Full-scale Reactor Research Articles

Modeling and optimization of biogas production from cow manure and maize straw using an adaptive neuro-fuzzy inference system

This study was focused on the prediction and optimization of biogas production from cow manure with maize straw under various total solid content (TS), Carbon to Nitrogen (C/N) ratio and stirring intensity. This research used full-scale (1200 L) batch reactor under mesophilic condition. An adaptive neuro-fuzzy interference system (ANFIS) was utilized to predict and optimize biogas production from anaerobic digestion. C/N ratio, TS and stirring intensity of substrates, each of them in three levels, were considered as input variables and biogas production was regarded as the output variable of the model. The coefficient of determination (R2) between observed and predicted biogas production values was 0.99 which showed good match and accuracy of the model. Highest biogas production was achieved from C/N ratio 26.76, TS 9% and moderate stirring. Biogas production increased about 8% with optimal conditions suggested by the ANFIS model.

A chemometric analysis on the fluorescent dissolved organic matter in a full-scale sequencing batch reactor for municipal wastewater treatment

Rapid monitoring of water quality is crucial to the operation of municipal wastewater treatment plants (WWTPs). Fluorescence excitation-emission matrix (EEM) in combination with parallel factor analysis (PARAFAC) has been used as a powerful tool for the characterization of dissolved organic matter (DOM) in WWTPs. However, a recent work has revealed the drawback of PARAFAC analysis, i.e., overestimating the component number. A novel method, parallel factor framework-clustering analysis (PFFCA), has been developed in our earlier work to resolve this drawback of PARAFAC. In the present work, both PARAFAC and PFFCAwere used to analyze the EEMs of water samples from a full-scale WWTP from a practical application point of view. The component number and goodness-offit from these two methods were compared and the relationship between the relative score change of component and the actual concentration was investigated to evaluate the estimation error introduced by both methods. PFFCA score and actual concentration exhibited a higher correlation coefficient (R 2 = 0.870) compared with PARAFAC (R 2<0.771), indicating that PFFCA provided a more accurate relative change estimation than PARAFAC. The results suggest that use of PARAFAC may cause confusion in selecting the component number, while EEM-PFFCA is a more reliable alternative approach for monitoring water quality in WWTPs.

Insights into sludge granulation during anaerobic treatment of high-strength leachate via a full-scale IC reactor with external circulation system

In this study, a full-scale internal circulation (IC) reactor coupled with an external circulation system was developed to treat high-strength leachate from a municipal solid waste (MSW) incineration plant, in which anaerobic sludge granulation was intensively investigated. Results showed that the IC reactor achieved excellent treatment performance under high organic loading rates (OLR) of 21.06–25.16kg chemical oxygen demand (COD)/(m3∙day). The COD removal efficiency and biogas yield respectively reached 89.4%–93.4% and 0.42–0.50m3/kgCOD. The formation of extracellular polymeric substances (EPS) was closely associated with sludge granulation. Protein was the dominant component in sludge EPS, and its content was remarkably increased from 21.6 to 99.7mg/g Volatile Suspended Solid (VSS) during the reactor operation. The sludge Zeta potential and hydrophobicity positively correlated with the protein/polysaccharide ratio in EPS, and they were respectively increased from −26.2mV and 30.35% to −10.6mV and 78.67%, which was beneficial to microbial aggregation. Three-dimensional fluorescence spectroscopy (3D-EEM) and Fourier transform infrared spectroscopy (FT-IR) analysis further indicated the importance of protein-like EPS substances in the sludge granulation. Moreover, it was also found that the secondary structures of EPS proteins varied during the reactor operation.

Inhibitory Effect of Coumarin on Syntrophic Fatty Acid-Oxidizing and Methanogenic Cultures and Biogas Reactor Microbiomes.

