Optimized Fed Batch Fermentation Process for Continuous Hydrogen Generation

Abstract

The invention presents an innovative approach for continuous hydrogen production through optimization of fed-batch fermentation process. The process integrates systematic parameter optimization, strategic feeding mechanisms and precise control strategies to enhance hydrogen yield adopting a two-phase optimization process. The substrate used as key nutrient source to the bacteria is crude glycerol, produced as by-product from biodiesel industries. Mesophilic bacteria, Klebsiella pneumoniae, that has the potential to acclimatize to crude glycerol is used in the current innovation. Initial batch experiments were conducted to determine the optimal temperature and pH conditions for dark fermentation, establishing the foundation for fed-batch process. The fed-batch process was then devised by incorporating variable substrate concentrations and inoculum sizes to optimize, in order to maximize the hydrogen production efficiency. A comprehensive control mechanism that synergistically manages the temperature, initial media pH, substrate availability and the microbial population dynamics to create a conducive environment for continuous hydrogen generation is developed through the two-phase optimization process. This approach resulted in the prolonged maintenance of an active microbial population, continuous availability of the substrate at the optimized process temperature and initial media pH that could facilitate optimum microbial activity, yielding improved hydrogen output compared to the traditional batch processes. Thus, the system demonstrates a significant potential for scaling up continuous biohydrogen production with improved efficiency and yield over the existing batch processes, emphasizing the need for sustainable hydrogen production methods to address the demand for renewable energy.

