A popular television commercial claims “happy cows come from California.” What if these “happy cows” could somehow help their coastal home state? Now they can – by defecating. Manure, cow feces, is a commonly used fertilizer, but studies have shown that it can also be an energy source of the best kind: renewable. In a state like California which has over 1.7 million cows, that could potentially be a significant amount of energy for use by small municipalities for treatment of wastewater while lowering their carbon footprints.
Anerobic digestion, the breakdown of organic substances without the presence of oxygen, is very commonly used in wastewater treatment practices as well as in the stabilization of animal wastes and produces methane as well as carbon dioxide.
Methane is a highly potent green house gas (GHG) with 23 times the warming potential of carbon dioxide. To our advantage, it can also be burned to become a power source. However, digestion of manure on its own does not produce enough methane to be an economically viable power source.
Enter sludge: The foul-smelling, brown, slimy component of wastewater. A mixture of sludge and manure digested together, a technology known as co-digestion, can create enough methane to capture and reuse.
The Inland Empire Utilities Agency used this concept to conduct a pilot study on the co-digestion of dairy manure to energy in Ontario, California. Food waste was mixed with the manure in holding tanks and stored prior to digestion to further enhance methane production.
This mixture was then passed into a blending tank with two chambers with seventy five thousand gallon capacities each where no mixing took place. Gas produced in this stage was collected and sent to internal combustion engines. The mixture then passed into a digester where it met sludge and was mixed thoroughly. It remained there for nineteen days, producing methane gas that was collected and sent to engines.
At the end of the study period, the results showed that methane gas production increased by six hundred twenty cubic meters per day, generating additional power of about one hundred eighty thousand kilowatt-hours per year, enough power to operate four hundred forty nine water heaters.
However, changes will need to be made to the current facilities. The collected gas will require cleaning for particulate matter and plant upgrades will have to be made in order to have pretreatment and holding tanks for food-manure mixtures. The facility conducting the study made a $1.4 million capital investment to implement the system.
This type of technology paves the way to a future where waste management is made sustainable through the use of other waste - a truly symbiotic relationship between humans and animals. Its implementation in states with large numbers of dairy farms, such as Wisconsin, seems to be a logical step in the process of becoming a more sustainable nation, particularly in the wastewater treatment sector which is held to a higher standard meant to set an example for other sectors.