Recovery of structural extracellular polymeric substances (sEPS) from aerobic granular sludge: Insights on biopolymers characterization and hydrogel properties for potential applications

Response mechanism of extracellular polymers in the remediation of chromium pollution by carbonate mineralizing bacteria

This study examines the adaptability of carbonate mineralizing bacteria in Cr(iii)-contaminated environments with varying Cr(iii) concentrations and their response mechanism via EPS. Cr(iii) removal efficiency declined with concentrations exceeding 1000 mg L-1, while the removal amount continued to rise, indicating strong Cr(iii) tolerance in the bacterium. Analysis of dynamic changes in EPS revealed a significant increase in production, with polysaccharides and proteins playing key roles in Cr(iii) binding. A notable increase in mannose in the monosaccharide composition of EPS suggests its involvement in Cr(iii) binding. Moreover, alterations in the protein secondary structure, such as a reduction in α-helix content and an increase in β-sheet and random coil structures, may enhance EPS interaction with Cr(iii). These findings demonstrate that EPS contributes to heavy metal remediation not only through its polysaccharide components but also through changes in protein structure, offering a new theoretical foundation for Cr(iii) bioremediation.

Effects of Extraction Methods on the Thermal Stability of Extracellular Polymeric Substances-Based Biomaterials from Wastewater Sludge

Various methods for recovering extracellular polymeric substances (EPS)-based biomaterials from wastewater sludge exist. However, the relationships between extraction methods and properties of biomaterials have not been fully explored. In this study, the thermal properties, including activation energy (AE) and thermal decomposition mechanism, of EPS-based biomaterials extracted by different methods have been determined by thermogravimetric analysis integrated with the deconvolution method. Simultaneously, the chemical properties of these biomaterials, such as the extraction yield, chemical composition, and functional groups, have been monitored to clarify the influences of extraction methods. Notably, proteins and humic-like substances have been found as the major components to determine thermal stability and AE. Moreover, the physicochemical method shows significant effects on enhancing extraction yield and AE, with the NaOH and heat methods proving to be outstanding by delivering the highest AE of 300 kJ/mol and a substantial char formation of 24%. The results have demonstrated the significant impact of extraction methods on the thermal stability of EPS-based biomaterials. Moreover, this finding provides insights into the linkages between the properties of EPS-based biomaterials and extraction methods to guide the selection of appropriate extraction methods tailored to specific applications, including flame-resistant materials.

Variation of viscoelastic properties of extracellular polymeric substances and their relation to anaerobic granule's mechanical strength in full-scale treatment plants

Extracellular polymeric substances (EPS) are considered to play a pivotal role in shaping granules' physical properties. In this contribution, we characterized the viscoelastic properties of EPS from granules of 9 full-scale industrial anaerobic reactors; and quantitatively investigated whether these properties correlate with granules' resistance to compression (Egranule) and shear strength (Sgranule). Most granules with a higher shear strength, also exhibited a stronger resistance to compression (r = 0.96, p = 0.002), except those granules that contained relatively more proteins in their EPS. Interestingly, these granules were also the most resistant to shear stress (Sgranule ≥ 110 ± 40 h). Furthermore, the EPS hydrogels of these granules had slower softening rates (κ < 0.9) compared to the others (κ ranged between 0.95 and 1.20), indicating stronger gels were formed. These findings suggest that the EPS hydrogel softening rate could be a key parameter to explain granule's shear strength.

Aerobic granulation and resource production under continuous and intermittent saline stress

Three sequential batch reactors (SBR) were operated to evaluate salt addition's impact on granulation, performance, and biopolymer production in aerobic granular sludge (AGS) systems. System R1 was fed without adding salt (control); system R2 operated with saline pulses, i.e., one cycle with salt (2.5 g NaCl/L) addition followed by another without salt; and R3 received continuous supplementation of 2.5 g NaCl/L. The results indicated that the reactors supplemented with salt presented higher concentrations of mixed liquor volatile suspended solids (MLVSS) and better settleability than R1, showing that osmotic pressure contributed to biomass growth, accelerated granulation, and improved physical characteristics. The faster granulation occurred in R2, thus proving the beneficial effects of intermittent salt addition through alternating pulses. Salt addition did not impair the simultaneous removal of carbon, nitrogen, and phosphorus. In fact, R2 showed better carbon removals. In conclusion, continuous or intermittent (pulsed) supplementation of 2.5 g NaCl/L did not lead to increased production of extracellular polymeric substances (EPS) and alginate-like exopolymers (ALE). This outcome could be attributed to the low saline concentration employed, a higher food-to-microorganism (F/M) ratio observed in R1, and possibly greater endogenous consumption of biopolymers in the famine period in R2 and R3 due to the greater solids retention time (SRT). Therefore, this study brings important results that contribute to a better understanding of the effect of salt in continuous dosing or in pulses as a selection pressure strategy to accelerate granulation, as well as the behavior of the AGS systems for saline effluents.

