Sludge Conditioning Research Articles

Modified field method for testing activated sludge condition in chambers with variable wastewater levels.

The paper presents a proposal to modify a field method of testing the condition of activated sludge using a 30-min volume of sludge (settling test). To verify the validity of the modified method of testing the condition of activated sludge, field tests were performed in two onsite wastewater treatment plants. In these plants, the reaction chambers were fed by gravity from the primary sedimentation tank throughout the day. For such treatment plants, the activated sludge condition test varies during a 24-h period. Testing the condition of activated sludge using the modified volume of sludge gives stable results over a 24-h period. To analyse the results, a statistical test was performed to compare the results obtained in the traditional volume of sludge and the modified one. The analysis showed that the results of the sludge volume test are incorrect if the wastewater sample is taken at a time other than the final filling of the bioreactor (just before the sedimentation phase) due to sludge thickening. The proposed modified sludge volume test allows the operator to perform the test at any time of day with a correct result.

Cost-effective evaluation of modified ochre soil and its combination with cationic polyacrylamide for municipal wastewater sludge conditioning

ABSTRACT One of the most costly stages of activated sludge wastewater treatment plants is the treatment and dewatering of waste sludge. Chemical conditioning of sludge, as one of the most widespread methods to enhance sludge dewaterability, accounts for a significant portion of operational expenses due to the consumption of expensive polymeric compounds. This research aims to assess the cost-effectiveness of ochre soil, modified with hydrochloric acid, as an affordable mineral for conditioning waste sludge in an activated sludge system. The optimal conditions for acid modifications are obtained using response surface methodology. Then, its performance is compared with conventional coagulants (ferric chloride and alum) and in combination with cationic polyacrylamide (CPAM). To assess the conditioning process efficiency, the specific resistance to filtration (SRF) parameter was employed. At an optimal dose of modified ochre soil (MOS) equal to 300 (mg/g dry solids), the SRF value decreased from 31.96 to 2.7 Tm/kg. The combination of 100 (mg/gDS) MOS with 0.5 (mg/gDS) CPAM showed as the most cost-effective among the coagulants tested, with a 31% greater SRF reduction compared to CPAM used alone. This study shows the practical efficacy of an eco-friendly natural mineral as a polymer alternative, with the potential for sludge dewatering.

The synergistic role of sludge conditioner FeCl3/Rice husk on co-combustion with coal gangue: Thermaldynamic behavior, gases pollutants control and bottom ash stabilization

Coal processing invariably generates substantial quantities of low calorific value waste, specifically coal gangue (CG), which can be advantageously utilized by combusting to yield valuable electrical energy. However, CG incur poor ignition and flame instability, and consequently is not suited to separate combustion. The co-combustion with sewage sludge (SS) has demonstrated positive impacts on energy recovery, whereas the SS dewatering may significantly influence the co-combustion behavior. Therefore, this study systematically investigated the impact of two typical sludge conditioner, namely FeCl3·6H2O and rice husk (RH), which functions as flocculant and skeletal builder, on their synergistic role on co-combustion with CG. The thermal dynamic combustion behavior, pollutant emissions, slag tendency and bottom ash stability and toxicity were systematically studied. A robust positive synergism is observed, attributed to heat compensation and the formation of alkali metal aluminosilicates from Rh during the ignition phase. Concurrently, the temperature dependent iron oxides evolution enhances the acceleration of O2 loop, thereby promoting the char combustion. After being jointly conditioned with Rh and FeCl3, the co-combustion with CG resulted in CCi being 3.46 times higher than that of C1S3, and the average activation energy in each stage was reduced by 49.1 %. Significantly, the sludge conditioner also contributes to the reduced exhausted gases such as CO2, SO2 and NO. The Rh in SS has been found to mitigate slagging and fouling tendencies, while the retention of Cr, Cu, Ni, and Pb is greatly improved due to the stabilization of silicate minerals in CG. The Artificial Neural Network (ANN) models were established to predict the thermogravimetric experimental data of CG-SS-Rh/Fe, which aims to provide a basis for the selection of optimal operating conditions in real industrial applications.

