Soluble Extracellular Polymeric Substances Research Articles

Predatory Bdellovibrio-and-like organism mixtures on efficient MBR in-situ membrane fouling diminishment and mechanisms

ABSTRACT Membrane fouling is a major hindrance that restricts the application of membrane bioreactors (MBRs). Bdellovibrio-and-like organisms (BALOs), as obligatory parasitic bacteria, prey upon various bacteria. In this study, the BALO mixtures were screened and found more effective in membrane fouling mitigation compared to the single BALO species and extended the membrane filtration period by as long as 33.3%. The higher BALO diversity reduced the potential foulants generation in the activated sludge by decreasing the sludge viscosity as high as 13.8 ± 0.6% than the pure culture of BALO. Meanwhile, the mixed BALOs demonstrated superior biofilm predation capabilities, with the content of soluble microbial products and extracellular polymeric substances on the biofilm decreasing by 26.1 ± 0.5% and 38.3 ± 0.2% as the most compared to the single BALO species involved system. Additionally, the BALO mixtures expanded the single strains’ host lysis spectrum of both the activated sludge and biofilm. The abundance of membrane-fouling-related bacteria such as Flavobacterium, Rhodobacter, and Labilithrix and pioneer bacteria such as Sphingorhabdus and Pseudomonas was significantly reduced. In summary, this study disclosed the significantly better membrane fouling mitigation effects of the BALOs with higher diversity, suggesting that the expansion of the host range is crucial for the further application of BALOs to enhance the anti-fouling performance of the MBR system.

Preliminary tests on carbon and nitrogen emissions and nutrients availability upon application of algal-bacterial granules to arid and low fertility soil

To remediate arid and low-fertility soil and explore the feasibility of controlling its carbon (C) and nitrogen (N) emissions, algal-bacterial aerobic granular sludge (AGS) was applied as soil additives and compared with bacterial AGS and cyanobacteria during 14 days’ incubation. Results show that algal-bacterial AGS as additives possesses a higher potential in terms of fertility recovery and soil physicochemical properties conservation. The additives may change the soil characteristics by decreasing soil pH (within 0.6) and water content (0.8–2.5 %) with increased electrical conductivity during the 14 days’ incubation. As for soil fertility, due to the high available phosphorus (P) content in algal-bacterial AGS, the soil available P content was significantly increased from 50 % to 170 % after incubation under different application rates or gaseous environments. N was also accumulated in the soil matrix with increased inorganic forms and less and acceptable N emission. The contents of soluble organic substances and extracellular polymeric substances (EPS) were significantly increased after incubation. Under ambient air and moderately elevated CO2 like 10 % conditions, carbon mineralization in the soil samples was lower than 15 % at low additives dosages; while under an elevated CO2 content (25 %) condition, a higher additives dosage may cause a rapid CO2 accumulation within 2 days with a substantial O2 consumption, leading to an anaerobic/anoxic environment corresponding to a higher C mineralization and/or N loss.

Effect of ciprofloxacin on the one-stage partial nitrification and anammox biofilm system: A multivariate analysis focusing on size-fractionated organic components

The impact of ciprofloxacin (CIP) in the partial nitrification and anammox biofilm system was investigated by multivariate analysis, focusing on size-fractionated organic components. The CIP dose of 10 μg/L did not inhibit the total nitrogen (TN) removal efficiency, even though the abundance of antibiotic resistant genes (ARGs) (i.e., qnrD, qnrB, qnrA, qnrS, and arcA) was elevated. However, a gradual higher CIP dosing up to 100 μg/L inhibited the TN removal efficiency, while the abundance of ARGs was still increased. Moreover, both the TN removal efficiency and the abundant ARGs were dwindled at 470 μg/L of CIP. As the CIP dose increased from 0 to 100 μg/L, the abundance of high molecular weight (MW) fractions (14,000 to 87,000 Da; 1000 to 14,000 Da) and humic/fulvic acid-like components in the soluble extracellular polymeric substances (HSS) decreased, with more increases of low MW (84–1000 Da; less than 84 Da) fractions and soluble microbial by-products in soluble extracellular polymeric substances (SMPS). Continuously increasing the CIP dose till 470 μg/L, an inverse trend of the changes of these organic components was noted, along with clear reductions of the microbial diversity and richness, and the abundance of key functional genes responsible for nitrogen removal. The predominance of functional gene amoA (related with ammonia oxidizing bacteria) was more significantly with more distribution of SMPS with relatively low MW and less distribution of HSS with relatively high MW, as well as polymer decomposing microorganisms such as Bryobacteraceae and the unclassified Saprospirales.

