Performance Of Anaerobic Granular Sludge Research Articles

A new strategy for accelerating recovery of anaerobic granular sludge after low-temperature shock: In situ regulation of quorum sensing microorganisms embedded in polyvinyl alcohol sodium alginate

Low-temperature could inhibit the performance of anaerobic granular sludge (AnGS). Quorum sensing (QS), as a communication mode between microorganisms, can effectively regulate AnGS. In this study, a kind of embedded particles (PVA/SA@Serratia) based on signal molecule secreting bacteria was prepared by microbial immobilization technology based on polyvinyl alcohol and sodium alginate to accelerate the recovery of AnGS system after low temperature. Low-temperature shock experiment verified the positive effect of PVA/SA@Serratia on restoring the COD removal rate and methanogenesis capacity of AnGS. Further analysis by metagenomics analysis showed that PVA/SA@Serratia stimulated higher QS activity and promoted the secretion of extracellular polymeric substance (EPS) in AnGS. The rapid construction of EPS protective layer effectively accelerated the establishment of a robust microbial community structure. PVA/SA@Serratia also enhanced multiple methanogenic pathways, including direct interspecies electron transfer. In conclusion, this study demonstrated that PVA/SA@Serratia could effectively strengthen AnGS after low-temperature shock.

Anaerobic granular sludge performance in an expanded granular sludge bed reactor treating calcium-rich wastewater by adjusting CaCO3 crystallization: Effect of upflow velocity and Ca2+ concentration

The role of upflow velocity and Ca2+ concentration in controlling the type and rate of CaCO3 crystallization and their impacts on the anaerobic granular sludge (AnGS) formation and performance in an expanded granular sludge bed (EGSB) reactor were studied. The results showed that an improved upflow velocity could promote metastable CaCO3 crystals and achieve the optimized portion of vaterite with a value of 84 % at 10 m/h with a small amount of aragonite, thus limiting the scaling in the reactor. The removal efficiency of Ca2+ was to some extent positively correlated to the influent Ca2+ concentration, but declined when Ca2+ exceeded a specific threshold. Vaterite was dominant with the increase of Ca2+ concentrations of the influent. Compared with granules in R1 (Ca2+ 10 mg/L) and R2 (Ca2+ 100 mg/L), granules cultivated in R3 (Ca2+ 800 mg/L) revealed maximum amount of biomass with biggest particle size distribution and fastest average settling rate, with relative stable COD removal efficiency and the fast optimized reactor capacity at OLR of 16 kgCOD/m3d. A low upflow velocity and a higher Ca2+ concentration promoted nucleus formation and granules growth at the initial cultivation stage of the EGSB reactor. The Ca2+ concentration had a significant impact on the bacterial community and favoured the growth of Tolumonas and Anaeromousa Anaeroarcus. Archaea, rather than bacteria, was strengthened to contribute more to methane production at a relatively high Ca2+ concentration.

Mediating the performance of anaerobic granular sludge by exogenous flavin supplementation: Flavin binding capacity and behavior, interspecies electron transfer, and methane production

Although flavins are known as effective electron mediators, the binding capacity of exogenous flavins by anaerobic granular sludge (AGS) and their role in interspecies electron transfer (IET) remains unknown. In this study, AGS was mediated by using three exogenous flavins of riboflavin (RF), flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD). Results showed that the total amounts of flavins associated with extracellular polymeric substance (EPS) of AGS increased by 2.03–2.42 and 3.83–4.94 folds, after exposure to 50 and 200 μM of exogenous flavins, respectively. A large portion of FMN and FAD was transformed into RF by AGS. Exogenous flavin mediation also stimulated the production of EPS and cytochrome c (c-Cyts) as well as cytochrome-bound flavins. The increased abundance of these electron mediators led to a reduced electrochemical impedance of EPS and improved extracellular electron transfer capacity. The methane production of AGS after mediation with exogenous RF, FMN, and FAD increased by 19.03–31.71%, 22.86–26.04%, and 28.51–33.44%, respectively. This study sheds new light on the role of exogenous flavins in promoting the IET process of a complex microbial aggregate of AGS.

