Insight into formation and biological characteristics of Aspergillus tubingensis-based aerobic granular sludge (AT-AGS) in wastewater treatment

Evaluation of aerobic granulation performance bioaugmented with the auto-aggregating bacterium Pseudomonas stutzeri strain XL-2 with heterotrophic nitrification-aerobic denitrification capacity

In this study, the possibility of an auto-aggregating bacterium Pseudomonas strain XL-2 with heterotrophic nitrification-aerobic denitrification capacity for improving granulation and nitrogen removal was evaluated. The results showed that the supplementation of strain XL-2 promoted granulation, making R1 (experimental group with strain XL-2) dominated by granules at 14 d, which was 12 days earlier than R2 (control group without strain XL-2). This was attributed to the promotion of extracellular polymeric substances (EPS) secretion, particularly proteins by adding strain XL-2, thereby improving the hydrophobicity of sludge and altering the proteins secondary structures to facilitate aggregation. Meanwhile, adding strain XL-2 improved simultaneous nitrification and denitrification efficiency of R1. Microbial community analysis indicated that strain XL-2 successfully proliferated in aerobic granule sludge and might induce the enrichment of genera such as Flavobacterium and Paracoccus that were favorable for EPS secretion and denitrification, jointly promoting granulation and enhancing nitrogen removal efficiency.

Ultra-rapid development of 'solid' aerobic granular sludge by stable transition/filling of inoculated 'hollow' mycelial pellets in hypersaline wastewater

To overcome the long start-up period in cultivating aerobic granular sludge (AGS) under hypersaline environment, mycelial pellets (MPs) of halotolerant fungus Cladosporium tenuissimum NCSL-XY8 were inoculated to try to realize the ultra-rapid development of salt-tolerant AGS by stable transition of 'hollow' MPs into 'solid' AGS without apparent fragmentation. The granules directly met the standard of AGS after inoculating MPs (Day 0), and it basically satisfied relatively strict standards of AGS (SVI30 < 50 mL/g, D50 > 300 μm, D10 > 200 μm and SVI30/SVI5 > 0.9) under anaerobic/aerobic mode during whole cultivation processes. Microstructure of the granular cross section clarified that MPs with hollow/loose inner layer transitioned into solid/dense AGS under anaerobic/aerobic mode within 7 days, while formed skin-like floating pieces and unstable double-layer hollow granules under aerobic mode. Organics removal reached relatively stable within 13 days under anaerobic/aerobic mode, 6 days faster than aerobic mode. This study provided a strategy for ultra-rapid and stable development of AGS, which showed the shortest granulation period in various AGS-cultivation strategies.

Rational construction of synthetic consortia: Key considerations and model-based methods for guiding the development of a novel biosynthesis platform

The rapid development of synthetic biology has significantly improved the capabilities of mono-culture systems in converting different substrates into various value-added bio-chemicals through metabolic engineering. However, overexpression of biosynthetic pathways in recombinant strains can impose a heavy metabolic burden on the host, resulting in imbalanced energy distribution and negatively affecting both cell growth and biosynthesis capacity. Synthetic consortia, consisting of two or more microbial species or strains with complementary functions, have emerged as a promising and efficient platform to alleviate the metabolic burden and increase product yield. However, research on synthetic consortia is still in its infancy, with numerous challenges regarding the design and construction of stable synthetic consortia. This review provides a comprehensive comparison of the advantages and disadvantages of mono-culture systems and synthetic consortia. Key considerations for engineering synthetic consortia based on recent advances are summarized, and simulation and computational tools for guiding the advancement of synthetic consortia are discussed. Moreover, further development of more efficient and cost-effective synthetic consortia with emerging technologies such as artificial intelligence and machine learning is highlighted.

