Aeration Costs Research Articles

Iron-retrofitted anaerobic baffled reactor system for rural wastewater treatment: Stable performance of nutrients removal with phosphorus recovery and minimal sludge production

An iron-retrofitted anaerobic baffled reactor (ABR) system was developed for the effective treatment of rural wastewater with reduced maintenance demand and aeration costs. Average removal efficiencies of chemical oxygen demand, total nitrogen and total phosphorus of 99.4%, 62.7% and 92.6% were achieved respectively, when the ABR system was operating at steady state. With effective bioreduction of FeIII in the anaerobic chambers, phosphorus was immobilized in the sludge as vivianite, the sole phosphorus-carrying mineral. The FeIII in the recirculated sludge induced Feammox in the ABR reactor, contributing 14.8% to total nitrogen removal. Biophase separation and enrichment of microorganisms associated with iron and nitrogen transformations were observed in the system after Fe dosing, which enhanced the removal of pollutants. The coupling of Feammox and vivianite crystallization to remove nitrogen and phosphorus in an iron-retrofitted ABR would appear to be a promising technology for rural wastewater treatment.

Effects of minimum dissolved oxygen setpoints for aeration in semi-intensive pond production of Pacific white shrimp (Litopenaeus vannamei)

Aeration is considered one of the most critical factors in shrimp farming as it affects the metabolism of shrimp and other living organisms within a pond. Maintenance of proper dissolved oxygen (DO) concentrations is critical, as low DO can cause stress, lower resistance to disease, and inhibit growth. Although the effects of single, short-term hypoxia events have been widely studied, little to no research has examined effects of repeated exposure to hypoxia during multiple diurnal cycles that shrimp may experience in aquaculture ponds. Even though the concept is simple, proper DO management is not simple. It is dependent on numerous factors and often based on anecdotal recommendations. The present trial was conducted to help elucidate the effects of DO management strategies on shrimp performance. The trial examined the effects of three different DO set points for automatic aeration on shrimp production and water quality parameters in earthen ponds. In sixteen earthen ponds (0.1 ha), juvenile Pacific white shrimp (⁓0.030 g) were stocked at a density of 25ind/m2. Minimal DO setpoints that activated automatic aeration in each of the treatments were 2.5, 3.5, and 4.5 mg O2/L, respectively. Shrimp were fed using the AQ1 passive acoustic monitoring system that was set to not feed while DO was below the threshold of a given treatment. Each of the treatments was applied to 5 ponds, except for treatment 1 (2.5 mg/L) which was applied 6 ponds as it was considered of higher risk. Shrimp growth performance and water quality indicators were monitored weekly. At the end of the 79–81-day trial, results showed that different aeration control treatments had no significant effect in terms of growth performance, feed inputs or productivity parameters. The final weight of the shrimp ranged between 33.3 and 33.6 g, with average final yields of 7500–8500 kg per ha. Nonetheless, mean electrical costs differed significantly between treatments, with higher DO setpoints treatments exhibiting a higher aeration cost with no discernible benefit. Water quality parameters showed no significant difference, except for morning and afternoon DO concentrations.

Kinetic model-based optimization in electro-activated sulfite system for carbamazepine degradation: Aeration and multiple dosages of sulfite

