Pathways of inhibition of filamentous sludge bulking by slowly biodegradable organic compounds.

The organic compound composition of wastewater, serves as a crucial indicator for the operational performance of activated sludge processes and has a major influence on the development of filamentous bulking in activated sludge. This study focused on the impact of typical soluble and slowly-biodegradable organic compounds, investigating the pathways through which these substrates affect the occurrence of filamentous bulking in systems operated under both high- and low-oxygen conditions. Results showed that slowly-biodegradable organic compounds lead to a concentrated distribution of microorganisms within flocs, with inward growth of filamentous bacteria. Both Tween-80 and granular starch treated systems exhibited a significant increase in protein content. The glucose system, utilizing soluble substrates, exhibited a markedly higher total polysaccharide content. Microbial communities in the Tween-80 and granular starch treated systems were characterized by a higher abundance of bacteria known to enhance sludge flocculation and settling, such as Competibacter, Xanthomonadaceae and Zoogloea. These findings are of high significance for controlling the operational performance and stability of activated sludge systems, deepening our understanding and providing a novel perspective for the improvement of wastewater treatment processes.

Evaluation of post-treatment after wastewater stabilization ponds at municipal wastewater treatment plant.

The primary objective of this study was to assess the operational conditions of the municipal wastewater treatment system. This system comprises a wastewater treatment plant that employs the activated sludge process, along with wastewater stabilization ponds as the third stage of treatment. The operating conditions of the wastewater stabilization ponds were observed during both normal operation and malfunction scenarios. The average values of the pollutant parameters at the inlet and outlet of the ponds did not differ significantly. However, an increase in the concentrations of total organic carbon (TOC) and phosphates was observed at the ponds' outlet. Specifically, the TOC increased from 2.25 mg/dm3 (inlet) to 5.02 mg/dm3 (outlet), while phosphates rose from 0.34 mg/dm3 (inlet) to 3.02 mg/dm3 (outlet). The analyzed pollutants in the wastewater stabilization ponds samples were characterized by seasonal variability, particularly concerning TOC, dissolved oxygen, ammonium nitrogen, and phosphates. During malfunctions, the highest pollutant load (including activated sludge and precipitated phosphorus) was delivered to the first wastewater stabilization pond, inducing the phenomenon of internal loading, leading to increase in phosphates concentrations. To mitigate such issues, the main force should be focused on the proper operation of the wastewater stabilization ponds and wastewater treatment plants.

Filamentous bacteria-induced sludge bulking can alter antibiotic resistance gene profiles and increase potential risks in wastewater treatment systems.

Sludge bulking caused by filamentous bacteria is a prevalent issue in wastewater treatment systems. While previous studies have primarily concentrated on controlling sludge bulking, the biological risks associated with it have been overlooked. This study demonstrates that excessive growth of filamentous bacteria during sludge bulking can significantly increase the abundance of antibiotic resistance genes (ARGs) in activated sludge. Through metagenomic analysis, we identified specific ARGs carried by filamentous bacteria, such as Sphaerotilus and Thiothrix, which are responsible for bulking. Additionally, by examining over 1,000 filamentous bacterial genomes, we discovered a diverse array of ARGs across different filamentous bacteria derived from wastewater treatment systems. Our findings indicate that 74.84% of the filamentous bacteria harbor at least one ARG, with the occurrence frequency of ARGs in these bacteria being approximately 1.5 times higher than that in the overall bacterial population in activated sludge. Furthermore, genomic and metagenomic analyses have shown that the ARGs in filamentous bacteria are closely linked to mobile genetic elements and are frequently found in potentially pathogenic bacteria, highlighting potential risks posed by these filamentous bacteria. These insights enhance our understanding of ARGs in activated sludge and underscore the importance of risk management in wastewater treatment systems.

Impact of nutrient deficiency on biological sewage treatment - Perspectives towards urine source segregation.

