Suspended Sludge Research Articles

Evaluation of the effectiveness of immobilization of activated sludge on composite materials “polyethylene:polysaccharides”

The aim of this work is to study the immobilization ability of new composite materials based on polyethylene (PE) and polysaccharides (PS) in relation to the biocenosis of activated sludge (AS). The objects of the study were selected composite materials of the following composition: PE : pure microcellulose (MCc), PE : waste microcellulose (MCw), PE : starch (ST), at a ratio of components PE : PS = 70:30 wt.%. The objectives of the study were to determine the main morphological parameters of new composites (porosity, roughness, density), assessment of hydrochemical and hydrobiological state of AS (silt index, mass concentration of silt, species composition) until it locks into composites, assessment of the immobilization ability of the studied materials by biomass weight gain, monitoring of the state of AS after fixing. The tests found that the composite of structure of PE : MCc of has a density of 410 kg/m3 and a porosity of 60%, the roughness of 3.5; the composite of structure of PE : MCw has a density of 590 kg/m3 and a porosity of 40%, roughness of 2.0, composite of structure of PE : ST has a density of 640 kg/m3 and a porosity of 50%, the roughness of 2.5; wherein the reference sample - PE - has the parameters: density 860 kg/m3 and a porosity of 0%, roughness 0. To determine the immobilization capacity of the new composite materials, a laboratory experimental immobilizer was used, which is a container filled with 70% of the useful volume of the active sludge suspension and 30% of the floating loading samples. Immobilization was carried out under aeration conditions during 2, 4, 8, 12, 24, 48, 72 hours. As a result of tests it is established that the sample of structure of PE : MCc for 72 hours of immobilization showed a gain of biomass of the order of 12%, the sample of structure of PE : MCw - 5%, the sample of structure of PE : ST – 7%, PE – 3%. The condition of the organisms AS after fixing was evaluated by washings with immobilized samples, as a result of microscopy of washouts, the presence of living representatives of the biocenosis of AS in all samples was established, but they differ in number: for the sample of structure of PE : MCc - numerous, PE : MCw, PE : ST - average number, PE - small number. Further studies on the modification of the synthetic polyolefin matrix by functional fillers, including those from a number of polysaccharides, are of interest, allowing to increase the affinity of the carrier material with the extracellular matrix of activated sludge.

Biofilm aging in full-scale aerobic bioreactors from perspectives of metabolic activity and microbial community

The objective of this study was to establish a quantitative response to biofilm aging from perspectives of metabolic activity and microbial community applied in distinct wastewater. Biofilms developed on soft, integrated and suspended biocarriers in three full-scale aerobic bioreactors under stable operations from municipal and industrial wastewater treatment plants, were tracked for more than 11 weeks for biofilm aging study. Results showed the first evidence of biofilm aging in full-scale aerobic bioreactors by adenylate energy charge (AEC) that biofilm needed to be reactivated when AEC was less than 0.6. Biofilm aged more easily on soft and integrated biocarriers and high salinity, high organic contents and high suspended sludge concentration accelerated the aging process of biofilm. Caldilinea and Acinetobacter predominated in aging biofilm on suspended biocarriers. This study offered a novel evaluation methodology of biofilm aging and was believed to provide important reference for biofilm regulation in biofilm-based wastewater treatment process.

Characterization of foaming and non-foaming sludge relating to aeration and the implications for membrane fouling control in submerged membrane bioreactors

In this study, two parallel aerobic MBRs were operated with different aeration diffusers (coarse-bubble aeration vs. fine-bubble aeration). It was found that fine-bubble aeration would cause serious foaming in the MBR system. The specific filtration resistance (SFR) of non-foaming sludge was similar to that of the sludge suspension in the foaming MBR, but almost 2–3 times larger than that of the foaming sludge liquor from the top layer of the foaming MBR. The intermediate pore blocking was the dominant fouling mechanism in batch filtration tests. The filtration performance of the sludge mixtures was governed by the combined effect of several major factors. There were more smaller flocs, less soluble microbial products (SMP) and less bound extracellular polymeric substances (EPSs) in the foaming sludge samples. Interfacial interaction calculation showed that the foaming sludge had a weaker adhesion ability. Comparison of foaming sludge and overflow foaming sludge revealed that the degree of foaming could affect the filtration behavior and physicochemical properties of the foaming sludge. The findings regarding the combined effect of aeration bubble size on foaming and fouling gave some implications for foaming and fouling control. Since fine-bubble aeration was detrimental for foaming control but beneficial for fouling mitigation, the selection of the optimal aeration intensity and diffuser would be a potentially effective strategy for the membrane fouling and foaming control in the MBR system.

