Water Content Of Sludge Cake Research Articles

Sludge dewaterability improvement in microbial fuel cell powered electro-Fenton system (MFCⓅEFs) coupled with chitosan quaternary ammonium salt

As improved and expanded wastewater treatment facilities, sludge dewatering is the essential process and major challenge due to the complex and abundant organic matter. Microbial fuel cell powered electro-Fenton system (MFCⓅEFs) has been demonstrated to generate •OH and destroy hydrophilic extracellular polymeric substances (EPS) as an improved method of high efficiency and low energy consumption. Nevertheless, the smaller particle size of the treated sludge and the release of partial organic matter into the supernatant can affect the sludge-water separation process. Chitosan quaternary ammonium salt (CQAS) as a renewable and biodegradability cationic coagulant can be involved in the follow-up treatment. The sludge after combined treatment exhibited better dewaterability, where the water content of sludge cake (WCSC), capillary suction time (CST), and specific resistance filtration (SRF) were 61.21%, 15.6 s, and 1.02×1012 m/kg (26.47%, 80.72% and 84.28% reduction), respectively. The oxidation of the MFCⓅEFs destroyed the cellular and EPS structure and the bridging flocculation and charge neutralization of CQAS caused the fine particles to squeeze each other. The combined treatment fully reduced the content of negative charge and hydrophilic substances on the surface, which affected the intensity change of N-H bond and altered the protein secondary structure to make it looser, thus releasing more bound water while improving aggregation characteristics. Overall, combined treatment can significantly improve sludge dewaterability and owns operational advantages of high efficiency, low energy and consumption, safety, and non-toxicity.

Sludge carbon quantum dots-activated peroxymonosulfate oxidation for sludge conditioning

Large amounts of waste activated sludge (WAS) are produced from biological treatment processes in wastewater treatment plants, and its effective disposal and reutilization are considered to be inevitable challenges in the world. In this work, carbon quantum dots derived from WAS (SCQDs) were successfully synthesized via hydrothermal method, which had a significant photoluminescence effect, excellent water solubility, and graphite structures with main elements of C, N, and O. Subsequently, its potential for peroxymonosulfate (PMS) activation under visible light for WAS conditioning was investigated. The results showed that SCQDs-activated PMS (SCQDs-PMS) system could effectively improve sludge dewaterability. Under experimental conditions, capillary suction time reduction and water content of sludge cake after conditioning were 81.2% and 72.6%, respectively. Reactive oxygen species including SO4·-, ·OH, and 1O2 produced in SCQDs-PMS system could effectively degrade extracellular polymeric substances (EPS) (especially tyrosine-like and tryptophan-like substances in tightly bound-EPS), inactivate microbial cells, and destruct α-helix structure of protein molecule, which resulted in the desirable release of EPS-bound water, consequently improving sludge dewaterability. This result was well supported by the variations in the transverse relaxation time of protons at low field nuclear magnetic resonance. Thus, this work explored a potential pathway of reutilizing sludge and a new activator for PMS activation. However, it should be noticeable that this work was the first attempt using SCQDs-PMS system for sludge conditioning, the future studies about system optimization and its wider application scenarios should be further investigated.

Insight into enhancing the performance of sludge dewatering using a novel flocculant CS–TA prepared through free radical-mediated conjugation

ABSTRACT Flocculation is one of the most significant conditioning methods for sludge dewatering. In the study, a novel flocculant CS–TA, prepared through free radical-mediated conjugation of tannic acid (TA) and chitosan (CS), was proposed to improve sludge dewatering. The characterisation using Fourier transform infra-red spectroscopy and X-ray diffraction analysis shows that the CS chain was the backbone of CS–TA, and the presence of CS–TA aromatic rings confirmed the conjugation of CS with TA. Moreover, the conditioning of CS–TA yielded the best dewatering performance at 30 mg g TS−1 with the water content of sludge cake by press filtration (Wsc) of 59.78% ± 0.3% and capillary suction time (CST) of 11.8s ± 0.35 s, compared to 98.2% ± 0.15% and 56.2 s ± 0.16 in raw sludge. The results of different influencing factors (e.g. pH and temperature) on flocculation efficiency indicated that CS–TA possessed the capacity for enhancing sludge dewaterability over a wide range of pH, and the optimal temperature was observed to be 35 °C. Furthermore, the increase of particle size and zeta potential implied the addition of CS–TA favoured the formation of larger particles charge neutralisation and adsorption bridging effect. In addition, extracellular polymer substances (EPS) analysis indicated that the decrease in the polysaccharide and protein contents in EPS after CS–TA addition could increase the relative hydrophobicity of sludge. Moreover, the contents of heavy metals in sludge and their leaching toxicity and environmental risk were reduced. This study provides comprehensive insights into the exploration of CS–TA for sludge dewatering and the maintenance of ecological security in an eco-friendly.