Enhancing sludge methanogenesis with changed micro-environment of anaerobic microorganisms by Fenton iron mud

Conductive materials have been demonstrated to enhance sludge methanogenesis, but few researches have concentrated on the interaction among conductive materials, microorganisms and their immediate living environment. In this study, Fenton iron mud with a high abundance of Fe(III) was recycled and applied in anaerobic reactors to promote anaerobic digestion (AD) process. The results show that the primary content of extracellular polymeric substances (EPS) such as polysaccharides and proteins increased significantly, possibly promoting microbial aggregation. Furthermore, with the increment of redox mediators including humic substances in EPS and Fe(III) introduced by Fenton iron mud, the direct interspecies electron transfer (DIET) between methanogens and interacting bacteria could be accelerated, which enhanced the rate of methanogenesis in anaerobic digestion (35.21 ± 4.53% increase compared to the control). The further analysis of the anaerobic microbial community confirmed the fact that Fenton iron mud enriched functional microorganisms, such as the abundance of CO2-reducing (e.g. Chloroflexi) and Fe(III)-reducing bacteria (e.g., Tepidimicrobium), thereby expediting the electron transfer reaction in the AD process via microbial DIET and dissimilatory iron reduction (DIR). This work will make it possible for using the recycled hazardous material – Fenton iron mud to improve the performance of anaerobic granular sludge during methanogenesis.

Effects of different N-acyl-serine lactone signaling molecules on the performance of anaerobic granular sludge.

Exogenous addition of acyl-homoserine lactone (AHL) signaling molecules can improve or inhibit the methane production performance of anaerobic granular sludge (AnGS) by quorum sensing (QS). To explore the specific effect of AHLs on AnGS, 2 μM of signal molecules were added to the reactor and we analyzed their effects on AnGS biodiversity, extracellular polymeric substance (EPS), specific methanogenic activity (SMA) and chemical oxygen demand (COD) removal rate of AnGS. The results indicated that the four types of AHLs improve the COD removal rate, SMA and organic composition of AnGS. The addition of N-(β-ketocaproyl)-dl-homoserine lactone (3O-C6-HSL) yielded the greatest increase in methanogenic activity, reaching a maximum of 30.83%. The four types of AHLs stimulate the secretion of EPS in AnGS by group sensing regulation. The addition of N-hexanoyl-l-homoserine lactone (C6-HSL), N-octanoyl-dl-lactone (C8-HSL) and 3O-C6-HSL induced the enrichment of Actinobacteria. Thus, the process of hydrolysis and acidification of AnGS is accelerated. The addition of N-butyryl-dl-homoserine lactone (C4-HSL), C6-HSL and 3O-C6-HSL promote the potential methanogenic metabolic pathway of AnGS. The addition of all AHLs directly or indirectly enhanced the methane metabolism pathway of sludge and improved the specific methane generation activity of AnGS. These results are expected to provide preliminary research data for enhancing the methane production efficiency of reactors and enriching the biological activity of AnGS.

Investigation of textile dyeing effluent using activated sludge system to assess the removal efficiency.

In this current work, the performance of an aerobic granular sludge (AGS) for real textile wastewater was investigated based on system operational parameters evaluation. The study was performed for 90 days, and sampling was done once a week in which textile dyeing effluent from the textile mill was collected and subjected to laboratory-scale treatment. The samples from the inlet, the outlet of the wastewater plant, and within the bioreactor were collected at various concentrations of mixed liquid suspended solids (MLSS), and hydraulic retention remained the same in the investigated period of 53 h. The objective of this study was to analyze the AGS system performance assessment by evaluating the effect of different MLSS concentrations on chemical oxygen demand (COD), total suspended solids (TSS), and oil/grease removal from real-based textile water. The results showed that removal of organic material from the process water increases with an increase in MLSS concentration in the bioreactor and gradually shifts removal of COD from 91.2% to 94.5%. As the concentration of microorganisms in the reactor (aeration tank) increases, the degradation of waste organics in the wastewater increases as well. Moreover, the % removal of TSS (83.5% to 98%) and removal of oil/grease (62.5% to 76.4%) were also increased. These results ultimately suggest that the utilization of an activated sludge system can effectively treat complex and highly polluted denim textile wastewater to avoid secondary pollution posed by this industry. PRACTITIONER POINTS: The effectiveness of aerobic granular sludge was investigated for industrial textile effluent. The increase in MLSS results in increase of % COD removal efficiency to 94.5%. The AGS system can efficiently treat complicated and highly contaminated textile wastewater.