Human urine contains 9 g/L of nitrogen (N) and 0.7 g/L of phosphorus (P). The recovery of N and P from urine helps close the nutrient loop and increase resource circularity in the sewage treatment sector. Urine contributes an average of 80 % N and 50 % P in sewage, whereby urine source segregation could reduce the burden of nutrient removal in sewage treatment plants (STPs) but result in N and P deficiency and unintended negative consequences. This review examines the potential impacts of N and P deficiency on the removal of organic carbon and nutrients, sludge characteristics and greenhouse gas emissions in activated sludge processes. The details of how these impacts affect the operation of STPs were also included. This review helps foresee operational challenges that established STPs may face when dealing with nutrient-deficient sewage in a future where source separation of urine is the norm. The findings indicate that the requirement of nitrification-denitrification and biological P removal processes could shrink at urine segregation above 80 % and 100 %, respectively. Organic carbon, N and biological P removal processes can be severely affected under full urine segregation. The decrease in solid retention time due to urine segregation increases treatment capacity up to 48 %. Sludge flocculation and settleability would deteriorate due to changes in extracellular polymeric substances and induce various forms of bulking. Beneficially, N deficiency reduces nitrous oxide emissions. These findings emphasise the importance of considering and preparing for impacts caused by urine source segregation-induced nutrient deficiency in sewage treatment processes.

Effects of enhanced biological phosphorus removal on rapid control of sludge bulking and fast formation of aerobic granular sludge.

This study investigated the effects of enhanced biological phosphorus removal (EBPR) on rapid sludge bulking control and fast aerobic granular sludge (AGS) formation by adding 20 % of EBPR activated sludge to the bulking activated sludge (BAS) reactor. The results indicate that activating EBPR activity swiftly improved BAS settleability within 16 days, thus resolving sludge bulking issues. Subsequently, a settling time-based selection was employed, resulting in the BAS granulation within another 16 days. The rapid achievement of EBPR activity improved the BAS settleability and facilitated the formation of sludge aggregates, thereby expediting BAS granulation. Inhibition of filamentous bacteria and enrichment of slow-growing organisms contributed to both sludge bulking control and aerobic granulation. Furthermore, the increase in proteins/polysaccharides ratio facilitated the granulation process. Additionally, total nitrogen removal increased from 59.4 % to 71.7 % because of the mature AGS formation. This study provided an approach to simultaneously control sludge bulking and promote aerobic granulation.

Pilot-scale investigation of performance and microbial community in a novel system combining fixed and suspended activated sludge.

The conventional activated sludge (CAS) process is a widely used method for wastewater treatment due to its effectiveness and affordability. However, it can be prone to sludge abnormalities such as sludge bulking/foaming and sludge loss, which can lead to a decrease in treatment efficiency. To address these issues, a novel bag-based fixed activated sludge (BBFAS) system utilizing mesh bags to contain the sludge was developed for low carbon/nitrogen ratio wastewater treatment. Pilot-scale experiments demonstrated that the BBFAS system could successfully avoid the sludge abnormalities. Moreover, it was not affected by mass transfer resistance and exhibited significantly higher nitrogen removal efficiency, surpassing that of the CAS system by up to 78%. Additionally, the BBFAS system demonstrated comparable organic matter removal efficiency to CAS system. 16S rRNA gene high-throughput sequencing revealed that the bacterial community structure within the BBFAS system was significantly different from that of the CAS system. The bacteria associated with ammonium removal were more abundant in the BBFAS system than in the CAS system. The abundance of Nitrospira in the BBFAS could reach up to 6% and significantly higher than that in the CAS system, and they were likely responsible for both ammonia-oxidizing and nitrite-oxidizing functions. Clear stratification of microbial communities was observed from the outer to inner layers of the bag components due to the gradients of dissolved oxygen and other substrates. Overall, this study presents a promising approach for avoiding activated sludge abnormalities while maintaining high pollutant removal performance.

Sludge bulking monitoring in industrial wastewater treatment plants through graphical methods: A dynamic graph embedding and Bayesian networks approach.

