Microbial communities of aerobic granules: granulation mechanisms

Long-term responses of antibiotic resistance genes under high concentration of enrofloxacin, sulfadiazine and triclosan in aerobic granular sludge system

It is worth to reveal the long-term responses of antibiotic resistance genes (ARGs) in aerobic granular sludge (AGS) system exposed to high level enrofloxacin (ENR), sulfadiazine (SDZ) and triclosan (TCS). In present study, ppm level ENR, SDZ and TCS were added into three AGS reactors, respectively. ARGs in ENR and SDZ systems showed trends of increasing first and then decreasing, which were contrary to that in TCS system. 80%, 56% and 40% ARGs in ENR, SDZ and TCS systems, respectively, were enriched after loading, but several ARGs still kept high enrichment values after the withdrawn of loadings. The dominant bacteria in ENR (Flavobacterium), SDZ (Candidatus_Competibacter and Defluviicoccus) and TCS (Defluviicoccus) systems might contribute to the reductions of ARGs. IntI1 altered the overall ARGs profiles through horizontal gene transfer. The interactions of bacterial communities and environmental factors might be responsible for the different ARGs patterns in ENR, SDZ and TCS systems.

Damage of heavy metals to Vallisneria natans (V. natans) and characterization of microbial community in biofilm

Heavy metals can cause a significant damage to submerged macrophytes and affect its periphyton biofilms in aquatic environments. This study investigated the effects of heavy metals such as copper (Cu), lead (Pb), cadmium (Cd) and their mixture on physiological and biochemical responses and ultrastructure characteristics of Vallisneria natans (V. natans). Furthermore, differences in structures of microbial communities were observed in biofilms. The results showed that Cu²⁺, Pb²⁺, Cd²⁺ and their mixture could destroy cell structure and photosynthetic system, and directly caused oxidative damage to submerged macrophyte and induced antioxidant enzyme system. In general, biomass and total chlorophyll content of V. natans noticeably decreased, while the activities of superoxide dismutase, peroxidase and catalase were enhanced by heavy metal stress inducement in restricted range, and the malondialdehyde content increased with the aggravation of the damage. The single heavy metal stress played a negative impact, however, the combined stress was not always synergistic effects on plants. High-throughput sequencing analysis suggested that heavy metals changed the abundance and structure of the microbial biofilm community. Proteobacteria and Bacteroidete were the dominant bacteria under heavy metal stress and other species and abundance of bacteria such as Firmicute, Cyanobacteria, Chloroflexi, Actinobacteria, Verrucomicrobia, Acidobacteria, Deinococcus-Thermus, Chlamydiae were also present. These findings provided useful information for further understanding about submerged macrophytes and periphyton biofilms responsed to heavy metal stress in aquatic environments in the future.

Rapid aerobic sludge granulation in an integrated oxidation ditch with two-zone clarifiers

Aerobic granular sludge (AGS) was rapidly cultivated in an integrated oxidation ditch with two-zone clarifiers by using a novel external sludge treatment and return mode to treat low concentrations of actual domestic sewage. The selective pressure created by the two-zone clarifiers can retain the well-settling granules and discharge light flocs with poor settleability. The granules stayed in the reactor, which induced bacterial attachment to the granules that acted as nuclei, while the discharged flocs can stimulate microorganisms to secrete large amounts of extracellular polymeric substances (EPS) under the external conditioning of CaCl₂ and natural air drying. Then, this surplus sludge was returned to the reactor to create more small granules that combined with each other through the action of hydraulic shear forces to achieve rapid granulation. The results showed that AGS was formed successfully in the reactor on day 18, and after 51 days of continuous operation, the biomass concentration and settling ability were further improved (the mixed liquor suspended solids (MLSS) and sludge volume index at 5 min (SVI₅) were stable at approximately 3500 mg/L and 40.0 mL/g, respectively). During the whole experimental period, the biological sludge activity was greatly improved, and the EPS and microbial community changed significantly, including an enrichment of microbes with EPS secretion and granule stabilization functions. The study results reveal that the pollutant removal efficiency improved after granulation. Furthermore, this approach required less energy and is eco-friendly for potential full-scale implementation.

Combined toxic effects of anatoxin-a and microcystin-LR on submerged macrophytes and biofilms

Hazardous substances, such as anatoxin-a and microcystin-LR, are released into the aquatic environment during cyanobacterial blooms, causing significant ecological risk. To assess the toxic effects of anatoxin-a, microcystin-LR and their combined exposure on submerged macrophytes and biofilms, Vallisneria natans was exposed to solutions containing different concentrations of anatoxin-a and microcystin-LR (0.05-5.00 μg L^-1). Results showed that Vallisneria natans was sensitive to anatoxin-a of 0.05 μg L^-1, and antagonistic effects were induced at combined microcystin-LR and anatoxin-a exposure. Single and combined exposure effectively induced antioxidant responses such as promoted activities of superoxide dismutase, peroxidase and catalase, as well as increased glutathione S-transferase, glutathione and malondialdehyde content. In addition, anatoxin-a and microcystin-LR could also be absorbed by Vallisneria natans and trigger plant defense responses, generating increased concentrations of the phytohormones abscisic acid and strigolactones. Moreover, the abundances and structure of the microbial community in periphyton biofilms were altered by combined anatoxin-a and microcystin-LR exposure. The enhanced concentration of N-acylated-l-homoserine lactone indicated that the assessed cyanotoxins had a significant influence on quorum-sensing in biofilm microbial communities. These results demonstrated that anatoxin-a and microcystin-LR at environmentally relevant concentrations could disrupt homeostasis, induce effective defense mechanisms of Vallisneria natans and alter biofilms in aquatic ecosystems.

Response of the submerged macrophytes Vallisneria natans to snails at different densities

The study investigated the responses of the submerged macrophyte Vallisneria natans (V. natans) to snails (Bellamya aeruginosa) at different densities, with changes in physiological parameters, morphology, leaf-epiphytic bacteria community and water quality parameters examined. The changes of water quality parameters (pH, total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC)) indicated that snails secreted nutrients into water. Changes in morphological and physiological parameters (fresh weight, root length, shoot height, chlorophyll, malondialdehyde (MDA), activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD)) demonstrated that the presence of snails were beneficial to the growth of submerged macrophytes. Microbial diversity analyses indicated that snails could decrease microbial community richness and diversity. At medium densities (340 ind. m^-2), an increase in snail density was beneficial to the growth of submerged macrophytes. The results of this study provide theoretical guidance and technical support for the maintenance and restoration of submerged macrophytes.

A comparative study on membrane fouling alleviation mechanisms by using nanoscale Fe3O4 and poly dimethyldiallylammonium chloride

Membrane bioreactor (MBR) has become a promising technology for wastewater treatment. However, membrane fouling frequently occurred which greatly increased operational expense. Two different membrane fouling alleviation mechanisms were explored in this study. Addition of poly dimethyldiallylammonium chloride (PDMDAAC) facilitated formation of flocs-flocs aggregates, which were more adaptable to the changing environment, resulting in less soluble microbial products (SMP) secretion. However, PDMDAAC lose activity gradually, and had a less sustainable effect on membrane fouling alleviation. Nanoscale Fe₃O₄ was applied to alleviate membrane fouling, and membrane sustainable filtration cycle extended 2-fold compared to the control group. Results showed that dehydrogenase activity in the reactor with optimal addition of nanoscale Fe₃O₄ increased 2.86 ± 0.11 times compared to control group. SMP (especially tryptophan protein-like substances) decreased to 9.79 ± 1.34 mg L^-1 with the addition of nanoscale Fe₃O₄, which was lower than that in the control group (15.31 ± 0.53 mg L^-1). It's speculated that nanoscale Fe₃O₄ performed as conductive material, which intensified interspecies electron transfer. The sludge dehydrogenase activity was then enhanced, which facilitated the utilization and microbial degradation of SMP, suppressing membrane fouling consequently.

