Formation Of Aerobic Granular Sludge Research Articles

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

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

The potential effects of N-Acyl homoserine lactones on aerobic sludge granulation during phenolic wastewater treatment

The formation of aerobic granular sludge (AGS) is relatively difficult during the treatment of refractory wastewater, which generally shows small granular sizes and poor stability. The formation of AGS is regulated by N-Acyl homoserine lactones (AHLs)-mediated quorum sensing (QS). However, the potential role of AHLs in AGS formation under the toxic stress of refractory pollutants and the heterogeneity in the distribution and function of AHLs across different aggregates are not well understood. This study investigated the potential effects of AHLs on the formation of AGS during phenolic wastewater treatment. The distribution and succession of AHLs across varying granular sizes and development stages of AGS were investigated. Results showed that AGS was successfully formed in 13 days with an average granular size of 335 ± 39 μm and phenol removal efficiency of >99%. The levels of AHLs initially increased and then decreased. C4-HSL and 3-oxo-C10-HSL were enriched in large granules, suggesting they may play a pivotal role in regulating the concentration and composition of extracellular polymeric substances (EPS). The content of EPS constantly increased to 149.4 mg/gVSS, and protein (PN) was enriched in small and large granules. Luteococcus was the dominant genus constituting up to 62% after the granulation process, and exhibited a strong association with C4-HSL. AHLs might also regulate the bacterial community responsible for EPS production, and pollutant removal, and facilitate the proliferation of slow-growing microorganisms, thereby enhancing the formation of AGS. The synthesis and dynamics of AHLs were mainly governed by AHLs-producing bacterial strains of Rhodobacter and Pseudomonas, and AHLs-quenching strains of Flavobacterium and Comamonas. C4-HSL and 3-oxo-C10-HSL might be the major contributors to promoting sludge granulation under phenol stress and play critical roles in large granules. These findings enhance our understanding of the roles that AHLs play in sludge granulation under toxic conditions.

The impact of reduced sulfur compounds on aerobic granular sludge formation and biological phosphorus removal

Biological sulfur conversion combined with phosphorus removal represents an innovative biotechnology for activated sludge (AS). However, its effect on the formation of aerobic granular sludge (AGS) remains unclear. This study aimed at determining the impact of sulfide and thiosulfate on the performance of enhanced biological phosphorus removal (EBPR) and on AGS formation. Using two lab-scale sequencing batch reactors (SBR), we compared EBPR performance, the degree of granulation, and the enriched microbial community with sulfide (SBR-S, 20 mg S/L) or thiosulfate (SBR-T, 140 mg S/L) as primary sulfur source. Results indicate that both reactors achieved comparable EBPR performance, with a phosphorus removal rate of 98% in SBR-T and 99% in SBR-S. SBR-T resulted in compact granules with fast settling properties, while SBR-S resulted in dense floccular sludge, referred to as “densified sludge”. Both systems enriched a comparable microbial community with shared dominant genera, including Ca. Competibacter, Thiothrix, Ca. Accumulibacter and Dechloromonas. The higher abundance of Thiothrix unzii throughout the operating time in SBR-T, reaching 19.4%, is believed to have enhanced the granulation process. This study provides important insight into the role of reduced sulfur compounds in sludge densification and EBPR performance, relevant to sulfur-rich wastewaters such as those from industrial sources.

Optimizing the formation of aerobic granular sludge and enhanced pollutant removal efficiency in a constant current variable voltage electric field

Aerobic granular sludge (AGS) disintegration occurs during long-term operation, decreasing particle settling performance and deteriorating the pollutant removal effect. Therefore, this experiment proposes an electric field synergistic AGS construction to improve the strength of particles and the efficiency of nitrogen and phosphorus removal. The study revealed that under the influence of an electric field, iron ions dissolved from the iron electrode and phosphate formed mineral nuclei inside the particles, which effectively increased the average size of the particles and increased the protein content of extracellular polymeric substances (EPS). The experimental results demonstrated that including Fe–C electrodes in the electric field group increased the TN removal rate to 86.65%, surpassing the rates observed in the blank without an electric field and C–C electrode electric field groups by factors of 1.13 and 1.11, respectively. Under the electric field, AGS enriched some functional microorganisms for denitrogenation, thus improving total nitrogen removal efficiency. Furthermore, the phosphorus removal efficiency in the electric field group featuring Fe–C electrodes exhibited a notable enhancement, reaching 90.16%. This improvement was 1.71 and 1.62 times that of blank without an electric field and C–C electrode electric field groups, respectively. The phosphorus removal efficacy of electrode-released iron is distinct from that of exogenous ferrous sulfate, with the former demonstrating superior activity and pronounced phosphorus removal capabilities. Therefore, this study comprehensively revealed AGS construction mechanism and pollutant removal efficacy under the electric field's synergistic effect.

