Aeration Energy Consumption Research Articles

Highly efficient electrosynthesis of hydrogen peroxide through reversible transformation between catechol and o-benzoquinone on polydopamine modified carbon black

Carbon-based materials are more promising catalysts for H2O2 electrochemical production. However, the common method for modifying carbon-based materials is surface functionalization with harsh and uncontrollable reaction conditions, hindering the precise regulation of the active sites. Herein, we proposed a carbon-based material modified by polydopamine (CB-PDA) that was easily prepared and used in air diffusion electrode system for H2O2 production. The rapid and reversible transformation between catechol and o-benzoquinone on PDA could improve the H2O2 selectivity from 75.5 % to 97.0 % during the electrocatalytic process. The detection of adsorbed *HOOH and *OOH in oxygen reduction reaction proved the preference of CB-PDA for the two-electron pathway. The H2O2 formation rate constant of CB-PDA increased significantly from 25.85 to 60.82 mM h−1. The highest cumulative H2O2 concentration could reach 10200 mg L−1 in 9 h. Long-term operation tests proved the good operational stability. Furthermore, this system was cost-effective without additional aeration energy consumption and could achieve rapid disinfection in 10 min, which would have great potential to be used in environmental remediation.

Start-up of a full-scale two-stage partial nitritation/anammox (PN/A) process treating reject water from high solid anaerobic sludge digestion (HSAD)

High solid anaerobic digestion (HSAD) achieves the benefits of high volumetric loading rates and lower reject water production, which, however, results in much more concentrated reject water with a remarkable increase in organics and nitrogen compared with that from conventional AD with low solid content. The high concentrations of ammonium (2000–3500 mg/L) and COD (3000–4000 mg/L) were reported to exert inhibition on anammox bacteria (AnAOB), posing challenges to the application of the partial nitritation/anammox (PN/A). To date, no cases of PN/A process start-up for sludge HSAD reject water were reported. This study demonstrated the start-up process of a 480 m3/d PN/A project without anammox sludge inoculation and treating HSAD reject water from a centralized dewatered sludge treatment plant. The project did not construct new infrastructures but utilized previously constructed tanks to upgrade the process from existing short-cut nitrification-denitrification to a two-stage PN/A process. Although no external anammox sludge inoculation was performed to save seeding sludge cost, the start-up was successfully achieved in about 9 months (273 days) based on a three-step method of “AnAOB enrichment - sludge acclimation - capacity doubling”. During start-up, the relative abundance of AnAOB (Candidatus_Kuenenia) increased from near zero to 12.0%. After start-up, the total inorganic nitrogen (TIN) removal load reached 0.74 kgN/(m3•d), with a total nitrogen removal efficiency of over 90%. Compared to the traditional nitrification-denitrification process, the PN/A process remarkably reduces the addition of organic chemicals and aeration energy consumption, saving approximately 4.2 million yuan (RMB) in operational costs annually. In summary, this research provides a full-scale reference for the start-up of the PN/A process treating sludge HSAD reject water.

Enhanced nitrogen removal from low C/N municipal wastewater through nitrification, partial denitrification and anammox via a step-feed strategy: Synergistic contribution by bacteria in biofilm and floc sludge

Energy-efficient nitrogen removal from carbon-limited municipal wastewater poses challenges. This study developed a novel partial denitrification and anammox (PD/A) process using a step-feed strategy in a single-stage integrated fixed-biofilm activated sludge (IFAS) system operated under sequencing batch mode. Despite relatively low temperatures (15.9–21.6 °C), biological nitrogen removal efficiency reached 80.5 % without the addition of external carbon sources. With the total inorganic nitrogen (TIN) of 48.9 ± 1.2 mg N/L, and C/N of 4.0 in influent, the TIN in effluent achieved 9.6 ± 1.5 mg N/L. Anammox bacteria (AnAOB) activity in the biofilm was 27.96 mg N/(g VSS·d), which was threefold greater than in floc sludge. Candidatus Brocadia (AnAOB) presented a high relative abundance in biofilm (0.53 %), whereas denitrifying bacteria including Thauera and Candidatus Competibacter were mainly retained in floc sludge. Overall, the coupling of step-feed strategy and IFAS offers novel insights into the efficient nitrogen removal from low C/N domestic sewage for retrofitting of municipal wastewater treatment plants, not only saving the energy consumption for aeration, but also fully utilizing carbon sources and ammonium in the influent for the PD/A process.