Coumarins are widely found in plants as natural constituents having antimicrobial activity. When considering plants that are rich in coumarins for biogas production, adverse effects on microorganisms driving the anaerobic digestion process are expected. Furthermore, coumarin derivatives, like warfarin, which are used as anticoagulating medicines, are found in wastewater, affecting its treatment. Coumarin, the structure common to all coumarins, inhibits the anaerobic digestion process. However, the details of this inhibition are still elusive. Here, we studied the impact of coumarin on acetogenesis and methanogenesis. First, coumarin was applied at four concentrations between 0.25 and 1 g · liter-1 to pure cultures of the methanogens Methanosarcina barkeri and Methanospirillum hungatei, which resulted in up to 25% less methane production. Acetate production of syntrophic propionate- and butyrate-degrading cultures of Syntrophobacter fumaroxidans and Syntrophomonas wolfei was inhibited by 72% at a coumarin concentration of 1 g · liter-1 Coumarin also inhibited acetogenesis and acetoclastic methanogenesis in a complex biogas reactor microbiome. When a coumarin-adapted microbiome was used, acetogenesis and methanogenesis were not inhibited. According to amplicon sequencing of bacterial 16S rRNA genes and mcrA genes, the communities of the two microbiomes were similar, although Methanoculleus was more abundant and Methanobacterium less abundant in the coumarin-adapted than in the nonadapted microbiome. Our results suggest that well-dosed feeding with coumarin-rich feedstocks to full-scale biogas reactors while keeping the coumarin concentrations below 0.5 g · liter-1 will allow adaptation to coumarins by structural and functional community reorganization and coumarin degradation.IMPORTANCE Coumarins from natural and anthropogenic sources have an inhibitory impact on the anaerobic digestion process. Here, we studied in detail the adverse effects of the model compound coumarin on acetogenesis and methanogenesis, which are two important steps of the anaerobic digestion process. Coumarin concentrations lower than 0.5 g · liter-1 had only a minor impact. Even though similar inhibitory effects can be assumed for coumarin derivatives, little effects on the anaerobic treatment of wastewater are expected where concentrations of coumarin derivatives are lower than 0.5 g · liter-1 However, when full-scale reactors are fed with coumarin-rich feedstocks, the biogas processes might be inhibited. Hence, these feedstocks should be utilized in a well-dosed manner or after adaptation of the microbial community.

Discrete Element Method–Based Investigations of Granular Flow in a Pebble Bed Reactor

In a pebble bed reactor (PBR) core, nuclear fuel in the form of pebbles moves slowly under the influence of gravity. Due to the dynamic nature of the core, a thorough understanding about slow and dense granular flow of pebbles is required from both a reactor safety point of view and a performance evaluation point of view. In the current study, validation of discrete element method (DEM)–based simulation for the pebble flow in a PBR was carried out. Validation of DEM-based simulations necessitates validation of the employed numerical method of simulating packed structure. Hence, a parametric sensitivity study of packing interaction properties was initially conducted and also validation of the numerical method simulating packed structure at first. The parametric sensitivity analysis suggests that static friction characteristics play an important role from a packed/pebble bed structural characterization point of view. In addition, the simulated packed structure approach has shown a good agreement with the available benchmark data. Afterward, the effect of two different half-cone angles of 30 deg and 60 deg on pebble flow field in a PBR was studied by EDEMTM-based simulations. Results of streamlines, velocity radial profiles, and direct observation of discharge indicated a plug-type flow in the upper cylindrical region, whereas results indicated converging-type flow near the bottom conical region. EDEMTM results of granular flow were validated against experimental benchmark data and show a fair agreement in terms of Lagrangian trajectories and velocity profile. Therefore, this validated EDEMTM-based simulation can be used to obtain reliable results of pebble dynamics in a PBR and to enhance understanding of this phenomenon in a PBR. However, additional experimental investigations are recommended to be carried out for different sizes of test reactors, different bottom cone angles, and different sizes of pebbles to further assess DEM simulation results before using them for full-scale reactor simulations.

Dynamics of two methanogenic microbiomes incubated in polycyclic aromatic hydrocarbons, naphthenic acids, and oil field produced water

