Aerobic Sludge Research Articles

Aerobic Sludge Granulation and Simultaneous Partial Nitrification, Denitrification, and Phosphorus Removal in an AOA-SBR with Low Dissolved Oxygen

Aerobic Sludge Granulation and Simultaneous Partial Nitrification, Denitrification, and Phosphorus Removal in an AOA-SBR with Low Dissolved Oxygen

Dynamics of antibiotic resistance agents during sludge alkalinization treatment

This study aimed to assess the removal of antimicrobial resistance agents (antibiotics, antibiotic-resistant bacteria - ARB, and antimicrobial resistance genes - ARGs) from aerobic and anaerobic sludges treated with quicklime (chemical alkalinization). Different mixing ratios (25%, 35%, and 45%) and contact times (2 h and 72 h) were evaluated. The findings revealed that anaerobic sludge responded more effectively to alkaline treatment, achieving better removal rates of antibiotics, ARB, and ARGs compared to aerobic sludge. The 45% lime treatment yielded the highest antibiotic removal rates, with average reductions of 19% in aerobic sludge and 28% in anaerobic sludge. The 35% lime treatment was the most effective in reducing ARGs across both types of sludge (average removal of 2 logs). The 25% lime treatment proved most efficient for removing ARB, with average reductions of 4 logs (aerobic) and 5 logs (anaerobic). The contact time between the sludge and quicklime also influenced the removal of resistance agents. An increase in the proportion of antibiotics and the absolute concentration of ARB and ARGs was observed after 72 h compared to the samples analyzed after 2 h of contact. This increase was more pronounced in aerobic sludge samples treated with 35% and 45% lime. Despite the overall reduction, none of the monitored resistant genes or bacteria were completely eradicated in both sludge samples, raising concerns about their potential dissemination into the environment.

Effects of different substrate ratios on the enrichment of anammox bacteria at low substrate concentration

Anammox bacteria (AnAOB) can be easily enriched under high temperatures and high substrate concentrations, while the application of the mainstream anammox process in low substrate municipal sewage is still relatively uncommon. Therefore, this study investigated the enrichment of AnAOB under conditions of low ammonia nitrogen and nitrite concentration at 25 °C. Results showed that using inoculated aerobic sludge, four ASBRs (R1, R2, R3 and R4) were successfully initiated with different influent substrate (NO2−-N/NH4+-N) ratios of 1.2, 1.32, 1.4 and 1.5, respectively, with reactor start-up times were 162, 150, 120 and 134 days, respectively. The values of ΔNO2--N/ΔNH4+-N in reactors were stable at 1.17, 1.32, 1.43 and 1.53 respectively. The increase in influent substrate ratios resulted in improved TN removal rates and accelerated consumption of chemical oxygen demand (COD) during the initial start-up stage. The maximum TN removal rates achieved in the four reactors were 76.09%, 79.24%, 82.82% and 82.63%, respectively. The color of sludge gradually changes from yellowish-brown to reddish-brown. Furthermore, the surface of sludge exhibited a porous mineral structure, with crater-like cavities. The dominant anammox species in the system was identified as Candida Brocadia (3.04%). According to qPCR, the abundance of hzsB in the system is 1.65 × 1012 copies/g VSS, confirming the effective enrichment of AnAOB.

Changes in the operation of the aerobic stabilisation chamber to increase the reliability of Nutrient pollution removal in a multi-phase biological reactor

The objective of the study was to optimise the operation of the aerobic stabilisation chamber so as to increase the efficiency of elimination of nitrogen and phosphorus compounds at the collective wastewater treatment plant in Dąbrowa Tarnowska. To demonstrate positive optimisation measures, the study was carried out in two periods, pre-modernisation and post-modernisation. The first part of the study took place from January 2016 to May 2020, with the latter from June 2020 to December 2023. The reliability of biogenic compounds removal in the treatment process was carried out using the Weibull method. The modernisation of the operation of the aerobic sludge stabilisation chamber resulted in the stabilisation and increased efficiency of the nitrification and denitrification processes in this treatment plant. The reliability of removal of nitrogen compounds in the post-modernisation period was 79 % compared to the pre-change period, which was 47 %. In the case of phosphorus compounds, no significant changes were found in the concentration in the treated effluent in either of the analysed periods.

