Search Results (25)

The widely utilized TiO₂ nanoparticles (NPs) tend to accumulate in wastewater and affect microbial growth. This work investigated the impacts of prolonged TiO₂ NP addition to filamentous aerobic granular sludge (AGS) using two identical sequencing batch reactors (SBRs, R1 and R2). R1 (the control) had no TiO₂ NP addition. In this reactor, filamentous bacteria from large AGS grew rapidly and extended outward, the sludge volume index (SVI₃₀) quickly increased from 41.2 to 236.8 mL/g, mixed liquid suspended solids (MLSS) decreased from 4.72 to 0.9 g/L, and AGS disintegrated on day 40. Meanwhile, the removal rates of COD and NH₄⁺-N both exhibited significant declines. In contrast, 5–30 mg/L TiO₂ NPs was added to R2 from day 21 to 100, and the extended filamentous bacteria were effectively controlled on day 90 under a 30 mg/L NP dosage, leading to significant reductions in COD and NH₄⁺-N capabilities, particularly the latter. Therefore, NP addition was stopped on day 101, and AGS became dominant in R2, with an SVI₃₀ and MLSS of 48.5 mL/g and 5.67 g/L on day 130. COD and NH₄⁺-N capabilities both increased to 100%. Microbial analysis suggested that the dominant filamentous bacteria—Proteobacteria, Bacteroidetes, and Acidobacteria—were effectively controlled by adding 30 mg/L TiO₂ NPs. XRF analysis indicated that 11.7% TiO₂ NP accumulation made the filamentous bacteria a framework for AGS recovery and operation without NPs. Functional analysis revealed that TiO₂ NPs had stronger inhibitory effects on nitrogen metabolism compared to carbon metabolism, and both metabolic pathways recovered when NP addition was discontinued in a timely manner. These findings offer critical operational guidance for maintaining the stable performance of filamentous AGS systems treating TiO₂ NP wastewater in the future. Full article

Industrial activated sludge plants in many sectors, including the dairy industry, face sludge separation problems caused by sludge bulking. Aerobic granular sludge (AGS) could be a solution by forming well-settling granules. The key to successful granulation is the microbial selection of slow-growing glycogen-accumulating organisms (GAOs) by introducing an anaerobic feeding/reaction step. The objective of the current study was to investigate the impact of two slow feeding strategies to achieve granulation in existing sequencing batch reactors treating real dairy wastewater, by microbial selection only. The first strategy consisted of slow 90 min mixed feeding. The second strategy combined 45 min static and 45 min mixed feeding to build up a substrate gradient. The feeding strategies did not affect the effluent quality, but significantly impacted the sludge morphology, settling properties, and microbial community composition. Mixed feeding led to filamentous overgrowth by Thiothrix species, up to 45% abundance, and deteriorating settling, with sludge volume index (SVI) values up to 125 mL/g. In contrast, static feeding yielded densified sludge with SVI values below 45 mL/g and up to 35% GAO abundance. In conclusion, the results show successful granulation when using a simple static slow feeding mode, which could benefit the industrial application of AGS technology. Full article

Microalgae demonstrate significant efficacy in wastewater treatment. Anaerobic digestion effluent (ADE) is regarded as an underutilized resource, abundant in carbon, nitrogen, phosphorus, and other nutrients; however, the presence of inhibitory factors restricts microalgal growth, thereby preventing its direct treatment via microalgae. The purpose of this study was to dilute ADE using various dilution media and subsequently cultivate Chlorella sp. to identify optimal culture conditions that enhance microalgal biomass and water quality. The effects of various dilution conditions were assessed by evaluating the biomass, sedimentation properties, and nutrient removal efficiencies of microalgae. The results demonstrate that microalgal biomass increases as the dilution ratio increased. The microalgae biomass in the treatments diluted with simulated wastewater was significantly higher than that with deionized water, but their effluent quality failed to meet discharge standards. The treatment diluted with deionized water for 10 times exhibited abundant microbial biomass with strong antioxidant properties. The corresponding total phosphorus concentration in the effluent (6.96 mg/L) adhered to emission limits under the Livestock and Poultry Industry Pollutant Emission Standards (8 mg/L), while ammonia nitrogen concentration (90 mg/L) was near compliance (80 mg/L). The corresponding microbial biomass, with a sludge volume index (SVI₃₀) of 72.72 mL/g, can be recovered economically and efficiently by simple precipitation. Its high protein (52.07%) and carbohydrate (27.05%) content, coupled with low ash (10.75%), makes it a promising candidate for animal feed and fermentation. This study will aid in understanding microalgal growth in unsterilized ADE and establish a theoretical foundation for cost-effective ADE purification and microalgal biomass production. Full article

