Improvement of sludge dewaterability by energy uncoupling combined with chemical re-flocculation: Reconstruction of floc, distribution of extracellular polymeric substances, and structure change of proteins

Accelerated sludge granulation of novel complete ammonium and nitrate removal via denitratation anammox over nitrite process at elevated loading rates

The Complete Ammonium and Nitrate Removal via Denitratation Anammox Over Nitrite (CANDAN) process was evaluated for rapid sludge granulation in a lab-scale sequencing batch reactor. Over 119 days under increasing nitrogen loading rates (NLRs), the system finally achieved average 89.2 % total nitrogen removal at 1.93 kg N/m3/d NLR, with sludge particle sizes increasing from 215.6 μm to 924.5 μm. Higher NLRs significantly increased extracellular polymeric substances, especially hydrophobic proteins, enhancing sludge hydrophobicity and aggregation. Metagenomic analysis identified Candidatus Brocadia and Thauera as predominant and key microbial genera for nitrogen removal. Furthermore, the upregulation of carbon metabolism under heightened NLRs facilitated the synthesis of hydrophobic amino acids, promoting sludge granulation. These findings demonstrate NLR-driven granulation mechanisms, highlight optimizing NLR as key for accelerating granulation, providing insights to improve start-up and operational efficiency of CANDAN systems.

Insights into the roles and mechanisms of coconut shell biochar and coke in anaerobic digestion of river snail rice noodle wastewater

The effects of coconut shell biochar and coke on anaerobic digestion of river snail rice noodle wastewater treatment were assessed, and the microbial community, and methane metabolic pathways were investigated. When the hydraulic retention time was 24 h, the average chemical oxygen demand (COD) removal rates in the reactors with coconut shell biochar and coke were 94.02% and 88.68%, respectively; when the hydraulic retention time was 12 h, the average COD removal rates were 91.32% and 85.47%, respectively. The addition of coconut shell biochar and coke increased the activity of protease in the sludge from 0.45% to 29.31% and from 1.00% to 21.35%, respectively. The addition of coconut shell biochar and coke to the two anaerobic reactors promoted the growth of Euryarchaeota, Proteobacteria, and Chloroflexi. In glycolysis, the key genes glk, pfk and pk were upregulated by 3.15%, 5.22%, and 0.44% in the coconut shell biochar reactor and 8.97%, 1.93% and 3.73% in the coke reactor, respectively, and the keytricarboxylic acid (TCA) cycle genes kor, frd, and mdh were also up-regulated.

In-situ rapid cultivation of aerobic granular sludge in A/O bioreactor by using Ca(ClO)2 pretreating sludge

The efficient utilization of residual sludge and the rapid cultivation of aerobic granular sludge in continuous-flow engineering applications present significant challenges. In this study, aerobic granular cultivation was fostered in a continuous-flow system using Ca(ClO)2-sludge carbon (Ca-SC). Ca-SC retained the original sludge properties, contributing to granular growth in an A/O bioreactor. By day 40, the granule diameters increased to 0.8 mm with the SVI30 decreased by 2.7 times. Moreover, Ca-SC facilitated protein secretion, reaching 98.06 mg/g VSS and enhanced the hydrophobicity to 68.4 %. The continuous-flow aerobic granular sludge exhibited a nutrient removal rate above 90 %. Furthermore, Tessaracoccus and Nitrospira were enriched to promote granular formation and nitrogen removal. The residual sludge was carbonized and reused in the traditional wastewater treatment process to culture granular sludge in situ, aiming to achieve "self-production and self-consumption" of sludge and promote the innovative model of "treating waste with waste" in urban sewage environmental restoration.

