Enhancement Of Dewaterability Research Articles

Enhancement of sludge dewaterability using amphoteric starch-based flocculant coupled with waste synthetic fibers

An amphoteric starch-based flocculant 3-chloro-2-hydroxypropyltrimethyl chloride modified carboxymethyl starch (CMSCTA) for sludge dewatering was prepared and evaluated as a potential greener and economical alternative to conventional flocculants. A novel method of combining carbon skeleton (synthetic fiber) with flocculant conditioned sludge for enhancing the sludge dewaterability was also studied. With the combined treatment using CMSCTA and polyester fiber (PET), the sludge moisture content decreased to 64.4 % from 96.5 % and the optimal filtration rate was 2.92 mL∙min−1. The amphoteric flocculant optimized the substitution degree of anionic and cationic groups, which was shown the CMSCTA improved dewatering performance by promoting the release of nitrogen-containing substances and maintaining a more stable floc particle size distribution span. The results suggested an adsorption bridging occurred in addition to charge neutralization. The anionic groups in the amphoteric flocculants inhibited the complete adsorption of the flocculants (tight link), increasing the possibility of establishing a bridge between the flocculants and multiple sludge particles. The mercury intrusion experiments showed the porosity of sludge increased from 9.9 % to 12.8 % after the combined treatment, where PET facilitated sludge dewatering by providing moisture channels and a rigid skeleton. Charge neutralization, inhibition of complete adsorption, and construction of skeletons and moisture channels are the main mechanisms of sludge dewatering by the combined conditioning of amphoteric starch-based flocculators and fibers. This study explored the synergistic effect of starch-based modified flocculants and fibers, which has important guiding significance for improving the dewatering performance of sludge.

Enhancing dewaterability of water resource recovery facility solids with electrochemical treatment through synergetic effects of acidification and cation removal

Solids dewaterability is vital for water resource recovery facilities to effectively manage and dispose treatment residuals, and current methods for improving dewaterability is at the expense of chemical consumption. Herein, an electrochemical approach that integrates anodic acidification, electrooxidation, and cation removal was investigated to enhance solids dewaterability. The results show that the specific resistance to filtration (SRF) was decreased by > 97 % for raw solids before anaerobic digestion, anaerobically digested solids (ADS), and primary solids. ADS exhibited the highest conductivity and required the least energy (34.9 ± 1.3 kWh m−3 treated solids). Increasing the applied current density reduced treatment time but demanded greater energy consumption. Both acidification and cation removal were critical to dewaterability enhancement: acidification facilitated the flocculation of solids flocs through protonation of functional groups and the leaching of divalent ions, while cation removal reduced competition for proton binding, leading to improved dewaterability. The input of electrical energy for the electrochemical treatment can potentially be offset by revenue from recovered nutrient products and use of renewable energy. This study has demonstrated the feasibility of using electrochemical processes for solids treatment and resource recovery.

Mutual-benefit modification of the coagulant solution and fly ash for enhanced sludge dewatering

Faced with the escalating volume of municipal sludge from wastewater treatment plants, urgent measures are required to enhance the sludge dewatering efficiency. This study introduces an innovative and cost-effective approach for mutual modifications of AlCl3 coagulant solution (AC) and fly ash (FA) powder as additives to significantly enhance sludge dewaterability. Unlike the traditional method that modifies agents alone, our technique achieves dual functionalities via blending FA with AC at room temperature. The modified FA (MFA) exhibits a 60 % increase in specific surface area to 2.176 m2/g and ζ-potential shift from –22.2 to +2.0 mV, meanwhile enhances the metal ions content in the modified AC (MAC) by dissolving 96.5 % of Ca, 70.3 % of Mg, 10.6 % of Fe, and 6.1 % of Al ions from FA. When sludge is treated with 5 % MAC and 10 % MFA, the water content in the filter cake is reduced from 84.9 % originally to 52.9 % through plate-frame pressure filtration (PFPF), a significant improvement over 65.4 % for that with unmodified AC and FA treatment, corresponding to the decreased specific resistance to filtration (SRF) and increased the filtration flux during the draining phase. The notable dewaterability enhancement through AC and FA modification is due to the enhanced flocculation and charge neutralization by the abundant metal ions in MAC, coupled with the MFA-facilitated water adsorption and drainage channel maintenance. This one-step, double-benefit modification not only surpasses traditional methods in dewatering efficiency but also reduces sludge treatment costs by 42.4 %, offering a sustainable solution to the increasing challenges of municipal sludge management.