This study investigates the densification/granulation of activated sludge with poor settleability, treating real industrial wastewater from a tank truck cleaning company. The wastewater is low in nutrients, acidic in nature, and high and variable in chemical oxygen demand (COD, ranging from 2770 mg·L⁻¹ to 14,050 mg·L⁻¹). A microbial selection strategy was applied to promote slow-growing glycogen-accumulating microorganisms (GAO) by the implementation of an anaerobic feast/aerobic famine strategy in a sequencing batch reactor (SBR). After 60 to 70 days, the uptake of carbon during the anaerobic phase exceeded 80%, the sludge morphology improved, and the sludge volume index (SVI) dropped below 50 mL·g⁻¹. 16S rRNA gene sequencing showed the enrichment of the GAOs Defluviicoccus and Candidatus Competibacter. Stable sludge densification was maintained when using a constant organic loading rate (OLR) of 0.85 ± 0.05 gCOD·(L·d)⁻¹, but the sludge quality deteriorated when switching to a variable OLR. In view of the integration of densified/granular sludge in a membrane bioreactor configuration, the filtration properties of the densified SBR sludge were compared to the seed sludge from the full-scale plant. The densified sludge showed a significantly lower resistance due to pore blockage and a significantly higher sustainable flux (45 vs. 15 L·(m²·h)⁻¹). Full article

This work investigated the role of an agnail device (manually made from a comb) on sludge size restriction and organic degradation in extended filamentous aerobic granular sludge-sequencing batch reactors (AGS-SBRs) with artificial wastewater. Two identical SBRs (R1 and R2) were employed in this experiment. Extended filamentous AGS with a large size was achieved in both SBRs by seeding the dewatering the sludge on day 40. R1 (the control) did not use the agnail aeration device, and the extended filamentous AGS system was finally disintegrated. However, R2 promptly employed the agnail device on days 56–59, the extended filamentous AGS size obviously decreased from 4.8 mm to 2.5 mm, and the dominant filamentous species, including Proteobacteria, Acidobacteria, and Choroflexi, gradually shrank at a low level, acting as a framework for AGS recovery. This was because enough nutrients diffused into the inside of small sludge for the filamentous living. Simultaneously, the sludge volume indexes (SVI₅ and SVI₃₀) sharply decreased from 155.8–103.9 to 51.7–46.6 mL/g, and the mixed liquid suspended solids (MLSSs) and extracellular polymeric substances (EPSs) in R2 both increased and were kept at 5816 mg/L and 69.1 mg/g·MLVSS, respectively. These contributed to enhancing the sludge’s structural stability to avoid AGS failure. COD and NH₄⁺-N in R2 were both degraded by simultaneous nitrification and denitrification (SND) processes throughout the experiment, which was not significantly influenced before or after the agnail aeration device was employed. These results indicate that the agnail device can effectively restrict AGS size and limit the extended filamentous overgrowth with nutrient diffusion into the sludge’s interior, which can prevent AGS disintegration. In addition, this device had no significant influence on organic degradation. Full article

Low-cost and easily accessible sludge treatment technologies are necessary in low- and middle-income countries. This study aimed to evaluate the use of Moringa oleifera seed powder (MO) as a natural sludge conditioner for supernatant quality improvement prior to thickening as a result of gravity settling. The zone settling rate (ZSR) and sludge volume index (SVI) were used to evaluate the gravity settling capacity. Supernatant clarification was evaluated in terms of the capacity to remove turbidity, apparent colour, Escherichia coli, and organic matter associated with zeta potential evolution. The effects on the values of pH and electrical conductivity were also evaluated. Finally, the effects on the toxicity (chronic and acute) of the supernatant effluent were examined. A significant supernatant quality improvement was observed with the addition of MO. The ZSR (0.16 cm/min) and SVI (53 mL/g) results showed that the sludge had good sedimentability, and the addition of MO maintained these characteristics in a statistical manner. Increasing the MO dosage increased the zeta potential of the supernatant, resulting in an optimal dosage of 1.2 g/L, with a removal of 90% turbidity, 70% apparent colour, 99% E. coli, and 40% organic matter. The pH and electrical conductivity values did not change with increasing MO dosage, which is a competitive advantage of MO addition compared to iron and aluminium salt addition. A reduction in the ability to remove organic matter was observed at higher dosages of the natural coagulant due to the presence of residual MO in the final effluent. The optimal MO dosage of 1.2 g/L did not affect the acute or chronic toxicity of the supernatant. These results emphasized that M. oleifera seed powder can improve the supernatant quality and can potentially be a low-cost and easily accessible conditioner for wastewater sludge thickening. Full article