Life cycle assessment as a driver for process optimisation of cellobiose lipids fermentation and purification

PurposeCellobiose lipids (CL) are biosurfactants produced by various Ustilaginaceae species in aerobic fermentations. They show high potential for application as alternatives to conventional oleochemical- or petrochemical surfactants. To ensure their environmentally friendly performance, we aimed to assess CL production from a life cycle perspective at an early developmental stage to identify process steps that have the highest impact on the environment. With this information, optimisation approaches can be derived.Materials and methodsFollowing a cradle-to-gate approach, we modelled the CL fermentation and purification process based on experimental data from the lab scale and process simulation data at a 10 m3 scale. For LCA, the impact categories (IC) abiotic depletion potential (ADP), eutrophication potential, photochemical ozone creation potential, global warming potential, acidification potential, and the primary energy demand were calculated for all process steps. Based on the obtained results, process bottlenecks were identified, and alternative process scenarios varying the related process parameters were simulated. These were used to assess the environmental impact reduction potential (EIRP) of an optimised process and draw recommendations for experimental process optimisation.Results and discussionThe obtained results showed that the fermentation caused ~ 73% of ADP and more than 85% of all other ICs. The major contributor was the electricity consumption for continuous fermenter aeration. Thus, reducing the fermentation duration from the initial 14 to 5 days would result in a decrease in all investigated ICs of up to ~ 27–52%. An increase in CL concentration results in a decrease in all ICs of a similar magnitude due to the higher yield per batch at comparable energy and material consumption. Although the share of purification process steps to all ICs is overall relatively small, implementing foam fractionation for in situ product recovery showed an additional EIRP of 18–27% in all purification IC shares.ConclusionsThe conducted LCA showed that overall, more EIRP can be achieved by optimising fermentation process parameters compared to purification process steps. This is mainly due to the long fermentation duration and large energy consumption for fermenter aeration. This highlights the importance of using LCA as a driver for process optimisation to identify process steps with high EIRP. While some of the results are specific to CL, other obtained results can be transferred to other fermentations.

High-efficiency metal-free electro-Fenton system on oxygenated graphene-based floating electrodes

Metal-free electro-Fenton (EF) are a promising technology for environmental remediation. This paper reports a novel EF modified with oxygenated graphene aerogel used as a floating electrode for efficient degradation of bisphenol A (BPA) through improved H2O2 yield combined with activation of hydroxyl radical (·OH) production. Impressively, the floating configuration of the electrodes allowed oxygen from the air to diffuse naturally into the reaction interface, reducing additional aeration energy consumption. The current efficiency of the floating system for H2O2 production was 40 times higher than the conventional vertical mode. The pollutant degradation trend exhibited a positive correlation with the ·OH production performance of the electrode. The modified catalyst system achieved the highest ·OH yield of 76.48 μM within 60 min, which was 2.72 times greater than that of the catalyst-free (28.10 μM) and 2.06 times higher than that of the unmodified catalyst (37.19 μM). Experiments and theoretical calculations indicated that the oxygen-containing functional groups introduced the graphene skeleton created new sites for in situ activation of electrogenerated H2O2, resulting in increased ·OH production. The primary activation sites were identified as the = O and –COOH groups, with the = O edges playing a particularly significant role. This system offers long-lasting stability and avoids secondary pollution, making it ideal for green environmental remediation compared to the traditional EF process.

