Trigg Ruehle

Human Waste to Usable Energy: Opportunities and Obstacles Introduction

•Reducing waste is one of the key issues our world faces today.•There has been tremendous push to increase recycling, reduce emissions, and decrease energy consumption. •One type of waste that is usually set aside or ignored which contains a significant amount of energy is our own human waste.•Disposing of human waste is a problem many societies have struggled and may result in fatal consequences.•It’s improbable that humans will be able to reduce human waste by modifying their own biological processes. •There is a sufficient amount of extractable energy remaining in human waste after the food is ingested and leaves the body. •This energy is often disregarded in today’s contemporary waste treatment plants.

http://spotlightchange.com/wp-content/uploads/2012/06/Sanergysustainable-Cycle.jpg

Background Information•The mass of human waste feedstock is mainly dependent on the amount of fiber that is consumed.•The consumption of high fiber in a person’s diets can provide up to four times the amount of wet-stool mass then a person with a shortage of fiber. [1]

• Adult with high fiber diet produces 349 grams of wet stool a day. [1]

•Estimation of human waste produced in the world in a year is 866 billion kilograms. [1]•Water makes up around 70% of human stool weight meaning 260 billion kilograms may be used as attainable fuel. [1]•Energy content of dry human waste is 2.3*10^7 J/kg

• Water goes through various treatment and cleaning stages and then is put back into the environment

• The sludge is sent to large tanks called digesters where the human waste is heated and the waste goes through a process known as “anaerobic digestion”. [5]

• Bacteria breaks down the biodegradable material which produces gas. [5]

• The gas is then recovered and sent to a gas cleaning machine to turn it into bio methane.

• After the bio methane is cleaned and smells like normal gas, the bio methane is fed to the natural gas grid. [5]

• Now the bio methane is in the gas network and is returned to people’s homes to use for various things such as heating and cooking.

http://inhabitat.com/uk prepares-to-use-human-poop-to-power-homes/

References[1] Cash, William. "Sewage Energy." Sewage Energy. Stanford

University, 28 Nov. 2010. Web. 10 Dec. 2013.

[2] Haindl, Sangeeta. "Loo Power: Human Waste for Energy!?" Justmeans. 3 BL Media, 11 Aug. 2013. Web. 10 Dec. 2013.

[3] Liggett, Brit. "UK Prepares to Use Human Poop to Power Homes | Inhabitat - Sustainable Design Innovation, Eco Architecture, Green Building." Inhabitat Sustainable Design Innovation Eco Architecture Green Building UK Prepares to Use Human Poop to Power Homes Comments. Inhabitat, 19 Apr. 2010. Web. 10 Dec. 2013.

[4] Lokko, Jessica Campell. "Ghana Turning Human Waste into Energy." Poop Power: Ghana Turning Human Waste into Energy. Thestar.com, 15 Sept. 2013. Web. 10 Dec. 2013.

[5] Goodier, Rob. "Ten Ways to Put Human Waste to Use." Engineering for Change. Engineering for Change, 21 Nov. 2012. Web. 10 Dec. 2013.

• A high fiber population could provide 5.98*10^18 J/year (World energy consumption 10^20 J/year) [1]

• A significant amount of the energy used in the world today goes towards waste treatment plants.

• Developed societies use plumbing to transport human waste to large treatment centers.

• In developing nations human waste can be dumped into water or exposed to air in order to remove the moisture content.

Possible Constraints • The feedstock is mostly water which makes

extraction of usable fuel expensive and complicated. [1]

• Drying and burning is possible, but the varied composition of feces and other matter will cause poor combustion and numerous emissions. [3]

• Working with these materials will be very unpleasant and a potential health hazard from the bacteria and diseases associated with fecal matter.

http://www.weblife.org/humanure/chapter3_7.html

Possible Opportunities

• In areas with no centralized plumbing, individual or community digesters can be used to extract energy for cooking and heating. [2]

• Impoverished country’s have the ability to produce 50% of needed energy from their waste and stop spread of disease from fecal matter. [4]

• Farms around the world can use their animal waste to power their facilities and even sell electricity back to the grid. [5]

• Potential quantity of methane produced at plants is significant enough to be used to generate electricity on a large-scale. [4]

• The methane can be used to generate hydrogen for fuel cells and gas turbines.

Potential SolutionsRural/ Poverty Stricken Nations • Collect waste from public toilets, homes, and

businesses and separate solid garbage from liquid garbage.

• Liquid waste is sent through a pump containing a 5/10000 ratio of polymer to water. [5]

• Polymer is used to remove the liquid from the waste (Separate the waste from fluid)

• The sludge waste is composted in drying beds and used as fertilizers for crops. [5]

• May be dried completely in ovens and broken down into small pellets. [5]

• Emit less carbon when burned as a biofuel.

http://www.thestar.com/news/world/2013/09/15/poop_power_ghana_turning_human_waste_into_energy.bb.html

Urban/Developed Nations • Human waste from toilets, baths, and sinks is

pumped from homes to sewage treatment plants.• The human waste enters settlement tanks to separate

the water from the sludge.

Biorenewable Systems