Soluble Extracellular Polymeric Substances Research Articles

Alleviating membrane fouling by enhanced bioelectricity generation via internal reflux of sludge mixed liquor in microbial fuel cell-membrane bioreactor (MFC-MBR) coupling system

The in-situ utilization of sludge mixed liquor was innovatively applied in microbial fuel cell and membrane bioreactor (MFC-MBR) coupling system. MFC-MBR coupling systems with different return flow ratio were designed to investigate the effects of return flow on bioelectricity generation and subsequently membrane fouling mitigation. The results indicated that bioelectricity generation was largely enhanced with the increasing return flow ratio. Furthermore, the slow growth of the transmembrane pressure (TMP) was found in MFC-MBR coupling systems that with return flow ratios of 0.50 and 0.75, respectively (0.66 kPa/d and 0.57 kPa/d). It was evident from the declined absolute value of zeta potential in systems with return flow ratio, which enlarged the flocculation of sludge particles and was in accordance with the particle size distribution. The increase rate of soluble microbial products (SMP) and extracellular polymeric substances (EPS) were also significantly dropped while the ratio of protein to polysaccharide in SMP and EPS rose in MFC-MBR coupling systems with return flow. Importantly, Bacteroidetes and Chlorobiaceae were more abundant in MFC-MBR coupling systems with higher return flow ratios. Thus, MFC-MBR coupling system with internal reflux of sludge mixed liquor was effective in improving bioelectricity generation and minimizing membrane fouling.

Pretreatment of Slaughterhouse Effluent Treatment Plant Sludge Using Electro-Fenton Process for Anaerobic Digestion

Sludge management is an integral process of an effluent treatment plant (ETP). This study aimed at using the electro-Fenton (EF) process for pretreatment of a cattle-based slaughterhouse ETP sludge to enhance biogas production from anaerobic digestion. EF-oxidation experiments were conducted in 0.5 L beakers with mild-steel electrodes, to study the effect of factors, viz., H2O2 concentration, current density and reaction time on soluble chemical oxygen demand (sCOD) concentration, soluble extracellular polymeric substances (sEPS) concentration and volatile suspended solids (VSS) removal efficiency. This was followed by the quantification of biogas production from the raw and pretreated sludge in anaerobic digestion (AD). Experimental conditions for the EF process were optimized using response surface methodology (RSM). At optimized experimental conditions, EF pretreatment resulted in an increase in sCOD and sEPS concentrations, from 0.91 g/L to 6.1 g/L and 0.18 g/L to 1.4 g/L, respectively. VSS removal efficiency was 68.1%. Batch anaerobic digestion studies demonstrated an enhancement in the specific biogas yield, from 110 NmL/g-VS to 460 NmL/g-VS.

Spatial distribution of fecal pollution indicators in sewage sludge flocs and their removal and inactivation as revealed by qPCR/viability-qPCR during potassium ferrate treatment.

Sludge reuse and utilization is one of important routines of disseminating fecal pollution to surface water and groundwater. However, it remains unclear the spatial distribution of fecal pollution indicators in sludge flocs and their reductions during sludge treatment processes. In this study, the abundances of fecal pollution indicators including cross-assembly phage (crAssphage), JC and BK polyomavirus (JCPyV, BKPyV), human adenovirus (HAdV), the human-specific HF183 Bacteroides (HF183) and Escherichia coli (EC) in soluble extracellular polymeric substances (S-EPS), loosely-bound EPS (LB-EPS), tightly-bound EPS (TB-EPS), and pellets of sludge flocs were determined, and the effect of potassium ferrate (PF) treatment on their removal and inactivation was investigated by using both qPCR and viability-qPCR. Results showed that all investigated indicators were detected in each fraction of sludge flocs. The PF treatment led to a great migration of indicators from sludge pellets to sludge EPS and some extent of their inactivation in each fraction of sludge flocs. The overall reductions of human fecal indicators in sludge determined by qPCR were 0-1.30logs, which were 0-2 orders of magnitude lower than those of 0.69-2.39logs detected by viability-qPCR, implying their inactivation by PF treatment to potentially alleviate the associated human health risks.

