Stability and nutrients removal performance of a Phanerochaete chrysosporium-based aerobic granular sludge process by step-feeding and multi A/O conditions

Structure-activity relationship of self-immobilized mycelial pellets and their functions in wastewater treatment

Mycelial pellets (MPs) represent an emerging class of eco-friendly, self-immobilized bioactive materials characterized by high biological activity, superior porous structure, and unique biocompatibility. Based on structure-activity relationships, this paper reviews MPs' applications, mechanisms, and advantages in wastewater treatment, while updating fundamental theories on their production optimization, structure characteristics, and surface properties. Emphasis is placed on MPs' three principal functions in remediating pollution: biodegradation via high biological activity, adsorption through porous aggregated structure and superior surface features, and bio-carrier role based on the three-dimensional carbonaceous skeleton. Furthermore, the multifunctionality of MPs improves sludge settleability and dewaterability, as well as enhances aerobic granular sludge granulation and structural stability. Future research priorities include scalable low-cost production, mechanical reinforcement strategies, development of engineered strains and composites, and safe disposal of pollutant-laden MPs. This work provides valuable insights into the use of MPs in wastewater treatment and identifies critical directions for advancing MPs technology.

Development of oriented microbial consortium-based compound enzyme strengthens food waste hydrolysis and antibiotic resistance genes removal: Deciphering of performance, metabolic pathways and microbial communities

Enzymatic hydrolysis has been considered as an eco-friendly pretreatment method for enhancing bioconversion process of food waste (FW). However, existing commercial enzymes and microbial monomer-based compound enzymes (MME) have the issues of uneven distribution of enzymatic activity and low matching degree with the components of FW, leading to low efficiency with enzymatic hydrolysis and removal of antibiotic resistance genes (ARGs). This study used FW as the substrate, under the co-culture system, produced a microbial consortium-based compound enzymes (MCE) with oriented and well-matching degree for FW hydrolysis and ARGs removal, of which the performance, metabolic pathways and microbial communities were also investigated in depth. Results showed that the best performance for ARGs was achieved by the MCE prepared by mixing 1:5 of Aspergillus oryzae and Aspergillus niger after 12 days fermentation. The highest soluble chemical oxygen demand (SCOD) concentration and ARGs removal could respectively reach 83.90 ± 1.67 g/L and 45.95% after MCE pretreatment. The analysis of metabolic pathways revealed that 1:5 MCE pretreatment strengthened the catalytic activity of carbohydrate-active enzymes, increased the abundances of genes involved in cellulose and starch degradation, polysaccharide synthesis, ATP binding cassette (ABC) transporters and global regulation, while decreased the abundances of genes involved in mating pair formation system, two-component regulatory systems and quorum sensing, thereby enhanced FW hydrolysis and restrained ARGs dissemination. Microbial community analysis further indicated that the 1:5 MCE pretreatment promoted growth, metabolism and richness of functional microbes, while inhibited the host microbes of ARGs. It is expected that this study can provide useful insights into understanding the fate of ARGs in food waste during MCE pretreatment process.

Characteristics and performance of algal-bacterial granular sludge in photo-sequencing batch reactors under various substrate loading rates

The algae-bacterial granular sludge (ABGS) technology has garnered significant attention due to its remarkable attributes of low carbon emissions. To investigate the performance of the ABGS system under various substrate loading rates, the parallel photo-sequencing batch reactors (P1 and P2) were set up. The results indicated that chlorophyll-a content and extracellular polymeric substance content were measured at 10.7 ± 0.3 mg/L and 61.4 ± 0.7 mg/g SS in P1 under relatively low substrate loading rate (0.9 kg COD/m3/d and 0.09 kg N/m3/d). Moreover, kinetic study revealed that the maximal specific P uptake rate for P1 reached 0.21 mg P/g SS/h under light conditions, and it achieved 0.078 mg P/g SS/h under dark conditions, highlighting the significant role on phosphorus removal played by algae in the ABGS system. The microbial analysis and scanning electron microscopy confirmed that filamentous algae predominantly colonize the surface in P1, whereas spherical bacteria dominate the surface of granular sludge in P2. Additionally, a diverse array of microorganisms including bacteria, algae, and metazoa such as Rotifers and Nematodes were observed in both systems, providing evidence for the establishment of a symbiotic system. This study not only confirmed the ability of ABGS for efficient N and P removal under different substrate loading conditions but also highlighted its potential to enhance the ecological diversity of the reaction system.

