New insights into mycelial pellets for aerobic sludge granulation in membrane bioreactor: Bio-functional interactions among metazoans, microbial communities and protein expression

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.

Chlorine disinfectant significantly changed microfauna habitat, community structure, and colonization mode in wastewater treatment plants

During the coronavirus disease 2019 epidemic, excessive chlorine disinfectants have been used to block the spread of severe acute respiratory syndrome-coronavirus 2, resulting in large amounts of residual disinfectants entering wastewater treatment plants (WWTPs) through sewage systems. So far, no relevant research has been conducted on the impact of chlorine disinfectants on microfauna, an important microbial component in activated sludge treatment systems. This study comprehensively investigated the changes in microfauna habitat, community structure, and colonization mode under the chlorine stress by combining the full-scale WWTP survey and laboratory-scale sequencing batch reactor experiments. The results showed that chlorine disinfectants significantly changed the community structure of microfauna, including decrease in sedentary ciliates and increase in free-living ciliates, amoebas, and flagellates. Besides the disinfection effect of chlorine disinfectants, the microfauna community was also influenced by changes in habitat and bacterial community. The loose structure and excessive extracellular polymeric substance (EPS) of activated sludge caused by chlorination would impact the colonization of sedentary ciliates, while it was conducive to the survival of free-living ciliates due to their predation on EPS as the nutrients. Bacteria in the activated sludge had strong interactions with protozoa, and their changes under chlorine stress directly affected the protozoan community and even indirectly affected the micro-metazoa community through the food chain.

IMPORTANCE

This study revealed that chlorine disinfectant significantly changed microfauna habitat, community structure, and colonization mode in wastewater treatment plants during the coronavirus disease 2019 pandemic. Chlorine disinfectant could destroy the structure and stability of sludge flocs, reduce the abundance of beneficial microfauna in activated sludge, and even affect the colonization of sedentary ciliates on sludge. In addition, chlorine disinfectants might induce environmental and ecological risks related to microfauna, such as elevated suspended solids and release of bacteria and microfauna in the effluents.

Dual isotope labelling combined with multi-omics analysis revealing the N2O source evolution in aerobic biological systems driven by salinity gradient

Salinity is considered a major factor influencing nitrous oxide (N2O) emissions from biochemical treatment of high-salinity wastewater, but its mechanism has not been thoroughly investigated. In this study, we investigated the effects of salinity on N2O emissions under aerobic conditions. As salinity rose from 0.66 % to 3.66 %, N2O emission flux first increased and then decreased, while the emission factor (EF) consistently increased, likely due to significant inhibition of nitrification at 3.66 % salinity. Nitrogen‑oxygen dual isotope labeling experiments demonstrated that the dominant N2O production pathway shifted with salinity: from nitrifier nitrification (NN, 36.07 %-40.97 %) at low salinity (0.66 %, 1.66 %), to nitrification-coupled denitrification (NCD, 51.67 %) at 2.66 %, and to nitrifier denitrification (ND, up to 80.81 %) at the salinity of 3.66 %. From the changes in bacterial relative abundances and expressions of 4 key functional genes (amoA, hao, nor, and nosZ) revealed by metatranscriptomic sequencing, Nitrosomonas, unclassified Rhodospirillales, and Nitrospira were identified as key contributors to NN, NCD, and ND pathways, respectively, as salinity increased. We also found that the differential expressed genes and metabolites involved in energy metabolism, oxidative phosphorylation, and metabolism of amino acids, pyrimidines, and nucleotides may affect N-cycling bacteria, thereby influencing nitrogen conversion and salinity tolerance as well. This study sheds light on nitrification process in response to salinity stress and offers insights for mitigating greenhouse gas emissions from high-salinity wastewater treatment.

Wastewater Treatment with Bacterial Representatives of the Thiothrix Morphotype

Bacteria of the Thiothrix morphotype, comprising the genera Thiothrix, Thiolinea and Thiofilum, are frequently encountered in domestic and industrial wastewater treatment systems, but they are usually not clearly differentiated due to the marked similarity in their morphologies. Methods ranging from light microscopy, FISH and PCR to modern high-throughput sequencing are used to identify them. The development of these bacteria in wastewater treatment systems has both advantages and disadvantages. On the one hand, the explosive growth of these bacteria can lead to activated sludge bulking or clogging of the treatment system's membranes, with a consequent decrease in the water treatment efficiency. On the other hand, members of the Thiothrix morphotype can improve the quality of granular sludge and increase the water treatment efficiency. This may be due to their capacity for sulfide oxidation, denitrification combined with the oxidation of reduced sulfur compounds, enhanced biological phosphate removal and possibly denitrifying phosphate removal. The recently obtained pangenome of the genus Thiothrix allows the explanation, at the genomic level, of the experimental results of various studies. Moreover, this review summarizes the data on the factors affecting the proliferation of representatives of the Thiothrix morphotype.

