Anaerobic digestion of food waste - Challenges and opportunities.

Yarrowia lipolytica has been developed as a production host for a large variety of biotechnological applications. Efficacy and safety studies have demonstrated the safe use of Yarrowia-derived products containing significant proportions of Yarrowia biomass (as for DuPont's eicosapentaenoic acid-rich oil) or with the yeast itself as the final product (as for British Petroleum's single-cell protein product). The natural occurrence of the species in food, particularly cheese, other dairy products and meat, is a further argument supporting its safety. The species causes rare opportunistic infections in severely immunocompromised or otherwise seriously ill people with other underlying diseases or conditions. The infections can be treated effectively by the use of regular antifungal drugs, and in some cases even disappeared spontaneously. Based on our assessment, we conclude that Y. lipolytica is a "safe-to-use" organism.

https://www.tandfonline.com/doi/pdf/10.3109/1040841X.2013.770386

Yarrowia lipolytica: safety assessment of an oleaginous yeast with a great industrial potential.

Anaerobic digestion is a technology that has been used by humans for centuries. Anaerobic digestion is considered to be a useful tool that can generate renewable energy and significant research interest has arisen recently. The underlying theory of anaerobic digestion has been established for decades; however, a great deal of current research is directed towards the optimization of anaerobic digestion under diverse digestion conditions. This review provides a summary of the processes underlying anaerobic digestion, commonly-utilized measurements of anaerobic sludge, operating parameters of anaerobic digesters, and methods of acceleration and optimization used to improve process efficiency. Recent developments in addition to older research are considered to provide a general but comprehensive summary of accumulated knowledge in the theory of anaerobic digestion, as well as considerations in the efficient operation of digesters. We have determined that the numerous factors pertinent to the design and operation of batch-based anaerobic digesters must each be considered to ensure the maximum efficiency and cost-effectiveness of a digester provided its respective operating conditions.

https://www.mdpi.com/1660-4601/15/10/2224/pdf/1

A review of the processes, parameters, and optimization of anaerobic digestion

Biological pretreatment (BP) is a promising approach for treating microalgae and lignocellulosic biomass (LCB) during biofuels production that uses mostly fungal and bacterial strains or their enzymes. Pretreatment with fungi requires long incubation time (weeks to months), whereas, bacterial and enzymatic pretreatments can be completed by only a few hours to days. Nevertheless, fungal pretreatment especially with white-rot fungi (WRF) is predominantly used in BP of biomass for its high efficiency and downstream yields. According to the recent reports, delignification of LCB by WRF may vary between 3% and 72% with a maximum 120% increase in the biofuel yield. Compared to the untreated microalgae biomass, the downstream yields of the respective biofuels were found to be increased by 22–159% after bacterial pretreatment, while enzymatic pretreatment improved as much as 485% of the final yield. Despite the results are promising, exploitation of BP on large scale is still bottlenecked by some technoeconomic hurdles, which need to be overcome through further fundamental and applied researches. This paper presents a comprehensive and in-depth review on BP for LCB and microalgae biomass by focusing on the relevant overviews and perspectives, technological approaches, mechanisms, influencing factors, and recent research progresses. Finally, challenges and future outlooks are discussed in the concluding sections.

Recent advances in biological pretreatment of microalgae and lignocellulosic biomass for biofuel production

The anaerobic digestion technology has been in existence for centuries and its underlying theory established for decades. It is considered a useful technology for the generation of renewable energy ...

