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One of the main methods for obtaining mixed fermentative acidogenic inocula is the isolation of spore-forming bacteria (SFB) from different mixed matrices. SFB have proven to be suitable inocula in Dark Fermentation systems, although they have certain limitations. In the present study, the formulation of a mixed consortium is studied, by combining SFB and Water Kefir (WK) in Mixed-Yeast-bacteria (MYB) fermentations tests. First, both inocula are properly selected and maintained. Then, a scan of different pretreatments is performed on stale bread that was selected as retrieved substrate for the MYB tests. MYB tests are conducted in batch mode, under anaerobic conditions, using the basic-pretreated stale bread. Systems inoculated with independent inocula (either SFB and WK, in a 10% v/v) and combined (WK+SPB, 5+5% v/v) are studied in a three-cycles compatibility experimental campaign. The gas production and yield, its composition and the liquid titers of organic acids and ethanol are measured to shed light on the fermentation dynamics in each case. The adaptation cycles resulted in progressively reduced lag phases for all systems, and interesting results were obtained for the WK+SFB system, which exhibited higher hydrolytic activity and achieved the highest hydrogen, ethanol and organic acid productivity. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen production, via Dark Anaerobic Fermentation, leads to a negative net energy balance because of the difference between the energy produced as hydrogen and the direct ones (heat and electricity) consumed to produce it. The residual metabolites (Volatile Fatty Acids and alcohols) at the end of hydrogen production are oxidized compounds with a high-energy value. This paper deals with experimental tests that were conducted to recovery the energy embedded in these metabolites. Two proofs of the tests have been realized following two strategies: i) production of biogas containing methane by methanogen microorganisms from liquid metabolites; ii) production of additional H2 from acetate as main constituted of Volatile Fatty acids (VFAs) by Microbial Electrolysis Cell (MEC) with a cation exchange membrane (CEM). Both technologies have shown to be feasible and offer a double positive effect: the total produced energy increased and a beneficial effect, due to the achievement of a greater abatement of the organic wastewater load in the effluent, was obtained. A detailed energy analysis has showed that the second methanogenic stage increases the overall energy efficiency of the two-stage process to a great extent compared to the H2 stage on its own. The introduction of a second step leads to a positive net energy production for the methanogenic step, while additional research is necessary for the case of hydrogen production by MEC, as this technology is still at the infancy stage. [Copyright &y& Elsevier]

Abstract: Two energy conversion parameters that are able to evaluate and score the pre-treatments and biohydrogen conversion processes of organic waste refuses have been introduced and applied using original experimental data. The parameters can be considered a suitable tool to score and select processes using rich lignocelluloses materials. The first efficiency (ξ) takes into account the quantity of energy that the process is able to extract as hydrogen, compared to the available amount of energy embedded in the refuse; the second efficacy (η) compares the energy conversion efficiency of the bioprocess using the refuse with the same energy conversion parameter obtained using glucose as a lignin-cellulose free substrate. Both the efficiency and efficacy have been applied in several experimental tests carried out with different kinds of experimental apparatus: an Erlenmeyer flask and bench bioreactor (2 L stirred-batch reactor STR), using mechanical (kitchen blade mixer) and chemical (HCl or NaOH for 24 h at 30 °C) pre-treated Organic Waste Market (OWM) refuse. The alkaline pre-treatment is the most efficient. A comparison of OWM efficiency with that of a glucose test under the same bench bioreactor experimental conditions, shows that the efficacy of energy production is 45%, which is equivalent to 7.3 L H2/kg as the gross material i.e. at its original undiluted strength. The paper shows that the two parameters are able to quantify the efficacy of energy production of such a bioprocess, including the pretreatment, using lignin-cellulose refuses, and to score different processes against glucose. [Copyright &y& Elsevier]

Abstract: A process aimed at producing energy needs to produce more energy than the energy necessary to run the process itself in order to be energetically sustainable. In this paper, an energy balance of a batch anaerobic bioreactor has been defined and calculated, both for different operative conditions and for different reactor scales, in order to analyze the sustainability of hydrogen production through dark anaerobic fermentation. Energy production in the form of hydrogen and methane, energy to warm up the fermentation broth, energy loss during fermentation and energy for mixing and pumping have been considered in the energy balance. Experimental data and literature data for mesophilic microorganism consortia have been used to calculate the energy balance. The energy production of a mesophilic microorganism consortium in a batch reactor has been studied in the 16–50 °C temperature range. The hydrogen batch dark fermentation resulted to only have a positive net production of energy over a minimal reactor dimension in summer conditions with an energy recovery strategy. The best working temperature resulted to be 20 °C with 20% of available energy. Hydrogen batch dark fermentation may be coupled with other processes to obtain a positive net energy by recovering energy from the end products of hydrogen dark fermentation. As an example, methane fermentation has been considered to energetically valorize the end products of hydrogen fermentation. The combined process resulted in a positive net energy over the whole range of tested reactor dimension with 45–90% of available energy. [ABSTRACT FROM AUTHOR]