A novel mycelial pellet applied to remove polycyclic aromatic hydrocarbons: High adsorption performance & its mechanisms

Mycelial pellets formed by Penicillium thomii ZJJ were applied as efficient biosorbents for the removal of polycyclic aromatic hydrocarbons (PAHs), which are a type of ubiquitous harmful hydrophobic pollutants. The live mycelial pellets were able to remove 93.48 % of pyrene at a concentration of 100 mg/L within 48 h, demonstrating a maximum adsorption capacity of 285.63 mg/g. Meanwhile, the heat-killed one also achieved a removal rate of 65.01 %. Among the six typical PAHs (pyrene, phenanthrene, fluorene, anthracene, fluoranthene, benzo[a]pyrene), the mycelial pellets preferentially adsorbed the high molecular weight PAHs, which also have higher toxicity, resulting in higher removal efficiency. The experimental results showed that the biosorption of mycelial pellets was mainly a spontaneous physical adsorption process that occurred as a monolayer on a homogeneous surface, with mass transfer being the key rate-limiting step. The main adsorption sites on the surface of mycelia were carboxyl and N-containing groups. Extracellular polymeric substances (EPS) produced by mycelial pellets could enhance adsorption, and its coupling with dead mycelia could achieve basically the same removal effect to that of living one. It can be concluded that biosorption by mycelial pellets occurred due to the influence of electrostatic and hydrophobic interactions, consisting of five steps. Furthermore, the potential applicability of mycelial pellets has been investigated considering diverse factors. The mycelia showed high environmental tolerance, which could effectively remove pyrene across a wide range of pH and salt concentration. And pellets diameters and humic acid concentration had a significant effect on microbial adsorption effect. Based on a cost-effectiveness analysis, mycelium pellets were found to be a low-cost adsorbent. The research outcomes facilitate a thorough comprehension of the adsorption process of pyrene by mycelial pellets and their relevant applications, proposing a cost-effective method without potential environmental issues (heat-killed mycelial pellets plus EPS) to removal PAHs.

Intensifying the simultaneous removal of nitrogen and phosphorus of an integrated aerobic granular sludge-membrane bioreactor by Acinetobacter junii

This work aims at intensifying the simultaneous removal of nitrogen and phosphorus of an integrated aerobic granular sludge (AGS) - membrane bioreactor (MBR) by Acinetobacter junii. After acclimation and enrichment in a sequencing batch reactor (SBR), Acinetobacter junii, a kind of denitrifying phosphate accumulating organism (DPAO), was successfully screened in the used SBR. Then it was verified to be capable of effectively enhancing the performance in the simultaneous removal of nitrogen and phosphorus of AGS-MBR. In the system, DPAO (Acinetobacter junii) mainly occurred in AGS, and the highest ratio even reached 22.8%, but its competitive advantages highly depend on the size of AGS. The presented results can cultivate AGS and enrich DPAO simultaneously to improve the removal of nitrogen and phosphorus of an AGS-MBR, which provide an environmentally friendly approach to upgrade traditional wastewater treatment processes.

Rapid, stable, and highly-efficient development of salt-tolerant aerobic granular sludge by inoculating magnetite-assisted mycelial pellets

Long cultivation time hinders the industrial applications of aerobic granular sludge (AGS) in treatment of hypersaline wastewater. Mycelial pellets (MPs) have been used to efficiently strengthen the flocculent sludge aggregation and accelerate the formation of AGS. However, the MPs-based AGS was easily crushed or fragmented into several small pieces/granules that brought the uncertainty and extended the transition process to form mature AGS. In this study, magnetite was used to strengthen MPs (halotolerant fungus Cladosporium tenuissimum NCSL-XY8), and co-culture and adsorption type of magnetite-assisted mycelial pellets (CMMPs and AMMPs) were prepared and used for acceleration of salt-tolerant aerobic granular sludge (SAGS) cultivation under 3% salinity conditions. Compared to inoculating MPs, the inoculation of either CMMPs or AMMPs could stably transition to mature SAGS without evident fragmentation, which obviously increased the certainty and stability of SAGS formation. Also, highly-efficient simultaneous nitrogen and carbon removal (∼98% TOC and ∼80% TN removal) could be reached in 8 days. Typically, the granules maintained perfect characteristics (D50 > 1300 μm, D10 > 350 μm, SVI30 < 45 mL/g, and SVI30/SVI5 = 1.0) during the whole cultivation/transition processes (Day 0-55) by using the inoculum of CMMPs. ITS rDNA sequencing revealed the inoculated fungus Cladosporium tenuissimum played key roles in the formation of SAGS. All the phenomena indicated the rapid, stable, and highly-efficient start-up of SAGS could be successfully realized by inoculating CMMPs.