Effect of magnetic field coupled magnetic biochar on membrane bioreactor efficiency, membrane fouling mitigation and microbial communities

The excitation by magnetic field was established to mitigate the membrane fouling of magnetic biochar (MB)-supplemented membrane bioreactor (MBR) in this study. The results showed that the transmembrane pressure (TMP) increase rates decreased by about 8 % after introducing the magnetic field compared with the magnetic biochar-MBR (MB-MBR). Membrane characterization suggested that the flocs in the magnetic field-magnetic biochar-MBR (MF-MB-MBR) formed a highly permeable developed cake layer, and a fluffier and more porous deposited layer on membrane surface, which minimized fouling clogging of the membrane pores. Further mechanistic investigation revealed that the decrease in contact angle of fouled membrane surface in MF-MB-MBR, i.e. an enhanced membrane hydrophilicity, is considered important for forming highly permeable layers. Additionally, the magnetic field was demonstrated to have a positive effect on the improvement of the magneto-biological effect, the enhancement of charge neutralization and adsorption bridging between sludge and magnetic biochar, and the reduction of formation of extracellular polymeric substances (EPSs), which all yielded sludge flocs with a large pore structure conducive to form a fluffy and porous deposited layer in the membrane surface. Furthermore, high-throughput sequencing analysis revealed that the magnetic field also led to a reduction in microbial diversity, and that it promoted the enrichment of specific functional microbial communities (e.g. Bacteroidetes and Firmicutes) playing an important role in mitigating membrane fouling. Taken together, this study of magnetic field-enhanced magnetic biochar for MBR membrane fouling mitigation provides insights important new ideas for more effective and sustainable operation strategies.

Sustained oxidation of Tea-Fe(III)/H2O2 simultaneously achieves sludge reduction and carbamazepine removal: The crucial role of EPS regulation

Establishing an economic and sustained Fenton oxidation system to enhance sludge dewaterability and carbamazepine (CBZ) removal rate is a crucial path to simultaneously achieve sludge reduction and harmless. Leveraging the principles akin to "tea making", we harnessed tea waste to continually release tea polyphenols (TP), thus effectively maintaining high level of oxidation efficiency through the sustained Fenton reaction. The results illustrated that the incorporation of tea waste yielded more favorable outcomes in terms of water content reduction and CBZ removal compared to direct TP addition within the Fe(III)/hydrogen peroxide (H2O2) system. Concomitantly, this process mainly generated hydroxyl radical (•OH) via three oxidation pathways, effectively altering the properties of extracellular polymeric substances (EPS) and promoting the degradation of CBZ from the sludge mixture. The interval addition of Fe(III) and H2O2 heightened extracellular oxidation efficacy, promoting the desorption and removal of CBZ. The degradation of EPS prompted the transformation of bound water to free water, while the formation of larger channels drove the discharge of water. This work achieved the concept of treating waste with waste through using tea waste to treat sludge, meanwhile, can provide ideas for subsequent sludge harmless disposal.

Targeted regulation of digestate dewaterability by the ozone/persulfate oxidation process

Dewatering is the first step in the subsequent treatment and disposal of food waste digestate (FWD). However, FWD is difficult to dewatering. In this study, persulfate was synergistic oxidized by ozone to improve digestate dewaterability. The optimal conditions was at pH = 3, O3＝40 mg/g TS and PDS＝0.1 g/g TS, under which the reductions in the normalized capillary suction time (NCST) and bound moisture (BM) of the FWD were 89.97% and 65.79%, respectively. Hydrophilic functional groups (oxygen- and nitrogen-containing groups) and hydrophilic protein molecular structures were decomposed by the reactive species of sulfate radical (SO4·-) and hydroxyl radicals (·OH) generated in the ozone-persulfate oxidation process, disrupting the binding between EPS and water molecules. The contributions of SO4·- and ·OH to digestate dewaterability were 42.51% and 28.55%. In addition, the introduction of H+ reduced electrostatic repulsion and contributed to the condensation of digestate flocs. The environmental implication assessment and economic analysis suggested that the O3/PDS oxidation process was cost-effective and has a low environmental implication when applied to the FWD dewaterability improvement process. These results can serve as a reference for the management of FWD and further improvement of FWD treatment and disposal efficiency.