In-depth insight into improvement of simultaneous nitrification and denitrification/biofouling control by increasing sludge concentration in membrane reactor: performance, microbial assembly and metagenomic analysis

Currently, severe membrane fouling and inefficient nitrogen removal were two main issues that hindered the sustainable operation and further application of membrane bioreactor (MBR). This study aimed to simultaneously alleviate membrane fouling and improve nitrogen removal by applying high sludge concentration in MBR. Results showed that high sludge concentration (12000 mg/L) enhanced total nitrogen removal efficiency (78 %) and reduced transmembrane pressure development rate. Microbial community analysis revealed that high sludge concentration enriched functional bacteria associated with nitrogen removal, increased filamentous bacteria fraction in bio-cake and inhibited Thiothrix overgrowth in bulk sludge. From molecular level, the key genes involved in nitrogen metabolism, electron donor/adenosine triphosphate production and amino acid degradation were up-regulated under high sludge concentration. Overall, high sludge concentration improved microbial assembly and functional gene abundance, which not only enhanced nitrogen removal but also alleviated membrane fouling. This study provided an effective strategy for sustainable operation of MBR.

Enhanced ammonia nitrogen and phenol removal by immobilized bacteria through composite mycelium pellet-driven quinone redox cycle

The composite mycelium pellet (CMP) was coupled with Pseudomonas sp. Y1 (CMP-Y1) to remove phenol and ammonia nitrogen (NH4+-N). The CMP was formed by the self-assembly of fungal mycelium with sponge iron (SIO), gallic acid (GA), and oxalic acid. The results showed that CMP with abundant pore size and successful internal loading of sponge iron containing iron nanoparticles. CMP could induce GA redox cycle to form Fenton-like reaction and thus achieve efficient phenol removal (93.32%, 24 h). Meanwhile, the removal efficiencies of phenol, NH4+-N, and chemical oxygen demand (COD) using CMP-Y1 at 12 h were 93.71, 92.40, and 89.00%, respectively. The increase in the electron transfer activity of strain Y1 by the addition of CMP could facilitate the nitrogen removal processes. In addition, high-throughput sequencing results indicated the abundance of antioxidant and repair genes was increased, which might be a strategy of strain Y1 to cope with oxidative stress. This strategy provided the possibility for the practical application of the combination of advanced oxidation and biological treatment, and offered new insights into the symbiotic system of fungi and bacteria.

Enhanced denitrification of the AO-MBBR system used for expressway service area sewage treatment: A new perspective on decentralized wastewater treatment

Decentralized wastewater treatment warrants considerable development in numerous countries and regions. Owing to the unique characteristics of high ammonia nitrogen concentrations and low carbon/nitrogen ratio, nitrogen removal is a key challenge in treating expressway service area sewage. In this study, an anoxic/oxic-moving bed biofilm reactor (A/O-MBBR) and a traditional A/O bioreactor were continuously operated for 115 days and their outcomes were compared to investigate the enhancement effect of carriers on the total nitrogen removal (TN) for expressway service area sewage. Results revealed that A/O-MBBR required lower dissolved oxygen, exhibited higher tolerance toward harsh conditions, and demonstrated better shock load resistance than traditional A/O bioreactor. The TN removal load of A/O-MBBR reached 181.5 g‧N/(m3‧d), which was 15.24% higher than that of the A/O bioreactor. Furthermore, under load shock resistance, the TN removal load of A/O-MBBR still reached 327.0 g‧N/(m3‧d), with a TN removal efficiency of above 80%. Moreover, kinetics demonstrated that the denitrification rate of the A/O-MBBR was 121.9% higher than that of the A/O bioreactor, with the anoxic tank biofilm contributing 60.9% of the total denitrification rate. Community analysis results revealed that the genera OLB8, uncultured_f_Saprospiraceae and OLB12 were the dominant in biofilm loaded on carriers, and OLB8 was the key for enhanced denitrification. FAPROTAX and PICRUSt2 analyses confirmed that more bacteria associated with nitrogen metabolism were enriched by the A/O-MBBR carriers through full denitrification metabolic pathway and dissimilatory nitrate reduction pathway. This study offers a perspective into the development of cost-effective and high-efficiency treatment solutions for expressway service area sewage.

Unraveling the rate-limiting step in microorganisms' mediation of denitrification and phosphorus absorption/transport processes in a highly regulated river-lake system

River-lake ecosystems are indispensable hubs for water transfers and flow regulation engineering, which have frequent and complex artificial hydrological regulation processes, and the water quality is often unstable. Microorganisms usually affect these systems by driving the nutrient cycling process. Thus, understanding the key biochemical rate-limiting steps under highly regulated conditions was critical for the water quality stability of river-lake ecosystems. This study investigated how the key microorganisms and genes involving nitrogen and phosphorus cycling contributed to the stability of water by combining 16S rRNA and metagenomic sequencing using the Dongping river-lake system as the case study. The results showed that nitrogen and phosphorus concentrations were significantly lower in lake zones than in river inflow and outflow zones (p < 0.05). Pseudomonas, Acinetobacter, and Microbacterium were the key microorganisms associated with nitrate and phosphate removal. These microorganisms contributed to key genes that promote denitrification (nirB/narG/narH/nasA) and phosphorus absorption and transport (pstA/pstB/pstC/pstS). Partial least squares path modeling (PLS-PM) revealed that environmental factors (especially flow velocity and COD concentration) have a significant negative effect on the key microbial abundance (p < 0.001). Our study provides theoretical support for the effective management and protection of water transfer and the regulation function of the river-lake system.