BackgroundOil field produced water (OFPW) is widely produced in large volumes around the world. Transforming the organic matter in OFPW into bioenergy, such as biomethane, is one promising way to sustainability. However, OFPW is difficult to biologically degrade because it contains complex compounds such as naphthenic acids (NAs), or polycyclic aromatic hydrocarbons (PAHs). Although active microbial communities have been found in many oil reservoirs, little is known about how an exotic microbiome, e.g. the one which originates from municipal wastewater treatment plants, would evolve when incubated with OFPW.ResultsIn this study, we harvested methanogenic biomass from two sources: a full-scale anaerobic digester (AD) treating oil and gas processing wastewater (named O&G sludge), and from a full-scale AD reactor treating multiple fractions of municipal solid wastes (named MS, short for mixed sludge). Both were incubated in replicate microcosms fed with PAHs, NAs, or OFPW. The results showed that the PAHs, NAs, and OFPW feeds could rapidly alter the methanogenic microbiomes, even after 14 days, while the O&G sludge adapted faster than the mixed sludge in all the incubations. Two rarely reported microorganisms, a hydrogenotrophic methanogen Candidatus methanoregula and a saccharolytic fermenter Kosmotoga, were found to be prevalent in the PAHs and OFPW microcosms, and are likely to play an important role in the syntrophic degradation of PAHs and OFPW, cooperating with methanogens such as Methanoregula, Methanosarcina, or Methanobacterium.ConclusionsThe dominant phyla varied in certain patterns during the incubations, depending on the biomass source, feed type, and variation in nutrients. The sludge that originated from the oil and gas processing wastewater treatment (O&G) reactor adapted faster than the one from municipal solid waste reactors, almost certainly because the O&G biomass had been “pre-selected” by the environment. This study reveals the importance of biomass selection for other crude oil-waste-related bioengineering studies, such as bioaugmentation and bioremediation.

Mechanical pretreatment at harvesting increases the bioenergy output from marginal land grasses

Meadow grass has recently gained increased attention as a substrate for full-scale biogas reactors. However, to increase its biodegradability, pretreatment is needed. In the present work, different harvesting machines were compared in order to assess their effect on biogas production. Specifically, a Disc-mower, an Excoriator and a Chopper were used to define the most appropriate machinery in order to improve the energy output per hectare for full-scale biogas plants. Among the harvesters, Excoriator, a novel simultaneous harvest and mechanical treatment, was found to significantly increase the methane yield of meadow grass by 20% compared to a classical Disc-mower. The positive effect was also validated by three kinetic model equations. The modified Gompertz model was the most capable of determining the kinetics of anaerobic digestion process, pointing out also the superiority of Excoriator. The usage of the novel harvester was associated with increased energy output, either for electrical/thermal energy generation or for transport fuel production, compared to the alternative machineries. Moreover, it was shown that the co-digestion of harvested biomass with different types of manure can enhance the bioenergy output of a full-scale biogas plant in a range of 12%–23%.

Microstructure of anammox granules and mechanisms endowing their intensity revealed by microscopic inspection and rheometry

The anammox process represents a sustainable and cost-effective technique for nitrogen removal from wastewater, where granulation of anammox bacteria could be of great benefit to the system performance. However, knowledge of the specific properties of anammox granules is currently unsatisfactory. In this study, the organization of anammox granules was comprehensively studied from macro to micro scale with a range of microscale techniques. Scanning and transmission electron microscopy and multiple fluorescence labeling combined with confocal laser scanning microscopy were included. Simultaneously, the associated mechanical properties were studied in-depth by rheometry in combination with selective enzymatic hydrolysis. Anammox granules follow a tertiary organization regime, where interactions between individual anammox bacteria made up the primary base, then, the grouping of anammox bacterial cells encapsulated within a thin extracellular polymeric substance (EPS) layer comprised a second arrangement level, and, finally, the cementing of these groups together with other bacteria and polymers gave rise to compact aggregates. α-Polysaccharides and proteins were considered the backbones of anammox granules, contributing greatly to their excellent intensity. β-Polysaccharides concentrated at the outer rims of anammox granules and combined with other macromolecules to form a buffer zone or protective barrier, beneath which anammox bacteria proliferated. Divalent cationic bridging for EPS binding was prevalent and of great significance within the dense anammox granules, while there was also much weak monovalent ionic interaction. The specific organization and composition of anammox granules endows them with excellent intensity and integrity, which can be of importance for full-scale reactor operations where diverse shocks can be expected.

Conversion of Petroleum Coke in a High-Pressure Entrained-Flow Gasifier: Comparison of Computational Fluid Dynamics Model and Experiment

High-pressure entrained-flow gasifier technology is used to convert solid carbonaceous feedstocks into synthesis gas, which can be used in an integrated gasification combined cycle power plant or as a feedstock for chemical or synthetic fuel production. Computational fluid dynamics (CFD) models, once validated, can be used to help design full-scale reactors. Model validation entails the comparison of model predictions to lab-scale or pilot-scale measurements. However, experimental measurements of high-pressure pilot-scale gasifiers usually consist only of wall temperatures and outlet gas temperature and composition, which are of limited use for model validation when the gasifier is operating well, providing information only about operating temperature, heat loss, and equilibrium gas composition. These do not provide a strong validation of the CFD model, whose main purpose is to make predictions of the flame size and shape and its ability to convert solid fuel to gas efficiently in a small volume. This paper presents a model validation based on data generated using CanmetENERGY’s 1 MWth high-pressure entrained-flow gasifier. To provide a stronger validation, the approach taken here is to compare the model predictions to the pilot-scale measurements over a range of operating conditions comprising higher (approximately 90%) carbon conversion and lower (approximately 80% or lower) carbon conversion. In effect, the comparison includes operating conditions for which gasification reactions are extended or delayed toward the outlet in order to capture key effects. It is found that the present CFD model is able to track the performance of the gasifier over the range of operating conditions and provides insight into the causes for limited carbon conversion.