Biological performance and membrane fouling of a microalgal-bacterial membrane photobioreactor for wastewater treatment without external aeration and carbonation

Biological nutrient removal processes involving the use of activated sludge (AS) to treat municipal wastewater normally result in high aeration energy consumption and significant greenhouse gas (GHG) emissions. Therefore, developing cost-efficient and environmentally friendly processes for wastewater treatment is vital. In this work, a novel non-aerated microalgal-bacterial membrane photobioreactor (MB-MPBR) was proposed, and its feasibility for organic contaminant and nutrient removals was evaluated, for the first time. The effects of inoculation ratio (microalgae to bacteria (M/B)) on the biological performance and membrane fouling were systematically investigated. The results showed that 95.9% of the chemical oxygen demand (COD), 74.5% of total nitrogen (TN), 98.5% of NH4+-N and 42.0% of total phosphorus (TP) were removed at an inoculation M/B ratio of 3:2 at steady state, representing a significant improvement compared to the M/B inoculation ratio of 1:3. Additionally, the higher inoculation M/B ratio (3:2) significantly promoted the biomass production owing to the favorable mutual exchange of oxygen and carbon dioxide between microalgae and bacteria. Cake layer formation was the primary fouling mechanism owing to the absence of aeration scouring on the membrane surface. The membrane fouling rate was slightly higher at the higher inoculation ratio (M/B = 3:2) owing to the increased biomass and extracellular polymeric substances (EPS) productions, despite the larger particle size. These results demonstrated that the non-aerated MB-MPBR could achieve superior biological performance, of which the inoculation M/B ratio was of critical importance for the initiation and maintenance of microalgal-bacterial symbiotic system, yet possibly caused severer membrane fouling in the absence of external aeration and carbonation. This study provides a new perspective for further optimizing and applying non-aerated MB-MPBR to enhance municipal wastewater treatment.

High effective generation of hydrogen peroxide by adjusting three-phase interfaces of gas diffusion electrode during the oxygen reduction reaction

Mass transfer of oxygen is a critical issue in the two-electron oxygen reduction reaction (2e− ORR) for the generation of hydrogen peroxide (H2O2). In this study, a novel constant velocity gas diffusion electrode (CVGDE) that can control the gas flow rate through the catalyst layer was fabricated, and the effect of the gas flow rate on three-phase interfaces (TPIs) formation and the mass transfer of oxygen in gas diffusion electrode (GDE) was investigated. In CVGDE, oxygen mass transfer was significantly improved, and the yield of H2O2 reached up to 73.65 mg cm−2 h−1 at 200 mA cm−2, which was 74.3 % higher than that of conventional GDE. Furthermore, the oxygen utilization efficiency of CVGDE reached 22.4 %, and the aeration energy consumption was decreased to 5.48 Wh kg−1, which was 1000 times less than the energy consumption required for H2O2 electrosynthesis. The experiments and theoretical calculations showed that the dynamic equilibrium state of TPI was achieved by the influence of both the electric field and air flow in the catalyst layer, which leading to a substantial increase in oxygen mass transfer and H2O2 yield. Finally, CVGDE was utilized in the electro-Fenton process for the degradation of organic contaminants. This study will contribute to the understanding of the oxygen mass transfer process in GDE.

Effects of micro-bubble aeration on the pollutant removal and energy-efficient process in a floc–granule sludge coexistence system

Abstract To investigate energy-saving approaches in wastewater treatment plants and decrease aeration energy consumption, this study successfully established a floc–granule coexistence system in a sequencing batch airlift reactor (SBAR) employing micro-bubble aeration. The analysis focused on granule formation and pollutant removal under various aeration intensities, and compared its performance with a traditional floc-based coarse-bubble aeration system. The results showed that granulation efficiency was positively associated with aeration intensity, which enhanced the secretion of extracellular polymeric substances (EPSs) and facilitated granule formation. The SBAR with the micro-aeration intensity of 30 mL·min−1 showed the best granulation performance (granulation efficiency 52.6%). In contrast to the floc-based system, the floc–granule coexistence system showed better treatment performance, and the best removal efficiencies of NH4+-N, TN, and TP were 100.0, 77.0, and 89.5%, respectively. The floc–granule coexistence system also enriched higher abundance of nutrients removal microbial species, such as Nitrosomonas (0.05–0.14%), Nitrospira (0.14–2.32%), Azoarcus (2.95–12.17%), Thauera (0.43–1.95%), and Paracoccus (0.76–2.89%). The energy-saving potential was evaluated, which indicated it is feasible for the micro-aeration floc–granule coexistence system to decrease the aeration consumption by 14.4% as well as improve the effluent.

