Industrial energy demands are rapidly outpacing the available fossil fuel sources, and the need for alternative energy sources is widely recognized.
Biogas production is fast gaining importance as a source of renewable energy apart from being a waste management solution. Energy and Environmental Experts have proposed biogas as one of the new sources. Biogas is a combustible mixture of gases produced from anaerobic digestion of organic material by a community of mycobacteria. Biogas is naturally produced in large quantities by landfills and waste-water treatment plants. Many farmers all over the world have invested in anaerobic digesters to produce small quantities of biogas from organic waste. Because of the wide availability and renewable nature of the organic materials and microbes required for biogas synthesis, biogas is a potentially effective and a sustainable energy source. Compared to natural gas, biogas production, processing, and use generate lower greenhouse gas emissions.
Biogas typically consists of 45-75% methane, 25-55% carbon dioxide (CO2), and small amounts of other compounds like hydrogen sulfide (H2S) and ammonia (NH3), ranging from hundreds to a thousand parts per million.
The methane in biogas is a valuable source of energy, while other components are impurities that pose major impediments to the commercial use of biogas.
The variable composition is due to the variety of materials that can be used for production of the biogas. CO2 has no energy yield through combustion and greatlyreduces the energy yield per volume of biogas due to its high concentration. H2S is toxic and highly corrosive, often damaging machinery used to transport and produce energy from biogas. It also forms a harmful pollutant, sulfur dioxide, upon combustion.
Removal of these impurities is necessary to make biogas an effective energy source.
5 Current methods of biogas purification involve chemical or mechanical processes, including chemical
scrubbing, chemical adsorption, filters, and membranes.
Operating conditions of bioreactors
- Temperature is an important parameter of fermentation, since, in the cultivation of many microorganisms, the temperature deviation by a couple of degrees can diminish dramatically the growth and biosynthesis productivity. Therefore the temperature needs to be monitored and controlled.
- The appearance of foam is a very undesirable phenomenon, because during its appearance, there is a risk to lose an essential part of the fermentation broth. While there is foaming, it is not possible to perform high-quality analyses and measurements hence the need to eliminate the foam.
- High hydraulic retention times are commonly used in bioreactors, as they provide greater contact time between substrate and biomass.
- The pH of a substrate has a significant effect on biogas production, because it affects the activity of bacteria to destroy organic matter into biogas. A low pH in the digester inhibits the activity of microorganisms involved in the digestion process particularly methanogenic bacteria.
- C/N Ratio
Bio-reactors that are not operated under optimal conditions are not efficient because they do not reach their potential in biogas production thus not effectively using the biomass energy. Optimization of Bio-reactor is the first step towards achieving energy efficiency of biomass energy.