Franklin updated on high-tech sludge processing plan

Franklin leaders caught a glimpse of the city’s likely solid waste treatment future Tuesday night.

The vision? Greenhouse-like buildings where about 7,400 pounds per day of treated “sludge” would go in one end, and out the other would come a “cake,” as one city staff member put it, of drier, more concentrated biosolids, ready to be sold as fertilizer.

At a work session with a packed agenda, the Franklin Board of Mayor and Aldermen heard a presentation about a proposed project that is slated to be a major component of Franklin’s long-planned overhaul of the way the it processes its waste.

The presentation looked at proposals to build a solar sludge drying system, which in conjunction with a process known as thermal hydrolysis, would result in what’s known as “Class A” solid waste.

Franklin updated on high-tech sludge processing plan

City leaders have already approved moving forward with a $50 million thermal hydrolysis system.

Franklin is expected to be among the first to use the technology — which essentially steam-heats waste to kill pathogens — in the United States. However, thermal hydrolysis has been used for years in Europe, according to a news release.

In October, city officials took a trip across the pond to “validate (the city’s analysis) by seeing, smelling and hearing these operations…”

The solar drying system, City Administrator Eric Stuckey said Tuesday, is more common.

The “Class A” designation means that waste would be clean enough to be sold to brokers and used as fertilizer.

Right now, the city trucks liquid tons of its unusable sludge to a special landfill about 100 miles away as part of a waste processing system that city officials have said is outdated and inefficient.

This week, city staff members made recommendations about companies who might be best-suited to complete the solar drying system, which would remove more water from the waste after the thermal hydrolysis, based on proposals that those groups submitted.

According to the presentation, the vendor Infilco Degremont Heliantis met the most criteria laid out in the city’s request for proposals out of the five submitted by four vendors. One proposal, however, was eliminated immediately because it didn’t provide a two-year warranty bond and didn’t meet enough other criteria.

The recommended solar sludge drying system is estimated to cost about $5.27 million up front and about $26,300 per year to operate and maintain.

The city’s board of mayor and aldermen will choose a vendor. Stuckey estimated that the city would choose a construction firm in the fall.

Other agenda items

Also at Tuesday’s work session, aldermen heard a presentation about controversial planned changes to its drinking water treatment plant, which draws water from the Harpeth River, and asked for options to ensure that the city’s housing reserve fund is replenished.

The fund is aimed at boosting affordable housing options throughout the city.

At the board’s meeting immediately after the work session, aldermen heard a presentation by Stuckey on the proposed budget for the upcoming fiscal year and gave final approval to rules formally allowing short term vacation rentals, like the ones available through sites like Airbnb, final approval.

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