Partial nitritation/anammox (PN/A) has been one of the most innovative developments in biological wastewater treatment in recent years. With its discovery in the 1990s a completely new way of ...ammonium removal from wastewater became available. Over the past decade many technologies have been developed and studied for their applicability to the PN/A concept and several have made it into full-scale. With the perspective of reaching 100 full-scale installations in operation worldwide by 2014 this work presents a summary of PN/A technologies that have been successfully developed, implemented and optimized for high-strength ammonium wastewaters with low C:N ratios and elevated temperatures. The data revealed that more than 50% of all PN/A installations are sequencing batch reactors, 88% of all plants being operated as single-stage systems, and 75% for sidestream treatment of municipal wastewater. Additionally an in-depth survey of 14 full-scale installations was conducted to evaluate practical experiences and report on operational control and troubleshooting. Incoming solids, aeration control and nitrate built up were revealed as the main operational difficulties. The information provided gives a unique/new perspective throughout all the major technologies and discusses the remaining obstacles.
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•More than 100 full-scale partial nitritation/anammox installations worldwide by 2014.•In depth survey of 14 full-scale installations.•Discussion of practical experiences, process control and troubleshooting.
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•nZVI-BC could enhance anaerobic co-digestion stability of sludge and food waste.•nZVI-BC pretreatment increased the cumulative methane production by 43.37%.•nZVI-BC improved organic ...matter removal efficiency and VFAs consumption.•Adding nZVI-BC promoted hydrogenotrophic methanogenesis through enhancing DIET.
This work evaluates the effects of biochar supported nano zero-valent iron (nZVI-BC) on anaerobic co-digestion (co-AD) of sewage sludge and food waste. Kinetic model analysis suggested that nZVI-BC addition significantly increased the methane production potential (R0) and daily methane production rate (Gm) by 42.87% and 49.87%, while the raw biochar only increased R0 and Gm by 5.11% and 6.73%, respectively. Supplementation of higher concentrations of nZVI-BC was not preferable as inhibition of methane productivity was appeared. nZVI-BC addition remarkably improved organics degradation efficiency, as the reduction rate of TCOD, VSS and TSS were increased by 34.93%, 11.44% and 13.96%, respectively. The microbial analysis demonstrated that nZVI-BC facilitated the growth of hydrogentrophic methanogens, while acetotrophic methanogens which can only use acetate as electron donor were restrained. The study demonstrated nZVI-BC can effectively strengthen methanogenesis mainly through the enhancement of DIET between bacteria and methanogens, and the enrichment of hydrogenotrophic methanogens.
•First combined chemical, microbial and thermodynamic study on AD process stability.•The effects of organic overload on the thermodynamics of VFAs were investigated.•Selection of equations for ...thermodynamic calculation depends on microbial analysis.•Thermodynamic disadvantage was more pronounced under high organic loadings.•The potential of changes in Gibbs free energy to identify process status was discussed.
Anaerobic digestion (AD) operating under organic overload stress usually increases the potential for process instability, leading to significant economic and ecological consequences. Volatile fatty acids (VFAs) accumulation is regularly considered a major factor during AD and their degradation is subject to thermodynamic constraints. To date, no study has systematically investigated the mechanisms of VFA degradation on process stability from the perspective of thermodynamics. Hence, increased substrate-to-inoculum ratio was applied in this study to simulate organic overload stress using batch tests with Hybrid Pennisetum. As a result, VFAs accumulation increased, accompanied by decreased methane yield, slower methane production kinetics and even severe process instability. Metagenomic analysis demonstrated that the accumulated propionate and butyrate were degraded by methyl-malonyl-CoA and the β-oxidation pathway while syntrophic acetate oxidation was preferred during acetate degradation. The deviation of stability parameters to varying degrees from the recommended threshold values was observed. However, a subsequent thermodynamic analysis revealed that moderate organic overload stress merely retarded the syntrophic oxidation of propionate, butyrate, and acetate. As a result, the methanogenic activity decreased, and the lag phase of AD was extended, but no adverse thermodynamic effects actually occurred. Changes in the Gibbs free energy for syntrophic propionate and acetate oxidation have the potential to better identify process stability. This study provided novel insights into the underlying thermodynamic mechanisms of VFA degradation and may have important implications for improving the current diagnostic mode for AD process stability.
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•Development of an inline measurement system for efficiency in laser metal deposition.•Real-time measurements of deposited mass and layer height in different conditions.•Monitoring powder catchment ...efficiency with coaxial optical triangulation.•Model for efficiency as a function of standoff distance and process parameters.•Identification of the driving parameters for the self-stabilization mechanism.