Specification

Description:FIELD OF INVENTION
[001] The innovation is in the field of biotechnology under the class of biochemical engineering/ renewable energy/biofuel production/ fermentation technology.
BACKGROUND AND PRIOR ART
[002] Hydrogen is highly recognized as a clean and efficient energy carrier that can potentially take up the fossil fuel's role in various domains. Biological routes of hydrogen production are predominantly gaining significance owing to their ability to use renewable feedstocks such as organic wastes generated from various sources. The currently in use chemical methods of hydrogen production require enormous amount of energy supply during the production process and are one of the major contributors to pollution and increase in greenhouse gases. Biological methods are largely energy independent and can be scaled up as sustainable, green technology.
[003] Traditionally, most of the studies related to biohydrogen have been carried out as batch processes using different waste organic materials as substrates. The outcomes of these studies report the limitations in hydrogen production such as the low productivity and intermittent operational challenges. Studies have also been carried out using continuous stirred tank reactors that has successfully demonstrated the long-term operation but due to its significant biomass washout at high dilution rates has limited its projectability to large scale up conditions. Research attempts are also being taken up using anaerobic sequencing batch reactors that can combine both batch and continuous systems. As this method reported to have improved the hydrogen yield, factors such as complexity in operation and incomplete substrate utilization are seen as the major road blocks, limiting the extendibility of this method to industrial scale production capacity. Studies have also been carried out to overcome the limitations experienced with the use of batch or continuous reactors such as continuously stirred tank reactor, anaerobic sequencing batch reactor. These reactors were devised to retain the biomass so as to overcome the washout condition at high dilution rates that resulted in high hydrogen production rates but posed challenges in terms of membrane fouling and higher operational costs. Research on fed- batch systems have been reported on limited scale with studies being carried out extensively on individual parameters such as pH, temperature or substrate concentration on their potential for improved yields. Studies reported on biohydrogen production lack comprehensive strategies to optimize fed-batch parameters for continuous production.
[004] The current innovation highlights the studies carried out by integrating multiple parameters optimizing strategies using a two-phase dark fermentation process. Crude glycerol, a by- product from biodiesel production plants is used as substrate and Klebsiella pneumoniae, a mesophilic bacterium that can well acclimatize to crude glycerol as substrate is used as microbial source. The two-phase devised process facilitates active microbial population dynamics for enhanced hydrogen yield on continuous production process in fed-batch system.
BRIEF DESCRIPTIONS OF DRAWINGS
[005] The two-phase experimentation system is shown in the two drawings of the experimental setup shown above. Drawing 1 shows the first stage process setup that comprises a bioreactor housed on a heating mantle equipped with a magnetic stirrer and PID controller. The bioreactor is connected to a pH indicator in order to monitor the changes in the pH during the fermentation process. The neck of the bioreactor has two ports off which one port is used to withdraw the gas generated during fermentation and the other port is used to introduce the PID probe into the bioreactor. Drawing 2 shows the second phase, where the experimental setup is devised as a fed-batch set up, where the feed inlet port is connected to a substrate dosing pump for continuous addition of the substrate at regulated flow rates.
[006] In both the batch experimental setup and the fed-batch system, the gas produced during the fermentation process is passed through a hydrogen gas detector and monitoring system to quantify and qualify the produced hydrogen and then it is collected in a water column. As hydrogen is very sparingly soluble in water, the gas collected in the column displaces the water in the column. This water displacement level is used to determine the rate of gas generated which is a crucial information for design of continuous bioreactor system. The collected gas is then transferred to a tedlar bag for gas storage.
SUMMARY OF THE INVENTION
[007] The invention presents an innovative fed-batch fermentation process designed for continuous biohydrogen production. The system integrates optimized process parameters, strategic feeding mechanisms and precise control strategies to enable prolonged microbial activity and thereby enhancing the hydrogen yield. The key aspects of the innovation are the versatility of two-phase optimization strategy that provides a comprehensive approach to optimize crucial factors in the process, contributing to improved hydrogen yield and continuous production capability, marking a significant advancement in the field of biohydrogen production.
[008] The two-phase optimization strategy has been devised by systematically evaluating the critical process parameters mainly the temperature and initial media pH, that are most crucial to optimize the hydrogen yield, in the first stage of batch experimentation. The second stage constitutes the fed-batch process optimization of another two critical variables such as substrate concentration and the inoculum size, needed to maintain the active microbial population dynamics for sustained hydrogen generation. A strategic feeding mechanism is thus devised for continuous uptake of the substrate to maintain the optimal nutrient level to facilitate the active growth state of the bacteria, while the optimized temperature and initial media pH values from batch studies help to regulate the metabolic heat generation and enzymatic activity favourable for continuous hydrogen production during the fed-batch fermentation process. This strategy has resulted in significant increase in hydrogen production compared to traditional batch process, which is attributed to optimized conditions and sustained microbial activity. The fed-batch process is versatile owing to its capability in using diverse organic wastes as substrates highlighting effective resources utilization. The minimal energy consumption during the process makes the process highly viable. Thus, with the adoption of the above strategic control mechanisms coupled with the versatility in using waste organic sources, the fed-batch process is acquiescent to scaling up, overcoming the key limitations faced in the traditional method. This promises a potential breakthrough for continuous hydrogen production at large scale thus paving way for sustainable energy generation.
DETAILED DESCRIPTION OF THE INVENTION
[009] The present invention relates to a fed-batch fermentation system designed for continuous biohydrogen production. This innovative system integrates process optimization techniques, strategic feeding mechanism, and precise control strategies to achieve sustained microbial activity and enhanced hydrogen yield. By addressing these key challenges in biohydrogen production, this invention represents a significant advancement in the field of renewable energy.