The effectiveness of biodrying waste treatment in full scale reactor

AbstractThe differences between the composting, stabilization and drying processes were discussed. The law criteria for mechanical-biological treatment plant were presented. The purpose of the article was to assess the effectiveness of biodrying MSW (municipal solid waste) in a full scale reactor taking into account the degree of biological decomposition of organic matter and its suitability for RDF (refuse derived fuel). Therefore the microbial activity was measured as the O2/96 h uptake. CO2/96 h production and the respiration activity AT4 for untreated and biodried waste were compared. The decomposition of organic matter was measured by loss on ignition (LOI) and total organic carbon (TOC). The product after the biodrying process was assessed according to the EURITS and PN-EN 15359 criteria for the quality of RDF (residual derived fuel). The result 8.48 MJ/kg of calorific value shows that bio- dried waste is ranked below the EURITS minimum level and can be classified as fifth class by PN-EN 15359 requirements. The amount of chlorine, mercury and lead fulfil the EURITS criteria. The microbial activity after processing in the biodrying reactor expressed as oxygen uptake exceeded the permissible level of 10 mg O2/g d.m. in the time range ten months. The regulatory parameters TOC &lt; 20% d.m. and LOI &lt; 35% d.m. criteria were not met.

Antibiotic Resistance Genes and Correlations with Microbial Community and Metal Resistance Genes in Full-Scale Biogas Reactors As Revealed by Metagenomic Analysis.

Digested residues from biogas plants are often used as biofertilizers for agricultural crops cultivation. The antibiotic resistance genes (ARGs) in digested residues pose a high risk to public health due to their potential spread to the disease-causing microorganisms and thus reduce the susceptibility of disease-causing microorganisms to antibiotics in medical treatment. A high-throughput sequencing (HTS)-based metagenomic approach was used in the present study to investigate the variations of ARGs in full-scale biogas reactors and the correlations of ARGs with microbial communities and metal resistance genes (MRGs). The total abundance of ARGs in all the samples varied from 7 × 10-3 to 1.08 × 10-1 copy of ARG/copy of 16S-rRNA gene, and the samples obtained from thermophilic biogas reactors had a lower total abundance of ARGs, indicating the superiority of thermophilic anaerobic digestion for ARGs removal. ARGs in all the samples were composed of 175 ARG subtypes; however, only 7 ARG subtypes were shared by all the samples. Principal component analysis and canonical correspondence analysis clustered the samples into three groups (samples from manure-based mesophilic reactors, manure-based thermophilic reactors, and sludge-based mesophilic reactors), and substrate, temperature, and hydraulic retention time (HRT) as well as volatile fatty acids (VFAs) were identified as crucial environmental variables affecting the ARGs compositions. Procrustes analysis revealed microbial community composition was the determinant of ARGs composition in biogas reactors, and there was also a significant correlation between ARGs composition and MRGs composition. Network analysis further revealed the co-occurrence of ARGs with specific microorganisms and MRGs.

First full-scale nitritation-anammox plant using gel entrapment technology for ammonia plant effluent

The first full-scale nitritation-anammox process using gel entrapment technology was evaluated for nitrogen removal. Ammonia plant effluents contained not only ammonium but also methanol, an anammox inhibitor. The nitrogen concentration and loading design were 690mg/L and 400kg-N/d, respectively. A nitritation reactor (170m3) filled with nitrification gel carriers was started up on day 20, with a resulting nitrification efficiency of 58%. A stable nitritation performance was observed without significant nitrate production for >1year. A nitrogen conversion rate of 3.2kg-N/m3/d was observed on the anammox reactor (100m3) filled with anammox gel carrier on day 69. The full-scale anammox reactor could be started up in approximately 2 months. Subsequently, stable nitrogen removal performance was observed for >1year. The average nitrogen loading, nitrogen conversion rate, and total nitrogen removal on the anammox reactor were 3.6kg-N/m3/d, 3.0kg-N/m3/d and 330kg-N/d, respectively. The nitrogen removal performance obtained in this study will facilitate further application of the anammox processes to many types of industrial wastewater treatment.