Electro-activated sulfite system (E-SO32−) was an emerging advanced oxidation technology, but its kinetics and process optimization have been overlooked. This study developed a first-principle kinetic model to investigate carbamazepine (CBZ) degradation and optimized this process by aeration and multiple dosages of SO32−. A low aeration rate (140 mL/min) remarkably accelerated sulfate radical (SO4•−) generation because of the enhanced rate of sulfite radical (SO3•−) reacting with oxygen. Thus, the degradation efficiency of CBZ improved from 71 % to 84 % and the electrical energy per order (EE/O) decreased from 4.55 to 2.32 kWh/m3/order at current density of 103 A/m2 and initial dosage of SO32− of 4 mM. However, further increasing the aeration rate diminished the enhancement of SO4•− generation rate due to the limited SO3•− generation, and excessive aeration resulted in decreased degradation efficiency and increased cost of aeration due to the direct oxidation of SO32− by oxygen. Consequently, matching of SO32− concentration, current density and aeration rate was crucial to maximize the generation rate of SO4•−. The most optimal strategy was at current density of 75 A/m2, aeration rate of 100 mL/min and SO32− concentration of 1.1 mM with multiple dosages. 95 % of CBZ was removed in 20 min, 18 % higher than that in single dosage. Finally, the optimal strategy for CBZ degradation was successfully applied in different water matrixes and real wastewater and well predicted by the kinetic model. Furthermore, degradation pathways of CBZ, including hydroxylation and deamidation, were elucidated from density functional theory and LC-MS detection. The toxicity of most intermediates decreased, while some intermediates possessed higher toxicity than CBZ. Overall, the firstly proposed combined strategy of aeration and multiple dosages of SO32− significantly facilitated the application of E-SO32− system in contaminants degradation.

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.

In-depth insight on microbial electrochemical systems coupled with membrane bioreactors for performance enhancement: a review.

A conventional activated sludge (CAS) system has traditionally been used for secondary treatment in wastewater treatment plants. Due to the high cost of aeration and the problem of sludge treatment, researchers are developing alternatives to the CAS system. A membrane bioreactor (MBR) is a technology with higher solid-liquid separation efficiency. However, the use of MBR is limited due to inevitable membrane fouling and high energy consumption. Membrane fouling requires frequent cleaning, and MBR components must be replaced, which reduces membrane lifetime and operating costs. To overcome the limitations of the MBR system, a microbial fuel cell-membrane bioreactor (MFC-MBR) coupling system has attracted the interest of researchers. The design of the novel bioelectrochemical membrane reactor (BEMR) can effectively couple microbial degradation in the microbial electrochemical system (MES) and generate a microelectric field to reduce and alleviate membrane fouling in the MBR system. In addition, the coupling system combining an MES and an MBR can improve the efficiency of COD and ammonium removal while generating electricity to balance the energy consumption of the system. However, several obstacles must be overcome before the MFC-MBR coupling system can be commercialised. The aim of this study is to provide critical studies of the MBR, MES and MFC-MBR coupling system for wastewater treatment. This paper begins with a critical discussion of the unresolved MBR fouling problem. There are detailed past and current studies of the MES-MBR coupling system with comparison of performances of the system. Finally, the challenges faced in developing the coupling system on a large scale were discussed.

Nitrite pathway in A2/O WWTPs: Modelling organic matter reduction, operational cost and N2O emissions

Deciding whether the implementation of the nitrite pathway is useful for the treatment of a given wastewater depends on several criteria such as organic matter availability, N and P removal, N2O emissions and operational costs. This work is a simulation-based study with a conventional Anaerobic/Anoxic/Oxic (A2/O) WWTP where the nitrite pathway can be implemented. The outcomes are general correlations to calculate the minimum COD requirements for a certain influent and a practical decision tree on the opportunities of nitrite pathway in A2/O WWTPs as a function of the influent wastewater composition (for P and N concentrations in the ranges 3–11 mgPO4−3-P·L−1 and 20–60 mg NH4+-N·L−1). This study shows that the implementation of the nitrite pathway reduces the COD requirements (depending on the influent, between 9 and 68%). It also can lead to a reduction in aeration costs. For an equivalent COD in the influent, the implementation of the nitrite pathway compared to the nitrate pathway results in a reduction of 41-47% in aeration costs and similar sludge production, leading to a reduction in the operational cost index of 10-16%. However, it is essential to note that this strategy can also lead to increased N2O emissions, with an emission factor for the nitrite pathway in the range of 2.5–17 times that of the nitrate pathway.

Scale-down of oxygen and glucose fluctuations in a tubular photobioreactor operated under oxygen-balanced mixotrophy.

