Alginate-like Exopolysaccharides Research Articles

Sludge-derived hierarchically porous carbon electrode prepared via CaCO3-assisted dual crosslinking for enhanced phosphate electrosorption

Electrosorption is considered a promising technology to remove charged pollutants in an efficient and green way, wherein the electrode materials are crucial for achieving its high performance. In this study, a Zr-containing hierarchically porous carbon electrode (ZHPC-1-Ca) tailored for phosphate removal was synthesized based on alginate-like exopolysaccharides (ALE), a biomass extract of excess sludge. The gel-forming ability of ALE provided a basis for obtaining a conductive carbon matrix with well-dispersed metal active sites, and the pore structure of ALE-derived electrodes was simply regulated via a dual-crosslinking strategy. In the synthesis, CaCO3 acted as both the hard template and the crosslinker, while Zr facilitated pore formation during the secondary crosslinking process. ZHPC-1-Ca exhibited a maximum electrosorption capacity of 12.40 mg g−1 at 1.2 V, with a low energy consumption of 3.166 kWh kg−1-P. The electrosorption behavior was well fitted with the pseudo-first-order kinetics and the Langmuir isotherm model. Moreover, ZHPC-1-Ca maintained stable electrosorption performance under pH 4–10 and during twenty capture-release cycles (85.2%). The electrosorption mechanisms were primarily elucidated as electrostatic attraction, ligand exchange, and Lewis acid-base interaction, contributing to the enhanced and selective phosphate removal. This study achieves a simple and controllable synthesis of hierarchically porous carbon electrodes using sludge biopolymers, which extends the application of sludge-derived carbon in phosphate electrosorption.

A novel method for immobilizing anammox bacteria in polyurethane foam carriers through dewatering

Biomass immobilization is an effective method for retaining the slow-growing anammox bacteria in reactors. A novel method for rapidly immobilizing anammox bacteria in polyurethane foam carriers through dewatering was proposed in this study. The polyurethane foam carriers sucked anammox sludge and then naturally dewatered for 12 h. 83.12 ± 3.24 % of the sucked sludge was retained within carriers under shear conditions. The specific anammox activity of the anammox bacteria retained in the carriers was lost by 19.95 ± 1.37 % during the dewatering process. This immobilization of anammox bacteria through dewatering process was mainly attributed to the cross-linking of alginate-like exopolysaccharides with Ca2+ and the network structure of polyurethane foam carrier. This dewatering immobilization provides an easy and low-cost method for the rapid immobilization of slow-growing anammox bacteria.

Sludge-derived biopolymers for in-situ synthesis of magnetic ALE-Fe-Zr composites for phosphate removal

Resource recovery of excess sludge has been important to achieve the sustainability of wastewater treatment, thereinto alginate-like exopolysaccharides (ALE) are considered as valuable bio-products with broad application potential. In this study, ALE were firstly employed as the biotemplates for fabricating controllable nanostructures to remove phosphate, the binding ability of ALE to metal ions (Fe3+ and Zr4+) effectively confined the in-situ growth of metal nanoparticles under calcination. The ALE-metal composites with a Fe/Zr molar ratio of 5 (ALE-Fe5-Zr) showed high phosphate removal efficiencies of 96.1% and 98.1% at 1 and 10 mg-P L−1, respectively, which was largely attributed to its homogeneity, high specific surface area, and mesoporous structure. The phosphate adsorption by ALE-Fe5-Zr composites fitted well with pseudo-second-order kinetics and Freundlich isotherm model. Meanwhile, the composites achieved stable phosphate removal performance under a wide pH range of 4–8, and showed a high selectivity to phosphate in the presence of Cl−, SO42−, NO3−, HCO3−, and F−. Moreover, ALE-Fe5-Zr composites maintained the favorable performance in treating real wastewater containing 2.47 mg-P L−1, and the phosphate concentration reached target discharge limit of 0.5 mg-P L−1 within 20 min. The reusability tests demonstrated that ALE-Fe5-Zr composites could be recovered by magnetic separation and kept 83.8% of original adsorption capacity after five cycles. The possible adsorption mechanisms involving electrostatic interaction, ligand exchange, and Lewis acid-base interaction were supported by batch experiments, FTIR, and XPS analyses. This work provided a facile route for synthesizing ALE-mediated magnetic composites with high efficiency, selectivity, and stability for phosphate removal.