In laser metal deposition (LMD) the height of the deposited track can vary within and between layers, causing significant deviations during the process evolution. Previous works have shown that in certain conditions a self-stabilizing mechanism occurs, maintaining a regular height growth and a constant standoff distance between the part and the deposition nozzle. Here we analyze the link between the powder catchment efficiency and the deposition height stability. To this purpose, a monitoring system was developed to study the deposition in different process conditions, using inline measurements of the specimen weight in combination with the layer height information obatined with coaxial optical triangulation. An analytical model was used to estimate the deposition efficiency in real-time from the height monitoring and the process parameters, which was verified by the direct mass measurements. The results show that the track height stabilization is associated to a reduction of the powder catchment efficiency, which is governed by the melt pool relative position with respect to the powder cone and the laser beam. For a given set of parameters, the standoff distance can be estimated to achieve the highest powder catchment efficiency and a regular height through the build direction.
It is of great interest to elucidate underlying mechanisms to maintain stability of anaerobic digestion, an important process in waste treatment. By operating triplicate anaerobic digesters ...continuously for two years, we found that microbial community composition shifted over time despite stable process performance. Using an association network analysis to evaluate microbial interactions, we detected a clear successional pattern, which exhibited increasing modularity but decreasing connectivity among microbial populations. Phylogenetic diversity was the most important factor associated with network topology, showing positive correlations with modularity but negative correlations with network complexity, suggesting induced niche differentiation over time. Positive, but not negative, correlation strength was significantly related (p < 0.05) to phylogeny. Furthermore, among populations exhibiting consistent positive correlations across networks, close phylogenetic linkages were evident (e.g. Clostridiales organisms). Clostridiales organisms were also identified as keystone populations in the networks (i.e., they had large effects on other species), suggestive of an important role in maintaining process stability. We conclude that microbial interaction dynamics of anaerobic digesters evolves over time during stable process performance.
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•Triplicate anaerobic digesters were operated continuously for two years.•A successional pattern of microbial interactions was observed despite process stability.•Clostridiales organisms were keystone populations in maintaining stable performance.•Phylogeny could shape positive but not negative interactions among microorganisms.
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•Machine learning algorithms has a great potential for modeling of composting.•Machine learning have shortcomings as well as superior features in composting.•The proper metric is a ...key for evaluating the algorithm as a realistic.•Complexity of composting can limit accurate prediction by experiment or theory.
Studies on developing strategies to predict the stability and performance of the composting process have increased in recent years. Machine learning (ML) has focused on process optimization, prediction of missing data, detection of non-conformities, and managing complex variables. This review investigates the perspectives and challenges of ML and its important algorithms such as Artificial Neural Networks (ANNs), Random Forest (RF), Adaptive-network-based fuzzy inference systems (ANFIS), Support Vector Machines (SVMs), and Deep Neural Networks (DNNs) used in the composting process. In addition, the individual shortcomings and inadequacies of the metrics, which were used as error or performance criteria in the studies, were emphasized. Except for a few studies, it was concluded that Artificial Intelligence (AI) algorithms such as Genetic algorithm (GA), Differential Evaluation Algorithm (DEA), and Particle Swarm Optimization (PSO) were not used in the optimization of the model parameters, but in the optimization of the parameters of the ML algorithms.
The mainstream partial nitritation/anammox (PN/A) process has been intensively studied but its stability remains a key challenge. It is shown here that biofilm thickness can exhibit a critical role ...in controlling the process stability of mainstream PN/A against dissolved oxygen (DO) variation. In a laboratory moving bed biofilm reactor (MBBR), PN/A performance was initially established in 200 days by controlling a low DO of 0.13 ± 0.07 mg O2/L in the bulk liquid, which deteriorated with an increase of DO (0.35 ± 0.13 mg O2/L) for over two months, and then rapidly recovered in a month with the initial low DO level re-applied. Biofilm thickness of PN/A carriers was measured during the experiment, which became significantly thinner (367 ± 146 μm) at mainstream conditions. The thin thickness primarily decreased the in-situ consumption rate of nitrite, rather than ammonium, when DO increased from 0.1 to 0.4 mg O2/L, due to that the thin thickness can only restrict anammox capacity. These results illustrated the role of biofilm thickness in regulating PN/A performance and microbial activities. Further investigation using an established model revealed the joint contribution of biofilm thickness and DO concentration to PN/A process, while particularly, the biofilm thickness can determine the optimal DO level for maximizing the nitrogen removal efficiency and system robustness against DO variation. These results highlight the need of considering biofilm thickness in PN/A process optimization and stability improvement in low-strength wastewater treatment.
