Grid columnar flat panel photobioreactor with immobilized photosynthetic bacteria for continuous photofermentative hydrogen production

Functional microorganisms in hydrogen production: Mechanisms and applications

The rapid growth of global energy demand accelerates the development of sustainable, clean, and renewable energy sources. Biohydrogen production, driven by functional microorganisms, offers a promising solution. Multiple species of bacteria, fungi, microalgae, and archaea were able to produce hydrogen. This study reviewed the typical strains, together with their hydrogen-production mechanisms, e.g., bio-photolysis, photo fermentation, and dark fermentation. Bacteria (e.g., purple non-sulfur bacteria) and microalgae (e.g., cyanobacteria) have been widely investigated, with respect to the limited fungi and archaea. It showed that temperature, pH, and substrate availability could all substantially influence the efficiency of biohydrogen production. Meanwhile, photo and dark fermentations are favored for future possible industrial applications. Furthermore, this review summarized practical applications of biohydrogen production, such as applications of bioreactors, waste treatments, and integrated systems for hydrogen production, highlighting the importance of functional microorganisms in advancing biohydrogen technology under global energy crisis.

Methods for the separation of hydraulic retention time and solids retention time in the application of photosynthetic microorganisms in photobioreactors: a review

Photosynthetic microorganisms have a wide range of biotechnical applications, through the application of their versatile metabolisms. However, their use in industry has been extremely limited to date, partially because of the additional complexities associated with their cultivation in comparison to other organisms. Strategies and developments in photobioreactors (PBRs) designed for their culture and applications are needed to drive the field forward. One particular area which bears examination is the use of strategies to separate solid- and hydraulic-residence times (SRT and HRT), to facilitate flow-through systems and continuous processing. The aim of this review is to discuss the various types of PBRs and methods which are currently demonstrated in the literature and industry, with a focus on the separation of HRT and SRT. The use of an efficient method of biomass retention in a PBR may be advantageous as it unlocks the option for continuous operation, which may improve efficiency, and improve economic feasibility of large-scale implementation of photosynthetic biocatalysts, especially where biomass is not the primary product. Due to the underexplored nature of the separation of HRT and SRT in reactors using photosynthetic microorganisms, limited literature is available regarding their performance, efficiencies, and potential issues. This review first introduces an overview into photosynthetic microorganisms cultivated and commonly exploited for use in biotechnological applications, with reference to bioreactor considerations specific to each organism. Following this, the existing technologies used for the separation of HRT and SRT in PBRs are explored. The respective advantages and disadvantages are discussed for each PBR design, which may inform an interested bioprocess engineer.

Towards industrial biological hydrogen production: a review

Increased production of renewable energy sources is becoming increasingly needed. Amidst other strategies, one promising technology that could help achieve this goal is biological hydrogen production. This technology uses micro-organisms to convert organic matter into hydrogen gas, a clean and versatile fuel that can be used in a wide range of applications. While biohydrogen production is in its early stages, several challenges must be addressed for biological hydrogen production to become a viable commercial solution. From an experimental perspective, the need to improve the efficiency of hydrogen production, the optimization strategy of the microbial consortia, and the reduction in costs associated with the process is still required. From a scale-up perspective, novel strategies (such as modelling and experimental validation) need to be discussed to facilitate this hydrogen production process. Hence, this review considers hydrogen production, not within the framework of a particular production method or technique, but rather outlines the work (bioreactor modes and configurations, modelling, and techno-economic and life cycle assessment) that has been done in the field as a whole. This type of analysis allows for the abstraction of the biohydrogen production technology industrially, giving insights into novel applications, cross-pollination of separate lines of inquiry, and giving a reference point for researchers and industrial developers in the field of biohydrogen production.

Light-dependent biohydrogen production: Progress and perspectives

The fourth industrial revolution anticipates energy to be sustainable, renewable and green. Hydrogen (H₂) is one of the green forms of energy and is deemed a possible solution to climate change. Light-dependent H₂ production is a promising method derived from nature's most copious resources: solar energy, water and biomass. Reduced environmental impacts, absorption of carbon dioxide, relative efficiency, and cost economics made it an eye-catching approach. However, low light conversion efficiency, limited ability to utilize complex carbohydrates, and the O₂ sensitivity of enzymes result in low yield. Isolation of efficient H₂ producers, development of microbial consortia having a synergistic impact, genetically improved strains, regulating bidirectional hydrogenase activity, physiological parameters, immobilization, novel photobioreactors, and additive strategies are summarized for their possibilities to augment the processes of bio-photolysis and photo-fermentation. The challenges and future perspectives have been addressed to explore a sustainable way forward in a bio-refinery approach.