Enhanced fixation of dissolved inorganic carbon by algal-bacterial aerobic granular sludge during treatment of low-organic-content wastewater

The microalgae-based wastewater treatment technologies are believed to contribute to carbon neutrality. This study investigated the inorganic carbon fixation performance in the algal-bacterial aerobic granular sludge (A-BAGS) process under cultivation at different concentrations of organic carbon (OC) and inorganic carbon (IC). The results indicated that A-BAGS in treating wastewater containing organics of 77 mg-C/L contributed little to the fixation of inorganic carbon, while the highest inorganic carbon removal efficiency of 50 % was achieved at the influent IC of 100 mg/L and OC of 7 mg/L. This high IC condition contributed to enhanced biomass growth rate and enhanced extracellular polymeric substances, while it did not affect the granular stability and nitrification efficiency. The microbial diversity was also largely enhanced. The results demonstrated the great potential of A-BAGS for simultaneous resource recovery in wastewater and inorganic carbon fixation, while operation conditions need to be further optimized.

Responses of straw foam-based aerobic granular sludge to atrazine: Insights from metagenomics and microbial community variations

Atrazine (ATZ) has caused serious environmental pollution, but the biodegradation of ATZ is relatively slow and inefficient. Herein, a straw foam-based aerobic granular sludge (SF-AGS) was developed, the spatially ordered architectures of which could greatly improve the drug tolerance and biodegradation efficiency of ATZ. The results showed that, in the presence of ATZ, chemical oxygen demand (COD), ammonium nitrogen (NH₄⁺-N), total phosphorus (TP), and total nitrogen (TN) were effectively removed within 6 h, and the removal efficiencies were as high as 93.37%, 85.33%, 84.7%, and 70%, respectively. Furthermore, ATZ stimulated microbial consortia to secrete three times more extracellular polymers compared to without ATZ. Illumina MiSeq sequencing results showed that bacterial diversity and richness decreased, leading to significant changes in microbial population structure and composition. ATZ-resistant bacteria including Proteobacteria, Actinobacteria, and Burkholderia laid the biological basis for the stability of aerobic particles, efficient removal of pollutants, and degradation of ATZ. The study demonstrated that SF-AGS is feasible for ATZ-laden low-strength wastewater treatment.

Bioaugmentation of intertidal sludge enhancing the development of salt-tolerant aerobic granular sludge

Three parallel bioreactors were operated with different inoculation of activated sludge (R1), intertidal sludge (ItS) (R2), and ItS-added AS (R3), respectively, to explore the effects of ItS bioaugmentation on the formation of salt-tolerant aerobic granular sludge (SAGS) and the enhancement of COD removal performance. The results showed that compared to the control (R1-2), R3 promoted a more rapid development of SAGS with a cultivation time of 25 d. Following 110-day cultivation, R3 exhibited a higher granular diameter of 1.3 mm and a higher hydrophobic aromatic protein content than that in control. Compared to the control, the salt-tolerant performance in R3 was also enhanced with the COD removal efficiency of 96.4% due to the higher sludge specific activity of 14.4 g·gVSS^-1·d^-1 and the salinity inhibition constant of 49.3 gL^-1. Read- and genome-resolved metagenomics together indicated that a higher level of tryptophan/tyrosine synthase gene (trpBD, tyrBC) and enrichment of the key gene hosts Rhodobacteraceae, Marinicella in R3, which was about 5.4-fold and 1.4-fold of that in control, could be the driving factors of rapid development of SAGS. Furthermore, the augmented salt-tolerant potential in R3 could result from that R1 was dominated by Rhodospirillaceae, Bacteroidales, which carried more trehalose synthase gene (otsB, treS), while the dominant members Rhodobacteraceae, Marinicella in R3 were main contributors to the glycine betaine synthase gene (ectC, betB, gbsA). This study could provide deeper insights into the rapid development and improved salt-tolerant potential of SAGS via bioaugmentation of intertidal sludge, which could promote the application of hypersaline wastewater treatment.