Hybrid conditioning of ionic liquid coupling with H2SO4 to improve the dewatering performance of municipal sludge.

Municipal sludge generated from wastewater treatment plants can cause a serious environmental and economic burden. A novel hybrid conditioning strategy was developed to enhance the dewatering performance of sludge, employing 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([C4mim][CF3SO3]) treatment combined with H2SO4 acidification. Following conditioning, the capillary suction time ( ), the specific resistance of filtration (SRF), and moisture content of the treated sludge were decreased to 1.99 ± 0.24 (s·L/g TSS), 1.33 ± 0.05 (1012m/kg), and 72.01 ± 0.94%, respectively. The results were superior to those achieved with sludge treated solely by H2SO4 acidification or [C4mim][CF3SO3] alone. The biomacromolecules within the sludge flocs were dissolved by [C4mim][CF3SO3], while simultaneously, the microorganisms were inactivated. Consequently, the colloidal-like structures of the sludge flocs were destroyed. Additionally, the ionizable functional groups of the biomacromolecules were instantly protonated by the introduced H+ ions, and their negative charges were neutralized during the H2SO4 acidification process. The presence of H+ ions promoted the weakening of electrostatic repulsion between the sludge flocs. As a result, an enhancement of sludge dewaterability was obtained after treatment with [C4mim][CF3SO3] and H2SO4 acidification. The finding of the intensification mechanism of sludge dewaterability brought by hybrid treatment of acidification and [C4mim][CF3SO3] provides novel insights into the field of sludge disposal.

Pivotal role of intracellular oxidation by HOCl in simultaneously removing antibiotic resistance genes and enhancing dewaterability during conditioning of sewage sludge using Fe2+/Ca(ClO)2

Pre-acidification has been shown to be crucial in attenuating antibiotic resistance genes (ARGs) during the conditioning of sewage sludge. However, it is of great significance to develop alternative conditioning approaches that can effectively eliminate sludge-borne ARGs without relying on pre-acidification. This is due to the high investment costs and operational complexities associated with sludge pre-acidification. In this study, the effects of Fe2+/Ca(ClO)2 conditioning treatment on the enhancement of sludge dewaterability and the removal of ARGs were compared with other conditioning technologies. The dose effect and the associated mechanisms were also investigated. The findings revealed that Fe2+/Ca(ClO)2 conditioning treatment had the highest potential, even surpassing Fenton treatment with pre-acidification, in terms of eliminating the total ARGs. Moreover, the effectiveness of the treatment was found to be dose-dependent. This study also identified that the •OH radical reacted with extracellular polymeric substance (EPS) and extracellular ARGs, and the HOCl, the production of which was positively correlated with the dose of Fe2+/Ca(ClO)2, could infiltrate the EPS layer and diffuse into the cell of sludge flocs, inducing the oxidation of intracellular ARGs. Furthermore, this study observed a significant decrease in the predicted hosts of ARGs and MGEs in sludge conditioned with Fe2+/Ca(ClO)2, accompanied by a significant downregulation of metabolic pathways associated with ARG propagation, thereby contributing to the attenuation of sludge-borne ARGs. Based on these findings, it can be concluded that Fe2+/Ca(ClO)2 conditioning treatment holds great potential for the removal of sludge-borne ARGs while also enhancing sludge dewaterability, which mainly relies on the intracellular oxidation by HOCl.

In-situ utilization of EPS improves the directional oxidation ability of Fe(III)/H2O2 and enhances sludge dewaterability

