Sludge Volume Index Research Articles

Research on the treatment of rice paper processing wastewater on a household scale by Upflow sludge blanket filtration model

This paper presents wastewater treatment from the rice paper processing at the household level using the Upflow sludge blanket filtration (USBF) model. The research team set up the experiment at the laboratory level with a capacity of 108 l/day. After 12 days of activation, the activated sludge reached: microbial density 2.8x1011 CFU/ml, sludge volume SV30 380 ml/l, sludge volume index SVI 116.6 ml/g with tested parameters including DO=2.5; pH=7; COD=1,000 mg/l, and testing duration of 16 hours. The treating performance was relatively high with total suspended solids TSS, COD, and BOD5 of 72, 91, and 95%, respectively. The quality of treated wastewater met the standards in Column B, the Vietnamese National Regulation for Industrial Wastewater Quality (QCVN 40:2011/BTNMT).

Analysis of 1H-benzotriazole removal efficiency from wastewater in individual process phases of a sequencing batch reactor SBR

The research focused on a very dangerous and commonly used compound which has carcinogenic and mutagenic impact on living organisms. 1H-benzotriazole (1H-BTR) is used as a corrosion inhibitor for installations in industrial plants, in the production of biocides, detergents, drugs, tires, rubber, in refrigeration systems and de-icing substances, while its derivates are UV stabilizers in plastics, paints, films and sunscreens. It is also an additive in petroleum products (lubricants, hydraulic fluids). The paper presents quantitative changes of 1H-BTR after sequencing batch reactor (SBR) process. The studies have been carried out for 411 cycles of SBR during which concentration of 1H-BTR was changed in the range of 50–1000 μg L−1. SBR operating cycle consisted of 6 phases: filling (dilution-40 min), mixing I (dephospatation-20 min), aeration with stirring (nitrification and oxidation of organic compounds-300 min), mixing II (denitrification-30 or 60 min), settling and decantation (separation-40 min), downtime (90 or 60 min). The technological parameters of the activated sludge (sludge volume index, solids and hydraulic retention time) were as similar as possible to those maintained in the real wastewater treatment plant (WWTP). Mixed liquor suspended solids concentration was 3.50 kg m−3. Conducted studies showed that industrial wastewater containing 1H-BTR can be effectively treated in SBR. The conducted studies showed that removal of 1H-BTR with more than 80% efficiency is possible at effluent concentrations not exceeding 200 μg L−1. Higher concentrations of 1H-BTR in wastewater lead to a sharp decrease in removal efficiency. The lowest removal efficiency (56.6%) was recorded at the initial 1H-BTR concentration of 100 μg L−1. On the other hand, the highest efficiency (88.2%) at the initial concentration of 1000 μg L−1. The concentration of 1H-BTR in treated wastewater was 1.1 μg L−1 in the control reactor and from 7.2 to 434.0 μg L−1 for an initial concentration from 50 to 1000 μg L−1, respectively. The aeration phase was superior in terms of 1H-BTR removal, regardless of the benzotriazole doze in the raw wastewater. In the anaerobic mixing phases I and II in the SBR, the decomposition of the 1H-BTR was 5.3 and 4.9 times slower, respectively, compared to aerobic conditions.

Densification of activated sludge for better settling performances: experimental characterization in batch column and model parameters calibration.

Conventional activated sludge (CAS) and densified sludge obtained using hydro-cyclone selective wasting were compared at a full-scale water resources recovery facility. The densified tested sludge, containing around 30-50% of aerobic granules, showed enhanced settleability with low and stable sludge volume index (SVI) compared to CAS, which suffered recurrent filamentous bulking. Further in-depth batch settling tests were carried out using a 40 cm diameter column fitted with ultrasonic transducers to monitor both sludge blanket height and vertical velocity profiles. Hindered settling and compression parameters were calibrated from the experiment for latter modelling use. Test sludge displayed more than doubled settling velocities compared to CAS, with hindered settling velocities remaining >3 m·h-1 even at high solids concentrations of 6.85 g·L-1. The compression regime was attained at much higher critical concentration for the test sludge. It also displayed enhanced thickening properties, with concentrations obtained after 30 min of settling being 20.9 and 8.5 g·L-1 respectively for test and control sludge. This allows for a substantial reduction of recirculation rates in practice. These results open perspectives in optimizing existing plant operation as well as clarifier design and modelling using densified sludge.

