{"id":37075,"key":"Biogas_fueled_electricity_plant","title":"Biogas fueled electricity plant","latest":{"id":1208359,"timestamp":"2025-11-28T00:00:14Z"},"content_model":"wikitext","license":{"url":"https://www.appropedia.org/Appropedia:Copyrights","title":"CC-BY-SA-4.0"},"source":"How much [[biogas]] could a sewage treatment plant produce from a population of 100,000 people through a well-planned sewer system?\n\nHere is a quick back of the envelope calculation to get this page started. Please find sources or corrections for these assumptions.\n\n== Assumptions ==\n\n* personal effluent = 120 liters/(person*day)\n* Effluent dirtyness = 800 mg<sub>BOD</sub>/l\n* biogas coefficient = 0.395 l<sub>biogas</sub>/g<sub>BOD</sub><ref>1 gram COD = 395 mL methane @ 35°C, 1 atm from http://fyi.uwex.edu/midwestmanure/files/2013/03/Myths-Minsconceptions-of-Digesters-Zitomer.pdf</ref>\n* digestor efficiency = 0.85\n* energy density of biogas = 0.036 MJ/l<ref>http://www.biomotion-tour.eu/media/downloads/brochures/BIOMOTION_biogas_EN_DEF.pdf</ref>\n\n== Calculations ==\n\nSo\n\n:''Volume = 100,000 people * 120 liters/(person*day) * 800 mg<sub>BOD</sub>/l * 1 g/1000 mg * 0.395 l<sub>biogas</sub>/g<sub>BOD</sub> * 0.85 = 3,223,200 liters/day of biogas''<ref>According to http://www.ncbi.nlm.nih.gov/pubmed/24185054, an improved biogas system can produce 12.5 m^3 per population equivalent per year. That is equivalent to 34.2 l/day/person which is close to our calculations.</ref>\n\nand\n\n:''Energy = 3,223,000 l/day *.036 MJ/l = 116,000 MJ/day (or about 32,232 kWh/day)''\n:''Energy/person = 116,000 MJ/day / 100,000 people = 1.16 MJ/person/day (or about 0.32 kWh/person/day)\n''\nBy comparison, in 2008, the per capita primary energy consumption of the United States was [[Wikipedia:World energy consumption|87,216 kWh/yr]] or 239 kWh/day. Thus in a developed country such as the US, the energy recoverable from a person's bodily wastes can only provide a tiny fraction of his or her primary energy consumption.\n\nBy another comparison, in 2009, the average annual electricity use for a U.S. home was about 11.7 kWh/person/day.<ref>\"In 2009, the average annual electricity consumption for a U.S. residential utility customer was 10,896 kWh, an average of 908 kilowatthours (kWh) per month\" from http://www.eia.gov/tools/faqs/faq.cfm?id=97&t=3 and average household size in 2000 was 2.59 people from http://factfinder.census.gov/servlet/SAFFFacts. So 908 kWh / 2.59 people / 30 day/month = 11.7 kWh/person/day.<ref>So biogas could meet 0.32 kWh / 11.7 kWh = 2.7% of our daily electricity usage.\n\n== Comparison with food intake ==\n\nThe energy content of human waste cannot exceed the energy content of the food that humans eat (energy in equals energy out plus accumulation). If the average person eats 2,500 [[Wikipedia:Calorie|food calories]] per day, that is equal to:\n\n* 2,500 Cal * 4.184 kJ/Cal = 10,460 [[Wikipedia:Kilojoule|kJ]]\n* 2,500 Cal * 0.001163 kWh/Cal = 2.9075 [[Wikipedia:Kilowatt-hour|kWh]]\n\nIf a biogas plant produces 61,000 kWh/day from the waste of 100,000 people, that represents about 61,000 kWh / 290,750 kWh = 21% of the energy content of the food they eat. Thus the 61,000 kWh figure satisfies the [[Wikipedia:sanity check|sanity check]] of being less than the energy content of the food eaten by the people producing the sewage. The actual energy content of human waste varies with diet. For example, diets higher in [[Wikipedia:Dietary fiber|fiber]] produce larger stool volume, i.e. the human digestive tract recovers less of the energy content of the food and more of it ends up in feces.\n\n== See also ==\n\n* [[Economic analysis of a biogas digester]]\n\n== References ==\n\n<references />\n\n{{Page data\n| license = CC-BY-SA-3.0\n}}\n\n[[Category:Biogas]]"}