Development of a dynamic feeding strategy for continuous-flow aerobic granulation and nitrogen removal in a modified airlift loop reactor for municipal wastewater treatment

This study investigated the aerobic sludge granulation and nitrogen removal performance in a modified airlift loop reactor treating municipal wastewater under different operation conditions. Dynamic feeding and aeration control were applied to create feast/famine conditions to facilitate microbial aggregation. Experimental results demonstrated that aerobic granular sludge could be cultivated in continuous-flow reactors fed with an optimized dynamic feeding condition. Fresh granules sizing 0.4-0.6 mm were observed in the reactors after a 61-day operation, then turned to matured granules after another 33-day operation with a compact structure, a stable size of 2-4 mm, and a low SVI of ~35 mL/g. Extracellular polymeric substances (EPS) analysis results showed that both EPS contents and the ratio of protein to polysaccharides increased with the granulation process, leading to an increase of cell hydrophobicity. Granular sludge exhibited a good nitrogen removal ability with a comparable level of specific nitrification rate and denitrification rate with those measured in state-of-the-art sequential batch reactors. Microbial population analysis showed an increase in the relative abundance of functional microbes, including Zoogloea, Nitrospira, Dechloromonas, and Thauera in the cultivated granules, suggesting a potentially crucial role of these microbes in sludge granulation and nitrogen removal. The dynamic feeding strategy and the reactor configuration are considered as critical factors for aerobic granulation under continuous-flow conditions for creating feast/famine conditions and allow sludge backflow without structure damage.

Promising carbon utilization for nitrogen recovery in low strength wastewater treatment: Ammonia nitrogen assimilation, protein production and microbial community structure

Acetic acid and sodium acetate are generally supplied to wastewater treatment plants (WWTPs) in China to improve total nitrogen (TN) and total phosphorus (TP) removal, and the addition of carbon source also facilitates to increase sludge growth rate and further provides material basis for the extraction of proteins and amino acids from activated sludge. To recycle ammonia nitrogen resources, a system that combined adsorption and anaerobic-anoxic-oxic (A/AAO) process for treating low strength wastewater was established. Experimental results showed that by the addition of carbon substrate from a mixture of anaerobically fermented adsorption sludge, the average removal efficiency of chemical oxygen demand (COD), ammonia nitrogen, TN, and TP were 88%, 96.9%, 93.9%, and 92.1%, respectively, and the ratio of nitrogen assimilation to nitrogen dissimilation significantly increased by a factor of 2.5. Through energy analysis (based on adenosine triphosphate, ATP), sludge flocculation capacity and settling property, it was found that the AAO process sludge presented the logarithmic growth characteristics. The respective sludge protein and amino acids contents increased by over 11.4% and 40.3%, and the synthetic products of glutamic acid, alanine and aspartate increased through the assimilation of ammonia nitrogen, thereby indicating that replenishing the carbon substrate could markedly enhance protein and amino acids contents in AAO process sludge. Moreover, the diversity of the microbial community in adsorption process was relatively rich, the diversity in the adsorption process sludge was the highest, while the diversity of the AAO process sludge evidently decreased. The microbial community in each process was similarly based on 16S rDNA gene sequence analysis, microflora was prominent in the AAO process, with Dechloromonas, Flavobacterium, Zoogloea, Unclassified_Rhodocyclaceae and Thauera as the dominant species. Promising carbon utilization facilitates contaminants removal in low strength wastewater treatment and is conducive to protein production through ammonia nitrogen assimilation.

Improving aerobic sludge granulation in sequential batch reactor by natural drying: Effluent sludge recovery and feeding back into reactor

One of the main problems in treating high volumes of wastewater is the long startup time required aerobic granular sludge (AGS), and this issue significantly limits the broad application of advanced AGS technology. To promote rapid AGS formation in the startup phase, a method was developed involving the recovery and natural drying of effluent sludge prior to feeding it back into the sequencing batch reactor (SBR). An analysis of the process shows that supplemented naturally dried sludge swiftly promoted sludge aggregation and granular sludge formation in the reactor, and feeding the SBR with naturally dried sludge aggregates (1.75 ± 0.05 g/L seven times) significantly shortened the granulation time in the startup phase by 14 days. In addition, MLSS, SVI₃₀, SVI₃₀/SVI₅, and the average granule size of AGS in the reactor were maintained at 4.66 g/L, 47.4 mL/g, 0.93, and 2.8 mm, respectively. When fed back into the bioreactor, the aggregates acted as nuclei/carriers in the rapid granulation and played a significant role in rendering the SBR operation stable. This approach could be used to eliminate the random granules aggregation-disintegration mechanism that occurs in the initial stage of AGS formation. The study results reveal that the removal rate of COD and NH₄⁺-N were above 95% and 96%, respectively. Furthermore, this approach requires less energy and significantly reduces the amount of sludge produced (as the effluent sludge is reused).

Bacterial enrichment in highly-selective acetate-fed bioreactors and its application in rapid biofilm formation

In this study, we systematically investigated the bacterial community dynamics in highly-selective (strong hydraulic selection pressure and high organic loading rate) bioreactors with acetate as the sole carbon source. 16S rRNA gene high-throughput sequencing and metagenomic sequencing results showed that phenolics-degrading bacteria (PDB), which were mainly Acinetobacter species, in the newly-formed aerobic granules could account for >70% of the total bacteria. Near full-length 16S rRNA gene sequences obtained by cloning suggest that the PDB are potentially novel species because they are distantly related to known Acinetobacter species. However, these PDB only temporarily appeared in the early stage of the granule formation and their abundance quickly decreased along the reactor operation. To retain these PDB, we demonstrated that the newly-formed aerobic granules could accelerate biofilm formation in moving bed biofilm reactors (MBBRs), and the biofilm carriers showed gradually-increased phenol degradation performance in the MBBRs. While, the bacterial community in biofilm significantly changed during the operation process of the MBBRs and the community structure became more complicated than that in the aerobic granules. Collectively, this study provides new insights into the microbial ecology of sludge granulation and biofilm formation process in the wastewater treatment systems for remediating phenolic matters.

Formation of partial-denitrification (PD) granular sludge from low-strength nitrate wastewater: The influence of loading rates

Granular sludge has been believed to be a promising technology in wastewater biological treatment. However, the formation of granules at low substrate concentration is a difficult task that has seldom been achieved. This study aimed at forming the granules in the recently developed partial-denitrification (PD, NO₃^--N→NO₂^--N) for nitrite production. Two sequencing batch reactors (SBRs) were operated at a low nitrate of 30 mg N/L with nitrate loading rate (NLR) of 0.12 (R1) and 0.24 kg N/m³/d (R2). Results showed that the granulation of PD sludge experienced a developing and matured process with the progressive increase in size followed by maintaining a stable value. Higher NLR resulted in a more rapid granulation with the larger and looser structure. While the granules under lower NLR appeared to be denser and more compact with better settling ability. Microbial communities of two SBRs were revealed to show little difference, with the PD functional bacteria of Thauera (50.7% in R1 and 55.4% in R2) dominated during the granulation process. The Flavobacterium, likely to be closely related with sludge granulation, accounted for a higher proportion in R2 (10.16%) than R1 (5.91%), which might result in a larger granule formed in R2. This study clearly confirmed the feasibility of granulation of PD sludge under low nitrogen loads, shedding new light on the low-strength nitrate wastewater treatment with an efficient and economical way.

