The City of Ames, IA uses methods to turn its trash into energy rather it than ending up in the landfill. That’s because the Ames power plant uses something called refuse-derived fuel (RDF), a combustible material produced from Story County’s garbage. This resource recovery serves as the county’s primary method of waste disposal, preventing much of the garbage from ending up in a landfill.
“Landfilling garbage has its own environmental consequences, so (refuse-derived fuel) was looked at as being pretty progressive then,” said Bob Haug, former director of the Iowa Association of Municipal Utilities. “I just don’t know if it still is.”
Ames’ refuse-derived fuel system began in 1975 as a solution to a rapidly-filling landfill. The idea to utilize the city’s waste as a form of fuel was based on a pilot program being tested in St. Louis, which demonstrated the ability to boil water by burning garbage, powering a turbine which could produce electricity. By converting the Ames’ already existing power plant to one which could utilize RDF, Story County’s dependence on landfill was greatly reduced.
Lorrie Hanson, speaking for the city’s Resource Recovery System, said using waste as fuel is as important today as it was when the program began. “I don’t believe it’s outdated — I believe landfills are outdated,” Hanson said. “The way that these landfills are designed makes it virtually impossible for decomposition to occur within a landfill, and the little [decomposition] that does occur will produce methane for many years to come, passively.”
Hanson said even landfills properly equipped with modern systems release a non-negligible amount of methane in addition to leachate, a liquid created when water mixes with toxic substances leached from the trash. Hanson also said the plant is more heavily regulated than other power plants due to the nature of its fuel.
Haug’s research has focused on the economic aspects of Ames’ power plant, comparing its cost to alternative sources of energy. Iowa is a part of the Midcontinent Independent System Operator (MISO) network, a marketplace for the buying, selling and distribution of energy in areas ranging from Louisiana to Manitoba, Canada. MISO prices energy based on real-time supply and demand, from sources including wind, solar and coal-based systems.
“These numbers are rough, but it’s about 6 cents per kilowatt-hour (kWh) to produce energy at the local power plant with a mixture of natural gas and refuse-derived fuel,” Haug said. “We have to run our power plant in order to be able to burn garbage, and so we’re burning garbage with gas at 6 cents per kWh at times when the market is 3 cents (per kWh).”
He said the average price per kWh on the MISO network was, on average, lower than that of the Ames power plant. On some days, Haug said, the supply of electricity can be high enough that the price per kWh can actually drop below zero. “On a windy day, or even on a moderately windy day, the state produces more kWh from wind energy than we have uses for or the transmission capacity to export,” Haug said. “We price electricity to make an incentive to decrease production, and so prices actually become negative so that it costs a power producer to put a kWh of electricity on the grid during these periods of high wind production. Those conditions occur quite often in Iowa, and we’re missing the opportunities to purchase at that price.”
Hanson said the price to produce electricity at the local plant may be higher than that of external sources, but said its operation was still critical. “That’s our charge — we are here to responsibly, sustainably and locally deal with our municipal solid waste,” Hanson said.