Reliability metrics and their management implications for open pond algae cultivation

Exploring the dynamics of algae-associated microbiome during the scale-up process of Tetraselmis sp. microalgae: A metagenomics approach

Microalgae have become a key source of valuable compounds, promoting commercial scale applications. However, biological contamination is one of the most critical problems associated with large scale algal production, especially in open systems such as raceway ponds. The current research is the first to assess the effectiveness of open raceway ponds in maintaining a pure culture of Tetraselmis sp., starting from 20 L culture up to 10,000 L culture. Microbial profiling of each successive stage revealed lower abundance of eukaryotic organisms, whereas bacterial abundance increased notably resulting in a significant decrease in Tetraselmis sp. abundance. Furthermore, several bacteria with algae growth-promoting properties were found throughout the various culture stages including Balneola, Roseovarius, and Marinobacter. However, some algae-suppressive bacteria were evidenced at later stages such as Ulvibacter, Aestuariicoccus, and Defluviimonas. Overall, due to the increasing bacterial concentration, considerations limiting bacterial contamination need to be taken.

Competitive algae biodiesel depends on advances in mass algae cultivation

The aim of this review was to study why, despite large investments in research and development, algae biodiesel is still not price competitive with fossil fuels. Microalgal production was confirmed to be a critical cost item (84 up to 93 %) for biodiesel regardless of the production technology. Techno-economic assessment revealed the main cost drivers during mass cultivation. It is argued that a breakthrough in the cultivation efficiency of microalgae is identified as a necessary condition for achieving price-competitive microalgal biodiesel. The key bottlenecks were identified as follows: (1) light and O₂ concentration management; (2) overnight respiratory loss of oil. It is concluded that most of the research on microalgae biodiesel yields economically over-optimistic presumptions because it has been based on laboratory scale experiments with a low level of interdisciplinary overlap.

Impacts of Fungal Disease on Algal Biofuel Systems: Using Life Cycle Assessment to Compare Control Strategies

While climate change has incentivized attention on sustainable fuel sources, algae has positioned itself as a both promising and problematic biofuel feedstock. Diseases such as fungal pathogens cause costly algal feedstock crashes, but the life cycle assessments (LCAs) used to analyze the viability of algal feedstocks for biofuel have yet to consider the impact of disease on life cycle metrics. Here, we incorporate a disease model into a well-documented LCA for algal biorefineries to compare two sustainability metrics, energy return on investment (EROI) and global warming potential (GWP). We begin by showing that failure to consider disease leads to overly optimistic LCA metric outputs. Then, we compare two leading control strategies of disease─chemical and biological. Our analyses show that biological engineering of a multispecies consortium of algae has a greater positive impact on LCA metrics than chemical control of the fungal pathogen using a fungicide. We expand how and when bi-cultures might advantageously exhibit the "dilution effect" whereby differentially susceptible species exhibit compensatory dynamics that stabilize feedstock production. Our results emphasize the impact of disease and suggest that multispecies consortia of algae can be biologically engineered to reduce greenhouse gas emissions and improve the economic viability of biofuel.

CO2 bio-mitigation using genetically modified algae and biofuel production towards a carbon net-zero society

CO₂ sequestration carried by biological methodologies shows enhanced potential and has the advantage that biomass produced from the captured CO₂ can be used for different applications. Bio-mitigation of carbons through a micro-algal system addresses a promising and feasible option. This review mostly focused on the role of algae, particular mechanisms, bioreactors in algae cultivation, and genetically modified algae in CO₂ fixation and energy generation systems. A combination of CO₂ bio-mitigation and biofuel production might deliver an extremely promising alternative to current CO₂ mitigation systems. Bio mitigation in which the excess carbon is captured and bio fixation which the carbon is captured by algae or autotrophs and used for producing biofuel. This review revealed that steps for biofuel production from algae include factors affecting, harvesting techniques, oil extraction and transesterification. This review helps environmentalists and researchers to assess the effect of algae-based biorefinery on the green environment.

Selection of Production Reliability Indicators for Project Simulation Model

Due to technological enhancements, traditional, qualitative decision-making methods are usually replaced by data-driven decision-making even in smaller companies. Process simulation is one of these solutions, which can help companies avoid costly failures as well as evaluate positive or negative effects. The reason for this paper is twofold: first, authors conducted a Quality Function Deployment analysis to find the most vital reliability indicators in the field of production scheduling. The importance was acquired from the meta-analysis of papers published in major journals. The authors found 3 indicators to be the most important: mean time between failure (MTBF), mean repair time and mean downtime. The second part of the research is for the implementation of these indicators to the stochastic environment: possible means of application are proposed, confirming the finding with a case study in which 100 products must be produced. The database created from the simulation is analyzed in terms of major production KPIs, such as production quantity, total process time and efficiency of the production. The results of the study show that calculating with reliability issues in production during the negotiation of a production deadline supports business excellence.

