Characteristics Of Granular Sludge Research Articles

Temperature-resilient superior performances by coupling partial nitritation/anammox and iron-based denitrification with granular formation

Partial nitritation-anammox (PN/A), an energy-neutral process, is widely employed in the treatment of nitrogen-rich wastewater. However, the intrinsic nitrate accumulation limits the total nitrogen (TN) removal, and the practical application of PN/A continues to face a significant challenge at low temperatures (<15 °C). Here, an integrated partial nitritation-anammox and iron-based denitrification (PNAID) system was developed to address the concern. Two up-flow bioreactors were set up and operated for 400 days, with one as the control group and the other as the experiment group with the addition of Fe0. In comparison to the control group, the experiment group with the Fe0 supplement showed better nitrogen removal during the entire course of the experiment at different temperature levels. Specifically, the TN removal efficiency of the control group decreased from 82.9 % to 53.9 % when the temperature decreased from 30 to 12 °C, while in stark contrast, the experiment group consistently achieved 80 % of TN removal in the same condition. Apart from the enhanced nitrogen removal, the experiment group also exhibited better phosphorus removal (10.6 % versus 74.1 %) and organics removal (49.5 % versus 65.1 %). The enhanced and resilient nutrient removal performance of the proposed integrated process under low temperatures appeared to be attributed to the compact structure of granules and the increased microbial metabolism with Fe0 supplement, elucidated by a comprehensive analysis including microbial-specific activity, apparent activation energy, characteristics of granular sludge, and metagenomic sequencing. These results clearly confirmed that Fe0 supplement not only improved nitrogen removal of PN/A process, but also conferred a certain degree of robustness to the system in the face of temperature fluctuations.

Carrier with cyclodextrin and quorum sensing synergy: An efficient method for selective enrichment of anammox bacteria

High-efficiency enrichment of functional bacteria is one of the biggest technical barriers to the application of anaerobic ammonium oxidation (anammox). This study combined biofilm carriers and quorum sensing to achieve rapid biomass accumulation. A biofilm carrier with biomass adsorption and quorum sensing regulation functions was developed for the rapid start-up of the reactor and enrichment of anammox bacteria (AnAOB). The nitrogen removal rates of the three reactors were further tested, and the carrier mechanism was explored. The start-up time of the reactor with the modified carriers was 28 days, which was ∼44 % shorter than that of the reactor without carriers. After 90 days of operation, the absolute abundance of total AnAOB was 3.2 times that in the control group. The modified carrier promoted the rapid adhesion of biomass through the hydrophobic cavity of cyclodextrin and induced rapid proliferation, enhancement of activity, and extracellular protein secretion of AnAOB through quorum sensing signaling molecules. Finally, a special hydrophobic biofilm with granular sludge characteristics was formed on the modified carrier through the self-assembly of hydrophobic biomass particles. Overall, we propose a novel approach to enrich anammox bacteria involving a combination of quorum sensing and biofilm carriers.

Culturing partial-denitrification (PD) granules in continuous flow reactor with waste sludge as inoculum: performance, granular sludge characteristics and microbial community

ABSTRACT Partial denitrification granular sludge (PDGS) can provide long-term stable nitrite for anaerobic ammonia oxidation (anammox). The cultivation of ordinary activated sludge from wastewater treatment plants into PDGS can further promote the application of PD in practical engineering. In this study, the feasibility of fast start-up of PDGS was explored by inoculating waste sludge in up-flow anaerobic sludge blanket (UASB) reactor with synergistic control of nitrogen load rate (NLR, 0.05–0.65 kg N/m3/d) and electron donor starvation (EDS) (240–168 mg L−1), and system performance, particle characteristics and microbial structure were studied. The results showed that PD-UASB started successfully within 48 days, the average nitrite accumulation rate (NTR) and nitrate removal ratio (NRR) reached 79.6% and 82.5% after successful initiation, accompanied by high abundance of PD bacteria (Thauera, Pseudomonas, unclassflied commamonadaceae and Limnobacter) (25.3%). The increase of PD activity, and the difference between nitrate reductase (NAR) and nitrite reductase (NIR) contributed to nitrite production. Besides, the sludge shifted from flocculated (≤0.5 mm, 95.37%) to granulated state (0.5–2 mm, 64.74%), which could be due to the increase of extracellular polymers (EPS) (especially T-EPS) and metabolism of specific microorganisms (Bacteroidota and Chloroflexi, 19.92%). Good sludge granulation promoted the settleability of PD (the SVI5 was 47.248 mL/ g. ss after successful start-up). In summary, good PD sludge granulation process could be achieved in a short time by synergistically controlling NLR and EDS.