Biopolymer recovery from waste activated sludge toward self-healing mortar crack

Activated sludge (AS) offers great potential for resource recovery considering its high organic and nutrient content. However, low recovery efficiency and high costs are directing the focus toward the high-valuable resource recovery. This study extracted 71.5 ± 5.9 mg/g VSS of alginate-like exopolysaccharides from AS (ALE/AS) and applied it to mortar as a novel biopolymer agent for crack self-healing. With a mortar crack of 120 μm, addition of 0.5 wt% ALE/AS yielded a high crack closure ratio of 86.5 % within 28 days. In comparison to commercial healing agents, marginal flexural strength reduction with ALE/AS addition (17.9 % vs 30.2–50.5 %) was demonstrated. The abundance of COO− group in GG blocks of ALE/AS resulted in a higher cross-link capacity with Ca2+, while the reduction of hydrophilic residues (e.g., COO− and OH) after complexation engendered a lower swelling capacity, which facilitated self-healing and flexural strength maintenance. Molecular dynamics (MD) revealed that lower Ca2+ diffusivity, arising from the stronger electrostatic interactions between the COO− groups and Ca2+, resulted in a high Ca2+ concentration around the cracks, leading to CaCO3 deposition and healed cracks. The outcomes of this study provided light on ALE-based mortar crack healing and presented a possibility for multi-level AS resource recovery.

Evaluation of sludge discharge methodologies in aerobic granular sludge reactors

We performed a comparison of different aerobic granular sludge (AGS) discharge methodologies in sequencing batch reactors (SBRs), evaluating the system efficiency, physical and microbiological characteristics of granules, and resource recovery of the discharged biomass. In R1, there was a selective discharge (30% top sludge and 70% bottom sludge, based on biomass weight) with SRT control (10–20 days). The same selective discharge was applied to R2, but with control of food to microorganisms (F/M) ratio (0.22–0.44 gCOD/gVSS·day). In R3, the discharge was conventional (similar to activated sludge reactors), i.e., mixed liquor during the aerobic period. Additionally, the best protocol of the lab-scale studies was used in a pilot-scale reactor (R4) treating municipal wastewater. R1 protocol was the best strategy for AGS formation, maintenance, and performance, achieving better removal efficiencies of COD (95%), total nitrogen (85%), and phosphorus (80%). Sludge discharge improved the system's performance and resource recovery, especially alginate-like exopolysaccharides (ALE).

Occurrence of heterotrophic nitrification-aerobic denitrification induced by decreasing salinity in a halophilic AGS SBR treating hypersaline wastewater

Heterotrophic nitrification-aerobic denitrification (HN-AD) is a novel alternative for nitrogen removal due to simultaneous nitrification and denitrification that occurs under aerobic conditions. Until now, ways in which to achieve aerobic nitrogen removal from wastewater via the HN-AD process have not been fully explored. In this study, autotrophic nitrification was converted into HN-AD in a halophilic aerobic granular sludge (HAGS) system when the wastewater salinity decreased from 30 to 20 g/L. Bacteria affiliated to the genus Paracoccus were dominant in the HAGS with a relative abundance of 56%, functioning with HN-AD. Accordingly, the indicative gene napA encoding for HN-AD was 5.1 × 109 copies/g HAGS. HAGS performing HN-AD exhibited a stable total inorganic nitrogen (TIN) removal efficiency performance in response to salinity variations of 10–40 g/L, owing to the stable HN-AD functional community. The significant inhibition of HN-AD was observed in both low salinity (≤5 g/L) and high salinity (≥50 g/L) conditions, accompanied by the disintegration of granules. Granular disintegration was triggered by the lower secretion of extracellular polymeric substances and alginate-like exopolysaccharides. HAGS performing HN-AD could simultaneously remove chemical oxygen demand and TIN from saline wastewater in a single aerobic tank, thus reducing the construction and operation costs.