[010] The invention employs a novel two-phase optimization process that forms the basis for its enhanced efficiency. The first phase involves batch experimentation to determine optimal conditions. The feed comprising a definite volume of the fermentation media with crude glycerol as substrate, inoculated with the mesophilic bacteria, Klebsiella pneumoniae is charged into the bioreactor, for batch studies. In this phase, experiments are conducted at three different temperatures, typically ranging from 30°C to 40°C, to identify the ideal thermal environment for hydrogen production. Concurrently, the system evaluates the initial pH of the media at three distinct levels of 5,8, 6,8 and 7.8, to ascertain the optimal acidic conditions for dark fermentation. The process control and monitoring of these parameters are integral to the invention's success. Temperature control is achieved through a PID (Proportional-Integral- Derivative) system that maintains the environment within ±1°C of the determined optimal value, compensating for metabolic heat generation through adaptive cooling. pH regulation employs industrial-grade pH probes for continuous monitoring. Maintenance of an anaerobic environment which is crucial for hydrogen production, is ensured through purging with inert gas, typically nitrogen, in order to maintain the required anaerobic conditions.
[011] Through rigorous data analysis with respect to the substrate consumption rate, hydrogen gas generation rate and its yield, the batch study determines the most favourable temperature and initial media pH, considering their interactive effects on hydrogen production and microbial stability.
[012] Building upon the outcomes gained from the batch experiments, the second phase implements a fed-batch process optimization step. This phase utilizes the optimal temperature and initial pH conditions identified earlier while, the second stage focusses on two critical variables such as substrate (crude glycerol) concentration and inoculum size of the bacteria. The system varies the substrate (crude glycerol) concentration, at levels between 50 mg/L and 150 mg/L, to determine the optimal nutrient environment for continuous hydrogen production. Substrate management is achieved through continuous monitoring of nutrient concentration while preventing substrate inhibition. Simultaneously, it evaluates different inoculum sizes, ranging from 7.5% to 12.5% (v/v), to identify the ideal microbial population for rapid start-up and sustained production. The substrate dosing pump adjusts the feeding rates to keep microorganisms in an active growth phase, implementing biomass retention strategies ensuring long-term stability of the hydrogen-producing culture. This comprehensive approach allows for the development of a sophisticated feeding strategy that responds dynamically to substrate uptake rates and microbial growth patterns. This strategy is a key feature that sets it apart from traditional batch processes.
[013] Gas collection and analysis form a critical component of the invention. The system continuously collects the produced biogas, subjecting it to real-time analysis using a hydrogen gas collection and monitoring system. This allows for precise quantification of hydrogen production rate and its yield.
[014] One of the key advantages of this invention is its scalability and flexibility. The simple process design allows for easy scale-up from laboratory to industrial scales. Moreover, the system is adaptable to various substrate types, including simple sugars like glucose, complex carbohydrates like cellulose, and even organic waste streams. This versatility opens up possibilities for integration with other bioprocesses, such as wastewater treatment or biorefinery operations.
[015] The potential applications of this invention are diverse and impactful. Beyond its primary role in renewable energy production, the system can be employed in waste-to-energy conversion, supporting circular economy initiatives. Crude glycerol is generally considered as a waste by- product from biodiesel production units, owing to the presence of acidic or alkali salts, solvents, free fatty acids and water. These constituents make crude glycerol a complex mixture that needs extensive treatment processes to purify it, which is also highly cost intensive. Thus, use of crude glycerol as the key substrate in this invention will also add value to biodiesel plants where the waste by-product is also converted to valuable energy carrier. Additionally, the system serves as an excellent platform for research and development in microbial hydrogen production, potentially leading to further advancements in the field.
[016] In conclusion, this invention represents a significant leap forward in biohydrogen production technology. By integrating precise control strategies, and continuous operation capabilities, it offers improved efficiency, stability, and scalability compared to existing methods. As the world increasingly turns towards sustainable energy solutions, this optimized fed-batch fermenter for continuous hydrogen production stands poised to play a crucial role in the future of clean energy production. , C , Claims:[017] 1. A method for continuous biohydrogen production process is devised using the following strategy:
i) Conducting batch fermentation experiments to determine optimal temperature and pH conditions for hydrogen production
ii) Implementing a fed-batch fermentation process using the determined optimal temperature and pH conditions with continuous monitoring and adjusting the limiting substrate concentration and microbial population by controlling the limiting substrate at calculated intervals to maintain microbial growth, thus ensuring sustained continuous hydrogen production.
[018] 2. The method of claim (i), wherein the optimal temperature and initial media pH conditions are determined by conducting batch experiments at multiple temperatures and initial media pH levels and analyzing the hydrogen yield to identify the most favorable conditions.
[019] 3. The method of claim (i), further comprises of analyzing the composition of produced biogas and adjusting the process parameters based on the biogas composition to maximize hydrogen content.
[020] 4. The method of claim (ii), wherein the fed-batch fermentation process is carried out by further optimizing the inoculum size and adjusting substrate feeding rate based on microbial growth patterns. The process parameters determined in claim (i) are controlled by maintaining the temperature within ±1°C of the determined optimal value and maintaining the initial media pH within ±0.2 units of the determined optimal value.
[021] 5. The method of claim (ii), wherein continuously monitoring and adjusting substrate concentration and microbial population comprises of real-time measurement of substrate uptake rates and assessment of microbial growth phases and regulating the feeding parameters based on the measured data to prevent inhibition of hydrogen production.
[022] 6. A system for continuous biohydrogen production is devised comprising a fermentation vessel equipped with temperature and pH control mechanisms, a substrate feeding mechanism capable of controlled, intermittent substrate addition with monitoring devices for real-time measurement of substrate concentration and microbial population and a gas collection and analysis system for quantifying and qualifying the produced hydrogen.
[023] 7. A continuous bioprocess has been developed by optimizing a fed-batch fermentation process for biohydrogen production by (i) determining optimal temperature and initial media pH through batch experiments, (ii) establishing a fed-batch process using the determined optimal conditions, (iii) varying the substrate concentration and inoculum size to identify optimal combinations, (iv) implementing a feeding strategy that maintains microbial populations in active growth phase, and (v) continuously adjusting process parameters to maximize the hydrogen yield and production rate.

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