Inefficient sludge dewatering can result in high costs for sludge treatment and disposal, as well as increased pollution of the environment. In this study, we constructed a double oxidation–reduction (Redox) cycle system of Fe(II)/Fe(III) and Fe(II)-extracellular polymeric substance (EPS)/Fe(III)-EPS by utilizing EPS in situ and collaborating with Fe (III) and H2O2 so as to regulate the performance of Fenton oxidation for efficiently enhancing the dewaterability. Results displayed the specific resistance to filtration (SRF) reduced from 34.1 ± 2.4 × 1012 m/kg to 16.2 ± 1.5 × 1012 m/kg with only 0.15 mmol Fe(III)/g VSS and 1.46 mmol H2O2/g VSS. Notably, the formation of relative stable Fe(III)-EPS complex was found under the interval addition of Fe(III) and H2O2. Four types of reactive species (hydroxyl radical (•OH), singlet oxygen (1O2), superoxide radical (O2•-) and Fe(IV)) which could effective destroy EPS structure during conditioning process, were generated after the addition of H2O2. It effectively promoted the transition from intracellular oxidation to extracellular oxidation under Fenton oxidation conditions, which reduced negative effects of cell lysis under excessive oxidation during sludge conditioning. The structure of EPS damaged significantly during the oxidation process, leading to the effective conversion of bound water to free water. Meanwhile, the existence of dissociative Fe(III) promoted the aggregation of sludge flocs, generating large channels or pores for sludge water to discharge, and then improving the dewaterability. Overall, [Fe(III)-EPS]/H2O2 treatment as an efficient sludge conditioning method can provide guidance for sludge dewaterability enhancement in urban sludge treatment and disposal.

Enhancement of sludge dewaterability by repeated inoculation of acidified sludge: Extracellular polymeric substances molecular structure and microbial community succession

Improving the dewatering performance of sewage sludge is of great scientific and engineering significance in the context of accelerated urbanization and increasingly strict environmental regulations. Acidified sludge (AS) can improve sludge dewatering performance, but the dewatering effect of repeated inoculation is unclear. The effects of long-term repeated inoculation of AS on the sludge dewaterability were investigated. The molecular structure and microbial community succession of extracellular polymeric substances (EPS) are emphasized. The results revealed that increasing the inoculation ratio of AS reduced the pH, absolute value of sludge zeta potential, and sludge particle size, and the decreasing trend was more evident with prolonging treatment time. Under the conditions of 30% and 50% AS inoculation, the dewatering performance of the sludge was significantly improved (p < 0.05). Compared with the raw sludge, the specific resistance of filtration (SRF) and capillary suction time of 30% inoculation were reduced by 64.3% and 50.1% after 30 cycles, respectively. Excluding loosely bound (LB)-EPS, soluble (S)-EPS and tightly bound (TB)-EPS exhibited a visible decrease, the protein in TB-EPS was significantly related to sludge dewaterability (p < 0.05). The fluorescent components of aromatic protein and fulvic acid-like substances in TB-EPS were significantly associated with SRF, with a correlation coefficient 0.99 (p < 0.05). Both the increase in the percentages of random coil and decrease in α-helix in TB-EPS contributed to improving dewaterability. Increasing Firmicutes and decreasing Chloroflexi levels improved the sludge dewatering capacity. Repeated inoculation did not disrupt the dewatering effect of AS rather increased the feasibility of the engineering application of AS. Considering the dewatering performance and cost synthetically, 30% AS inoculated ratio is feasible for practical applications.

Insights into Fe/N co-doped biochar on enhanced dewaterability of anaerobically digested sludge: Heterogeneous oxidation and skeleton builder

Although anaerobic digestion is a promising way for valorization of waste activated sludge, the process severely deteriorates the sludge dewaterability. Herein, a novel strategy of iron and nitrogen co-doped biochar (Fe-N-BC) activated peroxydisulfate (PDS) was developed to improve anaerobically digested sludge (ADS) dewaterability. Results showed that Capillary suction time (CST) and moisture content (MC) of ADS after conditioned with Fe-N2-BC-800/PDS system dropped to 43.4 s and 66.8% when the initial pH was 6.0, dose of Fe-N2-BC-800 was 0.6 g/g VS, dose of PDS was 0.9 mmol/g VS, and reaction time was 30 min, respectively. Quantitative analysis indicated that the heterogeneous oxidation initiated by Fe-N2-BC-800 primarily contributed to the enhancement of ADS dewaterability. Mechanistic results revealed that (S•O4−, O•H, and O21were generated as reactive oxygen species (ROS) through multiple active sites of Fe-N2-BC-800 during catalytic reaction. These highly ROS efficiently decomposed extracellular polymeric substances (EPS) and disintegrated ADS cells, thereby releasing bound and intracellular water into free water. Meanwhile, Fe-N2-BC-800/PDS significantly reduced hydrophilic biopolymers, improved hydrophobicity of ADS through adjusting protein secondary structure and enriching hydrophobic groups in sludge pellets. Furthermore, Fe-N2-BC-800 produced rigid and porous drainage routes in ADS as skeleton builder, inducing enhancement of ADS dewaterability combing with the strong oxidation. The proposed Fe-N2-BC-800/PDS treatment offers a novel and promising technology for high-efficiency enhancement of ADS dewaterability, providing a valuable reference for ADS deep dehydration.

