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We present a fast and accurate data-driven surrogate model for divertor plasma detachment prediction leveraging the latent feature space concept in machine learning research. Our approach involves constructing and training two neural networks. An autoencoder that finds a proper latent space representation (LSR) of plasma state by compressing the multi-modal diagnostic measurements, and a forward model using multi-layer perception (MLP) that projects a set of plasma control parameters to its corresponding LSR. By combining the forward model and the decoder network from autoencoder, this new data-driven surrogate model is able to predict a consistent set of diagnostic measurements based on a few plasma control parameters. In order to ensure that the crucial detachment physics is correctly captured, highly efficient 1D UEDGE model is used to generate training and validation data in this study. Benchmark between the data-driven surrogate model and UEDGE simulations shows that our surrogate model is capable to provide accurate detachment prediction (usually within a few percent relative error margin) but with at least four orders of magnitude speed-up, indicating that performance-wise, it has the potential to facilitate integrated tokamak design and plasma control. Comparing to the widely used two-point model and/or two-point model formatting, the new data-driven model features additional detachment front prediction and can be easily extended to incorporate richer physics. This study demonstrates that the complicated divertor and scrape-off-layer plasma state has a low-dimensional representation in latent space. Understanding plasma dynamics in latent space and utilizing this knowledge could open a new path for plasma control in magnetic fusion energy research., Comment: 24 pages, 15 figures

Microalgae are promising feedstocks for food, feed, fuel, fertilizers, fine chemicals and other value-added products, and are considered of great potential in wastewater treatment. Convenient acquisition of the cultivated microalgal biomass or easy separation of microalgae from the treated effluents, however, are the prerequisites of these applications. Biomass harvesting and dewatering in traditional suspended cultivation systems are costly and energy intensive, since volumes of liquid medium needs to be separated from the obtained diluted microalgal biomass. Attached systems can effectively overcome such limitations by introducing substratum into the liquid medium for microalgae attachment, and the attached biomass with magnitudes higher solid content can be collected via simple and straightforward harvesting methods such as mechanical scraping. As an emerging field with less than ten years of research history, systematic information on microalgae attachment and attached systems for biomass production and wastewater treatment has not been thoroughly reviewed. This review, therefore, analyzed the two-step mechanisms of microalgae attachment, discussed the influencing factors of attached microalgal growth including properties of substratum, properties of microalgal cells, turbulence of liquid medium, frequency of biomass harvesting, etc., and their possible impacts on microalgal biofilm formation and biomass production in attached systems. Classification of attached microalgal systems based on different criteria such as substratum orientation, relative position of microalgal cells and the culturing medium, system scales and culturing medium, was summarized. Performances of attached microalgal systems for biomass production and wastewater treatment were evaluated, with commonly used parameters identified and compared as well. Recommendations for future theoretical research and practical applications were also addressed in the manuscript. This review could offer much useful information on microalgal attachment and attached systems for biomass production and wastewater treatment, and may serve as guidance for future studies in related fields.

Microalgae cultivation is a promising candidate for autotrophic sequestrating CO 2 transformation into renewable bio-products. However, potential of microalgae has not been fully explored due to the bottlenecks of biomass harvesting during large-scale microalgae cultivation. A novel capillary-driven photobioreactor (CPBR) is proposed in this study for attached microalgae cultivation obtaining high biomass productivity and overcoming the biomass harvesting limitation in traditional suspended cultures. Performances on microalgal growth, cellular composition, nutrients uptake from water, and corresponding light utilization efficiencies were investigated and emphasized. During 12 days of system operation, attached microalgal biomass on the carriers were in the range of 83.6 g/m 2 -footprint area of 121.5 g/m 2 -footprint area, corresponding to light utilization efficiency of 3.3% to 4.8%. With proper carriers packing density of 16% to 32%, obtained biomass productivities of CPBR were approximately 10 g/m 2 /d (footprint area). Biomass composition analysis revealed that lipid and carbohydrates contents in attached microalgal biomass were higher than in suspended microalgal biomass with same cultivating conditions, proving the potential of microalgae cultivated in CPBR as feedstock of biofuels.

