Sludge Volume Index Research Articles

A novel two-stage aerobic granular sludge system for simultaneous nutrient removal from municipal wastewater with low C/N ratios

In this study, a novel two-stage aerobic granular sludge (AGS) system was developed to treat municipal wastewater. High removal efficiencies of phosphorus (91%) and nitrogen (81%) were obtained under a low influent carbon/nitrogen ratio of 5.4. The high nutrient removal was attributed to microbial segregation in the two sequencing batch reactors (SBRs). In the first reactor, the high abundance of polyphosphate-accumulating organisms (Candidatus Accumulibacter 15.3%) promoted a high rate of enhanced biological phosphorus removal (EBPR). In the second reactor, residual ammonium was autotrophically removed via partial nitritation/anammox (PN/A). Moreover, granular sludge was maintained in both SBRs with a sludge volume index of 40–80 mL/g, which reduced the settling time and improved the operational stability. Furthermore, batch tests and mass balance analysis revealed that most influent phosphorus (68%) and some organics (33%) were recovered from the waste sludge as struvite and methane, respectively. Overall, this study illustrates that the novel two-stage AGS system integrating EBPR and PN/A is promising for enhancing nutrient removal, as well as resource and bioenergy recovery from municipal wastewater.

Piecewise Sliding-Mode Control for Sludge Bulking Under Multiple Operating Conditions

The phenomenon of sludge bulking, which can be classified as slight or serious abnormal operating conditions according to sludge volume index (SVI), is a widespread problem in wastewater treatment process. In this article, a piecewise sliding-mode control (PSMC) strategy is developed to overcome the adverse effects and furthermore improve the operating performance for wastewater treatment process under different operating conditions of sludge bulking. First, a soft sensing model of SVI based on fuzzy neural network is established. Then, it can online determine the state of sludge and whether sludge bulking has occurred. Second, in view of the specific operating condition of sludge, a piecewise sliding-mode controller is designed. Then, the sludge bulking can be eliminated by regulating the concentration of dissolved oxygen and nitrate nitrogen. Third, the boundary condition of PSMC is evaluated. Then, the stability of the control system is proved on the basis of ensuring the boundary condition of PSMC. Finally, the performance of PSMC is verified in the benchmark simulation platform. The results further demonstrate the effectiveness of the proposed control method.

Removal of colloidal impurities by thermal softening-coagulation-flocculation-sedimentation in steam assisted gravity drainage (SAGD) produced water: Performance, interaction effects and mechanism study

Effective removal of colloidal impurities from steam-assisted gravity drainage (SAGD) produced water is essential for enhancing water recycling in industry. Response surface methodology (RSM) was employed to optimize the thermal softening-coagulation-flocculation-sedimentation process with softeners (Ca(OH)2, MgO and Na2CO3), poly-DADMAC as coagulant, and cationic polyacrylamide (PAM) as flocculant, and assess the interaction effects of operational variables for sludge volume index (SVI) and the removal efficiency of turbidity (TSS), particulate hardness, silica, total organic carbon (TOC) and total inorganic carbon (TIC) in synthetic SAGD produced water. The optimal conditions at 0.93 desirability were 67 mg/L poly-DADMAC dose, 14 min mixing time with softeners only, 200 rpm coagulation speed, and 16 min flocculation time. At this condition, the predicted maximum removal of turbidity, TSS, particulate hardness, silica, TOC and TIC were 99.2 %, 99.1 %, 99.4 %, 27.0 %, 69.0 %, and 30.3 %, respectively, and the value of SVI was 38.1 mL/g. Our results indicated that poly-DADMAC dose and mixing time with softeners only were the most influential factors for the treatment process. Furthermore, the temperature effect on removal mechanisms was investigated at optimal conditions under room temperature and high temperature (80 °C). The results of floc characterization and surface force measurement indicated that temperature could facilitate the removal of colloidal impurities via forming larger and denser flocs and changing their surface composition. The results also provided confirmation that adsorption and subsequent bridging are the main removal mechanisms in the coagulation-flocculation process. This study illuminates the importance of the interactions among operational variables and provides in-depth insights into the mechanism for the removal of colloidal impurities under high temperature.