The impacts of biodegradable and non-biodegradable microplastic on the performance and microbial community characterization of aerobic granular sludge

Introduction

Microplastics (MPs), identified as emerging contaminants, have been detected across diverse environmental media. Their enduring presence and small size facilitate the adsorption of organic pollutants and heavy metals, leading to combined pollution effects. MPs also accumulate in the food chain thus pose risks to animals, plants, and human health, garnering significant scholarly attention in recent years. Aerobic granular sludge (AGS) technology emerges as an innovative approach to wastewater treatment. However, the impacts of MPs on the operational efficiency and microbial characteristics of AGS systems has been insufficiently explored.

Methods

This study investigated the effects of varying concentration (10, 50, and 100 mg/L) of biodegradable MPs (Polylactic Acid, PLA) and non-biodegradable MPs (Polyethylene Terephthalate, PET) on the properties of AGS and explored the underlying mechanisms.

Results and discussions

It was discovered that low and medium concentration of MPs (10 and 50 mg/L) showed no significant effects on COD removal by AGS, but high concentration (100 mg/L) of MPs markedly diminished the ability to remove COD of AGS, by blocking most of the nutrient transport channels of AGS. However, both PLA and PE promoted the nitrogen and phosphorus removal ability of AGS, and significantly increased the removal efficiency of total inorganic nitrogen (TIN) and total phosphorus (TP) at stages II and III (P < 0.05). High concentration of MPs inhibited the growth of sludge. PET noticeably deteriorate the sedimentation performance of AGS, while 50 mg/L PLA proved to be beneficial to sludge sedimentation at stage II. The addition of MPs promoted the abundance of Candidatus_Competibacter and Acinetobacter in AGS, thereby promoting the phosphorus removal capacity of AGS. Both 50 mg/L PET and 100 mg/L PLA caused large amount of white Thiothrix filamentous bacteria forming on the surface of AGS, leading to deterioration of the sludge settling performance and affecting the normal operation of the reactor. Comparing with PET, AGS proved to be more resistant to PLA, so more attention should be paid to the effect of non-biodegradable MPs on AGS in the future.

Pressure of different level PFOS on aerobic granule sludge: Insights on performance, AGS structure, community succession, and microbial interaction responses

Perfluorooctane sulfonic acid (PFOS) has received much attention due to its potential environmental risks. However, the response of aerobic granular sludge (AGS) to PFOS exposure, particularly the microbial interactions, remains unclear. In this study, we investigated the particle structure of AGS, pollutant removal performance, community succession, and microbial interaction in the AGS system under different PFOS concentrations (0.1 and 1 mg/L). The mass balance showed that PFOS was mainly removed by adsorption with a removal rate of >85 %. PFOS caused some particles to break up and decreased the average particle size from 3.37 mm to 2.64 mm. It also significantly decreased the total nitrogen and total phosphorus removal rates, which was consistent with the deterioration of microbial activity, such as denitrification rate (25 % inhibition), phosphorus uptake rate (73.19 % inhibition), and phosphorus release rate (73.33 % inhibition). PFOS promoted the secretion of extracellular polymer (EPS) in AGS, especially proteins, leading to poor particle hydrophobicity. The network analysis illustrated that PFOS slowed down the information transfer between microorganisms, and increased the competition between them, which may be responsible for the deterioration of the system performance. Connections related to rare species accounted for >75 % of the network, suggesting that rare species have an indispensable role in community information exchange. In addition, rare species acted as seed banks for microorganisms, and under PFOS stress, they transformed into keystone species, which could contribute to system stabilization. This study provides new insights into the effects of PFOS on microbial interactions in AGS systems and the roles of rare species in the AGS microbial community.