The dewatering process reduces the water quantity in sludge, allowing the decrease in its volume, which facilitates its storage, transport, stabilization, and improves the post-treatment efficiency. Chemical polymers including aluminum sulphate and polyaluminum chloride were applied as flocculants in the conditioning process in order to prepare sludge for dewatering. However, these synthetic polymers may cause risks for human health, and should be substituted with ecofriendly and safe materials. These materials include plant-based flocculants, animal-based flocculants, and microbial-based flocculants. Sludge dewaterability was evaluated by considering many parameters, such as moisture content (MC), dry solids (DS), specific resistance to filtration (SRF), capillary suction time (CST), and sludge volume index (SVI). The use of microorganisms for sludge dewatering is an available option, since many strains (R. erythropolis, A. ferrooxidans, P. mirabilis, T. flavus, etc.) demonstrated their ability to produce polymers useful for dewatering sludge from various origins (chemically treated primary sludge, activated sludge, anaerobically digested sludge, etc.). For plant-based flocculants, only okra (Abelmoschus esculentus), cactus (Opuntia ficus Indica), moringa (M. oleifera), and aloe (A. vera) plants are examined for sludge dewatering. Compared to synthetic polymers, plant-based flocculants showed a viable alternative to chemicals and a step forward in green sludge treatment technology. Among the animal-based flocculants, chitosan and aminated chitosan were able to reduce the SRF (SRF reduction rate > 80%) of the anaerobically digested sludge. A new strategy using methylated hemoglobin also showed a significant enhancement in cake solid content of sludge (47%) and a decrease in sludge bound water content of 17.30%. Generally, extensive investigations are needed to explore and optimize all the related parameters (operating conditions, preparation procedure, production cost, etc.) and to choose the appropriate materials for large-scale application. Full article

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. Full article

Industrial wastewater discharges often contain high levels of organic matter and nutrients, which can lead to eutrophication and constitute a serious hazard to receiving waters and aquatic life. The purpose of this study was to examine the efficacy of using a sequencing batch reactor (SBR) to treat high-strength organic wastewater for the removal of both chemical oxygen demand (COD) and nutrients (nitrogen and phosphorus). At a constant COD concentration of approximately 1000 mg/L, the effects of cycle time (3 and 9 h) and various C:N:P ratios (100:5:2, 100:5:1, 100:10:1, and 100:10:2) were investigated using four identical SBRs (R1, R2, R3, and R4). According to experimental data, a significant high removal, i.e., 90%, 98.5%, and 84.8%, was observed for COD, NH₃-N, and PO₄³⁻-P, respectively, when C:N:P was 100:5:1, at a cycle time of 3 h. Additionally, when cycle time was increased to 9 h, the highest levels of COD removal (95.7%), NH₃-N removal (99.6%), and PO₄³⁻-P removal (90.31%) were accomplished. Also, in order to comprehend the primary impacts and interactions among the various process variables, the data was statistically examined using analysis of variance (ANOVA) at a 95% confidence level, which revealed that the interaction of cycle time and C/N ratio, cycle time and C/P ratio is significant for COD and NH₃-N removal. However, the same interaction was found to be insignificant for PO₄³⁻-P removal. Sludge volume index (SVI₃₀ and SVI₁₀) and sludge settleability were studied, and the best settling was found in R3 with SVI₃₀ of 55 mL/g after 9 h. Further evidence that flocs were present in reactors came from an average ratio of SVI ₃₀/SVI ₁₀ = 0.70 after 9 h and 0.60 after 3 h. Full article

The separation of light and heavy sludge, as well as the aggregation rate of floccular sludge, are two critical aspects of the rapid granulation process in sequencing batch reactors (SBRs) in the early stages. In this study, we investigated the impact of a method to improve both sludge separation and granulation by coupling effluent sludge external conditioning with FeCl₃ addition and then reintroducing it into the SBR. By supplementation with 0.1 g Fe³⁺ (g dried sludge (DS))⁻¹, the concentration of extracellular polymeric substances (EPS) and sludge retention efficiency greatly increased, whereas the moisture content and specific oxygen uptake rate (SOUR) sharply decreased within 24 h external conditioning. Aggregates (1.75 ± 0.05 g·L⁻¹) were reintroduced into the bioreactor once daily from day 13 to day 15. Afterwards, on day 17, aerobic granules with a concentration of mixed liquor suspended solids (MLSS) of 5.636 g/L, a sludge volume index (SVI₃₀) of 45.5 mL/g and an average size of 2.5 mm in diameter were obtained. These results suggest that the external conditioning step with both air-drying and the addition of Fe³⁺ enhanced the production of EPS in the effluent sludge and improved rapid aggregation and high sludge retention efficiency. Consequently, the reintroduced aggregates with good traits shortened the time required to obtain mature aerobic granular sludge (AGS) and properly separate light and heavy sludge. Indeed, this method jump-started the aggregation, and rapid granulation processes were successful in this work. Additionally, while the removal efficiency of chemical oxygen demand (COD) and nitrogen from ammonium (NH₄⁺-N) decreased when reintroducing the treated sludge into the SBR, such properties increased again as the AGS matured in the SBR, up to removal efficiencies of 96% and 95%, respectively. Full article