Integration of double nitrite autotrophic shunt enhances anammox-based wastewater treatment for sustainable nitrogen removal and energy efficiency

Anammox holds significant promise as a next-generation technology for achieving energy-positive wastewater treatment. However, its application remains challenging due to unstable nitrite supply and excessive nitrate residue. To address this, a groundbreaking Anammox bioprocess incorporating a double nitrite autotrophic shunt was developed within single system to realize energy-efficient nitrogen removal from wastewater. Partial nitrification/Anammox converted a portion of ammonia in leachate to nitrogen gas in oxic stage. Significantly, sulfur-driven partial denitrification utilizing sulfide as electron donor, efficiently reduced generated nitrate to nitrite in subsequent anoxic stage, facilitating nitrite reutilization via Anammox and removing residual ammonia. Over 200-day monitoring, bioprocess demonstrated desirable effluent quality with 9.0 mg/L NH4+-N, 0.6 mg/L NO2−-N, and 6.2 mg/L NO3−-N. Delightedly, efficient nitrogen removal efficiency of 97.8 % was achieved even under fluctuation conditions. Priority position held by Anammox consortium (Candidatus Kuenenia 11.2 %) mainly derives from similar growth rate of autotrophic bacteria within their shared ecological niche and stable nitrite supply, enabling Anammox to contribute impressive 72.4 % of nitrogen removal. By combing electron flow preference kinetic, stability toward fluctuation, core microbial community, the ecological niche of Candidatus Kuenenia and self consistent logic governing functional microorganisms were revealed. The cost-effective system exhibited significant advantages over conventional bioprocess, reducing organic matter demand by 100 %, aeration energy consumption by 61.7 %, and biomass production by 82.9 %.

End-to-end autonomous and resilient operability strategy of full-scale PN-SBR system: From influent augmentation to AI-aided optimal control and scheduling

This study developed an artificial intelligence (AI)-driven autonomous resilient operation of partial nitrification (PN) process to enhance the performance of a two-stage PN-anammox process by ensuring a specific NO2/NH4 ratio under varying influent conditions before the wastewater enters the subsequent anammox process. First, a mathematical model representing PN process was developed in a full-scale sequencing batch reactor (PN-SBR). That model was then calibrated using AI-driven multi-objective optimization targeting NH4, NO2, and NO3 using a comprehensive rank-based global sensitivity analysis framework to identify the biological kinetic and stoichiometric parameters that has high affection on the PN process. After validating the PN-SBR model with real-time measurements of the PN process, an AI-driven optimal aeration strategy (AI-OpAS) was developed for the targeted PN-SBR. The influent characteristics were augmented using the oversampling method and then clustered using varying influent conditions. The AI-OpAS used iterative approximate dynamic programming (iADP) to determine the optimal aeration length scheduling and optimal dissolved‑oxygen control policy to maintain autonomously the NO2/NH4 ratio while reducing aeration energy under diverse influent conditions. The results show that the proposed AI-OpAS can operate the PN-SBR process by achieving the proposed NO2/NH4 ratio of 1.1 and reducing overall aeration energy consumption by up to 31.38 % under varying influent conditions; furthermore, this AI-aided strategy of resilient operation can be extended to the other variables such as pH for autonomous and sustainable PN-SBR system simultaneously.

Widening the applicability of most-open-valve (MOV) strategy for aeration control at full scale WWTPs by combining fuzzy-logic control and knowledge-based rules

An adaptation of a pressure-based most-open-valve control strategy to be applied in aeration control systems of any full scale Wastewater Treatment Plant (WWTP) is described in this paper. This control strategy minimises aeration energy consumption by leading the aeration system to work under the minimum pressure level that is possible given the air distribution system design characteristics and the effluent criteria. Several fuzzy-logic-based control loops are used in the different levels of a supervisory control architecture where knowledge-based rules are also applied. Results obtained in the implementation of this control strategy in three WWTPs with different configurations showed the capability of fuzzy algorithms to maintain dissolved oxygen concentration and pressure always close to setpoint values. Average electrical energy savings of 25 %, 22 % and 16 %, where achieved, respectively, in each WWTP, quantified as kWh per kg of removed COD.