Integrating electrocoagulation process with up-flow anaerobic sludge blanket for in-situ biomethanation and performance improvement

In this study, the integration of the electrocoagulation (EC) process with anaerobic digestion as a novel in-situ biomethanation approach was considered for the first time. As a result of this integration (iron electrodes, current density of 1.5 mA/cm2 and an exposure mode of 10-min-ON/ 30-min-OFF), the carbon dioxide content of biogas reached below 2%. Also, the methane production rate improved by 18.0 ± 0.4%, whereas the removal efficiencies of chemical oxygen demand, turbidity, phosphate, and sulfate increased by 12.0 ± 1.5%, 30.7 ± 1.7%, > 99%, and 75.7%, respectively. Anaerobic granular sludge characteristics were also improved. Moreover, the EC process stimulated growth and quantity of functional microorganisms, especially Acinetobacter in bacterial and Methanobacterium in archaeal community. Methane concentration, however decreased due to possible excess hydrogen production. The application of the biogas as bio-hythane, and the optimization of the hybrid bioreactor to decrease hydrogen production, are possible avenues for further research.

Culturing Partial-Denitrification (Pd) Granules in Continuous Flow Reactor with Waste Sludge as Inoculum: Nitrite Accumulation Performance, Granular Sludge Characteristics and Microbial Community

Culturing Partial-Denitrification (Pd) Granules in Continuous Flow Reactor with Waste Sludge as Inoculum: Nitrite Accumulation Performance, Granular Sludge Characteristics and Microbial Community

Nitrogen and Phosphorus Removal from Domestic Sewage Aerobic Granular Sludge Under Intermittent Gradient Aeration

In this study, three SBR reactors R1, R2, and R3 were set up and operated using (A/O)3-SBR gradient aeration, (A/O)3-SBR constant aeration, and the conventional (A/O)-SBR mode, respectively. The nutrient removal performance and aerobic granular sludge characteristics under these aeration modes were explored using real municipal wastewater as the influent matrix. The experimental results revealed that for the R1, R2, and R3 particles during the stable period, the average removal rate of COD was 88.68%, 89.05%, and 88.96%, respectively, the average removal rate of TN was 76.97%, 71.99%, and 64.92%, respectively, the average removal rate of TP was 96.28%, 85.05%, and 78.97%, respectively, and the proportion of denitrifying phosphorus accumulating bacteria to phosphorus accumulating bacteria was 25.52%, 19.60%, and 12.77%, respectively. The results showed that the operation mode of anaerobic, aerobic, and anoxic was more conducive to the enrichment of denitrifying phosphorus accumulating bacteria (DPAOs), and that the gradient aeration was more enriched than the constant aeration mode, which is of great significance to low-intensity municipal domestic sewage treatment with an insufficient carbon source. At the same time, the dissolved oxygen in the aeration section of R1 was reduced step-by-step, which improved the simultaneous nitrification and denitrification rates of particles and the utilization rate of the internal carbon source, which was beneficial for the efficient removal of TN. The particle size of the three groups of reactors was 727.368, 815.072, and 895.041 μm respectively. As the transfer rate of the matrix decreased with particle size, the microorganisms in R2 and R3 may have caused anaerobic respiration to release harmful gas, thus damaging the particle structure, such that the particles in R2 and R3 were less dense than those in R1. In addition, the PN/PS values of R1, R2, and R3 were 6.31, 5.63, and 4.83, respectively, and the EPS content (in terms of VSS) was 103.97, 92.22, and 76.98 mg·g-1, respectively, at the time of particle stabilization, which revealed that the mode of intermittent gradient aeration was beneficial to stimulate the secretion of EPS. This was especially the case for the secretion of PN, which increased the PN/PS value, enhanced the cell hydrophobicity, and made the particles dense and stable.

