Intermittent Aeration Research Articles

Attached and suspended biomass kinetics in an IFAS-MBR system operated under intermittent aeration: Long-term monitoring under SRT variation

This study thoroughly investigates a Membrane BioReactor – Integrated Fixed Film Activated Sludge – Intermittent Aeration (MBR-IFAS-IA) pilot plant operated from a biokinetic point of view. Specifically, respirometric techniques were applied on suspended and attached biomass to evaluate kinetic and stoichiometric parameters. The main aim was to investigate how the simultaneous presence of biofilm and activated sludge could affect the kinetic behaviour and the role of the Sludge Retention Time (SRT) variation in the kinetic behaviour of the system. The results highlighted a mutual interaction between suspended biomass and biofilm in the IFAS-MBR configuration. In Period I both the heterotrophic yield and growth rate of suspended biomass were higher compared to that of biofilm, thus highlighting higher affinity with organic matter; in contrast, the biofilm showed high affinity with nitrification, with increased nitrification rates with decreasing SRT and sustaining nitrification in the activated sludge due to “seeding” effect. Therefore, the suggestion is that it is possible to operate IFAS-MBR systems at low SRT without hampering the nitrification ability due to the growth of nitrifiers in the biofilm. Respirometry has been confirmed to be an effective tool for evaluating biomass kinetic and stoichiometric parameters. The results of this study highlighted the effect of IFAS configuration and can help apply mathematical models in the design phase and monitor biomass viability during plant operations.

Investigation on aeration efficiency and energy efficiency optimization in recirculating aquaculture coupling CFD with Euler-Euler and species transport model

Aeration plays a crucial role in maintaining the overall health and sustainability of the recirculating aquaculture system. Conventional aeration operates continuous and consumes 35.06 % of equipment energy consumption. How to optimize aeration while ensuring normal fish growth remains a great challenge. To address these challenges, this research paper established a coupled model of computational fluid dynamics and species transport model (CFD-STM). Aeration tests were carried out in a 33.3 m3 culture tank using a 0.31 m diameter aerator to find out the impacts of operating variables (aeration flow rate, bubble diameter, inlet velocity, and aerator position) on oxygen transfer using a microporous aeration system. A CFD-STM model was coupled to obtain the optimum values of aeration parameters. Results revealed that the Standard Aeration Efficiency (SAE) reductions by 32.1 % for 50 % larger aeration flow rate and 86.4 % for 50 % larger bubble diameter, as well as SAE achieved 5.67 kg/kWh with an aerator position scale factor equal to 0.48. In addition, the energy consumption of the Roots blower was compared for a single aeration and dissolved oxygen saturation. Results indicated that smaller bubbles microbubbles can effectively improve oxygen transfer coefficient. The energy consumption was reduced by 15.7 % for 50 % larger aeration flow rate and 38.6 % for 50 % lower bubble diameter. Based on the results, this study demonstrated that CFD is a useful tool to optimize the aeration system design and operation in order to enhance aeration efficiency. It provides a theoretical foundation the future optimization of energy conservation through intermittent aeration practices.

Illuminating the role of powder carrier materials in shaping sludge aggregation in wastewater treatment: Insights from extended operation performance to microbial response mechanism

This study uncovered the response of novel micro-granule wastewater treatment technology to different powder carrier materials. Characteristics and distinctions among different systems were assessed based on process performance, sludge aggregation capacity, and microbial metabolism. Zeolite carrier system exhibited remarkable nitrogen removal efficiency of 89.6 ± 0.9 %, while diatomite carriers, in conjunction with intermittent aeration, enhanced simultaneous nitrification and denitrification from 2.6 % to 27.1 %. Iron-based carriers demonstrated efficient phosphorus removal (94.7 ± 1.2 %) through both chemical and microbial pathways. Specific surface area, pore structure and biocompatibility of powder carriers determined the formation and size of micro-granules. Tryptophan-like substances, C-(C/H), and Npr in extracellular polymeric substances strongly correlated with sludge hydrophobicity and granulation. Significant enrichment in norank_Comamonadaceae and Nitrosomonas in zeolite powder carrier system promoted partial nitrification and endogenous denitrification. Differences in metabolic pathways elucidated the up-regulation of amino acid synthesis, energy metabolism, and membrane transport as potential mechanisms driving micro-granule formation and efficient treatment performance.