Low-temperature-resistance granulation of activated sludge and the microbial responses to the granular structural stabilization

Completely loss of granular structural stability and reliable start-up of aerobic granular sludge (AGS) system are considered as the biggest challenges for its engineering application under seasonal temperature variation, especially extremely low temperatures. In this study, two identical sequencing batch reactors (SBR) were successfully start-up at 10 °C (R1) and 25 °C (R2), respectively, and then operated under a strategy of stepwise change of temperatures to investigate the stability of the granular sludge by examining its microbial characteristics, bis (3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP), extracellular polymeric substance (EPS) and sludge physiochemical properties. The results showed that AGS formed under the low temperature preferentially secrete EPS and c-di-GMP for stable granulation and improvement of its resistance to temperature changes. Meanwhile, R1 successfully obtained aerobic granulation with high biomass concentration and superior settleability, as well as high pollutant removal performance. In comparison, R2 took a longer time for granulation and was subjected to serious disintegration of AGS. The matrix structure partially formed by filamentous bacteria during the start-up stage in R1 was one of major reasons for its own superiority beyond R2 in granulation. Slow-growing organisms such as autotrophic nitrifying and Anammox bacteria, phosphorus accumulation organisms, EPS-producing genera, and c-di-GMP pathway-dependent genera, were exclusively enriched in the R1 and resulted in higher pollutants removal efficiencies and stable structure, whereas Sphaerotilus dominated in R2 that related closely with its unstable performance. Therefore, the strategy based on the stepwise change of temperatures from extremely low temperatures may be one feasible way for the sustainable application of AGS system, which is of significance to address the challenging problems of AGS applications.

The De Novo Synthesis of 2-Phenylethanol from Glucose by the Synthetic Microbial Consortium Composed of Engineered Escherichia coli and Meyerozyma guilliermondii

Synthetic microbial consortia show promising applications for fine chemical production, especially with long metabolic pathways. In this study, a synthetic microbial consortium consisting of Escherichia coli YLC20 and Meyerozyma guilliermondii MG57 was successfully constructed, which could achieve efficient de novo 2-phenylethanol (2-PE) production from glucose. A tyrosine-deficient E. coli YLC20 overexpressing genes of aroF and pheA was first constructed, which could accumulate 29.5 g/L of l-phenylalanine (l-Phe) within 96 h from glucose accompanied by the coproduction of acetate and α-ketoglutarate (α-KG). Furthermore, the engineered M. guilliermondii MG57 was constructed through the stepwise metabolic engineering strategy, which could facilitate the 2-PE synthesis from l-Phe. Moreover, the cosubstrate and material intervention strategies were applied to improve the stability of the microbial consortium and 2-PE production. Finally, the synthetic microbial consortium could de novo synthesize 3.77 g/L of 2-PE from 80 g/L of glucose, providing a reference for the de novo synthesis of fine chemicals with long metabolic pathways.

