tailieunhanh - Ebook The microbiology of anaerobic digesters: Part 2

(BQ) Part 2 book "The microbiology of anaerobic digesters" presents the following contents: Biogas, introduction to operational conditions, start up, sludge feed, retention times, temperature, nutrients, alkalinity and pH, upsets and unstable digesters, foam and scum production and accumulation, types of anaerobic digesters. | 9 Biogas Anaerobic digestion of municipal sludges results in the production of a mixture of gases Figure . Collectively these gases are referred to as digester gas or biogas. The only gas of economic value that is produced in an anaerobic digester is methane. In a properly operating digester most of the gas produced from a day s feed sludge appears within 24 hours. Methane can be used as a source of fuel. It is a natural flammable gas. Methane is odorless and burns cleanly Equation . Pure methane has a heat value of 1 000Btu ft3. When methane is mixed with carbon dioxide that is produced in an anaerobic digester its heat value decreases significantly. CH4 2O2 CO2 2H2O Typically biogas production in municipal anaerobic digesters is between 10 and 25 ft3 per pound of volatile solids degraded cu ft lb VS or kg VS. The heat value of biogas is approximately 500-600 Btu ft3 much lower than that of methane because of the dilution of methane by carbon dioxide. With increasing quantities of carbon dioxide in biogas decreasing heat values of biogas occur. If the carbon dioxide content of biogas becomes too large biogas will not allow for a self-sustained burn and supplemental fuel will be required. If the carbon dioxide fraction in the biogas increases above 30 the acid concentration in the sludge increases and the pH drops below . At pH values below significant acid fermentation occurs. The Microbiology of Anaerobic Digesters by Michael H. Gerardi ISBN 0-471-20693-8 Copyright 2003 by John Wiley Sons Inc. 73 74 BIOGAS Figure Anaerobic respiration occurs in the sewer main. Anaerobic respiration occurs in the biofilm lining the inside of the sewer main and in the sediment. Numerous gases are produced in an anaerobic digester. The gases produced in largest quantities are methane and carbon dioxide. By volume methane is 60 to 65 and carbon dioxide is 35 to 40 . Most municipal wastewater treatment plants use biogas to heat digesters to 32-35 C .

• Sinh học
• The microbiology of anaerobic digesters
• Introduction to operational conditions
• Unstable digesters
• Scum production and accumulation
• Types of anaerobic digesters
• Anaerobic digesters versus aerobic digesters
• Methane forming bacteria
• Anaerobic food chain
• Substrates and products
• Fermentation and fermentation