Enhanced dewaterability of food waste digestate by biochar/potassium ferrate treatments: Performance and mechanisms

The combined process of biochar (BC) and potassium ferrate (PF) offers a fascinating technique for efficient dewatering of digestate. However, the effects of BC/PF treatment on the dewaterability and mechanisms of FWD are still unknown. This study aimed to reveal the impact mechanisms of BC/PF treatment on digestate dewatering performance. Experimental results indicated that BC/PF treatment significantly enhanced the dewaterability of digestate, with the minimum specific resistance to filtration of (1.05 ± 0.02) × 1015 m·kg-1 and water content of 57.52 ± 0.51% being obtained at the concentrations of 0.018 g·g-1 total solid (TS) BC300 and 0.20 g·g-1 TS PF, which were 8.60% and 13.59% lower than PF treatment, respectively. BC/PF treatment proficiently reduced the fractal dimension, bound water content, apparent viscosity, and gel-like network structure strength of digestate, as well as increased the floc size and zeta potential of digestate. BC/PF treatment promoted the conversion of extracellular polymeric substances (EPS) fractions from inner EPS to soluble EPS, increased the fluorescence intensity of the dissolved compounds, and enhanced the hydrophobicity of proteins. Mechanisms investigations showed that BC/PF enhanced dewatering through non-reactive oxygen species pathways, i.e., via strong oxidative intermediate irons species Fe(V)/Fe(IV). BC/PF treatment enhanced the solubilization of nutrients, the inactivation of fecal coliforms, and the mitigation of heavy metal toxicity. The results suggested that BC/PF treatment is an effective digestate dewatering technology which can provide technological supports to the closed-loop treatment of FWD.

Deep-dewatering of sewage sludge using double dielectric barrier discharge (DDBD) plasma technology

Deep dewatering of sewage sludge is essential for optimizing disposal and resource recovery. This study explores the potential of Double Dielectric Barrier Discharge (DDBD) plasma for enhancing waste activated sludge (WAS) dewatering. Key operational parameters (applied voltage, treatment duration, and air feeding rate) were systematically investigated using a two-step approach: Single Factor-at-a-Time (SFAT) and central composite design (CCD) within the response surface methodology (RSM) framework. The aim was to identify influential factors and their optimal settings for maximizing dewatering efficiency while minimizing energy usage. Higher applied voltages (30 kV) and longer treatment durations (40 min) notably improved % moisture reduction (%MR) (92.92 % and 94.35 %, respectively). ANOVA analysis emphasized the equal and substantial impact of applied voltage and treatment duration on %MR and energy efficiency (EE), whereas the air feeding rate exhibited no significant effect. However, it's worth noting that %MR and EE did not display a strictly linear relationship, suggesting complex interactions. Furthermore, two soft sensing models were developed: a quadratic model for %MR and a linear model for energy efficiency (EE). Results showed minimal reductions in TOC content, maintaining values between 13.68 % and 14.28 % compared to untreated sludge 14.37 %. The study also revealed that ROS generated by DDBD plasma played a key role in sludge disintegration, as observed through SEM and FTIR, enhancing dewatering efficiency by the destruction of sludge flocs and the transformation of organic substances. In conclusion, DDBD plasma technology offers a sustainable solution for effective sludge dewatering in WWTPs, preserving organic content.