Enhancing short-chain fatty acids production via acidogenic fermentation of municipal sewage sludge: Effect of sludge characteristics and peroxydisulfate pre-oxidation.

This study first employed a combined pretreatment of low-dose peroxy-disulfate (PDS) and initial pH 10 to promote short-chain fatty acids (SCFAs) production via acidogenic fermentation using different types of sewage sludge as substrates. The experimental results showed that the yield of maximal SCFAs and acetate proportion after the combined pretreatment were 1513.82±28.25mg chemical oxygen demand (COD)/L and 53.64%, and promoted by 1.28 and 1.56 times higher, respectively, compared to the sole initial pH 10 pretreatment. Furthermore, in terms of the disintegration degree of sewage sludge, it increased by more than 18% with the combined pretreatment compared to the pretreatment of sole initial pH 10. Waste-activated sludge (WAS) from A2/O and Bardenpho processes were more biodegradable, explained by the 1.47- and 1.35-times higher disintegration rate than those from oxidation ditch and they favored acetate dominant fermentation. Correlation analysis revealed a strong correlation (p ≤ 0.01) between SCFAs production and soluble COD, total proteins, proteins in soluble-extracellular polymeric substances (SEPS), total polysaccharides, and polysaccharides in SEPS. Mechanism explorations showed that preoxidation with PDS enhanced the solubilization and biodegradability of complex substrates, and altered the microbial community structure during the fermentation process. Firmicutes and Tetrasphaera were proven to play a key role in improving SCFA production, especially in promoting acetate production by converting additional SCFAs into acetate. Additionally, the addition of PDS greatly promoted sulfur and iron-related metabolic activities. Finally, the combined pretreatment was estimated to be a cost-effective solution for reutilizing and treating Fe-sludge.

A step towards more eco-friendly and efficient microalgal harvesting: Inducing flocculation in the non-naturally flocculating strain Chlorella vulgaris (13-1) without chemical additives

Flocculation is often regarded as a cost-effective and reliable method for microalgal harvesting. However, the traditional method often requires the addition of chemical agents to induce flocculation. This carries certain disadvantages including the chemical contamination of the biomass and the subsequent need to remove the flocculants from the medium. To address these issues, this study aimed to induce flocculation in a naturally non-flocculating strain (Chlorella vulgaris 13-1) without resorting to chemical additives, with the ultimate goal of increasing harvesting efficiency. Scanning electron microscopy showed that Scotelliopsis reticulata UFA-2, a naturally flocculating strain, produces extracellular polymeric substances (EPS) whereas 13-1 does not. As a result, two methods were used to induce flocculation in 13-1: co-cultivation of UFA-2 and 13-1, and insertion of EPS produced by UFA-2 into the growth medium of 13-1. The co-cultivation of 13-1 with UFA-2 significantly increased the flocculation efficiency compared to that of 13-1 alone (30 % higher flocculation efficiency after one hour of settling and 52 % higher after three hours of settling). Alternatively, the insertion of dry tightly-bound (TB) UFA-2 EPS into 13-1 cultures also improved flocculation efficiency (by 19 % compared to the control), while addition of soluble or loosely-bound (LB) EPS was less efficient (less than 1 % and 10 %, respectively). FTIR results showed that the composition of TB-EPS was different to that of LB and soluble EPS. TB-EPS contained higher proportions of proteins and different types of carbohydrates, potentially contributing to its increased efficacy in inducing flocculation in microalgae.

Interface Engineering of PdPt Ultrafine Ethanol Electro-Oxidation Nanocatalysts by Bacterial Soluble Extracellular Polymeric Substances (s-EPS) to Break through Sabatier Principle.