Evaluation of characteristics and microbial community of anaerobic granular sludge under microplastics and aromatic carboxylic acids exposure

The influences of polyether sulfone (PES) microplastics and different structures aromatic carboxylic acids such as benzoic acid (BA), phthalic acid (PA), hemimellitic acid (HA), and 1-naphthoic acid (1-NA) on the performances and characteristics of anaerobic granular sludge as well as the microbial community were investigated. The chemical oxygen demand (COD) removal efficiency was the highest in the experimental group with 40 mg/L BA, reaching 90.1%. The inhibitory effect of aromatic carboxylic acids addition on the 2,3,5-triphenyltetrazolium chloride (TTC) activity was more obvious than that on 2-para (iodo-phenyl)-3(nitrophenyl)-5(phenyl) tetrazolium chloride (INT) activity. Compared with the control group (only 0.5 g/L PES microplastics, 60.6 mg TF·g TSS·h−1), the inhibition effect of TTC activity was 32.5 mg TF·g TSS·h−1 and 44.3 mg TF·g TSS·h−1 in the 40 mg/L HA and 40 mg/L 1-NA experimental groups, respectively. When aromatic carboxylic acids were added, the activities of acetate kinase and coenzyme F420 in the anaerobic granular sludge decreased. The excitation-emission matrix (EEM) fluorescence spectra indicated that loosely bound extracellular polymeric substances (LB-EPS) began to decay. After the addition of different aromatic carboxylic acids, the CC and CH functional groups of the anaerobic granular sludge increased, suggesting that aromatic carboxylic acids migrated to the surface of anaerobic granular sludge, such a transfer would lead to changes in anaerobic granular sludge performance. High-throughput sequencing technology showed that the dominant microbial communities in the anaerobic granular sludge were Proteobacteria, Methanothrix, and Methanomicrobia. After the addition of aromatic carboxylic acids, the relative abundances of Proteobacteria, Methanobacterium, and Methanospirillum increased. In the presence of PES, 1-NA had the most serious toxicity to the anaerobic granular sludge.

Effect of sludge age on aerobic granular sludge: Addressing nutrient removal performance and biomass stability

The effect of the sludge retention time (SRT) on the stability and performance of an aerobic granular sludge (AGS) sequencing-batch reactor (SBR) on the simultaneous organic matter, nitrogen and phosphorus removal from simulated domestic wastewater was assessed in a long-term study (392 days). Operated under alternating anaerobic-aerobic conditions, the reactor was subjected to four experimental conditions: uncontrolled SRT (run I), SRT of 30 (run II), 20 (run III) and 15 days (run IV). The results showed that COD removal was kept stable and over 90 % throughout the SBR operation, regardless of the SRT. On the other hand, by allowing the sludge age to be dependent on natural solids washout by effluent withdrawal (SRT of 47–61 days), phosphate removal was substantially low (15 %), as also observed at an SRT of 30 days. Filamentous bacteria overgrowth was noticed at the later conditions, which affected the stability of the granular biomass, leading to a deterioration of its settling properties. The ratio between the sludge volume index after 30 and 5 min of settling (SVI30/SVI5) was around 0.70. Biological phosphate removal started to thrive at the sludge age of 20 days (35 %), reaching around 100 % at SRT of 15 days, at which the highest P-release/COD uptake ratio (0.14 mg P/mgCOD) and specific phosphate uptake (11.4 mgPO43−-P/(gVSS h)) were observed. Under the lowest SRT applied, the granules exhibited better structural and settling properties, with the SVI30/SVI5 ratio reaching almost 1.0. Moreover, nitrification was kept stable, and, even though nitrite build-up occurred during the SBR cycle, nitrate was the main oxidized nitrogen form in the effluent. Average COD, ammonium and total nitrogen removal amounted to 93 %, 97 % and 58 %. Cycle tests under normal and special conditions were carried out to assess specific nitrification, denitrification and phosphate uptake rates, and elucidate the key players in the biological conversions processes taking place in the AGS reactor. No phosphate uptake coupled to nitrate reduction was noticed, implying that P removal was not driven by denitrifying dephosphatation activity. To track the dynamics of important microbial functional groups, fluorescence in situ hybridization analysis was conducted.

Polystyrene nanoplastics reshape the anaerobic granular sludge for recovering methane from wastewater

