Specific Filtration Resistance Research Articles

Role of extracellular polymeric substances in sludge dewatering under modified corn-core powder and sludge-based biochar pretreatments

Extracellular polymeric substances (EPS) which wrapped on sludge particles were deemed to hinder the outflowing of combined water in sludge system. The complex composition of EPS was the bottleneck for revealing its relationship with sludge dewaterability. In this study, a combined modified corn-core powder (MCCP) and sludge-based biochar (SBB) condition was executed to treat sludge for enhancing dehydration performance, and the concentration and the form distribution of organics in EPS, the variances of protein secondary structures were investigated. Correlation between the sludge dewaterability and EPS components were performed, found strong correlations among the net sludge solids yield (YN) and the specific resistance of filtration (SRF) (R = −0.923), Zeta potential (R = −0.971). Furthermore, the relationship between the secondary structures of protein and dehydration performance were strong related. With the optimal dosage of SBB and MCCP, aggregated strands and α -helix were released, indicated that the unfolding and despiralization in soluble EPS (S-EPS) were improved, disordered the sludge network, reduced the flowing resistance of bound water, finally enhancing sludge dewaterability.

Combined application of modified corn-core powder and sludge-based biochar for sewage sludge pretreatment: Dewatering performance and dissipative particle dynamics simulation

Sludge is an inevitable by-product of municipal wastewater treatment processes, and its high moisture content poses a major challenge for its subsequent treatment and disposal. Previous studies have explored the effects of applying modified corn-core powder (MCCP) on dewatering sludge. Here, we characterized the effects of applying both MCCP and sludge-based biochar (SBB) on dewatering sludge. Analysis of the anti-shear ability of SBB revealed that SBB was a skeleton builder with high compressive strength, demonstrating that SBB could maintain the permeability of sludge under high-pressure filtration processes and facilitate the flow of bound water. Dissipative particle dynamics (DPD) was used to simulated the sludge flocculating process and verify the feasibility of the experiment. As the simulation progressed, the reaction in the sludge network reached equilibrium and the simulated structure of the sludge became loose. The dewatering performance and physicochemical properties of the treated sludge were studied to further characterize the effect of this combined technology. Compared with MCCP-sludge, MCCP&SBB-sludge, which was treated by 20% DS (mass of dry solids in sludge) of SBB and 20% DS of MCCP, achieved superior dewaterability. This combined method reduced the specific resistance of filtration by 76% and enlarged the net sludge solids yield by 138%. Further study of the properties of MCCP&SBB-sludge revealed a loose structure that resembled the structure recovered by the simulation, suggesting that the DPD simulation method simulated the sludge flocculating process successfully. Therefore, the combined application of MCCP and SBB was superior for sludge dewatering because of the synergistic effects of MCCP and SBB.

Membrane fouling caused by biological foams in a submerged membrane bioreactor: Mechanism insights

Though sludge foaming often occurs and thus causes serious membrane fouling in membrane bioreactors (MBRs), the fouling mechanisms related with the foaming phenomenon have not been well addressed, hindering better understanding and solving foaming problem. In this work, it was interestingly found that, the foulants during the foaming period possessed extremely high specific filtration resistance (SFR) (over 1016 m kg−1) and strong adhesion ability to membrane surface. Chemical characterization showed that the proteins (178.57 mg/L) and polysaccharides (209.21 mg/L) in the foaming sample were about 6.4 times and 5.4 times of those in the supernatant sample, suggesting existence of a mechanism permitting continuous production of these foulants in the MBR during the foaming period. It was revealed that the fouling caused by foams was associated with gel layer filtration process, and the extremely high SFR can be interpreted by chemical potential change in the gel filtration process depicted in Flory-Huggins theory. Meanwhile, analyses by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory showed that the strong adhesion ability stemmed from the high interaction energy between the foaming foulants and membrane surface. In addition, 16S rDNA gene sequencing identified that the abundance of the foaming related bacteria species in the sludge suspension during the foaming period was more than 10 times of that during the non-foaming period. This study offered new mechanism insights into foaming fouling in MBRs.