Streptococcus mutans soluble extracellular polymeric substances and sodium molybdate as mixed corrosion inhibitor for X70 steel

Streptococcus mutans soluble extracellular polymeric substances and sodium molybdate as mixed corrosion inhibitor for X70 steel

The mechanism of extracellular polymeric substances in the formation of activated sludge flocs

In this study, activated sludge (AS) presented high aggregation ability of 56.9% to form flocs. To elucidate the effects of extracellular polymeric substances (EPS) on the AS flocs formation, four EPS fractions, including soluble EPS (S-EPS), loosely bound EPS (LB-EPS), ionic tightly bound EPS (ionic TB-EPS) and hydrophobic tightly bound EPS (hydrophobic TB-EPS), were extracted and characterized. The ionic TB-EPS were the largest fraction, accounting for 51.3% of the total EPS. By extracting EPS fractions, it was shown that ionic TB-EPS followed by hydrophobic TB-EPS played positive contribution to the formation of AS flocs, while both S-EPS and LB-EPS had negative effects. Furthermore, chemical reagents (Urea, SDS and EDTA) assays, zeta potential and spectroscopic assays were conducted to explore the role of hydrogen bonds, electrostatic interaction and hydrophobic interaction in the formation of AS flocs. The result showed that ionic TB-EPS contained sufficient cation-binding sites, such as -OH and CO-O- groups, and promoted AS aggregation through ion bridging. Hydrophobic TB-EPS contained hydrophobic groups and promoted AS aggregation through hydrophobic action. A high proportion of uronic acids resulted in high surface negative charge, which might be the reason that LB-EPS and S-EPS inhibited AS aggregation through electrostatic repulsion. From the perspective of molecule structure, the proteins in ionic TB-EPS had a loose structure, which fully exposed the inner cation-binding sites. This might be the critical reason why ion bridging acted as the main force for the formation of AS flocs. This study provided a new sight for the extraction of EPS fractions and expanded the understanding of EPS in the formation of AS flocs.

Performance Enhancement of an Upflow Anaerobic Dynamic Membrane Bioreactor via Granular Activated Carbon Addition for Domestic Wastewater Treatment

Developing low-carbon advanced processes for sustainable wastewater treatment is of great importance to increase bioenergy recovery and to reduce the greenhouse gas effect. In this study, the influence of adding 25 g/L of granular activated carbon (GAC) on the process performance was studied with a lab-scale GAC amended anaerobic dynamic membrane (G-AnDMBR) used to treat real domestic wastewater, which was compared to a control bioreactor without the GAC addition (C-AnDMBR). Due to the initial adsorption effect of GAC and the high microbial activity of the attached biomass of GAC, the G-AnDMBR achieved a better removal of the total chemical oxygen demand (TCOD) and turbidity compared to the C-AnDMBR, with the average removal rate increasing from 82.1% to 86.7% and from 88.7% to 93.2%. The gaseous methane production increased from 0.08 ± 0.05 to 0.14 ± 0.04 L/d, and the total methane production rate was enhanced from 0.21 ± 0.11 to 0.23 ± 0.09 LCH4/gCOD. Thus, the treatment performance of the G-AnDMBR was superior to that of the C-AnDMBR, and the addition of GAC could improve the effluent quality during the initial dynamic membrane formation process. In addition, the buffering effect of GAC made the G-AnDMBR maintain a relatively stable solution environment. The G-AnDMBR showed a transmembrane pressure (TMP) increasing rate of 0.045 kPa/d, which was obviously lower than that of the C-AnDMBR (0.057 kPa/d) because the nonfluidized GAC could trap fine sludge particles and adsorb soluble extracellular polymer substances (SEPSs), thus inhibiting the over formation of the dynamic membrane layer. A microbial property analysis indicated that GAC induced a change in the microbial community and enhanced the gene abundance of type IV pili and that it also potentially accelerated the direct interspecific electron transfer (DIET) among syntrophic bacteria and methanogens by enriching specific functional microorganisms. The results indicated that the integration of GAC and the AnDMBR process can be a cost-effective and promising alternative for domestic wastewater treatment and bioenergy recovery.

