[Recent advances in the structure and function of microbial community in anaerobic granular sludge]

Anaerobic granular sludge (AnGS), a self-immobilized aggregate containing various functional microorganisms, is considered as a promising green process for wastewater treatment. AnGS has the advantages of high volume loading rate, simple process and low excess sludge generation, thus shows great technological and economical potentials. This review systematically summarizes the recent advances of the microbial community structure and function of anaerobic granular sludge, and discusses the factors affecting the formation and stability of anaerobic granular sludge from the perspective of microbiology. Moreover, future research directions of AnGS are prospected. This review is expected to facilitate the research and engineering application of AnGS.

Rapid Start-Up Characteristics of Anammox under Different Inoculation Conditions

The long multiplication time and extremely demanding enrichment environment requirements of Anammox bacteria (AAOB) have led to difficult reactor start-ups and hindered its practical dissemination. Few feasibility studies have been reported on the recovery of AAOB activity initiation after inlet substrate disconnection caused by an unfavorable condition, and few factors, such as indicators of the recovery process, have been explored. Therefore, in this experiment, two modified expanded granular sludge bed reactors (EGSB) were inoculated with 1.5 L anaerobic granular sludge (AGS) + 1 L Anammox sludge (AMS) (R1) and 2.5 L anaerobic granular sludge (AGS) (R2), respectively. After a long-term (140 days) starvation shock at a high temperature (38 °C), the bacteria population activity recovery experiments were conducted. After 160 days, both reactors were successfully started up, and the total nitrogen removal rates exceeded 87%. Due to the experimental period, the total nitrogen removal rate of R2 was slightly higher than that of R1 in the final stage. However, it is undeniable that R2 had a relatively long activity delay during startup, while R1 had no significant activity delay during startup. The sludge obtained from R1 had a higher specific anammox activity (SAA). Analysis of the extracellular polymer substances (EPS) results showed that the extracellular polymer content in R1 was higher than that in R2 throughout the recovery process, indicating that R1 had higher sludge stability and denitrification performance. Scanning electron microscopy (SEM) analysis showed that more extracellular filamentous bacteria could be seen in the R1 reactor with better morphology of Anammox bacteria. In contrast, the R2 reactor had fewer extracellular hyphae and micropores as a percentage and higher filamentous bacteria content. The results of microbial 16SrDNA analysis showed that R1 used AAOB as inoculum to initiate Anammox, and the reactor was enriched with Anammox bacteria earlier and in much greater abundance than R2. The experimental results indicated that inoculating mixed anaerobic granular sludge and Anammox sludge to initiate an anammox reactor was more effective.

Evaluation of dye decolorization using anaerobic granular sludge from an expanded granular sludge bed based on spectrometric and microbiome analyses

The decolorization of 11 dyes by granular sludge from an anaerobic expanded granular sludge bed (EGSB) reactor was evaluated. Biological decolorization of Reactive Red 21, 23, and 180, and Reactive Yellow 15, 17, and 23 in model textile wastewater was observed for the first time after a 7-day incubation (over 94% decolorization). According to the sequencing analysis of 16S rRNA gene amplicons from EGSB granular sludge, the operational taxonomic unit related to Paludibacter propionicigenes showed the highest increase in relative abundance ratios in the presence of dyes (7.12 times on average over 11 dyes) compared to those without dyes.