Elimination of antibiotic resistance genes in waste activated sludge by persulfate treatment during the process of sludge dewatering

Two sludge conditioning modes (nanoscale zero valent iron modified by Ginkgo biloba L. leaf (G-nZVI)/sodium persulfate (PS) conditioning with different ratios (1:0, 1:0.1, 1:1 and 1:10) and G-nZVI/PS conditioning with continuous addition) in reducing the specific resistance of filtration (SRF) and removing antibiotic resistant genes (ARGs) were investigated. After 3 min, the SRF values decreased in following order: 2.45 × 108 m/kg (1:10) > 5.95 × 106 m/kg (1:0.1) > 3.72 × 106 m/kg (1:0) > 4.92 × 105 m/kg (1:1). In the continuous addition (1:1), the SRF value decreased from 1.04 × 108 m/kg to 6.47 × 106 m/kg at 9 min. Removal efficiency of ARGs was 2–6 orders of magnitude and no regeneration of ARGs was observed in sludge and water phase. When treated samples were incubated for 36 h, dominant microflora was negatively correlated with ARGs. This study revealed persulfate treatment could achieve dewatering and remove ARGs, simultaneously.

Different fouling propensities of loosely and tightly bound extracellular polymeric substances (EPSs) and the related fouling mechanisms in a membrane bioreactor

In this study, fouling propensities of loosely bound extracellular polymeric substances (LB-EPSs) and tightly bound EPSs (TB-EPSs) in a membrane bioreactor (MBR) were investigated. It was found that, both the LB-EPSs and TB-EPSs possessed rather high specific filtration resistance (SFR), and LB-EPSs possessed about three times higher SFR but a lower adhesion ability than the TB-EPSs. A series of characterizations demonstrated that LB-EPSs had higher ratio of proteins to polysaccharides (PN/PS ratio), lower CO bonds content, higher hydrophilicity, higher deformation or mixing ability and more abundant high molecular weight (MW) substances than TB-EPSs. Thermodynamic analyzes revealed that the total interaction energy between the TB-EPSs and membrane was always attractive and strengthened, well explaining the higher adhesion ability of the TB-EPSs than the LB-EPSs. Meanwhile, the filtration process was found to be associated with gel layer formation, and the high SFR of EPSs was caused by the chemical potential change in gel layer filtration. According to the Flory-Huggins lattice theory, LB-EPSs tended to form a gel layer with higher cross-linking and/or polymer entanglement level because they contained more abundant high molecular weight (MW) substance, corresponding to higher SFR than that of the TB-EPSs. The proposed thermodynamic mechanisms well interpreted the different fouling propensities of LB-EPSs and TB-EPSs in MBRs.

Evaluation of the dewaterability, heavy metal toxicity and phytotoxicity of sewage sludge in different advanced oxidation processes

This study thoroughly evaluated six types of sludge dewatering processes in terms of sludge dewaterability, environmental risk of heavy metal release and phytotoxicity. The assessed sludge dewatering processes included two conventional coagulants (polyacrylamide (PAM); FeCl3/CaO) and four advanced oxidation processes (AOPs) (Fenton’s reagent/CaO; Fe2+/Na2S2O8/CaO; Ca(ClO)2/FeCl3/walnut shell (WS); thermal and acid-washed zero-valent iron (TA-ZVI)/H2O2/CaO). Compared to the conventional coagulants, the use of AOPs as conditioners presents greater potential for sludge dewatering, as AOPs have dual roles in alleviating the environmental risk of heavy metals and the phytotoxicity of dewatered sludge. Among the four tested AOPs, Fenton’s reagent/CaO treatment achieved the highest sludge dewaterability improvement, with a higher water removal rate, lower specific resistance of filtration (SRF) and lower water content of dewatered sludge (Wc). This treatment was also the most cost-effective among the four AOPs. However, this method could not substantially mitigate the environmental risk due to the leaching toxicity of heavy metals and the phytotoxicity of dewatered sludge. Conversely, when considering the reduction of environmental risk, Ca(ClO)2/FeCl3/WS could be a better option, although its operational cost was slightly higher than that Fenton’s reagent/CaO. Collectively, this study provides novel insights for the selection of sludge conditioning treatments.

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.

