Influence of alternating electric field on deep dewatering of municipal sludge and changes of extracellular polymeric substance during dewatering

Modification of aged oily sludge (AOS) through pressure filtration and electro-dewatering methods under citric acid (CA) pretreatment

Aged oily sludge (AOS) exhibits more challenging properties compared to ordinary oily sludge, making modification treatments essential for improving dewatering efficiency. This study innovatively employs citric acid (CA) as a pretreatment agent for AOS and combines pressure filtration (PF) and electro-dewatering (EDW) to conduct volume reduction experiments, while investigating the dewatering mechanism of CA pretreatment. Under a pressure of 75 kPa, the AOS moisture content decreased slightly from 80.12 % to 78.00 %, while the addition of 0.02 g CA/g AOS further reduced it to 71.69 %. Under conditions of 25 kPa and 25 V/cm, EDW lowered the moisture content to 47.36 %, achieving faster average dewatering rate of 0.086 g/s. This study investigated the oil and water distribution within sludge cake layers, analyzed their migration during EDW, and explained the anodic drying phenomenon. Engineering applicability was assessed through energy consumption and calorific value analyses. Mechanistic insights revealed oil component changes, highlighting the roles of surfactants, electric field forces, pH, and temperature. Formula-based calculations were also conducted for field-driven processes. This study presents an innovative deep dewatering technology for AOS, investigating the dewatering mechanism from various perspectives, including demulsification, electric field, pH, and thermal effects. Additionally, it evaluates the energy consumption and economic cost, providing a theoretical foundation for its engineering applicability and offering new perspectives for the treatment and disposal of AOS.

Extracellular polymeric substances (EPS) in sewage sludge management: A call for methodological standardization

Extracellular polymeric substances (EPS) are crucial in sewage sludge management, influencing key processes such as sedimentation, dewatering, and drying. Despite their importance, the lack of standardized methods for EPS extraction and analysis has led to inconsistent research findings, hindering a thorough understanding of EPS's role in sludge treatment. This review paper addresses this issue by critically comparing various EPS extraction and analysis methods, emphasizing the urgent need for standardization in the field. Standardized methodologies will enable researchers to compare studies more accurately and derive meaningful insights into EPS's role across different stages of sludge treatment, ultimately advancing EPS knowledge and application in sludge management. Additionally, this paper summarizes findings from numerous studies on EPS impact in sedimentation, dewatering, and drying, offering a holistic view of their significance in sludge management. Moreover, it explores the potential EPS applications, highlighting both the future directions and the challenges associated with their production.

Reuse of wastewater and biosolids in soil conditioning: Potentialities, contamination, technologies for wastewater pre-treatment and opportunities for land restoration

This study reviews the potential use of various wastewaters-vinasse, swine, food industry, paper and pulp, municipal wastewaters, and biosolids-as soil conditioners for restoring degraded areas, focusing on the circular economy concept. Over 90 articles from 2013 to 2024 were analyzed to address current scientific concerns, including these effluents' resistance genes, hormones, and macro/micronutrients. The presence of contaminants was critically examined alongside the necessary treatment methods to prevent soil degradation and ensure soil quality improvement. These included contaminants of emerging concern (CECs), antibiotic resistance genes (AGRs), and pathogens. These contaminants can either be assimilated and degraded by the soil ecosystem or leach into groundwater, translocate to plants, or accumulate in surface soil, necessitating careful monitoring. Furthermore, the study critically evaluates the potential of various physical and biological treatment technologies, such as anaerobic digestion, composting, dewatering, stabilization ponds, biological reactors, membrane processes, rotating disks, and pelletizers, highlighting their effectiveness in mitigating contamination and enhancing soil quality. The long-term effects of wastewater reuse as soil conditioner depend on both wastewater characteristics and soil properties. The benefits of using wastewater as soil conditioners are found to be influenced by characteristics of both the soil and the wastewater, with improvements in soil physical properties (increased porosity and permeability) and chemical properties (increased soil organic carbon and nutrients). Overall, the literature suggests that while wastewaters hold promise as soil conditioners, their successful application depends on effective wastewater management strategies to optimize benefits and mitigate risks.

Enhancement of sludge dewaterability using combined technology of bioleaching and Fenton: Microscopic structure and hydrophilic/hydrophobic properties of sludge particles

Bioleaching and Fenton technology are commonly used preconditioning techniques for sludge dewatering. This study compared the dewatering mechanisms of different conditioning technologies. The results showed that bound water, specific resistance to filtration (SRF), and capillary suction time decreased from 3.95 g/g, 6.16 × 1012 m/kg, and 130.6 s to 3.15 g/g, 2.81 × 1011 m/kg, and 33 s, respectively, under combined treatment condition. Moreover, the free radicals, including ·OH, O2-·and Fe (Ⅳ), further damaged the cell structure, thus increasing the concentration of DNA in the S-EPS layer. This intense degradation sludge particle size decreased by 15.6% and significantly increased zeta potential. Under the combined technology, the α-helix and β-sheet decreased by 42.2% and 56.5%, respectively, destabilizing the spatial structure of proteins and promoting the release of bound water. In addition, the combined technology decreased (Ala/Lys) ratio in the TB-EPS layer by 67.6%, indicating the weakening of protein water-holding capacity. Moreover, the conversion of oxygen-containing compounds to nonpolar hydrocarbons increased the hydrophobicity of the sludge under a combined treatment, thus enhancing dewatering performance.