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.

Insights into the role of ·OH generated in Fe2+/CaO2/coal slime system for efficient extracellular polymeric substances degradation to improve dewaterability of sewage sludge

The disposal of massive sewage sludge and coal slime is a problem facing municipalities in China. A hypothesis for the co-disposal of sludge and coal slime is proposed to improve dewaterability by utilizing the beneficial role of coal slime as a filter assist and CaO2 enhanced system in this research. Results showed that capillary suction time, specific resistance to filtration and water content decreased dramatically from 49.3 s, 13.2 × 1012 m/kg and 84.85% to 19.1 s, 1.0 × 1012 m/kg and 50.07%, respectively, under the optimal conditions with 0.3/0.1/0.3-Fe2+/CaO2/coal slime g/g DS. The hydroxyl radicals generated in the Fe2+/CaO2 process acted on extracellular polymeric substances (EPS), resulting in a drop in the ratio of α-helix/(β-sheet + random coil) in the secondary structure of EPS proteins and a reduction in the concentration of aromatic proteins and tryptophan-like substances in TB-EPS, thereby enhancing the sludge dewaterability. Furthermore, coal slime as the skeleton building material induced a rise in sludge particle size and contact angle, lowering the hydrophilicity, compressibility of sludge and providing more channels to facilitate water flow. This work verified the promising application prospect of the Fe2+/CaO2/coal slime combined system in the enhancement of sludge dewaterability.

Synchronous biostimulants recovery and dewaterability enhancement of anaerobic digestion sludge through post-hydrothermal treatment

In this study, we investigated the effects of hydrothermal temperature on molecular reaction pathways and the plant growth of dissolved organic matters (DOMs) in anaerobic digestion sludge (ADS) via post-hydrothermal treatment (PHT). ADS-derived DOMs mainly comprise lignins/carboxyl-rich alicyclic molecules-like and proteins/aliphatic-like compounds featured with enriched N1-2O6-7 and O8-10 fragments. With the increase in the hydrothermal (HT) temperature, the relative abundance of the compounds with < 7O atoms in DOMs gradually increased in HT-treated samples. Furthermore, based on Fourier transforms ion cyclotron resonance mass spectrometry (FT-ICR-MS)-based reactomics, we found that CHON compounds possessed the highest reactivity, and that reaction of carbonyl (loss of glyoxal (−C2H2O2)) with unique reaction precursors possessed the largest number of high-frequency reactions at different HT temperatures. Consequently, DOM160 contained higher levels of N&O heterocyclic compounds and acetic acid, inhibiting pakchoi growth, and causing an increase in superoxide dismutase activity in the roots. However, DOM200 comprised a higher content of amino acids and humic/fulvic acids, increasing indole-3-acetic acid concentration and H+-ATPase activity in the pakchoi roots, thus exhibiting higher plant activity. Overall, the best HT temperature for ADS dewaterability and the recovery of organic matter was found to be 200 °C. These findings proposed a promising approach for synchronously recycling biostimulants, deep dewatering of ADS via PHT, and further improving the carbon–neutral operation of wastewater treatment plants.

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.

Comparison of dewaterability enhancement for river sediment by adding water transmitting channels in three dewatering procedures

The efficiencies of pressure filtration using air pressure (Air-P), suction (Suct-F), and filter pressing (Plate-P) were compared with and without the addition of water transmitting channels (WTCs). From the sediment, with initial water content of 60 ± 0.2 wt% and thickness of 5 cm, dry mud cakes with final water contents of 45.2 ± 0.1 wt%, 43.7 ± 0.1 wt% and 36.2 ± 0.4 wt% were obtained using Air-P, Suct-F and Plate-P respectively with 9 WTCs. The dewatering capacity increased by 100%, 200% and 100% compared to without WTCs. Layer water content analysis of the mud-cake after dewatering indicates that the WTCs added to the Air-P and Plate-P processes mainly enable filtration of free water from the upper layer, whereas the water in the middle and upper layer are sucked and filtered out through the WTCs during the Suct-F process. The water content of the upper layer decreased by 3.3%, 7.3% and 5.2% compared to without WTCs.