In-situ monitoring AHL-mediated quorum-sensing regulation of the initial phase of wastewater biofilm formation

Initial attachment plays an important role in biofilm formation in wastewater treatment processes. However, the initial attachment process mediated by N-acyl-homoserine lactones (AHLs) is difficult to be fully understood due to the lack of non-invasive and on-line investigation techniques. In this study, the AHL-regulated wastewater biofilm attachment was quantified using ultrasonic time-domain reflectometry (UTDR) as an in-situ and non-invasive monitoring technique. Results demonstrated that the reversible adhesion time in municipal and industrial wastewaters was significantly decreased in the presence of exogenous AHLs. Biofilm thickness in municipal and industrial wastewaters increased significantly with the addition of exogenous AHLs. Also, the addition of acylase delayed the initial biofilm formation (lengthened reversible adhesion time and decreased biofilm thickness and density). Compared with biofilm behavior in the presence of low concentrations of AHLs (4.92 ± 0.17 μg/L), both reversible adhesion time and biofilm thickness were not significantly increased (p > 0.05) with an increase in AHL concentration (9.75 ± 0.41 μg/L). Furthermore, the addition of exogenous AHLs resulted in significant changes in the attached bacterial community structures, in which both QS and quorum-quenching (QQ) bacteria were stimulated. The current work presents an effective approach to in-situ monitoring of the regulation of AHL-mediated QS in the initial attachment of biofilms, especially in the reversible adhesion process, which may provide a potential strategy to facilitate biofilm establishment in wastewater treatment processes.

Response of submerged macrophytes and periphyton biofilm to water flow in eutrophic environment: Plant structural, physicochemical and microbial properties

The integrated effects of water flow on submerged macrophytes (Vallisneria natans) and leaf biofilms were comprehensively investigated in eutrophic microcosm. Changes in aquatic environmental factors were analyzed and water flow was found to elevate eutrophic water quality, especially in terms of TP removal. The removal efficiency of TP reached 78.95% in flowing water, which was more than 10-fold higher than in static water. Water flow altered the morphological and physiological characteristics of plants, decreasing the cell wall thickness and rate of photosynthesis, while promoting the accumulation of soluble sugar and protein in leaves. The starch content also increased with water flow, and significantly larger starch granules were observed in chloroplast. Furthermore, oxidative damage was evidenced by the consistently higher content of malondialdehyde in flowing water. Superoxide dismutase (SOD), peroxidase (POD) and Catalase (CAT) were induced in plants exposed to water flow, as an antioxidant stress response. The results of 16S rRNA high-throughput sequencing analysis showed that the structure of the biofilm microbial community changed in response to water flow. These results expand our understanding of the effects of water flow on submerged macrophytes and periphyton biofilms in eutrophic environments.

Response of submerged macrophytes and leaf biofilms to the decline phase of Microcystis aeruginosa: Antioxidant response, ultrastructure, microbial properties, and potential mechanism

Decaying cyanobacterial blooms carry a potential risk for submerged macrophyte and periphyton biofilms in aquatic environments. This study comprehensively studied the responses in growth, oxidative response, detoxification pathway, and ultrastructure characteristics of aquatic plants to Microcystis aeruginosa (M. aeruginosa) exudates and extracts released during the decline phase. Particular emphasis was placed on the variation of extracellular polymeric substances (EPS) and quorum-sensing signaling molecules. The results showed that superoxide dismutase, peroxidase, and glutathione S-transferase were significantly induced as antioxidant response, and the malondialdehyde content increased. Increased content of MC-LR (1.129 μg L^-1) and NH₄⁺-N (1.35 mg L^-1) were found in the decline phase of M. aeruginosa, which played a vital role in the damage to submerged plants. In addition, a change in the amount of osmiophilic granules and a variation of organelles and membranes was observed. A broad distribution of α-d-glucopyranose polysaccharides was dominant and aggregated into clusters in biofilm EPS in response to exposure to decaying M. aeruginosa. Furthermore, exposure to exudates and extracts changed the abundance and structure of the microbial biofilm community. Increased contents of N-acylated-L-homoserine lactone signal molecule might result in a variation of biofilm EPS production in response to decaying M. aeruginosa. These results expand the understanding of how submerged macrophyte and periphyton biofilms respond to environmental stress caused by exudates and extracts of decaying M. aeruginosa.

Understanding the granulation of partial denitrification sludge for nitrite production

Partial-denitrification (PD) has previously been demonstrated to be another pathway for nitrite production, which provides a cost-effective approach for nitrate (NO₃^--N) removal through combing with anammox. In this study, the formation of PD granules was firstly investigated in a sequencing batch reactor (SBR) with influent nitrate of 60 mg N/L. The granulation process was explored via the physicochemical and biological characterization. Sludge granulation initiated within the first 20 days with an average size of 93.7 μm in diameter, it experienced a developing, shaping and matured periods, with a maximum size of 709.3 μm obtained. High nitrite production of PD was always maintained during the granulation with a mean nitrate-to-nitrite transformation ratio (NTR) of 88.3%, and in-situ maximum NO3-N reduction rate of 84.9 mg N/h/g VSS was obtained. Mature PD granules hold an excellent settling property with 5-min sludge volume index (SVI₅) of 32.0 mL/g MLSS obtained and smooth surface with large amounts of rod bacteria covered. CaCO₃ precipitates formed in the PD process played a vital role in the initial granulation, acting as the nucleus for cell attachment. Extracellular polymeric substances (EPS), mainly the proteins (PN) content, was found to be of supreme importance in granules developing and maintaining its structural stability. Besides, the abundance of Flavobacterium and norank_p__Gracilibacteria were revealed to be in accordance with the change of granules size, seemed to contribute to sludge granulation. The developed granule-based PD integrated with anammox process provides an engineering-feasible and economic-favorable solution for industrial nitrate wastewater treatment.

Microstructure, bacterial community and metabolic prediction of multi-species biofilms following exposure to di-(2-ethylhexyl) phthalate (DEHP)

The occurrence and transportation of phthalate esters in biofilms from natural and engineered sources have attracted considerable research interest. However, little information is available highlighting the responses of multi-species biofilms in terms of their physicochemical structure and bacterial community induced by phthalate esters. Di-(2-ethylhexyl) phthalate (DEHP), a model phthalate eater, was selected to treat multi-species biofilm aggregates, including an attached biofilm from a moving bed bioreactor (MBBR), a periphytic biofilm from a natural source and activated sludge in short-term exposure experiments (120 h). The production of extracellular polymeric substances (EPS) from the three biofilms initially decreased and then slightly increased after exposure to DEHP, consistent with the variation of the most dominant fluorescent compounds consisting of humic-acid-like organic substances. The MBBR and periphytic biofilms secreted more fluorescence compounds than the activated sludge during the exposure period. The organic matter in the EPS was converted into smaller molecules, while limited variation was observed in the functional groups and secondary protein structures. Acinetobacter and Bacillus demonstrated significant increases and were likely the key genera responsible for DEHP degradation. The combined use of spectral, chromatographic and sequencing analyses indicated that the periphytic biofilm was more resistant to DEHP, possibly owing to the presence of more mature assemblages, including cells with higher metabolic activity and a higher diversity within the bacterial community. This study provides insights into the microstructural and bacterial responses of multi-species biofilms following exposure to phthalate esters, and provides important guidance for bioremediation of phthalate esters using periphytic biofilms.

Impact of hydraulic retention time and organic matter concentration on side-stream aerobic granular membrane bioreactor

This study investigated the effect of hydraulic retention time (HRT) and chemical oxygen demand (COD) concentration on membrane fouling in aerobic granular membrane bioreactor (AGMBR) in a systematic approach. Changes in HRT (7, 10, and 15 h) and COD (500, 1000 and 1500 mg/L) were applied in five operational phases, to determine the most significant parameters to control membrane fouling for enhanced AGMBR performance. Membrane permeability loss was dramatically intensified with increase in HRT from 7.5 to 15 h and COD from 500 to 1000 mg/L. The highest polysaccharide content of loosely bound EPS (0.41 mg PS/mg VSS) and soluble microbial products (SMPs) (27 mg PS/L) occurred alongside poor AGMBR performance. Variations in membrane fouling were accompanied with considerable changes in Flavobacterium, Thauera and Paracoccus populations. Analysis of variance (ANOVA) demonstrated that HRT and interaction between HRT and COD were the most significant parameters in controlling membrane fouling.