Ascorbic acid reduction pretreatment enhancing metal regulation to improve methane production from anaerobic digestion of waste activated sludge

Conversion of waste activated sludge (WAS) to methane by anaerobic digestion (AD) is often limited by the slow rate of hydrolysis, and the presence of metal ions in sludge is regarded as a critical factor hindering sludge hydrolysis. This study developed a novel strategy to remove Fe from WAS by using ascorbic acid (VC) as a reducing agent under acidic conditions. The feasibility of reduction pretreatment in improving methane production of AD and its intrinsic mechanism were investigated. Results indicate that, under VC doses of 100 mmol/L and pH of 3.50, pretreatment removed 47.60 % of Fe, 59.88 % of Ca, and 51.86 % of Mg contained in the sludge. The removal of metal ions facilitated the disruption of sludge flocculation structure and extracellular polymeric substance (EPS) layers, leading to a 14.78 % increase in cell lysis and a decrease in fractal dimension values to 2.08. Batch AD experiments showed that VC pretreatment improved methane production, with an optimized net methane yield of 190.22 mL/g·VS, an increase of 134.75 % compared to raw WAS. The pretreatment affected the interfacial interaction energy of the sludge, leading to a transformation in the sludge surfaces from hydrophilic to hydrophobic, reducing the interaction between sludge molecules and increasing the number of binding sites available for enzymatic reactions. According to a study of microbial communities, it was found that VC pretreatment caused an increase in the presence of essential functional microbes responsible for hydrolysis, acidification, and methanation. This increase in acetoclastic and hydrogenotrophic methanogens resulted in a substantial enhancement in methane production. These results can be used to develop better pretreatment methods to enhance AD performance.

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.

Effects of ceramsite derived from sewage sludge combined with the O3-FeCl3/PAM process on the dewatering of waste-activated sludge and investigation of dewatering mechanisms

The high water content of waste-activated sludge restricts the subsequent disposal of sludge. The dehydration properties of O₃, ferric chloride (FeCl₃)/polyacrylamide, and sludge ceramsite sand (SCS) were studied. Simultaneously, the effect of combining the three was investigated to support the deep dehydration of waste-activated sludge. Experimental results showed that with13.42 mg/(g dry solids (DS)) of O₃, 109.89 mg/(g DS) of FeCl₃, and 100 mesh dosage of 70% DS of sludge ceramsite on weight, the highest sludge net yield was 7.13 kg/(m²·h) and the minimum specific resistance to filtration of sludge cake was 1.02 × 10¹² (m/kg). Compared with the compressibility of the raw sludge, the compressibility of the sludge cake decreased by 37.48%. Moreover, the Y_N (net yield) increased by 73.55%. The results demonstrate that the structure of cracking, flocculation, and hydrophobic framework is the mechanism of sludge dewatering in this combined process. This combined treatment process provides a new perspective for the realization of deep dewatering of sludge and is anticipated to be a successful sludge dehydration method.

Evaluation of Efficiently Removing Secondary Effluent Organic Matters (EfOM) by Al-Based Coagulant for Wastewater Recycling: A Case Study with an Industrial-Scale Food-Processing Wastewater Treatment Plant

The reuse of wastewater has been identified as an important initiative for the sustainable development of the environment; thus, the removal of secondary effluent organic matter (EfOM) to ensure the safety of reused wastewater is the key step and a subject of extensive research. In this study, Al₂(SO₄)₃ and anionic polyacrylamide were selected as coagulant and flocculant, respectively, for the treatment of secondary effluent from a food-processing industry wastewater treatment plant to meet the standard regulatory specifications for water reuse. In this process, the removal efficiencies of chemical oxygen demand (COD), components with UV₂₅₄, and specific ultraviolet absorbance (SUVA) were 44.61%, 25.13%, and 9.13%, respectively, with an associated reduction in chroma and turbidity. The fluorescence intensities (Fmax) of two humic-like components were reduced during coagulation, and microbial humic-like components of EfOM had a better removal efficiency because of a higher Log Km value of 4.12. Fourier transform infrared spectroscopy showed that Al₂(SO₄)₃ could remove the protein fraction of the soluble microbial products (SMP) of EfOM by forming a loose SMP protein complex with enhanced hydrophobicity. Furthermore, flocculation reduced the aromaticity of secondary effluent. The cost of the proposed secondary effluent treatment was 0.034 CNY t^-1 %COD^-1. These results demonstrate that the process is efficient and economically viable for EfOM removal to realize food-processing wastewater reuse.