Roles of n-hexadecane in the degradation of dibenzofuran by a biosurfactant-producing bacterium Rhodococcus sp.

The hydrophobic nature of dioxins is a major obstacle to their bioremediation. The present study attempted to improve the bioaccessibility of dioxins in two-phase partitioning bioreactors and activated sludge reactors. Dibenzofuran and n-hexadecane were used as model compounds for dioxins and non-aqueous phase liquids (NAPLs), respectively. First, biosurfactants produced by dioxin-degrading Rhodococcus sp. strain p52 were analyzed. Then, the role of n-hexadecane during the biodegradation of dibenzofuran was evaluated. The results showed that high NAPL ratios (n-hexadecane ≥40 g/L) in the two liquid-phase systems favored dibenzofuran removal, while the cell surface of strain p52 became extremely hydrophobic (>97%), which promoted its adhesion to NAPLs and subsequent transport of dibenzofuran from NAPL to the cells. In addition, a bioaugmented activated sludge reactor with n-hexadecane as the supplemented carbon source could not only facilitate the aerobic granular sludge formation but also improve dibenzofuran removal and the activated sludge settling properties. Simultaneously, conjugative transfer of catabolic plasmids was promoted. This study demonstrated the potential application of strain p52 with NAPLs for the bioremediation of dioxins.

Effects of high-concentration influent suspended solids on aerobic granulation in sequencing batch reactors treating real textile wastewater

The formation of aerobic granular sludge (AGS) in real textile wastewater (TWW) is time-consuming and challenging. The present study investigated the effects of high-concentration influent suspended solids (SS) on aerobic granulation, pollutant removal, microbial activity, and community in the real TWW treatment by using two sequencing batch reactors (R1: 41.7 ± 22.8 mg influent-SS/L; R2: 416.1 ± 21.4 mg influent-SS/L). The results showed that complete granulation was achieved in R1 within 97 days (SVI30: 34.5 mL/g, SVI30/SVI5 = 0.91), while it only required 52 days in R2 (SVI30: 18.2 mL/g, SVI30/SVI5 = 0.92). The high-concentration influent SS also enhanced compactness and settleability of AGS. Long-term adaption of sludge improved the COD removal from real TWW, which was possibly due to the increase in phyla Firmicutes and Actinobacteria abundances. The real TWW did not adversely affect the nitrification process as indicated by the high NH4+-N removal in both reactors (>93 %). Although the formation of compact AGS in R2 did not exhibit better removal performance under the present experimental condition, it exhibited the potential for better COD removal from real TWW as indicated by the higher microbial activity and functional bacterial abundances in R2 than in R1.

Study on the formation process and mechanism of aerobic granular sludge in the sequencing batch biofilter granular reactor.

Sequencing batch biofilter granular reactor (SBBGR) is a promising wastewater treatment technology owing to its low sludge yield and good toxicity tolerance. However, little attention has been paid to the formation process and mechanism of aerobic granular sludge in SBBGR. This study systematically investigated the formation process and mechanism of aerobic granular sludge in an SBBGR to provide a theoretical basis for optimizing the culture of aerobic granular sludge. Aerobic granular sludge with good performance was successfully cultivated after 40 days of incubation using synthetic wastewater as feed: the mixed liquid suspended solids and mixed liquor volatile suspended solids increased from 3.85 and 1.85 g/L to 31.38 and 24.74 g/L respectively, and the COD, TN, and TP removal efficiencies were 91.21%, 84.99%, and 58.14%, respectively. The experimental results showed that Amoebacteria and Bacteroides played an important role in the formation of aerobic granular sludge, filamentous bacteria acted as a three-dimensional skeleton surrounded by filling bacilli and rod-shaped bacteria, and proteins played a dominant role in promoting granulation during the culture process.