[Effects of PES and 2,4-DCP on the Extracellular Polymeric Substances and Microbial Community of Anaerobic Granular Sludge]

The effects of polyether sulfone (PES) microplastics and 2,4-dichlorophenol (2,4-DCP) on the loosely-bound extracellular polymeric substances (LB-EPS) and tightly-bound EPS (TB-EPS) of anaerobic granular sludge were investigated. In addition, high-throughput sequencing technology was used to analyze the changes in the microbial community and gene functions in the anaerobic granular sludge. The results revealed that the chemical oxygen demand (COD) removal rates of the 2,4-DCP and PES+2,4-DCP experimental groups were 35% and 37%, which were 57% and 55% lower than that of the blank control group, while the COD removal rates of the PES experimental group remained around 90%. After the addition of the PES microplastics and 2,4-DCP, the protein and polysaccharide contents in the LB-EPS decreased compared with the control group, and the polysaccharide content in TB-EPS increased the least. In presence of the PES microplastics and 2,4-DCP, the activity of coenzyme F₄₂₀ was inhibited. Through high-throughput sequencing, the microbial richness and diversity of the anaerobic granular sludge in the experimental group were reduced with the addition of the PES microplastics or 2,4-DCP. In the control group and the experimental group, the dominant bacteria at the phylum level were Proteobacteria (13.45%-44.47%), Firmicutes (6.86%-21.67%), and Actinobacteria (3.16%-18.11%). The abundance of β-Proteobacteria in the PES+2,4-DCP experimental group was reduced by 15.28%, while the abundance of γ-Proteobacteria increased by 28.44% compared with the control group. Based on the phylogenetic investigation of the communities using the reconstruction of unobserved states (PICRUSt) analysis, it was found that in the experimental group with the PES microplastics or 2,4-DCP, the genes related to the sludge energy metabolism function were 0.25%-0.72% more than the control group; therefore, the abundance of genes related to the transport function group decreased significantly.

Improving Biological Treatment of Real Bilge Wastewater With Zero Valent Iron and Activated Charcoal Addition

From the ships engine rooms a recalcitrant wastewater is produced called “bilge” which contains oil, metal working fluids, surfactants, and salinity. This study investigated the treatment of real bilge wastewater in short experiments using the following processes: (i) anaerobic digestion with granular sludge and ZVI addition for enhancement of methane production, (ii) activated charcoal addition to biological treatment (aerobic and anaerobic) for Chemical Oxygen Demand (COD) significant reduction and (iii) combination of ZVI and anaerobic charcoal addition for high performance treatment. The addition of ZVI in anaerobic sludge resulted in higher performance mostly in cumulative CH₄ production. The microbial profile of anaerobic granular sludge exposed to ZVI was determined and Acetobacterium and Arcobacter were the most dominant bacteria genera. Activated charcoal achieved higher COD removal, compared to biological degradation (aerobic and anaerobic). The combination of the two mechanisms, activated charcoal and biomass, had higher COD removal only for aerobic biomass. The combination of ZVI and activated charcoal to anaerobic digestion resulted in higher CH₄ production and significant COD removal in short contact time.

Iohexol Degradation by Biogenic Palladium Nanoparticles Hosted in Anaerobic Granular Sludge

To improve the degradation ability of anaerobic granular sludge (AGS) toward the iodinated contrast media (ICM) iohexol, biogenic nanoscale palladium (Pd) was formed in AGS via microbial reduction. The Pd hosted in AGS (Pd-AGS) was used for iohexol degradation. The effects of the electron donor, reaction medium, iodide ion fouling, and polymer embedding of the Pd-AGS on the reactivity were investigated. Our results showed the Pd-AGS increased the degradation rate of iohexol, with a conversion rate constant increased by 86.3-fold compared to the AGS control. Various organic compounds were investigated as electron donors to initiate the catalytic activity of Pd-AGS and the promotion achieved with the tested electron donors was in the following order: formate > lactate > ethanol > glucose > acetate. The Pd-AGS had high reactivity in deionized water at mild pH, and almost no reactivity under acidic (pH = 1.2) and alkaline (pH > 11) conditions. The presence of iodide ions in the medium inhibited the catalytic activity of Pd-AGS toward iohexol because of catalyst fouling. Embedding the Pd-AGS in alginate, chitosan, or polyvinyl alcohol (PVA) could prevent Pd loss but it also retarded the iohexol degradation rate. The Pd-AGS, as a combination of Pd catalyst and AGS, provides a novel strategy for iohexol degradation in polluted water and wastewater.