Nickel augmented biochar for sustaining produced water treatment to decarbonize oil and gas industrial waste using anaerobic-aerobic granular cylindrical periodic discontinuous batch reactors

This study assessed the efficacy of granular cylindrical periodic discontinuous batch reactors (GC-PDBRs) for produced water (PW) treatment by employing eggshell and waste activated sludge (WAS) derived Nickel (Ni) augmented biochar. The synthesized biochar was magnetized to further enhance its contribution towards achieving carbon neutrality due to carbon negative nature, Carbon dioxide (CO2) sorption, and negative priming effects. The GC-PDBR1 and GC-PDBR2 process variables were optimized by the application of central composite design (CCD). This is to maximize the decarbonization rate. Results showed that the systems could reduce total phosphorus (TP) and chemical oxygen demand (COD) by 76–80% and 92–99%, respectively. Optimal organic matter and nutrient removals were achieved at 80% volumetric exchange ratio (VER), 5 min settling time and 3000 mg/L mixed liquor suspended solids (MLSS) concentration with desirability values of 0.811 and 0.954 for GC-PDBR1 and GC-PDBR2, respectively. Employing four distinct models, the biokinetic coefficients of the GC-PDBRs treating PW were calculated. The findings indicated that First order (0.0758–0.5365) and Monod models (0.8652–0.9925) have relatively low R2 values. However, the Grau Second-order model and Modified Stover-Kincannon model have high R2 values. This shows that, the Grau Second Order and Modified Stover-Kincannon models under various VER, settling time, and MLSS circumstances, are more suited to explain the removal of pollutants in the GC-PDBRs. Microbiological evaluation demonstrated that a high VER caused notable rises in the quantity of several microorganisms. Under high biological selective pressure, GC-PDBR2 demonstrated a greater percentage of nitrogen removal via autotrophic denitrification and a greater number of nitrifying bacteria. The overgrowth of bacteria such as Actinobacteriota spp. Bacteroidota spp, Gammaproteobacteria, Desulfuromonas Mesotoga in the phylum, class, and genus, has positively impacted on granule formation and stability. Taken together, our study through the introduction of intermittent aeration GC-PDBR systems with added magnetized waste derived biochar, is an innovative approach for simultaneous aerobic sludge granulation and PW treatment, thereby providing valuable contributions in the journey toward achieving decarbonization, carbon neutrality and sustainable development goals (SDGs).

Partial nitrification and simultaneous denitrification in sequential anaerobic and aerobic reactors: performance and microbial community dynamics

ABSTRACT The removal of organic matter and nitrogen from domestic sewage was evaluated using a system composed of two sequential reactors: an anaerobic reactor (ANR) with suspended sludge and an aerobic (AER) reactor with suspended and adhered sludge to polyurethane foams. Nitrogen removal consisted of AER operating at low dissolved oxygen (DO) concentrations; this favoured the simultaneous nitrification and denitrification (SND) process. The concentration of COD and N were 440 mgO2.L−1 and 37 mgTN.L−1, respectively. The operation was divided into three phases (P), lasting 51, 53, and 46 days, respectively. The initial DO concentrations applied in the AER were: 3.0 (PI) and 1.5 mg.L−1 (PII and PIII). In PIII, the AER effluent was recirculated to the ANR at a ratio of 0.25. Kinetic assays were performed to determine the nitrification and denitrification rates of the biomasses (ANR and AER in PIII). Changes in the microbial community were evaluated throughout phases PI to PIII by massive sequencing. In PIII, the best results obtained for chemical oxygen demand (COD) and total nitrogen (TN-N) removal efficiencies, were close to 94% and 65%, respectively. Under these conditions, system effluent concentrations below 30 mg COD.L−1 and 15 mg TN-N.L−1 were verified. The nitritation and nitration rates were 10.5 and 6.5 mg N.g VSS−1.h−1, while the denitrification via nitrite and nitrate were 6.8 and 5.8 mg N.g VSS−1.h−1, respectively. A mixotrophic community was prevalent, with Rhodococcus, Nitrosomonas, Pseudomnas, and Porphyromonas being dominant or co-dominant in most of the samples, confirming the SND process in the AER sludge.