Unraveling the impacts of Cu+-based treatments on sludge dewaterability: The overlooked role of Cu3+

The high water content of sewage sludge increases the processing costs and hampers its further disposal. Fenton technology has proven to be efficient and been widely used to enhance sludge dewaterability, but it usually needs acidification and subsequent neutralization, thus consuming a lot of chemicals. It’s well documented that hydroxyl radicals produced in various Fenton or Fenton-like reactions play a crucial role in sludge dewatering. Based on the latest study, Cu+ and Cu+/H2O2 pretreatments for the enhanced dewaterability of sludge without extra pH adjustment were proposed. Results showed that Cu+ with and without H2O2 can significantly improve the dewatering performance of sludge, which was ascertained by a capillary suction time (CST) reduction rate of about 80 %. The proteins and polysaccharides in tightly-bound extracellular polymeric substance (TB-EPS) were decreased, while increased in soluble extracellular polymeric substance (S-EPS). In addition, a hydrophobic and porous surface was formed, and zeta potential increased after conditioned. These changes may release bound water and thus improve sludge dewaterability. The results of electron spin resonance and scavenging tests signaled that the Cu3+ was mainly accountable for the dissolution of EPS, rather than the hydroxyl radicals (OH). Our results substantiate and untangle a distinct reinforcement mechanisms for sludge dewatering by high valent copper (Cu3+). This study demonstrates for the first time that Cu3+ plays an important role in sludge dewatering, which has long been credited to hydroxyl radicals. It also urges re-evaluation of the Fenton(-like) system for sludge dewatering, given that Cu3+ could also cause potential oxidative destruction of EPS compared with reactive oxygen species.

Treating Tapioca Starch Industrial Wastewater Using Two-Phase Multi-Staged Up-Flow Anaerobic Sludge Blanket (MS-UASB)

A laboratory-scale, two-phase multi-staged up-flow anaerobic sludge blanket (MS-UASB) treatment system was monitored over time in order to evaluate its treatment efficiency and performance when treating non-diluted industrial tapioca starch wastewater under ambient temperature in Thailand. The system consisted of an acidification (AC) reactor and MS-UASB reactor and was operated for 280 days. The two-phase MS-UASB achieved a maximum organic loading rate (OLR) of 8 kg-COD/m3/day for the overall system and reached 80.5% of chemical oxygen demand (COD) removal efficiency. Based on the inlet wastewater of each reactor, the AC reactor removed 61.85% of suspended solids and achieved acidification of the wastewater to produce volatile fatty acids at over 50%. Meanwhile, the MS-UASB reactor achieved 74.5% COD removal efficiency. Further analysis found that the increase in soluble extracellular polymeric substances per bound extracellular polymeric substances (S-EPS/B-EPS) was related to the floating sludge phenomenon, which occurred under excess OLR condition.

Bioregulation of FeNi LDH morphology and electronic structure to highly promote electrocatalytic oxygen evolution

NiFe-based layered double hydroxides (LDHs) are currently the most efficient oxygen evolution reaction (OER) catalysts in alkaline medium. However, their shortcomings such as insufficient electron transport ability, few exposed active sites and susceptibility to aggregation hindered their further development. In this paper, soluble extracellular polymer substances (s-EPS) modified by urea was used as biosurfactant and pH regulator, micro-morphology and electronic structure of FeNi LDH were accurately regulated to upgrade its stability, electrical conductivity, electrochemical active surface area and kinetic process. Tryptophan residue protein in EPS is mainly responsible for the interaction between s-EPS and FeNi LDH. Experimental and theoretical calculation results demonstrate that the introduction of s-EPS can coordinate the morphology and electron distribution of active centers, consequently optimizing the adsorption energy of reaction intermediates and enhancing the inherent catalytic activity for OER. As expected, s-EPS@FeNi LDH exhibited excellent OER performance under alkaline conditions, and only had an overpotential of 220 mV at a current density of 10 mA cm−2, which is superior to other promising FeNi-based catalysts. This work sheds light on realizing the efficient assembly of LDH and s-EPS, and provides a reliable method for the morphology and electronic structure modification of LDH for more efficient OER.