Stress-responses of activated sludge and anaerobic sulfate-reducing bacteria sludge under long-term ciprofloxacin exposure

The activated sludge (AS) and sulfate-reducing bacteria (SRB) sludge systems were continuously operated for 200 days in laboratory to investigate the stress-responses of these two sludge systems under ciprofloxacin (CIP) exposure. It was found that CIP was effectively removed by SRB sludge via adsorption and biodegradation, but little biodegradation in AS system. The CIP biodegradation by SRB sludge made the SRB sludge system more sustainable and tolerant to long-term CIP exposure than AS system with significant (p < 0.05) CIP desorption and decrease of CIP removal. CIP shaped the microbial communities in AS and SRB sludge, and significantly (p < 0.05) inhibited the family Nitrosomonadaceae (ammonia-oxidizing bacteria (AOB)) and genus Nitrospira (nitrite-oxidizing bacteria (NOB)/complete ammonia oxidizer(comammox)) and the nitrogen removal in AS system. Moreover, CIP posed the increase of genus Zoogloea-like organisms and the non-filamentous bulking of AS, e.g. 313 ± 12 mL/g of sludge volume index (SVI) at phase V (influent CIP = 5000 μg/L). The genus Desulfobacter was enriched in SRB sludge system under long-term CIP exposure, and stimulated chemical oxygen demand (COD) removal and sulfate reduction. The increase of genera Zoogloea, Acinetobacter and Flavobacterium in AS, and Zoogloea and Acinetobacter in SRB sludge systems under CIP exposure promoted extracellular polymeric substances (EPS) production and CIP adsorption for self-protection of microbes against CIP toxicity. The functional groups of N-H, O-H, C-O-C and C=O in EPS of AS and SRB sludge provided adsorption sites for CIP and impeded CIP impact on microbial cells. The findings of this study provide an insight into the stress-responses of AS and SRB sludge under long-term CIP exposure, and exhibit the great potential of treating CIP-laden wastewater by SRB sludge system.

Coaggregation of bacterial communities in aerobic granulation and its application on the biodegradation of sulfolane

Aerobic granulation is regarded as the future technology for wastewater treatment that can replace conventional activated sludge. In this study, two approaches of forming sulfolane degrading aerobic granules (SDAG) were successfully developed and evaluated. These include adaptation of pre-grown granules to sulfolane environment and coaggregation of pre-grown granules with bacterial culture native to sulfolane contaminated site. The adaption method required a longer period to form robust SDAG compared to coaggregation method where degradation of sulfolane was observed within 24 h. Electronic images revealed dominant filamentous bacteria on the surface of granules while DNA analysis unveiled the complexity of the dynamic change of microbial community during aerobic granule formation. The rate of sulfolane degradation by coaggregated granules reduced as the concentration of carbon source increased, nevertheless, the rate increased with increased biomass. In addition, the presence of co-contaminants can slightly impact the ability of newly cultivated granules to degrade sulfolane. Finally, the stability and settleability of the new aerobic granules was investigated under different environmental conditions. About 30% of the aerobic granules were lost after 14 d of operation without any continuous supply of carbon sources. The surviving SDAGs continued to display an intact structure coupled with good settleability.

Enhanced aerobic granulation by inoculating dewatered activated sludge under short settling time in a sequencing batch reactor

The effect of dewatered activated sludge on aerobic granulation was investigated in a sequencing batch reactor (SBR) under short settling time. The results showed that dewatered sludge accelerated aerobic granulation and the granulation was completed within 5 days. On day 5, the aerobic granules were regular, compact, fast-settling and high granular strength and possessed excellent removal performance of carbon and nitrogen. The change trend of extracellular polymeric substances (EPS) was basically consistent with granular strength and granulation rate, indicating that EPS in granules played a vital function for granulation. Microbial community succession was investigated by pyrosequencing. In 5 days, microbial diversity was reduced and certain strains were rapidly enriched in the granules to become dominant species, serving on a crucial role in rapid granulation and pollutant removal as they could secrete excess EPS and possess the excellentability removing carbon and nitrogen pollutants.

Rapid control of activated sludge bulking and simultaneous acceleration of aerobic granulation by adding intact aerobic granular sludge

The feasibility of rapidly controlling activated sludge bulking and accelerating aerobic sludge granulation was evaluated by adding intact aerobic granular sludge (AGS) to the bulking activated sludge (BAS) reactor. Two ratios of AGS to BAS (0.2 in the first reactor (R1), and 0.4 in the second reactor (R2)) were tested. The results indicate that the addition of AGS immediately improved the settling ability of BAS (sludge volume index at 30 min (SVI₃₀) in R1 and R2 decreased from 173.1 mL/g to 130.8 and 91.3 mL/g, respectively) and gradually increased the biomass concentration (mixed liquor suspended solids (MLSS) in R1 and R2 increased to 4722 and 5190 mg/L, respectively), thus resolving the sludge bulking problem. Meanwhile, adding AGS not only promoted the BAS growth in aggregates, but also facilitated the selection of well-settling aggregates at an early stage. Consequently, the granulation process was significantly accelerated. The granulation time in R1 and R2 was 14 and 10 days, respectively, indicating that the higher ratio of AGS to BAS can result in the faster granulation. Partial nitrification could be maintained during the BAS granulation process when the initial inoculation of nitritation sludge was large enough. Additionally, the microbial community changed during the BAS granulation process. The genera Thauera and Zoogloea belonging to family Rhodobacteraceae were speculated to play an important role in the BAS granulation.

Effective removal of nitrate by denitrification re-enforced with a two-stage anoxic/oxic (A/O) process from a digested piggery wastewater with a low C/N ratio

The combined process of a long-term biogas digester and double anoxic/oxic tanks is very commonly used in piggery wastewater treatment in South China, but the effluent does not meet the discharge standard of total nitrogen (TN) and chemical oxygen demand (COD_Cr) due to a low C/N ratio and insufficient organic carbon in digested piggery wastewater. Thus, a typical two-stage anoxic/oxic (A1/O1/A2/O2) process, which is widely used to treat digested piggery wastewater in the engineering application, was selected for study on a laboratory scale. Finally, the average removal efficiency of ammonia nitrogen in the two-stage AO process was 98.7%; at the same time, the content of nitrate increased to 180-190 mg/L. To further eliminate nitrogen, an anaerobic tank (S1), which was equipped the sludge that was acclimated in our laboratory by a high nitrogen loading slurry, was employed to treat the effluent from the two-stage AO process and contributed more than 70% removal efficiency. Further analysis showed that ammonia-oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) in the O1 and O2 tanks together contributed to the conversion of ammonia nitrogen to nitrate, but the process of heterotrophic denitrification was inhibited in the A1 and A2 tanks because of insufficient carbon sources. In addition, most of the nitrate concentration was reduced under conditions with insufficient carbon sources, while Thauera-dominated the bacterial population in the sludge sample of the S1 tank.