Artificially constructing mixed bacteria system for bioaugmentation of nitrogen removal from saline wastewater at low temperature

To alleviate the inhibition effects of multi-stresses, a multi-bacterial bioaugmentation based on stimulating cell-to-cell interactions was applied to improve the stress potential of salt-tolerant aerobic granular sludge (AGS). Results showed that the consortium formed by a combination of salt-tolerant ammonia-nitrogen utilizing bacteria, salt-tolerant nitrite-nitrogen utilizing bacteria and salt-tolerant nitrate-nitrogen utilizing bacteria with a whole biomass ratio of 1:2:1 achieved maximum nitrogen consumption rate (μNH₄⁺-N, μNO₂^--N and μNO₃^--N of 1.03, 0.57 and 11.62 mgN/L·h, respectively) at 35 gNaCl/L salinity and 15 °C. The flocculent consortium was aggregated by Aspergillus tubingensis mycelium pellet, which was made into a compound bacterial agent (CBA), and the comprehensive nitrogen consumption capability of CBA was further improved to 2.47-4.36-fold of single functional bacteria. 5% CBA (m/m) was introduced into the seafood processing wastewater in batches, in winter (12-16 °C), the removal efficiencies of NH₄⁺-N and total nitrogen increased from 66.89% to 52.77% of native AGS system to 79.02% and 69.97% of nascent bioaugmentation system, respectively. The analysis of key enzyme activities demonstrated that the ammonia monooxygenase and nitrate reductase activities of the bioaugmentation system were increased to 2.73-folds and 1.94-folds those of the native system. Moreover, due to an increase of 6.18 mg/gVSS and 0.11 in the secreted exopolysaccharide and tightly-bound/total extracellular polymeric substances, respectively, bioaugmentation boosted the cell bioflocculation ability by 13.53%, which enhanced the robustness. This work provided a detailed and feasible technical proposal for enhancing the biological treatment performance of saline wastewater in cold regions.

Enhanced biohydrogen production of anaerobic fermentation by the Fe3O4 modified mycelial pellets-based anaerobic granular sludge

To improve the catalytic efficiency and stability of hydrogen-producing bacteria (HPB), the Fe₃O₄ nanoparticles modified Aspergillus tubingensis mycelial pellets (AT)-based anaerobic granular sludge (Fe₃O₄@AT-AGS) was developed. The Fe₃O₄@AT-AGS protected flora with abundant extracellular polymeric substances, which increased diversity and stability of flora in early and late stage. The porous structure enhanced mass transfer efficiency, thus promoted dominant flora transferred from lactate-producing bacteria (LPB) to HPB in middle stage. The Fe₃O₄ improved biomass of mycelial by 19.5 %. The enhancement of dehydrogenase and conductivity of Fe₃O₄ increased the HPB proportion, electron transfer, and butyrate fermentation in early and middle stage. The Fe₃O₄@AT-AGS enhanced HPB abundance, dehydrogenase activity and stability, and significantly inhibited propionate fermentation. The biohydrogen production and yield respectively reached 2792 mL/L and 2.56 mol/mol glucose. Clostridium sensu stricto 11 as dominant microbes reached 77.3 %. This provided strategy for alleviating inhibition of LPB and improving competitiveness of HPB during biohydrogen production.

Cooperation of heterotrophic bacteria enables stronger resilience of halophilic assimilation biosystem than nitrification system under long-term stagnation

