The main objective of this study was to demonstrate a computational approach of global sensitivity analysis (GSA) integrated with functional principal component analysis (fPCA) for activated sludge models through aggregation of time‐dependent model response patterns into time‐independent coefficients of functional principal components (PCs). This proposed approach addresses the main issue of time‐varying character of GSA indices when calculated solely on the time‐dependent model outputs. The GSA‐fPCA methodology was implemented using the rigorous model Activated Sludge Model No. 3 (ASM3) as case study. The approach transforms the time‐dependent model outputs into functional PCs prior to calculation of GSA indices to remove the time‐varying character of the calculated GSA indices. This work focused on the evaluation of the following key computational factors that may significantly influence the performance of the GSA‐fPCA methodology: (a) model parameter sampling range, (b) model simulation period, (c) basis functions system, and (d) state of the system being modeled—batch or continuous activated sludge process. Results show that first few functional PCs capture up to 100% of the curve patterns in the time‐dependent model outputs. The sensitivity indices calculated from the PC scores via Morris’ GSA technique elucidated parameter sensitivity patterns inherent to the complex mathematical structure of ASM3. Practitioner points Functional principal components‐mediated GSA technique to remove time‐varying character of sensitivity indices derived from time‐dependent dynamical models. Technique amenable to improving efficiency of capturing response patterns into few functional principal components through various basis functions. Identifying priority parameters for ASM3 model calibration requires specification of target model outputs to which parameter sensitivities are calculated. GSA‐fPCA offers a comprehensive numerical approach to manipulating models depending on the intended applications: simple fast‐responding models to complex models.
Current operations within wastewater treatment plants (WWTPs), particularly the anaerobic digestion and activated sludge processes, can be tapped for production of microbial lipids. This can be accomplished by directing the anaerobic digestion to produce short chain carboxylic acids (SCCAs) that can then be used as substrates for lipid production using activated sludge microbial consortium in an add-on aerobic lipid production unit (similar to an activated sludge process). This study was conducted to assess the suitability of a Test Medium (previously proven suitable for aerobic lipid production in activated sludge) for the proposed integrated system. Results showed that, when used for anaerobic fermentation, the Test medium produced 0.48 g-SCCAs/g-substrate that includes acetic, butyric, and predominantly (∼89 wt%), lactic acid. Subsequently, the Test Medium resulted to a peak lipid yield of ∼0.17 g/g-SCCAs. Complete substrate consumptions were observed without pH control when the Test Medium was used for both bioprocesses. These results suggest the suitability of the Test Medium for the integrated system for microbial lipids production. This could significantly simplify the implementation of the proposed integrated system, which could provide the basis for future urban biorefineries through existing WWTPs.
With an ever-increasing release of harmful greenhouse gases into the environment, there is an ongoing search for a renewable source of energy to replace the current means of producing energy. One promising source is from methanotrophic bacteria, which uses methane as its primary carbon source to produce valuable byproducts including lipids. These lipids could be used in the production of biofuels and other important industrial chemicals including plastics and surfactants. The use of methanotrophs would lower the amount of methane in the atmosphere from two sides, in the growth and cultivation of methanotrophs and in the replacement of conventional fossil fuels. The development of such a system requires a good understanding of the bacteria responsible and the steps of growth/culturing and extraction. An integrated system that uses every product of methanotrophic growth could impact multiple markets and help make this technique economically feasible as well as provide the groundwork for more sustainable engineering practices. Integration of this technology into an industrial setting would help spread the scope of this technique, and by using innovative sources of methane (landfills and locations of high organic decomposition), the extent of environmental benefits can expand even further. This technology allows for a more environmentally friendly alternative for fuels in both its production and utilization.
Right-of-way (ROW) land areas are required for all publicly owned transportation roadways representing over 40 million acres within the US alone. These relatively unused land assets could support potential farming land for plants and algae that contain high levels of lipids that could be used in the energy industry as an alternative fuel source. This process would offer many benefits including more efficient use of public land, eliminating mowing maintenance, increasing the bioenergy use in the US, providing visually appealing viewscapes, and helping to naturally reduce localized carbon dioxide. This paper analyzed the feasibility and potential optimization strategies of using this concept in the South-Eastern United States by scaling and comparing many of the benefits and risks associated with the selected lipid sources (soybeans, flax, sunflowers, Tung trees, Chinese tallow tree, and microalgae). Based on this assessment, the most attractive option appears to be growing flax in the winter and sunflowers in the summer with Tung Trees grown year-round as an alternative option. This would maximize lipids output while preserving and enhancing right-of-way land areas.
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