Microalgae-based bioenergy has been long considered as a promising substitute to replace the fossil fuels at large-scale. After the decades of research, several bottlenecks remain to be overcome to make the large-scale production of microalgal bioenergy commercially viable. In this review, the bottlenecks that restrict the commercial production of microalgal bioenergy are summarized as “high cost” and “low efficiency” and then identified in detailed categories. Several solutions which aim to solve the bottlenecks are presented and discussed correspondingly. The solutions presented in this review including cultivating in wastewater, recycling water and nutrients, utilizing the whole biomass, selecting indigenous strains, cultivating mixed-species, supplementing low-cost organic substrates, mixing vertically in reactor, optimizing metabolic pathway and attaching the cells on suspended-solids. Furthermore, a novel system integrated with the solutions, which is combined with the wastewater treatment system and characterized as the mixed-species cultivation of wild-selected mixotrophic microalgal strains in suspended-solid phase bioreactor based on low-cost substrate, is proposed to promote the scale-up of the microalgal cultivation for bioenergy production.

Time-dependent nonlinear simulation using the BOUT++ 3-field model is performed for a study of edge localized mode (ELM) dynamics in KSTAR H-mode plasmas. The simulated results of the ELM evolution are directly compared with the 2D ELM structures, measured by electron cyclotron emission imaging systems, from the initial growth to crash phase. The simulation results are qualitatively in good agreement with the observations. Specifically, it is notable in simulation and experiment that higher-n modes in a quasi-steady state phase evolve into lower-n modes close to the ELM-crash in time. It suggests that lower-n modes may be responsible for the onset of the crash. A postanalysis supports that nonlinear mode coupling between toroidal harmonics may drive the lower-n mode.

Reuse of secondary municipal effluent from wastewater treatment plants in water bodies could effectively alleviate freshwater resource shortage. However, excessive nutrients must be efficiently removed to prevent eutrophication. Compared with other means of advanced wastewater treatment, microalgae-based processes display overwhelming advantages including efficient and simultaneous N and P removal, no requirement of additional chemicals, O2 generation, CO2 mitigation, and potential value-added products from harvested biomass. One particular challenge of microalgae-based advanced municipal wastewater treatment compared to treatment of other types of wastewater is that concentrations of nutrients and N:P ratios in secondary municipal effluent are much lower and imbalanced. Therefore, there should be comprehensive considerations on nutrient removal from this specific type of effluent. Removal of nutrients and organic substances, and other environmental benefits of microalgae-based advanced municipal wastewater treatment systems were summarized. Among the existing studies on microalgal advanced nutrient removal, much information on major parameters is absent, rendering performances between studies not really comparable. Mechanisms of microalgae-based nitrogen and phosphorus removal were respectively analyzed to better understand advanced nutrient removal from municipal secondary effluent. Factors influencing microalgae-based nutrient removal were divided into intrinsic, environmental, and operational categories; several factors were identified in each category, and their influences on microalgal nutrient removal were discussed. A multiplicative kinetic model was integrated to estimate microalgal growth-related nutrient removal based majorly on environmental and intrinsic factors. Limitations and prospects of future full-scale microalgae-based advanced municipal wastewater treatment were also suggested. The manuscript could offer much valuable information for future studies on microalgae-based advanced wastewater treatment and water reuse.

While reverse osmosis (RO) is a promising technology for wastewater reclamation, RO concentrate (ROC) treatment and disposal are important issues to consider. Conventional chemical and physical treatment methods for ROC present certain limitations, such as relatively low nitrogen and phosphorus removal efficiencies as well as the requirement of an extra process for hardness removal. This study proposes a novel biological approach for simultaneous removal of nitrogen, phosphorus, and calcium (Ca 2+ ) and magnesium (Mg 2+ ) ions from the ROC of municipal wastewater treatment plants by microalgal cultivation and algal biomass production. Two microalgae strains, Chlorella sp. ZTY4 and Scenedesmus sp. LX1, were used for batch cultivation of 14–16 days. Both strains grew well in ROC with average biomass production of 318.7 mg/L and lipid contents up to 30.6%, and nitrogen and phosphorus could be effectively removed with efficiencies of up to 89.8% and 92.7%, respectively. Approximately 55.9%–83.7% Ca 2+ could be removed from the system using the cultured strains. Mg 2+ removal began when Ca 2+ precipitation ceased, and the removal efficiency of the ion could reach up to 56.0%. The most decisive factor influencing Ca 2+ and Mg 2+ removal was chemical precipitation with increases in pH caused by algal growth. The results of this study provide a new biological approach for removing nitrogen, phosphorous, and hardness from ROC. The results suggest that microalgal cultivation presents new opportunities for applying an algal process to ROC treatment. The proposed approach serves dual purposes of nutrient and hardness reduction and production of lipid rich micro-algal biomass.

A boundary plasma turbulence code BOUT is presented. The preliminary encouraging results have been obtained when comparing with probe measurements for a typical Ohmic discharge in CT-7 tokamak. The validation and benchmark of BOUT code and experimental diagnostic tools for fusion boundary plasma turbulence is proposed.