Durable Nano-Flower Structured Foam Coupled with Electrically-Driven in Situ Aeration Enable High-Flux Oil/Water Emulsion Separation with Dynamic Antifouling Ability.

The conventional membranes used for separating oil/water emulsions are typically limited by the properties of the membrane materials and the impact of membrane fouling, making continuous long-term usage unachievable. In this study, a filtering electrode with synchronous self-cleaning functionality is devised, exhibiting notable antifouling ability and an extended operational lifespan, suitable for the continuous separation of oil/water emulsions. Compared with the original Ti foam, the in situ growth of NiTi-LDH (Layered double hydroxide) nano-flowers endows the modified Ti foam (NiTi-LDH/TF) with exceptional superhydrophilicity and underwater superoleophobicity. Driven by gravity, a rejection rate of over 99% is achieved for various emulsions containing oil content ranging from 1% to 50%, as well as oil/seawater emulsions. The flux recovery rate exceeds 90% after one hundred cycles and a 4-h filtration period. The enhanced separation performance is realized through the "gas bridge" effect during in situ aeration and electrochemical anodic oxidation. The internal aeration within the membrane pores contributes to the removal of oil foulants. This study underscores the potential of coupling foam metal filtration materials with electrochemical technology, providing a paradigm for the exploration of novel oil/water separation membranes.

Diazotrophic nitrogen fixation through aerial roots occurs in Avicennia marina: implications for adaptation of mangrove plant growth to low-nitrogen tidal flats.

Nitrogen limitation of primary production is common in coastal ecosystems. Mangrove trees maintain high levels of nitrogen fixation around their roots. The interior aerial space of mangrove roots, in which atmospheric gas is supplied through lenticels, could be efficient sites for nitrogen fixation. We measured tidal variations of partial pressure of N2 in root aerenchyma and conducted field experiments using 15 N2 as a tracer to track N2 movement through aerial roots of Avicennia marina. We used the acetylene reduction assay to identify the root parts harboring diazotrophs. The nitrogenase activity and estimated nitrogen fixation through aerenchyma were higher in pneumatophores and absorbing roots than in cable roots. Positive correlations between root nitrogen contents and turnover rates of root nitrogen derived from N2 through aerenchyma suggested that the internal supply of N2 to diazotrophs could be the main source for nitrogen assimilation by A. marina roots. Our results confirmed that N2 is supplied to diazotrophs through aerial roots and that nitrogen fixation occurs in A. marina roots. The aerial root structures, which occur across families of mangrove plants, could be an adaptation to survival in not only low-oxygen environments but also tidal flats with little plant-available nitrogen.

A forced aeration system for microbial culture of multiple shaken vessels suppresses volatilization.

Shake-flask culture, an aerobic submerged culture, has been used in various applications involving cell cultivation. However, it is not designed for forced aeration. Hence, this study aimed to develop a small-scale submerged shaking culture system enabling forced aeration into the medium. A forced aeration control system for multiple vessels allows shaking, suppresses volatilization, and is attachable externally to existing shaking tables. Using a specially developed plug, medium volatilization was reduced to less than 10%, even after 45 h of continuous aeration (~ 60 mL/min of dry air) in a 50 mL working volume. Escherichia coli IFO3301 cultivation with aeration was completed within a shorter period than that without aeration, with a 35% reduction in the time-to-reach maximum bacterial concentration (26.5 g-dry cell/L) and a 1.25-fold increase in maximum concentration. The maximum bacterial concentration achieved with aeration was identical to that obtained using the Erlenmeyer flask, with a 65% reduction in the time required to reach it.

Emission Characteristics of Aerosols Generated during the Micro-Nano Bubble Aeration Process in Wastewater.