Exploring Aeration Strategies for Enhanced Simultaneous Nitrification and Denitrification in Membrane Aerated Bioreactors: A Computational Approach.

In this study we employ computational methods to investigate the influence of aeration strategies on simultaneous nitrification-denitrification processes. Specifically, we explore the impact of periodic and intermittent aeration on denitrification rates, which typically lag behind nitrification rates under identical environmental conditions. A two-dimensional deterministic multi-scale model is employed to elucidate the fundamental processes governing the behavior of membrane aerated biofilm reactors (MABRs). We aim to identify key factors that promote denitrification under varying aeration strategies. Our findings indicate that the concentration of oxygen during the off phase and the duration of the off interval play crucial roles in controlling denitrification. Complete discontinuation of oxygen is not advisable, as it inhibits the formation of anaerobic heterotrophic bacteria, thereby impeding denitrification. Extending the length of the off interval, however, enhances denitrification. Furthermore, we demonstrate that the initial inoculation of the substratum (membrane in this study) influences substrate degradation under periodic aeration, with implications for both nitrification and denitrification. Comparison between continuous and periodic/intermittent aeration scenarios reveals that the latter can extend the operational cycle of MABRs. This extension is attributed to relatively low biofilm growth rates associated with non-continuous aeration strategies. Consequently, our study provides a comprehensive understanding of the intricate interplay between aeration strategies and simultaneous nitrification-denitrification in MABRs. The insights presented herein can contribute significantly to the optimization of MABR performance in wastewater treatment applications.

Simultaneous carbon, nitrogen and phosphorus removal in sequencing batch membrane aerated biofilm reactor with biofilm thickness control via air scouring aided by computational fluid dynamics

Membrane aerated biofilm reactor (MABR) is challenged by biofilm thickness control and phosphorus removal. Air scouring aided by computational fluid dynamics (CFD) was employed to detach outer biofilm in sequencing batch MABR treating low C/N wastewater. Biofilm with 177–285 µm thickness in cycle 5–15 achieved over 85 % chemical oxygen demand (COD) and total inorganic nitrogen (TIN) removals at loading rate of 13.2 gCOD/m2/d and 2.64 gNH4+-N/m2/d. Biofilm rheology measurements in cycle 10–25 showed yield stress against detachment of 2.8–7.4 Pa, which were equal to CFD calculated shear stresses under air scouring flowrate of 3–9 L/min. Air scouring reduced effluent NH4+-N by 10 % and biofilm thickness by 78 µm. Intermittent aeration (4h off, 19.5h on) and air scouring (3 L/min, 30 s before settling) in one cycle achieved COD removal over 90 %, TIN and PO43−-P removals over 80 %, showing great potential for simultaneous carbon, nitrogen and phosphorus removals.

Microbial fuel cell in long-term operation and providing electricity for intermittent aeration to remove contaminants from sewage

Microbial fuel cells (MFCs) show promise in sewage treatment because they can directly convert organic matter (OM) into electricity. This study aimed to demonstrate MFCs stability over 750 days of operation and efficient removal of OM and nitrogenous compounds from sewage. To enhance contaminant removal, oxygen was provided into the anode chamber via a mini air pump. This pump was powered by the MFCs' output voltage, which was boosted using a DC-DC converter. The experimental system consisted of 12 sets of cylindrical MFCs within a 246L-scale reactor. The boosted voltage reached 4.7 V. This voltage was first collected in capacitors every 5 min and then dispensed intermittently to the air pump for the MFCs reactor in 4 s. This corresponds to receiving average DO concentration reaching 0.34 ± 0.44 mg/L at 10 cm above the air-stone. Consequently, the degradation rate constants (k) for chemical oxygen demand (COD) and biological oxygen demand (BOD) in the presence of oxygen were 0.048 and 0.069, respectively, which surpassed those without oxygen by 0.039 and 0.044, respectively. Aeration also marginally improved the removal of ammonia because of its potential to create a favorable environment for the growth of anammox and ammonia-oxidizing bacteria such as Candidatus brocadia and Nitrospira. The findings of this study offer in-depth insight into the benefits of boosted voltage in MFCs, highlighting its potential to enhance contaminant degradation. This serves as a foundation for future research focused on improving MFCs performance, particularly for the removal of contaminants from wastewater.