Bioethanol is one of the most promising renewable energy sources, and it can be used as an alternative to petroleum-derived products. Agro-food residues are the substrates most frequently used for bioethanol production through anaerobic fermentation. The cultivation of olive trees and olive oil production are important economic activities throughout all Mediterranean countries. The wastes derived from olive oil production include a liquid waste, known as Olive Mill Wastewater (OMW), and a semi-solid waste, called Olive Pomace (OP), which is rich is lignin and cellulose materials. The aim of this work is to evaluate the quantity of hydrogen and bioethanol that could be extracted from an OMW-OP mixture after Saccharomyces cerevisiae anaerobic fermentation. In addition, different pretreatments (ultrasonic pretreatment, basic pretreatment, and calcium carbonate addition) have been tested to increase the glucose concentration and, consequently, the bioethanol and hydrogen production in the reaction medium and to decrease the content of inhibiting polyphenols which are mainly present in the OMW. All of the pretreatments were shown to have improved the hydrogen and bioethanol concentration at the end of the fermentation. The basic and ultrasonic pretreatments resulted in the best bioethanol and hydrogen production. These two pretreatments contributed to the hydrolysis of the lignin and cellulose and to increasing the soluble sugars (in particular glucose) content in the reaction mixture. Calcium carbonate addition decreased the polyphenol concentration; the polyphenols inhibit the fermentation mediated by S. cerevisiae . [ABSTRACT FROM AUTHOR]

Food stores can find themselves in the position of having to dispose of different types of products, such as snacks, confectionery, prepackaged food, drinks and others, Sweet Product Residue (SPR), which presents a great opportunity to produce energy through Anaerobic Digestion (AD), due to its high sugar, carbohidrate and fat contents. In order to valorise SPR, this paper takes into consideration the all necessary treatments; owing the fact that the refuses are constitute by an organic part and packaging (plastic, paper and their combinations), a pretreatment able to remove the latter is necessary. SPR refuse was initially subjected to novel pretreatment approach: extrusion at 200 atm to remove the packaging, and a Basic Pre-treatment (BP) then tested through a Two-Stage AD (TSAD) process, for H 2 and CH 4 productions. The experimental results were analysed considering three parameters: Efficiency ( ξ ), which takes into account the quantity of the energy produced as hydrogen plus methane that the bioreaction is able to extract; Efficacy ( η ) , which takes into account the efficiency of the actual test, compared with that obtained from a reference test carried out with glucose; Energy Sustainability Index ( ESI ), which takes into account the total amount of energy produced as H 2 plus CH 4 , and the amount of energy consumed to pre-treat the refuse. The effectiveness of the extrusion process in removing the packaging was very high: about 80% of the organic part present in the SPR was recovered. The obtained results have pointed out that SPR is suitable for energy valorization process: ξ = 50%, η = 0.67 and ESI = 24.4, without the need of basic pre-treatment. [ABSTRACT FROM AUTHOR]

In an effort to produce more energy using organic wastes as an energy source, multistep anaerobic digestion (MAD) has gained attention in recent years. The energy potentiality of the MAD approach has been verified experimentally using two carbon sources: glucose, as the more easily biodegradable carbon source, and a rich lignocelluloses material (coffee seed skin) waste. Energy production is analysed by evaluating the energy produced as hydrogen plus methane using the efficiency (η) parameter to determine the energy produced versus the energy embedded in the sources. Four fermentation tests, each repeated three times, were performed: one-step and two-step AD with glucose, and one-step and three-step AD with coffee seed skins (including a pretreatment step). The two-step AD efficiency (η = 74.5%) using glucose was 48% higher than the one-step AD (50.4%), while the efficiency using lignocelluloses material was 28.5% (2.4 times higher than the one-step AD). The specific methane production reached 0.15 NL CH4 /g TVS using coffee seed skin, which is approximately 3-fold higher than the one-step AD (0.05 NL CH4 /g TVS ). This study confirms that the MAD process offers an opportunity to extract more energy from organic refuse that the one-step AD. [ABSTRACT FROM AUTHOR]