Evaluation of Filtration-backwash Modes on Membrane Fouling Control for Activated Sludge Suspensions Treatment

This study focused on the effects of three different filtration-backwash modes on membrane fouling control for various sludge suspensions treatment. A relatively slow flux decline profile showed that more frequent and shorter backwashing mode (Mode 1) had a less fouling tendency. Moreover, this mode possessed higher capacity to remove the reversible fouling with higher hydraulic cleaning efficiency (HCE) and lower hydraulically irreversible fouling index (HIFI). Typically, when fed with higher carbon-to-nitrogen ratio suspension (SBR6), the HCE value of Mode 1 was over twice as high as that of Mode 3 (less frequent and longer backwashing).

Novel insights into membrane fouling caused by gel layer in a membrane bioreactor: Effects of hydrogen bonding

Gel layer formation in some cases directly determines membrane fouling extent in membrane bioreactors (MBRs). While hydrogen bonding interactions extensively exist in gelling foulants and sludge suspension, their exact roles in fouling remain unveiled. Filtration results in this study showed that, specific filtration resistance (SFR) of a gel layer formed in the MBR was as high as 2.06 × 1019 m−1·kg−1 at 20 °C, and moreover, SFR of both the real gel and model gel (Poly(N-isopropylacrylamide) (PNIPAM)) decreased with temperature. Fourier-transform infrared spectroscopy (FTIR) analysis indicated that gel samples were abundant of good hydrogen bonding donors/acceptors to form hydrogen bonding, and hydrogen bonding strength decreased with temperature. From viewpoint of free energy, mathematical models depicting roles of hydrogen bonding were proposed. For the first time, contribution level of hydrogen bonding effects to total gel SFR was quantified to be around 20%. These results offered in-depth insights into membrane fouling in MBRs.

Influence of two types of sludge on the biogas production of assorted waste streams and the significance of beef cattle waste and liquid cheese whey in the organic fraction of municipal solid waste

The aim of this study was to assess the biogas production generated by the anaerobic co-digestion of two co-substrates—liquid cheese whey (LCW) and beef cattle waste (BCW)—mixed with the organic fraction of municipal solid waste (OFMSW) and inoculated with either granular or suspended sludge. At the end of co-digestion, a high biogas yield was observed for the granular sludge mixture of OFMSW and BCW, which provides support for beef cattle waste as a promising substrate for biogas production. The mixture of OFMSW and LCW resulted in an enhancement of biogas production compared to OFMSW alone; however, the characteristics of LCW led to instability during the process. The key finding was that the type of sludge used influences the biogas production of the mixture. For the two sludges tested, the reactors containing granular sludge produced more biogas than those with suspended sludge. Reactors inoculated with a granular sludge produced 70% more biogas with the mixture of OFMSW and BCW compared to those with the suspended sludge. The OFMSW and LCW mixture with granular sludge produced 16% more biogas than with the suspended sludge.

Ammonium persulfate-initiated polymerization of cationic starch-grafted-cationic polyacrylamide flocculant for the enhanced flocculation of oil sludge suspension

In this study, a novel, highly efficient and environmentally friendly flocculant, namely, cationic starch-grafted-cationic polyacrylamide (CS-g-CPAM), was synthesized by initiation polymerization of ammonium persulfate. First, CS-g-CPAM was polymerized with cationic starch(CS), acrylamide(AM) and diallyl dimethyl ammonium chloride (DMDAAC), and then the influence factors of graft polymerization were investigated, including total monomer concentration, initiator dosage, the monomer mass ratio of mAM: mCS: mDMDAAC, post-polymerization temperature and post-polymerization time. And the intrinsic viscosity of the CS-g-CPAM was measured by the one point method accurately. The chemical structures and morphology of the samples were characterized by Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermo-gravimetric and differential scanning calorimetry (TG-DSC), and scanning electron microscope (SEM). The CS-g-CPAM was utilized to flocculate the oil sludge suspension, the effects of CS-g-CPAM dosage, temperature and pH value on the flocculation performance were investigated. The results show that CS-g-CPAM has outstanding flocculation effect.