Characteristics of ANAMMOX Granular Sludge and Differences in Microbial Community Structure Under Different Culture Conditions

Anaerobic ammonium oxidation (ANAMMOX) granular sludge was cultured during different operating conditions by an expanded granular sludge bed (EGSB) reactor and up-flow anaerobic sludge bed (UASB) reactors, and the characteristics of the granular sludge and microbial community were compared. The results showed that the flocculent ANAMMOX sludge can be granulated after being operated for 384 days by the EGSB and UASB reactors. The average particle size reached 1.17 mm and 1.21 mm, respectively. The particle size ratio of each range (<0.2, 0.2-1.5, 1.5-3, and>3 mm) was 6.06%, 60.05%, 25.25%, and 8.64% in the EGSB reactor, and 7.40%, 58.90%, 32.04%, and 1.66% in the UASB reactor, respectively. The results of scanning electron microscopy showed that the bacterial flora during different operating conditions were mainly Brevibacterium and Cocci aggregates. High-throughput sequencing results showed that the Shannon index of the EGSB reactor was 7.52, higher than the 7.18 of the UASB reactor on day 384; Proteobacteria was the main phylum of the sludge at each stage, and Planctomycetes increased from 3.30% to 12.30% in the EGSB reactor and 13.30% in the UASB reactor on day 384. The main ANAMMOX genera in the EGSB reactor were Candidatus Brocadia, accounting for 7.53%, followed by Candidatus Kuenenia accounting for 1.61%, whereas in the UASB reactor, Candidatus Kuenenia was the dominant anaerobic ammonia genus, accounting for 7.54%, followed by Candidatus Brocadia, which accounted for 3.69%. The proportion of dominant species was related to the change in environmental factors. The proportion of Candidatus Brocadia was positively correlated with the up-flow rate and nitrogen removal rate (NRR), but negatively correlated with hydraulic retention time (HRT). Candidatus Kuenenia was positively correlated with nitrogen removal efficiency (NRE), NRR, and HRT, but negatively correlated with the up-flow rate.

Performance of anaerobic denitrifying upflow anaerobic sludge bed bioreactor (AD-UASB)

Nitrate-containing wastewater has a severely negative impact on the ecological environment, and anaerobic denitrification process is promising biotechnology for nitrate-containing wastewater treatment. The nitrogen removal performance of anaerobic denitrifying upflow anaerobic sludge bedbioreactor (AD-UASB) and granular sludge characteristics were investigated. The results showed the maximum nitrogen removal loading rate (NRR) was reached up to 28.6 kg/(m3·d) as nitrogen loading rate (NLR) was 28.8 kg/(m3·d). At the same time, the effluent NO3 −-N concentration and total nitrogen removal efficiency of AD-UASB was 5.09 mg/L and 99.51%, and the effluent NO2 −-N concentration was as low as 10.97mg/L without obvious accumulation. As NLR was elevated to 36 kg/(m3·d), the effluent NO3 −-N and NO2 −-N concentration were sharply increased to 199.62mg/L and 453.13mg/L, respectively, Thus, the denitrifying metabolic pathway was strongly suppressed which further led to the accumulation of NO2 −-N concentration and the collapse of AD-UASB performance. The granular sludge was broken up and washed out from the reactor, and meanwhile, the concentration of MLSS and MLVSS were declined to 55.09g/L and 24.7g/L, respectively. The research can provide a beneficial reference for the anaerobic denitrification biotechnology application in nitrate-containing wastewater treatment.

Influence of operation mode and wastewater strength on aerobic granulation at pilot scale: Startup period, granular sludge characteristics, and effluent quality