Improving anaerobic digestion sludge properties via heterogeneous activation of peroxydisulfate by CuMgAl-layered double hydroxide

Improving anaerobic digestion sludge (ADS) properties by conditioning technology is necessary for subsequent treatment and disposal. In this study, CuMgAl-layered double hydroxide (CuMgAl-LDH) was prepared by co-precipitation method and applied to activate peroxydisulfate (PDS) for ADS conditioning. Experimental results indicated that under the optimal treatment condition (0.15 g LDH/g TS and 0.2 g PDS/g TS addition), the water content of sludge cake and the time to filter decreased from initial 90.83 % to 82.91 % and 75 min to 39.5 min, respectively, and ortho-P as well as non-biodegradable organics contents in the AD liquor (ADL) also decreased remarkably, which was beneficial for ADS dewatering and subsequent ADL backflow treatment. CuMgAl-LDH activating PDS could produce abundant reactive oxygen species (ROS), resulting in microbial cell disruption, bound water release, sludge particle size decrease and non-biodegradable organics degradation. Mechanisms investigation based on the X-ray photoelectron spectroscopy, electron paramagnetic resonance and ROS quenching experiments results indicated that Cu(I)/Cu(II) redox cycle was responsible for PDS activation, and SO4−· made primary contribution to sludge flocs and cells disruption. This research provided preliminary guideline to design copper-based LDH/PDS system for ADS conditioning in wastewater treatment plants.

Optimization of electro-dewatering performance of oily sludge by voltage control and coal-powdered activated carbon (CPAC) addition

Electro-dewatering technology (EDW) exhibits promising prospects for oily sludge reduction treatment, owing to its remarkable dewatering efficiency. Unlike conventional oily sludge dewatering methods, EDW eliminates the need for chemical additives, mitigating the risk of secondary contamination. This study comprehensively investigates the impacts of voltage and coal-powdered activated carbon (CPAC) on the performance of EDW, as well as the properties of the dewatered sludge cake. Moreover, the underlying EDW mechanism is delved into the exploration. The water content decreased from 79.01% to 63.25% with the application of 40 V and 25 kPa pressure, while the dewatering rate increased from 0.025 g/s to 0.055 g/s, with the best electro-dewatering performance. Furthermore, the incorporation of CPAC significantly optimized the electro-dewatering performance, by reducing the viscosity, electrical resistance of the sludge cake and created more mechanical channels for water migration. Introducing 7.5% CPAC (wt.%) achieved the highest dewatering rate of 0.078 g/s with 57.14% final water content of sludge cake. The EDW process enabled discharge of heavy metal ions from oily sludge cake. Additionally, the addition of CPAC contributed to reduced unit energy consumption and improved calorific value of oily sludge cake. This study provides a sustainable and environmentally-friendly technology for the efficient dewatering and subsequent resource utilization of oily sludge, offering considerable potential for both environmental and economic benefits.

Chalcopyrite-activated sodium percarbonate oxidation for sludge dewaterability enhancement: Synergetic roles of •OH and 1O2

Efficient dewatering of sewage sludge is an energy- and carbon-saving procedure of sludge treatment in wastewater treatment facilities. Due to the limiting factors of hydrophilic extracellular polymeric substances, it is crucial to weaken the water-holding capacity and hydrophilicity for high-performance sludge-water separation. The current study successfully put forward a combination process of chalcopyrite + sodium percarbonate (SPC) to proficiently facilitate sludge dewaterability. Results showed that after the optimized treatment, the water removal efficiency augmented from 51.3 to 94.9%, while the water content of sludge cake declined from 90.1 to 52.0 wt%. Mechanism investigation demonstrated that the chalcopyrite + SPC system could consecutively generate reactive oxygen species via strong Fe3+/Fe2+ and Cu2+/Cu+ conversion cycles. The dominant reactive radical •OH and non-radical 1O2 could effectively degrade the macromolecular EPS into low-molecular biopolymers, decrease the high-polarity hydrophilic protein secondary structure and amino acids, and further reduce water-holding interfacial affinity. Afterward, the electrostatic force and interfacial free energy were decreased and turned out to enhance self-flocculation and flowability. Accordingly, bound water reduction and sludge-water separation efficiency were promoted. Furthermore, the chalcopyrite + SPC system could be viewed as a surrogate to Fenton/Fenton-like strategies for sludge dewaterability with economic advantage and low environmental risk. These findings inspire the application prospect of the chalcopyrite + SPC conditioning technique, which expects to save energy and reduce carbon emissions.