Palm Oil Mill Effluent Treatment Technology using Sequencing Batch Reactor (SBR) with Oxidation Reduction Potential (ORP) Monitoring

Palm oil industries have products like Crude Palm Oil (CPO), and 70% of others contain waste. One of the wastes is the liquid waste known as Palm Oil Mill Effluent (POME). The potential of POME to be reprocessed into clean water will be profitable. One of POME's reprocessing methods is the Sequencing Batch Reactor with Aerobic Granulated Sludge (SBR-AGS), which has five main phases: filling, idling, aeration, settling, and discharge, with a cycle time of 360 minutes. The first step in using this reactor is the start-up process, a granule-forming process from some sludge that has already acclimatized. In one complete cycle, the Oxidation-Reduction Potential (ORP) parameter is used to observe the electron transfer process that shows the oxygen supply into the reactor, which enables the condition of each phase in the process to be analyzed. The trend of ORP value is constantly changing in every phase. For the idling phase, the ORP tends to decrease in a value of (-300)-(-400) mV, and for the aeration phase, it will increase in a value of (-100)-100 mV.

An innovative fast-start aerobic anode microbial fuel cell biosensor for copper ion detection

The potential of microbial fuel cells (MFCs) based biosensors for water monitoring and early warning is widely recognized. However, the electrochemically active biofilms (EABs) are typically obtained under anaerobic conditions and the formation requires a lengthy time span, which critically limits the application and advancement of the MFCs based monitoring technology. To accelerate the formation rate of EABs and thus shorten the establishment time of MFCs to better meet the needs for early warning and detection of pollutants in the actual aerobic water environment, the aerobic sludge was employed as an inoculation source to construct the MFCs sensing system in this study. It was revealed that biofilms with stable electrochemical properties could be promptly formed within 35 h, reaching a level far ahead of previous studies. Moreover, toxicity tests for copper (Cu2+) ions at concentrations of 1 mg/L, 10 mg/L, and 50 mg/L demonstrated outstanding performance with the maximum inhibition rates of 19.99%, 46.65%, and 53.02% respectively. Remarkably, the response time was found to decrease significantly with the increase of copper ion concentrations. Our results thus open up a new avenue for achieving rapid start-up of MFCs in aerobic conditions, which facilitates the applicability of MFCs based biosensing technology.

Changes and stage disparity of aerobic sludge granulation with increasing organic load rate under low organotrophic conditions

The experiment focused the impact of increasing organic load rate (OLR) (0.6 kg COD·m−3·d−1 →1.2 kg COD·m−3·d−1) on the development of aerobic granular sludge (AGS) under low organotrophic conditions. During the sludge granulation process, the sludge characteristics and pollutant removal performance as the OLR increased under low organotrophic conditions in the reactor were better than that at constant OLR. At the end of the experiment, the mixed liquid suspended solid concentration and average particle size increased to 5.6 g/L and 1288.6 μm, and the removal efficiency of pollutants reached more than 80% with increasing OLR. However, the strengthening effect of the increasing OLR under low organotrophic conditions varied at the different stages during sludge granulation, indicating its stage disparity. In addition, the increase in OLR under low organotrophic conditions changed the extracellular polymeric substances distribution and chemical structure characteristics, with protein changes being more sensitive. With increasing OLR at granule formation stage, the microbial community structure varied obviously. Furthermore, the function bacterial Zoogloea, Plasticicumulans, and unclassified_Rhodocyclaceae were enriched, which might be the underlying cause of the stage disparity.

Thermal hydrolysis pretreatment of wastewater biosolids: Modelling the impact of the aerobic sludge age

This study investigates the impact of thermal hydrolysis pretreatment (THP) on the characteristics of wastewater biosolids, methane production, anaerobic biodegradability, and recycled sidestream nitrogen loads, as a function of the sludge age of the activated sludge (AS) system through a series of BioWin simulations of 3 different process configurations at sludge ages of 5, 10, 15, 20, 30, and 60 d, with and without thermal hydrolysis. BioWin's anaerobic digester and thermal hydrolysis units were calibrated by adopting and identifying various kinetic and operational parameters from the available literature and through series of full-scale plant simulations. Thermal hydrolysis improved the hydrolysis rates of the biosolids by 181%. Improvements in anaerobic biodegradability, mainly due to the conversion of endogenous products, ranged from 14% to 67% at sludge ages of 5–15 d. At sludge ages of 20–60 d, anaerobic biodegradability improved by 59% to 186% depending on the process configuration. At sludge ages of 15–60 d, methane production was relatively stable and insensitive to the biosolids composition. Despite the increase in the recycled nitrogen load by 42% to 127%, it only constituted 13% of the influent nitrogen load. Effluent ammonia concentrations remained unchanged and effluent nitrates concentrations only increased by 1.4 to 2 mg N/L, maintaining effluent standards without additional sidestream treatment.