Decreasing dietary nitrogen consumption improves wastewater treatment efficiency and carbon footprint.

This article aimed to connect protein consumption with the nitrogen load to wastewater treatment plants (WWTPs) in Finland. The influence of the changes in nitrogen consumption on the WWTP environmental footprint was estimated using process simulation. As the main result, a connection was found between nitrogen loads from food consumption and the incoming load to a WWTP. This was done by analysing protein consumption data from the Food and Agriculture Organization of the United Nations (FAO) and incoming nitrogen load data from the Finnish environmental institute, SYKE. The impact of nitrogen consumption was estimated using different diet scenarios. Decreasing dietary nitrogen consumption by 16-24% could decrease nitrous oxide emissions by 16-24% and aeration energy (AE) consumption by 6-11%. An increase in dietary nitrogen consumption of 6-42% could increase AE consumption by 2-14% when effluent requirements were met. When considering the environmental impact of this increased aeration, it corresponds to an increase of 2-16%. Furthermore, nitrous oxide emissions could rise by 6-42% This information can be valuable to WWTPs and even consumers for influencing incoming nitrogen loads.

An online intelligent management method for wastewater treatment supported by coupling data-driven and mechanism models

The management of traditional wastewater treatment plants(WWTPs) mostly rely on human experience, resulting in high cost and low efficiency under conservative operation mode. This study proposed an online intelligent management method based on plan library to improve the wastewater treatment performance. The operation plans in plan library were obtained based on the mechanism model (Activated Sludge Models) of a pilot Anaerobic-Anoxic-Oxic (A2/O) process, and each plan represents the optimal operation strategy under a specific influent condition. Then the plan library was input to train a data driven model, i.e. a Multi-Layer Perceptron (MLP) regression model. The trained MLP model can be used to generate more detailed online operation strategies for wastewater treatment process under different influent conditions. After a 124 days continuous operation of the A2/O process, the results shown, the proposed method can generate online operation strategies according to influent conditions, and the main effluent indicators meet the discharge standards continuously and stably. Meanwhile, compared with the manual operation mode, the aeration energy consumption was saved about 49.4 % by using the proposed method. The mechanism model and data-driven model were combined in this study, and it has scientific value and engineering significance for intelligent management of WWTPs.

Efficient nitrogen removal and partial elemental sulfur recovery by combined nitrite-Anammox and sulfate-Anammox: A novel strategy for treating mature landfill leachate

The application of anaerobic ammonia oxidation (Anammox) is of great significance due to its eco-friendly potential. Besides conventional nitrite-dependent Anammox (N-Anammox), sulfate can also serve as an electron acceptor for ammonia oxidation under anaerobic conditions (S-Anammox). For the first time, an innovative process integrating partial nitrification, N-Anammox, and S-Anammox (P-NA/SA) in one single system, was applied herein to treat mature landfill leachate (1079.6 mg/L NH4+-N, 1584.4 mg/L SO42--S) with oxic/anoxic operation mode. After 180 days of continuous operation, the nitrogen and sulfate removal efficiencies of 95.7% and 24.3%, respectively, were obtained. Importantly, valuable elemental sulfur was recovered with an average efficiency of 21.9%. Isotope analysis confirmed that N-Anammox and S-Anammox contributed to 65.6% and 27.5% of total inorganic nitrogen removal, respectively. Furthermore, S-Anammox was identified as a step-wise bioprocess, with biologically generated NO2−-N and S2− as intermediates. With enhancement of S-Anammox, partial nitrification pretreatment-step for nitrite generation in oxic stage became less necessary, leading to a remarkable 44% saving in aeration energy consumption. The Anammox bacteria gene (hydrazine synthase, HzsB) was highly abundant (1.2–2.5 × 108 copies/g·SS), with the dominant Anammox genus transforming from Candidatus_Kuenenia (4.6%→2.1%) to Candidatus_Brocadia (0.3%→3.2%). Anammox-mediated biotechnology by coupling N-Anammox and S-Anammox offers new insights into sustainable treatment of ammonia- and sulfate-containing wastewater.