Photobioreactors for cultivation and synthesis: Specifications, challenges, and perspectives

Due to their versatility and the high biomass yield produced, cultivation of phototrophic organisms is an increasingly important field. In general, open ponds are chosen to do it because of economic reasons; however, this strategy has several drawbacks such as poor control of culture conditions and a considerable risk of contamination. On the other hand, photobioreactors are an attractive choice to perform cultivation of phototrophic organisms, many times in a large scale and an efficient way. Furthermore, photobioreactors are being increasingly used in bioprocesses to obtain valuable chemical products. In this review, we briefly describe different photobioreactor set-ups, including some of the recent designs, and their characteristics. Additionally, we discuss the current challenges and advantages that each different type of photobioreactor presents, their applicability in biocatalysis and some modern modeling tools that can be applied to further enhance a certain process.

Enhanced photo-fermentative biohydrogen production from biowastes: An overview

Clean energy like hydrogen can be a promising strategy to solve problems of global warming. Photo-fermentation (PF) is an attractive technology for producing biohydrogen from various biowastes cost-effectively and environmentally friendly. However, challenges of low light conversion efficiency and small yields of biohydrogen production still limit its application. Thus, advanced strategies have been investigated to enhance photo-fermentative biohydrogen production. This review discusses advanced technologies that show positive outcomes in improving biohydrogen production by PF, including the following. Firstly, genetic engineering enhances light transfer efficiency, change the activity of enzymes, and improves the content of ATP, ammonium and antibiotic tolerance of photosynthetic bacteria. Secondly, immobilization technology is refined. Thirdly, nanotechnology makes great strides as a scientific technique and fourthly, integration of dark and photo-fermentation technology is possible. Some suggestions for further studies to achieve high levels of efficiency of photo-fermentative biohydrogen production are mentioned in this paper.

Rhodopseudomonas palustris: A biotechnology chassis

Rhodopseudomonas palustris is an attractive option for biotechnical applications and industrial engineering due to its metabolic versatility and its ability to catabolize a wide variety of feedstocks and convert them to several high-value products. Given its adaptable metabolism, R. palustris has been studied and applied in an extensive variety of applications such as examining metabolic tradeoffs for environmental perturbations, biodegradation of aromatic compounds, environmental remediation, biofuel production, agricultural biostimulation, and bioelectricity production. This review provides a holistic summary of the commercial applications for R. palustris as a biotechnology chassis and suggests future perspectives for research and engineering.

Development a novel hexagonal airlift flat plate photobioreactor for the improvement of microalgae growth that simultaneously enhance CO2 bio-fixation and wastewater treatment

A novel hexagonal airlift flat plate (HAFP) photobioreactor was designed to improve microalgae growth rate and compared with traditional flat plate (TFP) photobioreactor. The computational fluid dynamics (CFD) simulation was used to determine hydrodynamic parameters and optimal aeration rate in the photobioreactors. Additionally, the capability of the HAFP photobioreactor to enhance microalgae based CO₂ bio-fixation and wastewater treatment were investigated. The results of CFD simulation indicated that the HAFP photobioreactor could improve hydrodynamic parameters of turbulence kinetic energy (TKE), average fluid velocity, dead zone (DZ), and water shear stress (WSS) up to 78 %, 41 %, 44 % and 40 %, respectively, under optimal aeration rate of 0.6 vvm. The proposed HAFP photobioreactor showed a drastic improvement in microalgae growth (up to 61 %). The maximum CO₂ removal of 53.8 % and bio-fixation of 0.85 g L^-1 d^-1 were achieved in the HAFP photobioreactor which were approximately 70 % more than that in the TFP photobioreactor. The results suggested that the HAFP photobioreactor could accelerate nutrients removal and achieve remarkably higher efficiencies of 91 %, 99 %, 97 % and 93 % of ammonia (NH₃), nitrate (NO₃^-), phosphate (PO₄^3-) and chemical oxygen demand (COD) within seven days of cultivation.

Enhancement strategies for photo-fermentative biohydrogen production: A review

Biohydrogen production by photo fermentation is an attractive clean energy production approach with less environmental pollution and higher substrate conversion. In recent years, various measures have been used to improve biohydrogen production performance, but there is a lack of systematic and comprehensive summary and analysis. Hence, the recent literatures on enhancing biohydrogen production by photo fermentation were summarized, and the functional mechanisms of enhancement strategies were explained. In this work, these measures were divided into four categories according to their roles in photo fermentation, including substrate pretreatment, bacterial modification and immobilization, additive addition, reactor design optimization. It can be concluded that the optimal enhancement conditions of each strategy were affected by substrate type, strain and process parameters. According to the results of this work, it was expected to give readers a clear understanding and provide a scientific reference of the research of photosynthetic biohydrogen production.