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.

Prediction of Sludge Volume Index in a Wastewater Treatment Plant Using Recurrent Neural Network

Sludge Volume Index (SVI) is one of the most important operational parameters in an activated sludge process. It is difficult to predict SVI because of the nonlinearity of data and variability operation conditions. With complex time-series data from Wastewater Treatment Plants (WWTPs), the Recurrent Neural Network (RNN) with an Explainable Artificial Intelligence was applied to predict SVI and interpret the prediction result. RNN architecture has been proven to efficiently handle time-series and non-uniformity data. Moreover, due to the complexity of the model, the newly Explainable Artificial Intelligence concept was used to interpret the result. Data were collected from the Nine Springs Wastewater Treatment Plant, Madison, Wisconsin, and the data were analyzed and cleaned using Python program and data analytics approaches. An RNN model predicted SVI accurately after training with historical big data collected at the Nine Spring WWTP. The Explainable Artificial Intelligence (AI) analysis was able to determine which input parameters affected higher SVI most. The prediction of SVI will benefit WWTPs to establish corrective measures to maintaining stable SVI. The SVI prediction model and Explainable Artificial Intelligence method will help the wastewater treatment sector to improve operational performance, system management, and process reliability.

Quick and enhanced separation of Eosin Yellow dye from aqueous solution by FeCl3 interaction: thermodynamic study and treatment cost analysis

ABSTRACT Dyes and their metabolites have noxious and carcinogenicity potential and are known to be hazardous for human beings and other living organisms. The discharge of untreated wastewater comprising wide varieties of synthetic dyes into the water resources is one of the vital environmental problems. Therefore, in this study, the efficacy of the chemical coagulation method was explored using ferric chloride as a coagulant to remove the toxic dye Eosin Yellow (EY) from aqueous solution. The interaction between FeCl3 and EY dye was quick and profound at a solution pH of 2.2, yielding the brownish precipitate with a dye removal efficiency of more than 98%. An extremely high dye removal capacity of 1263 mg/g is reported for 100 mg/L of EY dye concentration at optimum experimental conditions. The possible chemical interaction between FeCl3 and EY dye can be attributed to the formation of polymeric complex, as oxygen atoms of carbonyl, phenolate and carboxylate groups of EY dye molecule interact strongly with Fe3+ ions. The presence of various coexisting anions could reduce the EY dye removal efficiency by 2%–5%; however, the required FeCl3 dose has increased from 64 to 170 mg/L. Thermodynamic studies showed that the interaction of EY dye with FeCl3 was exothermic and spontaneous in nature. The investigation of real industrial wastewater samples has exhibited a 90%–215% increase in the required FeCl3 dose as compared to the control experiment for the initial EY dye concentration from 100 to 750 mg/L. Sludge volume index analysis indicates that FeCl3 generated highly dense sludge with good settling characteristics. X-ray diffraction and field emissionscanning electron microscopy characterisation of the generated sludge indicate the polycrystalline nature with a combination of spherical and irregular shape grains of the sludge. Treatment cost analysis revealed that the cost involved in dye removal is in the range of 0.99–3.60 USD ($)/kg of dye removed.