Aerobic granular sludge development using diatomite for low-strength wastewater treatment

This paper presents an assessment of the start-up performance of aerobic granular sludge (AGS) for the treatment of low-strength (chemical oxygen demand, COD < 200mg/L) domestic wastewater by the application of a diatomite carrier. The feasibility was evaluated in terms of the start-up period and stability of the aerobic granules as well as COD and phosphate removal efficiencies. A single pilot-scale sequencing batch reactor (SBR) was used and operated separately for the control granulation and granulation with diatomite. Complete granulation (granulation rate ≥ 90%) was achieved within 20days for the case of diatomite with an average influent COD concentration of 184mg/L. In comparison, control granulation required 85days to accomplish the same feat with a higher average influent COD concentration (253mg/L). The presence of diatomite solidifies the core of the granules and enhances physical stability. AGS with diatomite recorded the strength and sludge volume index of 18 IC and 53mL/g suspended solids (SS) which is superior to control AGS without diatomite (19.3 IC, 81mL/g SS). Quick start-up and achievement of stable granules lead to an efficient COD (89%) and phosphate removal (74%) in 50days of bioreactor operation. Interestingly, this study revealed that diatomite has some special mechanism in enhancing the removal of both COD and phosphate. Also, diatomite has a significant influence on microbial diversity. The result of this research implies that the advanced development of granular sludge by using diatomite can provide promising low-strength wastewater treatment.

Implementation of an anaerobic selector step for the densification of activated sludge treating high-salinity petrochemical wastewater.

Sludge bulking is a common challenge in industrial biological wastewater treatment. Leading to difficulties such as bad sludge settling and washout, which is a problem also encountered in the petrochemical industry. Anaerobic feeding strategies can be used to induce the growth of storage-capable organisms, such as glycogen-accumulating organisms (GAO), leading to denser sludge flocs and better settling. In this study, the implementation of an anaerobic feeding strategy was investigated for high-salinity petrochemical wastewater (±35 g salts·L-1), using a sequencing batch reactor. Influent, effluent and sludge characteristics were analyzed throughout the operational period, which can be divided into three stages: I (normal operation), II (increased influent volume) and III (longer anaerobic mixing). Good effluent quality was observed during all stages with effluent chemical oxygen demand (COD) < 100 mgO2·L-1 and removal efficiencies of 95%. After 140 days, the sludge volume index decreased below 100 mL·g-1 reaching the threshold of good settling sludge. Sludge morphology clearly improved, with dense sludge flocs and less filaments being present. A maximum anaerobic dissolved oxygen carbon (DOC) uptake was achieved on day 80 with 74% during stage III. 16S rRNA amplicon sequencing showed the presence of GAOs, with increasing relative read abundance over time from 1 to 3.5%.

Application of biopolymer in turbidity removal and sludge settling behaviour of travertine-processing wastewater: Performance optimization using response surface methodology (RSM)

A flocculation process was performed to treat travertine-processing effluents with a high concentration of suspended solids using an eco-friendly biopolymer. The experiments were conducted through a standard jar test procedure to optimize the process parameters for sludge volume index (SVI) and turbidity removal. The effects of mixing time, suspension pH, and polymer dosage on treatment efficiency were investigated using central composite design, a standard technique in response surface methodology. The constructed response model was tested using the analysis of variance (ANOVA). Using the Design-Expert tool, the coefficients of regression models were computed. The Fischer value (F-value) was used to evaluate the significance and validity of the predicted model, while the coefficient of determination (R2) was applied to estimate the model significance by comparing the predicted data with the measured data. The optimized parameters obtained were polymer dose of 276.20 mg/L, suspension pH of 8.60, and mixing time of 4.20 min. The optimal SVI and turbidity values obtained were 1.36 mL/g and 2.99 NTU, respectively. Additionally, R2 values for SVI and turbidity were determined as 0.9337 and 0.8654, respectively. Also, the difference between adjusted R2 values and predicted R2 was less than 0.2. Validation tests showed that the response surface methodology is an effective method for optimizing the flocculation mechanism.