Fouling evolution of extracellular polymeric substances in forward osmosis based microalgae dewatering

Membrane fouling was still a challenge for the potential application of forward osmosis (FO) in algae dewatering. In this study, the fouling behaviors of Chlorella vulgaris and Scenedesmus obliquus were compared in the FO membrane filtration process, and the roles of their soluble-extracellular polymeric substances (sEPS) and bound-EPS (bEPS) in fouling performance were investigated. The results showed that fouling behaviors could be divided into two stages including a quickly dropped and later a stable process. The bEPS of both species presented the highest flux decline (about 40.0%) by comparison with their sEPS, cells and broth. This performance was consistent with the largest dissolved organic carbon losses in feed solutions, and the highest interfacial free energy analyzed by the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory. The chemical characterizations of algal foulants further showed that the severe fouling performance was also consistent with a proper ratio of carbohydrates and proteins contents in the cake layer, as well as the higher low molecular weight (LMW) components. Compared with the bEPS, the sEPS was crucial for the membrane fouling of S. obliquus, and an evolution of the membrane fouling structure was found in both species at the later filtration stage. This work clearly revealed the fundamental mechanism of FO membrane fouling caused by real microalgal suspension, and it will improve our understanding of the evolutionary fouling performances of algal EPS.

Improved Dewaterability of Waste Activated Sludge by Fe(II)-Activated Potassium Periodate Oxidation.

Fe(II)-activated potassium periodate (KIO4) oxidation was used to improve the dewaterability of waste-activated sludge for the first time. Compared with those of raw sludge, the capillary suction time (CST), specific resistance filtration (SRF), and water content of filter cake (WC) of sludge treated using the Fe(II)/KIO4 process under the optimal conditions (i.e., the initial pH = 6.8, KIO4 dose = 1.4 mmol/g volatile suspended solids, Fe(II)/KIO4 molar ratio = 1.2) decreased by 64.34%, 84.13%, and 6.69%, respectively. For conditioned sludge flocs, the Zeta potential and particle size were increased, and hydrophilic proteins in extracellular polymeric substances (EPS) were partly degraded, accompanied by the transformation of tightly bound EPS into soluble EPS and the conversion of dense sludge flocs into loose and porous ones. During Fe(II)/KIO4 oxidation, Fe(IV) and the accompanying •OH were determined as the predominant reactive species and the underlying mechanism of sludge EPS degradation was proposed. This work provides a prospective method for conditioning the sludge dewaterability.

Effect of salinity on removal performance of anaerobic membrane bioreactor treating azo dye wastewater.

Membrane bioreactor (MBR) is an attractive option method for treating azo dye wastewater under extreme conditions. The present study assessed the effect of salinity on the performance of anaerobic MBR in treating azo dye wastewater. Increased salinity showed adverse effects on the decolorization efficiency and chemical oxygen demand (COD) removal efficiency. The decolorization efficiency decreased from 95.8% to 82.3% and 73.1% with a stepwise increasing of salinity from 0 to 3% and 5%, respectively. The COD removal efficiency decreased from 80.7% to 71.3% when the salinity increased from 0 to 3% and then decreased to 58.6% at 5% salinity. The volatile fatty acids (VFAs) concentration also increased as the salinity increased. Furthermore, increased salinity led to the elevated production of soluble microbial products (SMP) and extracellular polymeric substances (EPS), which can provide a protective barrier against harsh environments. More serious membrane fouling was observed as the SMP and EPS concentrations increased. The concentration of loosely bound EPS (LB-EPS), tightly bound EPS (TB-EPS), and the polysaccharide/protein (PS/PN) ratios in LB-EPS and TB-EPS all increased when the salinity was elevated. The production of SMP and EPS was caused by the generation of PS in response to the saline environment. Lactobacillus, Lactococcus, Anaerosporobacter, and Pectinatus were the dominant bacteria, and Lactobacillus and Lactococcus were the decolorization bacteria in the MBR. The lack of halophilic bacteria was the main reason for the decreased decolorization efficiency in the salinity environment.

Soluble Extracellular Polymeric Substances Produced by Parachlorella kessleri and Chlorella vulgaris: Biochemical Characterization and Assessment of Their Cadmium and Lead Sorption Abilities.

