An acidophilic bacterial-archaeal-fungal ecosystem linked to formation of ferruginous crusts and stalactites.

The presence of specialized microbial associations between populations of chemoautotrophic bacteria and archaea with ascomycetous fungi was observed inside stalactite-shaped mineral formations in a highly acidic cave environment. Metagenomic, chemical and electron microscopy analyses were used to investigate the relevance of these microbial ecosystems in the formation of stalactites. Ferric hydroxide produced by acidophilic bacteria and archaea was shown to be deposited onto fungal hyphae, resulting in complex mineralized stalactite-shaped structures. Thus, both archaeal-bacterial and fungal members of the ecosystem were shown to play an active role in the formation of stalactites

Exploitation of experimental design methods and mathematical modeling for improving fermentative biohydrogen production processes

Abstract Considering the non-renewable nature of today's energy sources, alternative solutions need to be introduced to successfully fulfill the world's energy demands in the future. Biohydrogen production processes coupled to the treatment of different organic wastes might satisfy the requirements of a renewable and environmentally friendly energy carrier. A major drawback of this bioprocess is the low hydrogen production yield, thus, the optimization of the fermentation conditions is imperative for achieving a hydrogen-based economy. The most widely used optimization strategies refer to the design of experimental methods, by which certain factors are selected and deliberately varied in order to obtain the desired effects. In addition, the optimization process can be further improved through mathematical modeling and simulations. Some kinetic models have been proposed to describe the progress of substrate degradation and microbial growth coupled with hydrogen production and some soluble metabolite formation in a batch fermentationbased hydrogen production process. This review attempts to summarize the experimental design methods as well as the kinetic models and simulations that were used to investigate the effects of various factors on fermentative hydrogen production processes and to discuss the advantages and limitations of these optimization approaches

Treatment and valorization of municipal solid waste gasification effluent through a combined advanced oxidation – microalgal phytoremediation approach

Liquid effluents generated during the gasification process of municipal solid wastes (MSW) represent highly heterogenous and recalcitrant substrates, and thus require energy-intensive treatments prior to their discharge into the environment. However, these streams represent untapped carbon sources which can be converted, under the right conditions, to platform molecules, decreasing thus the elevated costs of current mitigation approaches. Thus, the present study describes a novel two-step chemical and biological effluent treatment process which co-generates microalgal biomass containing valuable functionalcomponents. The detoxification potential of ozone, ultrasonication and a combination of both of these advanced oxidation processes (AOPs) were initially evaluated using wastewater generated from scrubbing primary syngas produced from the gasification of MSW. The pretreated effluents were subsequentlyused to cultivate Chlorella vulgaris microalgae under various illumination (light/dark cycles of 24h/0h, 12h/12h and 0h/24h) and nutrient (supplementation of yeast extract) regimes, in order to assess theirpotential to further convert the remaining carbon into value-added functional biomolecules, such as photosynthetic pigments. The use of ozone, either individually or combined with ultrasounds, showed the best performances for the substrate detoxification prior to the biological treatment step. It was determined that 20 min of oxidative reaction using ozone coupled with ultrasounds was sufficient to degrade up to 70% of the total phenol compounds, 64% of the COD, and 75% of the color initially present in the gasification wastewater. The further microalgal phytoremediation and conversion experiments showed that 12 h of illumination per day, together with 0.5 g/L of yeast extract, generated the highestmicroalgae growth rate (0.29 d 1), biomass productivity (244 mg/L/d), photosynthetic pigment accumulation (12.0 and 4.5 mg/L of total chlorophyll and carotenoids, respectively) as well as total carbonremoval (57 %). Therefore, the combination of AOPs with mixotrophic cultivation of C. vulgaris demonstrates for the first time an alternative to current treatment strategies of highly-recalcitrant industrial wastewaters, which includes the further valorization of the carbon available in these streams

High-efficiency second generation ethanol from the hemicellulosic fraction of softwood chips mixed with construction and demolition residues

