Recent insights into the cell immobilization technology applied for dark fermentative hydrogen production

Highlights

• Dark H₂ fermentation performance could be enhanced with immobilized-cell systems.

• Immobilization method and matrix used influences fermentation efficiency.

• Adsorption and encapsulation are the preferred methods for immobilization.

• Microorganisms immobilized and the effect of carbon sources is reviewed.

• Effects of process variables and reactor design on H₂ fermentation are presented.

Abstract

The contribution and insights of the immobilization technology in the recent years with regards to the generation of (bio)hydrogen via dark fermentation have been reviewed. The types of immobilization practices, such as entrapment, encapsulation and adsorption, are discussed. Materials and carriers used for cell immobilization are also comprehensively surveyed. New development of nano-based immobilization and nano-materials has been highlighted pertaining to the specific subject of this review. The microorganisms and the type of carbon sources applied in the dark hydrogen fermentation are also discussed and summarized. In addition, the essential components of process operation and reactor configuration using immobilized microbial cultures in the design of varieties of bioreactors (such as fixed bed reactor, CSTR and UASB) are spotlighted. Finally, suggestions and future directions of this field are provided to assist the development of efficient, economical and sustainable hydrogen production technologies.

Introduction

The rising demand for energy production and energy consumption require scientists, engineers and a whole battery of research teams, all alike, to work out different viable schemes to produce energy with a much reduced ecological impact and carbon footprint. Subsequently, in relation to developing the hydrogen fuel research field and making the first steps in its potential development as a clean and optimized fuel economy, several green energy carriers have been studied in their performance to improve the biohydrogen production processes using different types of biomass (Algapani et al., 2016, Chandolias et al., 2016, Jariyaboon et al., 2015, Kumar et al., 2015a, Pachapur et al., 2015).

The major share of hydrogen production is currently derived from non-renewable fuel sources, principally by the conversion of methane and oil/naphtha. Consequently, cleaner techniques coupled with methods/protocols for the production of hydrogen from biomass present themselves as a more promising option, altogether. For this specific purpose, approaches and techniques which are mostly biological have been gathering research momentum and trying to emerge as green opportunities for hydrogen production. These techniques and methods are, in principle, categorized into light-dependent processes (biophotolysis of water and photo-fermentation) and light-independent ones. Dark fermentation (light-independent) is mostly preferred due to the higher production rates and maneuvering the organic fraction of biomass as feedstock (Boboescu et al., 2016, Sivagurunathan et al., 2016).

Biohydrogen production in the continuous system using suspended cells fails during the lower hydraulic retention times (HRT) due to the phenomenon of cell wash-out. In recent years, this problem had been prevailed over via various immobilization methods (Abreu et al., 2010, Frascari et al., 2013, Gomes et al., 2015, Han et al., 2015, Han et al., 2012, Lin et al., 2016, Park et al., 2015, Yokoi et al., 1997a). The development of cell immobilization technology for biohydrogen production aimed to improve the hydrogen production rate and yield, to address the key limitations associated with the suspended cells operation, and to improve the stability of continuous biohydrogen production. These include tolerance to the metabolic stress (such as pH, temperature, and organic loading rates), induced granules formation to enhance cell retention, and stable hydrogen productivity during long-term operations.

Notably the major milestones achieved in the immobilization methodologies are represented in Table 1. As it could be seen that many of the improvements have been made in the years 2003–2010. For example, Lin et al., 2009, have immobilized the sewage sludge using PVA to increase the production performance. Other important aspects and improvements are provided in Table 1. Moreover, immobilization of hydrogen producers and other important enzymes have opened the window for patents in this field. A few of the patents awarded in the immobilization field are summarized in Table 2. Some of the interesting patents include the “Artificial enzymatic pathway” for biohydrogen production by Virginia Tech. This novelty presents about, High yield water-based enzymatic process for the transformation of renewable polysaccharides to hydrogen using phosphorylases, phosphoglucomutases, hydrogenases and biocatalysts involved in the pentose-phosphate route. Similar aspects and other major outbreaks from 2010 onwards are summarized in Table 2.

The main objective of this present review is to provide the recent insights about immobilization technology in light independent (dark fermentative) hydrogen production, which includes the types of immobilization, novel carrier materials used, and the operational process parameters controlling the immobilization phenomenon. Besides, perspectives and concluding remarks have been narrated objectively in the last section with focus on the potential research and development roadmap towards a pilot scale process elaboration.