Unsatisfactory performance of ethanol oxidation reaction (EOR) catalysts hinders the application of direct ethanol fuel cells (DEFCs), while traditional alloy catalysts (like PdPt) is cursed by Sabatier principle due to countable active site types. However, bacterial soluble extracellular polymeric substances (s-EPS) owning abundent functional groups may help breacking through it by contrusting different active sites on PdPt and inducing them to play synergy effect, which is called interface engineering. Using s-EPS to engineer catalysts is more green and consumes lower energy compared to chemical reagents. Herein, PdPt alloy nanoparticles (≈2.1nm) are successfully in situ synthesized by/on s-EPS of Bacillus megaterium, an ex-holotype. Tryptophan residuals are proved as the main reductant. In EOR, PdPt@s-EPS shows higher activity (3.89mAcm-2 ) than Pd@s-EPS, Pt@s-EPS, Pt/C and most reported akin catalysts. Its stability and durability are excellent, too. DFT modelling further demonstrates that, interface engineering by s-EPS breaks through Sabatier principle, by the synergy of diverse sites owning different degrees of d-p orbital hybridization. This work not only makes DEFCs closer to practice, but provides a facile and green strategy to design more catalysts.

Biodegradation of phenanthrene-Cr (VI) co-contamination by Pseudomonas aeruginosa AO-4 and characterization of enhanced degradation of phenanthrene

Microorganisms capable of simultaneously remediating heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) pollution hold significant importance in bioremediation efforts. In this study, we investigated the ability of Pseudomonas aeruginosa AO-4 to simultaneously degrade phenanthrene (PHE) and reduce Cr (VI). Specifically, it has the ability to reduce 100 % of Cr (VI) (30 mg/L) while degrading 43.8 % of PHE (50 mg/L). In batch experiments, it was observed that the presence of Cr (VI) can enhance the degradation of PHE by strain AO-4. The solubility of PHE in soluble extracellular polymeric substances (S-EPS) was found to be related to the initial concentration of Cr (VI), which could explain why Cr (VI) promotes the degradation of PHE. Additionally, XPS analysis confirmed that Cr (VI) was reduced to Cr (III) with S-EPS produced by Pseudomonas aeruginosa AO-4. GC–MS analysis was conducted to analyze the degradation metabolites of phenanthrene, di(2-ethylhexyl) phthalate and 2TMS derivatives of salicylic acid were detected, indicating that Pseudomonas aeruginosa AO-4 is capable of degrading phenanthrene through two distinct pathways. These findings demonstrate the potential of Pseudomonas aeruginosa AO-4 in the treatment of co-contamination scenarios involving PAHs and HMs.

Bacterial adhesion inhibition by microalgal EPSs from Cylindrotheca closterium and Tetraselmis suecica biofilms.

In the food industry, successful bacterial pathogen colonization and persistence begin with their adhesion to a surface, followed by the spatial development of mature biofilm of public health concerns. Compromising bacterial settlement with natural inhibitors is a promising alternative to conventional anti-fouling treatments typically based on chemical biocides that contribute to the growing burden of antimicrobial resistance. In this study, three extracellular polymeric substance (EPS) fractions extracted from microalgae biofilms of Cylindrotheca closterium (fraction C) and Tetraselmis suecica (fraction Ta rich in insoluble scale structure and fraction Tb rich in soluble EPS) were screened for their anti-adhesive properties, against eight human food-borne pathogens belonging to Escherichia coli, Staphylococcus aureus, Salmonella enterica subsp. enterica, and Listeria monocytogenes species. The results showed that the fraction Ta was the most effective inducing statistically significant reduction for three strains of E. coli, S. aureus, and L. monocytogenes. Overall, EPSs coating on polystyrene surfaces of the different fractions increased the hydrophilic character of the support. Differences in bacterial adhesion on the different coated surfaces could be explained by several dissimilarities in the structural and physicochemical EPS compositions, according to HPLC and ATR-FTIR analysis. Interestingly, while fractions Ta and Tb were extracted from the same microalgal culture, distinct adhesion patterns were observed, highlighting the importance of the extraction process. Overall, the findings showed that EPS extracted from microalgal photosynthetic biofilms can exhibit anti-adhesive effects against food-borne pathogens and could help develop sustainable and non-toxic anti-adhesive surfaces for the food industry. KEY POINTS: •EPSs from a biofilm-based culture of C. closterium/T. suecica were characterized. •Microalgal EPS extracted from T. suecica biofilms showed bacterial anti-adhesive effects. •The anti-adhesive effect is strain-specific and affects both Gram - and Gram + bacteria.