Comparison of Effluent Suspended Solid Concentrations from Two Types of Rectangular Secondary Clarifiers

Secondary clarifiers play a significant role in the successful operation of activated sludge systems. Because of the restriction of available land, South Korean domestic wastewater treatment plants tend to employ rectangular clarifiers to settle mixed liquor suspended solids (MLSS) for activated sludge systems. A high MLSS concentration must be maintained in the bioreactor to ensure nitrification during winters, and achieve stringent effluent quality. The effluent suspended solid (SS) concentrations of two clarifier types currently being used in South Korea, primary rectangular clarifier-type and Gould Type I secondary clarifiers, were compared using computerized fluid dynamic simulations and hourly secondary effluent suspended solid concentrations. In addition, operational data such as hourly influent flow, daily MLSS concentrations, and sludge volume index were obtained and reviewed. This comparison reveals that the Gould Type I secondary clarifier is resilient to loading variation and produces effluent with a consistently lower suspended solid concentration than the primary rectangular clarifier-type under similar loading conditions and higher loading variations. The results suggest that the existing primary rectangular clarifier-type secondary clarifiers must be converted to Gould Type I.

Development and long-term operation of aerobic granular system for simultaneous removal of COD, nitrogen, and phosphorous in a conical SBR

This study evaluates the performance of a simple sequencing batch reactor (SBR) with conical geometric configuration in terms of aerobic granulation and simultaneous removal of COD, nitrogen, and phosphorous from synthetic wastewater. The reactor was operated for 328 days in 3 different phases. Stable granules measuring around 0.9±0.3 mm with good settling properties were formed in phase III of operation. Optimum removals of COD (90%), NH4+-N (91%), total nitrogen (87%), and PO43--P (83%) were achieved in phase III, while the influent concentrations were COD (640±32 mg/L), NH4+-N (53±2.5 mg/L), and PO43--P (9±0.6 mg/L). Mixed liquor suspended solids increased from 0.26 g/L to 2.3 g/L while sludge volume index (SVI30) decreased from 380 mL/g to 65 mL/g during start-up to end of the study, respectively. The conical geometry induces an effective velocity gradient along with aeration in the reactor for better flocculation of biomass which has a good impact on the formation of stable and resistant aerobic granules. This system in conical SBR is advantageous as it attains simultaneous nutrient removal (CNP) with effective biomass retention without automatic process control. This treatment system has the potential to employ in low volume wastewater treatment in many decentralized applications.

Adding waste iron shavings in a pilot-scale two-stage SBRs to develop aerobic granular sludge treating real wastewater

A pilot-scale two-stage SBRs added waste iron shavings was proposed and established to develop aerobic granular sludge for real wastewater treatment based on a previous lab-scale study. The results showed that aerobic granular sludge was successfully cultivated, and the treatment performance was satisfactory. The sludge volume index at 30 min (SVI30) was approximately 25.0 mL/g and the mean particle size reached approximately 0.8 mm. The mixed liquor suspended solids (MLSS) exceeded 14 g/L and 10 g/L in the two SBRs. The average removal rates of chemical oxygen demand (COD), total phosphorus (TP), ammonia nitrogen (NH4+-N), total nitrogen (TN), and suspended solids (SS) were 95.2%, 99.2%, 96.1%, 82.9%, and 95.0%, respectively. In addition, low total iron (TFe) concentrations were unlikely to impact the effluent. Two-stage SBRs can efficiently reduce the effluent SS concentration during early in the operation process, and improve the utilisation of carbon source from raw wastewater for denitrification. Overall, the coupling of iron shavings micro-electrolysis and biological processes promoted aerobic sludge granulation and pollutant removal.

Coupling of sponge fillers and two-zone clarifiers for granular sludge in an integrated oxidation ditch