Alginate-like exopolysaccharides in aerobic granular sludge: A review

Granular instability and a long granulation start-up period are significant challenges in implementing a full-scale aerobic granular sludge system. Identifying extracellular polymeric substances (EPS) components and their interactions is the key determinant to overcoming these challenges. Because of the high complexity of EPS, alginate-like exopolysaccharides (ALE) can be used as a model component as it is identified as the principal constituent of EPS. The feasibility of extracting ALE in aerobic granular sludge has been intensively studied; however, ALE characterization is still ongoing, and its role in EPS are still overlooked up until now. Moreover, research on its characteristics has demonstrated ALE to be a potential resource recovery. This review highlighted ALE’s physical and chemical characteristics, factors influencing ALE composition and content in aerobic granular sludge, and ALE as possible resource recovery. This review also discusses the correlation between ALE, EPS, and granulation processes in aerobic granular sludge systems.

Simultaneous recovery of phosphorus and alginate-like exopolysaccharides from two types of aerobic granular sludge

Wastewater treatment plants are expected to realize not only pollutants removal from wastewater but also resources recovery such as phosphorus (P) and alginate-like exopolysaccharides (ALE) from the produced sludge. In this study, ALE extraction and fractionation from the same activated sludge-derived bacterial aerobic granular sludge (AGS) and algal-bacterial AGS were performed in addition to P fate examination during ALE recovery. Results showed that the ALE content recovered from algal-bacterial AGS was 8.81 ± 0.02 mg/g-volatile suspended solids (VSS), about 2.8 times higher than that from bacterial AGS when fed with the same synthetic wastewater. Moreover, the mannuronic acid to guluronic acid (MG) blocks accounted for the largest proportion of ALE from the two granular sludges. In particular, the extracellular polymeric substances (EPS) extracted from bacterial and algal-bacterial AGS contained about 25.10 ± 1.85 and 19.53 ± 0.04 mg-P/g-SS, respectively, and both granular sludges possessed high P bioavailability of 97–99%.

Formation and ripening of alginate-like exopolymer gel layers during and after membrane filtration

The properties of biofilm EPS are determined by the multiple interactions between its constituents and the surrounding environment. Because of the high complexity of biofilm EPS, its constituents' characterisation is still far from thorough, and identification of these interactions cannot be done yet. Therefore, we use gels of bacterial alginate-like exopolysaccharides (ALEs) as a model component for biofilm EPS in this work. These gels have been examined for their cohesive properties as a function of CaCl2 and KCl concentration. Hereto, ALE gel layers were formed on membranes by dead-end filtration of ALE solutions. Accumulation of the cations Ca2+ and K+ in the gels could be well predicted from a Donnan equilibrium model based on the fixed negative charges in the ALE. This suggests that there is no specific binding of Ca2+ to the ALE and that on the time scale of the experiments, the Ca2+ ions can distribute freely over the gel and the surrounding solution. The concentration of fixed negative charges in the ALE was estimated around 1 mmol/g VSS (volatile suspended solids, organic mass) from the Donnan equilibrium. Moreover, an accumulation of H+ was predicted. Gels with more CaCl2 in the supernatant were more compact and bore a higher osmotic pressure than those with less CaCl2, revealing the role of Ca2+ ions in the network crosslinking. It is hypothesised that this mechanism later transitions into a rearrangement of the ALE molecules, which eventually leads to a fibrous network structure with large voids.

Resource recovery in aerobic granular sludge systems: is it feasible or still a long way to go?