Micro-nano bubble (MNB) aeration is an emerging technology that considerably enhances the aeration efficiency of wastewater. This study evaluates, for the first time, aerosolization at the water-air interface during MNB aeration. Our results show that the concentration of culturable mixed microorganisms (i.e., bacteria, fungi, and intestinal bacteria) in the in situ MNB generation (MNBs-G) phase is 2170 CFU/m3, 1.38 and 1.58-fold higher than those in medium-bubble aeration (MBA; 1568 CFU/m3) and small-bubble aeration (SBA; 1376 CFU/m3) aerosols, respectively. Conversely, the concentration of culturable mixed microorganisms in the MNB persistent dissolved oxygen (MNBs-O) phase is only 914 CFU/m3. Microbiological analysis shows a lower abundance of bacterial pathogens in MNBs-G (34.12%) and MNBs-O (34.02%) phases than in MBA (39.63%) and SBA (38.87%) aerosols. Acinetobacter is prevalent in MNBs-G (14.76%) and MNBs-O (8.22%) aerosols, whereas Bacillus and Arcobacter are prevalent in MBA (23.96%) and SBA (6.92%) aerosols, respectively. The total concentrations of chemicals [i.e., total organic carbon, water-soluble ions, and metal(loid)s] in aerosols formed via MNB aeration (205.98-373.74 µg/m3) are lower than those in MBA and SBA (398.69-594.92 µg/m3). Compared to MBA and SBA, the MNBs-G phase exhibits higher emissions of 12 elements in aerosols (i.e., NO3-, NO2-, Ca2+, Na+, K+, Mg2+, Zn, Cd, Fe, Mn, As, and Cr), whereas the MNBs-O phase generally shows lower emissions. These findings highlight the potential of optimized MNB aeration technology in considerably mitigating aerosol emissions and thereby advancing environmental sustainability in wastewater treatment.

Aeration-Free In Situ Fenton-like Reaction: Specific Adsorption and Activation of Oxygen on Heterophase Oxygen Vacancies.

Aeration accounts for 35-51% of the overall energy consumption in wastewater treatment processes and results in an annual energy consumption of 5-7.5 billion kWh. Herein, a solar-powered continuous-flow device was designed for aeration-free in situ Fenton-like reactions to treat wastewater. This system is based on the combination of TiO2-x/W18O49 featuring heterophase oxygen vacancy interactions with floating reduced graphene/polyurethane foam, which produces hydrogen peroxide in situ at the rates of up to 4.2 ppm h-1 with degradation rates of more than 90% for various antibiotics. The heterophase oxygen vacancies play an important role in the stretching of the O-O bond by regulating the d-band center of TiO2-x/W18O49, promoting the hydrogenation of *·O2- or *OOH by H+ enrichment, and accelerating the production of reactive oxygen species by spontaneous adsorption of hydrogen peroxide. Furthermore, the degradation mechanisms of antibiotics and the treatment of actual wastewater were thoroughly investigated. In short, the study provides a meaningful reference for potentially undertaking the "aeration-free" in situ Fenton reaction, which can help reduce or even completely eradicate the aeration costs and energy requirements during the treatment of wastewater.

Effects of aeration control strategies on nitrous oxide emissions in alternating anoxic-oxic sequencing batch reactor systems.

Reducing N2O emissions is key to controlling greenhouse gases (GHG) in wastewater treatment plants (WWTPs). Although studies have examined the effects of dissolved oxygen (DO) on N2O emissions during nitrogen removal, the precise effects of aeration rate remain unclear. This study aimed to fill this research gap by investigating the influence of dynamic aeration rates on N2O emissions in an alternating anoxic-oxic sequencing batch reactor system. The emergence of DO breakthrough points indicated that the conversion of ammonia nitrogen to nitrite and the release of N2O were nearly complete. Approximately 91.73 ± 3.35% of N2O was released between the start of aeration and the DO breakthrough point. Compared to a fixed aeration rate, dynamically adjusting the aeration rates could reduce N2O production by up to 48.6%. Structural equation modeling revealed that aeration rate and total nitrogen directly or indirectly had significant effects on the N2O production. A novel regression model was developed to estimate N2O production based on energy consumption (aeration flux), water quality (total nitrogen), and GHG emissions (N2O). This study emphasizes the potential of optimizing aeration strategies in WWTPs to significantly reduce GHG and improve environmental sustainability.

Responses of composition and metabolism of microbial communities during the remediation of black and odorous water using bioaugmentation and aeration.