Effects of microbubble pretreatment on physiochemical and microbial properties of excess activated sludge.

Fast increased amount of excess activated sludge (EAS) from wastewater treatment plants has aroused universal concerns on its environmental risks and demands for appropriate treatments, while effective treatment is dependent upon proper pretreatment. In this study, air-supplied microbubbles (air-MBs) with generated size of 25.18 to 28.25 μm were used for EAS pretreatment. Different durations (30, 60, 90, and 120 s) yielded sludge with varied physiochemical conditions, and 60 s decreased sludge oxidation status and significantly increased adenosine triphosphate (ATP) content. Soluble, loosely-bound, and tightly-bound extracellular polymeric substances (SEPS, LB-EPS, and TB-EPS) were extracted from the sludge through a stepwise approach and examined through three-dimensional excitation-emission matrix (3D-EEM) and quantitative analysis. The results showed that 60- and 120-s treatments generated stronger fluorescence intensities on dissolved organic matters (DOMs) of protein-like and fulvic acid in LB-EPS and TB-EPS, which indicated the decrease of counterparts in EAS, and therefore facilitated sludge dewaterability and reduction. The dominant microbial communities in EAS, including Proteobacteria, Bacteroidota, Chloroflexi, and Actinobacteriota, were not significantly affected by MB pretreatment. The results collectively revealed the effects of MB pretreatment on EAS and indicated that MBs could be an effective pretreatment technique for EAS treatment process.

RETRACTED: Enhanced biofiltration coupled with ultrafiltration process in marine recirculating aquaculture system: Fast start-up of nitrification and long-term performance

In marine recirculating aquaculture systems (RAS), the biological nitrification system usually suffers from long time start-up and proliferation of potential pathogenic bacteria under the high salinity stress. This study aims to develop a strategy for fast start- up and long-term biosecurity of marine RAS by using a combined biofiltration system (ceramic rings (CR) - granular activated carbon (GAC) - ultrafiltration (UF) process) in an actual marine RAS for selenotoca multifasciata. The ammonia nitrogen and dissolved organic matter (DOM) removal performance, membrane fouling characteristics and microbial communities during long-term operation (200 days) were investigated. The CR-GAC-UF process minimized the start-up time of the nitrification system to 14 days under low ammonia concentrations (below 2 mg/L). Long-term operation of the marine RAS with ammonia and nitrite nitrogen stabilized below 0.1 mg/L with a daily ammonia nitrogen removal rate of 91.7 %. The UF membranes were operated at fluxes at 15 LHM and the protein/polysaccharide ratios of soluble microbial products (SMP) and extracellular polymeric substances (EPS) on the membranes were stable below 0.5 with low fouling levels. A number of bacterial genera that have the potential to degrade protein and humic-like substances were recognized, which was related to the long-term DOM removal. Candidatus_Nitrosopumilus, Nitrosomonas_sp. and Nitrospira sp. ENR4 were detected as the core nitrifiers in CR-GAC-UF process, which were closely related to the amoABC, hao and nxrA genes (p < 0.05). With the multi-stage barrier of CR-GAC-UF, the heterotrophic plate count in therecirculating water was kept at 3 ± 1 CFU/mL and the relative abundance of potential pathogens declined gradually below 0.81 %. Taken together, this study provides a theoretical basis for the wider application of marine RAS.