Results of Adding Sludge Micropowder for Microbial Structure and Partial Nitrification and Denitrification in a Filamentous AGS-SBR Using High-Ammonia Wastewater

This work investigated the roles of sludge micropowder addition in microbial structure and partial nitrification and denitrification (PND) in an extended filamentous aerobic granular sludge-sequencing batch reactor (AGS-SBR) using high-ammonia wastewater. Type 1683 Acinetobacter with a high percentage became the dominant extended filaments, remarkably shifted and remained at a low level, acting as a framework for AGS recovery after micropowder addition. The sludge volume index (SVI5) decreased from 114 to 41.7 mL/g, mixed liquid suspended solids (MLSS) and extracellular polymers (EPS) both increased and balanced at 6836 mg/L and 113.4 mg/g•MLVSS, respectively. COD and NH4+-N were degraded to certain degrees in the end. However, the effluent NO2−-N accumulated to the peak value of 97.6 mg/L on day 100 (aeration stage), then decreased and remained at 45.3 mg/L with development of the stirring and micropowder supplemented in the SBR on day 160 (anoxic stage), while the influent NO2−-N always remained at zero. Interestingly, the influent/effluent NO3−-N both remained at zero throughout the whole experiment. These results demonstrated that PND was successfully obtained in this work. Sludge micropowder addition not only restrained the extended filaments’ overgrowth, but also contributed to PND realization with carbon released. Citrobacter and Thauera played an essential role in the PND process for high-ammonia wastewater treatment. Running condition, wastewater characteristic, and sludge structure played an important role in microbial composition.

Impact of cationic polyelectrolytes on activated sludge morphology and biological wastewater treatment in a Sequential Batch Reactor (SBR)

The variability of the sedimentation characteristics of activated sludge is a phenomenon that often occurs in biological wastewater treatment plants. Deterioration of sedimentation properties requires the application of polyelectrolytes. They affect the morphology of sludge flocs, facilitating and accelerating their deposition. On the other hand, the type of reagent used and its dose may affect the quality of the treated wastewater. This study investigates the effect of dosing two different cationic polyelectrolytes on the properties of activated sludge and treated wastewater parameters in lab-scale sequencing batch reactors (SBRs). During studies, doses of polyelectrolytes that significantly changed activated sludge flocs' morphology were applied. It caused an improvement of the sludge volume index (SVI) from 42 to even 80 % in relation to the control reactor. However, polymers overdose resulted in the SVI increase by 10–14 % and obtaining sludge flocs with a highly branched structure, difficult to thicken. The applied polymers Praestol 855BS and Superfloc C-18530 did not affect the chemical characteristics of the treated wastewater. The only significant effect was observed for the turbidity of the wastewater. Polymers doses reduced the value of that parameter by 54–64 %. In addition, a simulation of a technological failure for several days was introduced to assess the durability of the produced flocs and their impact on the effectiveness of wastewater treatment. The experiment showed that Praestol formed stable and durable flocs, while for Superfloc polymer, a slight temporary deterioration of wastewater quality was observed due to the lower cohesion of the activated sludge.

Potential of non-thermal discharge plasmas for activated sludge settling: effects and underlying mechanisms.

With increase in the construction of urban sewage treatment plants, the output of sludge also surges. Therefore, it is highly important to explore effective ways to reduce the production of sludge. In this study, non-thermal discharge plasmas were proposed to crack the excess sludge. High sludge settling performance was obtained, and the settling velocity (SV30) dramatically decreased from the initial value of 96% to 36% after 60 min of treatment at 20 kV, accompanied by 28.6%, 47.5%, and 76.7% decreases in mixed liquor suspended solids (MLSS), sludge volume index (SVI), and sludge viscosity, respectively. Acidic conditions improved the sludge settling performance. The presence of Cl- and NO3- slightly promoted the SV30, but CO32- has adverse effects. ·OH and O2˙- in the non-thermal discharge plasma system contributed to the sludge cracking, especially for ·OH. These reactive oxygen species destroyed the sludge floc structure; as a result, the total organic carbon and dissolved chemical oxygen demand obviously increased, the average particle size of the sludge decreased, and the number of coliform bacteria was also reduced. Furthermore, the microbial community abundance and diversity both decreased in the sludge after the plasma treatment.