Considering that aerobic granular sludge (AGS) exhibits a long granulation time in continuous flow and that the poor removal effects on N and P have severely restricted its large-scale application, a novel strategy was developed involving sponge fillers to construct an anoxic zone coupling two-zone clarifiers to promote granulation in an integrated oxidation ditch. The different pores in the sponge fillers were used to accelerate the accumulation and formation of aggregates under the impetus of water flow, meanwhile, the A/O operation mode and the formation of AGS were also improved the denitrification and phosphorus removal capacity of the reactor. The experimental results indicated that AGS was shaped in the anoxic and aerobic zones on day 30 and on day 43, respectively. When running for 90 days, the mixed liquor suspended solids (MLSS), sludge volume index (SVI5) and average particle size in the anoxic zone and aerobic zone were 5848 mg/L and 4812 mg/L, 31.2 mL/g and 35.8 mL/g, and 329.2μm and 362.3μm, respectively. During the granulation process, the EPS content in the anoxic zone was significantly higher than that in the aerobic zone, indicating that the sponge fillers played a dominant role in granulation. After the reactor reached steady conditions, the removal efficiencies of COD and N were 87.29%±2.61% and 60.11%±4.68%, respectively. The TP removal efficiency gradually increased from 26.90% on day 1 to 77.54% on day 90. Moreover, the microbial community transformed conspicuously throughout granulation, including an enrichment of microorganisms exhibiting EPS secretion and pollutants degradation.

Gravimetric selection of activated sludge for settling properties improvement and granular sludge formation – full scale case study

Abstract With an increasing frequency of extreme weather events wastewater treatment plant operators face a need to increase plant hydraulic capacity while continuing to comply with effluent quality requirements. An economically attractive way to meet this challenge is to significantly improve secondary settling tank performance and therefore assure safe wet weather plant operation. The objective of this study was to evaluate gravimetric selection technology conducted in hydrocyclones as a way for improving activated sludge settling characteristics in continuous flow BNR with a long sludge retention time and assess its ability to form granular sludge. Long term operational data and sludge morphology monitoring data were analysed. A significant drop in sludge volume index (SVI) (to values under 50 ml/g) and increase in return activated sludge solids concentration (to values above 20 g/L) was observed. Hydrocyclone installation consistently, selectively retained denser, larger flocs in the system and after a start-up phase large granules begin to appear. Gravimetric selection did not prevent the seasonal filamentous biomass outgrowth and temperature drop at the beginning of winter resulted in rapid rise of SVI and SST sludge blanket height especially after heavy rain. Technology under study proved to be effective under certain process conditions but it needs further research to consistently maintain low SVI values throughout the whole year.

Batch Electrochemical Treatment of Raw Pulp and Paper Mill Wastewater Using Electrode Combinations

SS and Cu electrodes were used in the electrochemical coagulation to treat pulp and paper mill wastewater using 4SS and 3SS 1Cu electrodes by applying cell voltages 12 – 24 V. Optimal cell voltage 18V showed COD removal of 89.64% for 4SS electrode and 84.74% for 3SS 1Cu electrode with simultaneous color removal of 99% and 90%. Other control factors used for optimal operation are sludge volume index (SVI), filterability, etc. SVI values were &lt;100 mL/g for 4SS electrodes. The filtration characteristics of the ECC-treated sludge were established to determine the specific cake resistance (α) and the resistance of the filter medium (Rm). Lower α and Rm values for 4SS and 3SS-1Cu electrodes were found at 60 min ET. Proximate and ultimate analyses showed that 4SS and 3SS-1Cu sludge could be used as additive as well as adsorbent material for treating low strength wastewater.

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.

Granulation strategies applied to industrial wastewater treatment: from lab to full-scale.

About one third of the industrial activated sludge (AS) plants worldwide suffer from bad settling sludge, often caused by filamentous bulking phenomena. The present study investigated the effectiveness of a sludge granulation/densification strategy, based only on a metabolic selection mechanism, to eliminate sludge bulking in a sequencing batch reactor (SBR) treating real industrial wastewater. The wastewater originated from a tank truck cleaning company transporting chocolate and beer. The proposed strategy involved the introduction of a slow unaerated/anaerobic feeding step in the SBR operation. On lab-scale, the new feeding strategy resulted in (1) excellent settling with a sludge volume index (SVI) decreasing from more than 300 mL·g-1 to 100 mL·g-1 and lower, (2) the elimination of sludge bulking genera and (3) the significant enrichment of glycogen-accumulating organisms (GAO), mainly Defluviicoccus and Candidatus Competibacter, and this in less than 80 days. The feeding strategy was then applied to the full-scale installation, yielding similar results: a stable average SVI of 37 mL·g-1 was reached after approximately 150 days. Full granulation was however not reached, which warrants further optimization. The present study shows that the proposed strategy can easily be applied in existing SBR systems to solve the problem of sludge bulking.