Enhanced microalgal growth and metabolites through co-cultivation with Escherichia coli in algal organic matter solution

Studies of how symbiotic bacteria interact with microalgae have been an area of interest for some time. However, there is still a knowledge gap on the role of algal organic matters in algal growth promotion and adaptive mechanisms of the co-cultures in medium containing high abundancy of dissolved algal organic matters. It remains unclear if high extra- and intra-cellular organic substances concentration influences algal development or subsequent algal organic matter productivity in the presence of bacteria. Therefore, this study aims to co-cultivate Escherichia coli NEB 5-alpha with broad range of marine and freshwater microalgae in fresh medium (T), soluble EPS (sEPS) and internal organic matter solution (IOM). Among screened species, only the growth of Cylindrotheca fusiformis and Chlorella vulgaris was promoted by E. coli at 1.15×106±2.08×104 cells mL−1 and 7.79×106±1.27×105 cells mL−1after 96 h. Xenic algal growth was further enhanced about 10 % more utilizing sEPS and IOM. However, the net EPS accumulation of the cells cultivated in sEPS and IOM was comparatively lower than that of the cells in T medium due to metabolite consumption. Elevation in the transparent exopolymer particles, total chlorophyll, total carbohydrate, total protein and lipid productivity up to 3.54-fold by cultivating the co-cultures in sEPS and IOM indicated an alteration of the microalgae's physiology. This is a new paradigm on how algal extracts promote xenic algal growth and metabolite production which pave a way for cost-effective biotechnological applications by reusing the algae medium with abundant organic matters.

Improved anaerobic sludge fermentation mediated by a tryptophan-degrading consortium: Effectiveness assessment and mechanism deciphering

The hydrolysis of extracellular polymeric substances (EPS) represents a critical bottleneck in the anaerobic fermentation of waste activated sludge (WAS), while tryptophan is identified as an underestimated constituent of EPS. Herein, we harnessed a tryptophan-degrading microbial consortium (TDC) to enhance the hydrolysis efficiency of WAS. At TDC dosages of 5%, 10%, and 20%, a notable increase in SCOD was observed by factors of 1.13, 1.39, and 1.88, respectively. The introduction of TDC improved both the yield and quality of short chain fatty acids (SCFAs), the maximum SCFA yield increased from 590.6 to 1820.2, 1957.9 and 2194.9 mg COD/L, whilst the acetate ratio within SCFAs was raised from 34.1% to 61.2–70.9%. Furthermore, as TDC dosage increased, the relative activity of protease exhibited significant increments, reaching 116.3%, 168.0%, and 266.1%, respectively. This enhancement facilitated WAS solubilization and the release of organic substances from bound EPS into soluble EPS. Microbial analysis identified Tetrasphaera and Soehngenia as key participants in WAS solubilization and the breakdown of protein fraction. Metabolic analysis revealed that TDC triggered the secretion of enzymes associated with amino acid metabolism and fatty acid biosynthesis, thereby fostering the decomposition of proteins and production of SCFAs.

Unraveling synergistic mechanisms of polyacrylamide coagulation and Fe2+/CaO2 Fenton-like oxidation to enhance sludge dewatering

Enhancing sludge dewatering can effectively reduce the operational costs of wastewater treatment plants. In the present study, a synergistic process combining polyacrylamide (PAM) coagulation with Fe2+/CaO2 Fenton-like oxidation was proposed to improve the performance of sludge dewatering. The findings indicate that pre-addition of PAM before Fe2+/CaO2 treatment yielded superior dewatering performance, reducing the water content from 78.6% to 73.1% and the capillary suction time (CST) from 32.9 s to 19.5 s, respectively. Even with a CaO2 dosage of 62.5 mg/g DS, the ultimate pH of the filtrate remained near neutral, and effective dewatering performance was consistently attained. Results of particle size and zeta potential revealed that the addition of PAM enhanced the particle size by electric neutralization and bridging, thus accelerating sludge filtration. Furthermore, Fe2+/CaO2 facilitated the conversion of hydrophilic organic matter in tightly bound EPS (TB-EPS) to soluble EPS (SB-EPS) and loosely bound EPS (LB-EPS), and lysis of the sludge cells, contributing to a decrease in water content. Molecular analysis of EPS through Fourier-transform infrared spectroscopy (FT-IR) further elucidated the breakdown of hydrophilic functional groups by this combined method. Additionally, the changes of Fe2+, Fe3+, and H2O2 concentrations were investigated to explore the mechanism of enhanced sludge dewatering from a kinetic perspective. Ultimately, the concentration of typical heavy metals in the treated sludge sample significantly decreased, leading to a reduction in environmental risks. Overall, this study employed the safe and stable CaO2 as the source of H2O2, combined with Fe2+ to form a Fenton-like system. Meanwhile, PAM was utilized to flocculate the sludge firstly, and then Fe2+/CaO2 oxidation system was carried out to enhance sludge dewatering, which provided a promising sludge dewatering approach with potential applications.