Optimizing carbon sources regulation in the biochemical treatment systems for coal chemical wastewater: Aromatic compounds biodegradation and microbial response strategies

The complex composition of coal chemical wastewater (CCW), marked by numerous highly toxic aromatic compounds, induces the destabilization of the biochemical treatment system, leading to suboptimal treatment efficacy. In this study, a biochemical treatment system was established to efficiently degrade aromatic compounds by quantitatively regulating the dosage of co-metabolized substrates (specifically, the chemical oxygen demand (COD) Glucose: COD Sodium acetate = 3:1, 1:3, and 1:1). The findings demonstrated that the system achieved optimal performance under the condition that the ratio of COD Glucose to COD Sodium acetate was 3:1. When the co-metabolized substrate was added to the system at an optimal ratio, examination of pollutant removal and cumulative effects revealed that the removal efficiencies for COD and total organic carbon (TOC) reached 94.61 % and 86.40 %, respectively. The removal rates of benzene series, nitrogen heterocyclic compounds, polycyclic aromatic hydrocarbons, and phenols were 100 %, 100 %, 63.58 %, and 94.12 %, respectively. Research on the physiological response of microbial cells showed that, under optimal ratio regulation, co-metabolic substrates led to a substantial rise in microbial extracellular polymeric substances (EPS) secretion, particularly extracellular proteins. When the system reached the end of its operation, the contents of loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) for proteins in the optimal group were 7.12 mg/g-SS and 152.28 mg/g-SS, respectively. Meanwhile, the ratio of α-Helix / (β-Sheet + Random coil) and the proportion of intermolecular interaction forces were also increased in the optimal group. At system completion, the ratio of α-Helix / (β-Sheet + Random coil) reached 0.717 (LB-EPS) and 0.618 (TB-EPS), respectively. Additionally, the proportion of intermolecular interaction forces reached 74.83 % (LB-EPS) and 55.03 % (TB-EPS). An in-depth analysis of the metabolic regulation of microorganisms indicated that the introduction of optimal ratios of co-metabolic substrates contributed to a noteworthy upregulation in the expression of Catechol 2,3-dioxygenase (C23O) and Dehydrogenase (DHA). The expression levels of C23O and DHA were measured at 0.029 U/mg Pro·g MLSS and 75.25 mg TF·(g MLSS·h)-1 (peak value), respectively. Correspondingly, enrichment of aromatic compound-degrading bacteria, including Thauera, Saccharimonadales, and Candidatus_Competibacter, occurred, along with the upregulation of associated functional genes such as Catechol 1,2-dioxygenase, Catechol 2,3-dioxygenase, Protocatechuate 3,4-dioxygenase, and Protocatechuate 4,5-dioxygenase. Considering the intricate system of multiple coexisting aromatic compounds in real CCW, this study not only obtained an optimal ratio for carbon source addition but also enhanced the efficient utilization of carbon sources and improved the capability of the system to effectively degrade aromatic compounds. Additionally, this paper established a theoretical foundation for metabolic regulation and harmless treatment within the biochemical treatment of intricate systems, exemplified by real CCW.

PHA and EPS production from industrial wastewater by conventional activated sludge, membrane bioreactor and aerobic granular sludge technologies: A comprehensive comparison

The present study has focused on the mainstream integration of polyhydroxyalkanoate (PHA) production with industrial wastewater treatment by exploiting three different technologies all operating in sequencing batch reactors (SBR): conventional activated sludge (AS-SBR), membrane bioreactor (AS-MBR) and aerobic granular sludge (AGS). A full aerobic feast/famine strategy was adopted to obtain enrichment of biomass with PHA-storing bacteria. All the systems were operated at different organic loading (OLR) rate equal to 1-2-3 kgCOD/m3∙d in three respective experimental periods. The AS-MBR showed the better and stable carbon removal performance, whereas the effluent quality of the AS-SBR and AGS deteriorated at high OLR. Biomass enrichment with PHA-storing bacteria was successfully obtained in all the systems. The AS-MBR improved the PHA productivity with increasing OLR (max 35% w/w), whereas the AS-SBR reduced the PHA content (max 20% w/w) above an OLR threshold of 2 kgCOD/m3∙d. In contrast, in the AGS the increase of OLR resulted in a significant decrease in PHA productivity (max 14% w/w) and a concomitant increase of extracellular polymers (EPS) production (max 75% w/w). Results demonstrated that organic carbon was mainly driven towards the intracellular storage pathway in the AS-SBR (max yield 51%) and MBR (max yield 61%), whereas additional stressors in AGS (e.g., hydraulic selection pressure, shear forces) induced bacteria to channel the COD into extracellular storage compounds (max yield 50%) necessary to maintain the granule's structure. The results of the present study indicated that full-aerobic feast/famine strategy was more suitable for flocculent sludge-based technologies, although biofilm-like systems could open new scenarios for other biopolymers recovery (e.g., EPS). Moreover, the AS-MBR resulted the most suitable technology for the integration of PHA production in a mainstream industrial wastewater treatment plant, considering the greater process stability and the potential reclamation of the treated wastewater.