Sludge bulking is a prevalent issue in wastewater treatment plants (WWTPs) that negatively impacts effluent quality by hindering the normal functioning of treatment processes. To tackle this problem, we propose a novel graph-based monitoring framework that employs advanced graph-based techniques to detect and diagnose sludge bulking events. The proposed framework utilizes historical datasets under normal operating conditions to extract pertinent features and causal relationships between process variables. This enables operators to trigger alarms and diagnose the root cause of the bulking event. Sludge bulking detection is carried out using the dynamic graph embedding (DGE) method, which identifies similarities among process variables in both temporal and neighborhood dependencies. Consequently, the dynamic Bayesian network (DBN) computes the prior and posterior probabilities of a belief, updated at each time step. Variations in these probabilities indicate the potential root cause of the sludge bulking event. The results demonstrate that the DGE outperforms other linear and non-linear feature extraction methods, achieving a detection rate of 99%, zero false alarms, and less than one percent incorrect detections. Additionally, the DBN-based diagnostic method accurately identified the majority of sludge bulking root causes, primarily those resulting from sudden drops in COD concentration, with an accuracy of 98% an improvement of 11% over state-of-the-art techniques.

Metabolomic pathway regulation for prevention and control of granule sludge bulking in thiosulfate-driven denitrification.

The performance of thiosulfate-driven denitrification (TDD) granule reactor and the mechanism of granule sludge bulking were investigated in this study. The results showed that TDD granule bulking occurred under 12 kgNm-3d-1 of nitrogen loading rate (NLR). The higher NLR promoted accumulation of intermediates in the carbon fixation pathway, including citrate, oxaloacetate, oxoglutarate and fumarate. The carbon fixation improved amino acids biosynthesis, which increased proteins (PN) in extracellular polymers (EPS) to 134.6 ± 11.8 mg/gVSS. The excessive PN altered the content, components and chemical groups of EPS, leading to change of granule structure and decline in settling property, permeability and nitrogen removal. By adopting the strategy of intermittently reducing NLR, excess amino acids in sulfur-oxidizing bacteria was consumed through microbial growth-related metabolism instead of EPS synthesis. Therefore, the nitrogen removal rate increased to 10.23 kg-Nm-3d-1 and maintained stable in the long term. The EPS contents decreased from 168.8 ± 13.5 mg/gVSS to 93 ± 11.5 mg/gVSS and the SVI5 decreased from 66 ± 3.5 ml/g to 25 ± 1.5 ml/g. These findings provide an effective strategy to prevent granule bulking and guide practical application of TDD process.

Non-filamentous sludge bulking induced by exopolysaccharide variation in structure and properties during aerobic granulation.

The forming mechanism of non-filamentous sludge bulking during aerobic granulation were investigated basing on three feeding strategies (R1 direct aeration after fast feeding, R2 anaerobic stirring after fast feeding and R3 anaerobic plug-flow slow feeding). Results showed that strong selection stress (shortening settling time) led to a sharp flocs washout and the subsequent increase of food to microorganisms (F/M) in R1 and R3 reactors, but not found in R2 due to the different strategies of feeding modes. With the increase of F/M, zeta potential and hydrophobicity of sludge surfaces significantly decreased and thus leading to an enhanced repulsive force and energy barriers for sludge aggregation. Particularly, when F/M exceeded 1.2 kgCOD/(kgMLSS·d), non-filamentous sludge bulking was ultimately triggered in R1 and R3. Further analysis showed that massive extracellular exopolysaccharide (PS) accumulated on the surfaces of non-filamentous bulking sludge due to the increased abundance of the microorganisms related to PS secretion during sludge bulking. In addition, significantly increased intracellular second messenger (c-di-GMP), a key substance regulating PS biosynthesis, was confirmed via its concentration determination as well as microbial function prediction analysis, which played a critical role in sludge bulking. Combing with the systematic detection from surface plasmon resonance system, rheometer and size-exclusion chromatography-multiangle laser light detection-refractive index system, higher molecular weight, compact conformation, higher viscosity and higher hydrophilicity was determined in sludge bulking PS relative to PS extracted from non-filamentous bulking sludge. Clearly, the changes of PS (content, structures and properties) driven by c-di-GMP are the dominant mechanism for the formation of non-filamentous sludge bulking during aerobic granulation. This work could provide theoretical support for successful start-up and application of aerobic granular sludge technology.