Oxygen-balanced mixotrophy (OBM) is a novel type of microalgal cultivation that improves autotrophic productivity while reducing aeration costs and achieving high biomass yields on substrate. The scale-up of this process is not straightforward, as non-ideal mixing in large photobioreactors might have unwanted effects in cell physiology. We simulated at lab scale dissolved oxygen and glucose fluctuations in a tubular photobioreactor operated under OBM where glucose is injected at the beginning of the tubular section. We ran repeated batch experiments with the strain Galdieria sulphuraria ACUF 064 under glucose pulse feeding of different lengths, representing different retention times: 112, 71 and 21 minutes. During the long and medium tube retention time simulations, dissolved oxygen was depleted 15 to 25 minutes after every glucose pulse. These periods of oxygen limitation resulted in the accumulation of coproporphyrin III in the supernatant, an indication of disruption in the chlorophyll synthesis pathway. Accordingly, the absorption cross section of the cultures decreased steeply, going from values of 150 - 180 m2 ·kg-1 at the end of the first batch down to 50 - 70 m2 ·kg-1 in the last batches of both conditions. In the short tube retention time simulation, dissolved oxygen always stayed above 10% air saturation and no pigment reduction nor coproporphyrin III accumulation were observed. Concerning glucose utilization efficiency, glucose pulse feeding caused a reduction of biomass yield on substrate in the range of 4 to 22% compared to the maximum levels previously obtained with continuous glucose feeding (0.9 C-g·C-g-1 ). The missing carbon was excreted to the supernatant as extracellular polymeric substances constituted by carbohydrates and proteins. Overall, the results point out the importance of studying large-scale conditions in a controlled environment and the need for a highly controlled glucose feeding strategy in the scale-up of mixotrophic cultivation. This article is protected by copyright. All rights reserved.

Symbiotic association of microalgae and plants in a deep water culture system.

In this study, microalgae culture (Chlorella vulgaris) and mint seedlings (Mentha spp.) were combined in a hydroponic system to improve plant growth. Mint seedlings were grown both in microalgae-containing and in microalgae-free trial groups, and both groups were subjected to aerated and non-aerated conditions to show the effect of aeration and microalgae co-cultivation on the mint weight and height. The plant quality was also determined with color measurements of the mint leaves. The increase in the weight of the plants was the highest in microalgae-containing and aerated group (0.47 g) and the lowest in microalgae-free and non-aerated group (0.22 g). On the other hand, the variation in the plant height was not significant between the groups, the growth was lateral. The best quality mint leaves were also produced in microalgae-containing and aerated group. Our results have revealed the symbiotic life of the mint plant placed in the hydroponic system with microalgae and demonstrated improved mint growth and quality. This co-cultivation system is also potentially more environmentally friendly compared to growing microalgae and mint independently because of lower cost of aeration and mixing for microalgae cultivation, higher nutrient consumption efficiency, and reduced nutrient outflow.

Aeration control strategy design based on dissolved oxygen and redox potential profiles for nitrogen and phosphorus removal from sewage in a sequencing batch reactor

Oxygen availability during different stages of biological nutrient removal (BNR) plays utmost critical role in all wastewater treatment techniques. Inadequate aeration control results in low treatment efficiencies and may lead to significantly higher costs. Hence, a strategically designed aeration scheme is very crucial. This study was carried out with the objective of maximising nitrogen and phosphorus removal from sewage by implementing an optimised aeration strategy. To achieve this, a 4-hour Anaerobic/Aerobic/Anoxic (AOA) cycle based on dissolved oxygen (DO) and oxidation-reduction potential (ORP) values was strategically designed, implemented and monitored in a 4.5 l laboratory-scale Sequencing Batch Reactor (SBR). On an average, feed waste consisted of 170 mg/l of biological oxygen demand (BOD), 228 mg/l of chemical oxygen demand (COD), 64 mg/l of total nitrogen (TN) and 33 mg/l of ortho-phosphate (PO43−). The average BOD, COD, TN and PO43− loading rates of 0.510, 0.684, 0.192 and 0.099 kg/(m3-d), respectively were applied to the reactor. During the 90-day operation of the SBR, it was observed that BOD, COD, TN and PO43− removal were achieved with 91%, 93%, 90% and 75% efficiencies, with removal rates of 0.477, 0.614, 0.173 and 0.075 kg/(m3-d), respectively. Also, the cycle study revealed that P removal occurred during the aerobic phase, while N removal occurred during the anoxic phase through denitrification. A mass balance analysis for N also revealed that denitrification and microbial uptake accounted for 59% and 41% of nitrogen removal, respectively. Study revealed that nutrient removal was achieved successfully while avoiding any unnecessary extended aeration costs. Such aeration strategy based on DO and ORP values could be deployed not only to optimise the aeration phase lengths, but could also be used for dynamic process control to manage fluctuations in influent characteristics and system conditions.