In the present study, the potential of lead and cadmium removal by the extracellular polymeric substances (EPS) produced from Parachlorella kessleri and Chlorella vulgaris were investigated. Carbohydrates were the dominant components of EPS from both analyzed species. The contents of reducing sugars, uronic acids, and amino acids were higher in EPS synthesized by C. vulgaris than in EPS from P. kessleri. The analysis of the monosaccharide composition showed the presence of rhamnose, mannose and galactose in the EPS obtained from both species. The ICP-OES (inductively coupled plasma optical emission spectrometry) analyses demonstrated that C. vulgaris EPS showed higher sorption capacity in comparison to P. kessleri EPS. The sorption capacity of C. vulgaris EPS increased with the increase in the amount of metal ions. P. kessleri EPS had a maximum sorption capacity in the presence of 100 mg/L of metal ions. The FTIR analysis demonstrated that the carboxyl, hydroxyl, and carbonyl groups of EPS play a key role in the interactions with metal ions. The present study showed C. vulgaris EPS can be used as a biosorbent in bioremediation processes due to its biochemical composition, the presence of significant amounts of negatively charged uronic acids, and higher sorption capacity.

Evaluation of membrane fouling at elevated temperature impacted by algal organic matter

Membrane distillation (MD) is a thermally driven technology applied in desalination and water reuse with utilisation of sustainable energy. However, algal organic matter (AOM) could foul membrane critically and plague MD's long-term operational stability. In this study, the soluble extracellular polymeric substance (sEPS) and intracellular organic matter with bound extracellular polymeric substance (IOM + bEPS) of two algal species (Amphora coffeaeformis and Navicula incerta) were exposed to 60 °C, 70 °C and 80 °C for 8 h with polypropylene hydrophobic membrane, simulating heated AOMs contacted with membrane inside MD unit, to study the temperature effect on membrane fouling. The dissolved carbohydrate and protein in the sEPS and IOM + bEPS samples generally increased after being heated. Heating caused cell lysis and the release and dissolution of carbohydrate and protein from sEPS, IOM and bEPS into water. As heating temperature increased, the carbohydrate release from the AOM usually increased. The contact angle of membrane contacted with sEPS and IOM + bEPS reduced significantly after heat treatment. The reduction in IOM + bEPS was larger than sEPS, in line with SEM analysis, indicating membrane surfaces and pores with IOM + bEPS fouled more severely than sEPS. It is due to higher hydrophobicity in IOM + bEPS causing adherence to membrane and presence of amphiphiles. High protein, lipid, and saturated fats proportions also cause severe fouling. SEM-EDX analysis indicated presence of O, Na, Cl and Mg elements, pointing to carbohydrate and lipids, and salt trapped in foulants. AOM heating and composition had direct effect to the membrane integrity, dictating severity of fouling in MD operations.

Soluble extracellular polymeric substance (SEPS) of histo-blood group antigen (HBGA) expressing bacterium Sphingobacterium sp. SC015 influences the survival and persistence of norovirus on lettuce

Foodborne norovirus (NoV) outbreaks linked to leafy greens are common due to a lack of efficient strategies to prevent NoV spread from contaminated surfaces. We previously found that Sphingobacterium sp. SC015 in lettuce phyllosphere expresses histo-blood group antigen (HBGA)-like substances in soluble extracellular polymeric substances (SEPS) that contribute to NoV adherence on lettuce. Here, we extracted SEPS from bacterium SC015 (SEPS-SC015), analyzed their chemical composition, and examined their roles in the survival and protection of NoV and surrogates [murine norovirus (MNV-1) and Tulane virus (TuV)] on lettuce. Presence of SEPS-SC015 significantly increased survival and persistence of human NoV (HuNoV), MNV-1, and TuV at days 7 and 14, compared with virus alone. HuNoV, TuV, and MNV-1 seeded with SEPS-SC015 were more resistant to heat (70 °C, 2 min) than these viruses alone. SEPS-SC015 also increased viral resistance to sodium hypochlorite inactivation by treatment with 30 and 300 ppm bleach at 26 °C for 10 min. However, SEPS-SC015 was not effective at protecting these viruses under UV inactivation. Binding of TuV to SC015 bacteria and SEPS-SC015, visualized using transmission electron microscopy, suggests that protection might be related to direct interaction between SEPS-SC015 and viral particles. This study provides important insights that will help inform strategies to improve food safety.