Scum yield and effectiveness of a hydrostatic removal device: case study of Laboreaux STP

This paper aimed to evaluate the effectiveness of a device to remove scum from the inner part of gas-liquid-solid separators of a full-scale upflow anaerobic sludge blanket reactor treating domestic sewage, as well as determining the scum yield coefficient for different reactors’ operating conditions. The experiments were carried out at the Laboreaux sewage treatment plant (Itabira, Minas Gerais, Brazil) and the effectiveness of the scum removal device was fully demonstrated, with median efficiencies ranging from 65 to 90%. The average scum yield varied from 6.8 to 14.6 mL of scum formed per kg COD applied.

Performance of Full-Scale UASB Reactors Treating Low or Medium Strength Municipal Wastewater

Upflow Anaerobic Sludge Blanket (UASB) reactors treating low or medium strength municipal wastewater were monitored under field conditions in India. The study aimed to evaluate the efficiency of the UASB process (in terms of organics, solids and nutrients removal) and to highlight the causes and remedies for odour nuisances. The UASB reactors represent a robust and efficient technology for sewage pre-treatment (COD removal: 51%; BOD: 56%; TSS: 54%), capable to generate renewable energy (biogas yield: 0.20–0.40 m3 kg−1 COD removed) under the conditions prevailing in India. The UASB performed significantly better when low strength wastewater (COD ~300 mg L−1) was treated, giving a final effluent COD of around 120 mg L−1, similar to aerobic treatment systems. In the case of medium strength municipal wastewater with high sulphate content (COD: 600 mg L−1; SO4: 175 mg L−1), a 10-fold increase of the effluent sulphide concentrations was recorded (from 3 to 34 mg L−1), compared to low strength sewage processing (from 1.5 to 7.0 mg L−1). As such, major odour nuisances (release of H2S) may originate from the anaerobic effluent itself, as well as from spontaneous biogas losses.

Continuous Aeration Control to Reduce N2O Emissions in a Full-Scale Sidestream Deammonification Reactor

Continuous Aeration Control to Reduce N₂O Emissions in a Full-Scale Sidestream Deammonification Reactor

Full-scale biodrying process of municipal solid waste

The paper presents the results obtained in the full-scale waste biodrying reactor. The studied facility includes in the biological stage a rectangular-shaped, galvanized steel reactor equipped with a module for active aeration connected with a stove and a bio-filter for removing odours. The undersize fraction (O days in the 150 m3 capasity reactor. Initial moisture content of the untreated waste was 54.65%. Moisture content was declined gradually during biodrying process. Temperature changes during 14th days of biodrying process were monitored with the maximum temperature 70°C. To assess the degree of stabilization of the biodried waste, the determination of the O2 uptake was measured. The oxygen demand of untreated waste was 53.16 mg O2 /g d.m. and after 14th days for biodried waste oxygen consumption was 19.78 mg O2 /g d.m. The results obtained in studies by respirometric dynamic method of oxygen uptake (expressed as O2 /96h parameter) had been compared to the results performed using the static method, where AT4 is the applied indicator.

A Single-Granule-Level Approach Reveals Ecological Heterogeneity in an Upflow Anaerobic Sludge Blanket Reactor.

Upflow anaerobic sludge blanket (UASB) reactor has served as an effective process to treat industrial wastewater such as purified terephthalic acid (PTA) wastewater. For optimal UASB performance, balanced ecological interactions between syntrophs, methanogens, and fermenters are critical. However, much of the interactions remain unclear because UASB have been studied at a “macro”-level perspective of the reactor ecosystem. In reality, such reactors are composed of a suite of granules, each forming individual micro-ecosystems treating wastewater. Thus, typical approaches may be oversimplifying the complexity of the microbial ecology and granular development. To identify critical microbial interactions at both macro- and micro- level ecosystem ecology, we perform community and network analyses on 300 PTA–degrading granules from a lab-scale UASB reactor and two full-scale reactors. Based on MiSeq-based 16S rRNA gene sequencing of individual granules, different granule-types co-exist in both full-scale reactors regardless of granule size and reactor sampling depth, suggesting that distinct microbial interactions occur in different granules throughout the reactor. In addition, we identify novel networks of syntrophic metabolic interactions in different granules, perhaps caused by distinct thermodynamic conditions. Moreover, unseen methanogenic relationships (e.g. “Candidatus Aminicenantes” and Methanosaeta) are observed in UASB reactors. In total, we discover unexpected microbial interactions in granular micro-ecosystems supporting UASB ecology and treatment through a unique single-granule level approach.