A novel process for simultaneous biological nutrient removal and waste activated sludge reduction in one-stage system without aeration

This study presented a novel process for simultaneous biological nutrient removal and waste activated sludge reduction in one-stage municipal wastewater treating system without aeration on the basis of endogenous partial denitrification, anammox and Candidatus Phosphoribacter dominated biological phosphate removal with sludge reduction (EPDA/PSR). The effluent total inorganic nitrogen and phosphate concentrations were 0.1 mg/L and lower than detection limit (0.1 mg/L), respectively, without dosing external carbon sources. Compared with partial denitrification-anammox process, the daily sludge production in EPDA/PSR process reduced by 50.8 %. The percentage of intact cells measured by flow cytometry reduced from 92.4 % to 77.3 % with the increase of aromatic protein, DNA content of supernatant, soluble microbial byproduct-like substance and decline of particle size. The sludge stabilization structure was destructed, and intracellular organics were released, which resulted in the reduction of sludge production. Microbial community structure at transcriptional level indicated that really working Candidatus Phosphoribacter (phosphorus accumulating organisms with fermentation capacity), Candidatus Competibacter (endogenous partial denitrification bacteria) and Candidatus Brocadia (anammox bacteria) reached 68.4 %, 9.84 % and 8.02 %, respectively, and Candidatus Kuenenia (anammox bacteria) did not play a role in EPDA/PSR system. The novel one-stage EPDA/PSR process realized high efficient biological nutrient removal, achieved waste activated sludge reduction and saved 100 % of aeration energy consumption cost and external carbon source dosage cost, which effectively developed internal carbon source and provided a new idea for wastewater treatment.

Energy-Efficient H2O2 Electro-production Based on an Integrated Natural Air-Diffusion Cathode and Its Application

Given the low oxygen mass transfer rate and high aeration energy consumption, the traditional two-electron oxygen reduction reaction (ORR) is restricted. In this study, the integrated natural air diffusion cathode (INAC) and a reactor configuration with the horizontal scale facing to air (FTA) demonstrated highly selective H2O2 production for the removal of organic contaminants. Simply synthesized by shaping the mixture of carbon black and polytetrafluoroethylene, the INAC exhibited not only massive pores in all directions for sufficient mass transfer but also the integrated configuration for low charge transfer resistance. Based on the oxygen mass transfer models, for the ORR reaction kinetics, the interface oxygen concentration index was higher than 40, contributing to the high current efficiency of H2O2 production (>90%). The oxygen diffusion model can provide the quantitative description of H2O2 synthesis for porous electrode optimized design. Combining the INAC with the reactor configuration with the FTA mode for free additional O2/air source supply, the electrical efficiency per order was lower than 0.14 kWh m–3, and the removal rate of sulfonamides per unit current could reach 11 mg min–1 A–1, reaching the best reports. This ultraefficient process equipped with the INAC and the FTA mode provides a meaningful practical application prospect for wastewater treatment.

Removal of sulfamethazine by a flow-Fenton reactor with H2O2 supplied with a two-compartment electrochemical generator