Thermodynamic modeling of converter sludge sintering

Currently, a promising area is the development of technologies for sintering or briquetting of converter sludge. Recycling of this sludge into production will allow solving a number of important tasks for modern metallurgy in the utilization of man-made waste, saving raw materials and reducing the cost of steel. The efficiency of utilizing useful components in the composition of briquettes is significantly higher than in any other state (in a fine or polydisperse fraction, in sorted form). In this paper, we consider the development and justification of an integrated approach to thermochemical sintering of converter sludge based on conditioning of iron-containing sludge by non-thermal adsorption dehydration and thermochemical sintering with simultaneous reduction of iron from oxides. Adsorption dehydration to a moisture content of 2 – 3 % is provided by a short-term contact of iron-containing slimes with a porous energy carrier, brown coal semi-coke, which is separated by pneumoseparation and sent for energy technological use, and the iron-containing product mixed with coals is subjected to thermo-oxidative coking. Coking is carried out in an annular furnace with a rotating hearth, where, when temperatures reach 1050 – 1100 °C, a large and durable lump material is formed with 55 – 60 % of the iron-containing product with almost complete reduction. Thermodynamic modeling of converter sludge sintering with coals was carried out. A tool for performing computational experiments using methods of thermodynamic modeling of the studied object was the Terra software package designed to calculate the thermodynamic properties and composition of the phases of equilibrium state of arbitrary systems with chemical and phase transformations. The results of thermodynamic modeling were fully confirmed by the experimental studies. The obtained material is an analog of ferrocox containing 35 – 39 % of iron and 45 – 49 % of carbon, while the zinc oxide content does not exceed 0.017 %.

A three-stage oxidation method improves sludge dewaterability by achieving sustained oxidation and phased enhanced coagulation: Ingeniously using H2O2 as a “converter”

Sludge reduction is essential for mitigating the environmental hazards associated with sludge. The use of ferric chloride (Fe(III)) catalyzed ferrate (Fe(VI)) can significantly enhance sludge dewaterability by increasing the Fe(VI) oxidation rate and maintaining in-situ enhanced coagulation. However, its weak oxidation ability at the sludge’s original pH limits its practical application. To address this, hydrogen peroxide (H2O2) strengthened Fe(VI)/Fe(III) was employed to efficiently improve sludge dewaterability without pH adjustment, thereby enhancing the environmental utilization capacity of sludge. Compared to raw sludge, the treatment of Fe(VI)/Fe(III)–H2O2 resulted in approximately the 95% reduction in specific resistance to filtration (SRF) and increased the bioavailable phosphorus (P) content in dewatered sludge. During the oxidation process, highly reactive species such as tetravalent iron (Fe(IV)) and hydroxyl radicals (OH) were generated, facilitating the release of tightly bound water in extracellular polymeric substances (EPS). Importantly, the oxidation process was divided into three stages (persistent moderate oxidation — fast strong oxidation — sustained weak oxidation) based on the predominant reactive species (Fe(IV) or OH). This division promoted more robust and more durable oxidation processes. Phased enhanced coagulation occurred during the oxidation process. The gradual increase in Fe(III) content led to the re-flocculation of damaged EPS, enlarging the size of sludge drainage pores/channels and improving water discharge efficiency. Additionally, the costs and carbon emissions of chemicals for the Fe(VI)/Fe(III)–H2O2 process were 18% and 52% lower than those of the traditional Fenton method. This study not only achieves the goals of sludge reduction and resource collection but also provides insights into selecting sludge conditioning methods that meet pollution reduction and carbon emission reduction requirements.