This study attempted to investigate the influence of operation mode and wastewater strength on startup period, aerobic granular sludge (AGS) characteristics, and system effluent quality at pilot scale. Granulation was monitored in three pilot-scale granular sequencing batch reactors (GSBRs). Comparative evaluation of AN/O/AX/O_SBR and O_SBR, fed with wastewater of the same composition but run with completely different SBR reaction phase arrangements (alternating vs. purely aerobic), revealed the effect of SBR operation mode. Comparative study of the GSBRs operated with alternating SBR reaction phases (AN/O/AX/O_SBR and AN/O_SBR) and fed with wastewater of different strength (high- vs. medium-strength) determined the effect of wastewater composition. Granulation time and granule size were regulated by wastewater strength and the resulting organic and sludge loading conditions. Whereas, AGS morphology, granule structure, and floccular proportion of AGS were attributed to SBR operation mode. Effluent clarity in terms of suspended solid concentration depended on wastewater strength. Subtle but distinct microbial selection strategies were in effect during granulation which were also imposed by wastewater strength. Due to strong correlation between the effluent and AGS microbial structures, demonstrated by biodiversity analysis, differences in the microbial composition of effluent biomass and washout patterns of the GSBRs could be explained by wastewater strength as well. Limited nutrient removal efficiencies, restricted by organic matter concentration, could be due to involvement of unorthodox nutrient removal pathways which warrants further investigation.

Efficient treatment of traditional Chinese pharmaceutical wastewater using a pilot-scale spiral symmetry stream anaerobic bioreactor compared with internal circulation reactor

It is a technical barrier to efficiently treat traditional Chinese pharmaceutical (TCP) wastewater, due to its high chemical oxygen demanding (COD) concentration (>5000 mg/L). This study proposed and employed a spiral symmetry stream anaerobic bioreactor (SSSAB) to treat TCP wastewater. Results showed that a pilot-scale SSSAB (150 L) could achieve COD removal efficiency of 94.8% and volumetric removal rate (VRR) of 19.7 ± 0.7 kg COD·(m³·d)−1 under room temperature, which were much higher than operation performance in internal circulation (IC) anaerobic reactor (COD removal efficiency and VRR were 85% and 11.3 ± 0.8 kg COD·(m³·d)−1, respectively). The maximum COD volume removal rate could attain 43.4 kg COD·(m³·d)−1. The characteristics of granular sludge in SSSAB were investigated from both temporal and spatial scales. During the operation period, the anaerobic granular sludge in SSSAB was of higher concentration and superior properties compared to the IC anaerobic reactor. The sludge concentration exhibited a spatially decline trend, decreasing from 61 g L−1 in the bottom to 34 g·L−1at the top of the bed, yet the average biomass concentration was still higher than that in IC reactor. According to shock tests with fluctuated real wastewater. the resistance of SSSAB to hydraulic and loading shock was up to 4.3 m h−1 and 42 (kg COD· h) · (m3)−1, respectively. The study demonstrated the proposed SSSAB is a promising reactor to treat high-concentration TCP wastewater.

Performances and microbial characteristics of granular sludge for autotrophic nitrogen removal from synthetic and mainstream domestic sewage

The completely autotrophic nitrogen removal over nitrite (CANON) process is an important component of energy self-sufficient sewage treatment plants, and the use of aerobic granular sludge is a profitable choice for the CANON process. In this study, the performance and microbial characteristics of CANON granular sludge were investigated for treating synthetic and mainstream domestic sewage. The average nitrogen removal rate (NRR) was 3.22 kg N m−3 d−1 during the high-rate operating period with high MLSS (4.09 g L−1) and DO (∼1.0 mg L−1) for treating synthetic sewage. When the influent was mainstream sewage, the average NRR was 1.11 kg N m−3 d−1. The effluent nitrate concentration was very low, and nitrate build-up was not found. High-throughput pyrosequencing results indicated that, Nitrosomonas and Candidatus Brocadia were the dominant genus in ammonia oxidizing bacteria (AOB) and anaerobic AOB (AAOB), respectively. The proportions of AOB and AAOB decreased during mainstream sewage treatment, but the reactor maintained good performance. The results confirmed the feasibility of using CANON granular sludge for treating mainstream sewage.