This study elucidated the effect patterns of aeration and bioaugmentation on indigenous microbial communities, metabolites, and metabolic pathways in the remediation of black and odorous water. This is crucial for the precise formulation and targeted development of effective microbial consortia, as well as for tracking and forecasting the bioremediation of black and odorous water. The results confirmed that combining bioaugmentation with aeration markedly enhanced the degradation of COD, NH4+-N, and TN and the conversion of Fe and Mn. Aeration significantly increased the relative abundance of Flavobacterium and Diaphorobacter, and the positive interbacterial interaction in the effective microbial consortia EM31 gave the constituent strain Klebsiella and Bacillus a dominant niche in the bioaugmentation. Furthermore, bioaugmentation improved the capacity of the indigenous microbial consortia to utilize basic carbon source, particularly the utilization of L-glycerol, I-erythritol, glucose-1-phosphate, and the catabolism of cysteine and methionine. Moreover, during the remediation of black and odorous water by aeration and bioaugmentation, Glucosinolate biosynthesis (map00966), Steroid hormone biosynthesis (map00140), Folate biosynthesis (map00790), One carbon pool by folate (map00670), and Tyrosine metabolism (map00350) were identified as key functional metabolic pathways in microbial communities.

Using ozone nanobubbles, and microalgae to promote the removal of nutrients from aquaculture wastewater: Insights from the changes of microbiomes.

Integrated aquaculture wastewater treatment systems (IAWTSs) are widely used in treating aquaculture wastewater with the aeration-microalgae unit serving as an important component. In this study, we artificially constructed an IAWTS and applied two aeration-microalgae methods: ordinary aeration or ozone nanobubbles (ONBs) with microalgae (Nannochloropsis oculata). The impact of N.oculata and ONBs on the removal performance of nutrients and the underlying micro-ecological mechanisms were investigated using 16S rRNA gene amplicon sequencing. The results demonstrated that the combined use of ONBs and N.oculata exhibited superior purification effects with 78.25%, 76.59% and 86.71% removal of CODMn, TN and TP. N.oculata played a pivotal role as the primary element in wastewater purification, while ONBs influenced nutrient dynamics by affecting both N.oculata and bacterial communities. N.oculata actively shaped bacterial communities, with a specific focus on nitrogen and phosphorus cycling in the micro-environment remodeled by ONBs. Rare bacterial communities displayed heightened activity in response to the changes in N.oculata, ONBs, and nutrient levels. These findings provide a novel approach to improve the technological processes the IAWTS, contributing to the advancement of sustainable aquaculture practices by offering valuable insights into wastewater purification efficiency and micro-ecological mechanisms.

Multi-anode enhanced the bioelectricity generation in air-cathode microbial fuel cells towards energy self-sustaining wastewater treatment.

Microbial fuel cells (MFCs) hold considerable promise for harnessing the substantial energy resources present in wastewater. However, their practical application in wastewater treatment is limited by inadequate removal of organic matter and inefficient power recovery. Previous studies have investigated aeration as a method to enhance the removal of organic matter, but this method is energy-intensive. To address this issue, this study proposed using MFC-recovered bioelectricity for aeration, thereby mitigating the associated expenses. An air-cathode MFC with multi-anode was constructed and optimized to maximize electricity supply for aeration. Carbon-felt anodes were chosen as the most effective anode configuration, due to the high abundance of electroactive bacteria and genes observed in the biofilm generated on their surface. By incorporating six carbon felt anodes, the MFC achieved a 1.7 and 1.1 fold enhancement in the maximum power and current density, respectively. The optimized MFC unit achieved a stable current density of 0.32 A/m2 and achieved COD removal of 60% in the long-term operation of 140 days in a 50 L reactor. In a reactor scaled up to 1600 L, 72 MFCs successfully powered a mini air pump work for 10 s after an 81-s charging period. The intermittent aeration resulted in partial increases in DO concentrations to 0.03-3.5 mg/L, which is expected to promote the removal of nitrogen compounds by the nitrification-anammox process. These groundbreaking results lay the foundation for self-sustaining wastewater treatment technologies.

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.

Effect of micro-aeration on syntrophic and methanogenic activity in anaerobic sludge.