Persistence evaluation of fecal pollution indicators in dewatered sludge and dewatering filtrate of municipal sewage sludge: The impacts of ambient temperature and conditioning treatments

Sludge resource utilization is one of the important routines for transmitting fecal pollution to water and soil, and sludge dewatering is a crucial step for sludge resource utilization. However, it remains unclear the decay characteristics and persistence of fecal pollution indicators after sludge dewatering. In this study, the persistence of six fecal pollution indicators, namely E. coli (EC), human-specific HF183 Bacteroides (HF183), human adenovirus (HAdV), human JC and BK polyomavirus (JCPyV and BKPyV), and crAssphage, in dewatered sludge cake and dewatering filtrate deriving from raw sewage sludge, as well as three types of sludge conditioned with polyacrylamide (PAM), Fenton's reagent, or Fe[III] and CaO were analyzed. The quantitative polymerase chain reaction (qPCR) and viability-qPCR methods were used to analyze the variation in abundances and infectivity of fecal pollution indicators in dewatered sludge cake or dewatering filtrate over the storage time, respectively. Decay predications of fecal pollution indicators over time were modeled using either the first-order or the biphasic decay model. The qPCR results revealed that fecal pollution indicators in dewatered sludge cake persisted longer than those in dewatering filtrate at the same temperature. Increasing temperature can accelerate the decay of fecal pollution indicators in both dewatered sludge cake and dewatering filtrate. Notably, sludge conditioning treatment may prolong the persistence of fecal pollution indicators in both dewatered sludge cake and dewatering filtrate. Viability-qPCR results indicated that the fecal pollution indicators (except HAdV) in dewatered sludge cakes deriving from both raw sewage sludge and conditioned sludges remained infectious for up to 30 days. After a storage period of 40 days, the abundances of fecal pollution indicators (except for EC) in sludge conditioned with Fenton's reagent were effectively decreased and meanwhile the infectivity of EC was reduced, exhibiting the lowest levels of fecal pollution. Therefore, both ambient temperature and conditioning treatment greatly impacted the decay characteristics and persistence of fecal pollution indicators in dewatered sludge cake and dewatering filtrate, and selecting suitable conditioning method can minimize environmental risks associated with fecal pollution in sewage sludge.

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.

Enhancing activated sludge dewatering performance: Impact of alum dosage on dehydration characteristics and microstructure

Sludge flocs encapsulate a significant amount of bound water, resulting in poor dewatering efficiency. To address this issue, the addition of alum (KAl(SO4)2·12H2O) has emerged as an effective strategy for enhancing sludge dewatering performance. This research specifically investigates the effects of various alum dosages on the dewatering characteristics of sludge. The introduction of alum alters internal temperature, pH levels, and intracellular osmotic pressure, which facilitates the release of trapped water within the flocs. Additionally, alum accelerates sludge sedimentation and promotes the agglomeration of smaller particles into larger ones, further improving dewatering efficiency. However, determining the optimal alum dosage for sludge conditioning is essential, as excessive amounts can lead to a decrease in dewatering performance.

Effect of conditioners used for sludge dewatering on the adsorption performance of sludge-derived adsorbent

Converting waste activated sludge into adsorbent is a promising alternative for sludge valorization. While various conditioners are widely employed in sludge conditioning and dewatering processes, the influence of these conditioners on the properties of sludge derived adsorbents remains largely unexplored. Four conditioners, including FeCl3, CaO, polyacrylamide, FeSO4·7 H2O/Na2S2O8, were used for sludge conditioning, and the sludge dewaterability and the adsorption performance of the resultant adsorbents were evaluated. The sludge dewaterability was markedly improved by the conditioners in a descending order as polyacrylamide, FeCl3, FeSO4·7 H2O/Na2S2O8, and CaO. The type of conditioner highly influenced the adsorption ability of the sludge adsorbent: FeSO4·7 H2O/Na2S2O8 enhanced the adsorption ability, while others deteriorated it. Infrared spectra, pore size distribution, and micromorphology analysis of the adsorbents suggest that: FeCl3 reduced mesopores through strong electrostatic interactions; CaO acted as a physical barrier for adsorption; polyacrylamide reduced the adsorbent surface area through hydrogen bond-driven bridging and potentially forming polymeric barrier; FeSO4·7 H2O/Na2S2O8 disrupted the sludge flocs and exposed abundant adsorption sites, promoting the adsorbent performance markedly. FeSO4·7 H2O/Na2S2O8 conditioning was thus beneficial to both sludge dewatering and adsorption. Adsorption of methylene blue by FeSO4·7 H2O/Na2S2O8-conditioned sludge adsorbent was best described by the pseudo-second-order model and Langmuir model, indicating the dominance of monolayer chemisorption. The adsorption mainly occurred in the mesopores of the adsorbent, with hydroxyl group and carbonyl in carboxyl group as the main binding sites. Both film and pore diffusion contributed to the adsorption rate, with pore diffusion serving as the main rate limiting step. Results highlight the beneficial effect of destructive conditioning method on sludge adsorbent performance.