Effects of extracellular polymeric substances on the aggregation of Aphanizomenon flos-aquae under increasing temperature.

Aphanizomenon flos-aquae (A. flos-aquae) blooms are serious environmental and ecological problems. Extracellular polymeric substances (EPSs) are among the most important indicators for the growth and aggregation of A. flos-aquae. In this study, the secretion of the EPS matrix under temperature rise (7–37°C) was investigated and the role of this matrix in A. flos-aquae aggregation was quantified. First, when the temperature increased, the aggregation ratio increased from 41.85 to 91.04%. Meanwhile, we found that when soluble EPSs (S-EPSs), loosely bound EPSs (LB-EPSs), and tightly bound EPSs (TB-EPSs) were removed successively, the aggregation ratio decreased from 69.29 to 67.45%, 61.47%, and 41.14%, respectively. Second, the content of polysaccharides in the EPS matrix was higher than the content of proteins under temperature change. The polysaccharide in TB-EPSs was closely related to the aggregation ability of A. flos-aquae (P < 0.01). Third, PARAFAC analysis detected two humic-like substances and one protein-like substance in EPSs. Furthermore, Fourier transforms infrared spectroscopy (FTIR) showed that with increasing temperature, the polysaccharide-related functional groups increased, and the absolute value of the zeta potential decreased. In conclusion, these results indicated that a large number of polysaccharides in TB-EPSs were secreted under increasing temperature, and the polysaccharide-related functional groups increased correspondingly, which reduced the electrostatic repulsion between algal cells, leading to the destruction of the stability of the dispersion system, and then the occurrence of aggregation. This helps us to understand the process of filamentous cyanobacterial aggregation in lakes.

Effects of hydrogen peroxide and calcium hypochlorite on chemical oxygen demand solubilization and disintegration of waste activated sludge by electro-chemical pretreatment

ABSTRACT The combination of electrochemical (EC) pretreatment with hydrogen peroxide (HP) and calcium hypochlorite (CHC) was investigated in this study for their effect on soluble chemical oxygen demand (CODs) and disintegration degree (DD) of waste activated sludge (WAS). For this aim, response surface methodology (RSM) and Box–Behnken design (BBD) were applied the determination of the optimum operational conditions. Operational conditions were varied between 0.2 and 2.0 mmol/g SS for HP and CHC dosages, 1–5 A for the applied current, 2–10 for the initial pH, and 15–45 min for the treatment time. Obtained results for each treatment were accurate and significant with correlation coefficients (R2) of 0.8639% and 0.9189% for EC combined with HP pretreatment and EC combined with CHC pretreatment, respectively. According to the obtained results, CODs increased in comparison to the raw sludge (168 mg/L) noting that CODs for EC – CHC (1155 ± 21 mg/L) was higher than EC – HP (811.5 ± 15 mg/L) at optimized conditions (for EC-HP pretreatment: HP dosage: 0.34 mmol/g TSS, Applied current:5 A, Initial pH:10, Time: 45 min, For EC-CHC pretreatment: CHC dosage: 0.23 mmol/g TSS, Applied current:4.83 A, Initial pH:10, Time: 40 min). Besides, the DD in terms of COD, total nitrogen (TN) and total organic carbon (TOC) (DDCOD, DDTN and DDTOC) registered increased values after the application of the EC treatment with both oxidants. The highest DDCOD, DDTN and DDTOC values were obtained with EC-CHC pretreatment for 11.34%, 20.34% and 9.18% respectively compared to EC-HP pretreatment (DDCOD: 7.37%, DDTN: 15.18% and DDTOC: 6.94%).

Novel Extrapolymeric Substances Biocoating on Polyvinylidene Fluoride Membrane for Enhanced Attached Growth of Navicula incerta.