The auto fluorescence characteristics, specific activity, and microbial community structure in batch tests of mono-chicken manure digestion

Batch tests inoculated with granular and suspended sludge of mono chicken manure (CM) digestion were conducted. Kinetic analysis showed a maximum bio-CH4 generation (6 mL/gVS/d) at an optimal TS of 10–12%. At a TS of 25%, serious inhibition was found for granular sludge and even greater inhibition for the suspended sludge caused by free ammonia. The auto fluorescence of Excitation–mission matrix with parallel factor analysis (PARAFAC) showed that the dissolved organic matter (DOM) varied between the form C1, C2, C3 and C4. The split component of the SMP-like C2 and protein-like C4 significantly related to the bio-methane production in time series. The canonical correlation analysis (CCA) indicated that ammonia, pH, and TS influenced the PARAFAC component significantly. The aceticlastic methanogens of the genus Methanosaeta and acetogens of the genus Syntrophobacter predominated in the CM sludge. The methanogens and acetogens formed a metabolic cooperation, making the process a stable methane produced activity.

Fabrication of high-performance antibiofouling ultrafiltration membranes with potential application in membrane bioreactors (MBRs) comprising polyethersulfone (PES) and polycitrate-Alumoxane (PC-A)

Novel nanocomposite ultrafiltration (UF) membranes were designed and fabricated using hydrophilic polycitrate-Alumoxane (PC-A) nanoparticles and polyethersulfone (PES) to achieve desirable performance for membrane bioreactor (MBR) system. Pure water flux (PWF) and fouling tests were employed to examine the effects of PC-A nanoparticles on the UF performance. FTIR spectra of the PC-A nanoparticles revealed that carboxylic acid and hydroxyl groups are created on the surface of the PC-A. The presence of these hydrophilic groups in PC-A resulted in greater hydrophilicity for the PC-A-modified UF membranes. Therefore, the PC-A-modified UF membranes exhibited higher PWFs compared to the unfilled PES membrane. Fouling resistance of the membranes was evaluated by activated sludge suspension filtration disclosed that the membrane modified with only 0.5 wt% of PC-A had the best antifouling characteristic as well as the greatest PWF. Hence, this optimal nanocomposite membrane was used in the MBR and variations of fluxes exanimated at different mixed liquor suspended solids (MLSS) concentrations of 6000, 10,000 and 14,000 mg/L. During filtration of the activated sludge, the fluxes increased with an increase in MLSS. A decrease in soluble microbial products, extracellular polymeric substance (EPS) from the bacterial cells, and cake formation fouling may result in gentler permeation flux decline over time.

Synthesis of nanocomposites from cationic polyacrylamide and modified carbon black: Application as flocculants for oily sludge suspension

Carbon black was modified using various liquid‐phase oxidation methods (modified carbon black = m‐CB, m = (1, 2, 3): 1, sulfuric acid/potassium permanganate method; 2, nitric acid method; 3, hydrogen peroxide method). With acetone–ethylene glycol as initiator, dimethyldiallylammonium chloride (DMDAAC) and acrylamide (AM) as monomer, cationic polyacrylamide (CPAM) was prepared by UV excitation of the monomer. The m‐CB/CPAM nanocomposites were synthesized using a hydrothermal method. The factors that affected the molecular weight of CPAM were investigated, including the total monomer concentration, the dosage of the complex initiator, the mass ratio of mAM:mDMDAAC and the UV irradiation time. The chemical structures and morphologies of the samples were characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental composition, X‐ray diffraction and scanning electron microscopy. 1‐CB/CPAM was utilized to flocculate oil sludge suspension, and the effects of 1‐CB quality, 1‐CB/CPAM dosage, temperature and pH value on the flocculation performance of 1‐CB/CPAM were investigated. The flocculation mechanism of 1‐CB/CPAM was also analyzed. The results show that 1‐CB/CPAM has an outstanding flocculation effect, and it flocculates oil sludge particles by adsorption bridging and charge neutralization in acidic and alkaline conditions.