Waste activated sludge conditioning in a new Fe2+/persulfate/tannic acid process: Effectiveness and optimization study to enhance dewaterability

Fe2+/persulfate process can be used to improve sludge dewaterability significantly. However, a large dose of chemicals was always needed and it will cause filter cloth clogging, equipment corrosion and sludge calorific value reduction in practice. In this study, a new Fe2+/persulfate/TA (tannic acid) process was put forward, which could reduce the use of inorganic reagents and keep the outstanding conditioning capability. A Box-Behnken experimental design method based on response surface methodology (RSM) was selected to assess the roles of independent variables including SPS (sodium persulfate), Fe2+ and TA, on sludge dewaterability characterized by capillary suction time, specific resistance of filtration, and water content of dewatered sludge cake. The optimized conditions were SPS dosage of 0.43 mmol/gTS (total solid), Fe2+ dosage of 0.58 mmol/gTS and TA dosage of 0.14 mmol/gTS, at which the water content of dewatered sludge cake showed (75.89 ± 0.01)% highly close to the predicted minimum water content of dewatered sludge cake using the fitted equation. Moreover, in the new process, sludge properties altered distinctly with the elimination of extracellular protein, supernatant viscosity reduction and particle size increase. Further investigations were needed to explore the underlying mechanism and practical application for a better and comphrensive understanding of Fe2+/SPS/TA process.

Exploring the efficacy and mechanism of tannic acid/Fe3+ conditioning for enhancing waste activated sludge dewaterability

Waste activated sludge (WAS), as a kind of hydrophilic colloid substance, is still a major technical challenge in wastewater treatment industry. For enhancing WAS dewaterability, the approach of tannic acid (TA)/Fe3+ conditioning was verified to be feasible. During conditioning, sludge extracellular protein decreased pronouncedly. Fluorescence quenching analysis revealed that Fe3+ reduced the binding sites of extracellular polymeric substances available for TA, and the formed TA-Fe3+ complexes possibly promoted TA aggregates’ settlement and compression. Sludge supernatant viscosity, absolute value of zeta potential and pH value also decreased distinctly, and sludge particle size became larger than that of raw sludge or Fe3+-conditioned sludge. Scanning electron microscope suggested that sludge surface morphology became more compacted and denser after TA/Fe3+ conditioning, which was helpful for the release of water trapped in sludge bio-polymeric network. With 0.15 mmol/gTS TA and 0.9 mmol/gTS Fe3+ conditioning, sludge capillary suction time, specific resistance of filtration and water content of dewatered sludge cake were decreased by 76.3%, 94.7% and 13.5%, respectively. The findings not only shed new light on the means of applying natural plant organic polymer coupled with inorganic cation to promote WAS dewaterability but offered a potentially theoretical principle of the utilization of plant waste containing TA in WAS treatment.

Effects of molecular weight distribution of soluble microbial products (SMPs) on membrane fouling in a membrane bioreactor (MBR): Novel mechanistic insights

While molecular weight distribution (MWD) is one of the most important properties of soluble microbial products (SMPs), mechanisms underlying effects of MWD of SMPs on membrane fouling have not well unveiled. In this study, it was found that, the supernatant of sludge suspension in a membrane bioreactor (MBR) for wastewater treatment can be fractionated into a series of SMPs samples with different molecular weight (MW) fraction. The real gel sample mainly formed by the rejected SMPs on membrane surface had a high specific filtration resistance (SFR) of 1.21 × 1016 m−1 kg−1. The SFR of SMPs samples and the model foulants of polyethylene glycol (PEG) increased with their MW. The change trend of SFR with MW cannot be sufficiently explained by three-dimensional excitation-emission matrix (EMM) and chemical compositions. Tyndall effect analysis indicated that gelating ability of SMPs and PEG in the solution increased with their MW. Scanning electron microscope (SEM) confirmed gel structure changes with the PEG MW. Accordingly, mechanisms based on Carman–Kozeny equation and Flory–Huggins lattice theory were proposed to interpret SFR of SMPs with low and high MW, respectively. Simulating these two mechanistic models on PEG samples resulted in the comparable SFR data to the experimental ones, indicating the correctness and feasibility of the proposed mechanisms. The proposed mechanisms provided in-depth understanding of membrane fouling regarding MW, facilitating to develop effective membrane fouling mitigation strategies.