Revealing the impacts of intermittent aeration on nitrogen and phosphorus removal in powder carrier system from interfacial thermodynamics and metagenomic analysis

Intermittent aeration strategy has attracted significant attention due to its benefits of low oxygen and carbon source consumption. However, the feasibility of intermittent aeration in the powder carrier process and its effect on micro-granule formation remain unclear. This study investigated the impacts of intermittent aeration on the powder carrier system through interfacial thermodynamics and metagenomic analysis. The results demonstrated that total nitrogen removal efficiency increased from 61.1 ± 2.6 % to 89.7 ± 3.7 % under intermittent aeration, while the PO43-–P removal efficiency increased from 47.6 ± 4.7 % to 81.6 ± 3.9 %. The interfacial free energy of micro-granules was reduced from –4.85 mJ/m2 to –16.03 mJ/m2 due to aeration mode, resulting in a larger micro-granule size (185.24 ± 15.25 μm) and enhanced aggregation ability. Significant enhancements in tryptophan-like substances and hydrophobic functional groups (β-sheet, protonated amines, and C-(C/H)) in EPS under intermittent aeration likely contributed to the increased hydrophobicity and reduced interfacial free energy. The abundances of norank_NS9_marine_group (4.17 %), norank_Comamonadaceae (4.57 %), and Terrimonas (3.44 %) were increased, further driving the synergy of nitrogen removal of simultaneous partial nitrification and denitrification and endogenous denitrification. Correlation analysis confirmed that intermittent aeration primarily affected gene expression involved in the partial nitrification process, and that denitrification genes were enriched by increased hydrophobic components and micro-granule size. These results provide deeper insights into the key influencing factors and mechanisms of the powder carrier system, and offer a theoretical basis for process optimization.

The bacterial community drive the humification and greenhouse gas emissions during plant residues composting under different aeration rates

ABSTRACT This study investigated the effects of different aeration intensities on organic matter (OM) degradation, greenhouse gas emissions (GHG) as well as humification during plant residue composting. Three intermittent aeration intensities of 0.084 (T low), 0.19 (T medium) and 0.34 (T high) L min−1kg−1 DM with 30 min on/30 min off were conducted on a lab-scale composting experiment. Results showed that OM mineralization in T high was more evident than T low and T medium, resulting in the highest humic acid content. Humic acid content in T medium and T high was 15.7% and 18.5% higher than that in T low. The average O2 concentration was 4.9%, 9.5% and 13.6% for T low, T medium and T high. Compared with T medium and T high, T low reduced CO2 and N2O emissions by 18.3%–39.6% and 72.4%–63.9%, but the CH4 emission was highest in T low. But the total GHG emission was the lowest in T high. Linear Discriminant Analysis Effect Size analysis showed that the core bacteria within T low mainly belonged to Anaerolineaceae, which was significantly negatively correlated to the emission of CH4. Thermostaphylospora, Unclassified_Vicinamibacteraceae and Sulfurifustis were identified as core bacteria in T medium and T high, and these genus were significantly postively correlated to CO2 and N2O emissions. Redundancy analysis showed that total orgnic carbon, O2 and electrical conductivity were the key factors affecting the evolution of bacterial community.