A novel continuous-flow H2O2 electrochemical generator using a natural air diffusion electrode (NADE) as the cathode was designed and the two compartments of the generator were separated by a cation exchange membrane. The reactor did not require aeration, which saved aeration energy consumption. The reactor showed good performance in generating H2O2 up to 50.8 mg/h/cm2 with the energy consumption of 25.2 kWh/kg H2O2, and maintained a high current efficiency of about 70–94% in the current density range of 20 to 100 mA/cm2. The yield of H2O2 and current efficiency remained high and stable in a wide pH range of 3 ∼ 9. H2O2 produced in the generator was delivered to a flow-Fenton reactor for the occurrence of the Fenton reaction and the degradation of sulfamethazine (SMT), which avoided the problem of excessive generation and ineffective consumption of H2O2 in the electro-Fenton process and improved the utilization rate of H2O2. Moreover, due to the introduction of H2O2 solution with low pH to the flow-Fenton reactor, the pH of the working solution did not need adjustment. The flow-Fenton process achieved 99% of SMT removal, 90% of H2O2 utilization rate, and 54% of TOC removal within 20 min under the optimum conditions. The degradation of several other contaminants (2,4-dichlorophenoxyacetic acid, tetracycline and carbamazepine) was investigated and all of the removals were maintained above 97%. The study is promising for the practical electrochemical production of H2O2 and application of flow-Fenton for contaminants degradation.

Improving the Performance of Biological Tanks in Wastewater Treatment Plants by Modifying the Conventional Ceramic Aerator

The purpose of the article is to study the process of aeration of wastewater using an aerator with an air-lift effect to ensure a uniform distribution of the concentration of suspended solids in the aeration tank of the model installation. Based on the result of the work carried out, experimental data were obtained and a theoretical description of the parameters of the aeration process, which increase the coefficients of mass transfer and the use of the reactor volume, and the costs of the process. The airlift effect increases the concentration of sludge. The airlift also helps in the spread of suspended solid in the tank, as mass transfer reactions during aeration increase by an average of 11.8%. Also, an increase in dissolved oxygen concentration from 3.02 mg / L to 3.5 mg / L, i.e., by 15%, which indicates an improvement in mass transfer and, accordingly, a decrease in energy consumption for aeration. However, the existing technological potential requires the introduction of variable equipment. An example of an alternative air dispersion system can be aerators with airlift effect.

Dynamic modelling of N2 O emissions from a full-scale granular sludge partial nitritation-anammox reactor.

Partial nitration-anammox is a resource-efficient pathway for nitrogen removal from wastewater. However, the advantages of this nitrogen removal technology may be counter-acted by the emission of N2 O, a potent greenhouse gas. In this study, mathematical modelling was applied to analyse N2 O formation and emission dynamics and to develop N2 O mitigation strategies for a one-stage partial nitritation-anammox granular sludge reactor. Dynamic model calibration for such a full-scale reactor was performed, applying a one-dimensional biofilm model and including several N2 O formation pathways. Simultaneous calibration of liquid phase concentrations and N2 O emissions leads to improved model fit compared to their consecutive calibration. The model could quantitatively predict the average N2 O emissions and qualitatively characterize the N2 O dynamics, adjusting only seven parameter values. The model was validated with N2 O data from an independent data set at different aeration conditions. Nitrifier nitrification was identified as the dominating N2 O formation pathway. Off-gas recirculation as a potential N2 O emission reduction strategy was tested by simulation and showed indeed some improvement, be it at the cost of higher aeration energy consumption.

Evaluating the potential impact of energy-efficient ammonia control on the carbon footprint of a full-scale wastewater treatment plant.

An assessment was performed for elucidating the possible impact of different aeration strategies on the carbon footprint of a full-scale wastewater treatment plant. Using a calibrated model, the impact of different aeration strategies was simulated. The ammonia controller tested showed its ability in ensuring effluent ammonia concentrations compliant with regulation along with significant savings on aeration energy, compared to fixed oxygen set point (DOsp) control strategies. At the same time, nitrous oxide emissions increased due to accumulation of nitrification intermediates. Nevertheless, when coupled with the carbon dioxide emissions due to electrical energy consumption for aeration, the overall carbon footprint was only marginally affected. Using the local average CO2 emission factor, ammonia control slightly reduced the carbon footprint with respect to the scenario where DOsp was fixed at 2 mg·L-1. Conversely, no significant change could be detected when compared against the scenarios where the DOsp was fixed. Overall, the actual impact of ammonia control on the carbon footprint compared to other aeration strategies was found to be strictly connected to the sources of energy employed, where the larger amount of low CO2-emitting energy is, the higher the relative increase in the carbon footprint will be.