Toxicity of Three Crystalline TiO2 Nanoparticles in Activated Sludge: Bacterial Cell Death Modes Differentially Weaken Sludge Dewaterability

The eco-toxicities of different crystalline phases of TiO₂-NPs are controversial, and the effects and mechanisms on activated sludge are unclear. Therefore, we assessed the acute-toxicities (8-h exposure) of P25, anatase, and rutile TiO₂-NPs in activated sludge using flow cytometry under simulated sunlight (hereafter-sun) and evaluated the relationship between sludge dewatering and bacterial cell death modes using Pearson's correlation coefficients ( r). Additionally, the response of the microbial community structure was examined by high throughput sequencing. Bacterial survival and death were observed by confocal laser scanning microscopy. Toxicity indicators (e.g., lactate dehydrogenase (LDH) and reactive oxygen species (ROS)) were determined. Overall, TiO₂-NPs toxicity was concentration-dependent and crystalline-phase-dependent. The responses of bacterial communities to crystalline phases were more obvious than that of dosage. P25-sun and anatase-sun caused necrosis-like cell death via strong photo-oxidation confirmed by 131%/123% (1 mg/L) and 301%/254% (50 mg/L) LDH released by the control, while rutile-sun induced apoptosis-like death via intracellular ROS production increased to 165% (1 mg/L) and 420% (50 mg/L) of the control. P25 and anatase NPs had higher protein and polysaccharide affinities, while rutile NPs exhibited stronger attachment onto phospholipids. TiO₂-NPs-sun reduced activated sludge dewaterability. Specific resistance to filtration (SRF) showed the strongest positive correlation with tightly bound extracellular polymeric substances (EPS) and total soluble microbial byproducts ( r = 0.974, p < 0.01) and was closely related to EPS content and composition, especially the increased bound water (BW) content and sludge protein concentrations. High Pearson correlation coefficients were observed between early apoptotic cells and BW content ( r = 0.952, p < 0.01) resulting from massive polysaccharides and between necrotic (including late apoptotic) cells and SRF ( r = 0.959, p < 0.01) resulting from high protein and EPS concentrations. Thus, in response to TiO₂-NPs, bacterial cell death modes differentially weakened sludge dewatering.

Long-term dynamics of the bacterial community in a Swedish full-scale wastewater treatment plant

The operational efficiency of activated sludge wastewater treatment plants depends to a large extent on the microbial community structure of the activated sludge. The aims of this paper are to describe the composition of the bacterial community in a Swedish full-scale activated sludge wastewater treatment plant, to describe the dynamics of the community and to elucidate possible causes for bacterial community composition changes. The bacterial community composition in the activated sludge was described using 16S rRNA gene libraries and monitored for 15 months by a terminal restriction fragment (T-RF) length polymorphism (T-RFLP) analysis of the 16S rRNA gene. Despite variable environmental conditions, a large fraction of the observed T-RFs were present at all times, making up at least 50% in all samples, possibly representing a relatively stable core fraction of the bacterial community. However, the proportions of the different T-RFs in this fraction as well as the T-RFs in the more variable fraction showed a significant variation over time and temperature. The difference in community composition between summer and winter coincided with observed differences in floc structure. These observations suggest a relationship between floc properties and bacterial community composition, although additional experiments are required to determine causality.

Treatment of the liquid phase of digestate from a biogas plant for water reuse

Biogas plants struggle with managing nitrogen-rich digestate from manure co-digestion. In this study, the biologically treated liquid phase of digestate from an aerobic granular sludge batch reactor (GSBR) containing oxidized nitrogen forms (NO_x), phosphorus, COD and total suspended solids was post-denitrified (P-D), and then ultrafiltered. In P-D, various hydraulic retention times (from 10 to 60 h) and biomass concentrations (from 6 to 14 g MLSS/L) were tested. Then, waste glycerin (GL) was added to the P-D reactor at a COD_GL/NO_x ratio of 1.1, causing a large number of phosphate-accumulating and denitrifying Janibacter sp., and PHB-accumulating and denitrifying Paracoccus sp. and Thauera sp. to be present in granules, which improved nutrient removal. The effluent was ultrafiltered at 0.3 and 0.5 MPa. After biological treatment supported with GL and followed by ultrafiltration, the purified liquid phase of the digestate met FAO standards for water reuse for irrigation.

Reactivation and pilot-scale application of long-term storage denitrification biofilm based on flow cytometry

The work provides a method on the basis of flow cytometry to evaluate the performance of denitrification biofilm during the preservation, reactivation and pilot-scale operation process. The viable cell ratio of denitrification biofilm significantly reduced and further led to the decrease of denitrification capacity after long-term preservation for 5 months. Protein component in tightly bound extracellular polymeric substances (TB-EPS) could serve to enhance microbial adhesion and promote denitrification biofilm formation. With the significant correlation of viable cell ratio and microbial characteristics, 4 °C was more appropriate for preserving denitrification biofilm and conducive to maintain the relatively high denitrification capacity. A maximum denitrification rate of 5.80 gNO₃^--N/m²·d was obtained in pilot-scale anoxic-oxic (AO) process and Dechloromonas became greater prevalence in denitrification suspended carriers. Furthermore, the enrichment of Pseudomonas, Parcubacteria, Acidovorax, Aquabacterium and Unclassified_Flavobacteriaceae enhanced biofilm formation and nutrient conservation. The significantly positive correlation between viable cell ratio and the ratio of nitrate reduction to COD consumption was discovered, and the indices of Chao, ACE, Shannon and Simpson of denitrification biofilm were positively correlated with viable cell ratio, meaning that flow cytometry analysis was reasonable and suitable to evaluate the performances of denitrification biofilm.

Determining the effects of aeration intensity and reactor height to diameter (H/D) ratio on granule stability based on bubble behavior analysis

Aerobic granular sludge was considered as a leading wastewater technology in the next century. However, the loss of granule stability limited the application of this promising biotechnology. Increasing aeration intensity and height to diameter (H/D) ratio were conventional strategies to enhance granule stability. In this study, hydraulic effects of aeration intensity and H/D ratio were explored basing on bubble behavior analysis. However, results revealed that due to viscous resistance, increasing aeration intensity and H/D ratio had limited effects on enhancing hydraulic shear stress, not to mention the extra operation and construction cost. A deflector component was further applied to regulate hydraulic shear stress on large granules under low aeration intensity and H/D ratio. Hydraulic shear stress of large granules was constantly around 3.0 times higher than that in the conventional reactor, resulting in higher percentage of granules within optimal size range (81.95 ± 5.13%). A high abundance of denitrifying bacteria was observed in reactors, which led to high TN removal efficiency of 88.6 ± 3.8%.

Impact of food-to-microorganisms ratio on the stability of aerobic granular sludge treating high-strength organic wastewater

This work investigated the long-term stability of aerobic granular sludge treating high-strength organic wastewater in a semi-pilot scale sequential batch reactor (SBR). The reactor was operated for 316 days under different operational conditions. It was found that the F/M ratio is an important parameter affecting granules formation and stability. Three selection mechanisms were investigated: (1) cultivation and maturation at moderately high influent COD concentration (2500 mg/L) followed by increase in influent COD concentration to 7500 mg/L; (2) stressed cultivation and operation at high influent COD concentration of 4500 mg/L; and (3) alternate feed loading strategy (variable influent COD concentration across the daily schedule of cycles at 50%, 75%, and 100% of the peak concentration of 5000 mg/L). It was found that adopting high OLR at the reactor start-up accelerated the formation of granules. However, the overgrowth of biomass under high organics concentration negatively affected the stability of granules and led to disintegration due to the presence of methanogens in the granule core. Cultivation at high organics concentration resulted in a rapid loss of microbial diversity and reactor failure. Under alternate feed loading, adequate selection of microbial community was maintained and resulted in stable reactor performance. Moreover, a strong correlation between F/M ratio and the granules settling ability was observed. When F/M ratio exceeded 1.5 gCOD/gSS.d, granules showed poor settleability and under very high sludge loading rates (above 2.5), sludge bulking occurred and led to washout of sludge due to the strong selection pressure of short settling time. Operating the reactor at F/M ratio of 0.5-1.4 gCOD/gSS.d appears to favor stable long-term granule stability.