Recovery potential of aerobic sludge biomass stressed with Cu(II) laden piggery wastewater

Piggery wastewater (PWW) contains a variety of pollutants, and lack of treatment infrastructure in piggery farms often results in the discharge of PWW into nearby drains, eventually reaching sewage treatment plants. It may adversely affect the sludge biomass of the treatment plants. This study investigated the effects of prolonged exposure to PWW and copper-laden (40 and 80 mg/L) PWW on the quality of sludge biomass. The results revealed that PWW-exposed reactors experienced a significant decrease in COD removal (65–76% compared to 95% in the control reactor). Additionally, there were changes in sludge characteristics, including a decreased sludge volume index (SVI) and an increased interface settling velocity (ISV). Further addition of PWW+Cu(II) stress significantly reduced COD removal (8–29%), the filamentous index and also lowered cell viability and enzyme activity. However, partial recovery was observed after discontinuing PWW+Cu(II) exposure, particularly at 40 mg/L of Cu(II) concentration. The study is significant for practical wastewater treatment, as it deals with multi-stress conditions caused due to Cu(II) metal laden piggery wastewater. The investigation recommends preliminary tests (microscopic examination and aerobic sludge biomass activity test) and confirmatory tests (cell viability tests and amplified ribosomal DNA restriction analysis) to be used for the evaluation of aerobic sludge biomass quality.

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

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

Deciphering the core bacterial community structure and function and their response to environmental factors in activated sludge from pharmaceutical wastewater treatment plants

Pharmaceutical wastewater is recognized for its heightened concentrations of organic pollutants, and biological treatment stands out as an effective technology to remove these organic pollution. Therefore, a comprehensive exploration of core bacterial community compositions, functions, and their responses to environmental factors in pharmaceutical wastewater treatment plants (PWWTPs) is important for understanding the removal mechanism of these organic pollutants. This study comprehensively investigated 36 activated sludge (AS) samples from 15 PWWTPs in China. The results revealed that Proteobacteria (45.41%) was the dominant phylum in AS samples, followed by Bacteroidetes (19.54%) and Chloroflexi (4.13%). While the dominant genera were similar in both aerobic and anaerobic treatment processes, their relative abundances exhibited significant variations. Genera like HA73, Kosmotoga, and Desulfovibrio were more abundant during anaerobic treatment, while Rhodoplanes, Bdellovibrio, and Hyphomicrobium dominated during aerobic treatment. 13 and 10 core operational taxonomic units (OTUs) were identified in aerobic and anaerobic sludge, respectively. Further analysis revealed that core OTUs belonging to genera Kosmotoga, Desulfovibrio, Thauera, Hyphomicrobium, and Chelativorans, were associated with key functions, including sulfur metabolism, methane metabolism, amino acid metabolism, carbohydrate metabolism, toluene degradation, and nitrogen metabolism. Furthermore, this study highlighted the crucial roles of environmental factors, such as COD, NH4+-N, SO42−, and TP, in shaping both the structure and core functions of bacterial communities within AS of PWWTPs. Notably, these factors indirectly affect functional attributes by modulating the bacterial community composition and structure in pharmaceutical wastewater. These findings provide valuable insights for optimizing the efficiency of biochemical treatment processes in PWWTPs.

Resilience of aerobic sludge biomass under chlorpyrifos stress and its recovery potential

Non-agricultural sources of pesticides in urban areas are responsible for their presence in domestic wastewater. Therefore, pesticides are typically found in sewage treatment plants in developed and developing countries as micro-pollutant. The presence of pesticides in the wastewater can impart stress on the aerobic sludge biomass and disrupt the functioning of the plant. However, there exists a knowledge gap regarding the resilience of aerobic sludge biomass towards stress due to the presence of pesticides in the wastewater. This study investigated the impact of chlorpyrifos (CPS) – a widely used pesticide, on sludge biomass and explored its recovery capability when CPS is discontinued in the influent. Four duplicate reactors were operated with different CPS concentrations ranging from 50 to 200 mg/L. Chemical oxygen demand (COD) removal for reactors has ranged within 18–73 % at the steady state of the stressed phase, whereas COD removal for the control reactor was 91 %. CPS stress slightly inhibited filamentous biomass growth. Biomass activity and cell viability have decreased significantly, whereas biochemical contents have varied slightly under CPS stress. The activities of the enzymes dehydrogenase and urease were significantly inhibited when compared to catalase and protease. Amplified ribosomal DNA restriction analysis reflected changes in the microbial community. The discontinuation of CPS has allowed aerobic sludge biomass to recover in its organic degradation capability (COD removal of more than 88 % at steady-state conditions of recovery phase operation), biomass growth, and cell viability. In addition, enzyme activities have retrieved to their original levels, and 78–93 % similarity of microbial community structure has been displayed between CPS-exposed and control reactor biomasses. Overall, the present study has indicated the orderly changes in the quality of aerobic sludge biomass under CPS stress through physico-chemical and biological characteristics. The study also has highlighted the self-recovery of sludge biomass characteristics stressed with different concentrations of CPS.