Wastewater treatment and microbial community dynamics in a sequencing batch reactor operating under photosynthetic aeration

A sequencing batch bioreactor (SBR) treating municipal wastewater was photosynthetically aerated using microalgae cultivated in a photobioreactor (PBR). Symbiotic interactions and CO2/O2 exchange were established between activated sludge in the SBR and microalgae in the PBR through hydrophobic hollow fiber membranes. Photosynthetic aeration enhanced COD removal in the SBR from 52.2% (without external aeration) to 90.3%, whereas N-NH4+ and P-PO43- removal increased by 63.5% and 90.4%, respectively. The SBR performance under photosynthetic aeration was comparable to that under mechanical aeration. However, no nitrification was observed in the SBR, indicating oxygen limitation and poor growth condition for nitrifiers. In the PBR, there was a rapid increase in biomass concentration and it stabilized at 3.0 g/L after 22 days of operation. High nitrogen demand in the PBR indicated the steady flow of inorganic carbon from the SBR through the membranes. Prolonged oxygen limitation and massive sludge attachment on the membranes resulted in low suspended sludge concentration in the SBR. Microbial community analysis indicated gradual enrichment of facultative and strictly anaerobic microorganisms in the SBR. These results highlight the potential of microalgae in lowering the cost of wastewater aeration and underline the challenges in sustaining symbiotic gas exchange during long-term.

Effect of anaerobic/aerobic duration on nitrogen removal and microbial community in a simultaneous partial nitrification and denitrification system under low salinity

In this study, the simultaneous partial nitrification and denitrification (SPND) process was investigated in a hybrid sequencing batch biofilm reactor (HSBBR) fed with synthetic wastewater with 1.2% salinity. Different anaerobic/aerobic (An/Ae) durations were selected for evaluating the removal performance of contaminants and the succession of the microbial community in the reactor. The highest organic matter removal efficiency was obtained at An/Ae hour ratio of 0/6.5, with an average chemical oxygen demand (COD) removal of 89.6% at the steady state. Similarly high nitrogen removal efficiencies were achieved at An/Ae hour ratios of 1/5.5, 1.5/5 and 2/4.5,with over 92% of average total nitrogen removed. This represents an increase of more than 10% compared to the mode with An/Ae hour ratio of 0/6.5. High-throughput sequencing analysis revealed that the increase of the An/Ae hour ratio changed the characteristics of the community structures in the HSBBR. Azoarcus was the most dominant genus when the An/Ae hour ratio was 0/6.5 in both suspended sludge (S-sludge) and biofilm, while Candidatus_Competibacter was the most abundant genus at An/Ae hour ratios of 2/4.5 and 3/3.5. Nitrosomonas was the only ammonia oxidizing bacteria (AOB) detected in this study. Nitrospira, a kind of nitrite oxidizing bacteria (NOB), was sensitive to salinity and altering the An/Ae mode; this was detected only in S-sludge samples in a fully aerobic mode with a low percentage of 0.1%. S-sludge and biofilm samples shared a similar bacterial composition. This research demonstrated that efficient nitrogen and carbon removal could be achieved via the SPND process by the symbiotic functional groups in a hybrid S-sludge and biofilm reactor.

Mechanisms and characteristics of biofilm formation via novel DEAMOX system based on sequencing biofilm batch reactor

A denitrifying ammonium oxidation (DEAMOX) process has been regarded as an innovative process to simultaneously treat ammonia and nitrate containing wastewaters, whereas very limited research has focused on its application in biofilm system. In this research, a novel DEAMOX process was established with fixed sponge carriers in a sequencing biofilm batch reactor (SBBR). To investigate biofilm formation process and characteristics can encourage further research on DEAMOX system optimization, deteriorated performance recovery strategies and application with actual wastewater. Total nitrogen removal efficiency was maintained at 93.0 % after 240 days of operation. With biofilm growth, the protein-like extracellular polymeric substances (EPS) and tightly-bound EPS (TB-EPS) of biofilms increased from 65.6 to 46.1, to 179.6 and 142.0mg gVSS-1, respectively, revealing that protein-like substances and TB-EPS promote biofilm formation. The mechanism of biofilm formation was discussed by analyzing the morphological development and functional bacterial activities of biofilms. Furthermore, high anammox activity was obtained in biofilms with specific NH4+N removal rates over 4.29 mgN gVSS-1h-1, which were significantly higher than in suspended sludge (2.56 mgN gVSS-1h-1). Quantitative polymerase chain reaction results showed that the abundance of anammox bacteria in biofilms increased from 1.87 % to 11.48 % with biofilm growth. These results imply that mature biofilms formed on carriers and the anammox bacteria were sufficient enriched in DEAMOX-SBBR system.