Industrial CO2 Capture by Algae: A Review and Recent Advances

The problem of global warming and the emission of greenhouse gases is already directly affecting the world’s energy. In the future, the impact of CO2 emissions on the world economy will constantly grow. In this paper, we review the available literature sources on the benefits of using algae cultivation for CO2 capture to decrease CO2 emission. CO2 emission accounts for about 77% of all greenhouse gases, and the calculation of greenhouse gas emissions is 56% of all CO2 imports. As a result of the study of various types of algae, it was concluded that Chlorella sp. is the best at capturing CO2. Various methods of cultivating microalgae were also considered and it was found that vertical tubular bioreactors are emerging. Moreover, for energy purposes, thermochemical methods for processing algae that absorb CO2 from flue gases were considered. Of all five types of thermochemical processes for producing synthesis gas, the most preferred method is the method of supercritical gasification of algae. In addition, attention is paid to the drying and flocculation of biofuels. Several different experiments were also reviewed on the use of flue gases through the cultivation of algae biomass. Based on this literature review, it can be concluded that microalgae are a third generation biofuel. With the absorption of greenhouse gases, the growth of microalgae cultures is accelerated. When a large mass of microalgae appears, it can be used for energy purposes. In the results, we present a plan for further studies of microalgae cultivation, a thermodynamic analysis of gasification and pyrolysis, and a comparison of the results with other biofuels and other algae cultures.

Barriers to microalgal mass cultivation

Economically successful microalgal mass cultivation is dependent on overcoming several barriers that contribute to the cost of production. The severity of these barriers is dependent on the market value of the final product. These barriers prevent the commercially viable production of algal biofuels but are also faced by any producers of any algal product. General barriers include the cost of water and limits on recycling, costs and recycling of nutrients, CO₂ utilization, energy costs associated with harvesting and biomass loss due to biocontamination and pond crashes. In this paper, recent advances in overcoming these barriers are discussed.

Abiotic and Biotic Damage of Microalgae Generate Different Volatile Organic Compounds (VOCs) for Early Diagnosis of Algal Cultures for Biofuel Production

Open microalgal ponds used in industrial biomass production are susceptible to a number of biotic and abiotic environmental stressors (e.g., grazers, pathogens, pH, temperature, etc.) resulting in pond crashes with high economic costs. Identification of signature chemicals to aid in rapid, non-invasive, and accurate identification of the stressors would facilitate targeted and effective treatment to save the algal crop from a catastrophic crash. Specifically, we were interested in identifying volatile organic compounds (VOCs) that can be used to as an early diagnostic for algal crop damage. Cultures of Microchloropsis gaditana were subjected to two forms of algal crop damage: (1) active grazing by the marine rotifer, Brachionus plicatilis, or (2) repeated freeze–thaw cycles. VOCs emitted above the headspace of these algal cultures were collected using fieldable solid phase microextraction (SPME) fibers. An untargeted analysis and identification of VOCs was conducted using gas chromatography-mass spectrometry (GC-MS). Diagnostic VOCs unique to each algal crop damage mechanism were identified. Active rotifer grazing of M. gaditana was characterized by the appearance of carotenoid degradation products, including β-cyclocitral and various alkenes. Freeze–thaw algae produced a different set of VOCs, including palmitoleic acid. Both rotifer grazing and freeze–thawed algae produced β-ionone as a VOC, possibly suggesting a common stress-induced cellular mechanism. Importantly, these identified VOCs were all absent from healthy algal cultures of M. gaditana. Early detection of biotic or abiotic environmental stressors will facilitate early diagnosis and application of targeted treatments to prevent algal pond crashes. Thus, our work further supports the use of VOCs for monitoring the health of algal ponds to ultimately enhance algal crop yields for production of biofuel.

Continuous measurements of volatile gases as detection of algae crop health

Algae cultivation in open raceway ponds is considered the most economical method for photosynthetically producing biomass for biofuels, chemical feedstocks, and other high-value products. One of the primary challenges for open ponds is diminished biomass yields due to attack by grazers, competitors, and infectious organisms. Higher-frequency observations are needed for detection of grazer infections, which can rapidly reduce biomass levels. In this study, real-time measurements were performed using chemical ionization mass spectrometry (CIMS) to monitor the impact of grazer infections on cyanobacterial cultures. Numerous volatile gases were produced during healthy growth periods from freshwater Synechococcus elongatus Pasteur Culture Collection (PCC) 7942, with 6-methyl-5-hepten-2-one serving as a unique metabolic indicator of exponential growth. Following the introduction of a Tetrahymena ciliate grazer, the concentrations of multiple volatile species were observed to change after a latent period as short as 18 h. Nitrogenous gases, including ammonia and pyrroline, were found to be reliable indicators of grazing. Detection of grazing by CIMS showed indicators of infections much sooner than traditional methods, microscopy, and continuous fluorescence, which did not detect changes until 37 to 76 h after CIMS detection. CIMS analysis of gases produced by PCC 7942 further shows a complex temporal array of biomass-dependent volatile gas production, which demonstrates the potential for using volatile gas analysis as a diagnostic for grazer infections. Overall, these results show promise for the use of continuous volatile metabolite monitoring for the detection of grazing in algal monocultures, potentially reducing current grazing-induced biomass losses, which could save hundreds of millions of dollars.