Cell adhesion is always the first step in biofilm development. With the emergence of attached cultivation systems, this study aims to promote a cost-effective approach for sustainable cultivation of microalgae, Navicula incerta, by pre-coating the main substrates, commercial polyvinylidene fluoride (PVDF) membranes with its own washed algal cells and self-produced soluble extracellular polymeric substances (EPS) for strengthened biofilm development. The effects of pH value (6 to 9), cell suspension volume (10 to 30mL), and EPS volume (10 to 50mL) were statistically optimized by means of response surface methodology toolkit. Model outputs revealed good agreement with cell adhesion data variation less than 1% at optimized pre-coating conditions (7.20 pH, 30mL cell suspension volume, and 50mL EPS volume). Throughout long-term biofilm cultivation, results demonstrated that EPS pre-coating substantially improved the attached microalgae density by as high as 271% than pristine PVDF due to rougher surface and the presence of sticky exopolymer particles. Nutrients absorbed via the available EPS coating from the bulk medium made the immobilized cells to release less polysaccharides on an average of 30% less than uncoated PVDF. This work suggests that adhesive polymer binders derived from organic sources can be effectively integrated into the development of high-performance novel materials as biocoating for immobilized microalgae cultivation.

The dewatering performance and cracking-flocculation-skeleton mechanism of bioleaching-coal fly ash combined process for sewage sludge

High water content in sludge will affect the transportation and subsequent disposal of sludge. Bioleaching is a biological sludge conditioning technology, which can effectively improve the dewatering performance of sludge and reduce the content of heavy metals in sludge. Coal fly ash, as a skeleton builder, can also improve the dewatering performance of sludge. In this study, bioleaching combined with coal fly ash (BL-CFA) process was employed to improve sludge dewatering performance. Based on the results of response surface methodology (RSM), the capillary suction time (CST) and water content (WC) of sludge decreased by 52.27% and 38.92%, respectively. The dewatering effect of BL-CFA is superior compared with single process. For extracellular polymeric substances (EPS), the content of protein and polysaccharide in tightly and loosely EPS (TB-EPS and LB-EPS) of sludge decreased after BL-CFA process, while that in soluble EPS (S-EPS) increased. Three-dimensional fluorescence indicated that the weakened fluorescent areas of proteinoid and soluble microbial by-product-like (SMP) organic in LB-EPS and TB-EPS, which is beneficial to the improvement of sludge dewatering performance. Fourier transform infrared (FTIR) spectroscopy showed that the polysaccharides and proteins in the sludge were cleaved and released into the supernatant after BL-CFA process. The variation of particle size revealed that flocculation occurred after adding CFA into acidified sludge, and a supporting structure was formed in the sludge with the assist of CFA through the analysis of the scanning electron microscopy (SEM). Based on the above results, a triple dehydration mechanism was proposed for BL-CFA process, namely, cracking-flocculation-skeleton construction, which endows the combined process with superior sludge dewatering effect and application potential.

Enhanced dewaterability of lake dredged sediments by electrochemical oxidation of peroxydisulfate on BDD anode

Dredged sediments, as a product of mitigating endogenous pollution of rivers and lakes, cause severe environmental pollution without suitable disposal. To reduce dredged sediments, the electrochemical oxidation (EO) of peroxydisulfate (PS) on a boron-doped diamond (BDD) anode (EO/BDD-PS) was utilized to enhance the dewaterability of the dredged sediments. The soluble chemical oxygen demand increased in the EO/BDD-PS system, and more than 70.0% of the specific resistance to filtration was reduced by EO/BDD-PS within 20 min. The optimal conditions were determined to be as follows: current density, 30 mA cm−2; PS dosage 4 g L−1; and initial pH, 6.96. After treatment with EO/BDD-PS, the electronegativity of the sludge flocs was alleviated and the particle size increased from 7.61 to 10.64 μm. Furthermore, proteins and polysaccharides were degraded, and tightly bound extracellular polymeric substances (TB-EPS) and loosely bound EPS (LB-EPS) were effectively transported to soluble EPS (S-EPS). Furthermore, humification of organic matter occurred in S-EPS and LB-EPS when the dredged sediment was treated with EO/BDD-PS. Dominant hydroxyl radicals (•OH) and sulfate radicals (SO4•−) were generated in the EO/BDD-PS system. Moreover, the efficiency of the filtrate as an electrolyte decreased slightly after recycling five times. Therefore, this method may be economical for enhancing the dewaterability of dredged sediments.