Electrochemically activated persulfate combined with tannic acid significantly improved sludge-dewatering performance: Sludge floc weight structure, Fe(II)/Fe(III), and organic component conversion

Sludge-dewatering effect is a key factor in sludge disposal. In this study, the conditioning system of electrochemically activated persulfate combined with tannic acid (EF-PDS/TA) was used to improve sludge-dewatering performance. Results showed that the sludge water content (Wc) and Specific resistance to filtration (SRF) decreased by 29.4 % and 93.3 %, respectively, under the optimal operating conditions, which significantly improved the sludge-dewatering effect. Through research, we found that SO4•− and ·OH were the main factors promoting the improvement in sludge-dewatering performance. After the reaction, the physicochemical properties of the sludge changed significantly, and the floc structure effectively cracked. Further analysis of Fe2+/Fe3+ conversion, EEM and FTIR showed that in the process of sludge conditioning, on the basis of EF promoting Fe2+/Fe3+ conversion through electron transfer between cathode and anode plates, TA addition further improved the conversion efficiency of Fe2+/Fe3+. The conversion rate was as high as 90 %, which improved the oxidation ability of sludge. The thermal energy generated by the EF ohmic heat effect can promote the complexation and precipitation of proteins in EPS by TA, and the energy can be effectively utilized. Moreover, EF and TA exerted a synergistic effect in promoting Fe2+/Fe3+ conversion and protein cleavage. Finally, the economic cost of the combined conditioning system was calculated, and the practical application value of the conditioning system was evaluated. The findings laid a theoretical foundation for further research in the field of advanced sludge oxidation.

Comprehensive analysis of the relationship between yield stress and dewatering performance in sludge conditioning: Insights from various treatment methods

Understanding the relationship between sludge yield stress (σy) and dewatering performance is essential for optimizing sludge conditioning processes. This study systematically investigates the effects of various conditioning methods—including thermal hydrolysis (TH), freezing/thawing (FT), anaerobic digestion (AD), polyaluminum chloride (PAC), polyacrylamide (PAM), and Fenton treatment (Fenton)—on sludge yield stress and its correlation with dewatering efficiency. Using linear regression, partial least squares regression (PLSR), and correlation heatmap analyses, we reveal significant variations in the correlation between σy and dewatering indexes, including moisture content (Mc), capillary suction time (CST), and bound water proportion (Wb/Wt), depending on the conditioning method and intensity. Under FT and PAM conditioning, σy shows a strong negative linear correlation with dewatering performance, with Pearson's r values exceeding −0.880, indicating that a decrease in σy corresponds to improved dewatering efficiency. Conversely, AD conditioning exhibits a positive linear correlation, with r values up to 0.993, suggesting that an increase in σy correlates with reduced dewatering efficiency. For TH, PAC, and Fenton treatments, the correlation between σy and dewatering metrics is highly sensitive to changes in treatment intensity. In the PLSR analysis, the VIP values, which quantify the importance of each predictor variable, indicate that Wb/Wt in TH conditioning (VIP = 1.649) and CST in PAC (VIP = 1.309) and Fenton (VIP = 1.299) conditioning strongly influence σy. This study highlights the significant impact of conditioning methods and intensities on the correlation between σy and dewatering performance. While σy provides valuable insights as a predictive indicator, its predictive power is limited in more complex conditioning scenarios. Therefore, optimizing conditioning intensity and incorporating multiple rheological parameters are essential for achieving superior sludge dewatering outcomes.

