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Published in Saeed Sahebdelfar, Maryam Takht Ravanchi, Ashok Kumar Nadda, 1 Chemistry, 2022
Saeed Sahebdelfar, Maryam Takht Ravanchi, Ashok Kumar Nadda
The anaerobic digestion involves four biological steps in series each with the aid of special microorganisms (Weiland, 2010): Hydrolysis. Hydrolysis of large organic molecules to simpler and soluble ones (e.g., carbohydrates to sugars and proteins to amino acids) by anaerobic bacteria.Acidogenesis. Conversion of the simple organic molecules to carbon dioxide, hydrogen, ammonia and organic acids (e.g., propionic acid) by acidogenic bacteria.Acetogenesis. Conversion of organic acids to acetic acid, along with additional hydrogen, ammonia and carbon dioxide by acetogenic bacteria.Methanogenesis. Decomposition of the acetic acid to methane and carbon dioxide by methanogenic bacteria.
Nanotechnology and Delivery System for Bioactive Antibiofilm Dental Materials
Published in Mary Anne S. Melo, Designing Bioactive Polymeric Materials for Restorative Dentistry, 2020
Jin Xiao, Yuan Liu, Marlise I. Klein, Anna Nikikova, Yanfang Ren
Dental caries is a dietary carbohydrate-modified bacterial infectious disease caused by biofilms and is one of the most prevalent chronic diseases of people worldwide (Paes Leme et al. 2006, Selwitz et al. 2007, Takahashi and Nyvad 2008). During the onset of dental caries, acidogenic bacteria like Streptococci could attach to enamel surfaces and metabolize dietary carbohydrates to organic acids. The frequent acidification favors the demineralization of enamel and selects for more aciduric species, like S. mutans, that further lower the environmental pH. Demineralization of enamel and degradation of the organic matrix in dentin lead to cavity formation and expansion (Takahashi and Nyvad 2011, 2016). It is the main cause of oral pain and tooth loss, affecting the oral health of human beings seriously and also creating a heavy financial burden; meanwhile, it has been associated with some systemic diseases as well (Fejerskov Ole 2003, Hu et al. 2011).
E. coli inactivation during excreta digestion in single-stage and two-stage systems
Published in Joy Nyawira Riungu, Off-Site Enhanced Biogas Production with Concomitant Pathogen Removal from Faecal Matter, 2021
Enhanced build-up of total VFA (TVFA) concentrations during co-digestion of sewage sludge and other organic waste can be achieved by inhibition of methanogenesis (Wang et al., 2014), through use of a two-stage reactor system, where hydrolysis/acidogenesis and methanogenesis are separated. The different species of micro-organisms involved in the AD process can be divided into two main groups of bacteria, namely organic acid producing and organic acid consuming or methane forming microorganisms (Rincón et al., 2008). They operate under different pH conditions: whereas the optimal pH for acidogenic bacteria activity ranges between 5 and 7 (Fang & Liu, 2002; Guo et al., 2010; Liu et al., 2006; Noike et al., 2005), methanogenic activity requires a minimum pH of 6.5 (Wang et al., 2014b; Yuan et al., 2006). Key drawback in the two-stage reactor is the high VFA concentration in the acidogenic reactor, which requires pH correction for stable methanogenesis (Zuo et al., 2014). Yet, the low pH and high VFA concentrations create very good pathogen inactivating conditions. Hence, an optimum must be found between good pathogen removal and well-functioning methanogenic digestion. In practice, the latter can be achieved by recycling part of the digestate upfront to be mixed with the acidified UDDT-FS-OMW.
Waste into energy conversion technologies and conversion of food wastes into the potential products: a review
Published in International Journal of Ambient Energy, 2021
Jeya Jeevahan, A. Anderson, V. Sriram, R. B. Durairaj, G. Britto Joseph, G. Mageshwaran
Co-digestion is a technique in which a variety of organic wastes are processed together in an anaerobic digestion system. This provides excess nutrients that stimulate biodegradation process, digestion rate and stabilisation. Co-digestion generally improves the yield of the anaerobic digestion systems (Shin et al. 2015). Anaerobic digestion involves both between acid-producing microorganisms (for acidogenic process) and methane-producing microorganisms (for methanogenic process). The growth rate of these acidogens and methanogens, substrate utilisation rate and sensitivity to environmental changes widely differ between acidogenic and methanogenic processes. Acidogenic process is relatively faster and is considered more stable during pH variation than that of the methanogenic process. Due to the unbalance between the growth rate and consumption of volatile fatty acids (VFAs), the problems like an accumulation of VFAs, low pH, and inhibition of methanogenic process may occur. The overloading of carbohydrates can lead to pH drop, while the overloading of proteins and lipids can cause inhibitory effects due to the increased levels of ammonia and long chain fatty acids. Due to these problems, significant efforts are required to avoid the anaerobic system failures (Chu et al. 2008).
Determinants of functional status of family size bio-digesters: empirical evidence from southern Ethiopia
Published in International Journal of Sustainable Energy, 2019
Biogas is a combustible gas that is mainly composed of methane (60–70%) and carbon dioxide (30–40%) (Kumar et al. 2011). Biogas is produced in anaerobic bio-digesters, which have a variety of designs and applications, ranging from small to large-scale operations. The anaerobic process involves the biological degradation of organic waste that produces both a nutrient-rich digestate as well as biogas. Anaerobic digestion consists of several interdependent, complex, sequential and parallel biological reactions that occur in the absence of oxygen. During this process, the products from one group of microorganisms serve as food for the next, resulting in the transformation of biomass, mainly into a mixture of methane and carbon dioxide (Mwirigi et al. 2014), which are major constituents of biogas. During the anaerobic digestion, a large number of active hydrolytic and acid-forming acidogenic bacteria, acting in concert, utilise organic substrates such as carbohydrates, proteins and lipids produce volatile fatty acids by acidogenesis, which are later converted to methane and carbon dioxide by methanogenic bacteria through methanogensis (Bond and Templeton 2011).
Shifts of acidogenic bacterial group and biogas production by adding two industrial residues in anaerobic co-digestion with cattle manure
Published in Journal of Environmental Science and Health, Part A, 2021
Guilherme Henrique da Silva, Nathan Oliveira Barros, Larice Aparecida Rezende Santana, Jailton da Costa Carneiro, Marcelo Henrique Otenio
The hydrolytic, acidogenic, and acetogenic bacteria, together with methanogens, are the key players acting at specific phases of the AB process and depend on each other for proper functioning. During this investigation, the Escherichia coli and Pseudomonas aeruginosa acidogenic bacteria were chosen to indicate the microbial population involved in the fermentation of the co-AD process. These acidogenic bacteria play a primary role in producing major substrates such as hydrogen, carbon dioxide, acetate, and short-chain organic acids, for methanogenesis.[42]