Enhancing Hydrogen Productivity of Photosynthetic Bacteria from the Formulated Carbon Source by Mixing Xylose with Glucose

To develop an efficient photofermentative process capable of higher rate biohydrogen production using carbon components of lignocellulosic hydrolysate, a desired carbon substrate by mixing xylose with glucose was formulated. Effects of crucial process parameters affecting cellular biochemical reaction of hydrogen by photosynthetic bacteria (PSB), i.e., variation in initial concentration of total carbon, glucose content in initial carbon substrate, and light intensity, were experimentally investigated using response surface methodology (RSM) with a Box-Behnken design (BBD). Hydrogen production rate (HPR) in the maximum value of 30.6 mL h^-1 L^-1 was attained under conditions of 39 mM initial concentration of total carbon, 59% (mol/mol) glucose content in initial carbon substrate, and 12.6 W m^-2 light intensity at light wavelength of 590 nm. Synergic effects of metabolizing such a well-formulated carbon substrate for sustaining the active microbial synthesis to sufficiently accumulate biomass in bioreactor, as well as stimulating enzyme activity of nitrogenase for the higher rate biohydrogen production, were attributed to this carbon substrate that can enable PSB to maintain the relatively consistent microenvironment in suitable culture pH condition during the optimized photofermentative process.

A Newly Designed Automatically Controlled, Sterilizable Flat Panel Photobioreactor for Axenic Algae Culture

In context of the global climate change, microalgae processes are gaining momentum as a biotechnological tool for direct fixation and valorization of greenhouse gases. Algae have the metabolic capacity to photosynthetically convert CO₂ into high value products, such as food additives, under economic boundary conditions. High cost, commercial flat panel gas-lift bioreactors for microalgae cultivation at laboratory scale provide either small volumes or no sterile operation, which limits academic research. This brief report presents initial data for a new type of sterile operating flat panel gas-lift bioreactor with a unique asymmetrical U-shape. It utilizes automatable process control technologies that adhere to industrial standards to enhance data reproducibility and aid industrial scale up. The practicability was demonstrated using a Chlorella sorokiniana cultivation, which showed the typical growth behavior. Due to the sophisticated implemented control engineering technology, pivotal parameters as pH and temperature can be determined within a range of ±0.1 units, which was confirmed experimentally. The new flat panel gas-lift photobioreactor presented in this brief report fills the technology gap at laboratory scale with an autoclavable volume of 7.2 L. Moreover, it is easy to rebuild by means of the hereby provided blueprint, while exhibiting a six-fold cost reduction compared to commercially available flat panel photobioreactors.

Photo-biological hydrogen production by a temperature-tolerant mutant of Rhodobacter capsulatus isolated by transposon mutagenesis

Screening of high temperature tolerant strains is important for photo-fermentative hydrogen production in natural conditions which exhibit wide temperature variations. Hence, a temperature-tolerant strain of Rhodobacter capsulatus was isolated by transposon mutagenesis. The mutant strain Rhodobacter capsulatus MX01 could convert cornstalk hydrolysate into hydrogen successfully, and exhibited better hydrogen production performance at higher culture temperature (33 °C and 37 °C) and light intensity (5000 lx and 7000 lx) than the wild type strain. At 33 °C and 5000 lx, the total hydrogen production yield and rate of MX01 from cornstalk hydrolysate were 3.64 ± 0.18 mol-H₂/g-cornstalk and 40.07 ± 1.70 mmol-H₂/(h·g-cornstalk), respectively. The energy conversion efficiency of cornstalk hydrolysate to hydrogen for the mutant strain MX01 was 10.6%. This higher temperature- and light intensity-tolerant mutant MX01 could carry out photo-fermentation at outdoor settings, which is important for eco-friendly, low-cost and energy-saving practical application of bio-hydrogen production.

The adherence-associated Fdp fasciclin I domain protein of the biohydrogen producer Rhodobacter sphaeroides is regulated by the global Prr pathway

Expression of fdp, encoding a fasciclin I domain protein important for adherence in the hydrogen-producing bacterium Rhodobacter sphaeroides, was investigated under a range of conditions to gain insights into optimization of adherence for immobilization strategies suitable for H₂ production. The fdp promoter was linked to a lacZ reporter and expressed in wild type and in PRRB and PRRA mutant strains of the Prr regulatory pathway. Expression was significantly negatively regulated by Prr under all conditions of aerobiosis tested including anaerobic conditions (required for H₂ production), and aerobically regardless of growth phase, growth medium complexity or composition, carbon source, heat and cold shock and dark/light conditions. Negative fdp regulation by Prr was reflected in cellular levels of translated Fdp protein. Since Prr is required directly for nitrogenase expression, we propose optimization of Fdp-based adherence in R. sphaeroides for immobilized biohydrogen production by inactivation of the PrrA binding site(s) upstream of fdp.