Study on the inhibition of sludge bulking in A2/O coupled system at low temperature by segmented inlet water mode.

This study aimed to propose a segmented influent method to inhibit sludge bulking. The sludge bulking phenomenon was observed in a A2/O coupled system treating municipal wastewater under low temperature (15 ± 0.5)°C. Adopting the segmented inlet water process, the distribution ratio of the inlet flow in the anaerobic zone and the aerobic zone were 2:1 and 1:1, the sludge bulking phenomenon was suppressed. The sludge loading rate (F/M) analysis showed that the F/M of the anaerobic zone with single-point inflow was only 0.15 kg COD·(kg MLSS·d)-1, which was prone to induce sludge bulking. However, the F/M concentration gradient of the system under segmented inlet water conditions was obvious, which could inhibit the sludge bulking caused by low F/M. The effluent removal results showed that the system had high removal rates of COD, NH4+-N, TN, and TP at a flow distribution ratio of 2:1, with average removal rates of 88.85% ± 2.94%, 91.26% ± 6.68%, 76.60% ± 5.60%, and 96.80% ± 2.17%, respectively. This study confirmed that the segment inlet method inhibited sludge bulking, while the flow distribution ratio of 2:1 also ensured efficient pollutant removal capacity of the system.

Effects of silica fume powder modified by oleic acid on the settleability of bulking sludge.

Modified silica fume powder with oleic acid through coupling agent was prepared based on the in situ utilizing long-chain fatty acids (LCFA) properties of Microthrix parvicella (M. parvicella) in the activated sludge system. The modification was confirmed by XRD and infrared spectrum. The contact angle analysis showed that the modification gave the silica fume powder a hydrophobic surface. The modified silica fume powder had a good combination with M. parvicella from the SEM and Gram staining measurements. The addition of modified silica powder has a certain effect on the settling capacity of sludge, but has little effect on the sludge treatment capacity, while the SVI dropped from 400.1 to 100.0 mL/g. These suggested that the modified silica fume powder could be used as an excellent weight-increasing agent to inhibit sludge bulking.

New insight into soluble extracellular metabolites during sludge bulking process based on excitation-emission matrix spectroscopy and ultrahigh-performance liquid chromatography-mass spectrometry.

Soluble extracellular metabolites (SEM) produced by microorganisms might significantly change during sludge bulking, which is a major operational problem caused by the excessive growth of filamentous bacteria. However, knowledge remains limited about the dynamics and potential role of SEM in the bulking of sludge. In this study, filamentous bulking was simulated in a laboratory-scale reactor and changes to SEM characteristics during the bulking process were investigated using excitation-emission matrix spectroscopy and ultrahigh-performance liquid chromatography-mass spectrometry. SEM components changed significantly at different phases of sludge bulking. Changes in SEM were closely correlated with the structure of the bacterial community. Based on the EEM profiles, significant increases in fulvic acid-like and humic acid-like substances in SEM were observed with the development of filamentous bulking. The degree of humification in SEM showed a clear increasing trend. Untargeted extracellular metabolomic analysis showed that the intensity of berberine and isorhamnetin in SEM increased significantly during the bulking phase, which might synergistically facilitate the development of filamentous bulking.

A sludge bulking wastewater treatment plant with an oxidation ditch-denitrification filter in a cold region: bacterial community composition and antibiotic resistance genes.