Potential use of tin tetrachloride and polyacrylamide as a coagulant-coagulant aid in the treatment of highly coloured and turbid matured landfill leachate

The effectiveness of using natural coagulants as flocculants and tetravalent metal salts as coagulants in the treatment of landfill leachate remains debatable. The main aim of this study is to assess how well the polymer polyacrylamide (PAM) could interact as a coagulant, coagulant aid or flocculant with the tetravalent metal coagulant tin tetrachloride (SnCl4) in the removal of contaminants from leachate. Thus, this study examined the performance of a mix of the rare four-valence metal SnCl4 as a coagulant and compared it with the organic-based coagulant and flocculant PAM (molecular weight of 3.46 × 104 Da and zeta potential of −57.9 mV). Optimal rapid/slow mixing and settling times were evaluated by performing a standard jar test. The optimal rapid mixing rates for SnCl4 and PAM were 220 rpm and 120 rpm, respectively. At these speeds, 98.4% reductions of colour and 98.7% of SS were obtained by using SnCl4 as opposed to 35.1% and 15.3% reductions for colour and SS, respectively, by using PAM. The best slow mixing speed for both coagulants was 60 rpm, with 98.4% and 98.6% reductions of colour and SS, respectively. Whereas PAM resulted in a 40.4% reduction in colour and an insignificant reduction in SS. SnCl4 performed better in colour and SS treatment at a faster settling time (40 min) than PAM, which required a settling time of 45 min. The optimal conditions for the application of SnCl4 as the sole coagulant were pH 8 and 10 000 mg/L SnCl4. Under these conditions, SnCl4 resulted in almost complete reductions in colour and SS. However, PAM was ineffective when applied as the sole coagulant. When 100 mg/L PAM was introduced as a coagulant aid, the dosage of SnCl4 decreased to 6000 mg/L. At this dosage, SnCl4 caused 94.3% and 95.9% reductions in colour and SS, respectively. After treatment, the settling rate and sludge volume index also significantly increased to 0.61 cm/min and 84.2 mL/g, respectively. Therefore, SnCl4 and PAM could be used together to remove pollutants effectively.

Aerobic granulation for polyhydroxyalkanoates accumulation using organic waste leachates

This work aimed to evaluate polyhydroxyalkanoates (PHA)-accumulating aerobic granular sludge (AGS) production using an inoculum of activated sludge and a prefermented medium consisting of leachates from the anaerobic hydrolysis of the organic fraction of municipal solid waste (OFMSW). Operating conditions induced the evolution in the biomass structure to obtain aerobic granules with an average diameter of 1 mm within the first 45 days. This process resulted in remarkable evolution in the settling properties, with a four-fold improvement in the sludge volume index (SVI) and the zone settling velocity (Vs), as well as a considerable increase in the density during the same period. Moreover, AGS exhibited a maximum PHA accumulation capacity of 0.215 g-PHA/g-VSS, which was two-fold higher than in the inoculum, indicating the enrichment of the biomass on PHA-accumulating microorganisms as a result of the application of the anaerobic feeding of the substrate and the operation with long famine periods; operating conditions reported as favorable for both, the cultivation of stable AGS and the selection biopolymers-accumulating microorganisms. However, the carbon balance revealed that VFA from the leachates was preferably used for EPS synthesis instead of PHA production, showing that microorganisms in AGS absorb organic carbon to convert it into EPS for internal structure maintenance.

Unraveling the effects of the particle size on biomass properties, microbial community, and functional genes of denitrifying granular sludge

A comparative study was conducted on the biomass properties, microbial community composition, and functional genes of four particle-size groups of denitrifying granular sludge (DGS) (S1: 0.1 ≤ d < 0.5 mm; S2: 0.5 ≤ d < 1.0 mm; S3: 1.0 ≤ d < 1.5 mm; S4: d ≥ 1.5 mm). The results showed that the settling velocity and wet density increased with an increase in particle size. The sludge volume index and water content were negatively correlated with the particle size. The production of extracellular polymeric substances (EPS) and the ratio of protein to polysaccharides increased initially and then decreased with an increase in the particle size. S3 achieved the highest EPS, which combined with Ca2+ ions, resulting in the highest integrity coefficient. A similar convex trend was observed for the specific denitrifying activity. Illumina sequencing and quantitative polymerase chain reaction indicated that microbial community diversity and richness increased with the particle size. S3 had the largest number of denitrifying genes. Statistical analysis revealed that Aquimonas and Pannonibacter, potential hosts of the narG/nirS/nirK/norB/nosZ genes and narG/nirS/nirK/nosZ genes, respectively, were crucial for nitrate removal in the larger-sized DGS (d ≥ 1.0 mm), whereas Lentimicrobium, a possible host of the napA gene, was primarily responsible for denitrification in the smaller-sized groups (d < 1.0 mm). These results indicated that DGS with a particle size of 1.0–1.5 mm had superior granular structural stability and denitrification capacity. This study provides a new perspective for cultivating DGS and enhancing its denitrification capacity and stability.