Long-term stagnation of biosystems (with no or very little wastewater) owing to seasonal downtime or failure maintenance brings great challenges to the performance recovery after system restart. In particular, the reduction of microbial activity and change of dissolved organic matter (DOM) affect the effluent quality and subsequent treatment procedures. Monitoring the dynamics and resilience of biosystems after long-term stagnation is important to formulate targeted countermeasures for system stability. However, the influence of long-term stagnation on autotrophic nitrification (AN) and heterotrophic assimilation (HA) biosystems has not been systematically explored. Here, we used halophilic AN and HA systems to study the stability and resilience of two nitrogen removal consortia after long-term stagnation. The results showed that 97.5 % and 93 % of ammonium and 47.0 % and 90.1 % of total nitrogen were removed using the halophilic AN and HA systems, respectively, in the stable period. After four weeks of stagnation, the HA system showed stronger resilience than AN system, in terms of faster recovery of treatment performance, and less fluctuations in sludge settleability and extracellular polymeric substances. In addition, after the stagnation period, the DOM of AN system was rich in low-molecular refractory humic acid, whereas that of HA system was rich in high-molecular proteins. The stagnation period led to the replacement of the dominant heterotrophic functional microorganisms, Paracoccus and Halomonas, with Muricauda and Marinobacterium in the HA system. The microbial network results revealed that the cooperation of heterotrophic bacteria enables stronger resilience of the HA system from prolonged stagnation than the AN system. In addition, the nitrogen removal efficiency, protein to polysaccharide ratio of EPS and fluorescence intensity of DOM were significantly correlated with the microbial community composition. These results suggest that AN system has greater risks in terms of treatment performance and sludge stability than the system after long-term stagnation.

Effect of fungal pellets on denitrifying bacteria at low carbon to nitrogen ratio: Nitrate removal, extracellular polymeric substances, and potential functions

This research aims to elucidate the effect of fungal pellets (FP) on denitrifying bacteria regarding nitrate (NO₃^--N) removal, extracellular polymeric substances (EPS), and potential functions at a low carbon to nitrogen (C/N) ratio. A symbiotic system of FP and denitrifying bacteria GF2 was established. The symbiotic system showed 100% NO₃^--N removal efficiency (4.07 mg L^-1 h^-1) at 6 h and enhanced electron transfer capability at C/N = 1.5. The interactions between FP and denitrifying bacteria promoted the production of polysaccharides (PS) in EPS. Both the increased PS and the PS provided by FP as well as protein and humic acid-like substances in EPS could be consumed by denitrifying bacteria. FP acted as a protector and provided habitat and nutrients for denitrifying bacteria as well as improved the ability of carbohydrate metabolism, amino metabolism, and nitrogen metabolism of denitrifying bacteria. This study provides a new perspective on the relationship between FP and denitrifying bacteria.

Adaptive regulation of activated sludge's core functional flora based on granular internal spatial microenvironment

A great deal of efforts has been put into studying the influence of the external macroenvironment for activated sludge to survive on microbial community succession, while granular internal spatial microenvironment should be given equal attention, because it is more directly involved in the information exchange and material transfer among microorganisms. This study systematically investigated the effects of granular microenvironment on spatial colonization and composition of sludge's core functional flora, and the corresponding difference of biological treatment performance. High content of extracellular-proteins (67.53 mg/gVSS) or extracellular-polysaccharide (65.02 mg/gVSS) stimulated the microbial flocculation and aggregation of 0.5-1.5 mm granules (GS) or 1.5-3.0 mm granules (GM), respectively, which was resulted from excellent cell hydrophobicity (59.26%) or viscosity (3.47 mPa s), therefore, constituted relatively dense porous frame. More hollow space existed in 3.0-5.0 mm granules (GL), which formed loose skeleton with 0.213 mL/g of total pore volume and 17.21 nm of average pore size. Combining scanning electron microscope images and fluorescent in-situ hybridization based microbiological analysis, aerobic nitrifiers were observed to wrap or surround anaerobic bacteria, or facultative/anaerobic bacteria were self-encapsulated, which created granule's unique microenvironment with alternating aerobic and anaerobic zones. GS has the most rich organic matter degrading bacteria and anaerobic heterotrophic denitrifiers, while GM and GL presented the greatest relative abundance of facultative and aerobic denitrifiers, respectively. The activity of dehydrogenase and nitrogen invertase of GM showed be 1.32-3.09 times higher than those of GS and GL, contributing to its higher carbon and nitrogen removal. These findings highlight the importance of granular microenvironment to adaptive regulation of activated sludge's core functional flora and corresponding pollutant removal performance.