Lately, wastewater treatment plants are much often being designed as wastewater-resource factories inserted in circular cities. Among biological treatment technologies, aerobic granular sludge (AGS), considered an evolution of activated sludge (AS), has received great attention regarding its resource recovery potential. This review presents the state-of-the-art concerning the influence of operational parameters on the recovery of alginate-like exopolysaccharides (ALE), tryptophan, phosphorus, and polyhydroxyalkanoates (PHA) from AGS systems. The carbon to nitrogen ratio was identified as a parameter that plays an important role for the optimal production of ALE, tryptophan, and PHA. The sludge retention time effect is more pronounced for the production of ALE and tryptophan. Additionally, salinity levels in the bioreactors can potentially be manipulated to increase ALE and phosphorus yields simultaneously. Some existing knowledge gaps in the scientific literature concerning the recovery of these resources from AGS were also identified. Regarding industrial applications, tryptophan has the longest way to go. On the other hand, ALE production/recovery could be considered the most mature process if we take into account that existing alternatives for phosphorus and PHA production/recovery are optimized for activated sludge rather than granular sludge. Consequently, to maintain the same effectiveness, these processes likely could not be applied to AGS without undergoing some modification. Therefore, investigating to what extent these adaptations are necessary and designing alternatives is essential.

Evaluation of the production of alginate-like exopolysaccharides (ALE) and tryptophan in aerobic granular sludge systems.

Theengineering and microbiological aspects involved in the production of alginate-like exopolysaccharides (ALE) and tryptophan (TRY) in aerobic granular sludge systemswere evaluated. The inclusion of short anoxic phase (A/O/A cycle-anaerobic, oxic, and anoxic phase) and the control of sludge retention time (SRT ≈ 10days) proved to be an important strategy to increase the content of these bioproducts in granules. The substrate concentration also has a relevant impact on the production of ALE and TRY. The results of the microbiological analysis showed that slow-growing heterotrophic microbial groups (i.e., PAOs and GAOs) might be associated with the production of ALE, and the EPS-producing fermentative bacteria might be associated with the TRY production. The preliminary economic evaluation indicated the potential of ALE recovery in AGS systems in decreasing the OPEX (operational expenditure) of the treatment, especially for larger sewage treatment plants or industrial wastewaters with a high organic load.

Pilot-scale aerobic granular sludge in the treatment of municipal wastewater: Optimizations in the start-up, methodology of sludge discharge, and evaluation of resource recovery

This work evaluated the formation, maintenance, performance, and microbiology of a pilot-scale aerobic granular sludge reactor treating low-strength municipal wastewater under tropical climate conditions. Additionally, different resource recovery possibilities (phosphorous, tryptophan, and alginate-like exopolysaccharides) were investigated from the produced sludge. Granulation occurred after 35 days without external carbon source supplementation (CODinf ≈ 461 mg/L; COD/DBO5 ≈ 3.2). Some protocols were implemented: (i) fat separation to decrease granule flotation; (ii) high exchange rates (60%) during rainy periods to increase the organic load; (iii) selective sludge discharge methodology. After granules formation, optimizations were done to improve reactor performance (COD, BOD, NH4+, and PO43− removals close to 90%), and energy demand reduced from 0.43 (start-up) to 0.25 kWh/m3 (after optimizations). The produced sludge had a high concentration of phosphorus (0.020 g P/g VSS), tryptophan (0.048 g tryptophan/g VSS), and alginate-like exopolysaccharides (0.219 g ALE/g VSS), indicating a good resource recovery possibility.

Application of aerobic granules-continuous flow reactor for saline wastewater treatment: Granular stability, lipid production and symbiotic relationship between bacteria and algae

In this study a continuous flow reactor (CFR) was employed to compare the feasibility of bacterial aerobic granular sludge (AGS-CFR) and algal-bacterial granular sludge (ABGS-CFR) for treating 1–4% saline wastewater. High salinity was found to enhance algae growth in ABGS-CFR, which exhibited slightly higher total nitrogen and phosphorus removal efficiencies at 1–3% salinity. ABGS-CFR maintained good granular stability at 1–4% salinity, while AGS-CFR gradually disintegrated at 4% salinity with 39.3% less accumulation of alginate-like exopolysaccharides in the extracellular polymeric substances. Indole-3-acetic acid (IAA) and superoxide dismutase (SOD) analysis suggested that bacteria and algae (Nitzschia) in ABGS-CFR formed a good symbiotic relationship under high salinity conditions, achieving rapid algae growth and 2 times lipid production. High salinity was conducive to enriching Halomonas and Nitzschia but unfavorable for Nitrosomonas and Flavobacterium. Results from this study could provide useful information on interactions between bacteria and algae in ABGS-CFR for its future practical application.