Mechanism of zero valent iron and anaerobic mesophilic digestion combined with hydrogen peroxide pretreatment to enhance sludge dewaterability: Relationship between soluble EPS and rheological behavior

This study proposed a novel two-step conditioning strategy to enhance activated sludge (AS) dewatering performance. The method involved a zero valent iron (ZVI), anaerobic mesophilic digestion (AMD) process, and hydrogen peroxide (H2O2) oxidation. Response surface methodology (RSM) was applied to achieve optimum dewatering conditions. After the combined conditioning, dewatering was significantly better in the treated sludge compared to the raw AS. The specific resistance of filtration (SRF) of the treated sludge decreased to 2.48 × 1011 m/kg; this SRF level was 93.60% lower compared to the raw AS. The bound water content (BWC) decreased to 1.19 g/g dry solid (DS); this BWC level was 15.2% lower compared to the raw AS. The water content of the treated sludge cake decreased to 44.18 ± 0.46%. An economic analysis shows that ZVI-AMD-H2O2 can be used in real-world settings. Investigations of the underlying mechanisms showed that small block structures were formed after conditioning; viscosity and the colloidal forces of the sludge decreased; and organic matter and BWC were released from inner extracellular polymeric substances (EPS) layers to form soluble (SB)-EPS. This study illuminated the relationship between SB-EPS and the rheological behavior of AS. There is a high correlation coefficient between rheological parameter τy and N-containing substances in SB-EPS (R = −0.993, p < 0.05). The ZVI-AMD-H2O2 process effectively changed the EPS content, especially protein materials. This led to a decrease in AS viscosity and an increase in sludge dewaterability.

New insights into membrane fouling by alginate: Impacts of ionic strength in presence of calcium ions.

While water chemistry (e.g., ionic strength, calcium concentration and organic foulants) is the primary property of surface water, its effects on membrane fouling in process of membrane-based water production and seawater pretreatment have not well investigated. In this study, fouling behaviors of alginate solutions in presence of different calcium ion concentration and ionic strength levels were investigated. It was found that alginate solutions complexing with 1.5mM calcium possessed a remarkably high specific filtration resistance (SFR) (above 3.596×1015mkg-1), and the SFR descended with calcium concentration and increased with ionic strength. A series of characterizations suggested that zeta potential, particle size, viscosity and morphology of alginate solutions were close related with foulant layer microstructure and these fouling behaviors. Based on these characterizations, the thermodynamics described by Flory-Huggins lattice theory was proposed to explain the remarkably high SFR of alginate gel for 1.5mM calcium level. Meanwhile, preferential intermolecular coordination combined with Flory-Huggins lattice theory was suggested to be responsible for the descend trend of SFR with calcium concentration. Furthermore, electrostatic double layer compression effect together with Flory-Huggins lattice theory could well interpret the increase trend of SFR with ionic strength. This study provided the essential mechanisms underlying effects of ionic strength on alginate fouling in presence of calcium ions, and thus deepened understanding of membrane fouling.

The combined effects of hydrothermal treatment and Na2S2O8/ CuFe2O4 magnetic oxidation on sludge dewaterability improvement

Na2S2O8/CuFe2O4 addition and hydrothermal pretreatment were combined in this paper to ameliorate the dewatering performance (DP) of sludge with specific-resistance of filtration (SRF), time of capillary suction (CST), and water content (Wc) as well as water types investigated. The results shown the synergistic effect between Na2S2O8/CuFe2O4 addition and hydrothermal pretreatment and the DP of sludge reached to the best when the hydrothermal temperature was 150oC, the addition amount of Na2S2O8 was 0.08 mmol/g-VSS and the mass ratio of Na2S2O8/CuFe2O4 was 2.0. Through the analysis of water distribution, it was also demonstrated that the sludge structure was destroyed with the surface moisture released. All the results obtained shown the significant impact of the combined methods on ameliorating DP of sludge and promoting sludge recovery and utilization.

Filtration behaviors and fouling mechanisms of ultrafiltration process with polyacrylamide flocculation for water treatment