Two-stage sequencing batch reactors with added iron shavings for nutrient removal and aerobic sludge granulation treating real wastewater with low carbon to nitrogen ratios

In response to the challenges of limited nutrient removal and the difficulty in forming aerobic granular sludge (AGS) with low carbon to nitrogen (C/N) ratios, a novel two-stage sequencing batch reactors (SBRs) (R1 and R2) system with added iron shavings was proposed and established. The results showed that AGS was developed and nitrogen (82.8 %) and phosphorus (94.7 %) were effectively removed under a C/N ratio at 1.7 ± 0.5. The average size of R1 and R2 increased from 45.3 μm to 138.7 μm and 132.8 μm. Under high biological selective pressure, phosphorus accumulating organisms like Comamonadaceae (14.8 %) and Chitinophagales (5.7 %) experienced enrichment in R1. Furthermore, R2 exhibited an increased abundance of nitrifying bacteria (2.3 %) and a higher proportion of nitrogen removal through autotrophic denitrification (＞17.5 %). Overall, this study introduces an innovative two-stage SBRs with added iron shavings, offering a novel approach for the treatment of low C/N ratios wastewater.

Vertical baffled reactor promoting aerobic sludge concentration for effective remediating unstable–load domestic wastewater: Performance, microbial properties and mechanism

The study evaluated the pollutant degradation ability and the microbial community of aerobic granular sludge (AGS) in the modified vertical baffle reactors (VBRs) in the treatment of unstable–load domestic wastewater. The AGS was cultivated in the reactor which was ensured by the special structure and sludge reflux system of VBRs. VBRs can maintain a high sludge concentration without sludge bulking, while long hydraulic retention time (HRT) ensured a high sludge concentration to improve the treatment capacity to unstable influent. Unstable–load domestic wastewater, with COD = 120–556 mg/L, TN = 19.97–81.54 mg/L, was applied as the influent for 180 days of continuous experiments, while the system achieved a stable removal effect on the indicator pollutants. On day 180, MLSS maintained at 7000 mg/L with the average particle size of sludge at 1000 μm. The increasing concentration of extracellular polymeric substances (EPS), especially polysaccharide (PS) was conducive to the bridging among particles to form AGS, which played an important role in maintaining the stability of granular sludge. The results of functional microbial communities showed that Proteobacteria was the most abundant phylum in aerobic sludge, while the Nitrospira was the dominant bacteria in genus level. The microbial community was biodiverse, and can achieve the effect of the simultaneous removal of multiple contaminants.

Stability and Biotransformation of 6:2 Fluorotelomer Sulfonic Acid, Sulfonamide Amine Oxide, and Sulfonamide Alkylbetaine in Aerobic Sludge.

The 6:2 fluorotelomer sulfonamide (6:2 FTSAm)-based compounds signify a prominent group of per- and polyfluoroalkyl substances (PFAS) widely used in contemporary aqueous film-forming foam (AFFF) formulations. Despite their widespread presence, the biotransformation behavior of these compounds in wastewater treatment plants remains uncertain. This study investigated the biotransformation of 6:2 FTSAm-based amine oxide (6:2 FTNO), alkylbetaine (6:2 FTAB), and 6:2 fluorotelomer sulfonic acid (6:2 FTSA) in aerobic sludge over a 100-day incubation period. The biotransformation of 6:2 fluorotelomer sulfonamide alkylamine (6:2 FTAA), a primary intermediate product of 6:2 FTNO, was indirectly assessed. Their stability was ranked based on the estimated half-lives (t1/2): 6:2 FTAB (no obvious products were detected) ≫ 6:2 FTSA (t1/2 ≈28.8 days) > 6:2 FTAA (t1/2 ≈11.5 days) > 6:2 FTNO (t1/2 ≈1.2 days). Seven transformation products of 6:2 FTSA and 15 products of 6:2 FTNO were identified through nontarget and suspect screening using high-resolution mass spectrometry. The transformation pathways of 6:2 FTNO and 6:2 FTSA in aerobic sludge were proposed. Interestingly, 6:2 FTSAm was hardly hydrolyzed to 6:2 FTSA and further biotransformed to perfluoroalkyl carboxylic acids (PFCAs). Furthermore, the novel pathways for the generation of perfluoroheptanoic acid (PFHpA) from 6:2 FTSA were revealed.