Bacterial community structure of activated sludge directly affects the stable operation of WWTPS, and these bacterial communities may carry a variety of antibiotic resistance genes (ARGs), which is a threat to the public health. This study employed 16S rRNA gene sequencing and metagenomic sequencing to investigate the bacterial community composition and the ARGs in a sludge bulking oxidation ditch-denitrification filter WWTP in a cold region. The results showed that Trichococcus (20.34%), Blautia (7.72%), and Faecalibacterium (3.64%) were the main bacterial genera in the influent. The relative abundances of norank_f_Saprospiraceae and Candidatus_Microthrix reached 10.24% and 8.40%, respectively, in bulking sludge, and those of norank_f_Saprospiraceae and Candidatus_Microthrix decreased to 6.56 and 7.10% after the anaerobic tank, indicating that the anaerobic tank had an inhibitory effect on filamentous bacteria. After 20 mJ/cm2 UV disinfection, about 540 bacterial genera, such as Romboutsia (7.99%), Rhodoferax (7.98%), and Thermomonas (4.13%), could still be detected in the effluent. The ARGs were 345.11 ppm in the influent and 11.20 ppm in the effluent; 17 subtypes, such as sul1, msrE, aadA5, ErmF, and tet(A), could be detected throughout the entire process. These ARG subtypes were persistent ARGs with a high health risk. Network analysis indicated that the changes in filamentous bacteria norank_f_Saprospiraceae abundance mainly contributed to the abundance shift of MexB, and Acinetobacter mainly increased the abundance of drfA1. These results above will provide theoretical support for the sludge bulking and ARGs controls of WWTPs in cold regions.

Transboundary intercellular communications between Penicillium and bacterial communities during sludge bulking: Inspirations on quenching fungal dominance.

Fungal bulking is caused by the evolution toward a fungi-dominant unbalanced sludge system, which is indeed the phenomenon of fungi competing against bacterial cells. We hypothesized that the cross-kingdom intercellular communication between fungi and bacteria was internal driving force that stimulated fungal bulking. In this study, we identified three signal molecules related to Penicillium fungi bulking under low-pH stress in an activated sludge reactor, which inspired us to propose a sludge bulking prevention strategy using the quorum quenching theory. When pH dropped from 7.0 to 4.5, the abundance of Penicillium increased from 12.5% to 44.8%. However, some functional bacterial genera, such as Nitrosomonas and Sphingopyxis, were washed out from the sludge. The production of quorum-sensing (QS) molecules N-Heptanoyl-L-homoserine lactone (C7-HSL), N-Dodecanoyl-L-homoserine lactone (C12-HSL), and N-Tetradecanoyl-L-homoserine lactone (C14-HSL) was regulated with sludge bulking; especially the response of the latter two was significantly negative to Penicillium blooming (P < 0.05). To test their roles, trace commercial C12-HSL and C14-HSL were added to Penicillium culture, successfully causing 8.3% and 30.2% inhibition of mycelial formation, respectively. They also contributed to the improvement of activated sludge settleability by 6.1% and 39.7%, respectively (represented by sludge volume index). The transcriptome technique further revealed the regulation of the expression of genes in |logFC| >1, involving signal transduction, mycelium synthesis, and metabolic pathways. Our study provided an innovative strategy for controlling fungal bulking from the perspective of microbial transboundary informatics.

[Aerobic Granulation Stability and Microbial Diversity of Filamentous Bulking Sludge].

Filamentous bacteria, as one of the common bacteria types in wastewater biological treatment, are considered to be the main factor to induce sludge bulking. However, because of its special filamentous shape, it plays a crucial role in the formation of sludge particles. Taking filamentous bulking sludge as the research object, the effect of filamentous bacteria on the sludge granulation process and maintaining the stability of sludge granules was studied, and the microbial diversity of the sludge system was analyzed. Filamentous bulking sludge (SVI=241.56 mL·g-1) and flocculated sludge (SVI=64.22 mL·g-1) were respectively inoculated to carry out granulation culture. The results showed that the time of particle appearance of bulking sludge and flocculated sludge was 20 days and 40 days, respectively; the mature particle sizes were 650 µm and 700 µm, respectively; and the granulation time of bulking sludge was only half that of flocculated sludge. After adding the anoxic zone, the granules were broken to differing degrees, but the SV30/SV5 value of mature granules recovered to 1 after short-term fluctuation, and the stability of the mature granules was stronger. The analysis of microbial community structure showed that the relative abundance of norank_o__Saccharimonadales, unclassified_o__Saccharimonadales, and unclassified_f__Saccharimonadaceae increased from 0.05%, 0.01%, and 0.01% to 4.09%, 3.15%, and 1.12%. The existence and accumulations of these hydrophobic bacteria were important for rapid granulation. The removal rates of COD, NH4+-N, and TN were 94%, 99%, and 35% and 92%, 97%, and 30%, respectively, in SBR1 of bulking sludge and SBR2 of flocculated sludge, and the removal rates of TP were 60% and 30%, respectively.