This study aims to investigate thermodynamic mechanisms of filtration behaviors of ultrafiltration (UF) process with polyacrylamide (PAM) flocculation for surface water treatment, which has not been investigated previously. It was interestingly found that, filtration of durably mixed sodium alginate (SA) solution corresponded to an extraordinarily high specific filtration resistance (SFR) (3.28 × 1014 m·kg−1 without polyacrylamide addition) and a V-shaped profile of SFR characterized by a sharp fall followed by a correspondingly sharp rise along with the increase in PAM addition concentration. Experimental characterizations suggested that, membrane fouling was mainly caused by the gel layer formation rather than the pore clogging and cake/floc formation. Rather than the chemical composition change, the changes of the solution physicochemical properties (pH and zeta potential) and foulant morphology are associated with above-mentioned interesting filtration behaviors. Accordingly, the thermodynamic mechanisms of the filtration behaviors were proposed. It was proposed that, the thermodynamics of polymeric network described by the Flory-Huggins lattice theory were responsible for the extraordinarily high SFR of SA gel layer. Low dosage of PAM addition decreased the negative zeta potential and homogeneity of the gel system, causing the reduced SFR. In contrast, further PAM addition increased the negative zeta potential and homogeneity of the gel system, and then increased the SFR of the gel layer. These results reasonably explained the V-shaped profile of SFR. This study provided significant insights into the effects of PAM addition on ultrafiltration behaviors of alginate solution.

Membrane fouling by alginate in polyaluminum chloride (PACl) coagulation/microfiltration process: Molecular insights

While polyaluminum chloride (PACl) coagulation- microfiltration (MF) process is one of the most popular methods for surface water treatment, the fouling mechanism underlying this process has not well explored. In this study, sodium alginate (SA) was used as the model organic matter. It was interestingly found that, specific filtration resistance (SFR) of alginate-aluminum complexes initially increased to an ultra-high value of 1.40 × 1015 m−1 kg−1, and then sharply declined to rather low level of 3.85 × 1012 m−1 kg−1 with the increase in PACl dosage from 0 to 500 mg/L. A series of characterizations of the foulant samples showed that the alginate-aluminum complexes suffered a morphology transition from gel form to floc/cake form with the PACl dosage increase. Density functional theory (DFT) calculation indicated the preferential coordination of aluminum ions with the terminal carboxyl groups of the alginate chains at low PACl level, facilitating homogeneous gel formation. The ultra-high SFR of gel was interpreted by the Flory-Huggins lattice theory. High PACl level resulted in the coordination of aluminum ions with the non-terminal carboxyl groups and reduced the surface charge, and thus, caused gel collapse and floc formation, corresponding to rather low SFR values. Preferential coordination combined with the Flory-Huggins lattice theory revealed in this study offered a molecular level fouling mechanism in the coagulation- microfiltration (MF) process for water treatment.

A study on the differences in the flocculation of dredged slurries and the influencing mechanisms.

In the water treatment process of natural water bodies, a large amount of dredged slurry with high water content is generated and required for treatment. The coagulation-flocculation method can improve the efficiency of separation, and a suitable scheme is of great significance. It is unclear whether there is a significant difference in flocculation and separation of dredged slurries from different sources and which constituents dominate this process. Facing these problems, the tests were conducted for dredged sediments from 10 different sources, including rivers, lake, and ocean. Under the same flocculation conditions, the difference in the increment of particle size d10, the specific resistance of filtration, and the suspended solids (SS) of the supernatant after sedimentation are 0-4.6 times, 0-2.4 orders of magnitude, and 0-4 orders of magnitude, respectively. It was found that the main constituents in the dredged slurries, such as clay minerals, fulvic acid and humic acid, impact on flocculation and separation effects by affecting the zeta potential of the particles. However, there is no single constituent in the dredged slurry which dominates the flocculation and separation effect. When these constituents are incorporated, the zeta potential exhibited in the slurry determines the difference in flocculation and separation effects.

Molecular insights into the impacts of iron(III) ions on membrane fouling by alginate.

Molecular mechanisms responsible for the filtration behaviors of sodium alginate (SA) in presence of different iron(III) ion concentration were explored in this study. It was found that specific filtration resistance (SFR) of alginate mixtures (1.0 gSA/L) firstly increased and then decreased to a trough with iron(III) concentration increase from 0 to 2.5 mM. Alginate mixture interacting with 0.1 mM iron(III) possessed an SFR as high as 1.65 × 1014 m kg-1, which could be explained by Flory-Huggins lattice theory related with gel filtration. Optical observation showed significant morphology transition (from gel to granular solids) of foulant layers with iron(III) concentration increase. A series of characterizations indicated the change of microstructure, pH and surface charge of alginate mixture with iron(III) concentration. Density functional theory (DFT) simulation suggested that iron(III) ion preferentially forms coordination bonds with three terminal carboxyl groups of alginate chains, facilitating elongation and cross-linking of alginate chains. Such a coordination mode induces formation of a slime and homogeneous gel, corresponding to high SFR. Continuous increase in iron(III) concentration leads to non-terminal coordination, which makes alginate chains more clustered and coiled. This effect, together with effects of the reduced surface charge and electric double layer compression, significantly decrease SFR of alginate mixtures. This study provided deep molecular insights into effects of iron(III) ions on alginate fouling.