Insight into the effect of particulate organic matter on sludge granulation at the low organic load: Sludge characteristics, extracellular polymeric substances and microbial communities response

This paper investigated the effect of particulate organic matter (POM) on sludge granulation under low organic load. The results showed that POM promoted the formation of aerobic granular sludge (AGS) with a chemical oxygen demand (COD) fraction of 25%, and POM also enhanced the sludge settleability and biomass retention. However, when the COD fraction of POM increased to 50% and 75%, the AGS performance deteriorated. The analysis of extracellular polymeric substances revealed that the POM (accounted for ≤ 50% of COD in the influent) suppressed the secretion of extracellular protein. Analysis of the microbial community showed that species diversity was lower in the POM-fed system, with Rhodocyclaceae being the predominant bacteria responsible for carbon source degradation. Additionally, molecular ecological network analysis demonstrated that when the COD fraction of the POM exceeded 50%, the connectivity and modularity between microbial species decreased, which may explain the sludge performance deterioration.

REVIEW OF AEROBIC GRANULAR SLUDGE TECHNOLOGY AND APPLICATION IN WASTEWATER TREATMENT

This paper focuses on introducing an overview of aerobic granular sludge technology, granulation, removal efficiency and application of aerobic granules in wastewater treatment. Aerobic granular sludge has a bacterial layered structure including anaerobic, anoxic and aerobic bacteria in order from inside to outside layer, so it is capable of simultaneous chemical oxygen demand, nitrogen and phosphorus removal. Granular sludge also has capacity to remove persistent organic substances and adsorb heavy metals. As a result, aerobic granular sludge technology can be effectively applied for municipal and industrial wastewater treatment. Many wastewater treatment plants applying aerobic granular sludge technology have been deployed, most commonly in Europe and especially in the Netherlands, which is the first place to apply this technology in practical wastewater treatment with Nereda® trademark. However, aerobic granular sludge is stable on batch reactors and takes months to form stable granular sludge. Therefore, it is necessary to have further researches on the granulation mechanism and affective factors to shorten the time of aerobic granular sludge formation as well as maintain the long-term stability of the granular sludge and develop continuous reactors to maintain the stability of the aerobic granular sludge to meet the requirement of wastewater treatment plants in practice.

The knock-on effects of different wastewater feeding modes: Change in microbial communities versus resistance genes in pilot-scale aerobic sludge granulation reactors

To explore the effects of wastewater feeding modes on the formation of aerobic granular sludge (AGS) and the complex relationships between resistance genes and bacteria, two pilot-scale sequencing batch reactors (SBRs) were established. The SBR with influent wastewater introduced uniformly through pipes at bottom was designated as BSBR, and the SBR with inlet wastewater flowing directly from top was TSBR. BSBR formed dense AGS due to uniform wastewater feeding at bottom, while TSBR failed to cultivate AGS. Metagenomic sequencing illustrated that rapid growth of AGS in BSBR was accompanied with increase of antibiotic resistance genes (ARGs) abundance, but ARGs diminished when the size of AGS was stable. The ARGs continued to elevate in TSBR, and abundance of metal resistance genes (MRGs) was always higher than that in BSBR. Two reactors had markedly different bacterial community, microbes in BSBR owned stronger activity, conferred greater potential to proliferate. AdeF in two systems had the most complex gene-bacteria relationships which would undergo HGT within bacterial genus. The different feeding modes of wastewater directly led to the changing size of sludge, which caused knock-on effects of variations in the abundance of microbial communities and resistance genes. This study provided promising suggestions for the rapid cultivation of AGS and control of resistance genes at pilot-scale.

Aerobic granular sludge formation and stability in enhanced biological phosphorus removal system under antibiotics pressure: Performance, granulation mechanism, and microbial successions

Wastewater containing antibiotics can pose a significant threat to biological wastewater treatment processes. This study investigated the establishment and stable operation of enhanced biological phosphorus removal (EBPR) by aerobic granular sludge (AGS) under mixed stress conditions induced by tetracycline (TC), sulfamethoxazole (SMX), ofloxacin (OFL), and roxithromycin (ROX). The results show that the AGS system was efficient in removing TP (98.0%), COD (96.1%), and NH4+-N (99.6%). The average removal efficiencies of the four antibiotics were 79.17% (TC), 70.86% (SMX), 25.73% (OFL), and 88.93% (ROX), respectively. The microorganisms in the AGS system secreted more polysaccharides, which contributed to the reactor's tolerance to antibiotics and facilitated granulation by enhancing the production of protein, particularly loosely bound protein. Illumina MiSeq sequencing revealed that putative phosphate accumulating organisms (PAOs)-related genera (Pseudomonas and Flavobacterium) were enormously beneficial to the mature AGS for TP removal. Based on the analysis of extracellular polymeric substances, extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, and microbial community, a three-stage granulation mechanism was proposed including adaption to the stress environment, formation of early aggregates and maturation of PAOs enriched microbial granules. Overall, the study demonstrated the stability of EBPR-AGS under mixed antibiotics pressure, providing insight into the granulation mechanism and the potential use of AGS for wastewater treatment containing antibiotics.