Evaluation of pre-magnetization on the dewaterability of waste activated sludge treated by ozonation

The dewaterability of waste activated sludge (WAS) plays the key role in sludge dewatering in wastewater treatment plants. The magnetic field as a source of clean energy has been reported to be able to cause changes in sludge properties and to enhance sludge dewatering by chemical treatment. This paper focuses on the effect of pre-magnetization on the sludge dewatering performance by ozonation. The results showed that ozonation reduced the capillary suction time (CST) and water content of sludge cake (Wsc) of WAS. The CST reduced from 21.5 ​s to 12.7 ​s; and the Wsc reduced from 85.6% to 85%. However, the addition of pre-magnetization with a magnetic field did not make much improvement of the dewaterability. Further investigation on sludge properties such as EPS, TOC, particle size, and the SEM images of the treated WAS showed that the pre-magnetization prior to ozonation led to stronger oxidation and WAS particle broken, which was proofed not necessarily correlated to sludge dewaterability enhancement.

Effect of modified kaolin conditioning sludge on organic matter properties

This paper studied the dewatering performance of modified kaolin conditioned sludge, and focused on the molecular composition and transformation of extracellular biological organic matter (EBOM) and supernatant dissolved organic matter (DOM) during the conditioning process. The results showed that the sludge dewatering performance was significantly improved after conditioning with modified kaolin. Under the dosage of 20% DS (200 g conditioner was added to each 1 kg sludge dry solids), the specific resistance to filtration (SRF) of sludge was reduced by 85.05%, the water content of sludge cake was decreased to 66.70%, and the time to filter (TTF) reduction rate was increased to 71.35%. The modified kaolin can broke the structure of sludge floc, which caused the transfer of organic matter from the solid phase to the liquid phase, thus promoting the release of bound water. In this process, the hydrophilic fraction in the inner layer of the sludge floc was released and enhanced the aromaticity of supernatant DOM. The transfer of proteins of the acidic fractions and polysaccharides of each fraction in the sludge EBOM to the supernatant DOM occurred. The reduction of hydrophobic and transitional proteins, hydrophobic and neutral humic acid-like substances, soluble microbial byproducts-like and fulvic acid-like materials in the sludge EBOM facilitated the breakage of the sludge floc.

Enhanced paper sludge dewatering and in-depth mechanism by oxalic acid/Fe2+/persulfate process

As a typical advanced oxidation process, Fe2+-persulfate (PDS) oxidation technology has been widely and efficiently reported for enhancing sludge dewaterability. However, higher dosage of Fe2+ must be added, which will restrain the oxidation efficiency of Fe2+-PDS process. In this work, the oxalic acid (OA)/Fe2+-PDS process was studied to improve paper sludge dewatering. With the OA dosage of 6 μmol (g total solid (TS))−1, Fe2+ dosage of 0.3 mmol (g TS)−1, and PDS dosage of 0.6 mmol (g TS)−1, sludge dewaterability was improved more efficiently. The specific resistance to filtration and water content of sludge cake were decreased by 70.7% and 8.0%, respectively. In comparison with Fe2+-PDS process, the viscosities of sludge suspension and supernatant were further reduced by 3.73% and 51.77%, respectively, and the contents of extracellular polymeric substances fractions were increased. The improved sludge dewaterability in OA/Fe2+-PDS process was mainly contributed by the synergistic effect of oxidative disintegration by free radicals and flocs re-flocculation, the contributions of which were the orders: metal cations > sulfate radical > hydroxyl radical. OA enhanced the efficient disintegration of sludge flocs, released more bound water, generated more Fe3+-oxalate complexes, and finally increased the sludge particle size significantly, forming a larger aggregation and obvious cracks. Additionally, the stabilization of several heavy metals was improved due to the chelating capacity of OA. These works will provide a novel approach for sludge dewatering in the PDS oxidation process.