Characteristics of a Self-Forming Dynamic Membrane Coupled with a Bioreactor in Application of Anammox Processes.

A novel anammox self-forming dynamic membrane bioreactor (SFDMBR) was proposed to achieve an efficient anammox process with high biomass retention and cost-effective operation. The cake layer formed on nylon mesh (pore size, 20-25 μm) was referred to as a dynamic membrane (DM). The high permeability of the DM layer contributed to low transmembrane pressure (TMP), which kept below 10 kPa for 50 days in one filtration cycle of 82 days. Compared to the high TMP (mainly > 20 kPa) in the MBR using polyvinylidene fluoride (PVDF) microfiltration membrane, energy can be significantly conserved in the SFDMBR. Besides, the mature DM layer achieved efficient biomass retention comparable to that of PVDF membrane, which favored anammox bacteria enrichment. Concomitantly, an appropriate microenvironment for autotrophic anammox bacterial growth with well-controlled extracellular polymeric substances (EPS) concentration (33.22 mg·g-1 VSS) was achieved in SFDMBR. According to specific filtration resistance (SFR) analysis, reducing the EPS concentration in the bulk sludge improves sludge filterability and alleviate fouling, which was achieved in the SFDMBR system with a low SFR of 1.47 × 1012 m-1·kg-1. Our results show that the cost-effective operations and technical merits make anammox SFDMBRs promising for practical applications.

Enhanced waste activated sludge dewaterability by tannic acid conditioning: Efficacy, process parameters, role and mechanism studies

Abstract Extracellular polymeric substances (EPS), especially proteins, exert a vital role in sludge dewatering. Tannic acid (TA), a plant secondary metabolite, is capable of bonding with proteins, and herein we employed it as a novel conditioner for sludge dewatering. The results indicated that TA enhanced sludge dewaterability with high reductions of 81.3% capillary suction time, 87.5% specific resistance of filtration and 13.4% water content of dewatered sludge under the optimized process parameters: TA dosage of 0.15 mmol/gTS, stirring speed of 200 r/min for 1 min, and settling time of 15 min. TA altered sludge properties pronouncedly including viscosity, particle size, zeta potential, pH and EPS contents and correlation analysis revealed their associations with sludge dewaterability. Moreover, EPS fluorescent components, sludge functional groups and surface morphology were detected for a better understanding of TA conditioning mechanism. The findings provide not only the feasibility of TA but also the potential of TA-containing plant waste in sludge treatment.

Distinction between polymeric and ceramic membrane in AnMBR treating municipal wastewater: In terms of irremovable fouling

Polymeric flat-sheet membrane (FS) and ceramic flat-tubular membrane (CM) are the most widely-used membranes in anaerobic membrane bioreactor (AnMBR). However, fouling mechanism on FS and CM were rarely compared before and needed to be deeply illuminated. In this work, distinction of irremovable fouling formed on polyvinylidene fluoride FS and Al2O3 CM in AnMBR treating municipal wastewater was studied. Lab-scale AnMBR operation showed that FS presented severer irremovable fouling and faster fouling rate. Foulants characterization revealed that irremovable fouling of FS was composed of more organics (FS = 0.91, CM = 0.35 g-TOC/m2-membrane) and biomass (FS = 47.3, CM = 8.65 × 1010 cell/m2-membrane), leading to gel layer loosely structured. Conversely, irremovable fouling of CM contained more inorganics (FS = 0.08, CM = 0.55 g/m2-membrane), facilitating dense gel layer with larger specific filtration resistance. Membrane cleaning tests found that gel layer on FS was efficiently removed by NaClO, while gel layer on CM was loosened by NaClO but destructed by citric acid. NaClO/NaOH both reduced resident bacteria, whereas increased the proportion of live cells. Irreversible fouling on FS involved more organics while more inorganics on CM. Irreversible biofouling could utilize citric acid as substrate for metabolism and proliferation. This study not only helps to probe fouling mechanism with different membrane materials, but also aids to develop differentiated effective cleaning strategy to corresponding membrane modules.