Influential mechanism of water occurrence states of waste-activated sludge: Specifically focusing on the pore characteristics dominated by cation-organic interactions

The solid pore characteristics are commonly considered as the important influential factors on waste-activated sludge (WAS) dewaterability, and should be related to the cohesive force of bio-flocs dominated by cation-organic interactions at solid-water interface. This study aimed to establish an approach for regulating the solid pore structure of WAS by cationic regulation. The influential mechanism of WAS dewaterability was accordingly explored from the perspective of the pore characteristics dominated by cation-organic interactions. Primarily, with the gradient removal or addition of bivalent cations, the varying pore structure of WAS flocs was tracked by in-situ synchrotron X-ray computed microtomography imaging technique (CMT). The three-dimensional visual model was established to quantify the pore structure parameters of WAS flocs. Following the visualization analysis, the artificial intelligence means, the gradient-weighted class activation mapping (Grad CAM) of three-dimensional convolutional neural network (3D-CNN), was applied for the first time to explore the linkages among solid surface properties, solid pore structure, water occurrence states and sludge dewaterability. It was found that the number and volume of isolated pores jointly determined the mobility and the fractions of vicinal water and interstitial water (p-value ≤ 0.02); also, the decreasing polar or acid-based interfacial free energy with the cationic addition was accompanied with the decreasing isolated pore mean-volume (Pearson coefficient=-0.77, p-value < 0.01). These results indicated that the pore structure characteristics determined the water occurrence states, but the solid porosity strongly depended on the interfacial properties. Accordingly, the molecular docking was applied to explore the interfacial reaction mechanism between Ca2+/Mg2+ and solid compositions in terms of complexation sites, molecular dynamics and free energy calculations. As a result, how the cation-organic interactions affected the pore characteristics through solid surface modification could be clarified, which is expected to serve as theoretical foundation for the development of novel sludge conditioning technologies, i.e., more efforts should be devoted to increasing the dense degree of sludge particles through weakening the hydration repulsion of solid surface.

Promotion of aromatic amino acids of extracellular polymeric substance targeted transformation via sulfite mediated iron redox cycling in sludge solid-liquid separation

Highly hydrophilic extracellular polymeric substance (EPS) with gel-like structure seriously plagues the development of sludge deep dewatering. Oxysulfur radicals-based oxidation driven by iron-bearing mineral proposes a promising strategy for effective EPS decomposition. However, the transformation and involved interaction mechanisms of aromatic proteins are still controversial due to the complex EPS structure. Herein, sulfite mediated siderite (denoted as Fe(II)/S(IV)) was developed for targeted transformation aromatic amino acids in EPS oxidation to strengthen sludge solid-liquid separation. The enhanced sludge dewaterability were benefited from the Fe(II)/S(IV) bonded interaction assisted by Fe3+/Fe2+ as redox interface that facilitating the release of intracellular bound water via diminish the hydrophily and bind strength with solid protons. The amide region nitrogen of aromatic amino acids (especially tyrosine and tryptophan) originating from EPS presented looser structure and lower spatial site resistance, which were attributed to the exposure of hydrophobic sites in amino groups after Fe(II)/S(IV) treatment. Furthermore, the effective decline of aromatic amino acids in inner layer-EPS (loosely bound EPS and tightly bound EPS) was directed from Fe-N targeted interaction by triggering a series of sulfate-based radical chain reactions. The good correlation between electron transfer amount (R2 = 0.926) and Fe-N (R2 = 0.925) with bonding interaction demonstrated that the complexation of aromatic amino acids with Fe sites on siderite/sulfite via Fe-N bonds, accounting for efficient sludge solid-liquid separation. This study deepens the understanding of sludge organic matter targeted transformation and provides a tactic for iron-based conditioning of sludge.