Improving sludge dewaterability by free nitrous acid and lysozyme pretreatment: Performances and mechanisms

Reducing the water content of waste activated sludge (WAS) is critical for sludge treatment and disposal in wastewater treatment plants (WWTPs). In this study, a new combined conditioning processes by using lysozyme (LZM) and free nitrous acid (FNA) were proposed and demonstrated to enhance the dewaterability of WAS. The water content of sludge cake dropped from 82.82 % to 68.42 % (1 h FNA treatment + 1 h LZM treatment) and 69.52 % (6 h FNA treatment + 1 h LZM treatment) with the combined FNA and LZM treatment; and the corresponding capillary suction time (CST) reduction efficiency increased 49.29 % (1 h FNA treatment + 1 h LZM treatment) and 52.98 % (6 h FNA treatment + 1 h LZM treatment). A comprehensive investigation conducted in this study revealed the underlying mechanism of dewaterability improvement lies in the transformations of extracellular polymeric substances (EPS). The combined conditioning led to enhanced hydrophobicity in the sludge, as suggested by FTIR protein secondary structure and interfacial free energy. The reduced zeta potential and the potential barrier indicated the reduction of the repulsive force of sludge particles and the bound water content in the conditioned floc. The hydrophobicity, flow permeability and flocculability were enhanced after combined treatment, leading to the release of bound water.

Electrochemically driven Fe0-activated sulfite oxidation for enhancing sludge dewaterability

Sulfate radical (SO4·-)-based advanced oxidation processes (SR-AOPs) are promising for sludge dewatering. In this work, an electrochemically driven Fe0-activated sulfite system (E/Fe/sulfite) was developed and demonstrated for sustainably releasing Fe2+ to activate sulfite for dewatering waste activated sludge. Under the optimal conditions (sulfite dosage = 40 mg/g dry solids, current density = 30 mA/cm2, pH = 6, and time = 60 min), the reduction of capillary suction time and water content of sludge cake were 87.9 ± 2.8 % and 73.1 ± 0.8 %, respectively. The improved dewatering performance was attributed to the degradation of tightly-bound extracellular polymeric substances, along with the decreased live/dead cell ratio and the increased permeability of sludge flocs. The thermal effect (∼21–59 °C) in the E/Fe/sulfite system accelerated the release of intracellular proteins, which could be effectively degraded by the strong oxidizing SO4·-. The results also suggested that electrochemical oxidation and thermal effect in the E/Fe/sulfite system had a synergistic impact on improving sludge dewaterability. According to the density functional theory calculation, the hydrophobic amino acids produced from protein degradation were favorable for forming the drainage channels and enhancing sludge dewaterability. This study provides new insights for understanding the SR-AOPs and their applications to sludge treatment.

Multiple environmental risk assessments of heavy metals and optimization of sludge dewatering: Red mud–reed straw biochar combined with Fe2+ activated H2O2

In this study, Fe-rich biochar (RMRS-BC) was prepared from red mud and reed straw to improve sludge dewatering and transformation of heavy metals (HMs, including Cd, Cr, Cu, Pb, and Zn). The optimal concentrations of RMRS-BC, Fe2+, and H2O2 to promote sludge dewaterability were identified by response surface methodology (RSM). The optimal dosages of RMRS-BC, Fe2+, and H2O2 were 74.0, 104.9, and 75.7 mg/g dry solids (DS), respectively. The corresponding capillary suction time (CST) and water content of sludge cake were 14.3 s and 51.25 wt%. For the improvement mechanism, heterogeneous and homogeneous Fenton reactions occurred due to RMRS-BC and Fe2+ activating H2O2. The extracellular polymeric substances (EPS) decomposed into dissolved organic matter (proteins and polysaccharides), thereby promoting the transformation of bound water to free water and further reducing the water content of the sludge cake. The research quantitatively assessed the environmental risk of heavy metals in the conditioned sludge cake based on bioavailability and ecotoxicity, pollution levels and potential ecological risks. Compound conditioning using RMRS-BC, Fe2+, and H2O2 could significantly improve the solubility and reduce the leaching toxicity of HMs. In general, RMRS-BC combined with Fe2+ to activate H2O2 provided an effective method to enhance sludge dewaterability and reduce HMs risk.