An integrated hydrodynamic-biokinetic model to optimize the treatment processes in a laboratory-scale, pilot-scale, and full-scale bioreactor

One major disadvantage of membrane bioreactors (MBRs) is the high operating and aeration costs, and optimizing the process to attain economic efficiency is essential. In this study, a hydrodynamic - biokinetic integrated model was developed by combining a multiphase computational fluid dynamics (CFD) model with a population balance (PBM) submodel, an activated sludge (ASM1) submodel, and a combined (EPS – SMP) CES submodel. The developed integrated model was used to investigate the efficiency of treatment of bioreactors on three different scales (case 1- laboratory, case 2 – pilot, and case 3- full-scale system). The simulated values of bubble size count, total chemical oxygen demand (TCOD), total nitrogen (TN), ammonical nitrogen (SNH), nitrate‑nitrogen (SNO), EPS, and SMP concentrations were well validated with the experimental results, with an error percentage of 2.8 %, 6.32 %, 2.25 %, 0.53 %, 1.19 %, 4.62 %, and 2.05 %, respectively. The validated model is then extended for sensitivity analysis to identify optimum conditions (H/B ratio, H/S ratio, and bubble size) to reduce TCOD and TN concentration. The maximum percentage reduction in TCOD and TN concentrations in the most optimum scenario was 20 and 23 %, respectively, for case 3. Also, a reduction of 32 % in the cost of aeration was observed (for case 3) when the bubble size was reduced to 5 mm (from the current value of 7 mm). The preceding results suggest that the integrated model successfully optimized the treatment processes.

Microalgae-bacterial biomass outperforms PN-anammox biomass for oxygen saving in continuous-flow granular reactors facing extremely low-strength freshwater aquaculture streams

The dissolved oxygen (DO) concentration in water streams is one of the most important and critical quality parameters in aquaculture farms. The main objective of this study was to evaluate the potential of two Continuous Flow Granular Reactors, one based on Partial Nitrification-Anammox biomass (Aquammox CFGR) and the other on Microalgae-Bacteria biomass (AquaMab CFGR), for improving dissolved oxygen availability in the recirculation aquaculture systems (RAS). Both reactors treated the extremely low-strength effluents from a freshwater trout farm (1.39 mg NH4+-N/L and 7.7 mg TOC/L). The Aquammox CFGR, removed up to 68% and 100% of ammonium and nitrite, respectively, but the DO concentration in the effluent was below 1 mg O2/L while the anammox activity was not maintained. In the AquaMab CFGR, bioaugmentation of aerobic granules with microalgae was attained, producing an effluent with DO concentrations up to 9 mg O2/L and removed up to 77% and 80% of ammonium and nitrite, respectively, which is expected to reduce the aeration costs in fish farms.

Boosting hydrogen peroxide accumulation by a novel air-breathing gas diffusion electrode in electro-Fenton system

Electro-Fenton (EF) is a promising electrochemical technology in degrading recalcitrant organic pollutants. However, the technology faces problems of high energy consumption, low cathodic oxygen transfer rate and low H2O2 production efficiency. Therefore, a novel air-breathing gas diffusion electrode (GDE) with multiform hydrophobic layers was prepared by a facile method. The novel GDE allows the air to diffuse to the triphase interface spontaneously, eliminating the cost of aeration. Also, the multiform hydrophobic layers can greatly improve the oxygen transfer rate and expand the triphase interfaces in the GDE, resulting in a high H2O2 accumulation of 44.30 mg L−1 cm−2 h−1 without aeration, which was 18 times higher than that of the virgin cathode. A 100% degradation efficiency of sulfadiazine (SDZ) was achieved with the fabricated GDE in 10 min in EF system. Moreover, theoretical calculations were performed for accurately elucidating the SDZ degradation mechanism and pathway.