Using lignocellulosic residues for bioethanol production could provide an alternative solution to current approaches at competitive costs once challenges related to substrate recalcitrance, process complexity and limited knowledge are overcome. Thus, the impact of different process variables on the ethanol production by Saccharomyces cerevisiae using the hemicellulosic fraction extracted through the steam-treatment of softwood chips mixed with construction and demolition residues was assessed. A statistical design of experiments approach was developed and implemented in order to identify the influencing factors (various nutrient addition sources as well as yeast inoculum growth conditions and inoculation strategies) relevant for enhancing the ethanol production potential and substrate uptake. Ethanol yields of 74.12% and monomeric sugar uptakes of 82.12 g/L were predicted and experimentally confirmed in bench and bioreactor systems. This innovative approach revealed the factors impacting the ethanol yields and carbohydrate consumption allowing powerful behavioral predictions spanning different process inputs and outputs

METAGENOMICS INVESTIGATION OF ANAEROBIC DEGRADATION ECOSYSTEMS

Biomethane has gained increasing attention in the recent years as an alternative, local energy source option. Biogas is generated during the anaerobic digestion of organic materials via a multistep process catalyzed by complex microbial communities. This review aims at providing a concise summary of recent studies on the microbial communities in various biogas reactors. The effects of acid composition, C/N ratio, mixing and the geometry of the anaerobic digester on the microbial ecosystem are discussed. The biogas microbial communities show extensive fluctuations in response to changes in temperature, substrate type, pH, type of volatile fatty acids, organic loading rate, etc. The goals to ensure efficient anaerobic degradation and to maximize the biogas production require the better understanding of these bacterial-archaeal ecosystems, since functional stability strongly correlates with the state and composition of microbial communities. The safe and controlled intensification of biogas production would be an important step to make biogas a real competitor of fossil fuels

A novel hybrid first and second generation hemicellulosic bioethanol production process through steam treatment of dried sorghum biomass

Sweet sorghum was subjected to an impregnation step, which recovered most of the 1st generation sugars, prior to a steam-treatment extraction of the 2nd generation sugars, at three different severity factors (SF). A medium severity (3.56 SF) treatment proved to be an optimal compromise between the amount of sugars extracted and the fermentation inhibitors generated following the subsequent depolymerization approaches applied on the broth. Next, a series of detoxification approaches (ozonation, overliming and a combination of both) were investigated following a concentration and depolymerization step. Results show that higher steam-treatment severity required more intense detoxification steps. However, when combining the 1st and 2nd generation streams at a 2:1 ratio, the inhibitors did not affect the fermentation process and ethanol yields above 90% of the theoretical maximum were achieved

Exploitation of experimental design methods and mathematical modeling for improving fermentative biohydrogen production processes

Considering the non-renewable nature of today's energy sources, alternative solutions need to be introduced to successfully fulfill the world's energy demands in the future. Biohydrogen production processes coupled to the treatment of different organic wastes might satisfy the requirements of a renewable and environmentally friendly energy carrier. A major drawback of this bioprocess is the low hydrogen production yield, thus, the optimization of the fermentation conditions is imperative for achieving a hydrogen-based economy. The most widely used optimization strategies refer to the design of experimental methods, by which certain factors are selected and deliberately varied in order to obtain the desired effects. In addition, the optimization process can be further improved through mathematical modeling and simulations. Some kinetic models have been proposed to describe the progress of substrate degradation and microbial growth coupled with hydrogen production and some soluble metabolite formation in a batch fermentationbased hydrogen production process. This review attempts to summarize the experimental design methods as well as the kinetic models and simulations that were used to investigate the effects of various factors on fermentative hydrogen production processes and to discuss the advantages and limitations of these optimization approaches

Surpassing the current limitations of biohydrogen production systems: The case for a novel hybrid approach

The steadily increase of global energy requirements has brought about a general agreement on the need for novel renewable and environmentally friendly energy sources and carriers. Among the alternatives to a fossil fuel-based economy, hydrogen gas is considered a game-changer. Certain methods of hydrogen production can utilize various low-priced industrial and agricultural wastes as substrate, thus coupling organic waste treatment with renewable energy generation. Among these approaches, different biological strategies have been investigated and successfully implemented in laboratory-scale systems. Although promising, several key aspects need further investigation in order to push these technologies towards large-scale industrial implementation. Some of the major scientific and technical bottlenecks will be discussed, along with possible solutions, including a thorough exploration of novel research combining microbial dark fermentation and algal photoheterotrophic degradation systems, integrated with wastewater treatment and metabolic by-products usage. (C) 2016 Elsevier Ltd. All rights reserved