The aerobic granulation, pollutant removal, and microbial community in real textile wastewater (TWW) treatment were compared using conventional activated sludge (CAS) and preformed aerobic granular sludge (AGS) in synthetic wastewater as seed in two reactors, reactor-1 (R1) and reactor-2 (R2), respectively. The results showed that complete granulation was achieved in R1 (sludge volume index at 5 min (SVI₅) and 30 min (SVI₃₀): 19.4 mL/g; granule size: 210 μm) within 65 days, while it only required 28 days in R2 (SVI₅ and SVI₃₀: 27.3 mL/g; granule size: 496 μm). The removal of COD, NH₄⁺-N and TN in R1 (49.8%, 98.8%, and 41.6%) and R2 (53.6%, 96.9%, and 40.8%) were comparable in 100% real TWW treatment, but stable performance was achieved much faster in R2. The real TWW had an inhibitory effect on heterotrophic bacteria activity, but it had no inhibition on ammonia-oxidizing bacteria activity. AGS with a larger particle size had a higher microbial tolerance to real TWW. Furthermore, filamentous Thiothrix in the AGS in R2 disappeared when treating real TWW, leading to the improvement of sludge settleability. Thus, seeding preformed AGS is suggested as a rapid start-up method for a robust AGS system in treating real TWW. Full article

In this study, three 1.2-L aerobic granular sludge sequencing batch reactors (AGS-SBRs) were used to cultivate nitrifying and nitrifying-denitrifying granules (w/supplemental carbon) and investigate sidestream treatment of synthetic-centrate and real-centrate samples from Ashbridges Bay Treatment Plant (ABTP) in Toronto, Ontario, Canada. Results showed that although the cultivation of distinct granules was not observed in the nitrifying reactors, sludge volume index (SVI₃₀) values achieved while treating real and synthetic centrate were 72 ± 12 mL/g and 59 ± 11 mL/g (after day 14), respectively. Ammonia-nitrogen (NH₃-N) removal in the nitrifying SBRs were 93 ± 19% and 94 ± 16% for real and synthetic centrate, respectively. Granules with a distinct round structure were successfully formed in the nitrifying-denitrifying SBR, resulting in an SVI₃₀ of 52 ± 23 mL/g. NH₃-N, chemical oxygen demand (COD) and phosphorus (P) removal in the nitrifying-denitrifying SBR were 92 ± 9%, 94 ± 5%, and 81 ± 14% (7th to 114th day), respectively with a low nitrite (NO₂-N) and nitrate (NO₃-N) concentration in the effluent indicating simultaneous nitrification-denitrification (SND) activity. High nutrient removal efficiencies via the nitrification and SND pathways shows that AGS technology is a viable process for treating sidestreams generated in a WWTP. Full article

Aerobic granular sludge (AGS) application in treating municipal wastewater has been greatly restricted due to its low stability. It has been found that operation parameters have a great impact on stability. The organic loading rate (OLR) and dissolved oxygen (DO) concentration are two very important parameters that impact stability. In this study, the organic loading rate (OLR) and aeration rate were studied to verify their influence on AGS system stability, which is indicated by determining pollutant removal performance, including chemical oxygen demand (COD), ammonia nitrogen, and total nitrogen (TN). The physical and chemical property changes of AGS and the effects of pollutant removal during the formation of AGS were systematically investigated. The AGS was formed after about 25 days and remained stable for about 45–50 days. The AGS was light-yellow globular sludge with an average particle size of 1.25 mm and a sludge volume index (SVI) of 33.9 mL/g. The optimal condition was obtained at an OLR of 4.2 kg COD/m³·d, aeration rate of 4 L/min, and a hydraulic retention time (HRT) of 4 h. The corresponding removal efficiencies of COD, ammonia nitrogen, and TN were 94.1%, 98.4% and 74.1%, respectively. The study shows that the AGS system has great potential for pollutant removal from wastewater. Full article

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. Full article

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 (R_0.5, 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. Full article