Micro-aeration was shown to improve anaerobic digestion (AD) processes, although oxygen is known to inhibit obligate anaerobes, such as syntrophic communities of bacteria and methanogens. The effect of micro-aeration on the activity and microbial interaction in syntrophic communities, as well as on the potential establishment of synergetic relationships with facultative anaerobic bacteria (FAB) or aerobic bacteria (AB), was investigated. Anaerobic sludge was incubated with ethanol and increasing oxygen concentrations (0-5% in the headspace). Assays with acetate or H2/CO2 (direct substrates for methanogens) were also performed. When compared with the controls (0% O2), oxygen significantly decreased substrate consumption and initial methane production rate (MPR) from acetate or H2/CO2. At 0.5% O2, MPR from these substrates was inhibited 30-40%, and close to 100% at 5% O2. With ethanol, significant inhibition (>36%) was only observed for oxygen concentrations higher than 2.5%. Oxygen was consumed in the assays, pointing to the stimulation of AB/FAB by ethanol, which helped to protect the syntrophic consortia under micro-aerobic conditions. This highlights the importance of AB/FAB in maintaining functional and resilient syntrophic communities, which is relevant for real AD systems (in which vestigial O2 amounts are frequently present), as well as for AD systems using micro-aeration as a process strategy. KEY POINTS: •Micro-aeration impacts syntrophic communities of bacteria and methanogens. •Oxygen stimulates AB/FAB, maintaining functional and resilient consortia. •Micro-aeration studies are critical for systems using micro-aeration as a process strategy.

Valorization of waste engine oil to mono- and di-rhamnolipid in a sustainable approach to circular bioeconomy.

This study aims to valorize waste engine oil (WEO) for synthesizing economically viable biosurfactants (rhamnolipids) to strengthen the circular bioeconomy concept. It specifically focuses on investigating the influence of key bioprocess parameters, viz. agitation and aeration rates, on enhancing rhamnolipid yield in a fed-batch fermentation mode. The methodology involves conducting experiments in a stirred tank bioreactor (3 L) using Pseudomonas aeruginosa gi |KP 163922| as the test organism. Central composite design and response surface methodology (CCD-RSM) are employed to design the experiments and analyze the effects of agitation and aeration rates on various parameters, including dry cell biomass (DCBM), surface tension, tensoactivity, and rhamnolipid yield. It is also essential to determine the mechanistic pathway of biosurfactant production followed by the strain using complex hydrophobic substrates such as WEO. The study reveals that optimal agitation and aeration rates of 200 rpm and 1 Lpm result in the highest biosurfactant yield of 29.76 g/L with minimal surface tension (28 mN/m). Biosurfactant characterization using FTIR, 1H NMR, and UPLC-MS/MS confirm the presence of dominant molecular ion peaks m/z 543.9 and 675.1. This suggests that the biosurfactant is a mixture of mono- and di-rhamnolipids (RhaC10C10, RhaRhaC10C12:1, RhaRhaC12:1C10). The findings present a sustainable approach for biosurfactant production in a fed-batch bioreactor. This research opens the possibility of exploring the use of pilot or large-scale bioreactors for biosurfactant production in future investigations.

Handling the inhibitory role of product accumulation during sophorolipid fermentation in a bubble column reactor with an in situ foam recovery.

Sophorolipid (SL) production by Candida catenulata from sunflower fatty acids was studied in a bubble column reactor (BCR). The specific oxygen uptake rate was 0.021 mg gcell-1 min-1 which indicates the importance of aeration in SL biosynthesis. The measurement of oxygen transfer rate (OTR) in the BCR showed a satisfactory OTR value of about 0.093 min-1 in the system. However, further SL production was stopped after 30 h in the BCR mainly due to the product accumulation in the culture and its inhibitory effects on cell growth and SL synthesis. Since an extensive foam was generated in the BCR under the absence of an antifoam agent, the development of an in situ foam recovery system provided the integration of production and separation of SL to handle the problem. The application of the foam recovery system enhanced biomass and titer SL concentration by 38.5 and 28.2% in comparison with the conventional BCR, respectively. Further studies in the system were performed by monitoring the size of bubbles and their effects on the biomass and SL enrichment in the foam stream at different aeration rates where the SL enrichment varied from 900 to 100% at 12 and 50 h of the fermentation.

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.

Strategies to attenuate ciprofloxacin inhibition on enhanced biological phosphorus removal from wastewater and its recoverability.