Nutrients removal in overloaded WWTP by intermittently aerated IFAS: Effects of biofilm carrier and intermittent aeration cycle

Updating of the current Urban Waste Water Treatment Directive (91/271/EEC) will demand stricter regulations for nutrients removal. In this frame, wastewater treatment plants (WWTPs) of small-to-medium potential will face new challenges for achieving process intensification. Integrating intermittent aeration (IA) and integrated fixed-film activated sludge (IFAS) technologies could be a promising solution to meet such requirements. This study analyzed how IA cycles affected nutrients removal in IFAS reactors with different biofilm carriers (e.g., plastic and sponge media). The plants responses to different carbon/nitrogen/phosphorous (C/N/P) ratios were evaluated while operating under low sludge retention time (SRT) to simulate overloaded conditions.A short IA cycle (1 h) with an aeration/not aeration ratio of 2:1 enabled high organic carbon and nitrification performances when operating at high C/N/P (11.8/1/1), whereas low denitrification and phosphorous removal yields were obtained because of the short not-aerated phase. Decreasing C/N ratio (8.8/1/1) without changing the IA cycle resulted in nitrification worsening because of the reduced metabolic kinetics of biofilm. Under such load conditions, a higher IA cycle (2 h) was necessary to improve process performance. A longer not-aerated phase was also positive for denitrification and phosphorous removal because of the establishment of anoxic and anaerobic environments within the bulk and inner biofilm layers. Besides, results suggested that sponge carriers offered advantages over plastic ones, enabling a higher biofilm retention capacity, better nutrient removal, as well as robustness and resilience to operating condition changes. This would result in simpler management systems for implementing the IA process, thus reducing process complexity and costs.

Enhancing the microbial advanced oxidation of P-nitrophenol in sediment through accelerating extracellular respiration with electrical stimulation

Microbial advanced oxidation, a fundamental process for pollutant degradation in nature, is limited in efficiency by the weak respiration of indigenous microorganisms. In this study, an electric field was employed to enhance microbial respiration and facilitate the microbial advanced oxidation of p-nitrophenol (PNP) in simulated wetlands with alternation of anaerobic and aerobic conditions. With intermittent air aeration, an electric field of 0.8 V promoted extracellular electron transfer to increase Fe2+ generation through dissimilatory iron reduction and the production of hydroxyl radicals (•OH) through Fenton-like reactions. As a result, the PNP removal rate of the electrically-stimulated group was higher than that of the control (72.15 % vs 46.88 %). Multiple lines of evidence demonstrated that the electrically-induced polarization of respiratory enzymes expedited proton-coupled electron transfer within the respiratory chain to accelerate microbial advanced oxidation of PNP. The polarization of respiratory enzymes with the electric field hastened proton outflow to increase cell membrane potential for adenosine triphosphate (ATP) generation, which enhanced intracellular electron transportation to benefit reactive oxygen species generation. This study provided a new method to enhance microelectrochemical remediation of the contaminant in wetlands via the combination of intermittent air aeration.

Enhanced treatment performance and reduction of antibiotic resistance genes of biochar-aeration vertical flow constructed wetland for treating real domestic wastewater

Constructed wetlands (CWs) are widely utilized for domestic wastewater treatment, yet there is a relative scarcity of research focused on the treatment of real domestic wastewater. This study evaluated the enhanced treatment performance and nitrous oxide (N2O) emissions in CWs by integrating biochar with intermittent aeration, the removal of antibiotic resistance genes (ARGs) was also assessed. The results indicated that the biochar-aeration CW significantly improved denitrification, achieving a total nitrogen removal efficiency of 42.83 %. Notably, biochar-aeration CW exhibited the lowest N2O emission fluxes (31.28–726.49 μg m−2 h−1). Furthermore, the introduction of biochar fostered the development of tightly bound extracellular polymeric substances, primarily attributed to biofilm production. The biochar-aeration CW effectively reduced the four targeted ARGs (sul-I, sul-II, tet-O, tet-W) by 0.41–1.43 log. These findings would be beneficial for understanding the function of biochar-intermittent aeration technology in enhancing the treatment capacity of CWs for domestic wastewater treatment.