Impact of cathodic biofouling on the uneven performance of individual units and scale-up power efficiency in parallel-connected air-cathode microbial fuel cells

Membrane-less air-cathode microbial fuel cell (MFC), as one of the low-cost and potentially scalable modules in the bioelectrochemical technology, can treat wastewater and produce electricity without additional membrane and aeration cost. Nevertheless, the formation of biofilm (i.e., biofouling) on cathodes is observed to deteriorate the cathode performance. This study constructs an eight-unit membrane-less air-cathode MFC and aims to evaluate effects of cathodic biofouling on the performance of individual unit and the scale-up power efficiency during parallel connection. Results indicate cathodic biofoulings affect the cathodic performance by deteriorating both voltage and current output, further causing the performance variation among different cathodes. Moreover, the decrease of power densities by increasing the number of parallel-connected units is observed. Cyclic voltammetry demonstrates the onset potential decreases from 0.4 V to 0.1 V after cathodic biofouling. Electrochemical impedance spectroscopy reveals the polarization resistance of the biofouling cathode increases around two folds. In addition, we also find correlation between cathodic performance and microbial community and association between cathodic performance and unit position in the eight-unit MFC. Overall, our results suggest cathodic biofouling can be the key factor to limit the performance of parallel connection and warrant the need for further research to improve scale-up power efficiency.

A new and improved aquaponics system model for food production patterns for urban architecture

Productive cities are one of the most important ways to achieve urban sustainable development. In the comprehensive production function, food production is the most basic function and should be defined as a priority. Considering the characteristics of buildings and the limitations of the urban environment, aquaponics is a safe and healthy green technology that protects the ecological environment and that has high potential to combine urban buildings and plant cultivation technology. Research on aquaponic systems has become increasingly mature, but some new problems that cannot be ignored, such as low nitrogen utilization efficiency, high aeration cost and noise problems, and unreliable water quality. In this study, a new aquaponics system model (photosynthesis reoxygenation aquaponics, PRO-AP) was proposed, and it was expected that the structure of the system can be adjusted by adding macroalgae to improve the existing problems in aquaponics. An experiment was conducted to preliminarily explore the feasibility of the proposed mode of operation. Spirogyra was added to the aquaponics system, and the DO, pH, TDS, EC, ammonia nitrogen and removal of the key nutrients from the systems were monitored during the operation. The results showed that the dissolved oxygen content in the system increased markedly and that the pH drop caused by nitrifying bacteria could be balanced when Spirogyra was irradiated with effective light. In addition, Spirogyra played a certain role in biofiltration in the aquaponic system, which reduced the values of TDS and EC, the contents of NH4+, NO3− and PO43− also decreased, and the nitrite content first increased and then decreased after a period of time. Finally, under the ratio of fish and vegetables in this experiment, the existence of Spirogyra did not create a negative image of the yield and root system of vegetables in aquaponics systems. The results showed that the aquaponic system with macroalgae has a stronger self-regulation ability. PRO-AP is an effective method in urban food production and is a very promising mode of production in the sustainable development of productive cities.

How elevation dictates technology selection in biological wastewater treatment

Most wastewater treatment facilities are built using procedures from previous designs which are predominantly from sites and regions not located at high elevation. Recognizing this limitation, we assessed the effects of elevation above sea level on the suitability of process configurations and technologies as well as their associated energy costs. Using the International Water Association (IWA) benchmark simulation model No. 2 (modified Ludzack-Ettinger process layout) as a reference, we simulated scenarios including different activated sludge process configurations, operating under different environmental and process conditions. In order to include a wide sample of environmental conditions, data on atmospheric pressure, wastewater temperature, air temperature, and relative humidity (for average, warmest, and coldest months) were collected from municipal wastewater treatment plants located at different latitudes and elevations. The results confirm that elevation is a driver against the selection of diffused aeration technologies. Aeration costs for aerobic wastewater treatment are highly influenced by local project conditions, particularly by elevation and wastewater temperature, which together influence the driving force for oxygen transfer into water. When the driving force is low, operating costs are high. Recommendations for designing treatment processes effectively, including diffused aeration systems operating at high elevations above sea level, are proposed.

