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Engineering Students Look at Redevelopment of Depleted Quarry
Senior design projects offer ideas for local areas.
Mark Fischenich, Mankato Free Press, 3-27-2017
Anearly depleted 54-acre quarry in the heart of Mankato could be redeveloped as the site of a mammoth indoor farm for lettuce and other leafy greens, according to a group of senior civil engineering students.
Or the quarry, located south of Highway 14 and west of Third Avenue, could become a fish farm capable of producing 5 million Asian bass each year, according to a second group of Minnesota State University, Mankato students.
Along with massive amounts of food, either of those projects could create hundreds of new jobs, according to the students who have been studying the ideas for months as part of their senior capstone project.
But if the owners of the quarry — which abuts a residential neighborhood — would prefer a quiet, low-traffic, picturesque reuse of the property, a third group of engineering students has an alternative: a 52-million-cubic-foot body of water that would become Mankato’s largest lake but would also serve as a sort of battery to store energy from renewable sources such as wind and solar power.
The senior design projects are an academic exercise, the most challenging assignment of the four or five years the students spend at Minnesota State Mankato.
Some past projects completed by previous seniors, however, have been implemented — at least in part — and the 2016-17 senior class expresses confidence that their ideas might have a future.
“I actually believe this is a very good project that has a very high potential to be implemented in Mankato,” said John Shamla of the indoor produce garden. “... There are very good odds.”
The estimated construction costs of each proposal are still being finalized as the teams prepare for a public presentation of their plans at Minnesota State Mankato’s Ostrander Auditorium on April 11. Because of the ambitious scope of the ideas, all would require substantial private investment.
“I think it’s a good idea,” Amy Nguyen said of the fish farm. “And I think it can happen if we can find the investor.”
The pumped storage hydroelectric system, a concept much more common in mountainous areas, actually turned out to be feasible in Mankato, according to Jonathan Rudolph.
“There’s already interest from Xcel in our project,” Rudolph said.
Here’s a look at each of the three:
World’s largest vertical farm
Picture the Walmart distribution center on Mankato’s east side, fill it with lettuce, herbs and other leafy vegetables thriving in a vertical hydroponic growing system. The “Gardens Under Glass” year-round agricultural production facility would be even bigger. Perhaps more familiar to local shoppers, the planned indoor farm would be three times the size of the Mankato Mills Fleet Farm store.
The original project name — “Gardens Under Glass” — is actually no longer applicable. Rather than designing the buildings to take advantage of free sunshine, the team decided it made more sense to use artificial light and highly insulated walls to minimize heat loss.
Solar panels on the roof to offset lighting costs and a geothermal temperature-control system (being studied by the civil engineering students’ mechanical engineering colleagues) are under consideration.
So why would it make sense to grow lettuce in Minnesota in January rather than just shipping it from sunny, warm California? Transportation savings are a major factor, but so is the water shortage in the West.
“They have a lot of heat, a lot of sun, but not a lot of water,” said John Shamla, who leads the structural team of “Gardens Under Glass.”
The proposal involves a 314,000-square-foot building and a 192,500-square-foot building. Vegetables would be grown in nutrient-rich water with vertical rows of plants in the two-story buildings. It would be a closed-loop growing system, so water would be reused as much as possible.
The facility would employ more than 400 full-time workers to grow, harvest and prepare the produce for distribution, according to the team.
Barramundi fish farm
Also known as Asian sea bass, barramundi are natives of Australia. Nutritious and tasty, the species is increasingly popular in fish farms. Nguyen noticed that the Number 4 American Bar and Kitchen in downtown Mankato was selling a barramundi entree for $22. (The Thai coconut curry barramundi is actually up to $25 now.) “We can probably reduce that price,” Nguyen said.
The fish farm would also put money in the pockets of traditional farmers. Soybeans would be the primary fish food, and the facility would be sending a high-quality fertilizer, processed from the fish waste and treated with an ultraviolet system to kill all pathogens, back to the farms.
The water used in the fish farm would be provided by the nearby Mankato Wastewater Treatment plant/ Mankato Energy Center water reclamation plant, which the students analyzed and learned met standards for aquaculture.
“We talked to them and got a pretty good deal on the water,” she said of city officials.
The fish production process would start with a hatchery, followed by a quartet of fingerling tanks. The growing fish would then move through a series of a half-dozen 45-foot-diameter, 10-foot-deep tanks before reaching the two-pound harvest weight after eight or nine months.
But could a Mankato barramundi farm be an environmental disaster — the future equivalent of the southern state fish farms that accidentally released the invasive Asian carp into the Mississippi River? After all, the proposed quarry location is adjacent to the Minnesota River.
“I get that question a lot,” Nguyen said. “We called the DNR, and they were concerned about that as well.”
The team has at least three answers to the concern. First, barramundi survives in waters between 77 and 95 degrees. (The Minnesota River was hovering around 41 degrees last week and drops to just above freezing in January.) Secondly, the designs for the fish farm place the facility above the 100-yearflood level and include a retaining wall between the building and the river. And thirdly, no live fish would be allowed to leave facility.
The three-story building — which would include office, freezer and processing space — would employ 100 or more workers, Nguyen said.
At first glance, the idea seems strange. Purchase electricity to pump water uphill and later use gravity to send the water back downhill and through turbines to generate electricity. More electricity would be required to accomplish the first phase than would be generated in the second.
The reason a pumped storage hydroelectric system makes sense is because supply and demand of electrical power don’t always match up, and science hasn’t developed efficient ways to store large amounts of electrical power, said Tanner Wild, project manager of the third civil engineering team.
Under the team’s proposal, the Jefferson quarry would be converted into a reservoir holding 52 million cubic feet of water. Another earthen reservoir would be created on 100 acres of land on Mankato’s bluffs.
Two enormous Francis turbines would pump water to the upper reservoir at night when electrical demand is low and power is cheap or when wind turbines and solar arrays are producing more power than the electrical grid needs. Then, when power demand peaks on weekdays and during summer heat waves, the water would flow back down to the lower reservoir, spin the turbines and produce 25 megawatt/hours each of electrical power.
“We’ll release it and use gravity as a free resource,” Wild said.
The concept isn’t revolutionary — at least not in more vertically varied locations.
“We are at a disadvantage with Minnesota being one of the flattest places in the United States,” Wild said. “But I believe we have made it work.”
The Germania Park neighborhood would see much less activity at the quarry site under the pumped storage hydroelectric plan.
“With our facility, we’ll only have three or four employees,” said Jack Moyer, who worked on construction and water resource issues for the team. “... And high aesthetics.”
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