Pilot-scale demonstration of aerobic granular sludge augmentation applied to continuous-flow activated sludge process for the treatment of low-strength municipal wastewater

This study investigated the application of aerobic granular sludge (AGS) augmentation strategy to continuous-flow activated sludge (AS) process (mainstream) for the treatment of low-strength municipal wastewater using a pilot-scale demonstration plant. A sidestream sequencing batch reactor (SBR) was adopted for AGS production, and the AGS produced was supplied to a mainstream reactor. In the sidestream, a simultaneous feeding and drawing SBR was operated. AGS rapidly formed in terms of sludge volume index (SVI) and AGS fraction and stabilized (SVI30: 62 ± 5 mL g−1, AGS fraction: 40–60 %). The installation of a novel SBR cycle, with alternately repeated steps of short and long aeration times, further improved the settleability (SVI30: 47 ± 6 mL g−1) and contributed to an increase in AGS production by ∼50 %. AGS augmentation increased the AGS fraction (20–30 %) in mainstream, and SVI30 improved to <100 mL g−1. As the organic loading rate (OLR) to the mainstream increased, the AGS fraction increased to ∼50 %, suggesting the growth of AGS in mainstream. Despite the OLR variations, the stable settleability (<100 mL g−1 of SVI30) and relatively high retention of the MLSS enabled stable removal of tBOD and ammonium (94 ± 4 and 98 ± 1 %, respectively). This is the first study that demonstrated the potential use of AGS augmentation strategy in a continuous-flow process at the pilot scale for the treatment of low-strength municipal wastewater.

Comparison of ultrasound and UV technologies to control bulking and foaming in a wastewater treatment facility. A case study in an industrial park in Morelos, Mexico

Most wastewater treatment plants use activated sludge-based biological systems for this purpose. The latter must effectively remove organic matter and, at the same time, show good sedimentability. However, sometimes there is an excessive proliferation of certain bacteria, giving rise to filamentary swelling, compromising the excellent sedimentability of the sludge. In this sense, the study’s objective was to evaluate the effect of applying two different technologies, the application of low-frequency ultrasound and UV radiation. Some bench-scale experiments were performed using the bulked sludge from the secondary clarifier of a wastewater treatment facility in an industrial park (CIVAC) in Morelos, Mexico, affected by filamentous organisms. Results showed that for the UV application for two, four, and 6 min, the settleability of the mixed liquor suspended solids was not improved; on the other hand, the cavitation effect caused by the ultrasound application demonstrated effective action against the destruction of filamentous organisms. The 10 min condition showed a significant decrease in the filament integrity of the microorganisms and a significant improvement of sedimentation velocity and sludge volume index (SVI) values and settleability of the sludge, but not enough to satisfy national discharge regulations related to total suspended solids in the treated effluent. Molecular identification indicates the presence of the genera Thauera and Brevundimonas in the sludge.

Direct start-up of aerobic granular sludge system with dewatered sludge granular particles as inoculant