[Effects of Magnetic Fe3O4 Nanoparticles on the Characteristics of Anaerobic Granular Sludge and Its Interior Microbial Community]

In this study, the effects of magnetic Fe₃O₄ nanoparticles (Fe₃O₄ NPs) on soluble microbial products (SMP), loosely bound extracellular polymeric substances (LB-EPS), and tightly bound extracellular polymeric substances (TB-EPS) in anaerobic granular sludge were examined. In addition, the anaerobic granular sludge interior microbial community dynamics were investigated using high-throughput sequencing. The results demonstrated that the removal rate of COD was 83.6% after long-term exposure in the experimental reactor, namely, the anaerobic reactor containing Fe₃O₄ NPs. It was reduced by 5.7% in comparison with the removal rate in the control reactor. The total amount of TB-EPS in anaerobic granular sludge in the experimental and control reactors was 178.20 mg·g^-1 and 138.24 mg·g^-1, respectively, while the total amount of SMP in anaerobic granular sludge was 34.88 mg·L^-1 and 27.44 mg·L^-1, respectively. With regard to the LB-EPS in anaerobic granular sludge in the experimental reactor, the peak of humic acid disappeared and the peak intensity of coenzyme F₄₂₀ decreased slightly using excitation-emission matrix (EEM) fluorescence spectra. In terms of the microbial community dynamics in the experimental reactor, the abundance of Methanobacterium was greatly augmented from 76.15% to 86.76%; whereas, the abundance of Methanothrix decreased from 17.1% to 7.51%. This indicated that Methanothrix was more sensitive to Fe₃O₄ NPs. Moreover, the changes in bacterial communities were evident:①the abundance of Proteobacteria dropped from 66.44% to 47.16%; ② the abundance of Actinobacteria grew from 8.97% to 17.33%; and ③ the abundance of Bacteroidetes increased from 8.07% to 17.74%. The increasing abundance of Actinobacteria and Bacteroidetes plays a positive role in the anaerobic hydrolysis of organic matter.

Microbial and nutritional regulation of high-solids anaerobic mono-digestion of fruit and vegetable wastes

The anaerobic digestion of single fruit and vegetable wastes (FVW) can be easily interrupted by rapid acidogenesis and inhibition of methanogen, and the digestion system tends to be particularly unstable at high solid content. In this study, the anaerobic digestion of FVW in batch experiments under mesophilic condition at a high solid concentration of 10% was successfully conducted to overcome the acidogenesis problem through several modifications. Firstly, compared with the conventional anaerobic sludge (CAS), the acclimated anaerobic granular sludge (AGS) was found to be a better inoculum due to its higher Archaea abundance. Secondly, waste activated sludge (WAS) was chosen to co-digest with FVW, because WAS had abundant proteins that could generate intermediate ammonium. The ammonium could neutralize the accumulated volatile fatty acids (VFAs) and prevent the pH value of the digestion system from rapidly decreasing. Co-digestion of FVW and WAS with TS ratio of 60:40 gave the highest biogas yield of 562 mL/g-VS and the highest methane yield of 362 mL/g-VS. Key parameters in the digestion process, including VFAs concentration, pH, enzyme activity, and microbial activity, were also examined.

[Long-term Impacts of TiO2 Nanoparticles on the Stability of an Anaerobic Granular Sludge Bioreactor]

