Possibilities of upgrading solid underutilized lingo-cellulosic feedstock (carob pods) to liquid bio-fuel: Bio-ethanol production and electricity generation in fuel cells - A critical appraisal of the required processes

The exploitation of rich in sugars lingo-cellulosic residue of carob pods for bio-ethanol and bio-electricity generation has been investigated. The process could take place in two (2) or three (3) stages including: a) bio-ethanol production originated from carob pods, b) direct exploitation of bio-ethanol to fuel cells for electricity generation, and/or c) steam reforming of ethanol for hydrogen production and exploitation of the produced hydrogen in fuel cells for electricity generation. Surveying the scientific literature it has been found that the production of bio-ethanol from carob pods and electricity fed to the ethanol fuel cells for hydrogen production do not present any technological difficulties. The economic viability of bio-ethanol production from carob pods has not yet been proved and thus commercial plants do not yet exist. The use, however, of direct fed ethanol fuel cells and steam reforming of ethanol for hydrogen production are promising processes which require, however, further research and development (R&D) before reaching demonstration and possibly a commercial scale. Therefore the realization of power generation from carob pods requires initially the investigation and indication of the appropriate solution of various technological problems. This should be done in a way that the whole integrated process would be cost effective. In addition since the carob tree grows in marginal and partly desertified areas mainly around the Mediterranean region, the use of carob’s fruit for power generation via upgrading of its waste by biochemical and electrochemical processes will partly replace fossil fuels generated electricity and will promote sustainability

Case study of viability of bioenergy production from landfill gas (LFG)

The landfill gas (LFG) produced from the existing landfill site in Heraklion city, Crete island, Greece, is not currently exploited to its full potential. It could however be exploited for power generation and/or combined heat and power (CHP) production in near future by fully unlocking its energy production potential of the gas generated from the landfill site. This gas (LFG) could feed a 1.6 MWel power plant corresponding to the 0.42% of the annually consumed electricity in Crete. The LFG utilization for power generation and CHP production has been studied, and the economics of three energy production scenarios have been calculated. An initial capital investment of 2.4 to 3.2 M €, with payback times (PBT) of approximately 3.5 to 6 years and Net Present Values (NPV) ranging between 2 to 6 M € have been calculated. These values prove the profitability of the attempt of bioenergy production from the biogas produced from the existing landfill site in Heraklion city, Crete. Based on the current economic situation of the country, any similar initiative could positively contribute to strengthening the economy of local community and as a result the country, offering several other socioeconomic benefits like e.g. waste minimization, creation of new job positions etc. by increasing, at the same time, the Renewable Energy Sources (RES) share in energy production sector etc. Apart from the favorable economics of the proposed waste to energy production scheme, all the additional environmental and social benefits make the attempt of a near future exploitation of the landfill gas produced in Heraklion, an attractive short term alternative for waste to bio-energy production

Nanocarbons from acid pretreated waste coffee grounds using microwave radiation

This study investigates the use of microwave radiation to produce nanocarbons from Waste Coffee Grounds (WCG). It is first step to demonstrate the potential of integrating the microwave power to conventional methods of carbonaceous materials and nanocarbons production, aiming to overcome their high production cost. The process parameters and interactions investigated were: microwave radiation power (W), temperature (°C) and residence time (min). Results obtained from the lab-scale experiments indicated the optimum conditions for maximizing the nanocarbons yield (wt%) from the H₂SO₄ acid pretreated WCG at 200 °C, 850 for 60 min resulting in a 87.6 wt% char yield which ranged between the average size of 100–140 nm and lower. Moreover, the optimum conditions to achieve the maximum yield of nanocarbons (wt%) where: same temperature (200 °C), lower microwave power (650 W) and residence time (45 min). Then a yield of 60 wt% nanocarbons of average sizes 60 nm were produced, indicating the potential of this method to produce value-added biomaterials (spherical shaped nanocarbons) applicable for future scientific breakthroughs

Wheat straw bio-refining. Part II: Optimization of the microwave radiation with sulphuric acid pre-treatment and its enzymatic hydrolysis for fermentable sugars