Regulation of exogenous acyl homoserine lactones on sludge settling performance: Monitoring via ultrasonic time-domain reflectometry.

Despite extensive studies, a comprehensive solution for sludge bulking has not yet been found. This study improves the sludge settling performance via quorum sensing (QS) by adding exogenous acyl homoserine lactones (AHLs). First, a novel approach based on ultrasonic time-domain reflectometry, which can automatically and in-situ assess a sludge volume index (SVI), was developed using the displacement in the ultrasonic spectra as a feasible indicator (R2 = 0.98, p < 0.01). Next, the effects of typical AHLs, i.e., 3OC6-HSL, C12-HSL, and 3OC14-HSL, on sludge settling properties were investigated. Results indicated that the three AHLs significantly promoted the sludge settleability by 1.90, 2.03, and 1.62 times, respectively. The regulation mechanisms were investigated from the perspective of sludge physicochemical properties and biological community interactions. The draining degree of water to extracellular polymeric substances (EPS) significantly increased (p < 0.05) with all three AHLs. Meanwhile, the hydrophobic tryptophan content increased with the addition of 3OC6-HSL and C12-HSL. Hence, EPS hydrophobicity was promoted, which is conducive to microbial aggregation. In addition, molecular ecological networks of activated sludge (AS) indicated that bacterial community structures were more complex and species interactions were more intense when adding 3OC6-HSL and C12-HSL. Meanwhile, additional keystones were identified, with the proportion of QS species increasing by 63.6% and 22.2%, respectively. Exogenous 3OC6-HSL eventually decreased the gross relative abundance of filamentous bacteria by 2.37%. Overall, appropriate AHLs could enhance community stability and microbial cooperation by strengthening the communication hub role of QS species, thereby suppressing the overgrowth of filamentous bacteria and improving the sludge settleability. This study provides an effective strategy to determine the appropriate AHL to rapidly eliminate filamentous bulking problems.

Recent advances in understanding the ecology of the filamentous bacteria responsible for activated sludge bulking.

Activated sludge bulking caused by filamentous bacteria is still a problem in wastewater treatment plants around the world. Bulking is a microbiological problem, and so its solution on species-specific basis is likely to be reached only after their ecology, physiology and metabolism is better understood. Culture-independent molecular methods have provided much useful information about this group of organisms, and in this review, the methods employed and the information they provide are critically assessed. Their application to understanding bulking caused by the most frequently seen filament in Japan, 'Ca. Kouleothrix', is used here as an example of how these techniques might be used to develop control strategies. Whole genome sequences are now available for some of filamentous bacteria responsible for bulking, and so it is possible to understand why these filaments might thrive in activated sludge plants, and provide clues as to how eventually they might be controlled specifically.

AHLs-mediated quorum sensing threshold and its response towards initial adhesion of wastewater biofilms.

