Dark fermentation

Dark fermentation

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Dark fermentation is the fermentative
Fermentative hydrogen production
Fermentative hydrogen production is the fermentative conversion of organic substrate to biohydrogen manifested by a diverse group of bacteria using multi enzyme systems involving three steps similar to anaerobic conversion. Dark fermentation reactions do not require light energy, so they are...

 conversion of organic substrate to biohydrogen
Biohydrogen
Biohydrogen is defined as hydrogen produced biologically, most commonly by algae and bacteria. Biohydrogen is a potential biofuel obtainable from both cultivation and waste organic materials.-Introduction:...

. It is a complex process manifested by diverse group of bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 by a series of biochemical reactions involving three steps similar to anaerobic conversion
Anaerobic digestion
Anaerobic digestion is a series of processes in which microorganisms break down biodegradable material in the absence of oxygen. It is used for industrial or domestic purposes to manage waste and/or to release energy....

. Dark fermentation differs from photofermentation
Photofermentation
Photofermentation is the fermentative conversion of organic substrate to biohydrogen manifested by a diverse group of photosynthetic bacteria by a series of biochemical reactions involving three steps similar to anaerobic conversion...

 because it proceeds without the presence of light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...

.

Fermentative/hydrolytic microorganisms hydrolyze complex organic polymers to monomers which are further converted to a mixture of lower molecular weight organic acids and alcohols by obligatory producing acidogenic bacteria.

Utilization of wastewater
Wastewater
Wastewater is any water that has been adversely affected in quality by anthropogenic influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry, and/or agriculture and can encompass a wide range of potential contaminants and concentrations...

 as a potential substrate for biohydrogen
Biohydrogen
Biohydrogen is defined as hydrogen produced biologically, most commonly by algae and bacteria. Biohydrogen is a potential biofuel obtainable from both cultivation and waste organic materials.-Introduction:...

 production has been drawing considerable interest in recent years especially in the dark fermentation process. Industrial wastewater as a fermentative substrate
Substrate (chemistry)
In chemistry, a substrate is the chemical species being observed, which reacts with a reagent. This term is highly context-dependent. In particular, in biochemistry, an enzyme substrate is the material upon which an enzyme acts....

 for H2 production addresses most of the criteria required for substrate selection viz., availability, cost and biodegradability (Angenent, et al., 2004; Kapdan and Kargi, 2006). Chemical wastewater (Venkata Mohan, et al., 2007a,b), cattle wastewater (Tang, et al., 2008), dairy process wastewater (Venkata Mohan, et al. 2007c), starch hydrolysate wastewater (Chen, et al., 2008) and designed synthetic wastewater (Venkata Mohan, et al., 2007a,2008b) have been reported to produce biohydrogen
Biohydrogen
Biohydrogen is defined as hydrogen produced biologically, most commonly by algae and bacteria. Biohydrogen is a potential biofuel obtainable from both cultivation and waste organic materials.-Introduction:...

 apart from wastewater treatment
Sewage treatment
Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...

 from dark fermentation processes using selectively enriched mixed cultures under acidophilic conditions. Various wastewaters viz., paper mill wastewater (Idania, et al., 2005), starch effluent (Zhang, et al., 2003), food processing wastewater (Shin et al., 2004, van Ginkel, et al., 2005), domestic
Home
A home is a place of residence or refuge. When it refers to a building, it is usually a place in which an individual or a family can rest and store personal property. Most modern-day households contain sanitary facilities and a means of preparing food. Animals have their own homes as well, either...

 wastewater (Shin, et al., 2004, 2008e), rice winery wastewater (Yu et al., 2002), distillery and molasses based wastewater (Ren, et al., 2007, Venkata Mohan, et al., 2008a), wheat straw wastes (Fan, et al., 2006) and palm oil mill wastewater (Vijayaraghavan and Ahmed, 2006) were also studied as fermentable substrates for H2 production along with wastewater treatment. Using wastewater
Wastewater
Wastewater is any water that has been adversely affected in quality by anthropogenic influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry, and/or agriculture and can encompass a wide range of potential contaminants and concentrations...

 as a fermentable substrate facilitates both wastewater treatment apart from H2 production. The efficiency of the dark fermentative H2 production process was found to depend on pre-treatment of the mixed consortia used as a biocatalyst, operating pH, and organic loading rate apart from wastewater characteristics (Venkata Mohan, et al., 2007d,2008c,d, Vijaya Bhaskar, et al., 2008d).

In spite of its advantages, the main challenge observed with fermentative H2 production processes are relatively low energy conversion efficiency from the organic source. Typical H2 yields range from 1 to 2 mol of H2/mol of glucose, which results in 80-90% of the initial COD remaining in the wastewater in the form of various volatile organic acids (VFAs) and solvents, such as acetic, propionic, and butyric acids and ethanol . Even under optimal conditions about 60-70% of the original organic matter remains in solution. Bioaugmentation
Bioaugmentation
Bioaugmentation is the introduction of a group of natural microbial strains or a genetically engineered variant to treat contaminated soil or water....

 with selectively enriched acidogenic consortia to enhance H2 production was also reported (Venkata Mohan, et al., 2007b). Generation and accumulation of soluble acid metabolites causes a sharp drop in the system pH and inhibits the H2 production process. Usage of unutilized carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 sources present in acidogenic process for additional biogas production sustains the practical applicability of the process. One way to utilize/recover the remaining organic matter in a usable form is to produce additional H2 by terminal integration of photo-fermentative processes of H2 production (Venkata Mohan, et al., 2008e) and methane by integrating acidogenic processes to terminal methanogenic processes.

See also

  • Biogas
    Biogas
    Biogas typically refers to a gas produced by the biological breakdown of organic matter in the absence of oxygen. Organic waste such as dead plant and animal material, animal dung, and kitchen waste can be converted into a gaseous fuel called biogas...

  • Biohydrogen
    Biohydrogen
    Biohydrogen is defined as hydrogen produced biologically, most commonly by algae and bacteria. Biohydrogen is a potential biofuel obtainable from both cultivation and waste organic materials.-Introduction:...

  • Biological hydrogen production (Algae)
  • Biomass
    Biomass
    Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

  • Electrohydrogenesis
    Electrohydrogenesis
    Electrohydrogenesis or biocatalyzed electrolysis is the name given to a process for generating hydrogen gas from organic matter being decomposed by bacteria. This process uses a modified fuel cell to contain the organic matter and water...

  • Fermentation (biochemistry)
    Fermentation (biochemistry)
    Fermentation is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. In contrast, respiration is where electrons are donated to an exogenous electron acceptor, such as oxygen,...

  • Microbial fuel cell
    Microbial fuel cell
    A microbial fuel cell or biological fuel cell is a bio-electrochemical system that drives a current by mimicking bacterial interactions found in nature....


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