Performance of a recirculated biogas-sparging anaerobic membrane bioreactor system for treating synthetic swine wastewater containing sulfadiazine antibiotic

Anaerobic Membrane Bioreactor (AnMBR) is an efficient system for treating synthetic swine wastewater (SW). However, the presence of antibiotics in SW discourages the activity of microorganisms, resulting in less pollutants removal and biogas production. In this paper, a recirculated biogas-sparging anaerobic membrane bioreactor system was used to treat swine wastewater containing sulfadiazine (SDZ). The effects of different concentrations of SDZ on the AnMBR system’s performance were explored, in terms of pollutant removal, biogas production, membrane fouling and microbial community. Results indicated that the larger concentration of SDZ triggered a strong suppression in the system’s performance. When treating 1.0 mg/L SDZ, the biogas-sparging AnMBR system achieved about 77 % COD removal and 0.23 L/g CODremoved biogas production, which without SDZ fell to 21 % COD being removed and dropped biogas production by 30 %. As well, the presence of SDZ (1.0 mg L) increased by about half the amount of soluble microbial product (SMP) and extracellular polymeric substances (EPS) with lower protein/polysaccharide ratio and reduced sludge particle size by 49 %. Meanwhile, microbial community analysis revealed that the abundance of Firmicutes increased while Chloroflexi diminished. These jointly contributed to a shorter membrane fouling cycle declining from the initial 23 d to 7 d. Furthermore, the shift from acetoclastic methanogens to hydrogenotrophic methanogens resulted in less methane production due to the presence of SDZ, while the hydrogenotrophic methanogen Methanobacterium promoted the degradation of SDZ. The work showed AnMBR can effectively treat swine wastewater containing antibiotics and provides basis for practical application.

Iron-Nitrogen Amendment Reduced Perfluoroalkyl Acids' Phyto-Uptake in the Wheat-Soil Ecosystem: Contributions of Dissolved Organic Matters in Soil Solution and Root Extracellular Polymeric Substances.

Understanding the mechanisms underlying perfluoroalkyl acids (PFAAs) translocation, distribution, and accumulation in wheat-soil ecosystems is essential for agricultural soil pollution control and crop ecological risk assessment. This study systematically investigated the translocation of 13 PFAAs under different iron and nitrogen fertilization conditions in a wheat-soil ecosystem. Short-chain PFAAs including PFBA, PFPeA, PFHxA, and PFBS mostly accumulated in soil solution (10.43-55.33%) and soluble extracellular polymeric substances (S-EPS) (11.39-14.77%) by the adsorption to amino- (-NH2) and hydroxyl (-OH) groups in dissolved organic matter (DOM). Other PFAAs with longer carbon chain lengths were mostly distributed on the soil particle surface by hydrophobic actions (74.63-94.24%). Iron-nitrogen amendments triggered (p < 0.05) soil iron-nitrogen cycling, rhizospheric reactive oxygen species fluctuations, and the concentration increases of -NH2 and -OH in the DOM structure. Thus, the accumulation capacity of PFAAs in soil solution and root EPS was increased. In sum, PFAAs' translocation from soil particles to wheat root was synergistically reduced by iron and nitrogen fertilization through increased adsorption of soil particles (p < 0.05) and the retention of soil solution and root EPSs. This study highlights the potential of iron-nitrogen amendments in decreasing the crop ecological risks to PFAAs' pollution.

Enhanced disintegration mechanism of surplus activated sludge to improve dewatering by thermally activated persulfate oxidation under mild temperature.