Wastewater has been identified as an important carrier for nanoplastics, which could elicit unintended impacts on critical microbial processes. However, the long-term impacts of nanoplastics on anaerobic granular sludge (AGS) for methane recovery from wastewater and the mechanisms involved remains unclear. In this study, we investigated the long term exposure-response relationship between polystyrene nanoplastics (Nano-PS) and AGS. In continuous test over 120 days with 86 days’ Nano-PS exposure, feeding wastewater with 10 μg/L of Nano-PS had no significant impacts on the AGS performance. In comparison, higher levels (i.e., 20 and 50 μg/L) of Nano-PS decreased methane production and chemical oxygen demand (COD) removal by 19.0–28.6% and 19.3–30.0%, respectively, along with volatile fatty acids (VFA) accumulation. More extracellular polymeric substance (EPS) was induced by 10 μg/L of Nano-PS as a response to protect microbes, but higher levels (i.e., 20 and 50 μg/L) of Nano-PS decreased EPS generation, causing a decline in granule size and cell viability. Fluorescence tagging found that a large number of Nano-PS agglomerated/accumulated on the outer layer of AGS and even transferred into deeper layers of AGS over exposure time, producing toxic effects to adherent microorganisms, e.g., Longilinea sp., Paludibacter sp. and Methanosaeta sp.. The oxidative stress induced by Nano-PS was revealed to be a key factor for reshaping the AGS, reflected by the increased reactive oxygen species (ROS) generation and lactate dehydrogenase (LDH) release. The sodium dodecyl sulfate (SDS) leached from Nano-PS was also demonstrated to restrain the activities of antioxidant enzymes, thereby further lessening resistance to oxidative stress induced by Nano-PS. This work improves our ability to predict the risks associated with this ubiquitous contaminant in the environment.

Effect of cephalexin after heterogeneous Fenton-like pretreatment on the performance of anaerobic granular sludge and activated sludge

Effects of Fe3O4 NPs heterogeneous Fenton-like pretreatment on the physicochemical properties and microbial community structure of anaerobic granular sludge (AGS) and activated sludge (AS) with cephalexin were investigated. Results showed that the average removal rate of chemical oxygen demand (COD) by the AGS was 80.9%, 85.9%, 90.3% and 91.6%, respectively, at cephalexin without pretreatment, pretreatment with 20% (H2O2), 40% (H2O2) and 60% (H2O2). Compared to the reactor without pretreatment, the COD removal rate increased by 24.14% with 60% (H2O2) pretreatment for the AS. Dehydrogenase levels in the AS were 313.05, 351.12, 434.81 and 480.77 mg TF (g·h)−1, which increased with higher concentrations of the pretreatment. Three-dimensional fluorescence (EEM) spectra analysis showed that the absorption peak intensities of humic acid in soluble microbial products (SMP) decreased in the AGS with increasing pretreatment. In the AGS, the dominant bacterial populations were Levilinea, Litorilinea and Clostridium sensu stricto. Clostridium sensu stricto accounting for 4.35% without pretreatment, while it was as high as 17% when it was pretreated with 60% (H2O2). The increase in the proportion of Clostridium sensu stricto was beneficial to the removal of organic pollutants. The pretreatment was also beneficial to the growth of acetic acid producing Methanothrix. For the AS, Gemmobacter were the dominant species, which increased from 6.56% to 32.61% after increasing the pretreatment to 40% (H2O2). Furthermore, the microbial capacities of amino acid metabolism and carbohydrate metabolism were enhanced by addition of pretreatment.

Long-term effects of multi-walled carbon nanotubes on the performance and microbial community structures of an anaerobic granular sludge system.

Multi-walled carbon nanotubes (MWCNTs) released into the sewage may cause negative and/or positive effects on the treatment system. The objective of this study was to explore over 110days' effect of MWCNTs on the performance of anaerobic granular sludge and microbial community structures in an upflow anaerobic sludge blanket (UASB) reactor. The results showed that MWCNTs had no significant effect on the removal of chemical oxidation demand (COD) and ammonia in UASB reactor, but the total phosphorus (TP) removal efficiency increased by 29.34%. The biogas production of the reactor did not change. The anaerobic granular sludge tended to excrete more EPS to resist the effects of MWCNTs during the long-term impact. Illumina MiSeq sequencing of 16S rRNA gene revealed that MWCNTs did not affect the microbial diversity, but altered the composition and structure of microbial community in the reactor. In this process, Saccharibacteria replaced Proteobacteria as the highest abundant bacterial phylum. MWCNTs promoted the differentiation of methanogen structure, resulting in increase of Methanomassiliicoccus, Methanoculleus, and the uncultured WCHA1-57. These results indicated that MWCNTs impacted the performance of UASB reactor and the structures of the microbial community in anaerobic granular sludge.