Enhancement of sludge dewaterability by electrolysis coupled with peroxymonosulfate oxidation process: Performance, mechanisms and implications

With the rapid increase in waste activated sludge (WAS), it is urgent to develop appropriate dewatering processes to diminish sludge volume and improve disposal efficiency. In this study, an advanced oxidation process using electrolysis coupled with peroxymonosulfate (E/PMS) was applied to improve the dewaterability of WAS. The results indicated that the sludge water content (WC) and capillary suction time (CST) dropped from 98.4 ± 0.2% and 220.1 ± 2.3 s to 70.7 ± 0.8% and 63.0 ± 1.2 s, respectively, under the following conditions: an electrolysis voltage of 20 V, an electrolysis time of 20 min, and 200 mg/g TS PMS. The increase in sludge zeta potential, surface hydrophobicity, and flowability indicated a significant improvement in sludge dewaterability. SO4•−, O•H, and O21 generated in the E/PMS process were responsible for the improvement of WAS dewaterability. These reactive oxygen species damaged extracellular polymeric substances (EPS), decreased fluorescent EPS components, and transformed the extracellular protein secondary structures by influencing the H-bond actions that maintain the α-helix. The bound water content, and apparent viscosity of WAS were found to be reduced, which was also attributed to an increase in dewatering capacity. Additionally, E/PMS treatment enhanced the degradation of organic matter in sludge and reduced the toxicity of the filtrate as well as the bioavailability of heavy metals. The cost analysis found that the E/PMS process was relatively economical and has great potential for practical application.

Exploring the feasibility and potential mechanism of synergistic enhancement of sludge dewaterability by ultrasonic cracking, chitosan re-flocculation and sludge-based biochar adsorption of water-holding substances

A method based on sludge-based biochar (SBB) skeleton adsorption of water-holding substances coupled with ultrasonic (US) cracking and chitosan (CTS) re-flocculation was proposed to strengthen sludge dewatering. Combined conditioning can greatly improve the sludge dewatering performance, the specific resistance to filtration (SRF), capillary suction time (CST), cake moisture content (MC) of sludge were reduced by 92.98 %, 78.46 %, 16.35 %. By analyzing the Zeta potential, relative hydrophobicity, water distribution, particle size distribution, filtrate organic matter, and extracellular polymeric substances (EPS) composition and structure of sludge, it was found that US, CTS and SBB showed significant synergistic effects. US disintegrated sludge flocs and promoted the transformation of functional groups on EPS, breaking the bond between solid and water molecules, releasing some bound water and intracellular substances, which laid the foundation for SBB to adsorb water-holding substances. CTS reconstituted flocs and crosslinked with protein (PN) to form complexes, which changed the spatial conformation of proteins. SBB adsorbs the water-holding substances such as protein and polysaccharide (PS) released in the outer EPS, promotes the dissolution of inner EPS, further promotes the denaturation and transformation of protein secondary structure, and improves the hydrophobic expression of sludge. Moreover, the combined conditioning reduces the compressibility of sludge and improves the water filtration efficiency. US+CTS+SBB is a green and promising combination technology, which has a certain reference value for sludge deep dehydration.

Application of CaO2-enhanced peroxone process to adjust waste activated sludge characteristics for dewaterability amelioration: Molecular transformation of dissolved organic matters and realized mechanism of deep-dewatering