Simultaneous change of microworld and biofilm formation in constructed wetlands filled with biochar

As the regulator of constructed wetlands (CWs), biochar is often used to enhance pollutant removal and reduce greenhouse gas emission. Biochar is proved to have certain effects on microbial populations, but its effect on the aggregation of microbial flocs and the formation of biofilms in the CWs has not been thoroughly investigated. Therefore, the above topics were studied in this paper by adding a certain proportion of biochar in aerated subsurface flow constructed wetlands. The results indicated that after adding biochar in the CWs, pollutant removal was enhanced and the removal rate of NH4+-N was increased from 80.76% to 99.43%. The proportion of hydrophobic components in extracellular polymeric substances (EPS) was reduced by adding biochar from 0.0044 to 0.0038, and the affinity of EPS on CH3-SAM was reduced from 5.736 L/g to 2.496 L/g. The weakened hydrophobic and the reduced affinity of EPS caused the initial attachment of microorganisms to be inhibited. The relative abundance of Chloroflexi was decreased after adding biochar, reducing the dense structural skeleton of biofilm aggregates. Correspondingly, the abundance of Bacteroidetes was increased, promoting EPS degradation. Biochar addition helped to increase the proportion of catalytic active proteins in extracellular proteins and decrease the proportion of binding active proteins, hindering the combination of extracellular proteins and macromolecules to form microbial aggregates. Additionally, the proportions of three extracellular protein structures promoting microbial aggregation, including aggregated chain, β-sheet, and 3-turn helix, were decreased to 23.83%, 38.37% and 7.76%, respectively, while the proportions of random coil and antiparallel β-sheet that inhibited microbial aggregation were increased to 14.11% and 8.11%, respectively. An interesting conclusion from the experimental results is that biochar not only can enhance pollutants removal, but also has the potential of alleviating biological clogging in CWs, which is of great significance to realize the sustainable operation and improve the life cycle of CWs.

Effect of C/N on the microbial interactions of aerobic granular sludge system

The main focus of this study was to evaluate the operational stability and changes in microbial interactions of aerobic granular sludge (AGS) systems at reduced C/N (16, 8 and 4). The results showed that the removal efficiency of total nitrogen and total phosphorus decreased from 95.99 ± 0.93% and 84.44 ± 0.67% to 48.46 ± 1.92% and 50.93 ± 2.67%, respectively, when C/N was reduced from 16 to 4. The granule settling performance and stability also deteriorated. Molecular ecological network analysis showed that the reduction of the C/N ratio made the overall network as well as the subnetworks of the Proteobacteria and Bacteroidota more complex and tightly connected. Similarly, the subnetworks of two dominant genera (Thiothrix and Defluviicoccus) became more complex as the C/N decreased. Meanwhile, the decreased C/N ratio might promote competition among microbes in these overall networks and subnetworks. In conclusion, reduced C/N added complexity and tightness to microbial linkages within the AGS system, while increased competition between species might have contributed to the deterioration in pollutant removal performance. This study adds a new dimension to our understanding of the effects of C/N on the microbial community of AGS using a molecular ecological network approach.

Adaptation mechanisms of microalgal-bacterial granular sludge to outdoor light-limited conditions

Microalgal-bacterial granular sludge (MBGS) has attached attention for sustainable wastewater treatment, but it remains elusive whether it can adapt to outdoor light-limited conditions. This paper investigated the biological adaptation mechanisms of MBGS to outdoor light-limited diel conditions using real municipal wastewater. The results indicated that MBGS still had excellent pollutants removal performance, and that both the extracellular polymeric substances and glycogen content of MBGS increased significantly. The main functional microalgae and bacteria were revealed to be Leptolyngbyaceae and Rhodanobacteria, respectively. Further analyses indicated that the abundance of genes encoding PsbA, PsbD, PsbE, PsbJ, PsbP, Psb27, Psb28-2, PsaC, PsaE, PsaL, PsbX, PetB, PetA, and PetE increased in photosystem. Meanwhile, the abundance of gene encoding Rubisco decreased but the gene abundance regarding to crassulacean acid metabolism cycle increased. These suggested that MBGS could adjust the photosynthetic pathway to ensure the completion of photosynthesis. This study is anticipated to add fundamental insights for the MBGS process operated under outdoor light-limited conditions.

