Enhancement of Microbial Oil and Biodiesel Production from Activated Sludge by Cultivation on Short Chain Fatty Acids

The enhancement of microbial oil in municipal sewage activated sludge by cultivation on short chain fatty acids (SCFAs) as carbon sources was investigated. Previous works showed that activated sludge microbial consortia can accumulate lipidic oil when cultivated on high carbon-to-nitrogen ratio using sugars as carbon sources. The commercialization of this sugar-based technology, however, is challenged by the high cost of the sugar substrates. This study proposes to use as alternative carbon sources the SCFAs that are inherent stream constituents in wastewater treatment. The model SCFAs used in this study are acetic acid, propionic acid, and butyric acid. Unlike sugars, these SCFAs are toxic to many microorganisms even at relatively moderate concentrations. Therefore, this study implemented and examined several techniques that reduce toxicity and enhance utilization of SCFAs for lipid accumulation. First, the extent of inhibition and utilization of the short chain fatty acids as functions of mass fractions and loading of the SCFAs were evaluated using respirometric method and flask cultivation experiments. Then, the biomass growth and oil accumulation of activated sludge at various loading of SCFAs, loading of nitrogen source, and pH levels were evaluated by fed-batch cultivation in bioreactors. Afterwards, the stabilization of lipid-derived fatty acid methyl esters (FAMEs) profiles and the selection of microbial community of activated sludge were tested. Finally, the techno-economic potential of an integrated anaerobic digestion and oil accumulation of municipal wastewater sewage sludges was evaluated via order-of-magnitude simulations. Results show that the effects of pH, SCFAs mass fractions, and SCFAs loading were significant factors in the inhibition of activated sludge. The SCFAs were utilized in the following order: acetic acid > butyric acid > propionic acid. Activated sludge could accumulate up to 20% (w/w) lipids under acetic acid fed-batch cultivation. Fluorescence microscopy images of neutral lipids show that the microbial cells accumulating lipids were in the size range of yeasts. This observation is complemented by the finding that budding yeasts proliferated and dominated during lipid accumulation on acetic acid. Further improvements are needed on activated sludge lipid accumulation from SCFAs to achieve economical integration with anaerobic digestion

Detecting Plant-Wide Oscillation Propagation Effects of Disturbances and Faults in a Chemical Process Plant Using Network Topology of Variance Decompositions

This work demonstrates for the first time the application of network topology of variance decompositions in analyzing the connectedness of chemical plant process variable oscillations arising from disturbances and faults. Specifically, the time-based connectedness and frequency-based connectedness of variables can be used to compute the net pairwise dynamic connectedness (NPDC), which originated as a volatility spillover index for financial markets studies in the field of econometrics. This work used the anomaly-detection benchmark Tennessee-Eastman chemical process (TEP) dataset, which consists of 41 measured variables and 11 manipulated variables subjected to various faulty operating conditions. The data analytics was performed using key functions from the R-package ‘ConnectednessApproach’ that implements connectedness computations based on time and frequency. The NPDC coefficient matrices were then transformed into network adjacency matrices for the rendering of the network topology of connectedness for TEP. The resulting network topologies allow a comprehensive analysis of oscillation effects across all plant-measured and manipulated variables. Analyzing the directed connectedness of the system dynamics at short-range, mid-range, and long-range frequencies showed how the oscillation effects of disturbances and faults propagate and dissipate in the short-term, mid-term, and long-term periods

An Assessment of Methanotrophs Producing Industrial-Grade Lipids for Biofuels and Other Commercial Chemicals

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

Adsorption kinetic modeling using pseudo-first order and pseudo-second order rate laws: A review

Adsorption for water and wastewater treatment has been the subject of many research in the scientific community, focusing mainly on either equilibrium or kinetic studies. Adsorption kinetics are commonly modeled using pseudo-first and pseudo-second order rate laws. Analyses of published works in the past two decades indicated that the pseudo-second order is considered to be the superior model as it can represent many adsorption systems. However, critical assessment of modeling techniques and practices suggests that its superiority could be a consequence of currently acceptable modeling norms which tend to favor the pseudo-second order model. The partiality was due to several modeling pitfalls that are often neglected. In addition, commonly used model validation tools are often used haphazardly and redundantly. As such, they cannot sufficiently provide any kind of certainty on the validity of a model. To eliminate modeling biasness, a new validation method was proposed and was then employed to re-examine previously published adsorption kinetic data

Using Self-Organizing Map Algorithm to Reveal Stabilities of Parameter Sensitivity Rankings in Microbial Kinetic Models: A Case for Microalgae

Microalgae are multi-purpose microbial agents due to their capability to efficiently sequester carbon dioxide and produce valuable biomass such as protein and single-cell oils. Formulation and tuning of microalgae kinetics models can significantly contribute to the successful design and operation of microalgae reactors. This work aimed to demonstrate the capability of self-organizing map (SOM) algorithm to elucidate the patterns of parameter rankings in microalgae models subject to stochastic variations of input forcing functions–bioprocess influent component concentration levels. These stochastic variations were implemented on a modeled chemostat with a deterministic microalgae kinetic model consists of ten time-dependent variables and eighteen model parameters. The methodology consists of two major stages: (1) global sensitivity analysis (GSA) on the importance of model parameters with stochastic sampling of bioreactor influent component concentrations, and (2) training of self-organizing maps on the datasets of model parameter rankings derived from the GSA indices. Results reveal that functional principal components analysis can project at least 99% of the time-dependent dynamic patterns of the model variables on B-splines basis functions. The component planes for hexagonal lattice SOMs reveal that the sensitivity rankings some parameters in the algae model tested can be stable over a wide range of variations in the levels of influent component concentrations. Therefore, SOM can be used to reveal the trends in multi-dimensional data arrays arising from the implementation of GSA of kinetic models under stochastic perturbation of input forcing functions

