Josh Thompson had a massive challenge.

Within 60 days — the end of October 2022 — the landfill would reduce the volume of biosolids accepted from the North Wastewater Treatment Plant by 700 wet tons per month. The facility in Henderson, Kentucky, produced 19,000 wet tons annually.

“We had spent most of 2022 investigating alternative dewatering systems to replace our two 30-year-old, 2.5-meter belt filter presses,” says Thompson, treatment superintendent with Henderson Water Utility.

“After testing three different screw presses, we had selected one and believed there was time to complete a large capital project. The 60-day deadline stopped that idea.” Instead, the utility chose an innovative second-stage dehydrator. It yields biosolids at 40-45% solids, significantly reducing the weight and volume of material going to landfill.

EXPLORING OPTIONS

Henderson’s activated sludge plant (15 mgd design, 6 to 7 mgd average, 25.5 mgd peak flow from combined sewers) treats wastewater in two extended aeration basins. UV-disinfected effluent is discharged to the Ohio River.

While looking for a new landfill site, management planned to use multiple geotextile bags to dewater and store biosolids on site, and to offload press-dewatered material to a lined field covered with tarps. “We were grasping at straws to find a viable solution,” says Thompson.

In October 2022, senior utility staff and a consulting engineer spoke to ELODE USA representatives. “They had a second-stage biosolids dryer that used electro-osmosis to reduce cake weight by 50% or more,” says Thompson. “We immediately set up a pilot test for that month.”

In three minutes, the 1-meter dehydrator dewatered wet biosolids at 14-16% solids to 45% solids, reducing cake weight by 67%. Based on that result, the utility made an emergency purchase of a 3-meter EODS-3000 dehydrator, the first 3-meter ELODE unit in the nation and the third globally.

Unfortunately, it didn’t arrive from the South Korean manufacturer in time, and the biosolids kept coming. “For a utility our size, we produce a lot of them,” says Thompson. “Our largest industrial user is a paper mill.”

PLANT PREPARATIONS

With the dehydrator on a ship bound for California, Thompson called the landfill owner to ask for a deadline extension. Instead, the situation worsened. After another 60 days, the landfill would not accept wet biosolids from any wastewater treatment plant. Years of doing so had destabilized the site, and heavy equipment was sinking.

“Even ELODE biosolids were considered too wet, and we had until Jan. 1, 2023, to figure out what to do,” says Thompson. “Then, the week before Christmas, we secured a different landfill for both plants and could breathe again.” (The other facility, the Forrest E. Stokes Wastewater Treatment Plant, treats an average of 2.57 mgd.)

The 10-by-15-foot, 8-foot-high dehydrator was scheduled to arrive before contractors could build a proper structure to house it. So Thompson eyed the plant’s 60-by-100-foot open-sided biosolids warehouse. ELODE USA president Alex Min and his staff supervised the machine’s installation in May 2023.

“The warehouse’s 14-foot-high ceiling stressed the tow truck driver as we figured out how to lift the 9.5-ton machine from the crate with the jib crane and set it in position,” says Thompson.

Contractors then built a 30-by-50-foot enclosure around the unit but didn’t have time to include conveyance from the stockpiled biosolids to the 13-foot-high hopper.

Training for the operators involved learning the control panel and how changing the settings affected the process. “We adjusted the speed of the belt, the amount of power going to it, and the amperage until we found the sweet spot for our solids,” says Thompson. “Then we did the same thing with the speed of the feed conveyors to ensure the cake was distributed evenly going into the dehydrator.”

HOW IT WORKS

In daily operation, a CASE 621D end loader fills a day hopper with cake, which a conveyor feeds between the dehydrator’s center drum (anode) and belt. The inside of the drum is coated to ensure a consistent and proper positive electrical flow. A chain (cathode) on the back of the belt carries the negative charge.

When current is applied, the voltage causes the negative-charged biosolids particles to migrate to the positive anode (drum) and drives the positive-charged water onto the belt. The manufacturer says electro-osmosis uses one-fourth the energy of thermal dryers.

“We’re seeing 35-37% solids leave the machine, but as the material continues to steam off, it reaches 40-45% solids by the time it arrives at the dump container,” says Thompson. “The unit runs nonstop, filling a 40-yard roll-off in about 36 hours, so we’re constantly sending loads to the landfill.”

Electro-osmosis generates heat, and the temperature inside the machine is 180 degrees F. The dehydrator has a fan in both 12-inch exhaust ports, and piping vents the heated air to the building exterior.

“The system removes a large portion of the heat and nearly all the humidity,” says Thompson. “We also mounted four 36-inch air-mover fans on the walls and leave the ceiling vents open.” In summer, the building temperature averages 95 degrees F.

FINE-TUNING

While everyone was pleased at how well the unit ran, there were growing pains. “Alex and his staff have worked tirelessly to resolve any issues,” says Thompson.

Originally, the open screw conveyor discharged dried solids into a truck, but the conveyor’s 30-degree pitch caused the screw to clog. Switching to containers made it possible to lower the pitch to 20 degrees, fixing the problem.

It was no surprise that some small components loosened during the ocean voyage and cross-country road trip. “We’re not certain, but a month after installation we suspect a bolt fell out, creating a short between the drum and the chain,” says Thompson. “The short threw sparks and welded the object to slag. We could only guess at what it was.”

Some other metal contamination has occurred when the end loader scoops up biosolids for transport. “Items as small as a dime or a nail can cause shorting and burn holes in the belts,” says Thompson. “The loader also picks up occasional stones, and they poke holes as well.” To address that issue the utility is considering installing a metal detector.”

CONCLUSION

The 3-meter dehydrator is the largest unit available, yet at maximum capacity it processes only 40% of the plant’s biosolids. Therefore, the utility is considering a second unit.

As of last October, the dehydrator had run nonstop for two months; not long enough to establish hard numbers on long-term hauling and landfill costs. However, after accounting for the dehydrator’s power consumption, the utility expects to see net operational savings of about $11,000 per month.

“The savings figure was higher originally, but the new landfill has a considerably lower tipping fee, meaning return on investment is longer than expected,” says Thompson.

Thompson was initially skeptical of the technology but has found it sound. “The advertising claim is true. It really does reduce our solids by 60% in three minutes. This technology could be a game-changer for our industry.”