Granulation of halophilic sludge inoculated with estuarine sediments for saline wastewater treatment

As a solution of the sludge loss in the treatment of saline wastewater, the granulation of halophilic sludge was explored in this study. The inoculated estuarine sediment was granulated to an average diameter of 1155 ± 102 μm under the selective settling pressure in the airlift sequencing batch reactor (SBR) when the influent organic loading rate (OLR) was doubled to 0.36 g COD/L·day. The results indicated that the OLR doubled the amount of total extracellular polymeric substance (EPS) and that protein was predominant in the EPS (72.8 ± 2.0%). The correlation between aggregate size and protein content was better than that between aggregate size and polysaccharide content. The amount of alginate-like exopolysaccharides (ALE) increased linearly at the mature granular stage, co-occurring with the compact and elastic structure of the granules. According to the results of 16S rRNA high -throughput sequencing, the Shannon-Weaver index of mature granule decreased by >50% compared to the inoculated sediment. Bacteria of Propionibacteriaceae family constituted 34% of the population in granules and were in symbiotic relationship with halophiles of family Rhodocyclaceae, Vibrionaceae, Flavobacteriaceae, and Cryomorphaceae. The aerobic halophilic granular sludge showed COD removal efficiency of 90.9 ± 0.8% and ammonia removal efficiency of 72.6 ± 4.0% for 30 g/L saline wastewater. An average nitrite accumulation ratio of 94.5 ± 2.9% was observed during nitrification. Granulation of halophilic sludge provides an effective solution to the saline sludge loss problem, which is a step forward to realize the biological treatment of saline wastewater by halophiles.

Enhanced amount and quality of alginate-like exopolysaccharides in aerobic granular sludge for the treatment of salty wastewater

Osmotic pressure provided by salty wastewaters is an important influencing factor for alginate-like exopolysaccharides (ALE) in aerobic granular sludge (AGS). Therefore, research on the influence of salinity (NaCl 0 R1, 10 g/L R2, 30 g/L R3) on AGS and its ALE formation was conducted. A salinity of 1% induced larger particle size with smooth spheroidal shape and enhanced granular strength in R2. The TOC and ammonia removal were unaffected in both R2 and R3, but the P removal was greatly enhanced. ALE was much enriched at moderate salinity (1% NaCl). The amount of ALE reached 49.8 mg/g VSS at 140 d in R2, which was much higher than in R1 (26.8 mg/g VSS) and R3 (28.9 mg/g VSS), possibly due to the activation of gene algC expression in AGS of R2. ALE also showed the largest GG block fractionation and MW in R2, which indicated the greatest enhancement of mechanical properties. Moreover, enrichment of glucosamine, lipid content, and octadecanamide derivative in ALE of R2 endowed it with medicinal potential, stronger water-barrier property, and reduction of the products’ friction coefficients, respectively. Therefore, AGS based on ALE is a potential technology for treatment of salty wastewater.

Aerobic granular biomass technology: advancements in design, applications and further developments

AbstractAerobic granular sludge is seen as the future standard for industrial and municipal wastewater treatment. Through a Dutch research and development program, a full-scale aerobic granular biomass technology has been developed – the Nereda® technology – which has been implemented to treat municipal and industrial wastewater. The Nereda® system is considered to be the first aerobic granular sludge technology applied at full-scale and more than 40 municipal and industrial plants are now in operation or under construction worldwide. Further plants are in the planning and design phase, including plants with capacities exceeding 1 million PE. Data from operational plants confirm the system's advantages with regard to treatment performance, energy-efficiency and cost-effectiveness. In addition, a new possibility for extracting alginate-like exopolysaccharides (ALE) from aerobic granular sludge has emerged which could provide sustainable reuse opportunities. The case is therefore made for a shift away from the ‘activated sludge approach’ towards an ‘aerobic granular approach’, which would assist in addressing the challenges facing the wastewater treatment industry in Asia and beyond.