Key microbial populations involved in anaerobic degradation of phenol and p-cresol using different inocula

Background: Anaerobic digestion is an alternative bioprocess used to treat effluents containing toxic compounds such as phenol and p-cresol. Selection of an adequate sludge as inoculum containing an adapted microbial consortium is a relevant factor to improve the removal of these pollutants. The objective of this study is to identify the key microorganisms involved in the anaerobic digestion of phenol and p-cresol and elucidate the relevance of the bamA gene abundance (a marker gene for aromatic degraders) in the process, in order to establish new strategies for inocula selection and improve the system's performance. Results: Successive batch anaerobic digestion of phenol and p-cresol was performed using granular or suspended sludge. Granular sludge in comparison to suspended sludge showed higher degradation rates both for phenol (11.3 ± 0.7 vs 8.1 ± 1.1 mg l-1 d-1) and p-cresol (7.8 ± 0.4 vs 3.7 ± 1.0 mg l-1 d-1). After three and four re-feedings of phenol and p-cresol, respectively, the microbial structure from both sludges was clearly different from the original sludges. Anaerobic digestion of phenol and p-cresol generated an abundance increase in Syntrophorhabdus genus and bamA gene, together with hydrogenotrophic and aceticlastic archaea. Analysis of results indicates that differences in methanogenic pathways and levels of Syntrophorhabdus and bamA gene in the inocula, could be the causes of dissimilar degradation rates between each sludge. Conclusions: Syntrophorhabdus and bamA gene play relevant roles in anaerobic degradation of phenolics. Estimation of these components could serve as a fast screening tool to find the most acclimatized sludge to efficiently degrade mono-aromatic compounds.

Performance and kinetic model of degradation on treating pharmaceutical solvent wastewater at psychrophilic condition by a pilot-scale anaerobic membrane bioreactor

A pilot-scale anaerobic membrane bioreactor (AnMBR) was operated for 435 days in this study, aiming to treat pharmaceutical solvent wastewater containing m-Cresol (MC), isopropanol (IPA) and N,N-Dimethylformamide (DMF) pollutants at different temperatures of 35 ± 3 °C, 25 ± 3 °C, 15 ± 3 °C and 25 ± 3 °C, respectively. The reactor reached average total removal efficiencies of about 96%, 97.2% and 98% of MC, IPA and DMF at psychrophilic condition (15 ± 3 °C). Higher physical removal rate was obtained at 15 ± 3 °C due to the important contribution of membrane filtration. At this stage, the biogas production, methane content and specific methanogenic activity and extracellular polymeric substances of suspended sludge were observed with the lowest level. Moreover, the kinetic models for solvent degradation were established at different temperatures, results showed the smaller maximum specific substrate degradation rate of MC and IPA, besides, the lowest degradation rate of three solvents were obtained at 15 ± 3 °C.

Comparative Analysis on Corrosion Behavior of 316SS and 304SS in Subcritical and Supercritical Aqueous Systems

The corrosion characteristics of 316SS and 304SS in subcritical and supercritical aqueous systems including chloride of approximate 4600 mg/L at 25 MPa and 250 °C, 350 °C, 425 °C, and 520 °C are comparatively investigated. Some local corrosion areas occurred on the surfaces of SS316, not on that of 304SS, at 250 °C and 425 °C, while at 350 °C, all the sample surfaces were covered by large amounts of corrosion products and clay materials due to the predominant precipitation for the formation of the outer subscale. Whether in reducing subcritical and supercritical industrial sludge suspension or in oxidizing supercritical sludge system, 304SS owns better corrosion resistance than 316SS due to higher chromium concentration of former.

Thermodynamic prediction and experimental investigation of short-term dynamic membrane formation in dynamic membrane bioreactors: Effects of sludge properties.

In dynamic membrane bioreactors (DMBRs), a dynamic membrane (DM) forms on a support material to act as the separation membrane for solids and liquids. In this study, batch filtration tests were carried out in a DMBR using nylon mesh (25 μm) as support material to filtrate sludge suspensions of variable properties from three different sources to evaluate the effects on the short-term DM formation process (within 240 min). Furthermore, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory was applied to analyze the sludge adhesion and cohesion behaviors on the mesh surface to predict quantitative parameters of the short-term DM formation process (including initial formation and maturation stage). The filtration results showed that the order of the initial DM formation time (permeate turbidity <1 NTU as an indicator) was as follows: sludge with poor settleability and dewaterability < normal sludge < sludge with poor flocculability. Moreover, normal sludge (regarding settleability, dewaterability, flocculability, and extracellular polymeric substance) showed a more acceptable DM formation performance (short DM formation time, low permeate turbidity, and high permeate flux) than sludge with poor settleability, dewaterability and flocculability. The influence of sludge properties on the initial DM formation time corroborates the prediction of sludge adhesion behaviors by XDLVO theory. Additionally, the XDLVO calculation results showed that acid-based interaction, energy barrier, and secondary energy minimum were important determinants of the sludge adhesion and cohesion behaviors. Therefore, short-term DM formation process may be enhanced to achieve stable long-term DMBR operation through positive modification of the sludge properties.