Analysis on Performance and Microbial Community Dynamics of a Strengthen Circulation Anaerobic Reactor Treating Municipal Wastewater

A strengthen circulation anaerobic reactor (SCAR) treating artificial municipal wastewater was investigated under different volumetric loading rate(VLR) and the reactor performance, characteristics of granular sludge and microbial community structure were also tested in this experiment. The results of the experiment demonstrated that the hydraulic retention time (HRT) of 6h could be regarded as the key parameter dominating the efficient operation of SCAR reactor, in which condition the COD removal efficiency was above 75%. The coenzyme F420and the maximum specific methanogenic activity (SMA) of granular sludge increased with increasing VLR, and the EPS contents, especially TB-EPS in the granule sludge also increased obviously. Consistently, the characteristics of anaerobic granular sludge and the removal efficiency of the reactor were influenced by both sludge loading and HRT. The microbial community structure and its spatial distribution in the reactor were also affected by sludge loading, while the relative abundance of the microbial community with different metabolic characteristics in different spatial positions changed with the adjustment of the sludge loading.

Characteristics of Denitrification Inhibiting Sulfate Reducing Process

In this study, a set of two-stage UASB reactor was used to study the characteristics of denitrification inhibiting sulfate reduction in oil field gathering and transportation system and some high salt wastewater, and the characteristics of granular sludge and microbial characteristics were studied after the stable operation of the process. The results showed that the addition of NaNO2 increased the number of denitrifying bacteria (DNB) from 7.0×103 CFU·(100 mL)-1 to 7.3×105 CFU·(100 mL)-1 and remained stable in the process from start to mature. The competitive inhibition caused by DNB decreased the number of SRB from 8.0×105 CFU·(100 mL)-1 to 7.6×104 CFU·(100 mL)-1. Meanwhile, the sulfate reduction was inhibited, and the inhibition rate increased and finally stabilized to 82%. The study on mass ratio of microbial mass to nitrite effecting on denitrification efficiency showed that the inhibition rate of S2- was the highest, reaching 92%, when the mass ratio was 1200. The inhibition rate of the process could remain at about 92%, with good stability. The particle size and sedimentation rate of granular sludge were measured to determine whether the process conditions were favorable for the formation of granular sludge. The study showed that the denitrifying granular sludge formed was brown, basically ellipsoidal and spherical, with smooth surface and high density. Before the denitrification inhibition, the particle size of granular sludge was 1.0-1.4 mm and the average diameter was 1.17 mm, and after denitrification inhibition, the particle size distribution was 1.2-1.6 mm, the average particle size was 1.21 mm, which indicated that the denitrification inhibition increased the size of granular sludge. The average sedimentation velocity of denitrifying granular sludge was 47.6 m·h-1, which revealed the good settling performance of the granular sludge. The results of PCR-DGGE analysis showed that the denitrification inhibition reduced the number of microbial species from 18 to 14 and the number of dominant species decreased from 4 to 3, indicating the decreasing microbial diversity. The similarity of microbial population before and after nitrification was 62.6% and the population structure changed greatly from SRB to DNB. The number of dominant SRB species decreased from 4 to 2 after denitrification inhibition and the abundance of every species decreased obviously. The main functional bacterial species of the inhibition process was uncultured Sulfurimonas sp., which is a kind of autotrophic denitrifying bacteria. It dominated and competed with SRB for electrons, inhibiting the sulfate reduction and the production of sulfide.

Influence of carbon source on nutrient removal performance and physical–chemical characteristics of aerobic granular sludge

The impact of carbon source variation on the physical and chemical characteristics of aerobic granular sludge and its biological nutrient (nitrogen and phosphorus) removal performance was investigated. Two identical sequencing batch reactors, R1 and R2, were set up. Granular biomass was cultivated to maturity using acetate-based synthetic wastewater. After mature granules in both reactors with simultaneous chemical oxygen demand (COD), ammonium and phosphorus removal capability were achieved, the feed of R2 was changed to municipal wastewater and R1 was continued on synthetic feed as control. Biological phosphorus removal was completely inhibited in R2 due to lack of readily biodegradable COD; however, the biomass maintained high ammonium and COD removal efficiencies. The disintegration of the granules in R2 occurred during the first two weeks after the change of feed, but it did not have significant impacts on settling properties of the sludge. Re-granulation of the biomass in R2 was then observed within 30 d after granules’ disintegration when the biomass acclimated to the new substrate. The granular biomass in R1 and R2 maintained a Sludge Volume Index close to 60 and 47 mL g−1, respectively, during the experimental period. It was concluded that changing the carbon source from readily biodegradable acetate to the more complex ones present in municipal wastewater did not have significant impacts on aerobic granular sludge characteristics; it particularly did not affect its settling properties. However, sufficient readily biodegradable carbon would have to be provided to maintain simultaneous biological nitrate and phosphorus removal.