Inductive effect of functional microbial consortia in promoting the rapid granulation of aerobic granular sludge in an internal circulation-membrane bioreactor

The added functional microbial consortia (SAB) was found to accelerate the formation of aerobic granular sludge (AGS) in a continuous experiment lasting 150 days, where the primary AGS was first observed on day 7 and the bioreactor was started-up very quickly and performed well in removing the main pollutants. According to the obtained results, Streptomyces sp. Esraa could form a skeleton to support the formation of AGS, while Bacillus cereus aggregated microorganisms by secreting a large amount of extracellular polymeric substances (mainly protein) continuously, and extracellular polymeric substances immediately increase from 97 mg/gMLVSS to 1551 mg/gMLVSS. With the succession of microbial community, the abundance of Streptomyces and Bacillus in sludge decreased significantly on day 21, from 43.22% to 1.78% and from 5.87% to 0, respectively, while the abundance of Bacillus in AGS remained 0.1% on day 120, and SAB was gradually replaced by other dominant microorganisms, which indicated that the added SAB exhibited an inductive effect on the formation of AGS.

Environmentally relevant level of perfluorooctanoic acid affect the formation of aerobic granular sludge

The growing increasing occurrence of perfluorooctanoic acid (PFOA) in wastewater has raised concerns about its potential impact on the environment. Nevertheless, the impact of PFOA at environmentally relevant level on the formation of aerobic granular sludge (AGS) is still a ‘black box’. This study thus aims to fill this gap by comprehensive investigation of sludge properties, reactor performance and microbial community during the formation of AGS. It was found that 0.1 mg/L PFOA delayed the formation of AGS, causing relatively lower proportion of large size AGS at the end of operation process. Interestingly, the microorganisms contribute to the reactor's tolerance to PFOA by secreting more extracellular polymeric substances (EPS) to slow or block the entry of toxic substances into the cells. During the granule maturation period, the reactor nutrient removal especially chemical oxygen demand (COD) and total nitrogen (TN) were affected by PFOA, decreasing the corresponding removal efficiencies to ∼81.2% and ∼69.8%, respectively. Microbial analysis further revealed that PFOA decreased the abundances of Plasticicumulans, Thauera, Flavobacterium and Cytophagaceae_uncultured, but it has promoted Zoogloea and Betaproteobacteria_unclassified growth, which maintained the structures and functions of AGS. The above results revealed that the intrinsic mechanism of PFOA on the macroscopic representation of sludge granulation process was revealed, and it is expected to provide theoretical insights and practical support for direct adoption of municipal or industrial wastewater containing perfluorinated compounds to cultivate AGS.

Understanding the role of polyurethane sponges on rapid formation of aerobic granular sludge and enhanced nitrogen removal

Long formation time and limited simultaneous nitrification–denitrification (SND) are still the problems for aerobic granular sludge (AGS) application. This study presents a novel strategy to simultaneously promote sludge granulation and enhance nitrogen removal. This new approach consists of adding polyurethane sponges (PUS) and applying intensive aeration periodically. To demonstrate the effectiveness of this strategy and understand the role of PUS, two sequencing batch reactors (R1: without PUS; R2: PUS addition) were used. The results show that the granulation time in R2 (14 days) was much shorter and the nitrogen removal (80.7 %) was much higher when compared to the R1 (75 days and 64.8 %). Biofilm was rapidly formed on PUS because of the porous network structure, resulting in the low suspended biomass concentration. Thus, a close to discrete non-flocculent settling type was created, which promoted the selection of well-settling aggregates rapidly and efficiently. Meanwhile, biofilm was detached from PUS by intensive aeration, providing the nucleus (fragments of biofilm) in-suit for microbial adhesion. Under the combined effects, the aerobic granulation process was significantly accelerated. The total biomass amount was maintained during initial granulation because of the rapid biofilm formation, resulting in the stable removal of NH4+-N at a rapid start-up period. The rapid formation of biofilm and fast granulation created more anoxic zones during aeration and thereby enhanced SND. The biofilm formation also increased the relative abundances of aerobic denitrifiers (Dokdonella and Denitratisoma), autotrophic denitrifiers (Sulfuritalea), and hydrolytic/fermentativebacteria (Ferruginibacter, Opitutus, and Lactobacillus), which enhanced the SND performance and endogenous denitrification.