Pilot-scale comparison of biological nutrient removal (BNR) using intermittent and continuous ammonia-based low dissolved oxygen aeration control systems.

Sensor driven aeration control strategies have recently been developed as a means to efficiently carry out biological nutrient removal (BNR) and reduce aeration costs in wastewater treatment plants. Under load-based aeration control, often implemented as ammonia-based aeration control (ABAC), airflow is regulated to meet desired effluent standards without specifically setting dissolved oxygen (DO) targets. Another approach to reduce aeration requirements is to constantly maintain low DO conditions and allow the microbial community to adapt to the low-DO environment. In this study, we compared the performance of two pilot-scale BNR treatment trains that simultaneously used ABAC and low-DO operation to evaluate the combination of these two strategies. One pilot plant was operated with continuous ABAC while the other one used intermittent ABAC. Both processes achieved greater than 90% total Kjehldal nitrogen (TKN) removal, 60% total nitrogen removal, and nearly 90% total phosphorus removal. Increasing the solids retention time (SRT) during the period of cold (∼12 °C) water temperatures helped maintain ammonia removal performance under low-DO conditions. However, both processes experienced poor solids settling characteristics during winter. While settling was recovered under warmer temperatures, improving settling quality remains a challenge under low-DO operation.

Quantification of energy and cost reduction from decreasing dissolved oxygen levels in full-scale water resource recovery facilities.

Aeration systems often lack the efficiency to maintain a desired residual dissolved oxygen (DO) concentration in the tank in part because little consideration is given to the dynamic daily and seasonal loading conditions. Although advanced aeration controllers exist, the majority of plants have DO set points typically based on common practice and literature values rather than site-specific conditions, which can result in DO set points higher than those necessary to meet treatment objectives. DO set point reduction strategies have primarily been proposed through either static or dynamic simulations. In this study, the substantial improvements associated with DO set point reduction are demonstrated at full scale. A yearlong characterization of full-scale aeration dynamics captured the effect of diurnal and seasonal fluctuations on oxygen transfer and energy demand and so facilitated the estimation of the potential savings of DO reduction strategies. Full-scale validation provided direct evidence of DO reduction strategies inducing an overall enhancement of oxygen transfer efficiency along the different bioreactors, while confirming that energy savings as high as 20% were feasible. This study quantifies the influence of oxygen transfer efficiency on operating choices and site-specific conditions (control strategy, loading conditions, and influent flow variability). PRACTITIONER POINTS: We quantified the energy reduction and cost savings associated with a DO reduction in an aeration tank. For each 0.2mg/L of DO decreased, the average power demand reduction per unit water treated exceeded 17%. Field measurements of dynamic alpha values eliminate the uncertainty in estimating aeration energy and cost savings from DO variations.

Reduction in VOC emissions by intermittent aeration in bioreactor landfills with gas-water joint regulation