Aerobic granular sludge (AGS) is a promising technology for engineering applications in the biological treatment of sewage. New objective is to skip the conventional granulation step to integrate it into a continuous-flow reactor directly. This study proposed a method for integrating spherical pelletizing granular sludge (SPGS) into a new patented aerobic granular sludge bed (AGSB), a continuous up-flow reactor. AGSB system could be startup directly, and after 120 days of operation, the SPGS maintained a relatively intact spherical structure and stability. With an initial high chemical oxygen demand (COD) volume loading of over 2.0 kg/(m3·d), this system achieved the desired effect as the same as a mature AGS system. The final mixed liquid suspended solids, and the ratio of 30 min–5 min sludge volume index (SVI30/SVI5) were 20,000 mg/L, and 0.84, respectively. Although hydraulic elution and filamentous bacteria (FBs) had a slightly negative impact on initial phase pollutant removal, the final removal rates for COD, total nitrogen (TN), ammonia nitrogen (NH4+-H), and total phosphorus (TP) were 90%, 70%, 95%, and 85%, respectively. The presence of specific functional microorganisms promoted the secretion of extracellular polymeric substances (EPS), from 90.65 to 209.78 mg/gVSS. The maturation process of SPGS altered the microbial community structures and reduced the species abundance of microbes in sludge.

Social network of filamentous Sphaerotilus during activated sludge bulking: Identifying the roles of signaling molecules and verifying a novel control strategy

Filamentous bulking is a common problem in wastewater treatment plants (WWTPs), resulting in poor sludge settleability and bad effluent quality. Existing control methods generally kill filaments at the cost of destroying the floc structures, due to the lack of knowledge on microbial interactions. Filamentous bulking is essentially an abnormal filamentous evolution depending on the sophisticated communication between floc-formers and filaments mediated by signal molecules (SMs). This study firstly identified 3-OH-C10-HSL (237 suspended solids (SS)) to drive Sphaerotilus bulking, and a quorum quenching (QQ) technology precisely inhibited bulking occurrence with maintaining floc stability and excellent bioactivity. The social network was established to clearly reveal the interacting communication between Sphaerotilus and its neighbors release functional SMs. It was further discovered that 3-OH-C10-HSL activated the signal receptor luxR of Sphaerotilus, and following up-regulated the transcriptional expressions of gluconeogenesis pathway and flagellum assembly (1.07–7.77-fold). As expected, adding its analogue 3-OXO-C10-HSL effectively quenched Sphaerotilus’ abundance<0.27 %, and decreased sludge volume index (SVI) below 150 mL/g. The morphology features and surface properties were both restored to the normal level, and specific oxygen uptake rate (SOUR) was improved by 26–35 % than that in the non-bulking sludge. This study improves our understanding of filamentation mechanisms, and represents progress towards the development of precise anti-bulking strategies.

Effect of pistachio shell as a carbon source to regulate C/N on simultaneous removal of nitrogen and phosphorus from wastewater

Acid-pretreated pistachio shells were used as carbon sources to investigate the effects of carbon source dosage on simultaneous nitrogen and phosphorus removal under different carbon/nitrogen (C/N) ratios (7, 9, and 11). Results showed that C/N was positively correlated with mixed liquor suspended solids (MLSS) (R2 = 0.998, p < 0.01) and f value (R2 = 0.975, p < 0.05). Moreover, it was negatively correlated with the sludge volume index (SVI) (R2 = − 0.959, p < 0.05). C/N was also significantly negatively related to chemical oxygen demand removal rate (R2 = − 0.986, p < 0.05) and positively related to ammonia nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) removal rate (p < 0.05), the correlation coefficients were 0.992, 0.990 and 0.994, respectively. In the reactor with C/N of 11, the MLSS concentration and f value were the highest, the SVI was the lowest, and the removal efficiencies of NH4+-N (85.49 % ± 1.96 %), TN (84.19 % ± 1.42 %) and TP (94.10 % ± 1.67 %) were the highest. Furthermore, the relative abundance of denitrifying bacteria was the highest in the reactor. The abundance of nitrifying bacteria and phosphorus-removal bacteria was also relatively high.