Distinct roles of biochar and pyrite substrates in enhancing nutrient and heavy metals removal in intermittent-aerated constructed wetlands: Performances and mechanism

Constructed wetlands have been widely employed as a cost-effective and environmentally friendly alternative for treating primary and secondary sewage effluents. In this study, biochar and pyrite were utilized as electron donor substrates in intermittent-aerated vertical flow constructed wetlands to strengthen the nutrient and heavy metals removal simultaneously, and the response of nutrient reduction and microbial community to heavy metals stress was also explored. The results indicated that biochar addition exhibited a better nitrogen removal, while pyrite addition greatly promoted the phosphorus removal. Moreover, the high removal efficiencies of Cu2+, Pb2+ and Cd2+ (above 90%) except for Zn2+ were obtained in each system. However, the exposure of heavy metals decreased phosphorus removal while had little effect on nitrogen removal. The influent load and intermittent aeration implementation led to a significant shift in microbial community structures, but microbial biodiversity and abundance decreased under the exposure of heavy metals. Particularly, Thiobacillus and Ferritrophicum, associated with sulfur autotrophic denitrification and iron autotrophic denitrification, were more abundant in pyrite-based wetland systems.

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).

Aerobic composting characteristics of corn straw and pig manure under dynamic aeration

ABSTRACT The conventional aeration method is compulsorily continuous ventilation or aeration at equal intervals, and a uniform aeration rate does not vary during composting. A dynamic on-demand aeration approach based on the diverse oxygen consumption of microorganisms at different composting stages could solve the problems of insufficient oxygen supply or excessive aeration. This study aims to design an aerobic composting system with dynamic aeration, investigate the effects of dynamic aeration on the temperature rise and physicochemical characteristics during the aerobic composting of corn straw and pig manure, and optimise the control parameters of oxygen concentration. Higher temperatures and longer high-temperature durations were achieved under dynamic aeration, thereby accelerating the decomposition of organic compounds. Dynamic aeration effectively reduced the aeration frequency, the convective latent heat and moisture losses, and the power consumption in the middle and later stages of composting. The dynamic aeration regulated according to the oxygen concentration of 14%–17% in the exhaust was optimum. Under the optimal conditions, the period above 50 ℃ lasted 8.5 days, and the highest temperature, organic matter removal, and seed germination index reached 65.82 ℃, 37.59%, and 74.59%, respectively. The power consumption was decreased by 33.58% compared to the traditional intermittent aeration. Dynamic aeration would be a competitive approach for improving aerobic composting characteristics and reducing the power consumption and the hot exhaust gas emissions, especially in the cooling maturation stage, which was of great significance for realising the low-cost production of composting at scale and promoting the blossom of the organic fertiliser industry.

The efficiency of enhanced nitrogen and phosphorus removal in a vertical flow constructed wetland using alkaline modified corn cobs as a carbon source

Adding carbon sources to constructed wetlands can improve nitrogen removal efficiency. Modifying plant biomass can solve problems such as excessive release of nitrogen, phosphorus, and organic matter in the initial stage and insufficient carbon supply in the later stage. This article utilized alkali-modified corn cob as a carbon source to construct vertical flow constructed wetlands and to study the carbon release characteristics of alkali-modified corn cob, as well as its removal effect on organic matter in wastewater. The results indicated that the solid-to-liquid ratio in the alkali modification process of corn cob was 1:10, and it was found that the best treatment method for alkali modified corn cob was to use a sodium hydroxide concentration of 2%, a treatment time of 12 h, and a temperature of 20 °C. Its surface roughness increases, which is beneficial for releasing carbon sources and promoting the growth of microbial attachment. Furthermore, the porosity also increases and. Intermittent aeration could significantly enhance the removal of NH4+-N, and TP in constructed wetlands. The average removal rates of NH4+-N and TP were 60.93% and 89.50%, respectively, and the average removal rates of COD, NO3--N and TN were 60.67%, 98.38% and 83.73%, respectively. At the same time, alkali-modified corn cobs were used as carbon sources. It can effectively remove NO3--N and promote denitrification in constructed wetlands.