Recovery of dehydrated aerobic granules: A comparison

Dehydrated aerobic granules, if can be sufficiently recovered without significant loss of structural stability and biological activities, presents a promising long-time storage option in practical use. This study dehydrated aerobic granules by six protocols: air drying at 25 or 50 °C, freeze-dry, acetone or ethanol dehydration, and microwave heating, and then recovered them in liquid medium, with the measured characteristics being reported. The granule stability has no correlation with measured settleability, hydrophobicity or extracellular polymeric substances compositions; instead, is correlated with the functional strains presented in the recovered granules. Air dry dehydration minimally damage the functional strains including genus Brevundimonas and genus Comamonas and markedly deteriorated structural breaker such as Acinetobacter of Moraxellaceae to lead to stable and tough recovered granules.

Characteristics and performance of aerobic algae-bacteria granular consortia in a photo-sequencing batch reactor

The characteristics and performance of algae-bacteria granular consortia which cultivated with aerobic granules and targeted algae (Chlorella and Scenedesmus), and the essential difference between granular consortia and aerobic granules were investigated in this experiment. The result indicated that algae-bacteria granular consortia could be successfully developed, and the algae present in the granular consortia were mainly Chlorella and Scenedesmus. Although the change of chlorophyll composition revealed the occurrence of light limitation for algal growth, the granular consortia could maintain stable granular structure, and even showed better settling property than aerobic granules. Total nitrogen and phosphate in the algal-bacterial granular system showed better removal efficiencies (50.2% and 35.7%) than those in the aerobic granular system (32.8% and 25.6%) within one cycle (6 h). The biodiesel yield of aerobic granules could be significantly improved by algal coupled process, yet methyl linolenate and methyl palmitoleate were the dominant composition of biodiesel obtained from granular consortia and aerobic granules, respectively. Meanwhile, the difference of dominant bacterial communities in the both granules was found at the order level and family level, and alpha diversity indexes revealed the granular consortia had a higher microbial diversity.

Formation of aerobic granular sludge and the influence of the pH on sludge characteristics in a SBR fed with brewery/bottling plant wastewater

A laboratory-scale sequencing batch reactor (SBR) was operated for 450 days to assess aerobic granule formation when treating brewery/bottling plant wastewater by consistent application of a feast/famine regime. The experiment was divided into three major periods according to the different operational conditions: (I) no pH control and strong fluctuations in organic loading rate (OLR) (1.18 ± 0.25 kgCOD·(m³·day)^-1), (II) pH control and aeration control strategy to reduce OLR fluctuations (1.45 ± 0.65 kgCOD·(m³·day)^-1) and (III) no pH control and stable OLR (1.42 ± 0.18 kgCOD·(m³·day)^-1). Aerobic granule formation was successful after 80 days and maintained during the subsequent 380 days. The aerobic granular sludge was characterized by SVI₅ and SVI₃₀ values below 60 mL.g^-1 and dominated by granular, dense structures. An oxygen uptake rate based aeration control strategy insured endogenous respiration at the end of the aerobic phase, resulting in stable SBR operation when the influent composition fluctuated. The quantitative polymerase chain reaction results show no significant enrichment of Accumulibacter or Competibacter during the granulation process. The 16S rRNA sequencing results indicate enrichment of other, possibly important species during aerobic granule formation while treating brewery wastewaters.

The mechanisms of granulation of activated sludge in wastewater treatment, its optimization, and impact on effluent quality

Granular activated sludge has gained increasing interest due to its potential in treating wastewater in a compact and efficient way. It is well-established that activated sludge can form granules under certain environmental conditions such as batch-wise operation with feast-famine feeding, high hydrodynamic shear forces, and short settling time which select for dense microbial aggregates. Aerobic granules with stable structure and functionality have been obtained with a range of different wastewaters seeded with different sources of sludge at different operational conditions, but the microbial communities developed differed substantially. In spite of this, granule instability occurs. In this review, the available literature on the mechanisms involved in granulation and how it affects the effluent quality is assessed with special attention given to the microbial interactions involved. To be able to optimize the process further, more knowledge is needed regarding the influence of microbial communities and their metabolism on granule stability and functionality. Studies performed at conditions similar to full-scale such as fluctuation in organic loading rate, hydrodynamic conditions, temperature, incoming particles, and feed water microorganisms need further investigations.

Responses of wastewater biofilms to chronic CeO2 nanoparticles exposure: Structural, physicochemical and microbial properties and potential mechanism

With the accelerated application of CeO₂ nanoparticles (NPs), wastewater treatment plants will increasingly receive CeO₂ NPs, thus inevitably causing CeO₂ NPs to encounter microaggregates. Here, we comprehensively elucidate the responses in the structural, physicochemical and microbial properties of wastewater biofilms to chronic exposure (75 days) to different CeO₂ NPs concentrations, with a particular emphasis on the protective mechanisms of stratified extracellular polymeric substances (EPSs). Chronic exposure to 0.1 mg/L CeO₂ NPs boosted the content and broadened the distribution of α-d-glucopyranose polysaccharides (PS), while the sharply increased production and breadth of β-d-glucopyranose PS, forming a formidable shield, was a response to 10 mg/L CeO₂ NPs. After the bacteria were exposed to CeO₂ NPs, loosely bound EPSs (LB-EPSs) aggregated into macromolecules (increasing in apparent molecular weight (AMW)) but at a lower abundance, whereas the average AMW in tightly bound EPSs (TB-EPSs) decreased. The acetyl content and (α-helix+3-turn helix)/β-sheet value of TB-EPSs increased to resist CeO₂ NPs. Furthermore, long-term exposure to CeO₂ NPs decreased cell viability, reduced microbial diversity and shifted the microbial composition. N-acylated-l-homoserine lactone concentrations increased with increased density of Pseudomonas, which was associated with PS-regulated control, thus promoting PS production in EPSs in response to CeO₂ NPs. These results expand the understanding of how microaggregates resist environmental stress caused by NPs.

Microbial community structure and function in aerobic granular sludge

Aerobic granular sludge (AGS), a self-immobilized microbial consortium containing different functional microorganisms, is receiving growing attention, since it has shown great technological and economical potentials in the field of wastewater treatment. Microbial community is crucial for the formation, stability, and pollutant removal efficiency of aerobic granules. This mini-review systematically summarizes the recent findings of the microbial community structure and function of AGS and discusses the new research progress in the microbial community dynamics during the granulation process and spatial distribution patterns of the microbiota in AGS. The presented information may be helpful for the in-depth theoretical study and practical application of AGS technology in the future.

Shifts in bacterial community composition and abundance of nitrifiers during aerobic granulation in two nitrifying sequencing batch reactors

Shifts in bacterial community composition and abundance of nitrifiers during aerobic granulation, and the effects of wastewater composition on them were investigated using Illumina sequencing and quantitative PCR. The bacterial diversity decreased sharply during the post-granulation period. Although cultivated with different wastewater types, aerobic granular sludge (AGS) formed with similar bacterial structure. The bacterial structure in AGS was completely different from that of seed sludge. The minor genera in seed sludge, e.g., Arcobacter, Aeromonas, Flavobacterium and Acinetobacter, became the dominant genera in AGS. These genera have the potential to secrete excess extracellular polymer substances. Whereas, the dominant genera in seed sludge were found in less amount or even disappeared in AGS. During aerobic granulation, ammonia-oxidizing archaea were gradually washed-out. While, ammonia-oxidizing bacteria, complete ammonia oxidizers and nitrite-oxidizing bacteria were retained. Overall, in this study, the bacterial genera with low relative abundance in seed sludge are important for aerobic granulation.