The inhibiting effects of ciprofloxacin (CIP) on enhanced biological phosphorus removal (EBPR) were investigated with no change in reactor operation and with increased aeration rate and sludge retention time (SRT) to explore inhibition-alleviating solutions. Additionally, performance recoverability was evaluated. The results showed that the phosphorus removal efficiency in the presence of 0.002-0.092 mg/L CIP for 7 days was only 12.5%. Increasing the aeration rate relieved inhibition (33.5% phosphorus removal efficiency on Day 7), and increasing SRT slowed EBPR performance deterioration. The EBPR performance recovered from CIP inhibition and increases in the aeration rate and SRT resulted in different recovery phenomena. The maximum PO43--P release rate continued to decrease in the first 2 days of the recovery stage and then gradually increased. However, the maximum PO43--P uptake rate immediately increased at different rates among reactors, which might be attributed to variations in the microbial community structure, decreased poly-P content, and enhanced abundances of ABC transporters and quorum sensing. It was found that some microorganisms associated with phosphorus removal were more tolerant to CIP than glycogen accumulating organisms. Moreover, the increased relative abundance of the qepA gene indicated that the microorganisms in the EBPR system had strong antibiotic resistance capacity. The bacterial community structure was significantly affected by CIP and could not recover to the initial structure. The results help to provide technical support for the operation of the EBPR process in the presence of CIP and to increase the understanding of system recoverability.

Experimental and numerical simulation research on the transport process of bubble clusters in aeration system.

Improving gas-liquid mass transfer efficiency in aeration systems contributes to energy savings, cost reduction, and enhanced efficiency in wastewater treatment. However, due to the complex nonlinear interactions among bubbles in turbulence, understanding the transport mechanisms of non-uniform bubble clusters in turbulence remains unclear. This study employs a combined approach of experimental research and numerical simulations to investigate the shape, diameter distribution, trajectory, and velocity of bubbles under different aeration port sizes and flow rates. The diameter distribution of bubble clusters exhibits a bimodal distribution. Bubble trajectories during ascent mainly exhibit two types of motion patterns: "Z" shaped and linear. Increasing aeration port size and flow rate both lead to an increase in the maximum bubble diameter. Higher initial flow rates and smaller port sizes induce greater lateral velocity fluctuations in bubbles. The proposed numerical simulation method serves as a reference for simulating the transport of non-uniform bubble clusters.

Integrated aerobic-anaerobic digestion of highly solids-loaded corn stover and swine manure under dynamic aeration: Temperature rise, physicochemical characteristics, and methane production.

This research aimed to design an integrated aerobic-anaerobic reactor with dynamic aeration that was automatically regulated based on real-time oxygen concentration and investigate the aerobic pretreatment and subsequent dry co-anaerobic digestion (co-AD) characteristics of highly solids-loaded corn stover and swine manure in terms of temperature rise, physiochemical characteristics, and methane production. The high-temperature feedstocks from the aerobic pretreatment phase rapidly entered the AD phase without transportation and effectively improved the start-up and methane production of the co-AD. Oxygen concentration range, aeration rate, and pretreatment time affected the cumulative aeration time, temperature rise, and organic matter removal interactively during aerobic pretreatment, and a low aeration rate was relatively preferable. Although the lignocellulose removal increased with the increase in pretreatment duration, the maximal lignin elimination efficiency only reached 1.30%. The inoculum injection in the transition phase from aerobic pretreatment to co-AD and the leachate reflux during co-AD were also critical for producing methane steadily apart from aerobic pretreatment. The cold air weakened the temperature rise of aerobic pretreatment, and the low-temperature leachate reduced the methane production in the co-AD process. An oxygen concentration range of 13%-17%, aeration rate of 0.10 m3/(min·m3), pretreatment time of 84 h, inoculum loading of 40%, leachate refluxing thrice per day, and double-layer inoculation were optimum for improving the integrated aerobic-anaerobic digestion system's ability to resist low temperatures and achieving high methane production. The maximal cumulative and volatile solids (VS) methane yields of corn stover and swine manure reached 444.58 L and 266.30 L/kg VS.

Treatment of cow manure from exercise pens: A laboratory-scale study of the effect of air injection on conventional and alternative biofilters.