Background: The potential of microwave-assisted heating for enhancing the alkaline pretreatment of lignocellulosic waste is highlighted in this work.Objective: To maximize separation of fermentable sugars from wheat straw.Methods: Wheat straw hydrolysis assisted by microwave was carried out by setting up a statistical experimental design method and further investigating the main process parameters, namely: temperature (°C), microwave power (W), NaOH concentration (M) and wheat straw pre-treatment time (min) towards maximization of fermentable sugars extraction from wheat straw. The reducing sugars yield (response) of the alkaline pre-treated and microwaved wheat straw in lab scale provided data for building a predictive model which reflected interactions, significance and impact of the process parameters (factors) on the wheat straw hydrolysis yield.Results: SEM and FTIR images of untreated and alkaline pre-treated wheat straw were studied for investigating the morphological changes of wheat straw surface quality and structure resulting from the microwave and/or alkaline pre-treatment. In addition reducing sugars yield of 87%wt. from wheat straw pre-treated at 180°C, 550W microwave power, 0.65M of NaOH for 25min was achieved. This result was significantly higher compared to the one from the straw which was only hydrolysed enzymatically (30 %wt).Conclusion: It was found that shorter pre-treatment times were obtained at higher temperatures, alkali concentration and moderate microwave power levels. The results obtained were further optimized and indicated that the microwave-assisted alkaline pre-treatment of wheat straw technique is an attractive pre-treatment method which reduces the wheat straw pre-treatment time and enhances the hydrolysis yield

Probing synergies between lignin-rich and cellulose compounds for gasification

The fixed bed gasification of lignin rich and deficient mixtures was carried out to probe the synergistic effects between two model compounds, Lignin Pink (LP) rich in Na and Cellulose Microcrystalline (CM). Reaction conditions utilized the most commonly used air ratios in current wood gasifiers at 750 °C and 850 °C. It was found that by increasing the lignin content in the mixture, there was a selectivity change from solid to gas products, contrary to a similar study previously carried out for pyrolysis. This change in product mix was promoted by the catalytic effect of Na edge recession deposits on the surface of the char. As a result, the water gas shift reaction was enhanced at 850 °C for the LP48CM52 mixture across all air ratios, this was evidenced by a strong correlation between the produced H2 and COx. Meanwhile, by lowering the lignin content in the mixtures, the reactivity of cellulose microcrystalline was found to generate more char at higher temperature, similar to lignin mixtures when undergoing pyrolysis

Airborne transmission of biological agents within the indoor built environment: a multidisciplinary review

The nature and airborne dispersion of the underestimated biological agents, monitoring, analysis and transmission among the human occupants into building environment is a major challenge of today. Those agents play a crucial role in ensuring comfortable, healthy and risk-free conditions into indoor working and leaving spaces. It is known that ventilation systems influence strongly the transmission of indoor air pollutants, with scarce information although to have been reported for biological agents until 2019. The biological agents’ source release and the trajectory of airborne transmission are both important in terms of optimising the design of the heating, ventilation and air conditioning systems of the future. In addition, modelling via computational fluid dynamics (CFD) will become a more valuable tool in foreseeing risks and tackle hazards when pollutants and biological agents released into closed spaces. Promising results on the prediction of their dispersion routes and concentration levels, as well as the selection of the appropriate ventilation strategy, provide crucial information on risk minimisation of the airborne transmission among humans. Under this context, the present multidisciplinary review considers four interrelated aspects of the dispersion of biological agents in closed spaces, (a) the nature and airborne transmission route of the examined agents, (b) the biological origin and health effects of the major microbial pathogens on the human respiratory system, (c) the role of heating, ventilation and air-conditioning systems in the airborne transmission and (d) the associated computer modelling approaches. This adopted methodology allows the discussion of the existing findings, on-going research, identification of the main research gaps and future directions from a multidisciplinary point of view which will be helpful for substantial innovations in the field

Mobile gasification units for sustainable electricity production in rural areas: the SMARt-CHP project

This paper presents a 5 kW th biomass gasification pilot unit along with experimental results concerning producer gas composition. A chemical equilibrium mathematical model is also introduced and a comparison of measured and calculated results is presented. The experience gained from the unit operation led to the idea of manufacturing a mobile gasification unit able to utilize agricultural wastes in rural areas of Greece. In this project, called SMARt-CHP, the biomass gasifier coupled to an internal combustion engine will be extensively used under real world conditions for combined heat and power production, using different types of residues (wine prunings, corn stalks, etc.) characteristic of agriculture in Northern Greece. The main aims of SMARt-CHP are to attempt to demonstrate how logistics and biomass availability problems can be addressed, to inform the general public about the particular environmental issues, concerns, and opportunities in decentralized bioenergy production from agricultural residues, and to promote the applicability of a mature technology, bridging the gap between technology development and application. © 2010 American Chemical Society