The migration regularity and removal mechanism of antibiotic resistance genes during in situ enzymatic hydrolysis and anaerobic digestion of food waste

This study developed a high efficiency compound enzyme (fungal mash) produced in situ from food waste (FW) used for improving hydrolysis and anaerobic digestion (AD) efficiency of FW. Results showed that the soluble COD and methane yield were respectively increased by 67.80% and 16.58% after 24 h in situ enzymatic hydrolysis of food waste by fungal mash. Furthermore, most of target ARGs in FW were also reduced by 45-94% after 24 h in situ enzymatic hydrolysis, while the total tested ARGs and intI1 were respectively further removed by 44-55% and 21-73% in subsequent AD process. In-depth analysis showed that fungal mash could effectively reduce potential hosts and control the horizontal transfer of ARGs during the in situ enzymatic hydrolysis and AD process. Ultimately, correlation analysis and redundancy analysis indicated that the evolution of bacterial communities and changes in intI1 where the common driving forces for the fate of ARGs.

Efficient partial nitrification with hybrid nitrifying granular sludge based on a simultaneous fill/draw SBR mode

In this study, a simultaneous fill/draw SBR was applied to investigate the feasibility of partial nitrification process with inoculation of matured aerobic granular sludge. The system operated stably over 120 days with the relatively high ammonium removal efficiency (≥ 98.83%) and nitrite accumulation rate (≥ 89.60%). Moreover, a hybrid flocs/granules system was formed stably after long-term operation. The nitrite-oxidizing bacteria (NOB) was suppressed effectively because of the combined effect of simultaneous fill/draw mode and intermittent aeration conditions. Furthermore, batch tests were separately tested with isolated granules (> 200 μm) and flocs (< 200 μm), showing that the specific ammonia oxidation rate of granules and flocs were 15.94 ± 2.85 and 66.77 ± 0.83 mg N/(g MLSS·h), respectively. Correspondingly, the abundance of Nitrosomonas as a typical AOB in granules (6.24%) and flocs (11.94%) was obtained via the microbial diversity analysis, while NOB was almost hardly detected in granules and flocs.

Effect of minute amounts of arsenic on the sulfamethoxazole removal and microbial community structure via the SBR system

In this study, the effect of arsenic on the sulfamethoxazole (SMX) removal efficiency and microbial community structure was investigated over 60 days using the SBR process. The results showed that the presence of arsenic had no significant impact on the system performance, the removal efficiencies of two reactors, R1 (the control test) and R2 (with the addition of arsenic), were 13.36 ± 5.71 and 14.20 ± 5.27%, which were attributed to the adsorption of SMX by fulvic acid-like substances and tryptophan-like proteins of extracellular polymeric substances. Compared to the seed sludge, the species number indicated that R2 possessed the richer diversity, while R1 possessed the lower diversity on day 60, which might be relative to the transferring of antibiotic resistance genes (ARGs) in sludge bacterial communities; the minute amounts of arsenic could make the relative levels of Sul1 and Sul2 genes which encode ARGs of sulfonamides in R2 (2.07 and 2.47%) be higher than that in R1 (1.65 and 1.27%), which made the bacterial community of the R2 system more adaptable to SMX stress. Therefore, the minute amounts of arsenic weakened the effect of SMX on the system and enhanced the stability of the microbial community structure.

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.

Historical development and prospect of intimately coupling photocatalysis and biological technology for pollutant treatment in sewage: A review

Through the synergistic effect of photocatalysis and biodegradation, intimately coupling photocatalysis and biological (ICPB) technology could improve the removal rate and mineralization rate of refractory pollutants and reduce the toxicity of intermediate products. ICPB system was characterized with the advantages of simple operation, low energy consumption and high treatment efficiency. As a new sewage treatment technology, ICPB system has shown great potential in the treatment of refractory pollutants, and has been widely concerned. In this study, the research progress of photocatalyst, carrier and biofilm in ICPB system were discussed, and the degradation mechanism was introduced. The shortcomings of the current ICPB system were pointed out, and the possible research directions of ICPB in the future were proposed. This review aimed to deepen the understanding of ICPB technology and promoted the further development of ICPB technology in the treatment of refractory pollutants.

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.