WASTEWATER TREATMENT AT MODERATE TEMPERATURES USING UASB REACTOR

The use of anaerobic biodegradation to treat municipal wastewater is a promising technology, because of the relatively low capital expenditures required and the potential to create biogas, which can be used as a source of energy. The UASB reactor is a high-rate system that operates as a suspended sludge blanket system with granular sludge growth system. Treatment occurs at the contact of the up flow passing wastewater with the sludge blanket at the bottom of the reactor and produced biogas is collected at top of the reactor. The effluent could be used for irrigation, because the included nutrients are not affected by the treatment. Much more interesting at actual time are renewable energies and the retrenchment of CO2-Emission. With the anaerobic treatment of municipal wastewater not only the CO2-Emission could be reduced but also gained “clean” energy supply by biogas. Most important for the sustainability of this process is the gathering of methane from the liquid effluent of the reactor, because the negative climate-relevant effect from the outgassing methane is much higher than the positive effect from saving CO2Emission. In this study UASB reactors were used with a flocculent sludge blanket for the biodegradation of the carbon fraction in the wastewater with different temperatures and concentrations. The SMA was determined and evaluated; also the biogas emission was controlled. Also a static modelling for COD fractioning and SMA was done. It could be shown, that the positive effect is much higher for municipal wastewater with high concentrations in hot climate.

Impacts of ammonium loading on nitritation stability and microbial community dynamics in the integrated fixed-film activated sludge sequencing batch reactor (IFAS-SBR)

This study investigates the impact of ammonium concentration on the establishment of partial nitrification microbial community in an integrated fixed-film activated sludge (IFAS) reactor. Partial nitrification was achieved successfully under room temperature when the NH4+-N concentration in the feeding was greater than 400 mg/L. Molecular analysis confirmed that ammonia oxidizing bacteria (AOB) abundance increased and nitrite oxidizing bacteria (NOB) number reduced at high ammonium loading conditions. Compared with biofilm, suspended sludge played a major role in ammonium removal, which contributed to 66% total ammonium removal. Biosorption and biodegradation were found to be the two main mechanisms for ammonium removal in the IFAS system.

Impacts of different morphologies of anammox bacteria on nitrogen removal performance of a hybrid bioreactor: Suspended sludge, biofilm and gel beads

The difficulties in the anaerobic ammonium oxidation (anammox) process mainly consist of low microbial growth rates and long start-up times of bioreactors. The morphologies of anammox bacteria might affect nitrogen removal performance and microbial community. In this study, three morphologies of anammox bacteria, namely, suspended sludge, biofilm and suspended sludge embedded in gel beads, were compared in a hybrid bioreactor under anoxic conditions (DO concentration < 0.1 mg L−1). The results show that the average total inorganic nitrogen removal efficiency of a hybrid bioreactor reached 67 ± 15% with a maximum value of 80% for continuous synthetic wastewater feeding, and that the specific total inorganic nitrogen removal rate reached 15.75 mg·(gVSS·h)−1 regardless of the organic matter stress. Batch tests indicate that mainly suspended sludge (67%) and biofilm (26%) contributed to the anammox process, with the specific total inorganic nitrogen removal rate reaching 10.55 and 4.05 mg·(gVSS·h)−1, respectively. However, the embedding of sludge in gel resulted in nitrification instead of anammox with a nitrification rate of 0.20 ± 0.01 mg·(L·h)−1 due to the expansion of gel beads floating on the water surface. Therefore, a pore-forming technique was developed to produce more channels for gas dispersion inside the gel beads. In terms of microbial community, Candidatus Kuenenia involved in the anammox group was the most abundant genus in biofilm (43.4%) and suspended sludge (15.7%), while Nitrospira occupied the largest proportion in gel beads (25.6%). This study offers useful information for the selection of anammox bacteria morphology.