Julián Carrillo-Reyes

Microbial communities from 20 different hydrogen-producing reactors studied by 454 pyrosequencing

To provide new insight into the dark fermentation process, a multi-lateral study was performed to study the microbiology of 20 different lab-scale bioreactors operated in four different countries (Brazil, Chile, Mexico, and Uruguay). Samples (29) were collected from bioreactors with different configurations, operation conditions, and performances. The microbial communities were analyzed using 16S rRNA genes 454 pyrosequencing. The results showed notably uneven communities with a high predominance of a particular genus. The phylum Firmicutes predominated in most of the samples, but the phyla Thermotogae or Proteobacteria dominated in a few samples. Genera from three physiological groups were detected: high-yield hydrogen producers (Clostridium, Kosmotoga, Enterobacter), fermenters with low-hydrogen yield (mostly from Veillonelaceae), and competitors (Lactobacillus). Inocula, reactor configurations, and substrates influence the microbial communities. This is the first joint effort that evaluates hydrogen-producing reactors and operational conditions from different countries and contributes to understand the dark fermentation process.

Biohydrogen and methane production via a two-step process using an acid pretreated native microalgae consortium

A native microalgae consortium treated under thermal-acidic hydrolysis was used to produce hydrogen and methane in a two-step sequential process. Different acid concentrations were tested, generating hydrogen and methane yields of up to 45mLH2gVS-1 and 432mLCH4gVS-1, respectively. The hydrogen production step solubilized the particulate COD (chemical oxygen demand) up to 30%, creating considerable amounts of volatile fatty acids (up to 10gCODL-1). It was observed that lower acid concentration presented higher hydrogen and methane production potential. The results revealed that thermal acid hydrolysis of a native microalgae consortium is a simple but effective strategy for producing hydrogen and methane in the sequential process. In addition to COD removal (50-70%), this method resulted in an energy recovery of up to 15.9kJ per g of volatile solids of microalgae biomass, one of the highest reported.

Biohydrogen production from microalgae

Abstract Two biological methods for hydrogen production involving microalgae are revised. In one method, microalgae use the light energy to produce hydrogen from water. In the second one, bacteria capable of fermenting the carbohydrates (either structural or stored in the microalgal cell wall) are utilized to produce hydrogen. Different approaches for using direct and indirect biophotolysis and strategies for using microalgae as feedstock for dark fermentation are presented and discussed. Finally, a life cycle assessment on hydrogen production by these two methods is used to identify the technological bottlenecks, detecting the weaknesses and focusing the research efforts needed.

Hydrolysis of microalgal biomass using ruminal microorganisms as a pretreatment to increase methane recovery

The use of ruminal fluid as a source of hydrolytic microorganisms for the pretreatment of a native consortium of microalgae (essentially Senedesmus) was investigated. The hydrolytic enzyme activity of the ruminal culture was first enriched in a bioreactor. Then, using the enriched culture, the effect of the microalgae to the ruminal fluid ratio (S/X) on the hydrolysis and subsequent production of methane was investigated. An S/X ratio of 0.5 showed the best hydrolysis efficiency (29%) reaching in a second stage process a methane yield of 193mL CH4g COD-1. The processing time (pretreatment plus methanization) was only 7days. The predominant ruminal hydrolytic bacteria selected in the enrichment were principally Clostridium, Proteocatella and Pseudomonas.

Microscopy Applied In Biomass Characterization

This chapter serves as an introduction to the major types of microscopy that are applied to the characterization of lignocellulosic biomasses. The covered techniques include optical microscopies (light, Raman, and confocal microscopy), scanning probe microscopy, and electron microscopy. This chapter provides a general description of the principles, advantages and drawbacks, type of information that can be obtained using the different microscopic techniques, and includes a wide range of examples on the use of such techniques to characterize lignocellulosic biomass samples before and after pretreatments. Finally, some of the reviewed microscopic techniques were used to visualize samples of wheat straw nodes before and after acid and alkali pretreatments. This chapter is designed to help scientists select the best microscopic technique to study biomass feedstocks with recalcitrant natures.