Microbial community structure in aerobic and fluffy granules formed in a sequencing batch reactor supplied with 4-chlorophenol at different settling times

Toxic compounds, such as 4-chlorophenol (4-CP), which is a common pollutant in wastewater, are removed efficiently from sequencing batch reactors (SBRs) by microorganisms. The bacterial community in aerobic granules formed during the removal of 4-CP in a SBR was monitored for 63days. The SBR reactor was operated with a constant filling and withdrawal time of 7 and 8min and decreasing settling time (30, 5, 3 and 2min) to induce the formation of aerobic granules. During the acclimation period lasting 15days (30min settling time) had a strong effect on the bacterial community. From day 18 onwards, Sphingobium and Comamonadaceae were detected. Rhizobiaceae were dominant from day 24 to day 28 when stable aerobic granules were formed. At day 35, fluffy granules were formed, but the bacterial community structure did not change, despite the changes in the reactor operation to inhibit filamentous bacteria growth. This is the first report on changes in the bacterial community structure of aerobic and fluffy granules during granulation process in a reactor fed with 4-CP and the prediction of its metabolic pathways.

Bacterial community dynamics within an aerobic granular sludge reactor treating wastewater loaded with pharmaceuticals

Pharmaceuticals are micropollutants often present in wastewater treatment systems. In this study, the potential impact of such micropollutants on the bacterial population within aerobic granular sludge (AGS) bioreactor was investigated. The AGS bacterial community structure and composition were accessed combining DGGE fingerprinting and barcoded pyrosequencing analysis. Both revealed the existence of a dynamic bacterial community, independently of the pharmaceuticals presence. The AGS microbiome at both phylum and class levels varied over time and, after stopping pharmaceuticals feeding, the bacterial community did not return to its initial composition. Nevertheless, most of the assigned OTUs were present throughout the different operational phases. This core microbiome, represented by over 72% of the total sequences in each phase, probably played an important role in biological removal processes, avoiding their failure during the disturbance period. Quantitative-PCR revealed that pharmaceuticals load led to gradual changes on the abundance of ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB) and polyphosphate-accumulating organisms (PAO) but their persistence during that phase demonstrated the resilience of such bacterial groups. AGS microbiome changed over time but a core community was maintained, probably ensuring the accomplishment of the main biological removal processes.

Aerobic granular sludge technology: Mechanisms of granulation and biotechnological applications

Aerobic granular sludge (AGS) is a novel microbial community which allows simultaneous removal of carbon, nitrogen, phosphorus and other pollutants in a single sludge system. AGS is distinct from activated sludge in physical, chemical and microbiological properties and offers compact and cost-effective treatment for removing oxidized and reduced contaminants from wastewater. AGS sequencing batch reactors have shown their utility in the treatment of abattoir, live-stock, rubber, landfill leachate, dairy, brewery, textile and other effluents. AGS is extensively researched for wide-spread implementation in sewage treatment plants. However, formation of AGS takes relatively much longer time while treating low-strength wastewaters like sewage. Strategies like increased volumetric flow by means of short cycles and mixing of sewage with industrial wastewaters can promote AGS formation while treating low-strength sewage. This article reviewed the state of research on AGS formation mechanisms, bioremediation capabilities and biotechnological applications of AGS technology in domestic and industrial wastewater treatment.

Performance and microbial characteristics of biomass in a full-scale aerobic granular sludge wastewater treatment plant

By modification of the operational conditions of batch reactors, a municipal wastewater treatment plant was upgraded from activated sludge to aerobic granular sludge (AGS) technology. After upgrading, the volume of the biological reactors was reduced by 30%, but the quality of the effluent substantially improved. The concentration of biomass in the reactors increased twofold; the average biomass yield was 0.6 g MLVSS/g COD, and excess granular sludge was efficiently stabilized in aerobic conditions. Canonical correspondence analysis based on the results of next-generation sequencing showed that the time of adaptation significantly influenced the microbial composition of the granules. In mature granules, the abundance of ammonium-oxidizing bacteria was very low, while the abundance of the nitrite-oxidizing bacteria Nitrospira sp. was 0.5 ± 0.1%. The core genera were Tetrasphaera, Sphingopyxis, Dechloromonas, Flavobacterium, and Ohtaekwangia. Bacteria belonging to these genera produce extracellular polymeric substances, which stabilize granule structure and accumulate phosphorus. The results of this study will be useful for designers of AGS wastewater treatment plants, and molecular data given here provide insight into the ecology of mature aerobic granules from a full-scale facility.

Analysis of aerobic granules under the toxic effect of ampicillin in sequencing batch reactors: Performance and microbial community

To study the change of the aerobic granules' microbial community in the present of antibiotics, ampicillin (AMP) was selected as a model component. With acetate as carbon source, different concentrations of AMP (5, 10 and 15 mg L^-1) were applied to the inflow intermittently and the results showed that the stability of the aerobic granules was maintained below 10 mg L^-1 AMP. Simultaneously, under exposure to 5 and 10 mg L^-1 AMP, the COD removal efficiency in the batch reactors remained at 86% and AMP was degraded almost completely with a removal efficiency of 97%. However, the EPS concentration and dehydrogenase activity decreased constantly with increasing AMP dosage. High-throughput sequencing analysis revealed that Proteobacteria was the most prominent phylum in the whole experiment and contributed to the degradation of AMP. The percentages of Azoarcus and Mycoplana increased at 10 mg L^-1 AMP. In addition, Hydrogenophaga and Enterococcus played a key role in the microbial metabolism.

Transformation of anaerobic granules into aerobic granules and the succession of bacterial community

In this study, we demonstrated that anaerobic granular sludge could be successfully transformed into aerobic granular sludge in a continuous up-flow reactor in 45 days. An aerobic microbial community successfully developed in the granules and high organic matter and nitrogen removal performance was achieved. Under an ammonia nitrogen loading rate of 0.8 kg N/(m³ day), ammonia nitrogen and the total nitrogen removal efficiency of the reactor reached up to 100 and 93%, respectively. An obvious bacterial community shift in granular sludge was observed during the transformation process. By comparing with the bacterial community in aerobic granules cultivated from floccular activated sludge, some bacteria (affiliated with Comamonadaceae, Xanthomonadaceae, Rhodocyclaceae, Moraxellaceae, and Nitrosomonadaceae) playing significant roles in maintaining the structures and functions of aerobic granules were identified. After the transformation, the granules could be clearly separated into the inner core and outer shell. 16S rRNA gene sequencing results indicated many bacterial species present in both the inner core and outer shell; however, their abundance differed significantly. Overall, this study confirms the feasibility of transforming anaerobic granules into aerobic granules and provides novel approaches and insights to understand the microbial ecology in granular sludge.

Simultaneous partial nitrification and 2-fluorophenol biodegradation with aerobic granular biomass: Reactor performance and microbial communities

An aerobic granular bioreactor was operated for over 4months, treating a synthetic wastewater with a high ammonium content (100mgNL^-1). The inoculum was collected from a bioreactor performing simultaneous partial nitrification and aromatic compounds biodegradation. From day-56 onwards, 2-fluorophenol (2-FP) (12.4mgL^-1) was added to the feeding wastewater and the system was bioaugmented with a 2-FP degrading bacteria (Rhodococcus sp. FP1). By the end of operation, complete 2-FP biodegradation and partial nitrification were simultaneously achieved. Aerobic granules remained stable over time. During the 2-FP loading, a shift in the community structure occurred, coinciding with the improvement of 2-FP degradation. DGGE analysis did not allow to infer on the bioaugmented strain presence but pyrosequencing analysis detected Rhodococcus genus by the end of operation. Together with other potential phenolic-degraders within granules, these microorganisms were probably responsible for 2-FP degradation.