Evaluation of the Methane Production Potential of Catfish Processing Wastewater Using Various Anaerobic Digestion Strategies

The U.S. catfish industry is a major industry that has been declining over the years due to imports competition and growing operational costs. Catfish processing wastewater management and high energy requirement put a large financial burden on catfish processing facilities. Recovered protein-based solids have provided some value-added co-products, however, more co-products are needed to offset processing costs. Anaerobic digestion is a proven waste treatment method that produces methane, which is an energetic co-product that can be used within the processing facilities. This study was conducted to evaluate the potential of anaerobic digestion as an alternative to the currently used aerobic biotreatment of catfish processing wastewater. Initial assessments indicated the recalcitrance of the full-strength wastewater to anaerobic digestion, yielding only ~4 m3 per ton (U.S.) of input chemical oxygen demand (CODinput). Thus, several strategies were evaluated to improve the methane yield from the wastewater. These strategies include nutrient (nitrogen and sulfur) amendment, along with ozone, HCl, and NaOH pretreatment. The results showed that nutrient amendment was the most suitable strategy for improving the digestibility of the catfish processing wastewater. A methane yield of 121–236 m3/ton (U.S.) CODinput was obtained, with a purity of 67–80 vol.%. These results are similar to yields and purities of biogas from other feedstock, such as food waste, wastewater solids, and fish canning wastewater. This indicates that anaerobic digestion could be a viable alternative for simultaneous treatment and energetic co-product generation from catfish processing wastewater

Formulation of a Simulated Wastewater Influent Composition for Use in the Research of Technologies for Managing Wastewaters Generated during Manned Long-Term Space Exploration and Other Similar Situations—Literature-Based Composition Development

The prospect of humans inhabiting planetary bodies is gaining interest among research and development communities, with the moon being considered as a transitory base camp and Mars the next planet humans will inhabit. NASA’s Mission to Mars program is set to have humans inhabiting Mars within on-planet space camps by the Year 2030, which has tremendously increased research and development for space exploration—including research oriented toward human life support in long-term planetary lodging camps. The sustenance of human life on Mars will not be trivial due to the unavailability of an appropriate atmosphere and usable water. This situation requires a self-sustaining human life support system that can provide the basic needs such are breathable air, potable water, food, and energy. The feasibility of sending a payload with resources adequate to support long-term human inhabitation is not reasonable, which means every resource within a Mars space camp is valuable, including human-produced wastes. A biorefinery system that treats wastewater and can also produce valuable products such as oxygen, food, and energy offers a form of circular utilization of valuable resources. To conduct research for such systems requires a wastewater influent that is representative of the wastewater to be generated by the space crew within this isolated, confined environment, which is different from what is generated on Earth due to limited variability in diet, human activity, and lifestyle in this confined area. Collection of actual wastewater influent from an isolated environment supporting humans is challenging. Additionally, to ensure a safe working environment in the laboratory and avoid the imposed threat of handling actual human feces, the proposed synthetic, non-human feces containing wastewater influent formulation offers an easy-to-produce and safer-to-handle option. This paper reviews several synthetic wastewater compositions that have been formulated for space exploration purposes. None of the formulations were found to be realistic nor adequate for a space-camp-type scenario. Thus, the formulation of a synthetic wastewater for simulating a wastewater influent from a human space-based camp is proposed in this paper. In addition, the physical, chemical, and biodegradation characteristics of the final formulation designed are presented to illustrate the value of the proposed influent formulation

Analysis of Methanotroph Populations from Various Sources for Production of High-Value Products

Methanotrophs are bacteria that can consume methane as their sole carbon and energy source to produce a wide variety of high-value products such as lipids, biopolymers, ectoine, and single cell proteins (SCPs). Collected samples from various sources were subjected to DNA extraction followed by 16S rRNA analysis to determine the identity and relative abundance of their microbial population. Several taxa of methanotrophs were detected in the samples including Type I (Methylobacter), Type X (Methylocaldum), Type II (Methylocystis, Methylosinus, and Beijerinckia), and Type III (Verrucomicrobium). This paper expounds the effects of environmental/cultivation conditions on the growth and population of different types of methanotrophs. The results could be used to systematically identify source(s) of natural consortia that can be enriched and developed to produce specific target product(s) under a given cultivation conditions/limitations

Analysis of Methanotroph Populations from Various Sources for Production of High-Value Products

Methanotrophs are bacteria that can consume methane as their sole carbon and energy source to produce a wide variety of high-value products such as lipids, biopolymers, ectoine, and single cell proteins (SCPs). Collected samples from various sources were subjected to DNA extraction followed by 16S rRNA analysis to determine the identity and relative abundance of their microbial population. Several taxa of methanotrophs were detected in the samples including Type I (Methylobacter), Type X (Methylocaldum), Type II (Methylocystis, Methylosinus, and Beijerinckia), and Type III (Verrucomicrobium). This paper expounds the effects of environmental/cultivation conditions on the growth and population of different types of methanotrophs. The results could be used to systematically identify source(s) of natural consortia that can be enriched and developed to produce specific target product(s) under a given cultivation conditions/limitations