Physical Characteristics and Removal Performance of Aerobic Granular Sludge in Biological Treatment of Domestic Wastewater

This study aims to demonstrate the formation of aerobic granular sludge (AGS) for domestic wastewater treatment applications in hot climate and low humidity conditions (e.g. Saudi Arabia) as well as to characterize and examine the bioreactor performance in removing organic matter and nutrients. Based on the study, aerobic granular sludge (seeded with domestic activated sludge from Al-Madina Wastewater Treatment Plant and fed with synthetic wastewater with an organic loading rate (OLR) of 1.6 kg COD m−3d−1) was successfully cultivated with average size ranging from 1 to 2 mm in a laboratory scale sequencing batch reactor (SBR) system operated at 30 days with a complete cycle time of 3 h and at the working temperature of 30 ± 1°C. Results also showed that the aerobic granular sludge formed had excellent settling ability (settling velocity, 38.98 mh−1 and MLSS, 7.8 gL−1) and great removal performance of COD and nutrient (i.e. more than 90%).

Do increased organic loading rates accelerate aerobic granulation in hypersaline environment?

It is a common sense that high organic loading rate (OLR) leads to the faster formation of aerobic granular sludge (AGS), while the effects of increased OLR on the direct development of salt-tolerant aerobic granular sludge (SAGS) in hypersaline wastewater is still unknown. In this study, four identical sequencing batch reactors (SBRs) were directly fed with 3% salinity wastewater and operated at different OLRs to cultivate SAGS. Granules firstly appeared on Day 10, 7, 5, and 8, and dominated on Day 23, 16, 10, and 13 in four SBRs operated under OLR of 2.4, 3.6, 4.8, and 7.2 kg COD/m3·d, respectively. The former three granules matured on Day 29 (D50 of 550 µm), 25 (D50 of 639 µm), and 25 (D50 of 808 µm), respectively, while the loose and fluffy filamentous granules cultivated under the highest OLR failed to reach the traditional criterion of AGS. Overall, increased OLR could accelerate the formation of AGS that had larger sizes and lower microbial diversities. However, unlike salt-free wastewater, the appropriate OLR for rapid formation of compact AGS in hypersaline wastewater was only 3.6 kg COD/m3·d, since the higher OLRs with higher hydraulic selection pressure led to the massive sludge loss and the formation of instable fluffy granules during granulation period. Bacterial community analysis revealed Corynebacterium, Marinobacterium, Paracoccus, Halomonas, and Vibrio were the main genera in four SBRs, in which Corynebacterium had certain abundance at all OLRs, and Vibrio and Paracoccus favored low OLR, while Halomonas and Marinobacterium dominated the SBRs with high OLRs. This study contributed to a better understanding of SAGS granulation under different OLR conditions in hypersaline wastewater.

Insights into function of hydrocyclone separator and modified volcanic rock coagulant on formation of aerobic granular sludge

AbstractHydrocyclone separator and novel coagulants were adopted to separately enhance the granulating process of aerobic granular sludge. For hydrocyclone separator, although there was no obvious large particle, it was feasible to improve the sludge sedimentation capacity, indicated by the sludge volume index. Moreover, the nitrogen removal performance was promoted by the separator with a nitrogen removal rate of 8.2 mg/(L·h), nearly two times of system without a separator. Meanwhile, nitrogen‐related microbial communities were stimulated, for example, Thauera and Nitrosomonas. Another method of coagulation by the modified volcanic rock promoted the sludge settling performance. The optimum coagulating conditions were the coagulant size of 100 μm with dosage of 6 g/L. The addition of polyacrylamide played a weak role in granulation. Overall, the role of hydrocyclone separator and modified volcanic rock coagulant belonged to the improvement of the settleability of sludge and the aggregation of sludge, respectively.

