂A-Fe⁰/PS induced excellent enhancement for sludge dewaterability could be credited to the reduction and chelating capacity of ascorbic acid. Free radicals including SO₄^•-, O₂^•- and •OH produced in the H₂A-Fe⁰/PS process destroyed proteinaceous components and humic substances in sludge extracellular polymeric substances (EPS), thus reducing the negative charge and water holding capacity of sludge, improving the sludge rheological properties. As a result, the dewatering performance of sludge has been significantly improved.

Application of Advanced Oxidation Technology in Sludge Conditioning and Dewatering: A Critical Review

Sludge dewatering is an important link in sludge treatment. In practical engineering, the dewatering effect of unconditioned sludge is very poor. The use of advanced oxidation technology can improve sludge dewatering performance, reduce sludge capacity, and remove micro-pollutants, which is beneficial for sludge post-treatment and disposal. Based on the current status of sludge conditioning and dehydration, the characteristics of the advanced oxidation method for sludge dehydration were systematically explained using various free radical reaction mechanisms and dehydration conditions. The effects of various advanced oxidation technologies on sludge conditioning and dewatering has been extensively discussed. Finally, the application prospects of the advanced oxidation technology in sludge conditioning and dewatering are presented.