In the present study, the fate and long-term effect of TiO₂ nanoparticles (NPs) on anaerobic granular sludge (AGS) was evaluated in an anaerobic methanogenic system. In the short-term experiment, the methane production rate decreased when the dosage of TiO₂ NPs was greater than 150 mg·g^-1. However, no significant difference in the products of acidification and methanation between the control and 150 mg·g^-1(as VSS) of TiO₂ NPs assays was observed, indicating low bacteria cytotoxicity of TiO₂ NPs on AGS in dark anaerobic digestion. The operation data of the AGS bioreactor showed that acidogens was more sensitive to prolonged exposure to TiO₂ NPs with the accumulation of VFAs and a decrease of biogas production in the TiO₂ NPs containing reactor. The inhibiting effect of TiO₂ NPs on the AGS might be attributed to the physical restraints. The average TiO₂ concentration escaping with the effluent was 0.632 mg·L^-1, suggesting most of the NPs were retained inside the reactor. The long-term presence of TiO₂ NPs could alter the composition of the microbial communities in the AGS, since the amount of Methanosarcina increased by 115.6%. The results also indicated that the treatment of short-term sudden exposure to TiO₂ NPs using batch tests might not be appropriate for interpreting their cumulative effects on the AGS, since a long time was need for the TiO₂ NPs to show negative effects on the microbial populations in the AGS. Our study could supply useful proof for assessments of potential risks for TiO₂ NPs on anaerobic activated sludge.

[Effects of Salinity on the Operation of EGSB Reactors and the Anaerobic Granular Sludge]

The existence of high concentrations of salinity and organics would have a great impact on the microorganisms when using bioreactors to treat wastewater. Thus, it is necessary to find bioreactors resistant to high concentrations of salinity. The effect of salinity on an expanded granular sludge bed reactor (EGSB) was studied by increasing the Cl^- concentration from 0 to 10000 mg·L^-1 using simulated high salinity wastewater with a COD volume loading of 3.267 kg·(m³·d)^-1. The results show no obvious inhibitory effect of Cl^- on the microorganism when the concentration of Cl^- was below 7500 mg·L^-1. Above 1.3 m³·(m³·d)^-1 volumetric gas production rate was maintained and COD removal rate could achieved 98.1% when the Cl^- concentration up to 7500 mg·L^-1 while the large particle size of anaerobic granular sludge occupying the majority of of the system. The anaerobic granular sludge was seriously affected when the Cl^- concentration as 10000 mg·L^-1. The community structure of the anaerobic granular sludge was analyzed using high-throughput sequencing when the Cl^- concentration was 0 and 5000 mg·L^-1. The results show that the salinity stress produced different dominant groups. The dominant species were Methanobacterium, Methanospirillum, Methanothrix, and Paludibacter when the Cl^- concentration was 5000 mg·L^-1, but Methanoregula and Longilinea were the dominant species when the Cl^- concentration was 0.

Evidence of glycoproteins and sulphated proteoglycan-like presence in extracellular polymeric substance from anaerobic granular sludge

The protein fraction of extracellular polymeric substance (EPS) from two anaerobic granular sludge samples was characterized with sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and a far western blotting method. SDS-PAGE was used with various staining applications to obtain a protein (silver), glycoprotein [periodic acid-Shiff's (PAS)] or proteoglycan-like (Alcian blue at pH 2.5 (carboxylic group) or 1 (sulphated group)) fingerprint. The fingerprints of the EPS denatured protein from the two sludge samples differed. Some proteins are specific to Soluble (S) or Bound (B)-EPS (20-100 kDa). Denatured proteins with a polysaccharide moieties characterization are more present in B-EPS. Glycoproteins with α-d-mannosyl and/or α-d-glucosyl (90, 50, 40 kDa) were detected. Proteoglycan-like and sulphated proteoglycan-like substances are also detected, mainly in B-EPS. A 68 kDa sulphated proteoglycan-like substance contains two glucidic residue types: α-d-mannosyl and/or α-d-glucosyl and N-acetyl-β-d-glucosamine. Such heteroproteins are present around the membrane as well as the surface-layer from Archaea and from some bacteria. The glycoprotein and sulphated proteoglycan-like substance are assumed to contribute to anaerobic granule strength, thanks to their ability to perform interactions of various nature (ionic, hydrophobic, Ca(2+) as divalent cation bridging, etc.).