Carbon footprint reduction by coupling intermittent aeration with submerged MBR: A pilot plant study

To find a possible trade-off between effluent quality, sludge production, energy consumption and GHG emissions, this study monitored the carbon and nutrient removal and greenhouse gas (GHG) emissions in a membrane bioreactor (MBR) pilot plant with intermittent aeration (IA). The pilot plant was operated by alternating aerobic and anoxic conditions inside the biological reactor. Up to 98.2 % of carbon and 76.4 % of nitrogen were respectively remove through this MBR pilot plant with IA. The carbon footprint was equal to 2.4 kgCO2eq m−3. Indirect emissions contributed the most to the carbon footprint (55.3 %), mainly due to energy consumption, despite the alterations in aeration during the pilot plant operation. The result of this study provides theoretical guidance for building the wastewater treatment plant in a sustainable way.

Comammox Nitrospira cooperate with anammox bacteria in a partial nitritation–anammox membrane bioreactor treating low-strength ammonium wastewater at high loadings

Research has revealed that comammox Nitrospira and anammox bacteria engage in dynamic interactions in partial nitritation–anammox reactors, where they compete for ammonium and nitrite or comammox Nitrospria supply nitrite to anammox bacteria. However, two gaps in the literature are present: the know-how to manipulate the interactions to foster a stable and symbiotic relationship and the assessment of how effective this partnership is for treating low-strength ammonium wastewater at high hydraulic loads. In this study, we employed a membrane bioreactor designed to treat synthetic ammonium wastewater at a concentration of 60 mg N/L, reaching a peak loading of 0.36 g N/L/day by gradually reducing the hydraulic retention time to 4 hr. Throughout the experiment, the reactor achieved an approximately 80 % nitrogen removal rate through strategically adjusting intermittent aeration at every stage. Notably, the genera Ca. Kuenena, Nitrosomonas, and Nitrospira collectively constituted approximately 40 % of the microbial community. Under superior intermittent aeration conditions, the expression of comammox amoA was consistently higher than that of Nitrospira nxrB and AOB amoA in the biofilm, despite the higher abundance of Nitrosomonas than comammox Nitrospira, implying that the biofilm environment is favorable for fostering cooperation between comammox and anammox bacteria. We then assessed the in situ activity of comammox Nitrospira in the reactor by selectively suppressing Nitrosomonas using 1-octyne, thereby confirming that comammox Nitrospira played the primary role in facilitating the nitritation (33.1 % of input ammonium) rather than complete nitrification (7.3 % of input ammonium). Kinetic analysis revealed a specific ammonia-oxidizing rate 5.3 times higher than the nitrite-oxidizing rate in the genus Nitrospira, underscoring their critical role in supplying nitrite. These findings provide novel insights into the cooperative interplay between comammox Nitrospira and anammox bacteria, potentially reshaping the management of nitrogen cycling in engineered environments, and aiding the development of microbial ecology-driven wastewater treatment technologies.

Fe(II)/Fe(III) cycle actuating a novel process to remove organics in waste pit mud from Maotai: Performance and mechanism

In this study, a novel method relying on iron cycle through intermittent aeration was proposed to treat organic matter in waste sealed pit mud from Moutai. Firstly, ferrihydrite was used to verify dissimilatory iron reduction could remove organics from the pit mud; then, the effect of iron cycle induced by intermittent aeration on organics was investigated. The results showed that the removal efficiency of organics was increased by 8.2 % after the addition of ferrihydrite, then intermittent aeration was carried out, Fe(II) content decreased after aeration and increased again after stopping aeration, indicating that iron cycle occurred. Additionally, the total chemical oxygen demand (TCOD) content further decreased by18.8 % in the reactor with intermittent aeration, significantly higher than that in the unaerated group (11.8 %) (p < 0.05). Due to the short aeration time (about once a week, 200–500 mL/min, 30 min for each aeration), aerobic microorganisms were undetected, which further indicated that iron cycle enhanced the removal of organics. Finally, intermittent aeration was conducted in the fermentation system of pit mud without adding iron, and the indigenous iron in the pit mud was also recycled. After 31 days, the TCOD removal efficiency increased by 15.6 % in the aeration group compared with that in the control group. Microbial analysis showed that some microorganism that degraded refractory organics, including iron reducing bacteria, were enriched in the aerated reactors, such as WCHB1–32, ADurb. bin053–1, Lentimicrobium, and Aneurinibacillus, Geobacteraceae. These indicated that organic matter removal can be enhanced by relying on its indigenous iron.