Insights into cetyl trimethyl ammonium bromide improving dewaterability of anaerobically fermented sludge

Cetyl trimethyl ammonium bromide (CTAB) is considered a promising sludge dewatering conditioner, but its potential dewatering mechanism has not been thoroughly understood. This study, therefore, aims to fully investigate how CTAB improves sludge dewaterability. Experimental results showed that after sludge was conditioned by 75 mg/g TSS CTAB, capillary suction time (CST), specific resistance to filtration (SRF), and the water content of sludge cake (WCSC) by vacuum filtration decreased from 164.1 ± 10.7 s, 1.90 ± 0.05 × 1012 m/kg, and 97.36 ± 0.12 % to 32.1 ± 1.4 s, 0.18 ± 0.01 × 1012 m/kg, and 70.55 ± 0.21 %, respectively. Mechanism revelations showed that CTAB could neutralize the negative charges on EPS surface and reduce the repulsive force between sludge particles to reduce the Zeta potential; CTAB could also enhance the hydrophobicity and the adhesion among the sludge particles to reduce the surface energy, and CTAB could release the intracellular water by damaging the outer membrane of sludge cells. The presence of CTAB also decreased the concentrations of PO43-, humic acid, and proteins in the liquid phase through electrostatic attractive or hydrophobic interactions. All these CTAB-caused variations in either the solid or liquid phase of sludge could result in the enhancement of sludge dewaterability. The findings deepen our understanding of CTAB affecting sludge dewatering and also might guide engineers to exploit promising strategies to facilitate sludge dewatering in the future.

Enhanced sludge dewaterability by a novel MnFe2O4-Biochar activated peroxymonosulfate process combined with Tannic acid

The high moisture content of sludge is a key factor limiting its subsequent treatment and disposal. Herein, a novel method of MnFe2O4-biochar (MFB) activated peroxymonosulfate (PMS) combined with tannic acid (TA) was conducted to improve sludge dewatering. The effects of different concentrations of MFB, PMS, and TA on waste activated sludge (WAS) dewaterability were investigated. The water content of sludge cake dropped to 40.80% when the initial pH was 5.0, and the concentration of PMS, MFB, and TA was 0.64 mM/g DS, 100 mg/g DS, and 0.12 mM/g DS respectively, demonstrating that MFB/PMS/TA could effectively enhance sludge dewaterability. Analyzing the changing of sludge properties and characterizing MFB confirmed that the enhancement of sludge dewaterability occurred in two phases. First, TA accelerated the valence transformation of Fe and Mn to promote PMS activation, which strengthened the oxidation capacity of the system. Second, TA complexed and precipitated protein to enhance the compressibility and dewaterability of sludge. Furthermore, MFB/PMS/TA treatment could increase the calorific value of treated sludge, and after the combined treatment, the sludge biochar also had a better pore structure, indicating that the sludge after the combined treatment posed a good prospect of resource utilization. These findings provide a novel strategy for the practical application of achieving efficient sludge deep dewatering, providing a valuable reference for downstream sludge utilization.

Transformation of typical components in anaerobically digested sludge during its conditioning process by KMnO4

Many efforts have been made to improve the dewaterability during anaerobically digested sludge (ADS) conditioning. However, the conversion of substances in ADS conditioning, as an important process of sludge treatment and application, has received little attention. This study investigated the transformation process of typical components in sludge such as extracellular polymeric substances (EPS), sulfide, Fe and Mn species. The effects of KMnO4 dosage and pH change on the ADS conditioning were investigated in detail. The results showed that the sludge particle size and capillary suction time decreased with the increase of KMnO4 dosage. The water content of sludge cake by vacuum filtration gradually dropped from 84.5% to 78.8% after conditioning with 0–5.0 g KMnO4/L sludge. Based on fluorescence excitation-emission matrix, EPS and dissolved organic carbon measurements, the improvement of sludge dewaterability was due to the disruption of EPS and the release of intracellular substances. Interestingly, 11.5% sulphides (S2−) in ADS were oxidized into SO42− at KMnO4 dosage of 3.0 g/L, which can effectively inhibit the release of hazardous H2S even the sludge pH changed to 2 in conditioning process. Moreover, about 30 mg/L of PO43− in centrifugate can be completely immobilized by the generated iron, manganese and their binary oxides as a result of the interaction between Fe2+ and KMnO4. These findings provided a new insight to explore the sludge conditioning process and the transformation of typical components.