The dewatering treatment is an essential process for the treatment and disposal of surplus activated sludge (SAS), and improving sludge dewatering performance is still a challenge and has become a research hotspot in recent years. The oxidation and disintegration of bacterial cells and extracellular polymeric substances (EPS) by active radicals produced by advanced oxidation processes (AOPs) were extremely promising to achieve deep sludge dewatering. This paper systematically studied the efficiency and mechanism of thermally activated persulfate (TAP) oxidation technology to the improvement of SAS dewatering performance. The results showed that the relative filterability (CST0/CST) was increased 2.52 times with 2.0 mmol/g VSS potassium peroxydisulfate (PDS) at 80 °C in 90 min. Under this condition, the Zeta potential of SAS significantly decreased from - 14.8 to - 1.44 mV, while the average particle size (dp50) decreased from 52.981 to 48.259 μm. Thermal treatment disrupted the sludge structure to release large amounts of EPS including polysaccharides and protein. Meanwhile, the results of three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectra showed that the TAP treatment could expedite the disintegration of sludge, facilitating the decrease of total EPS content and conversion of tightly bound EPS (TB-EPS) to loosely bound EPS (LB-EPS) and soluble EPS (S-EPS). The mechanism of TAP process to improve SAS dewatering performance was revealed, which could contribute to breaking the bottleneck of sludge depth dewatering and provide a theoretical and technical basis for its practical application.

Excess Sludge Disintegration by Discharge Plasma Coupled with Thiosulfate

Surplus sludge disposal and treatment are major issues in wastewater treatment plants. Discharge plasma oxidation is an effective approach for sludge dewatering and digestion. In this study, excess sludge disintegration by non-thermal discharge plasma coupled with thiosulfate (TSA) was investigated. After 20 min of the single discharge plasma treatment, the soluble chemical oxygen demand (SCOD) increased to 404.93 mg L−1, and it climbed even more to 549.08 mg L−1 after adding 15 mmol L−1 of TSA. The water content of the filter cake also reduced even more in the presence of TSA. There was an appropriate dosage of TSA available. In the discharge plasma coupled with TSA system, reactive oxygen species (·OH and O2−) were generated and had significant involvement in the disintegration of the sludge. The addition of TSA enhanced the production of OH. These reactive oxygen species decomposed the floc structures and facilitated the transformation of organic compounds, resulting in a decrease in the average size of the sludge aggregates. The ratio of soluble extracellular polymer substances (S-EPS) was enhanced, while the ratio of the tightly bound fraction was reduced after the treatment. Thus, discharge plasma coupled with TSA promoted microbial cell lysis and facilitated the release of intracellular organic matter and bound water, ultimately enhancing the sludge’s dewaterability.

Behavior of organic components and the migration of heavy metals during sludge dewatering by different advanced oxidation processes via optical spectroscopy and molecular fingerprint analysis.

A comparative study of the different advanced oxidation processes (Fe(II)-Oxone, Fe(II)-H2O2, and Fe(II)-NaClO) was carried out herein to analyze the characteristics of organic components and the migration of heavy metals in waste activated sludge. With the Fe(II)-Oxone and Fe(II)-H2O2 treatments, sludge dewaterability was significantly improved, however, sludge dewaterability was deteriorated by the Fe(II)-NaClO treatment. The enhanced sludge dewaterability by the Fe(II)-Oxone and Fe(II)-H2O2 treatments was strongly correlated with the shifted organic components, particularly proteins, in soluble extracellular polymeric substances (S-EPS), while the deteriorated sludge dewaterability by the Fe(II)-NaClO treatment was strongly correlated with the over release of organic components from bound EPS (B-EPS) to S-EPS. For both the Fe(II)-Oxone and Fe(II)-H2O2 treatments, the radicals preferentially attacked humic acid-like organic components over the protein-like organic components in S-EPS, while for the Fe(II)-NaClO treatment, interestingly, the radicals preferentially attacked the protein-like organic components in both S-EPS and B-EPS. The hydrophilic functional groups like phenolic OH and CO of polysaccharides may be more preferentially migrated to S-EPS of sludge by the Fe(II)-NaClO treatment compared to the other two treatments. With the Fe(II)-Oxone and Fe(II)-H2O2 treatments, the proportion of aliphatic compounds as well as the much oxygenated organic components with a low desaturation and a low molecular weight increased. While with the Fe(II)-NaClO treatment, the proportion of low oxygenated organic components with a high desaturation and a high molecular weight increased. The concentration of total organic carbon, particularly the concentration of proteins, may be the key factor determining the shift of Zn and Cu from sludge solid to liquid phase, along with the high oxidation extent of organic components and close binding to CHOS and CHON compounds as indicated by density functional theory (DFT) calculation. This study systematically revealed the simultaneous sludge dewatering and migration of heavy metals when the role of organic components was factored into herein.

