Georgia Antonopoulou

Using cheese whey for hydrogen and methane generation in a two-stage continuous process with alternative pH controlling approaches.

This study focuses on the exploitation of cheese whey as a source for hydrogen and methane, in a two-stage continuous process. Mesophilic fermentative hydrogen production from undiluted cheese whey was investigated at a hydraulic retention time (HRT) of 24 h. Alkalinity addition (NaHCO(3)) or an automatic pH controller were used, to maintain the pH culture at a constant value of 5.2. The hydrogen production rate was 2.9+/-0.2 L/Lreactor/d, while the yield of hydrogen produced was approximately 0.78+/-0.05 mol H(2)/mol glucose consumed, with alkalinity addition, while the respective values when using pH control were 1.9+/-0.1 L/Lreactor/d and 0.61+/-0.04 mol H(2)/mol glucose consumed. The corresponding yields of hydrogen produced were 2.9 L of H(2)/L cheese whey and 1.9 L of H(2)/L cheese whey, respectively. The effluent from the hydrogenogenic reactor was further digested to biogas in a continuous mesophilic anaerobic bioreactor. The anaerobic digester was operated at an HRT of 20 d and produced approximately 1L CH(4)/d, corresponding to a yield of 6.7 L CH(4)/L of influent. The chemical oxygen demand (COD) elimination reached 95.3% demonstrating that cheese whey could be efficiently used for hydrogen and methane production, in a two-stage process.

Review of feedstock pretreatment strategies for improved anaerobic digestion: From lab-scale research to full-scale application.

When properly designed, pretreatments may enhance the methane potential and/or anaerobic digestion rate, improving digester performance. This paper aims at providing some guidelines on the most appropriate pretreatments for the main feedstocks of biogas plants. Waste activated sludge was firstly investigated and implemented at full-scale, its thermal pretreatment with steam explosion being most recommended as it increases the methane potential and digestion rate, ensures sludge sanitation and the heat needed is produced on-site. Regarding fatty residues, saponification is preferred for enhancing their solubilisation and bioavailability. In the case of animal by-products, this pretreatment can be optimised to ensure sterilisation, solubilisation and to reduce inhibition linked to long chain fatty acids. With regards to lignocellulosic biomass, the first goal should be delignification, followed by hemicellulose and cellulose hydrolysis, alkali or biological (fungi) pretreatments being most promising. As far as microalgae are concerned, thermal pretreatment seems the most promising technique so far.

Operation and characterization of a microbial fuel cell fed with pretreated cheese whey at different organic loads.

Electricity production from filter sterilized cheese whey at different organic loads (0.35, 0.7, 1.5, 2.7 and 6.7gCOD/L respectively) was investigated in a two-chamber microbial fuel cell (MFC). The best performance of the cell was observed at the highest concentration of the pretreated (filter sterilized) cheese whey (6.7gCOD/L) corresponding to a maximum power density of approximately 46mW/m(2). Experiments using glucose (0.35gCOD/L) were also performed for comparison reasons. The study of the open-circuit impedance characteristics of the MFC and of the individual electrodes revealed that the open-circuit impedance of the MFC depended to practically the same extent on both the ohmic resistance between the anode and cathode and the overall polarization resistance. The polarization resistance of the MFC decreased significantly under closed-circuit conditions, which in turn implies that the ohmic overpotential is the main contribution to the energy losses in two-chamber MFCs.

ADM1-based modeling of methane production from acidified sweet sorghum extract in a two stage process.

The present study focused on the application of the Anaerobic Digestion Model 1 on the methane production from acidified sorghum extract generated from a hydrogen producing bioreactor in a two-stage anaerobic process. The kinetic parameters for hydrogen and volatile fatty acids consumption were estimated through fitting of the model equations to the data obtained from batch experiments. The simulation of the continuous reactor performance at all HRTs tested (20, 15, and 10d) was very satisfactory. Specifically, the largest deviation of the theoretical predictions against the experimental data was 12% for the methane production rate at the HRT of 20d while the deviation values for the 15 and 10d HRT were 1.9% and 1.1%, respectively. The model predictions regarding pH, methane percentage in the gas phase and COD removal were in very good agreement with the experimental data with a deviation less than 5% for all steady states. Therefore, the ADM1 is a valuable tool for process design in the case of a two-stage anaerobic process as well.

Biomethane and biohydrogen production via anaerobic digestion/fermentation

Abstract: Biomass is a renewable source for energy production by means of bioprocesses such as fermentation/anaerobic digestion. Biohydrogen and biogas are gaseous fuels produced by these processes. In this chapter, the basic principles and various technological aspects affecting the efficiency of fermentation and anaerobic digestion processes are presented. The hydrogen and methane yields from various types of biomass are reported, and difficulties and future trends in the area of anaerobic digestion are discussed.

A novel approach of modeling continuous dark hydrogen fermentation

In this study a novel modeling approach for describing fermentative hydrogen production in a continuous stirred tank reactor (CSTR) was developed, using the Aquasim modeling platform. This model accounts for the key metabolic reactions taking place in a fermentative hydrogen producing reactor, using fixed stoichiometry but different reaction rates. Biomass yields are determined based on bioenergetics. The model is capable of describing very well the variation in the distribution of metabolic products for a wide range of hydraulic retention times (HRT). The modeling approach is demonstrated using the experimental data obtained from a CSTR, fed with food industry waste (FIW), operating at different HRTs. The kinetic parameters were estimated through fitting to the experimental results. Hydrogen and total biogas production rates were predicted very well by the model, validating the basic assumptions regarding the implicated stoichiometric biochemical reactions and their kinetic rates.

12 – Production of biogas via anaerobic digestion

: Anaerobic digestion is a biological process that converts the organic matter present in various types of wastes (sewage sludge, agro-industrial wastes, OFMSW, energy crops) into: (1) biogas (rich in methane, suitable to be used for heat and/or electricity generation) (2) biosolids (microorganisms grown on the organic matter and unconverted particulate residues mostly fibres which can be used as soil conditioner), and (3) liquor (dissolved organic matter, recalcitrant to anaerobic degradation and nutrients, which may be used as liquid fertiliser). The vast improvement in various scientific fields (reactor engineering, modelling and control practices, molecular tools) helped to gain a better insight of the process. In addition, the policy to promote biogas utilisation contributed in boosting the application of the anaerobic digestion technology to achieve a two-fold goal: energy production and waste minimisation. All these aspects are discussed in what follows.

Biological and fermentative production of hydrogen

Abstract: This chapter discusses all the biological hydrogen production processes such as indirect and direct water biophotolysis, biological water gas shift, photo and dark fermentation and hydrogen production through microbial electrolysis cells. Dark fermentation or fermentative hydrogen production is focused on this chapter, since it is considered as the most promising compared to all biological hydrogen production methods. However, there are significant remaining barriers to practical application. The chapter includes the limitations of each process and suggests several methods that are aimed at overcoming these barriers.

Chapter 2:Farming and Harvesting

The competitiveness and sustainability of the biodiesel and vegetable oil market can be achieved through increasing the quantity of total biomass cultivated and the yield of the vegetable oil. Furthermore, pre-treatment technologies aiming to increase the bulk density and decrease the water content of the biomass can be employed to reduce the cost of biomass transportation and storage. The valorisation of the by-products (straw, stalk, leaves) through conversion processes into high-value-added chemicals and biomaterials as well as energy also contributes to improving the economics of the whole biorefinery scheme.