Exogenous acyl-homoserine lactones adjust community structures of bacteria and methanogens to ameliorate the performance of anaerobic granular sludge

Quorum sensing (QS) signalling has been extensively studied in single species populations, activated sludge, biofilm and aerobic granular sludge. However, ecological roles of QS in anaerobic granular sludge, particularly in the content of the relationship between QS signalling and microbial community composition and function, have been rarely reported. Herein, five acyl-homoserine lactones (AHLs) molecules were added in the anaerobic granular sludge system for treating traditional Chinese medicine (TCM) wastewater respectively. The results indicated that the introduction of specific AHLs could enhance the abilities of organic matters removal and methanation in anaerobic granular sludge, and meanwhile, exogenous AHLs played an important role to regulate the concentration of EPS. Sequencing analysis indicated that microbial community structures of bacteria and methanogens changed to varying degrees by adding AHLs. This study suggested that exogenous AHLs could play a role in mediating microbial community structure, thereby enhancing the performance of anaerobic granular sludge. The regulatory mechanism of AHLs on community structure was discussed, and a speculative action model was established. Exogenous regulation by selective enhancement of AHLs-mediated QS in anaerobic granular sludge provided an innovative and attractive strategy for strengthening wastewater treatments.

Effect of heterogeneous Fenton-like pre-treatment on anaerobic granular sludge performance and microbial community for the treatment of traditional Chinese medicine wastewater

The effect of a heterogeneous Fenton-like pre-treatment on the anaerobic processes, characteristics and microbial community of sludge was investigated for traditional Chinese medicine (TCM) wastewater containing rhein. When the concentrations of rhein were 50mg/L and 100mg/L, the toxic effect was physiological toxicity for anaerobic granular sludge. Using a single double circle (DC) reactor for the treatment of TCM wastewater containing rhein at concentrations of 15–20mg/L, the chemical oxygen demand (COD) removal rate was 69%, and coenzyme F420 was nearly undetectable in the 3D-excitation-emission matrix (EEM) spectra of soluble microbial products (SMP). The abundances of Methanoregula, Methanobacterium, Methanosphaerula were only 5.57%, 2.39% and 1.08% in the DC reactor, respectively. TCM wastewater containing rhein could be successfully treated by the combination of the heterogeneous Fenton-like pre-treatment and the DC reactor processes, and the COD removal rate reached 95%. Meanwhile, the abundances of Methanoregula, Methanobacterium, Methanosphaerula increased to 22.5%, 18.5%, and 13.87%, respectively. For the bacterial community, the abundance of Acidobacteria_Gp6 decreased from 6.99% to 1.07%, while the abundances of Acidobacteria_Gp1 and Acidobacteria_Gp2 increased from 1.61% to 6.55% and from 1.28% to 5.87%, respectively.

Effect of an azo dye on the performance of an aerobic granular sludge sequencing batch reactor treating a simulated textile wastewater

This study analyzed the effect of an azo dye (Acid Red 14) on the performance of an aerobic granular sludge (AGS) sequencing batch reactor (SBR) system operated with 6-h anaerobic-aerobic cycles for the treatment of a synthetic textile wastewater. In this sense, two SBRs inoculated with AGS from a domestic wastewater treatment plant were run in parallel, being one supplied with the dye and the other used as a dye-free control. The AGS successfully adapted to the new hydrodynamic conditions forming smaller, denser granules in both reactors, with optimal sludge volume index values of 19 and 17 mL g−1 after 5-min and 30-min settling, respectively. As a result, high biomass concentration levels and sludge age values were registered, up to 13 gTSS L−1 and 40 days, respectively, when deliberate biomass wastage was limited to the sampling needs. Stable dye removal yields above 90% were attained during the anaerobic reaction phase, confirmed by the formation of one of the aromatic amines arising from azo bond reduction. The control of the sludge retention time (SRT) to 15 days triggered a 30% reduction in the biodecolorization yield. However, the increase of the SRT values back to levels above 25 days reverted this effect and also promoted the complete bioconversion of the identified aromatic amine during the aerobic reaction phase. The dye and its breakdown products did not negatively affect the treatment performance, as organic load removal yields higher than 80% were attained in both reactors, up to 77% occurring in the anaerobic phase. These high anaerobic organic removal levels were correlated to an increase of Defluviicoccus-related glycogen accumulating organisms in the biomass. Also, the capacity of the system to deal with shocks of high dye concentration and organic load was successfully demonstrated. Granule breakup after long-term operation only occurred in the dye-free control SBR, suggesting that the azo dye plays an important role in improving granule stability. Fluorescence in situ hybridization (FISH) analysis confirmed the compact structure of the dye-fed granules, microbial activity being apparently maintained in the granule core, as opposed to the dye-free control. These findings support the potential application of the AGS technology for textile wastewater treatment.