Application of zero-valent iron/sulfite system for aerobically digested sludge conditioning

• ZVI/sulfite was favorable to improve AeDS dewaterability. • Dosages of ZVI and sulfite, reaction time, and pH in ZVI/sulfite were optimized. • S-AOP was the determinant process for the improvement of AeDS dewaterability. • TB-EPS degradation and release of EPS bound water led to improve dewaterability. • Reuse of recovered ZVI for improving AeDS dewaterability was satisfactory. Aerobic digestion is widely used to stabilize and reduce waste activated sludge in the decentralized wastewater treatment plants, but it would deteriorate sludge dewaterability. Thus, improving the dewaterability of aerobically digested sludge (AeDS) is of vital significance for sludge disposal and management. This study investigated the possibility of zero-valent iron (ZVI)/sulfite system for promoting the dewaterability enhancement of AeDS. The results showed that ZVI/sulfite system was favorable to improve the dewaterability of AeDS. The highest reduction of capillary suction time and the lowest value of water content of sludge cake were (81.7 ± 3.6)% and (69.3 ± 1.2)%, respectively, under the optimal experimental conditions (reaction time = 60 min, ZVI = 0.9 mmol/g volatile solids (VS), sulfite = 1.2 mmol/g VS, pH = 6, and purging air). Compared to Fe 2+ /sulfite and Fe 3+ /sulfite systems, ZVI/sulfite system was more favorable to improve the dewatering performance of AeDS. The results also demonstrated that the main radical species in ZVI/sulfite system were sulfate radical and hydroxyl radical, which could effectively degrade tightly-bound extracellular polymeric substances and then led to the release of bound water and the increase of zeta potential. Consequently, the dewatering performance of AeDS was obviously enhanced. Additionally, the reusability of recovered ZVI in ZVI/sulfite system for AeDS conditioning was satisfactory.

Aerobically digested sludge conditioning by Fe2+/citrate chelated-Fe2+ activated peroxymonosulfate oxidation

This work investigated the dewatering efficiency of aerobically digested sludge (AeDS) conditioned by peroxymonosulfate (PMS) activation using Fe2+ and citrate chelated-Fe2+ (Fe2+-Cit) as activators. The results showed that compared to Fe2+-PMS oxidation, Fe2+-Cit-PMS oxidation was more capable of improving AeDS dewaterability because of the strengthened activation of PMS by Fe2+-Cit. Under the optimal conditions (PMS = 0.9 mmol/g volatile solids (VS), Fe2+ = 0.6 mmol/g VS, and citrate = 0.3 mmol/g VS), capillary suction time reduction, water content of sludge cake, and centrifuged weight reduction were 88.3%, 67.2%, and 39.7%, respectively. The contributions of sulfate radical, hydroxyl radical, and iron ions to the enhanced AeDS dewaterability were in the sequence of sulfate radical > hydroxyl radical > iron ions. The enhanced AeDS dewaterability was mainly contributed from the efficient decomposition of tightly bound extracellular polymeric substances and the neutralization of negative surface charge. Through the addition of citrate, the primary iron species in the liquid phase of AeDS was converted from Fe2+ in Fe2+-PMS system into Fe3+ in Fe2+-Cit-PMS system. Additionally, this work demonstrated that Fe2+-PMS oxidation and Fe2+-Cit-PMS oxidation were both helpful to improve the stabilization of heavy metals in AeDS.

Peroxide/Zero-valent iron (Fe0) pretreatment for promoting dewaterability of anaerobically digested sludge: A mechanistic study