Integrated fixed-biofilm activated sludge reactor as a powerful tool to enrich anammox biofilm and granular sludge

A pilot-scale activated sludge bioreactor was filled with immobile carrier to treat high ammonium wastewater. Autotrophic nitrogen elimination occurred rapidly by inoculating nitrifying activated sludge and anammox biofilm. As the ammonium loading rate increased, nitrogen removal rate of 1.2kgNm−3d−1 was obtained with the removal efficiency of 80%. Activated sludge diameter distribution profiles presented two peak values, indicating simultaneous existence of flocculent and granular sludge. Red granular sludge was observed in the reactor. Furthermore, the results of morphological and molecular analysis showed that the characteristics of granular sludge were similar to that of biofilm, while much different from the flocculent sludge. It was assumed granular sludge was formed through the continuous growth and detachment of anammox biofilm. The mechanism of granular sludge formation was discussed and the procedure model was proposed. According to the experimental results, the integrated fixed-biofilm activated sludge reactor provided an alternative to nitrogen removal based on anammox.

Studies on the interactions of Ca2+ and Mg2+ with EPS and their role in determining the physicochemical characteristics of granular sludges in SBR system

The main objectives of the present study were to investigate the interactions of divalent metals (Ca2+ and Mg2+) with protein and polysaccharide components of extracellular polymeric substances (EPS) and to deduce their role in imparting different physicochemical characteristics to aerobic granules in sequencing batch reactor (SBR) system. Three reactors were run for 60 days; R-1 functioned as a control reactor, whereas R-2 and R-3 were operated by dosing 25mg/L of Ca2+ and Mg2+, respectively, and the other operating conditions were similar in all of the SBRs. The granulation rate, particle size and sludge settleability were rapidly increased by Ca2+ addition, whereas the sludge dewaterability was significantly enhanced by Mg2+ augmentation. During the investigations, R-1, R-2 and R-3 had 1.31, 2.98 and 1.58 times higher quantities of polysaccharides, whereas proteins were 1.28, 1.74 and 2.41 times, respectively, more abundant than seed sludge. The divalent metals profoundly changed the composition of EPS, but their total contents were almost similar. XPS and FTIR results showed that Ca2+ bonded strongly with hydroxyl groups of polysaccharides due to there being less steric hindrance than proteins, and Mg2+ preferably bonded with amide groups of proteins and found no such hindrance due to its smaller size and thus changed the composition of EPS, which eventually altered the granular sludge characteristics.

Start-up performance and granular sludge features of an improved external circulating anaerobic reactor for algae-laden water treatment.

The microbial characteristics of granular sludge during the rapid start of an enhanced external circulating anaerobic reactor were studied to improve algae-laden water treatment efficiency. Results showed that algae laden water was effectively removed after about 35 d, and the removal rates of chemical oxygen demand (COD) and algal toxin were around 85% and 92%, respectively. Simultaneously, the gas generation rate was around 380 mL/gCOD. The microbial community structure in the granular sludge of the reactor was complicated, and dominated by coccus and filamentous bacteria. Methanosphaera, Methanolinea, Thermogymnomonas, Methanoregula, Methanomethylovorans, and Methanosaeta were the major microorganisms in the granular sludge. The activities of protease and coenzyme F420 were high in the granular sludge. The intermittent stirring device and the reverse-flow system were further found to overcome the disadvantage of the floating and crusting of cyanobacteria inside the reactor. Meanwhile, the effect of mass transfer inside the reactor can be accelerated to help give the reactor a rapid start.