Quorum sensing (QS) plays a crucial role during initial biofilm formation, however the QS threshold and the response of biofilm formation towards N-acyl-homoserine lactones (AHLs) remains largely unknown due to the limitation of nondestructive online methods for monitoring bacterial adherence and the complexity of QS system, which limits the application of QS signal reagents in biofilm reactors. In this study, bacterial QS threshold and its response of biofilm formation to AHLs in purely cultured Sphingomonas rubra biofilm as well as in three different wastewater biofilms #1-3 were investigated via real time cell analysis (RTCA). The main perspective was to study the biomass adherence in response to 12 different forms of AHLs at different concentrations. Results showed that bacterial adhesion was significantly improved by exogenous AHLs with the maximum increase of 2.26-, 2.36-, 2.52-, and 2.80- times biomass production in the four respective biofilms. Although the preferred form of AHL differed for various biofilms, the long-chain AHLs (12-14 carbons) resulted in an overall improvement of bacterial adhesion due to their stronger hydrophobicity and hydrolysis resistance. In addition, bacterial QS threshold of AHLs was observed to have a wide range of concentration from 10 ng/L to 10 µg/L. Meanwhile, QS response time to AHLs also showed a significant difference in different biofilms. Biofilm #2 inoculated with bulking sludge had lower QS threshold of 10 ng/L and faster response to most AHLs that is less than 6 h. Thus, considering the improvement of biofilm adhesion by AHLs, 10 ng/L of C12-HSL, 10 ng/L of C12-HSL, and 10 ng/L of C6-HSL were preferentially selected for wastewater biofilms #1-3 respectively. Unexpectedly, adding high-concentration of AHLs detected in sludges did not significantly improved the bacterial adhesion. Infact the addition of these AHLs at low concentrations or even undetected concentrations substantially improved bacterial adhesion, which could be explained by bacterial communities composition. According to the Pearson correlation analysis, 62% of the top 50 most abundant genera in bacterial communities were significantly negatively related to the response time of multiple AHLs, representing their fast QS response. The QS bacteria, Dechloromonas and Nitrospira have fast QS response for C4-HSL and C8-HSL while, Comamonadaceae has fast QS response for 3OC8-HSL, 3OC10-HSL, 3OC12-HSL, and 3OC14-HSL. In contrast, the rest 38% of the top most abundant genera, such as Ferruginibacter, Hyphomicrobium, and Terrimonas quickly responded to only one AHL, showing significant negative relationship with the response time of C6-HSL. Overall, this study provides an effective and convenient means to select appropriate AHL reagents to promote bacterial adhesion in biofilm systems. Moreover, it also suggests that exogenous AHLs may be useful in improving the settling property of bulking sludge.

[Microbial Community Structure for Sewage Wastewater Treatment Plants in Winter].

Constructing an effective control strategy for the daily operation of sewage treatment plants daily operation is an important criterion for the removal performances of nutrient stable in winter. To investigate microbial community structure, functional groups, and relationships between population dynamics and effluent variation, activated sludge obtained from 4 plants, which were running stably in a low temperature period (8-15℃) in northern China, were sampled. The high-throughput sequencing results indicated that the microbial community had good richness in the low temperature period during which the abundance of Actinobacteria increased. Nitrosomonas, a key functional ammonia oxidation bacterium, was greatly affected by the decreasing temperature, while Denitrifies, a highly diverse core group with wide distribution, maintained stable abundance indicating less influence of decreasing temperature. The denitrification efficiency was only associated with the mixed liquor reflux ratio. Tetrasphaera was widely present in four processes and played an important role for the removal of biological phosphorus. Sludge bulking phenomena caused by filamentous bacteria overgrowth occurred frequently in winter; however the quality of effluents was slightly influenced.

Enhancement of nitrification efficiency during sludge bulking by magnetic field under long sludge retention time.

The aim of the present study is to investigate the potential of magnetic field application as an alternative approach for controlling sludge bulking due to long sludge retention time (SRT) while enhancing nitrification efficiency upon the occurrence. Two sequencing batch reactors, reactor A (SBRA, magnetic field intensity 88.0 mT) and reactor B (SBRB, control) were operated under long SRT to induce the growth of filamentous microorganisms. The effect of magnetic field on nitrification, viz. ammonia-nitrogen (NH4-N) and nitrite removal, as well as biomass properties were studied under the sludge bulking condition. Results indicated that nitrification efficiency of SBRA was consistently higher with 90% NH4-N removal and 74-81% nitrite removal, which could be credited to the enhanced biomass properties of activated sludge due to the induced magnetic field. Metabolism activity and biodegradability of aerobic bacteria were also enhanced through the application of magnetic field, even under long SRT condition. This was evidenced by the average oxygen uptake rate (OUR) in SBRA that was higher with 11.7 ± 1.2 mg/L·h compared to SBRB with 9.5 ± 0.4 mg/L·h. Occurrence of filamentous sludge bulking was likewise minimized.