Microalgal-bacterial granular sludge for municipal wastewater treatment: From concept to practice

Recently, increasing interest has been placed in microalgal-bacterial granular sludge (MBGS) in the journey towards the energy and carbon neutrality of municipal wastewater treatment. Different from aerobic granular sludge, the performance of MBGS is mainly determined by the mutualism and symbiosis between coexisting microalgae and bacteria. It appears from the literature that most of studies on MBGS were conducted at small benchtop scales under controlled conditions with synthetic wastewater. Therefore, this article attempts to look into the major engineering gaps between the knowledge generated from numerous laboratory research works and the large-scale application of MBGS, including massive production of MBGS, type of bioreactor, effect of alternate photo and dark metabolisms on effluent quality, resource recovery from waste MBGS, etc. It is clearly demonstrated that MBGS is still at its infant stage, and more effort is strongly needed to identify the technological bottlenecks of full-scale applications, while providing corresponding engineering solutions.

Rapid start-up of photo-granule process in a photo-sequencing batch reactor under low aeration conditions: Effect of inoculum AGS size

The photo-granule process is an effective and economically feasible alternative for wastewater treatment, but little information is available regarding how to speed up the photo-granulation process. In this study, the effect of inoculum aerobic granular sludge (AGS) size on the start-up of the photo-granule process was investigated under low aeration conditions (superficial gas velocity of 0.5 cm/s). For this purpose, the inoculum AGS was sorted into various size-categories (0.4-0.8 mm, 0.8-1.4 mm, 1.4-2.2 mm, and > 2.2 mm) to serve as individual inoculum sludge. The excellent settling properties (SVI₅ of 39.3 mL/g), strong mechanical strength, efficient nutrient removal (COD: 94.2-97.1%; TN: 80.1-84.8%; TP: 60.4-91.5%), and high biodiesel yields (12.11 mg/g MLSS) were rapidly achieved in the system inoculated with 0.8-1.4 mm AGS. The granulation process was facilitated by filamentous algae as the nucleus, extracellular polymeric substances as the backbone, and the enrichment of functional bacteria (such as Thauera and Sphingorhabdus). Furthermore, the inherent influencing mechanisms of inoculum AGS size on the photo-granulation were revealed from cellular hydrophobicity, surface thermodynamics, and sludge aggregation behavior. This study provides a novel start-up approach of the photo-granule process by inoculating with the optimal AGS size, which is convenient, practically feasible and significantly reduced the aeration consumption.

A comparison between exogenous carriers enhanced aerobic granulation under low organic loading in the aspect of sludge characteristics, extracellular polymeric substances and microbial communities

In this study, polymeric ferric sulfate (PFS), aluminum sulfate (AS) and diatomite were added to enhance the aerobic granulation under low organic loading rate (OLR) of 0.6 kg·COD/(m³·d), and their effects of aerobic granule formation, extracellular polymeric substances (EPS) secretion and microbial community were investigated. The results showed that adding carriers could facilitated the growth of aerobic granules and improve the sludge settleability and biomass retention. Nutrient removal efficiencies were also enhanced. Compared with diatomite, adding PFS and AS resulted in more significant increase in EPS production, especially for the extracellular proteins. For microbial community, the dominated bacteria (Zoogloea, 18.47-23.95%) in the mature granular consortia were similar. Moreover, the introduction of PFS and diatomite contributed to the enrichment of Paracoccus, which was responsible for denitrification. Adding carriers potentially activated the functional genes related to metabolism and genetic information processing, and PFS had the most significant effects.

Promoting the granulation process of aerobic sludge via a sustainable strategy of effluent reflux in view of AHLs-mediated quorum sensing

Aerobic granular sludge (AGS) has excellent performance in wastewater treatment. However, the formation and mechanism of AGS by effluent reflux are not fully understood in sequential batch reactors (SBRs). In this study, two reactors were constructed, among which R1 was the control group, and the R2 reactor refluxed one-fourth of the supernatant of the effluent to the influent water. In the reactor of R2, the granules had better COD and TN removal efficiencies and resistance to external shocks, and AGS produced more extracellular polymeric substances (EPS). Analysis of microbial community indicated that AHLs-mediated microbes, denitrifying microbes, and EPS producers were enriched. At the same time, the correlation between 3OC6-HSL, C8-HSL, C12-HSL and PN was 0.89*, 0.94** and 0.92* respectively, the possible mechanism of enhanced granulation was mainly the promotion of AHLs by effluent reflux. Therefore, the effluent reflux strategy could be an innovative and sustainable strategy that validates the function of AHLs-mediated QS to accelerate aerobic sludge granulation and maintain its structural stability.