Impact of several sludge dewatering conditioners on municipal sludge pyrolysis properties, kinetics, by-products, and environmental risk assessment

The pyrolysis characteristics of four different types of conditioned sludge were ascertained, and PAM, CaO, K2FeO4, and K2FeO4-CaO-PAM (KCP) conditioners were employed as sludge dewatering conditioners. The sludge pyrolysis reaction's activation energy (E) dropped with the addition of four conditioners. CaO, PAM, KCP, and K2FeO4 were the sequences of E needed for the pyrolysis of four different types of conditioned sludge. The addition of K2FeO4, CaO, and KCP resulted in an increase in the yields of H2 and CO. Except for the K2FeO4 conditioning sludge carbon, the pyrolytic carbon of the other three groups of samples showed an increase in S contents, while the pyrolytic carbon of the four groups of samples treated with conditioners clearly showed lower C and N contents compared to the raw sludge carbon. Protein-N made up the majority of N in sludge pyrolytic carbon. After adding conditioner, the level of organic sulfur decreased. Organic sulfur could then be broken down by K2FeO4 and CaO. The four conditioners efficiently mitigated the ecological and environmental risks posed by heavy metals. Alkynes were the most abundant result in pyrolytic volatiles of sludge pyrolysis; the other products included acids, alcohols, lipids, furans, ketones, phenols, hydrocarbons, N-components, and so on. All samples' acids, alcohols, and ketones from pyrolysis were decreased once the conditioner was added. The acid reduction rate reached 66.7 %, and the alkynes clearly increased during the KCP conditioned sludge's pyrolysis. The sulfur level of the bio-oil was decreased by all four conditioners. Everything mentioned above indicated that the KCP aided in the subsequent pyrolysis of the sludge, leading to the production of an advantageous pyrolysis bio-oil.

Insight into simultaneously sludge dewatering and antiviral drugs removal by integrated particle electrodes assisted electrochemical oxidation

Given the widespread occurrence of pandemic influenza, antiviral drugs (ATVs) as emerging pollutants which are ubiquitously present in wastewater and become concentrated in sewage sludge (SS). Therefore, achieving the simultaneous elimination of ATVs during sludge dewatering holds significant importance. Herein, six representative ATVs including amantadine, rimantadine, memantine hydrochloride, imiquimod, oseltamivir, and morpholidine were detected in sewage sludge. Their partitioning between solid and liquid phases was also examined under simultaneous sludge conditioning by particle electrodes-assisted electrochemical process (3D-SAC). The findings indicated that 3D-SAC significantly enhanced sludge dewaterability, achieving a moisture content reduction to 64.22 %. The total removal rates of the six ATVs ranged from 17.97 % to 66.22 %, closely associated with the degree of sludge cells cracking. Sludge lysis resulted in the destruction of protein-like EPS structures, exposing hydrophobic bonding sites, finally releasing more bonded water and ATVs into filtrate. The ·OH induced hydroxylation, backbone cleavage, and ring-opening of ATVs occurred concurrently as the sludge flocs disrupted and structural transformed. Environmental risk assessment revealed that the ecological risks and potential toxicity associated with the sludge filtrate were significantly diminished following electrochemical conditioning (EC). This process achieved the dual objectives of contaminant degradation and enhanced sludge dewatering.

Ozone/percarbonate-Fe3+ conditioning enhanced pressurized electro-osmotic dewatering (PEOD) of waste activated sludge: Feasibility and mechanisms