Landfill mining and reclamation is a new strategy for addressing the lack of space available for new landfills and realizing the sustainable development of landfills. A gas-water joint bioreactor landfill is regulated by injecting water and/or recirculating leachate, and a blasting aeration system to optimize waste stabilization. In this study, four landfill reactors were constructed to investigate the effects of ventilation methods, including continuous (20 h d−1) and intermittent aeration (4 h d−1 in continuous or 2-h aeration per 12 h, twice a day), on the degradation of organic matter and volatile organic compound (VOC) emissions in comparison with traditional landfills. A total of 62 VOCs were detected in the landfill reactors. Among them, halogenated compounds had the highest abundance (39.8–65.4 %), followed by oxygenated compounds, alkanes and alkenes, and aromatic compounds. Both intermittent and continuous aeration could accelerate the degradation of landfilled waste and increase the volatilization rate of VOCs. Compared with intermittent aeration, the degradation of landfilled waste was more quickly in the landfill reactor with continuous aeration. However, intermittent aeration could create anaerobic-anoxic-aerobic conditions, which were conducive to the growth and metabolism of anaerobic and aerobic microorganisms in landfills and thereby reduced more than 63.4 % of total VOC emissions from the landfill reactor with continuous aeration. Moreover, intermittent aeration could reduce the ventilation rate and decrease the cost of aeration by 80 % relative to continuous aeration. Firmicutes, Bacteroidetes, Proteobacteria and Tenericutes predominated in the landfill reactors. The environmental variables including organic matter and VOCs concentrations had significant influences on microbial community structure in the landfilled waste. These findings indicated that intermittent aeration was an effective way to accelerate the stabilization of landfilled waste and reduce the cost and environmental risks in bioreactor landfills with gas-water joint regulation.

Survival strategy of comammox bacteria in a wastewater nutrient removal system with sludge fermentation liquid as additional carbon source

Complete ammonia oxidizing (comammox) bacteria are frequently detected in wastewater biological nutrient removal (BNR) systems. This study identified “Candidatus Nitrospira nitrosa”-like comammox bacteria as the predominant ammonia oxidizers (97.5–99.4%) in a lab-scale BNR system with acetate and sludge fermentation liquid as external carbon sources. The total nitrogen and phosphorus removals of the system were 75.9% and 86.9% with minimal N2O emission (0.27%). Low ammonia concentration, mixotrophic growth potentials and metabolic interactions with diverse heterotrophs collectively contributed to the survival of comammox bacteria in the system. The recovered draft genomes of comammox bacteria indicated their potentials in using acetate and propionate but not butyrate. Acetate and propionate indeed stimulated the transcription of comammox amoA genes (up-regulated by 4.1 folds compared with no organic addition), which was positively correlated with the ammonia oxidation rate of the community (r = 0.75, p < 0.05). Comammox bacteria could provide vitamins/cofactors (e.g., cobalamin and biotin) to heterotrophs (e.g., Burkholderiaceae), and in return receive amino acids (e.g., phenylalanine and tyrosine) from heterotrophs, which they cannot synthesize. Compared with comammox bacteria, ammonia oxidizing bacteria (AOB) exhibited lower metabolic versatility, and lacked more pathways for the synthesis of amino acids and vitamin/cofactors, leading to their washout in the studied system. BNRs with comammox bacteria as the major nitrifiers hold great potentials in achieving superior performance at low aeration cost and low N2O emission and at full-scale plants.

Oxygen supply management to intensify wastewater treatment by a microbial electrochemical snorkel

The microbial electrochemical snorkel (MES) is a low-cost, low-maintenance technology that could considerably reduce wastewater treatment costs by reducing the need for aeration. An MES is a single electrode. The lower part, in the anoxic zone of the bioreactor, oxidizes organic matter by transferring electrons to the electrode. The upper part, in the oxic zone, releases the electrons by reducing dissolved oxygen. This study gives new insights into the correlation between the MES potential, the concentration of dissolved oxygen and COD abatement, thus enabling practical rules to be extracted for running the MES in optimal conditions, particularly for adjusting the aeration zone and frequency.Here, aeration promoted the cathodic reaction and increased the MES potential to a maximum (0.0 to 0.1 V/SCE). After aeration stopped, the potential dropped to a minimum (< -0.4 V/SCE). With 26 cm high MESs, sequential aeration at the top was not sufficient to support an effective cathodic zone, while aeration at the bottom was detrimental to the formation of the microbial anode. With MESs 48 cm high and aeration set up in the highest quarter, 30 minutes of aeration every 4.5 hours gave potential variations that were stable for weeks. The MESs continued to oxidize organic matter 30 minutes after the aeration had stopped. In this period, the MESs removed 3 to 6.3 times more COD than the control reactors. Increasing the electrode capacitance is therefore suggested as an effective way to further decrease the aeration cost by decreasing the aeration frequency.