Influence of temperature on aerobic granular sludge formation and stability treating municipal wastewater with high nitrogen loadings

This study investigated the influence of temperature (20 and 30 °C) on the formation and stability of aerobic granules in sequential batch reactors (SBR). Therefore, two lab-scale SBRs operated at 20 and 30 °C (SBR₂₀ and SBR₃₀) were used. The reactors were fed with municipal wastewater (COD_t:TN:TP 100:15:1.7), leading to mean organic loading rates (OLR) of 1.3 ± 0.4 kgCOD_t m^-3 day^-1. Both reactors had the same height/diameter ratio of 4.2 and were inoculated with activated sludge from a municipal wastewater treatment plant. The operational conditions were also the same for both temperatures and lasted in stable process parameters for over 100 days. By optimizing the aeration and oxygen concentration, a high removal efficiency of NH₄-N (∼99%) and COD (∼90%) was achieved in both reactors, despite the poor C:N:P ratio at the influent. Furthermore, a relatively low oxygen concentration of 2 mg L^-1 was defined as the set point for the control strategy. Nevertheless, granulation at 30 °C was significantly faster, resulting in more stable sludge volume index (SVI) values (SVI₁₀/SVI₃₀ < 1.1). The granules formed at 30 °C were also larger, more compact, and considerably more stable against system disturbances. However, at higher temperatures, larger granules might be required for nitrate removal because of the increased oxygen diffusion rates. Finally, microbiological 16S rRNA gene amplicon analysis for both systems indicated major differences relatively to the inoculum sludge only for nitrogen-degrading organisms.

Biogranulation process facilitates cost-efficient resources recovery from microalgae-based wastewater treatment systems and the creation of a circular bioeconomy

Energy self-sufficient wastewater treatment designs can reduce net energy consumption and achieve resources recovery. Microalgae are regarded as a promising candidate for developing a circular bioeconomy in wastewater treatment plants (WWTPs) due to its potential for simultaneous wastewater remediation and high value-added materials production. Much effort has been made to overcome the high production costs for microalgae; however, biomass harvesting still remains as the bottleneck for its large-scale application. In this study, the novel biogranulation system facilitating easier and faster microalgae harvesting was firstly compared with the conventional suspended culture for energy-efficiency and sustainability assessment on microalgae (Ankistrodesmus falcatus var. acicularis) cultivation using the synthetic anaerobic digestion liquor. Results demonstrated that the biogranulation system enhanced volumetric biomass productivity (223.17 ± 11.82 g/m³/day) by about 4.4 times compared to that from the suspended system (41.57 ± 2.08 g/m³/day) under the same environmental conditions. It was noticed that lipids, carbohydrates and proteins were accumulated in microalgae cells along with nutrients remediation, and the microalgae granules with much higher proteins content (313.28 ± 26.67 mg/g-VSS) could be easily harvested through 2 min gravity sedimentation with little impact on the contents of carbohydrates and lipids. In the whole cultivation and harvesting process, the biomass mass-based electricity consumption and footprint demand by the biogranulation system were reduced by 58% and 76%, respectively. Results from this study provide a cost-effective and sustainable approach for microalgae in the treatment of nutrients rich digestion liquor with simultaneous production of valuable biomaterials.

A review on mycelial pellets as biological carriers: Wastewater treatment and recovery for resource and energy

Mycelial pellets, a new environment friendly biological carrier, have received wide attention from researchers due to porosity, stability and unique biocompatibility. In this article, the theoretical basis and mechanism of mycelial pellets as a biological carrier were analyzed from the properties of mycelial pellets and the interaction between mycelial pellets and other microorganisms. This article aims to collate and present the current application and development trend of mycelial pellets as biological carriers in wastewater treatment, resource and energy recovery, especially the symbiotic particle system formed by mycelial pellets and microalgae is an important way to break through the technical bottleneck of biodiesel recovery from wastewater. This review also analyzes the research hotspots and trends of mycelial pellets as carriers in recent years, discusses the challenges faced by this technology, and puts forward corresponding solutions.

