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

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 fermentation-based 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

Exploring the link between environmental pollution and economic growth in EU-28 countries: Is there an environmental Kuznets curve?

This study examines the Environmental Kuznets Curve hypothesis (EKC), considering the primary energy consumption among other country-specific variables, for a panel of the EU-28 countries during the period 1990-2014. By estimating pooled OLS regressions with Driscoll-Kraay standard errors in order to account for cross-sectional dependence, the results confirm the EKC hypothesis in the case of emissions of sulfur oxides and emissions of non-methane volatile organic compounds. In addition to pooled estimations, the output of fixed-effects regressions with Driscoll-Kraay standard errors support the EKC hypothesis for greenhouse gas emissions, greenhouse gas emissions intensity of energy consumption, emissions of nitrogen oxides, emissions of non-methane volatile organic compounds and emissions of ammonia. Additionally, the empirical findings from panel vector error correction model reveal a short-run unidirectional causality from GDP per capita growth to greenhouse gas emissions, as well as a bidirectional causal link between primary energy consumption and greenhouse gas emissions. Furthermore, since there occurred no causal link between economic growth and primary energy consumption, the neo-classical view was confirmed, namely the neutrality hypothesis

Plotted graphs between GDP per capita and greenhouse gas emissions intensity of energy consumption in EU-28.

<p>Source: Authors’ own elaboration.</p

Brief literature review on the causal relation between CO₂ emissions and economic growth.

<p>Brief literature review on the causal relation between CO₂ emissions and economic growth.</p

Plotted graphs between GDP per capita and greenhouse gas emissions from transport in EU-28.

<p>Source: Authors’ own elaboration.</p

The output of Westerlund panel cointegration test.

<p>The output of Westerlund panel cointegration test.</p

Summary review of literature invalidating EKC hypothesis.

<p>Summary review of literature invalidating EKC hypothesis.</p

Mean value of pollutant emissions in EU-28.

<p>Source: Authors’ own elaboration. Notes: For the definition of variables, please see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195708#pone.0195708.t004" target="_blank">Table 4</a>.</p

Plotted graphs between GDP per capita and emissions of non-methane volatile organic compounds in EU-28.

<p>Source: Authors’ own elaboration.</p