Bioenergy-producing two-stage septic tank and floating wetland for onsite wastewater treatment: Circuit connection and external aeration

This study designed a two-stage, electrode-integrated septic tank-floating wetland system and assessed their pollutant removal performances under variable operational conditions. The two-stage system achieved mean organic, nitrogen, phosphorus, and coliform removal percentages of 99, 78, 99, and 97%, respectively, throughout the experimental run. The mean metals (chromium, cadmium, nickel, copper, zinc, lead, iron, and manganese) removal percentages ranged between 81 and 98%. Accumulated sludge, filler media, and the hanging root mass contributed to pollutant removals by supporting physicochemical and biological pathways. The mean effluent organic concentration and coliform number across the two-stage system were 20 mg/L and 1682 CFU/100 mL, respectively, during the closed-circuit protocol, which was beneath the open-circuit-based performance profiles, i.e., 32 mg/L and 2860 CFU/100 mL, respectively. Effluent organic, nitrogen, phosphorus, metals, and coliform number ranges across the two-stage system were 9–17 mg/L, 13–24 mg/L, 1–1.5 mg/L, 0.001–0.2 mg/L, and 1410–2270 CFU/100 mL, respectively during intermittent and continuous aeration periods. The air supply rate differences influenced pollutant removal depending on the associated removal mechanisms. The non-aeration phase produced higher effluent pollutant concentrations than the aeration periods-based profiles. The overall mean power density production of the septic tank ranged between 107 and 596 mW/m3; 110 and 355 mW/m3 with the floating wetland. The bioenergy production capacity of the septic tank was positively correlated to external air supply rates. This study demonstrates the potential application of the novel bioenergy-producing septic tank-floating wetland system for wastewater treatment in decentralized areas.

Enhancing wastewater treatment with a novel separated algae membrane oxygenated activated sludge reactor

In this investigation, a separated algae membrane oxygenated activated sludge wastewater treatment reactor was developed. During the phase of aeration pump absence, the system, featuring a separated algae biofilm oxygenation activated sludge mechanism with an internal reflux ratio of 5 and a C/N ratio of 10, demonstrated remarkable efficiency in pollutant removal. Specifically, it achieved COD, TN, NH4+-N, and TP removal rates of 96.6 %, 81.9 %, 98.6 %, and 95.5 %, respectively. Despite a decline in dissolved oxygen (DO) during the transition of wastewater from the algae membrane reactor to the aerobic tank, the internal circulation reflux ratio of 5 ensured that the oxygen-enriched effluent from the algae membrane photoreactor maintained a stable DO level in the aerobic tank, ranging from 1.5 to 2.0 mg/L, thus meeting the oxygen demand of the activated sludge. Alterations in the aeration method had a notable impact on the diversity of the microbial community. Notably, the community shifted from bacteria adapted to intermittent aeration to those acclimated to internal recirculation for oxygen supply. The dominant microbial position was reinforced, with the Patescibacteria phylum and the norank_f__norank_o __ Saccharimonadales genus emerging as the dominant entities within the community. Under internal circulation reflux aeration, filamentous green algae persisted, resulting in a significant increase in biomass and chlorophyll content by 3.07 and 2.93 times, respectively. Furthermore, microalgae exhibited elevated protein and polysaccharide content, which increased by 3.14 and 3.16 times, respectively, due to the influence of the internal circulation reflux process, promoting the maturation of the algae membrane.