Pressurized electro-osmotic dewatering (PEOD) process is an emerging technology for high-efficiency solid-liquid separation of sludge and has garnered extensive interest. This study proposed a novel sequential conditioning process based on ozone (O3)/percarbonate (SPC) treatment followed by Fe3+ coagulation, namely O3/SPC-Fe3+ conditioning, to improve the performance of PEOD. The optimal operating conditions and the related dewatering performance of O3/SPC-Fe3+ conditioning-PEOD process were investigated to verify the feasibility. The mechanisms of the O3/SPC-Fe3+ conditioning on improving PEOD process were also discussed from the enhancement of the water/filtrate flow in pores. The results showed that 53.44 % water content and 0.95 g/g dry solid (DS) of bound water in dewatered sludge cake were attained in the O3/SPC-Fe3+ conditioning-PEOD process with optimal O3 aeration time of 12 min, SPC dosage of 0.0610 g/g DS and Fe3+ dosage of 0.0310 g/g DS for sludge conditioning then 346 kPa mechanical pressure and 40 V voltage for dewatering. During the O3/SPC-Fe3+ conditioning-PEOD process, the extracellular polymeric substance (EPS) matrix was disintegrated, and the inner EPS migrated to the outside along with water. The values of α-helix/(β-sheet + random coil) adjusted by O3/SPC-Fe3+ conditioning process decreased to 7.38 and 5.12 in slime and LB-EPS, respectively, and these changes transformed to expose more hydrophobic sites. After conditioning, the proportion of protein-N decreased drastically from 81.67 % to 62.34 %, while the proportion of inorganic-N increased significantly from 18.33 % to 37.66 %, indicating that partial protein-N in EPS altered to inorganic-N. The enhancement of PEOD by the O3/SPC-Fe3+ process can be attributed to the EPS hydrophobicity transformation and the degradation/mineralization of EPS by oxidation of generated ·OH. The former triggered the reduction of water/filtrate viscosity within the interfacial region of pores. The latter provoked the decrease of bulk viscosity of water/filtrate within the pores. These two effects relieved the viscous resistance to water/filtrate flow within pores and promoted dewatering.

A systematic investigation of peracetic acid oxidation and polymeric coagulants re-flocculation to enhance activated sludge dewatering: Multi-porous skeleton structures

In this research, the effects of peracetic acid (PAA), polymeric flocculants, and their combined conditioning on improving the dewatering performance were comprehensively evaluated. The results showed that sludge cake moisture content, capillary suction time (CST), and specific resistance to filtration (SRF) were 70.6%, 48.1 s, and 3.42 × 1012 m/kg after adding 0.10 g/gMLSS PAA for 50 min, representing reductions of 12.60%, 40.32%, and 33.98%, respectively. Additionally, conditioning of sludge with polyferric sulfate (PFS), polyaluminum chloride (PAC), and cationic polyacrylamide (CPAM) enhanced sludge properties in the following order: CPAM > PAC > PFS. After the PAA oxidation and re-flocculation process, the optimal dosages of PFS, PAC, and CPAM were reduced to 1.5 g/L, 0.9 g/L, and 0.04 g/L, respectively. The sludge dewatering performance significantly improved, with sludge cake moisture content measuring 65.8%, 66.3%, and 61.7%, respectively. Moreover, the spatial multi-porous skeleton structures were formed via re-flocculation to improve the sludge dewatering. Furthermore, economic evaluation validated that the pre-oxidation and re-flocculation process could be considered an economically viable option. These research findings could serve as a valuable reference for practical engineering applications.

Investigating the Dewatering Efficiency of Sewage Sludge with Optimized Ratios of Electrolytic Manganese Residue Components.

As an industrial waste residue, Electrolytic Manganese Residue (EMR) can greatly promote sludge dewatering and further particle-size optimization can significantly strengthen sludge dewaterability. In this study, the effects of ammonium sulfate, calcium sulphate dihydrate, and manganese carbonate in EMR on sludge dewatering performance were investigated using the response surface optimization method. It was found that the optimized ratio of three components in EMR was 1.0:1.6:2.2 based on capillary suction time (CST), specific resistance of filtration (SRF), and zeta potential of dewatered sludge. The composition ratio of particle-size optimized EMR was modified based on the above optimization, resulting in a significant increase in sludge dewatering performance (CST and SRF reduced by 8.7% and 11.2%, respectively). Compared with those in original sludge, the content of bound extracellular polymeric substances in the conditioned sludge with optimized ratio was drastically reduced while that of soluble extracellular polymeric substances was slightly increased, which was in accordance with the decline of fluorescence intensity. These findings indicated the disintegration of extracellular polymeric substances, the enhancement of hydrophobicity, and dewatering properties of the sludge. In summary, optimized EMR can effectively intensify the dewaterability of sludge, providing a competitive solution for dewatering and further disposal of sludge.

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.

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

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