Recuperação de biopolímeros de lodo biológico e seu uso como biossorvente de fósforo

ABSTRACT Biopolymers can be recovered from aerobic sludge and used for environmental applications, such as phosphorus adsorbent material, instead being sent to sanitary landfills. In this resource recovery perspective, this work aimed to study the recovery of alginate-like exopolymer (ALE) from activated sludge (AS) compared to aerobic granular sludge (AGS). ALE-based biosorbent was prepared and tested to remove phosphorus from aqueous solutions, and the adsorption kinetics and isotherm models were studied. The recovery yield of ALE from a full-scale wastewater treatment plant (WWTP) AS (18.7%) was close to that obtained from a pilot-scale AGS (22%). ALE recovered from AS presented hydrogel properties and humic substances in its composition, which are important features for future applications. The equilibrium of the adsorption was reached after 10 minutes. The Langmuir isotherm model and the PFO kinetic model best fitted to the experimental data, resulting in maximum adsorption capacity of 8.164 mgP·gALE. Thus, ALE recovered from AS has the potential to be used as a phosphorus biosorbent from effluents and further used as a nutrient delivery system with hydrogel properties.

Study on culture of stable aerobic granular sludge

In this study, three reactors were established with anaerobic plug-flow times of 1.5 hours, 1 hour, and 0.5 hours. The results indicated that the anaerobic plug-flow time of 1 hour constructed favorable "feast- famine" period ratio, promoting the enrichment of microorganisms that stored and utilized the internal carbon source, such as Phosphate and Glycogen Accumulating Organisms (PAO and GAO). This resulted in the formation of granular sludge with both short granulation time and structural stability. In contrast, shortening the anaerobic feed time to 0.5 hours was detrimental to the growth of GAO, leading to slow granularization of aerobic sludge. The anaerobic influent time of 1.5 h leads to the shortening of starvation period and poor stability of particle structure.

Pollution Mitigation in Vermicelli Wastewater: Integrated Fenton and Aerobic Sludge Treatment for Water Quality Improvement.

Vermicelli production generates wastewater that is rich in organic and nutrient pollutants, which poses significant environmental challenges. Conventional biological treatments, either alone or in combination with other methods, often fail to achieve high efficiency and operational stability. This study explored the potential of the Fenton process, followed by aerobic activated sludge treatment, to enhance the biodegradability and mineralization of organic substances in vermicelli wastewater. Orientation experiments were performed to examine the effects of operating variables such as pH, reaction time, settling time, and ratio H2O2/Fe2+ on COD removal in order to select the optimal conditions for operating the model in a batch of 20 L, that is, pH = 3, reaction time of 90 min, settling time of 90 min, and ratio of H2O2/Fe2+ used 3 : 1 (4.5 : 1.5 g/L). The removal efficiencies of COD, BOD5, TN, TP, and SS reached 75.83%, 67.26%, 28.24%, 26.63%, and 91.9%, respectively. The BOD5/COD increased from 0.52 to 0.63, facilitating aerobic activated sludge, which had batch conditions of 15 L with pH of 6.5-8.5, DO ≥3 mg/L, additional nutrients with a dose of 12 mg/L, retention time of 14 h, and settling time of 2 h. As a result, the removal rate of those parameters climbed quite notably, except in SS (95.6%, 96.0%, 84.6%, 84.1%, and 83.6%), and their concentration parameters remained within the allowance levels of the National Technical Regulation in Vietnam before being discharged into the environment. However, the efficiency of treatment in the aerobic activated sludge stage for removing COD and BOD5 was not as high as anticipated (83% and 87.33%, respectively) owing to the influence of the high TDS concentration. Thus, additional research is required to address this challenge. The integrated treatment system combining the Fenton process with aerobic activated sludge demonstrated significant potential for the effective reduction of organic and nutrient pollutants in vermicelli wastewater, thereby achieving compliance with regulatory standards. However, the observed limitations in COD and BOD5 removal efficiency, likely due to elevated TDS levels, indicate the need for further investigation and optimization to enhance the overall treatment performance.