Peroxide/Zero-valent iron (Fe0) was reported to promote dewaterability of anaerobically digested sludge (ADS), but the mechanism of how Peroxide/Fe0 facilitates ADS dewatering is unknown. This study therefore aims to uncover the details of how Peroxide/Fe° elevates ADS dewaterability. Experimental results showed that with 0.6 g Fe0/g TSS and 0.08 g peroxide/g TSS, capillary suction time, specific resistance to filtration, and time to filtration of ADS was 50.7 %, 41.4 %, and 54.4 % of that in the control, respectively. In this condition, water content of sludge cake decreased from 91.2 % ± 0.5 % (the control) to 68.6 % ± 1.3 %. The mechanism explorations revealed that the elevated dewaterability was mainly caused by role of OH and Fe(II)/Fe(III) species during Peroxide/Fe° pretreatment. OH decreased the polysaccharides and proteins in extracellular polymeric substance (EPS), then injured the cytoderm & cytomembrane through the releases of lactate dehydrogenase and N-acetylglucosamine, and further facilitated the decrease of intracellular substances, which disengaged the water trapped in ADS. In addition, the cell lysis caused by OH facilitated forming macro-pores. Moreover, OH converted the conformational structure of extracellular proteins, which may strengthen the ADS hydrophobicity, promoting the discharge of unbound water and ADS flocculation. Meanwhile, Fe(II)/Fe(III) benefited aggregating the denatured ADS particulates.

Ultrasound enhanced zero-valent iron-activated peroxymonosulfate oxidation for improving dewaterability of aerobically digested sludge

Abstract In this work, ultrasound (US) assisted zero-valent iron (ZVI)-activated peroxymonosulfate (PMS) oxidation was used to improve the dewaterability of aerobically digested sludge (AeDS). Capillary suction time (CST) reduction, centrifuged weight reduction (CWR), and water content of sludge cake (Wc) were determined to evaluate AeDS dewaterability. The results showed that the optimal reaction time, PMS dosage, ZVI dosage, and US power were 20 min, 50 mg/g total solids (TS), 100 mg/g TS, and 50 W, respectively. Under the optimum conditions, CST reduction, Wc, and CWR were 89.2%, 67.9%, and 40.4%, respectively. The quenching experiments showed that sulfate radical was the dominant radical species in the US-ZVI-PMS system while hydroxyl radical in the ZVI-PMS system. Compared to ZVI-PMS treatment, US-ZVI-PMS treatment was more conducive to improve sludge dewaterability, suggesting that US assistance destructed the passive film of ZVI and accelerated its corrosion, consequently resulting in more production of sulfate radical. The significant degradation of tightly bound extracellular polymeric substances (EPS) of AeDS after US-ZVI-PMS treatment led to the releases of EPS bound water and even the intracellular water, consequently improving AeDS dewaterability. Additionally, US-ZVI-PMS treatment presented the advantages of sludge disintegration and charge neutralization. The ZVI cycle tests demonstrated that the reusability and stability of the recovered ZVI in the US-ZVI-PMS system were desirable, leading to the cost savings.

Ultrasonic coupled bioleaching pretreatment for enhancing sewage sludge dewatering: Simultaneously mitigating antibiotic resistant genes and changing microbial communities.

In this study, ultrasonic as a pretreatment coupled with bioleaching was used to enhance sludge dewaterability. Changes in microbial diversity and antibiotic resistant genes (ARGs) were studied during the combined treatment process. The results show that under optimal conditions, combined ultrasonic and bioleaching treatment led to decreases in the specific resistance of filtration and bioleaching time by 7.59% and 12.5%, respectively, compared with single bioleaching process. Using high pressure filtration system, the water content of sludge cake treated by the combined treatment was decreased to 58.04%, which was 10.04% lower than bioleaching sludge. After combined treatment, the microbial diversity and the total number of bacteria in the sludge decreased significantly, which caused the decreases in the absolute abundance of sulfonamide and tetracycline ARGs by 1.56-1.58 and 0.34-1.23 log units, respectively. However, the decrease in the total bacterial biomass was greater than the decrease in the number of potential hosts carrying the tetracycline ARG, resulting in an increase in the relative abundance of tetracycline gene. Furthermore, this study proposed a mechanism of the dewatering and ARGs, involving the combined ultrasonic and bioleaching treatment: Firstly, ultrasonic cavitation causes extracellular polymeric substances (EPS) to fall off the surface of sludge; Secondly, this faster and directly makes bacteria cells affected by bio-acidification and bio-oxidation. In this case, the cells could be more easily destroyed by the combined ultrasonic and bioleaching treatment, compared with individual bioleaching treatment; As a result, stronger dewaterability and more removal rates of ARGs were achieved under the combined treatment. The economic analyses showed that the combined ultrasonic and bioleaching treatment is a more practical and economical technique for achieving deep dewatering of sludge.