Enhancing robustness of activated sludge with Aspergillus tubingensis as a protective backbone structure under high-salinity stress

High salt seriously destroys the stable interactions among key functional species of activated sludge, which in turn limits the performance of high-salinity wastewater biological treatment. In this study, pelletized Aspergillus tubingensis (AT) was used as a protective backbone structure for activated sludge under high-salinity stress, and a superior salt-tolerant AT-based aerobic granular sludge (AT-AGS) was developed. Results showed that the COD and NH₄⁺-N removal efficiencies of salt-domesticated AT-AGS were 11.83% and 7.18% higher than those of salt-domesticated flocculent activated sludge (FAS) at 50 gNaCl/L salinity. Compared to the salt-domesticated FAS, salt-domesticated AT-AGS showed stronger biomass retention capacity (with a MLVSS concentration of 7.92 g/L) and higher metabolic activity (with a dehydrogenase activity of 48.06 mgTF/gVSS·h). AT modified the extracellular polymeric substances pattern of microbes, and the total extracellular polysaccharide content of AT-AGS (80.7 mg/gVSS) was nearly twice than that of FAS (46.3 mg/gVSS) after salt-domestication, which demonstrated that extracellular polysaccharide played a key role in keeping the system stable. The high-throughput sequencing analysis illustrated that AT contributed to maintain the microbial richness and diversity of AT-AGS in high-salt environment, and Marinobacterium (with a relative abundance of 32.04%) became the most predominant genus in salt-tolerant AT-AGS. This study provided a novel insight into enhancing the robustness of activated sludge under high-salinity stress.

Tannery Wastewater Recalcitrant Compounds Foster the Selection of Fungi in Non-Sterile Conditions: A Pilot Scale Long-Term Test

This study demonstrated that a microbial community dominated by fungi can be selected and maintained in the long-term under non-sterile conditions, in a pilot-scale packed-bed reactor fed with tannery wastewater. During the start-up phase, the reactor, filled with 0.6 m³ of polyurethane foam cubes, was inoculated with a pure culture of Aspergillus tubingensis and Quebracho tannin, a recalcitrant compound widely used by tannery industry, was used as sole carbon source in the feeding. During the start-up, fungi grew attached as biofilm in carriers that filled the packed-bed reactor. Subsequently, the reactor was tested for the removal of chemical oxygen demand (COD) from an exhaust tanning bath collected from tanneries. The entire experiment lasted 121 days and average removals of 29% and 23% of COD and dissolved organic carbon (DOC) from the tannins bath were achieved, respectively. The evolution of the microbial consortium (bacteria and fungi) was described through biomolecular analyses along the experiment and also developed as a function of the size of the support media.

Impact of hydraulic retention time on swine wastewater treatment by aerobic granular sludge sequencing batch reactor

In this study, the effect of hydraulic retention time (HRT) on the performance of aerobic granular sludge (AGS) treating swine wastewater (SW) in sequencing batch reactor (SBR) was investigated. The HRT was set at 4.8, 6, 8, 12, and 16 h and performed in five parallel aerobic granular sludge sequence batch reactors (AGSBRs), respectively. The results showed that sedimentation performance and biomass concentration were improved by decreasing the HRT from 16 to 8 h. However, when further decreasing HRT from 8 to 4.8 h, the AGS performance became worse. The AGS process with HRT of 8 h exhibited high pollutant removal efficiency, and an abundant microbial community and a stable microbial community structure were observed. High-throughput 16S rRNA analysis revealed that there were significant differences between the microorganisms in AGS samples with HRT of 8 h at the phylum level and that the dominant microbes changed as the process proceeded. At the genus level, the species and relative abundance of microorganisms gradually evolved for AGS stability in all cases.