Physical conditioning methods for sludge deep dewatering: A critical review

Sludge is an inevitable waste product of sewage treatment with a high water content and large volume, it poses a significant threat of secondary pollution to both water and the atmosphere without proper disposal. In this regard, dewatering has emerged as an attractive method in sludge treatment, as it can reduce the sludge volume, enhance its transportability and calorific value, and even decrease the production of landfill leachate. In recent years, physical conditioning methods including non-chemical conditioners or energy input alone, have been extensively researched for their potential to enhance sludge dewatering efficiency, such as thermal treatment, freeze-thaw, microwave, ultrasonic, skeleton builders addition, and electro-dewatering, as well as combined methods. The main objective of this paper is to comprehensively evaluate the dewatering capacity of various physical conditioning methods, and identify key factors affecting sludge dewatering efficiency. In addition, future research anticipated directions and outlooks are proposed. This work is expected to provide valuable insights for developing efficient, eco-friendly, and low-energy consumption techniques for deep sludge dewatering.

Research progress in improving sludge dewaterability: sludge characteristics, chemical conditioning and influencing factors

Sludge from wastewater treatment processes with high water content and large volume has become an inevitable issue in environmental management. Due to the challenging dewatering properties of sludge, current mechanical dewatering methods are no longer sufficient to meet the escalating water content standards of sludge. This paper summarizes the characteristics of various sludge and raises reasons for the their dewaterability differences. Affected by extracellular polymeric substances, biological sludge is hydrophilic and negatively charged, which limits the dewatering degree. The rheological properties, flocs, ionic composition, and solid phase concentration of the sludge also influence the dewatering to some extent. For these factors, the chemical conditioning measures with simple operation and excellent effect improve its dewaterability, which mainly include flocculation/coagulation, acid/alkali treatment, advanced oxidation, surfactant treatment and combined treatment. There is a growing necessity to explore the development of new chemical conditioning agents, even though traditional agents continue to remain widely used. However, the development of these new agents should prioritize finding a balance between various factors such as efficiency, effectiveness, ease of operation, environmental safety, and cost-effectiveness. Electrochemical dewatering enhances solid-liquid separation, and its coupling with chemical conditioning is also an excellent means to further reduce water content. In addition, the improvement of press filter is an effective way, which is influenced by pressure, processing time, sludge cake thickness and pore structure, filter media etc. In general, it is essential to develop new conditioning agents and enhance mechanical filtration press technology based on a thorough understanding of various sludge properties. Concurrently, an in-depth study of the principles of mechanical pressure filtration will contribute to establishing a theoretical foundation for effective deep sludge dewatering and propel further advancements in this field.

Responses of applied voltages on the archaea microbial distribution in sludge digestion

As the development of urban population led to the increase of domestic water consumption, consequently the generation of surplus sludge (SS) produced increasingly during sewage treatment processes. In order to enhance the SS resource utilization efficiency, an electricity-assisted anaerobic digestion (EAAD) system was employed to examine the alterations in the digestion broth and the characteristics of gas production. Additionally, the response of applied voltages on the distribution of archaeal community near various electrodes within the sludge was explored. The results revealed that the application of high voltages exceeding 3.0 V hindered the CH4 production but stimulated the CO2 generation. Subsequently, both CH4 and CO2 production were impeded by the applied voltages. Furthermore, the increased voltages significantly decreased the abundance of Methanomicrobia, Methanosaeta, and Methanosarcina, which were crucial determinants of CH4 content in biogas. Notably, the excessively high voltages intensities caused the AD process to halt and even inactivate the microbial flora. Interestingly, the distribution characteristics of archaeal community were influenced not only by the voltages intensity but also exhibited variations between the anode and cathode regions. Moreover, as the applied voltage intensified, the discrepancy of responses between the cathode and anode regions became more pronounced, offering novel theoretical and technical foundations for the advancement of electricity-assisted with AD technology.

Phosphorus Recovery from Whole Digestate through Electrochemical Leaching and Precipitation

Phosphorus (P) recovery from biosolids can play an important role in a circular economy. Herein, an electrochemical phosphorus recovery cell (EPRC) was proposed and examined to recover P from municipal whole digestate via simultaneous leaching and precipitation. The anode of the EPRC released P as aqueous PO₄^3--P through acidification, achieving the highest leaching efficiency of 93.3% under a current density of 30 A m^-2. When the leached P solution was treated in the cathode, native metals including Ca and Fe facilitated electrochemically mediated PO₄^3--P precipitation (EMP) and precipitated ∼99% of the leached P in the cathode chamber. Around 54.3-78.7% of total P existed in two harvestable forms: suspended solids in the cathode effluent and immobilized P in the cathode chamber. The solid products contained 28.42-33.51% of P₂O₅, comparable to the high-grade phosphate rock. Higher current densities reduced cathode scaling and resulted in a lower content of heavy metals in the solid products. An acidic solution was reused three times and effectively maintained cathode performance during a 42-cycle operation, achieving a consistent P recovery efficiency of nearly 80%. Those results have demonstrated the feasibility of the EPRC for recovering P from P-rich solid wastes.

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.