Valorization of sewage sludge for facile and green wood bio-adhesives production

A method is presented herein for the design of wood bio-adhesives using sewage sludge extracts (SSE). SSE was extracted from SS using deep eutectic solvents and processed with glycerol triglycidyl ether (GTE) to disrupt the secondary structure of proteins. An additive was also used to improve mechanical performance. The resulting bio-adhesive (SSE/GTE@TA) had a wet shear strength of 0.93 MPa, meeting the Chinese national standard GB/T 9846-2015 (≥0.7 MPa). However, the high polysaccharide content in SSE would weaken the mechanical properties of wood bio-adhesives. The key to improve bio-adhesive quality was the formation of a strong chemical bond via Maillard reaction as well as higher temperatures (140 °C) to reduce polysaccharide content via dehydration. This approach has lower environmental impact and higher economic efficiency compared to incineration and anaerobic digestion of sewage sludge. This work provides a new perspective on the high-value utilization of SS and offers a novel approach to developing bio-adhesives for the wood industry.

Granule formation mechanism, key influencing factors, and resource recycling in aerobic granular sludge (AGS) wastewater treatment: A review

The high-efficiency and additionally economic benefits generated from aerobic granular sludge (AGS) wastewater treatment have led to its increasing popularity among academics and industrial players. The AGS process can recycle high value-added biomaterials including extracellular polymeric substances (EPS), sodium alginate-like external polymer (ALE), polyhydroxyfatty acid (PHA), and phosphorus (P), etc., which can serve various fields including agriculture, construction, and chemical while removing pollutants from wastewaters. The effects of various key operation parameters on formation and structural stability of AGS are comprehensively summarized. The degradable metabolism of typical pollutants and corresponding microbial diversity and succession in the AGS wastewater treatment system are also discussed, especially with a focus on emerging contaminants removal. In addition, recent attempts for potentially effective production of high value-added biomaterials from AGS are proposed, particularly concerning improving the yield, quality, and application of these biomaterials. This review aims to provide a reference for in-depth research on the AGS process, suggesting a new alternative for wastewater treatment recycling.

Alginate-like polymers from full-scale aerobic granular sludge: content, recovery, characterization, and application for cadmium adsorption

Aerobic granular sludge (AGS) is a proven resource for the recovery of biopolymers like alginate-like polymers (ALP). This is the first report on the dynamics of ALP produced by AGS (ALP-AGS) in a full-scale wastewater treatment plant (WWTP), optimization of ALP recovery from AGS, and adsorption of cadmium (Cd2+) by ALP. Recovery of ALP was highest when using 120 mL of 0.2 M Na2CO3 at 70 °C for 45 min. Seasonal (1.5 years, over 3100 cycles) and intra-cycle changes in ALP-AGS in the WWTP were monitored. The ALP content in AGS increased in the transition period between winter and spring, reaching over 150 mg/g MLSS. In the batch reactor cycle, the ALP-AGS level peaked 2 h after the start of aeration (mean peak level: 120 mg/g MLSS), then decreased about two-fold by the end of the cycle. The ALP-AGS had a small surface area and a lamellar structure with crystalline outgrowths. The optimal conditions of Cd2+ adsorption with ALP were a dosage of 7.9 g d.m./L, a pH of 4-8, and an equilibrium time of 60 min. Carboxyl and hydroxyl groups were the key functional groups involved in Cd2+ adsorption. According to the Sips model, the maximum Cd2+ adsorption capacity of ALP-AGS was 29.5 mg/g d.m., which is similar to that of commercial alginate. AGS is a richer source of ALP than activated sludge, which ensures the cost-effectiveness of ALP recovery and increases the sustainability of wastewater treatment. Information on the chemical properties and yields of ALP from full-scale WWTPs is important for downstream applications with the recovered ALP.