Sludge dewaterability is commonly poor due to the hydrophilic biopolymeric substances. The highly efficient oxidation process is of great significance for extracellular biopolymers disintegration and bound water discharge. This work investigated the novel CaO2-enhanced peroxone (CaO2/O3) process to adjust sludge characteristics for dewaterability enhancement and focused on the molecular composition and transformation of dissolved organic matters (DOM). CaO2/O3 (60/40 mg/gTS (total solid)) treatment showed more powerful sludge solubilization of 57.8% and cell death proportion of 46.1% over single CaO2 or O3 treatment. Hydrophilic extracellular polymeric substances, especially protein-like substances, were substantially degraded, and their conformation turned to be more hydrophobic, and carbohydrate-like, aminosugars-like, and lignins-like substances increased in CaO2/O3 process. Meanwhile, CaO2/O3 handling resulted in more decomposition of CHO-containing compounds than N-containing or S-containing compounds. Subsequently, 60 mg/gTS PFS (polyferric sulfate) reflocculation exerted a strengthened role in eliminating proteins & lipids-like, lignins-like, and unsaturated hydrocarbons-like substances, and especially S-containing compounds, which compensated for the unsatisfactory removal effects of these substances in the CaO2/O3 oxidation process. Therefore, the CaO2/O3-PFS treated sludge with less hydrated DOM easily harvested deep-dewatering in pressure filtration. Furthermore, it was noteworthy that the presence of CaO2 created an alkaline environment and served as the source of sustained-release H2O2, which accelerated O3 decomposition and greatly improved •OH generation. These findings provided molecular insight into a novel sludge conditioning approach for ideal dewaterability based on the CaO2-enhanced peroxone process in sludge treatment.

Enhancement of sludge dewaterability by three-dimensional electrolysis with sludge-based particle electrodes

Electrochemical sludge conditioning was widely used to enhance sludge dewaterability. However, the limited area of plane electrodes results in poor dewatering efficiency and high energy consumption. The long period electrolysis with high cell voltage leads to the dissolution of extracellular polymeric substance (EPS), which accelerates the deterioration of sludge dewaterability. Herein, a clean and cost-saving method was proposed to enhance sludge dewaterability in this study. The capillary suction time (CST) of sludge conditioned with a three-dimensional electrochemical reactor (3D-ER) with sludge-based particle electrodes (SPE) decreased from 65.5 s to 29.6 s within 10 min while the water content decreased from 98.56% to 65.30% by mechanical filtration. The polarization of SPE in the electric field induced significant sludge flocs decomposition and EPS dissolution with a low energy consumption of 0.0020 kWh·L−1. The addition of commercial activated carbon (CAC) and SPE increased the calorific value of dewatered sludge as solid fuels. The SPE with the hydrophilic groups and silicon oxide provided more polar channels for water release than CAC, leading to an enhanced sludge dewaterability. These findings provided a new insight for improving sludge dewaterability and resource utilization in a closed loop in wastewater treatment plants.

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.

Sludge dewaterability enhancement under low temperature condition with cold-tolerant Bdellovibrio sp. CLL13

The dewatering performance of waste activated sludge (WAS) is generally deteriorated under low temperature due to the increase of viscosity, which would exacerbate the difficulties in sludge treatment and disposal. In this study, the cold-tolerant Bdellovibrio sp. CLL13 was successfully screened for efficient sludge biolysis, and it dramatically improved the sludge dewaterability while no significant biolysis effects were observed for the mesophilic BALO strain at 12 °C. The reduction rates of the sludge capillary suction time (CST), the specific resistance of filtration (SRF), the sludge dry weight, and the fecal coliform bacteria concentration at the optimal reaction time of 14 h were 40.1 ± 0.2%, 69.6 ± 0.7%, 7.7 ± 0.4%, and 78.5 ± 0.4%, respectively, when the mixed liquid suspended solids (MLSS) content was between 10.8 and 29.6 g/L, the input dosage of CLL13 was 8.8 × 106 PFU/mL sludge, and the DO level was 1.2 mg/L. Meanwhile, the viscosity reduction rate, the relative hydrophobicity increasement rate, and the bound water reduction rate were 20.3 ± 1.2%, 6.9 ± 0.7%, and 29.4 ± 1.0%, respectively. The ratios of protein content to polysaccharides content in the extracellular polymeric substances (EPS) decreased significantly. In addition, the degradation of the macromolecular substances in EPS and the increase of the soluble chemical oxygen demand, the total nitrogen, the total phosphorus, and the lactate dehydrogenase levels were observed. Therefore, the cold-tolerant CLL13 induced the sludge biolysis and compromised the negative effects of low temperature on the sludge dewatering performance, which should be beneficial for the efficient WAS biolysis treatment application in the near future under low temperature.

Degradation of extracellular polymeric substances (EPS) and enhancement of sludge dewaterability by filamentous fungus Penicillium rubens

Degradation of extracellular polymeric substances (EPS) and enhancement of sludge dewaterability by filamentous fungus Penicillium rubens