Influence of the organic loading rate on the performance and the granular sludge characteristics of an EGSB reactor used for treating traditional Chinese medicine wastewater

The effects of the organic loading rate (OLR) on the performance and the granular sludge characteristics of an expanded granular sludge bed (EGSB) reactor used for treating real traditional Chinese medicine (TCM) wastewater were investigated. Over 90% of the COD removal by the EGSB reactor was observed at the OLRs of 4 to 13 kg COD/(m(3) day). However, increasing the OLR to 20 kg COD/(m(3) day) by reducing the hydraulic retention time (HRT 6 h) reduced the COD removal efficiency to 78%. The volatile fatty acid (VFA) concentration was 512.22 mg/L, resulting in an accumulation of VFAs, and propionic acid was the main acidification product, accounting for 66.51% of the total VFAs. When the OLR increased from 10 to 20 kg COD/(m(3) day), the average size of the granule sludge decreased from 469 to 258 μm. There was an obvious reduction in the concentration of Ca(2+) and Mg(2+) in the granular sludge. The visible humic acid-like peak was identified in the three-dimensional excitation-emission matrix (EEM) fluorescence spectra of the soluble microbial products (SMPs). The fatty acid bond, amide II bond, amide III bond, and C-H bond bending were also observed in the Fourier transform infrared (FTIR) spectra of the SMPs. Methanobacterium formicicum, Methanococcus, and Bacteria populations exhibited significant shifts, and these changes were accompanied by an increase in VFA production. The results indicated that a short HRT and high OLR in the EGSB reactor caused the accumulation of polysaccharides, protein, and VFAs, thereby inhibiting the activity of methanogenic bacteria and causing granular sludge corruption.

Effects of Anaerobic Granular Sludge Characteristics on Initial Adsorption of Organic Pollutants

The adsorption capacity of anaerobic granular sludge is affected in varying degrees by its characteristics, thus the efficiency of anaerobic treatment of organic pollutants in wastewater is restricted by these characteristics too. This paper studied with a static batch method at the laboratory scale the effect of characteristics of anaerobic granular sludge on initial adsorption of organic pollutants in wastewater. The results showed that the initial organic pollutant adsorption efficiency of anaerobic granular sludge was significantly related with its specific surface area and extracellular polymers. When specific surface area increased to 178.9 m2g-1from 108.2 m2g-1, the adsorption efficiency was increased by 6.1% from 70.2% to 76.3%;the increase of extracellular polymer content raised the adsorption rate by about 6.0%; the increase of hydrophobic and Zeta potential of anaerobic granular sludge could also greatly improve the adsorption efficiency of organic pollutants by 15.6%and 10.2% respectively. The initial organic pollutant adsorption performance presented a parabolic curve with increase of the sludge particle size, settling velocity and sludge volume index of anaerobic granular sludge. The above results indicated significant effect of the characteristics of anaerobic granular sludge itself on its adsorption removal efficiency of organic pollutants in waste water. Therefore, cultivating anaerobic granular sludge with excellent adsorption performance is a key to improving anaerobic biological treatment efficiency of organic wastewater.

Physicochemical and Morphological Characteristics of Granular Sludge in Upflow Anaerobic Sludge Blanket Reactors

Granular sludge formed in upflow anaerobic sludge blanket reactors play an important role in the field of anaerobic treatment due to their engineering advantages over conventional flocculent forms, such as rich microbial diversity, high solid retention time due to its superior settling characteristics, maximizing the microorganisms-to-space ratio, and greater ability to withstand shock loadings or temperature changes. A better understanding of granule characteristics is highly useful and vital for efficient operation of bioreactors. Recently, developments in the characterization of microbial granules have been made with innovative approaches and sophisticated technologies. This article provides an up-to-date review from the past two decades in the understanding of physicochemical and morphological characteristics of granular sludge with regard to granule size, settling velocity, specific gravity, sludge volume index, volatile suspended solids–to–suspended solids ratio, ash content, inorganic chemical content, crystalline structure, molecular functional groups, microbial structure and composition, microbial communities, and methanogenic activity. Addition of external additives such as synthetic and natural polymers and vitamins may enhance the characteristics of granular sludge. Bioaugmentation might be a useful tool for improving the stability and significantly reducing the length of start-up periods. Application of easily degradable cosubstrates such as glucose, sucrose, cellulose, molasses solution, and volatile fatty acids is highly beneficial in treating toxic wastewaters and improving sludge characteristics. Emerging knowledge on such characteristics might exhibit the optimization of microbial granulation as one of the most reliable techniques in anaerobic treatment. Future research directions are also highlighted.