Performance and microbial population dynamics during stable operation and reactivation after extended idle conditions in an aerobic granular sequencing batch reactor

The evolution of removal performance and bacterial population dynamics of an aerobic granular sequencing batch reactor were investigated during stable operation and reactivation after prolonged storage. The system was run for a period of 130days including the stable condition phase, storage period and the subsequent reactivation process. Excellent removal performance was obtained during the stable operation period, which was decayed by the extended idle conditions. The removal efficiencies for both carbon and nitrogen decayed while phosphorus removal remained unaffected. Both granules structure and physical properties could be fully restored. Microbial populations shifted sharply and the storage perturbations irreversibly altered the microbial communities at different levels. Extracellular polymeric substances (especially protein) and key groups were identified as contributors for storage and re-startup of the aerobic granular system.

Development of algae-bacteria granular consortia in photo-sequencing batch reactor

The development and properties of algae-bacteria granular consortia, which cultivated with the algae (Chlorella and Scenedesmus) and aerobic granules, was investigated in this experiment. The results indicated that the granular consortia could be successfully developed by selection pressure control, and the algal biomass and extracellular polymeric substances (EPS) concentration in the consortia showed notable correlation with the operating parameters of reactor. The maximum specific removal rates of total nitrogen and phosphate were obtained from the granular consortia with the highest algal biomass, yet the correlation between the fatty acid methyl esters yield and the algal biomass in the consortia was not markedly observed. The seed algae maintained dominance in the phototroph community, whereas the cyanobacteria only occupied a small proportion (5.2-6.5%). Although the bacterial communities with different operational strategies showed significant difference, the dominated bacteria (Comamonadaceae, 18.79-36.25%) in the mature granular consortia were similar.

Microbial Population Dynamics and Ecosystem Functions of Anoxic/Aerobic Granular Sludge in Sequencing Batch Reactors Operated at Different Organic Loading Rates

The granular sludge process is an effective, low-footprint alternative to conventional activated sludge wastewater treatment. The architecture of the microbial granules allows the co-existence of different functional groups, e.g., nitrifying and denitrifying communities, which permits compact reactor design. However, little is known about the factors influencing community assembly in granular sludge, such as the effects of reactor operation strategies and influent wastewater composition. Here, we analyze the development of the microbiomes in parallel laboratory-scale anoxic/aerobic granular sludge reactors operated at low (0.9 kg m^-3d^-1), moderate (1.9 kg m^-3d^-1) and high (3.7 kg m^-3d^-1) organic loading rates (OLRs) and the same ammonium loading rate (0.2 kg NH₄-N m^-3d^-1) for 84 days. Complete removal of organic carbon and ammonium was achieved in all three reactors after start-up, while the nitrogen removal (denitrification) efficiency increased with the OLR: 0% at low, 38% at moderate, and 66% at high loading rate. The bacterial communities at different loading rates diverged rapidly after start-up and showed less than 50% similarity after 6 days, and below 40% similarity after 84 days. The three reactor microbiomes were dominated by different genera (mainly Meganema, Thauera, Paracoccus, and Zoogloea), but these genera have similar ecosystem functions of EPS production, denitrification and polyhydroxyalkanoate (PHA) storage. Many less abundant but persistent taxa were also detected within these functional groups. The bacterial communities were functionally redundant irrespective of the loading rate applied. At steady-state reactor operation, the identity of the core community members was rather stable, but their relative abundances changed considerably over time. Furthermore, nitrifying bacteria were low in relative abundance and diversity in all reactors, despite their large contribution to nitrogen turnover. The results suggest that the OLR has considerable impact on the composition of the granular sludge communities, but also that the granule communities can be dynamic even at steady-state reactor operation due to high functional redundancy of several key guilds. Knowledge about microbial diversity with specific functional guilds under different operating conditions can be important for engineers to predict the stability of reactor functions during the start-up and continued reactor operation.

Responses of the Microalga Chlorophyta sp. to Bacterial Quorum Sensing Molecules (N-Acylhomoserine Lactones): Aromatic Protein-Induced Self-Aggregation

Bacteria and microalgae often coexist during the recycling of microalgal bioresources in wastewater treatment processes. Although the bacteria may compete with the microalgae for nutrients, they could also facilitate microalgal harvesting by forming algal-bacterial aggregates. However, very little is known about interspecies interactions between bacteria and microalgae. In this study, we investigated the responses of a model microalga, Chlorophyta sp., to the typical quorum sensing (QS) molecules N-acylhomoserine lactones (AHLs) extracted from activated sludge bacteria. Chlorophyta sp. self-aggregated in 200 μm bioflocs by secreting 460-1000 kDa aromatic proteins upon interacting with AHLs, and the settling efficiency of Chlorophyta sp. reached as high as 41%. However, Chlorophyta sp. cells were essentially in a free suspension in the absence of AHLs. Fluorescence intensity of the aromatic proteins had significant (P < 0.05) relationship with the Chlorophyta sp. settleability, and showed a positive correlation, indicating that aromatic proteins helped aggregate microalga. Transcriptome results further revealed up-regulation of synthesis pathways for aromatic proteins from tyrosine and phenylalanine that was assisted by anthranilate accumulation. To the best of our knowledge, this is the first study to confirm that eukaryotic microorganisms can sense and respond to prokaryotic QS molecules.

Rapid aerobic granulation in an SBR treating piggery wastewater by seeding sludge from a municipal WWTP

Aerobic sludge granulation was rapidly obtained in the erlenmeyer bottle and sequencing batch reactor (SBR) using piggery wastewater. Aerobic granulation occurred on day 3 and granules with mean diameter of 0.2mm and SVI₃₀ of 20.3mL/g formed in SBR on day 18. High concentrations of Ca and Fe in the raw piggery wastewater and operating mode accelerated aerobic granulation, even though the seed sludge was from a municipal wastewater treatment plant (WWTP). Alpha diversity analysis revealed Operational Taxonomic Units, Shannon, ACE and Chao 1 indexes in aerobic granules were 2013, 5.51, 4665.5 and 3734.5, which were obviously lower compared to seed sludge. The percentages of major microbial communities, such as Proteobacteria, Bacteroidetes and Firmicutes were obviously higher in aerobic granules than seed sludge. Chloroflexi, Planctomycetes, Actinobacteria, TM7 and Acidobacteria showed much higher abundances in the inoculum. The main reasons might be the characteristics of raw piggery wastewater and granule structure.

Influence of CeO2 NPs on biological phosphorus removal and bacterial community shifts in a sequencing batch biofilm reactor with the differential effects of molecular oxygen

The effects of CeO₂ nanoparticles (CeO₂ NPs) on a sequencing batch biofilm reactor (SBBR) with established biological phosphorus (P) removal were investigated from the processes of anaerobic P release and aerobic P uptake. At low concentration (0.1mg/L), no significant impact was observed on total phosphorus (TP) removal after operating for 8h. However, at a concentration of 20mg/L, TP removal efficiency decreased from 83.68% to 55.88% and 16.76% when the CeO₂ NPs were added at the beginning of the anaerobic and aerobic periods, respectively. Further studies illustrated that the inhibition of the specific P release rate was caused by the reversible states of Ce³⁺ and Ce⁴⁺, which inhibited the activity of exopolyphosphatase (PPX) and transformation of poly-β-hydoxyalkanoates (PHA) and glycogen, as well as the uptake of volatile fatty acids (VFAs). The decrease in the specific P uptake rate was mainly attributed to the significantly suppressed energy generation and decreased abundance of Burkholderia caused by excess reactive oxygen species. The removal of chemical oxygen demand (COD) was not influenced by CeO₂ NPs under aerobic conditions, due to the increased abundance of Acetobacter and Acidocella after exposure. The inhibitory effects of CeO₂ NPs with molecular oxygen were reduced after anaerobic exposure due to the enhanced particle size and the presence of Ce³⁺.