New insights into enhanced biodegradation of 4-bromphenol in a nitrate-reducing system: Process performance and mechanism

Due to the recalcitrant nature of halogenated phenol, conventional anaerobic bioprocess is often limited by low removal efficiency and poor process stability. At the presence of electron acceptors such as nitrate, 4-bromophenol (4-BP) removal efficiency is significantly higher than that in the anaerobic control system, but the mechanism involved is still unclear. Therefore, an up-flow nitrate-reducing bioreactor (NRBR) was designed and consecutively performed for 215 days to explore the synergistic mechanism for BPs biodegradation and nitrate reduction. Complete 4-BP biodegradation could be obtained in NRBR at HRT and 4-BP loading rate of 24 h and 0.29 mol m - 3d - 1, while the TOC removal and nitrate reduction efficiencies were as high as 91.33±2.11% and 98.31±1.33%, respectively. Population evolution analyses revealed that the microorganisms involved in 4-BP debromination and biodegradation (Candidatus Peregrinibacteria, Denitratisoma, Anaerolineaceae and Ignavibacterium) as well as nitrate reduction (Denitratisoma, Anaerolineaceae, Limnobacter and Ignavibacterium) were significantly enriched in NRBR. Major intermediates during 4-BP biodegradation, including 4-bromocatechol, 4‑bromo-6-oxo-hexanoic acid and succinic acid were identified, while a distinct 4-BP biodegradation pathway via hydration, aromatic-ring cleavage, hydrolysis debromination and oxidation was expounded. Metagenomic analysis indicated that oxidation (had, pht4, boh, butA), hydrolysis debromination ((S)-2-haloacid dehalogenase) and bio-mineralization (gabD, sdhA) of 4-BP were largely enhanced in NRBR. Moreover, carbon, nitrogen, energy and amino acid metabolisms were significantly facilitated with the injection of nitrate in order to provide energy and electron, thus enhanced microbial activities and enzymatic reactions in NRBR. The proposed mechanism provides new insights into our mechanistic understanding of halogenated phenol biodegradation and the development of sustainable bioremediation strategies.

Insights into thermal hydrolysis pretreatment temperature for enhancing volatile fatty acids production from sludge fermentation: Performance and mechanism

To reveal the impact of thermal hydrolysis pretreatment (THP) temperature on the unclear mechanisms of volatile fatty acids (VFAs) production, four groups were established with different temperatures (100, 120, 140 and 160 °C), and high throughput sequencing technology was utilized. The results indicated that the optimal VFAs production occurred at 140 °C. Moreover, as the THP temperature increased, the proportion of acetic acid also increased, accounting for 10.8% to 26.7% of the VFAs, compared to only 4.9% in the control group. Mechanism investigations revealed that THP facilitated the hydrolysis and release of biodegradable organic matter. Moreover, the abundance of VFAs production and hydrolytic microorganisms and related metabolic functional genes expression were evidently improved by THP. Overall, this study deepens the understanding of the mechanisms through which different THP temperatures stimulate the production of VFAs through acidogenic fermentation, providing technical support for future THP application in sludge treatment.

Rapid establishment of algal-bacterial granular sludge system by applying mycelial pellets in a lab-scale photo-reactor under low aeration conditions: Performance and mechanism analysis

Light-driven algal-bacterial granular sludge (ABGS) is an innovative low-carbon technology with significant merits in treating municipal wastewater, but how to shorten the photogranulation process, especially under low aeration conditions, is largely unknown. Herein, two strategies were proposed to accelerate the start-up of the ABGS system in photo-sequencing batch reactors (PSBRs) with a low superficial gas velocity of 0.5 cm/s. Compared to directly dosing mycelial pellets (MPs), applying MPs to flocculate algae and using the formed algal-mycelial pellets (AMPs) as carriers enhanced the establishment of the algal-bacterial symbiosis. The ABGS system developed rapidly within 20 days, with a large particle diameter (mean diameter of 321 μm) and excellent settleability (SVI₃₀ of 55.4 mL/g). More importantly, this system could be stably operated for at least 100 days, mainly attributed to the reinforced secretion of protein with unique secondary structure and elevated hydrophobic functional groups. As for the reactor performance, the average removal efficiencies of the ABGS system were 97.8% for organic matter, 80.0% for total nitrogen, and 84.4% for phosphorus. The enrichment of functional bacteria and algae, and the up-regulation of functional genes and enzymes involved in electron production and transport processes likely drove the transformation of the pollutants, underlining the inherent mechanism for the excellent nutrient removal performance. This study provides a promising approach to solve the problem of a long ABGS start-up period and unstable granular structure under low aeration conditions, which is significant for achieving effective wastewater treatment without energy intensive aeration.