Pretreatment of Organic Wastes for Hydrogen Production
Various organic wastes can be used as low-cost substrate for fermentative hydrogen production, which significantly reduces the hydrogen production cost. Furthermore, biohydrogen production from organic wastes can achieve dual benefits of clean energy gene
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Pretreatment of Organic Wastes for Hydrogen Production
4.1
Overview
Organic wastes refer to the wastes rich in organic matters, which can be broken down into carbon dioxide, water, methane, or simple organic molecules by micro-organisms. Increasing living standard brings the increase of wastes generation. Take solid wastes as example, in US alone, municipal wastes generation increased from 88.1 million tons in 1965 to 258.5 million tons by 2014; in China, waste activated sludge production has increased from 3.25 to 6.25 million tons dry solids in 6 years by 2013 (Yang et al. 2015). Direct disposal of organic wastes may pollute water, air, and impair the living quality of human beings. Increasing amount of organic wastes is becoming a serious problem. The European Council Directive on the Landfill of Wastes 1999/31/EC provided that within 2016, landfilled biowaste production should be reduced to 35% of the amount produced in 1995 (Cesaro and Belgiorno 2014). Considering the energy contained in organic matters, energy recovery from organic wastes is attracting people’s attention. Quite a few studies have explored the feasibility of using various organic wastes as substrate for hydrogen production. The organic wastes used in dark fermentative hydrogen production mainly comprise waste activated sludge, algae biomass, cellulose-base biomass, food waste and organic wastewater. During the dark fermentation process, complex organic matters are firstly disintegrated into soluble matters, which mainly include proteins, carbohydrates and lipids. Then, these molecules are further hydrolyzed to smaller molecules like amino acids, monosaccharaides and long chain fatty acids. Then, it comes to the acidogenesis and acetogenesis process, besides the target product H2, a wide range of intermediates and byproducts include soluble metabolites and CO2 are formed. The terminal liquid products are mainly composed of acetate acid, butyrate acid, ethanol and propionic acid. The composition depends on microbial species, fermentation conditions as well as substrate sources and pretreatment process (Fig. 4.1).
© Springer Nature Singapore Pte Ltd. 2017 J. Wang and Y. Yin, Biohydrogen Production from Organic Wastes, Green Energy and Technology, DOI 10.1007/978-981-10-4675-9_4
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4 Pretreatment of Organic Wastes for Hydrogen Production
Fig. 4.1 Biodegradation steps and biological processes involved in fermentative hydrogen production from organic wastes
4.2
Main Structural Components of Organic Wastes
Composition of organic wastes is complex (Table 4.1), while anaerobic cultures are usually inefficient in hydrolyzing macromolecules. Thus, pretreatment is usually necessary to promote the disintegration and hydrolysis of biomass. During the pretreatment process, complex structures of biomass are collapsed, leaving free cells. Then, cell walls and membranes are solubilized, releasing the trapped components. Subsequently, crystal and polymeric structures of macromolecules are destroyed, generating molecules readily available for hydroge
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