Woodchips in stand-off pads for wintering cows have been applied in countries like Ireland and New Zealand. Their primary role is to protect soils by effectively filtering nutrients during wet conditions, while ensuring a healthy and comfortable environment for the cows. The stand-off pad concept has the potential to be adopted in Canada to provide year-long outdoor access to tie-stall dairy cows. The objective of this study was to evaluate the effect of alternative filtering materials and bed aeration under controlled laboratory conditions. Twelve biofilter columns (0.3 m in diameter and 1-m high) were installed in 12 environmentally-controlled chambers (1.2-m wide by 2.4-m long), and divided into four treatments: a bed of conventional woodchips or an alternative mix of organic materials (sphagnum peat moss, woodchips and biochar) with and without aeration (flux rate set at 0.6 m3/min/m2). Approximately 0.6 L of semi-synthetic dairy manure and 1 L of tap water were poured on the biofilters during two experimental periods of 4 weeks, simulating the effect of either winter or summer conditions (room temperature below or over 10 °C) on the retention of nutrients and fecal bacteria. Results showed that the alternative biofilters under both summer and winter conditions were more efficient in removing COD, SS, TN, and NO3-N than conventional biofilters (maximum efficiencies of 97.6%, 99.7%, 96.4%, and 98.4%, respectively). Similarly for E. coli, they achieved a minimum concentration of 1.8 Log10 CFU/100 ml. Conventional biofilters were more efficient for PO4-P removal with a maximum efficiency of 88.2%. Aeration did not have any significant effect under the tested temperature conditions. Additional factors such as media adaptation time as well as aeration flow during this period should be considered.

Intermittent aeration mitigating carbon emission from landfills with gas-water joint regulation.

Landfill is a significant source of atmospheric CH4 and CO2 emissions. In this study, four landfill reactor systems were constructed to investigate the effects of different ventilation methods, including continuous aeration (20 h d-1) and intermittent aeration (continuous aeration for 4 h d-1 and 2 h of aeration every 12 h, twice a day), on properties of landfilled waste and emissions of CH4 and CO2, in comparison to a traditional landfill. Compared with continuous aeration, intermittent aeration could reduce the potential global warming effect of the CH4 and CO2 emissions, especially multiple intermittent aeration. The CH4 and CO2 emissions could be predicted by the multiple linear regression model based on the contents of carbon, sulfur and/or pH during landfill stabilization. Both intermittent and continuous aeration could enhance the methane oxidation activity of landfilled waste. The aerobic methane oxidation activity of landfilled waste reached the maximums of 50.77-73.78 µg g-1 h-1 after aeration for 5 or 15 d, which was higher than the anaerobic methane oxidation activity (0.45-1.27 µg g-1 h-1). CO2 was the predominant form of organic carbon loss in the bioreactor landfills. Candidatus Methylomirabilis, Methylobacter, Methylomonas and Crenothrix were the main methane-oxidating microorganisms (MOM) in the landfills. Total, NO2--N, pH and Fe3+ were the main environmental variables influencing the MOM community, among which NO2--N and pH had the significant impact on the MOM community. Partial least squares path modelling indicated that aeration modes mainly influenced the emissions of CH4 and CO2 by affecting the degradation of landfilled waste, environmental variables and microbial activities. The results would be helpful for designing aeration systems to reduce the emissions of CH4 and CO2, and the cost during landfill stabilization.

Multi-stage aeration regime to regulate organic conversion toward gas alleviation and humification in food waste digestate composting.

Aerobic composting has been considered as a pragmatic technique to convert food waste digestate into high-quality biofertiliser. Nevertheless, massive gaseous emission and immature product remain the primary challenges in food waste digestate composting. Thus, the performance of multi-stage aeration regimes to improve gaseous emissions and organic humification during food waste digestate composting was investigated in this study. In addition to continuous aeration with a constant intensity of 0.3 L kg·dry mass (DM)-1·min-1, two multi-stage decreased aeration regimes were designed as "0.3-0.2-0.1" and "0.3-0.1-0.1" L·kg·DM-1·min-1 from the thermophilic to cooling and then mature stages, respectively. Results showed that the decreased aeration regimes could alleviate nitrous oxide (N2O) and ammonia (NH3) emission and slightly enhance humification during composting. The alleviated N2O and NH3 emission were mainly contributed by abiotically reducing gaseous release potential as well as biotically inactivating denitrifers (Pusillimonas and Pseudidiomarina) and proliferating Atopobium to reduce nitrate availability under lower aeration supply. The "0.3-0.2-0.1 L kg·DM-1·min-1" regime exhibited a more excellent performance to alleviate N2O and NH3 emission by 27.5% and 16.3%, respectively. Moreover, the decreased aeration regimes also favored the enrichment of functional bacteria (Caldicoprobacter and Syntrophomonas) to accelerate lignocellulosic biodegradation and thus humic acid synthesis by 6.5%-11.2%. Given its better performance to improve gaseous emissions and humification, the aeration regime of "0.3-0.2-0.1 L kg·DM-1·min-1" are recommended in food waste digestate composting in practice.