Enhanced Settling and Dewatering of Oil Sands Mature Fine Tailings with Titanomagnetite Nanoparticles Grafted with Polyacrylamide and Lauryl Sulfate

In this study, a three-in-one nanoflocculent that consists of nanoparticles of titanomagnetite (NTM) grafted with multiple segments of hydrophobically modified chains of polyacrylamide (PAM) with sodium laurel sulfate (SLS) was developed for enhanced settling and dewatering of oil sands mature fine tailings (MFT). The existence of NTM allowed more than one segment to graft/functionalize (i.e., hydrophobic and hydrophilic) on the same surface. This three-in-one nanoflocculent not only provides better exposure for the functionalized species, but it also increases the nanoflocculant specific gravity and dispersibility for better interactions. The NTM was initially synthesized by the coprecipitation method and subsequently grafted with PAM and SLS at room conditions. The flocculation and dewatering performance of the as-synthesized nanoflocculants was evaluated using the initial settling rate (ISR), supernatant turbidity, sludge volume index, capillary suction time (CST), and specific resistance to filtration (SRF). Flocculation of the MFT suspension using the novel optimized nanoflocculants at 3000 ppm had 15 times faster ISR, and the supernatant turbidity, CST, and SRF had stronger outcomes than the traditionally used 20,000 ppm commercial anionic PAM. This study demonstrates the potential of designing nanoflocculants to effectively enhance settling and dewatering of oil sands tailings, while reducing the required amount of coagulants.

Contact stabilization process for hospital wastewater treatment: effects of colloidal organic matter

Abstract In this study, the treatability of hospital wastewater was investigated using a contact stabilization process on a laboratory scale. A detention time of one hour was selected for sludge settling and separation of treated effluent, and removal efficiency was measured at contact times of 30, 60, and 90 min, and stabilization times of 4.5 and 5.5 h. Based on the different detention times, 6 series of experiments were designed. Results showed that after an initial rapid COD removal in the first 30 min, COD values fluctuate in the time range of 30–90 min. However, in the case where COD values reduce in the second stage, this recovery is negligible; thus, the time of 30 min is considered as the optimal detention time for the contact reactor. Sludge volume index (SVI) values of 119.20 and 109.17 mL/g were obtained for stabilization times of 4.5 and 5.5 h, respectively. Therefore, the longer the stabilization time, the closer the SVI is to 100 mL/g. Moreover, lower settled sludge volume (SSV) value at 5.5 h of stabilization shows better characteristics compared to 4.5 h of stabilization. Furthermore, COD removal efficiency at the optimum contact time is higher when 5.5 h is selected for stabilization.

Enhanced aerobic granular sludge formation by applying Phanerochaete chrysosporium pellets as induced nucleus.

The long start-up period is a major challenging issue for the widespread application of aerobic granular sludge (AGS). In this study, a novel rapid start-up strategy was developed by inoculating Phanerochaete chrysosporium (P. chrysosporium) pellets as the induced nucleus in a sequencing batch airlift reactor (SBAR) to enhance activated sludge granulation. The results demonstrated that P. chrysosporium pellets could effectively shorten the aerobic granulation time from 32 to 20days. The AGS promoted by P. chrysosporium pellets had a larger average diameter (2.60-2.74mm) than that without P. chrysosporium pellets (1.78-1.88mm) and had better biomass retention capacity and sedimentation properties; its mixed liquor suspended solids (MLSS) and sludge volume index (SVI30) reached approximately 5.2g/L and 45mL/g, respectively. The addition of P. chrysosporium pellets promoted the secretion of extracellular polymeric substances (EPS), especially protein (PN). The removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) in P. chrysosporium pellets reactor were 98.91%, 89.17%, 64.73%, and 94.42%, respectively, which were higher than those in the reactor without P. chrysosporium pellets (88.73%, 82.09%, 55.75%, and 88.92%). High throughput sequencing analysis indicated that several functional genera that were responsible for the formation of aerobic granules and the removal of pollutants, such as Acinetobacter, Pseudomonas, Janthinobacterium, and Enterobacter, were found to be predominant in the mature sludge granules promoted by P. chrysosporium pellets.

