Molecular insights into impacts of EDTMPA on membrane fouling caused by transparent exopolymer particles (TEP)

A synergistic approach integrating potassium ferrate oxidation with polyacrylamide flocculation to enhance sludge dewatering and its mechanisms

Sludge dewatering is a critical phase in sludge treatment and disposal, significantly impacting storage, transportation, and subsequent handling. This study introduces an innovative approach combining potassium ferrate (PF) oxidation and polyacrylamide (PAM) flocculation to synergistically enhance sludge dewatering efficiency. PF disrupts EPS and releases bound water, while PAM restores floc structure, addressing the limitations of standalone oxidation. Initial PF conditioning significantly reduced sludge water content (Wc) to 75.18 %, attributed to the oxidative breakdown of extracellular polymeric substances (EPS) and the release of bound water. However, higher PF doses increased specific filtration resistance (SFR) and capillary suction time (CST), indicating deteriorated filterability. The subsequent addition of PAM mitigated these issues, further reducing Wc to 73.64 %, SFR from 12.75 × 1012 m/kg to 3.62 × 1012 m/kg, and reduced CST from 88.95 s to 32.3 s, demonstrating marked improvements in dewatering performance. Characterization studies revealed the underlying mechanisms: PF-induced sludge fragmentation and EPS degradation, followed by PAM-mediated re-flocculation and structural reorganization. Further, applying XDLVO theory and Flory-Huggins lattice theory revealed changes in the sludge's surface hydrophilicity and the system's chemical potential, improving SFR and enhancing dewatering efficiency while reducing moisture content. This investigation not only offers an innovative dewatering approach but also underpins the mechanism of improved dewaterability.

Transparent exopolymer particles (TEP) research: From the ocean to water treatment

Transparent Exopolymer Particles (TEP), closely related to the carbon cycle due to their high carbon-to-nitrogen ratio, have become a hot research topic. However, despite the growing interest in this field, there is a lack of comprehensive analysis providing a clear developmental background and quantitative research on the overall trends of TEP studies. To address the gap, this article utilizes VOSviewer and CiteSpace to conduct a bibliometric analysis of TEP research. The results show that the largest contribution of publications in this field is in the United States and it has become an increasingly interdisciplinary research topic. We identify that the current research focus of TEP is mainly on the application of membrane fouling, marine microbial and biogeochemical cycle. In addition, the research focus has shifted from the role of TEP in the marine carbon cycle to its influence on membrane fouling. This study systematically and comprehensively carries out quantitative visualization and analysis of TEP, providing a basis and reference for in-depth understanding of the current status of TEP research as well as grasping the development trend.

Membrane fouling mechanisms in the presence of microplastics and organic matter: The unexpected mitigating role of Ca2

Ultrafiltration (UF) is demonstrated to be highly effective in the removal of microplastics (MPs), but the presence of coexisting foulants introduces significant uncertainties into the associated membrane fouling behaviors. In this study, membrane fouling mechanisms were investigated when MPs, represented by polystyrene (PS), coexisted with typical organic foulants (sodium alginate, SA) and inorganic ions (Ca2+). Fouling tests revealed that the order of Ca2+ addition significantly impacted the fouling behavior of the SA-PS combined foulants. Specifically, the specific filtration resistance (SFR) was reduced by 40.82 % in the SA-PS-Ca2+ foulants and by 90.92 % in the SA-Ca2+-PS foulants, compared to the SA-PS foulants. X-ray photoelectron spectroscopy and density functional theory calculations indicated that sufficient cross-linking of Ca2+ with SA molecular chains in the SA-Ca2+-PS foulants, forming a large-scale 3D network that encapsulated more PS particles and resulted in larger flocs than those found in the SA-PS-Ca2+ foulants. According to extended Flory-Huggins theory, the improved filtration performance of the SA-PS combined foulants was due to substantial changes in chemical potential during their transition from gel to flocs upon Ca2+ addition. Furthermore, interfacial thermodynamic analyses suggested that increased repulsion between SA-Ca2+-PS foulants and between them and the membrane led to a looser fouling layer, significantly mitigating membrane fouling. This study elucidates the fouling mechanisms in the presence of MPs and other foulants from the perspectives of energy changes and molecular structures, providing novel insights for developing strategies to mitigate membrane fouling.

Enhanced sludge dewatering using a novel synergistic iron/peroxymonosulfate-polyacrylamide method

In the sludge dewatering process, a formidable challenge arises due to the robust interactions between extracellular polymeric substances (EPS) and bound water. This study introduces a novel, synergistic conditioning method that combines iron (Fe2+)/peroxymonosulfate (PMS) and polyacrylamide (PAM) to significantly enhance sludge dewatering efficiency. The application of the Fe2+/PMS-PAM conditioning method led to a substantial reduction in specific filtration resistance (SFR) by 82.75% and capillary suction time (CST) by 80.44%, marking a considerable improvement in dewatering performance. Comprehensive analyses revealed that pre-oxidation with Fe2+/PMS in the Fe2+/PMS-PAM process effectively degraded EPS, facilitating the release of bound water. Subsequently, PAM enhanced the flocculation of fine sludge particles resulting from the advanced oxidation processes (AOPs). Furthermore, analysis based on the Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory demonstrated shifts in interaction energies, highlighting the breakdown of energy barriers within the sludge and a transition in surface characteristics from hydrophilic (3.79 mJ m-2) to hydrophobic (-61.86 mJ m-2). This shift promoted the spontaneous aggregation of sludge particles. The innovative use of the Flory-Huggins theory provided insights into the sludge filtration mechanism from a chemical potential perspective, linking these changes to SFR. The introduction of Fe2+/PMS-PAM conditioning disrupted the uniformity of the EPS-formed gel layer, significantly reducing the chemical potential difference between the permeate and the water in the gel layer, leading to a lower SFR and enhanced dewatering performance. This thermodynamic approach significantly enhances our understanding of sludge dewatering and conditioning. These findings represent a paradigm shift, offering innovative strategies for sludge treatment and expanding our comprehension of dewatering and conditioning techniques.

Hydrothermal synthesis of a photocatalyst based on Byrsonima crassifolia and TiO2 for degradation of crystal violet by UV and visible radiation

This work presents a one-step synthesis methodology for preparing a hydrochar (HC) doped with TiO2 (HC-TiO2) for its application on the degradation of crystal violet (CV) using UV and visible radiation. Byrsonima crassifolia stones were used as precursors along with TiO2 particles. The HC-TiO2 sample was synthesized at 210 °C for 9 h using autogenous pressure. The photocatalyst was characterized to evaluate the TiO2 dispersion, specific surface area, graphitization degree, and band-gap value. Finally, the degradation of CV was investigated by varying the operating conditions of the system, the reuse of the catalyst, and the degradation mechanism. The physicochemical characterization of the HC-TiO2 composite showed good dispersion of TiO2 in the carbonaceous particle. The presence of TiO2 on the hydrochar surface yields a bandgap value of 1.17 eV, enhancing photocatalyst activation with visible radiation. The degradation results evidenced a synergistic effect with both types of radiation due to the hybridized π electrons in the sp2-hybridized structures in the HC surface. The degradation percentages were on average 20% higher using UV radiation than visible radiation under the following conditions: [CV] = 20 mg/L, 1 g/L of photocatalyst load, and pH = 7.0. The reusability experiments demonstrated the feasibility of reusing the HC-TiO2 material up to 5 times with a similar photodegradation percentage. Finally, the results indicated that the HC-TiO2 composite could be considered an efficient material for the photocatalytic treatment of water contaminated with CV.