Simultaneous removal of carbon, nitrogen, and phosphorus from landfill leachate using an aerobic granular reactor

In this study, aerobic granular reactor (AGR) was used to treat landfill leachate by changing the concentrations of chemical oxygen demand (COD) (668 ± 110-1149 ± 93 mg/L), ammonia (NH 3 –N) (30 ± 3.3-48 ± 1.3 mg/L), and phosphorus (PO 4 –P) (147 ± 18-221 ± 17 mg/L). The average COD removal was gradually reduced from 81 to 75%, increasing COD concentrations from 668 ± 110 to 1149 ± 93 mg/L. In phase I, the maximum removal of COD (94%) and NH 3 –N (85%) were observed at influent concentrations of 668 ± 110 mg/L and 30 ± 3.3 mg/L, respectively. Significant removal of PO 4 –P was observed, resulting in a maximum of up to 87%, further reducing up to 34% due to an increase in influent PO 4 –P concentration. The SVI 30 reduced from 77 mL/g to 24.15 mL/g towards the end of phase III indicates the formation of granular biomass. The stability of AGR was also investigated in extreme conditions like shut-down and shock-loading phases. The treatment of real leachate diluted with wastewater ( ∼ 20:80% v/v) in AGR showed a significant COD, NH 3 –N, and PO 4 –P removal of 62%–65%, 61%–93%, and 56%–64%, respectively. Mass balance analysis indicated that the AGR requires a lower nitrogen percentage for microbial assimilation than the COD and phosphorus. Proteobacteria and Planctomycetes were identified as the predominant (80%) bacterial community in aerobic granules responsible for removing COD, NH 3 –N, and PO 4 –P from leachate using AGR. The maximum biodegradation rate ( r max ) and half-saturation constant ( K s ) of COD in AGR were determined as 123.5 mg/L h and 309 mg/L, respectively. • Aerobic Granular Reactor (AGR) successfully treated landfill leachate. • Carbon, nitrogen, and phosphorus simultaneously removed using AGR. • A decrease in sludge volume index (SVI 30 ) indicates granule formation. • AGR showed better performance at higher shock loading of leachate. • Proteobacteria and Planctomycetes are predominant species in AGR.

Development and characteristics of microalgae-bacteria aerobic granules treating low strength municipal wastewater

This study aims to assess the feasibility of cultivating microalgae-bacteria aerobic granular sludge using low-strength municipal wastewater (<200 mg COD/L) as a substrate. A laboratory-scale photo-sequencing batch reactor was inoculated with activated sludge and fed with municipal wastewater. The development and characteristics of microalgae-bacteria aerobic granular sludge were observed for 90 days. The average COD removal efficiency of this system was 71%. The granulation process was observed to occur on day 28, indicated by a high biomass accumulation and decreasing sludge volume index (SVI). After 90 days of cultivation, MLSS value was found to be 3.7 g/L and SVI30 at 18.9 mL/g. In addition, the diameter of the granules was significantly increased. Mature microalgae-bacteria aerobic granules were developed with an average and a maximum diameter of 0.65 mm and 6 mm, respectively. Moreover, cocci-shaped bacteria and microalgae cells were observed to reside on the granular surface during observation using field emission scanning electron microscopy (FESEM). The granules exhibited an excellent settling velocity at 80 m/h. The findings suggest the possibility of using low-strength wastewater to develop microalgae-bacteria aerobic granular sludge.

Cold temperature drives the re-granulation of disintegrated partial nitritation granules in a continuous-flow reactor

To investigate the effect of temperature on the recovery of aerobic granule stability, two continuous-flow reactors inoculated with disintegrated partial nitritation granules were operated at different temperatures for organic-free wastewater treatment. Granules disintegration and partial nitritation deterioration further occurred in the reactor (R1) operating at 25–28 °C. However, successful sludge re-granulation with a decrease of sludge volume index (SVI5) from 73 mL/g to 35 mL/g was observed in the reactor (R2) operated with the decreasing temperature from 20 °C to 12 °C. The reduced temperatures decreased the activity and growth rate of nitrifiers (from 47.2 mg/g VSS/h to 21.3 mg/g VSS/h), and selected the extracellular polymeric substance (EPS) producing bacteria (e.g., Flavobacterium and Rhodobacteraceae sp.). Correspondingly, an enhanced secretion of tightly-bound EPS (200.3–224.6 mg/g VSS in R2 vs 166.8–152.5 mg/g VSS in R1), particularly proteins, and an increased expression of quorum sensing-related enzyme genes (2.98% in R2 vs 2.75% in R1) were obtained. All of this contributed to the cold temperature-driven sludge re-granulation. The recovery of granular structure promoted the stable maintenance of efficient partial nitritation at low temperatures. Overall, this study gives insights into the positive role of cold temperatures on the stability of partial nitritation granules.