Insight into sludge dewatering by periodate driven directly with Fe(Ⅱ): Extracellular polymeric substances solubilization and mineralization

The production of waste activated sludge is expanding in tandem with the significant growth in the global population. It is important to explore sludge pretreatment technology to achieve sludge reduction. In this study, deep sludge dewatering was achieved by using Fe2+-catalyzed periodate (Fe2+/PI) conditioning. The result showed that capillary suction time was reduced by 48.27% under the optimum Fe2+ and PI dosages. ·OH, FeⅣ, O2·-, 1O2, and IO3· generated from the reaction between Fe2+ and PI, while ·OH (49.79%) and FeⅣ (47.76%) contributed significantly to sludge dewatering. Investigations of the mechanism revealed that the synergistic action of radical species oxidation and iron species flocculation in Fe2+/PI conditioning led to the mineralization and aggregation of hydrophilic substances in extracellular polymeric substances. The hydrophobic groups on the protein surface were more exposed to soluble extracellular polymeric substances and reduced protein-water interaction. The variations in zeta potential and particle size also verified the presence of a synergistic effect of oxidation and flocculation. The morphology observations revealed that the increased frictional forces generated when water flowed over the raw sludge (RS) surface prevented the rapid passage of internal water. In addition, the hydrophobic and electrostatic interactions in the sludge samples were essential influences that promoted flocculation and sedimentation of the sludge. This research aids engineers by providing a new option to better optimize sludge management while also deepening understanding of the Fe2+/PI conditioning involved in sludge dewatering.

Organic carbon source excites extracellular polymeric substances to boost Fe0-mediated autotrophic denitrification in mixotrophic system

Fe0-mediated autotrophic denitrification (ADN) can be suppressed by iron oxide coverage resulting from Fe0 corrosion. The mixotrophic denitrification (MDN) coupling Fe0-mediated ADN with heterotrophic denitrification (HDN) can circumvent the weakening of Fe0-mediated ADN over operation time. But the interaction between HDN and Fe0-mediated ADN for nitrogen removal of secondary effluent with deficient bioavailable organics remains unclear. When the influent COD/NO3−-N ratio increased from 0.0 to 1.8–2.1, the TN removal efficiency was promoted significantly. The increased carbon source did not inhibit ADN, but promoted ADN and HDN synchronously. The formation of extracellular polymeric substances (EPS) was also facilitated concomitantly. Protein (PN) and humic acid (HA) in EPS increased significantly, which capable of accelerating electron transfer of denitrification. Due to that the electron transfer of HDN occurs intracellularly, the EPS with the capacity of accelerating electron transfer had a negligible influence on HDN. But for Fe0-mediated ADN, the increased EPS as well as corresponding PN and HA facilitated TN and NO3−-N removal significantly, while accelerated the electron release originating from Fe0 corrosion. The bioorganic-Fe complexes were generated on Fe0 surface after used, meaning that the soluble EPS and soluble microbial products (SMP) participated in the electron transfer of Fe0-mediated ADN. The coexistence of HDN and ADN denitrifiers demonstrated the synchronous enhancement of HDN and ADN by the external carbon source. From the perspective of EPS and related SMP, the insight of enhancing Fe0-mediated ADN by external carbon source is beneficial to implement high-efficiency MDN for organics-deficient secondary wastewater.