Planting the seed

A field trip to a landfill may not be a child’s idea of fun, but students in Bethlehem, New Hampshire, are breaking that stereotype. The North Country Environmental Landfill in Bethlehem provides more than just a look at waste, it also gives students an opportunity to learn how to grow plants in a greenhouse heated with a geothermal system.

“The kids just love going there. They’re constantly asking when they can go back and what can they do there,” Steve Hoyt, library, media and STEM (science, technology, engineering and math) technology administrator at Bethlehem Elementary School, says. “It gets them thinking about agriculture, and they can bring the plants back.”

GOING GREEN

Kevin Roy is site operations manager for the North Country Environmental Landfill, operated by Rutland, Vermont-based Casella Waste Systems Inc. He says the landfill began using geothermal heating after he raised the question of how heat generated at the landfill could be recovered for the site maintenance building.

He partnered with Bob Grillo, vice president, chief geotechnical engineer and project manager for CMA Engineers, Portsmouth, New Hampshire, and in August 2011 created the system that the greenhouse and landfill still use.

“The landfill generates heat and is 20 to 40 degrees Fahrenheit hotter than the ground,” Roy says. “The landfill geothermal system is much more efficient and economical than a conventional below-ground-based system.”

The system uses 1½-inch high-density polyethylene (HDPE) piping placed 2 feet apart to cover 10,000 square feet of landfill liner. The pipes use roughly 75 gallons of water per minute to collect the heat from the landfill and spread it to the maintenance building and greenhouse.

“The system is always operating at a 70-degree-Fahrenheit temperature in the winter, as opposed to a conventional in-ground system that’s operational at 32 degrees because of low ground temperatures,” Grillo says. “Landfills are always generating heat, so it’s super efficient.”

The system generates around 250,000 British thermal units (Btu) per hour, equal to roughly enough heat for three homes. The original system pilot, installed in 2012, cost around $50,000 to build, and the return on investment took around five years. The pilot was paid for by the landfill owner, North Country Environmental Services (NCES).

Roy and Grillo say an expansion is underway that will make the system five times its current size to generate heat for buildings and greenhouses in a neighboring industrial park. The expansion will create six times the total capacity, generating enough energy for 18 to 20 homes.

Roy says, “The project is living proof that landfill geothermal is viable. It has become the center of open houses and site tours.”

The project’s success caused Casella to implement three more geothermal projects at different landfills.

Once the pilot project ran for two winters and Roy confirmed there were additional Btu left in the system, he contacted Hoyt and asked if they would be interested in building a greenhouse classroom for the elementary school.

HOW IT’S MADE

Hoyt and Roy have been friends for five years. But before collaborating with Roy, Hoyt was working in a remote greenhouse with a retired teacher. “It was a plain, plastic-type greenhouse,” he says.

The pair of teachers used a coil from a warehouse to create a wood-powered boiler system to keep it warm during the winter. They also installed an Arduino system, a motherboard that monitors soil and air moisture and temperature. With the Arduino system, a user can monitor these levels remotely.

“Kevin knew I was involved for quite a while, and we started bantering back and forth,” Hoyt says. “Then he said, ‘We can do one of those over here.’ And we decided that, yes, we’ll build a greenhouse.”

Roy, Hoyt and Grillo formed a committee to build the greenhouse, which started as a basic structure, much like the one Hoyt used. But, as students started to participate, the team decided to build an engineered greenhouse.

“There are approved specs on it, it’s made of steel and it’s structurally sound,” Hoyt says. “That added to the expenses—it’s not your run-of-the-mill greenhouse.”

The greenhouse was built by Stuppy Greenhouse Manufacturing Inc. of North Kansas City, Missouri, and is 18 feet wide by 24 feet long with a 10-foot sidewall height. Columns in the greenhouse were manufactured from 4-inch-by-2-inch steel or from 4-inch-by-4-inch steel with a minimum yield strength of 50,000 pounds per square inch (psi).

The top and bottom cords of the roof trusses were made from 3-inch-by-2-inch steel, and aluminum connections attach the truss webbing to the cords.

Roof purlins made of 3-inch-by-2-inch steel were connected to the trusses using bolts, and end walls were framed by 3-inch-by-2-inch rectangular steel tubing. The roof, side walls and end walls of the structure were covered with double-walled polycarbonate.

Hoyt says heat comes up from under the plant beds, 16-foot-by-14-foot structures with 12-foot-by-8-foot beds, heating the soil and beds simultaneously.

“Students can reach in and do a planting or reading or whatever they need to do,” Hoyt says.

The warm air comes from a 250-foot pipe buried in the ground. The greenhouse stays at 48 Fahreinheit all year, so it can be considered warm during the winter and cool in the summer.

GROWING AND LEARNING

Bethlehem Elementary has a gifted-and-advanced program known as REACH that allows students from fourth to sixth grade one hour per week to work on different projects. The greenhouse has become an option that students can participate in throughout the school year.

The REACH students began using the greenhouse for a school beautification project. The students planted and monitored two beds’ worth of flowers. Once the flowers were ready, students transplanted them to the school.

After growing the flowers, the students began experimenting with different soils, fruits, vegetables and climates.

“We were picking strawberries in January, which is unheard of in this climate,” Hoyt says. Green beans, peppers and tomatoes were then added to the strawberry bed. In the other beds, students grew herbs and beets.

“We came up with experiments in class,” Hoyt says, "[like] if plants grow better in compact soil or loose soil. In science and math curriculum, we use videos and data from the greenhouse.”

Hoyt says he intends to set up a page on the school’s website to house greenhouse data.

The data will be open to the public, and Hoyt says webpage visitors will be able to suggest certain experiments or topics. Video from the greenhouse is livestreamed to the school, so Hoyt and the students can monitor it remotely.

In the beginning, getting students to the greenhouse was difficult because Hoyt was the only chaperone certified to drive students to the landfill. More certified drivers have since come on board, and now classes of seven to 20 children per trip go to the greenhouse at least once per week for four or five weeks in the school year.

“With all the hurdles teachers have to get to, taking that much time out for science is a big thing,” Hoyt says.

The sixth grade students created a short film about the greenhouse, the geothermal system used to heat it and the benefits of both projects. They won $450 to be used for school supplies at the seventh annual North Country Student Film Festival. The film, titled “The BES Greenhouse,” won in the Innovation North of the 44^th category.

Along with biological science, students also are learning about the renewable energy that heats the greenhouse and the landfill. Hoyt says an assignment that students usually work on in relation to this project is writing a paper about the advantages and disadvantages of renewable energy.

“The pros and cons of jobs, saving our environment—that’s how I tried to tie it all into the greenhouse itself,” Hoyt says. “It was a research project on the subject culminating in a paper.”

Hoyt says out of 18 children who wrote research papers, 16 believed any negatives of renewable energy were “far outweighed” by the jobs and energy created from landfill gas.

The author is assistant editor of Waste Today and can be contacted at hcrisan@gie.net.