Electrochemical oxidation of ofloxacin using a TiO2-based SnO2-Sb/polytetrafluoroethylene resin-PbO2 electrode: Reaction kinetics and mass transfer impact

Electrochemical oxidation has been proposed for the destruction of organic contaminants; however, this process is hampered by low oxidation efficiency and high energy cost. Accordingly, we developed a TiO2-based SnO2-Sb/polytetrafluroethylene resin (FR)-PbO2 electrode that was based on TiO2 nanotubes. We tested the performance of the electrode on an antibiotic, ofloxacin, and identified the major pathway of ofloxacin oxidation. We found growing TiO2 nanotubes on Ti material increased current efficiency, and the electrical efficiency per order (EE/O, kWh/m3) for oxidation was decreased by 16.2%. Our electrode requires a large overpotential before electrons flow, which minimizes oxygen evolution, reduces hydrogen peroxide and ozone generation, and favors hydroxyl radicals (HO) production. We found the electron efficiency (EE) during oxidation was as high as 88.45%. In other words, 88.45% of the electrons that flow out of the electrode cause oxidation. The effects of current density, initial concentration, pH value and electrolyte concentration were investigated. A differential column batch reactor (DCBR) was used to simulate the performance of continuous plug flow reactor and we found that the destruction of ofloxacin followed pseudo-first order model. We also evaluated the impact of mass transfer on electrochemical performance. The effects of fluid velocity and electrode spacing on oxidation rate were evaluated by determining the mass transfer coefficient and the effectiveness factor Ω (between 0 and 1). Our experiments and calculations indicated that the mass transfer reduced oxidation rate by more than 55% (Ω<0.45) for an electrode spacing of 1cm at a fluid velocity of 0.033m/s. Unlike studies carried out using completely mixed batch reactor, the DCBR can simulate the flow conditions in pilot or full scale reactors; consequently, observed pseudo-first order rate constants in the DCBR can be used for preliminary design.

Bacterial community assembly in activated sludge: mapping beta diversity across environmental variables.

Effect of ecological variables on community assembly of heterotrophic bacteria at eight full‐scale and two pilot‐scale activated sludge wastewater treatment plants (AS‐WWTPs) were explored by pyrosequencing of 16S rRNA gene amplicons. In total, 39 samples covering a range of abiotic factors spread over space and time were analyzed. A core bacterial community of 24 families detected in at least six of the eight AS‐WWTPs was defined. In addition to the core families, plant‐specific families (observed at <50% AS‐WWTPs) were found to be also important in the community structure. Observed beta diversity was partitioned with respect to ecological variables. Specifically, the following variables were considered: influent wastewater characteristics, season (winter vs. summer), process operations (conventional, oxidation ditch, and sequence batch reactor), reactor sizes (pilot‐scale vs. full‐scale reactors), chemical stresses defined by ozonation of return activated sludge, interannual variation, and geographical locations. Among the assessed variables, influent wastewater characteristics and geographical locations contributed more in explaining the differences between AS‐WWTP bacterial communities with a maximum of approximately 26% of the observed variations. Partitioning of beta diversity is necessary to interpret the inherent variability in microbial community assembly and identify the driving forces at play in engineered microbial ecosystem.

Nitrous oxide emissions from one-step partial nitritation/anammox processes.

Measurements of nitrous oxide were made at pilot- and full-scale plants to evaluate greenhouse gas emissions from one-step partial nitritation/anammox processes applied in moving bed biofilm reactors treating reject water. It was found that 0.51-1.29% and 0.35-1.33% of the total nitrogen loads in the pilot- and full-scale reactor, respectively, were emitted as nitrous oxide. Between 80 and 90% of nitrous oxide emissions were in gaseous form and the rest amount was found in the reactor effluent; over 90% of nitrous oxide emissions occurred in the aerated period and less than 8% in the non-aerated period in the full-scale study. Nitrous oxide productions/consumptions were closely related to aeration and the nitrogen loads applied in the system.