Enhanced sludge dewaterability by ferrate/ferric chloride: The key role of Fe(IV) on the changes of EPS properties

The complex characteristics of extracellular polymeric substances (EPS) seriously affect the improvement of sludge dewaterability. Ferrate (Fe(VI))/ferric chloride (Fe(III)) was applied through its strong oxidability to effectively enhance sludge dewaterablity by changing the properties of EPS in this study. Results confirmed that water content (WC), specific resistance to filtration (SRF) and capillary suction time (CST) fell from 82.8 %, 9.3 × 10¹⁰ s²/g and 35.1 s to 76.1 %, 2.6 × 10¹⁰ s²/g and 16.2 s, respectively, when adding 12 mg Fe(VI)/g VSS and 12 mg Fe(III)/g VSS with the dosing interval of 5 min. Investigations of the mechanism strongly suggested that Fe(VI) was successfully catalyzed by Fe(III), promoting the generation of methyl phenyl sulfone (PMSO₂) and facilitating the electron transfer, with Fe(IV) having the major role in the oxidation process. Furthermore, sludge water-holding capacity and hydrophilicity waned after oxidation due to the destruction of EPS structure, which promoted the decrement of bound water to enhance the discharge of sludge water, so as to improve the efficiency of dewatering.

In-Situ Sludge Reduction in Membrane-Controlled Anoxic-Oxic-Anoxic Bioreactor: Performance and Mechanism

Conventional and advanced biological wastewater treatment systems generate excess sludge, which causes socio-economic and environmental issues. This study investigated the performance of membrane-controlled anoxic-oxic-anoxic (AOA) bioreactors for in-situ sludge reduction compared to the conventional anoxic-oxic-oxic membrane bioreactor (MBR_control). The membrane units in the AOA bioreactors were operated as anoxic reactors at lower sludge recirculation rates to achieve hydrolysis of extracellular polymeric substances (EPS) and extensive endogenous respiration. Compared to MBR_control, the AOA bioreactors operated with 90%, and 80% recirculation rates reduced the sludge growth up to 19% and 30%, respectively. Protein-like components were enriched in AOA bioreactors while fulvic-like components were dominant in MBR_control. The growth of Dechloromonas and Zoogloea genra was promoted in AOA bioreactors and thus sludge reduction was facilitated. Metagenomics analysis uncovered that AOA bioreactors exhibited higher proportions of key genes encoding enzymes involved in the glycolysis and denitrification processes, which contributed to the utilization of carbon sources and nitrogen consumption and thus sludge reduction.

Enhanced Dewatering of Activated Sludge by Skeleton-Assisted Flocculation Process

Sludge dewatering is the fundamental process of sludge treatment. Environmentally friendly and efficient sludge conditioning methods are the premises of sludge to achieve dehydration reduction and resource utilization. In response to sewage plant sludge dehydration, fly ash (FA), polymerized aluminum chloride (PAC), and polymer sulfate (PFS) were studied separately to determine their sludge dehydration performance, and the effects of these three conditioner composite regulations on sludge dehydration properties were studied. Compared to the sludge treated only with conditioner, the average particle size of floc increased and the organic matter content in the filtrate decreased. The sludge dewatering efficiency after the conditioning effect is better than that after conditioning a single conditioner. After PFS conditioning with fly ash, the water content and specific resistance (SRF) of the sludge cake can be reduced to 76.39% and 6.63 × 10¹⁰ m/kg, respectively. The moisture content and specific resistance (SRF) of the sludge cake can be reduced to 76.10% and 6.91 × 10¹⁰ m/kg, respectively. The pH of the sludge and filtrate changed slightly after PAC conditioning with fly ash coupling. These results indicate that fly-ash coupled with PAC and fly-ash coupled with PFS are expected to become a novel and effective environmental protection combined conditioning method for sludge dewatering.