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•N-removal efficiency >80% is achieved via PN/A in a mainstream MBBR.•The mainstream PN/A is stably realized at DO concentration of 0.13 ± 0.07 mgO2/L.•Biofilm thickness controls the maximal capacity of anammox rather than AOB or NOB.•A narrow DO range (0.15-0.20 mgO2/L) is required for high N-removal in thin biofilm.
The process stability of water-in-oil (W/O) Pickering emulsions (10 or 20 wt% water), co-stabilized by 0.14 wt% of polyphenol crystals (curcumin or quercetin) dispersed in a soybean oil phase, plus ...2.0 wt% whey protein isolate (WPI) or 0.1–2.0 wt% whey protein microgel (WPM) particles present in the inner aqueous phase, was assessed by measuring the apparent viscosity (η), water droplet size (via light scattering) and microstructural changes (via confocal laser scanning microscopy, CLSM). Stability was measured as a function of temperature (25–50 °C), using a shear rate cycle between 0.1 and 100 s−1 to highlight shear- and time-dependent hysteresis of η. All the emulsions showed shear thinning to some extent, but those without added WPI or WPM particles in the aqueous phase exhibited coalescence at increasing shear rate, that was more pronounced at higher temperatures. Emulsions containing WPI in the dispersed phase were stable, whilst those containing WPM particles showed a decrease in mean droplet size (D4,3) on shearing due to the disruption of the aggregates of droplets, polyphenol crystals and/or WPM particles in the continuous oil phase, but with no droplet coalescence. The low shear rate (0.1 s−1) viscosity showed an increase with increasing WPM particle concentration. This increase, plus CLSM of the emulsions, suggested that the WPM particles increased W/O emulsion stability not only via their adsorption to the inner surface of the water droplets, but possibly also due to them promoting the formation of mixed weak flocs of polyphenol crystals + WPM particles + small water droplets in the oil phase attached to the surface of the main population of water droplets.
•Water-in-oil Pickering emulsions stabilized by biocompatible ingredients.•Unique interfacial complex of polyphenol crystals and protein/microgels used.•Process stability of emulsions tested at varying temperatures and shear rates.•Shear stability a 50 °C improved via crystal + protein complexation.•Shear stability enhanced with proteinaceous microgels at the interface.
•AcoD operates at high OLRs under diverse co-substrates’ properties and composition.•Modelling requirements for AcoD are more complex than mono-digestion.•pH variation & inhibitory intermediate ...accumulation are essential for AcoD modelling.•ADM1-based model is sophisticated and an improved practicality is required for AcoD.•Conversion & distribution of S, P, and N are underdeveloped in current AcoD models.
Anaerobic co-digestion (AcoD) is a pragmatic approach to simultaneously manage organic wastes and produce renewable energy. This review demonstrates the need for improving AcoD modelling capacities to simulate the complex physicochemical and biochemical processes. Compared to mono-digestion, AcoD is more susceptible to process instability, as it operates at a higher organic loading and significant variation in substrate composition. Data corroborated here reveal that it is essential to model the transient variation in pH and inhibitory intermediates (e.g. ammonia and organic acids) for AcoD optimization. Mechanistic models (based on the ADM1 framework) have become the norm for AcoD modelling. However, key features in current AcoD models, especially relationships between system performance and co-substrates’ properties, organic loading, and inhibition mechanisms, remain underdeveloped. It is also necessary to predict biogas quantity and composition as well as biosolids quality by considering the conversion and distribution of sulfur, phosphorus, and nitrogen during AcoD.
Additive manufacturing (AM) is currently one of the most promising and advanced tools to make high-end components. For industrial acceptance of these components, there is a demand for the delivery of ...high quality parts, certified under recognized standards. Pre-requisites for such certified parts are the certification of the powder feed-stock and the use of qualified facilities. Such a certification and qualification project encompasses different challenges regarding both powder testing and print process stability. Today there are insufficient quantitative acceptance criteria for AM metal powders in the standards. The main challenge is determining which properties to test and how to define some key indicators that can guarantee consistent quality of the end product. To face this challenge several relevant powder properties were tested in order to link powder performance to the properties of the printed material. To guarantee process stability and repeatability, a good knowledge and control of the different process parameters and their influence on the material quality is needed. Hence, an extensive study on the homogeneity of properties over the 3D printer platform was performed. A qualification testing platform was designed to guarantee and periodically check the quality of the printed AM316L material. The proper procedures and parameter settings were determined and fixed. This methodology finally lead to the qualification of the ENGIE Laborelec Powder Lab and the ENGIE Fabricom AM printing facility and the certification of AM 316L material through a recognized external qualification body. This initiative paves the way to ensure industrial acceptance of the selective laser melting process for high quality applications.
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