Enrichment and characterization of a psychrophilic ‘Candidatus Accumulibacter phosphatis’ culture

Enhanced Biological phosphorous removal (EBPR) processes, often operated at low temperatures, are utilised world-wide, but currently little is known regarding enrichment cultures and the characteristics of active organisms (“Candidatus Accumulibacter phosphatis” (Accumulibacter)) under psychrophilic conditions. This study assesses the long-term performance, metabolic activity, microbial community characteristics and sludge morphology in an EBPR community enriched from activated sludge at 10 °C. Long solid retention times (SRT) and low temperatures resulted in the dominance of Accumulibacter type II over type I. Despite changes in the microbial community, P-removal efficiencies did not show obvious differences and although no specific measures were implemented, the enriched Accumulibacter-PAO culture formed stable dense granules. A high level of Alginate-like exopolysaccharides (ALE) were observed, with a large number of Guluronic acid-Guluronic acid (GG) blocks derived from the biomass at 10 °C. This characteristic favors sludge granulation, increasing the mechanical strength of granules formed, which encourages solid-liquid separation and consequently, contributes to the stable operation of EBPR systems.

Seawater-based wastewater accelerates development of aerobic granular sludge: A laboratory proof-of-concept

This study aimed to develop an aerobic granular sludge process for the efficient treatment of highly saline wastewater and understand the granulation process in a seawater-based multi-ion matrix. Five identical sequencing batch airlift reactors (SBARs) are used to treat synthetic saline sewage with different proportions of real seawater (0%–100%). The results confirm that aerobic granular sludge can be successfully developed with various proportions of seawater up to 100% and show that seawater not only significantly accelerates granulation but also generates stronger granular structures than does freshwater. The increased presence of gel-forming alginate-like exopolysaccharides in the granules explains why a greater proportion of seawater leads to higher density and improves the cohesive strength of the granules. SEM-EDX analysis further revealed substantial presence of both Ca2+ and Mg2+ phosphate in the granule core as well as in the outer layers providing extra bridging forces in addition to alginate-like exopolysaccharides for accelerating the granule formation and maintaining the structure. It is hoped that this work could explore another approach for saline sewage treatment and bring some clues for the mystery of granulation mechanism.

NMR and MALDI-TOF MS based characterization of exopolysaccharides in anaerobic microbial aggregates from full-scale reactors.

Anaerobic granular sludge is composed of multispecies microbial aggregates embedded in a matrix of extracellular polymeric substances (EPS). Here we characterized the chemical fingerprint of the polysaccharide fraction of EPS in anaerobic granules obtained from full-scale reactors treating different types of wastewater. Nuclear magnetic resonance (NMR) signals of the polysaccharide region from the granules were very complex, likely as a result of the diverse microbial population in the granules. Using nonmetric multidimensional scaling (NMDS), the 1H NMR signals of reference polysaccharides (gellan, xanthan, alginate) and those of the anaerobic granules revealed that there were similarities between the polysaccharides extracted from granules and the reference polysaccharide alginate. Further analysis of the exopolysaccharides from anaerobic granules, and reference polysaccharides using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) revealed that exopolysaccharides from two of the anaerobic granular sludges studied exhibited spectra similar to that of alginate. The presence of sequences related to the synthesis of alginate was confirmed in the metagenomes of the granules. Collectively these results suggest that alginate-like exopolysaccharides are constituents of the EPS matrix in anaerobic granular sludge treating different industrial wastewater. This finding expands the engineered environments where alginate has been found as EPS constituent of microbial aggregates.

Accelerated aerobic granulation using alternating feed loadings: Alginate-like exopolysaccharides

Alginate-like exopolysaccharides (ALE) likely contribute markedly to strength of aerobic granules. This study cultivated aerobic granules from propionate wastewaters using strategies with different organic loading rates (OLRs) (4.4–17.4kg/m3-d). When the OLR increased suddenly, the constituent cells (Pseudomonas, Clostridium, Thauera and Arthrobacter) were stimulated to secret extracellular cyclic diguanylate (c-di-GMP) and produced excess ALE, which formed a large quantity of sticky materials that served as the precursor of aerobic granules. Formation of excess ALE was the prerequisite for accelerated granulation. Conversely, this study observed no enrichment of poly guluronic acid blocks in ALE during granulation.