Improvement of biomass aggregation in sludge bulking by magnetic field application

AbstractHigh biomass aggregation is commonly associated with good solid–liquid separation that can inhibit the occurrence of sludge bulking. The application of magnetic fields in the removal of pollutants has been studied previously but the relation between a magnetic field with biomass aggregation and its effect on pollutant removal efficiency receives very little attention. This present study was conducted to analyze the effect of the magnetic field toward biomass aggregation that can eventually contribute to the good removal performance of the pollutants. Two continuous laboratory‐scale sequencing batch reactors known as Reactor A and Reactor B were set up. Reactor A was equipped with an 88 mT magnetic field while Reactor B acted as the control. Reactor A recorded higher biomass aggregation with the range of 75.0–95.2% compared to Reactor B which possessed mostly medium aggregation with an average of 65.5%. As a result, lower sludge volume index (SVI) was recorded in Reactor A (25.8 ml/g) compared to Reactor B (73.1 ml/g). Likewise, Reactor A showed significantly higher chemical oxygen demand (COD) and ammonia‐nitrogen removal compared to Reactor B. These findings imply that the magnetic field successfully improves biomass aggregation, therefore improving the removal performance under the sludge bulking occurrence.

Responses of Nitrogen Removal, Extracellular Polymeric Substances (EPSs), and Physicochemical Properties of Activated Sludge to Different Free Ammonia (FA) Concentrations

To investigate the effect of free ammonia (FA) on the nitrogen removal performance, extracellular polymeric substances (EPSs), and physicochemical properties of activated sludge, four laboratory-scale sequencing batch reactors (SBRs) were operated at FA concentrations of 0.5, 5, 10, and 15 mg/L (R0.5, R5, R10, and R15, respectively). Results showed that nitrogen removal and the production of EPSs and their components (including polysaccharides, proteins, and nucleic acid) significantly increased with the increased FA concentration from 0.5 to 10 mg/L; however, they decreased with a further increase in FA to 15 mg/L. Moreover, the capillary suction time (CST), specific resistance of filtration (SRF), and sludge volume index (SVI) decreased when FA concentration increased, indicating that better settleability and dewaterability of activated sludge was obtained. Additionally, a path diagram showed that Nitrosomonas was positively correlated, while Denitratisoma was negatively correlated with EPSs and their components. Thauera was positively correlated, while Zoogloea was negatively correlated with the settleability and de-waterability of activated sludge.

Role of initial bacterial community in the aerobic sludge granulation and performance

The structure of bacterial community was greatly varied from different seed sludge sources, which affected the sludge characteristics. To explore the role of different functional bacteria in AGS granulation and pollutant degradation, three different resources of seed sludge obtained from pharmaceutical wastewater (R1), livestock (R2), and municipal sludge (R3) were employed in this study. Results showed that the initial bacterial community had important significance for AGS formation and pollutants removal. Seed sludge taken from R3 granulated faster than those from R1 and R2. A large number of mature granules were formed after 20 days of operation in R3. In addition, the final mixed liquor suspended solids (MLSS) reached 6853 mg L−1, with 48 mL g−1 sludge volume index (SVI) in R3, indicating that it had better settling performance and granulation. In the stable stage of R3, the removal rates of COD, NH4+-N, and TN reached 99.2%, 98.5%, and 97.6%, respectively. The α-diversity analysis showed that the bacterial community of seed sludge greatly determined the microbial composition of AGS. Firmicutes, Gracilibacteria, and Spirochaetes were abundant in R3, which maintained the structures and functions of aerobic granules. This study might provide approaches and insights for AGS culture from different sludge sources.