Effects of oxytetracycline on aerobic granular sludge process: Granulation, biological nutrient removal and microbial community structure

Formation of aerobic granular sludge (AGS), process performance and microbial community structure were investigated in lab-scale sequencing batch reactors (SBR) operated without and with oxytetracycline (OTC). Granulation of activated sludge and appearance of AGS was observed in parallel SBRs operated without and with OTC. However, formation of well-settling aerobic granules was relatively faster in the SBR fed with 100 μg/L OTC and observed within 2 weeks of start-up. Ammonium, total nitrogen, and phosphorus removals were quickly established in the AGS cultivated without OTC. In contrast, nitrogen and phosphorus removals were lower in the OTC fed SBR. But, a gradual improvement in nitrogen and phosphorus removals was observed. After 45 days, nitrogen and phosphorous removals were stabilized at 99% and 70%, respectively, due to establishment of OTC-tolerant community. qPCR revealed the impact of OTC on ammonium oxidizing bacteria, polyphosphate accumulating organisms and their enrichment during exposure to OTC. Ammonium and phosphorus were majorly removed via nitritation-denitritation and enhanced biological phosphorus removal (EBPR) pathways, respectively, in the presence of OTC. Brevundimonas (35%), Thaurea (14%) sp. Ca. Competibacter (5.6%), and Ca. Accumulibacter (4.2%) were enriched in OTC-fed AGS. Of the two OTC-tolerant strains isolated, Micrococcus luteus exhibited growth and efficient OTC biotransformation at different OTC concentrations. Moreover, M. luteus was predominantly growing in the form of aggregates. Key traits such as tolerance, biotransformation and high autoaggregation ability allowed a niche for this strain in the granules. This work has important implications in understanding the effect of antibiotics on AGS and designing AGS based treatment for antibiotic-laden wastewaters.

Influence of temperature on aerobic granular sludge formation and stability treating municipal wastewater with high nitrogen loadings

This study investigated the influence of temperature (20 and 30 °C) on the formation and stability of aerobic granules in sequential batch reactors (SBR). Therefore, two lab-scale SBRs operated at 20 and 30 °C (SBR20 and SBR30) were used. The reactors were fed with municipal wastewater (CODt:TN:TP 100:15:1.7), leading to mean organic loading rates (OLR) of 1.3 ± 0.4 kgCODt m−3 day−1. Both reactors had the same height/diameter ratio of 4.2 and were inoculated with activated sludge from a municipal wastewater treatment plant. The operational conditions were also the same for both temperatures and lasted in stable process parameters for over 100 days. By optimizing the aeration and oxygen concentration, a high removal efficiency of NH4–N (∼99%) and COD (∼90%) was achieved in both reactors, despite the poor C:N:P ratio at the influent. Furthermore, a relatively low oxygen concentration of 2 mg L−1 was defined as the set point for the control strategy. Nevertheless, granulation at 30 °C was significantly faster, resulting in more stable sludge volume index (SVI) values (SVI10/SVI30 < 1.1). The granules formed at 30 °C were also larger, more compact, and considerably more stable against system disturbances. However, at higher temperatures, larger granules might be required for nitrate removal because of the increased oxygen diffusion rates. Finally, microbiological 16S rRNA gene amplicon analysis for both systems indicated major differences relatively to the inoculum sludge only for nitrogen-degrading organisms.

The formation of aerobic granular sludge for the treatment of real landfill leachate using a granular sequencing batch reactor at a constant volume

AbstractLeachate generated in a landfill may not be treated by conventional biological treatment due to its nature and complexity. The process of forming aerobic granules in batch sequencing reactors having features such as; reducing the settling process time and saving energy consumption and high decomposition rate have been noticed by researchers. In the present study, the structure of sequencing batch reactors (SBRs) was evaluated for the formation of granules, which were subsequently utilized for the treatment of landfill leachate. The experiment was initiated by using the GSBR, containing 1200 ml with different apparatuses, to develop granular sludge, and synthetic wastewater was added to reinforcement. The selected parameters for the operational hydraulic retention time (HRT) of the wastewater (6‐h cycles) included feeding, idle, aeration, settling, and discharge. Furthermore, the controlled conditions were the dissolved oxygen (DO) range of 2–2.2 mg/L, temperature range of 20–23℃, and pH of 7.5–8.3. The chemical oxygen demand (COD), mixed liquor suspended solids (MLSS), and sludge volume index (SVI) daily were measured at the influent and effluent of GSBR reactor. The main properties of aerobic granular sludge were identified during the research procedures, and the remarkable settling and potent, high‐density microbial structure of the granules were confirmed. The mean size of the formulated granules was estimated at 7.46 ± 1.8 mm, and the volume of the biomass also increased from approximately 1607 to 4137 mg/L through the granulation process. Moreover, 98% of the influent chemical oxygen demand (COD) could be removed by the formulated granular sludge, and the final‐stage organic loading rate was estimated at 5.65 COD/m3/day. According to the results, GSBRs could be employed for the formulation of aerobic granular sludge for the treatment of landfill leachate.