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A Review of the Chemistry of Anaerobic Digestion : Methods of Accelerating and Optimizing Process Efficiency

Citric acid (CA) is mainly produced in a biotechnological process using Aspergillus niger. In this process, large amounts of wastes have to be removed. Since the use of Yarrowia lipolytica for CA production is an environmental compatible alternative method, the CA production was optimized in regard to growth temperature and pH as well as substrate and product inhibition. The highest value of the maximum specific growth rate at pH 6.5 was found to be μ max = 0.192 h -1 , whereas the largest amount of CA of 24.91 g/L as well as the highest selectivity of the bioprocess (89.9 % CA) and the maximum yield (0.22 g CA /g Glucose ) were obtained at pH 6.0. During the growth phase, the temperature optimum was found to be in the range of 30-34°C (μ max = 0.132 h -1 ). Nevertheless, the highest concentration of CA during the production phase was obtained at 30°C (41 g/L CA, 93.1 % CA, 0.55 g CA /g glucose ). In studying the substrate inhibition of the process, a clear tendency of decrease in the maximum specific growth rate was detected when the initial glucose concentration was increased from 50 g/L μ max = 0.17 h -1 ) to 200 g/L (μ max = 0.055 h -1 ). The addition of 120 g/L CA to the culture broth at the start of the production phase reduced the production of CA from 32.1 g/L to 7.4 g/L.

Optimization of Citric Acid Production from Glucose by Yarrowia lipolytica

Effect of particle size reduction and ensiling fermentation on biogas formation and silage quality of wheat straw

This review gives an overview of the current knowledge concerning the problem of foam formation in the process of anaerobic digestion in biogas plants that utilize renewable resources or biogenic waste material for biogas production. Process upsets in biogas production induced by foam formation can have a negative impact on the efficiency of biogas plants. The foam can block gas pipes and cause severe damage to the bioreactor equipment, ranging from a failure of the feeders to a damage of the roof of the biogas plant. The most common foam removal methods - stirring in the foam, adding anti-foaming agents, diminishing substrate feeding, and altering the biogas reactor management - are not always successful. However, the reasons for the excessive foam formation during the biogas production process have not yet been elucidated in detail. In contrast, foam building in the rumen of ruminants as a cause for bloat has been studied thoroughly. In general, the interaction between proteins, polysaccharides (mucilage), and small plant particles is assumed to be the crucial factor. As the fermentation process in the rumen has many similarities with the biogas production process, the current research results on bloat in ruminants are summarized and compared with the process of foaming in biogas plants.

/pdf/comparative-review-of-foam-formation-in-biogas-plants-and-1ve72kpbft.pdf

Comparative review of foam formation in biogas plants and ruminant bloat

The proportion of biogas in the mix of renewable energies is still remarkably high. The process of anaerobic digestion (AD) provides the basis of biogas production but often leads to excessive foaming. Identifying the reasons for foaming is difficult for biogas plant operators because many factors may play a role. It is therefore difficult for laboratory research to give answers to this specific problem, as the consistency of the digestate itself plays a crucial part in the foam formation process. Hence, careful investigation of foaming in full-scale biogas plants is important in order to identify the main causes and to develop strategies for the prevention of foaming. Fifteen operators of biogas plants treating biogenic waste have been reviewed in order to estimate the frequency of foaming events in full-scale biogas plants. Samples from foaming digestates were subsequently analyzed. Seven foaming periods in five biogas plants were investigated closely in order to ascertain the causes of foaming events. It was noted that 80% of surveyed biogas plants have had excessive foam formation during the AD process. The foam of two wastewater-treating biogas plants contained filamentous microorganisms. An abrupt temperature increase and the use of grain products and yeasts were identified to be the reason for foaming in four cases. It was, however, not possible to identify the real causes of the foaming event in two cases. Foam formation is a common phenomenon in waste-processing biogas plants. It is important to identify the reasons for foaming because this knowledge helps biogas plant operators to prevent foam formation in the future.

/pdf/foam-formation-in-full-scale-biogas-plants-processing-ohfw8fzzz6.pdf

Lucie Moeller

Papers

Optimization of Citric Acid Production from Glucose by Yarrowia lipolytica

Effect of particle size reduction and ensiling fermentation on biogas formation and silage quality of wheat straw

Comparative review of foam formation in biogas plants and ruminant bloat

Foam formation in full-scale biogas plants processing biogenic waste

Foam formation in biogas plants caused by anaerobic digestion of sugar beet.