Joining Forces

Two Michigan cities collaborate on a new dewatering facility to ensure cost-effective biosolids management for many years to come

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The weather in Kent County, Mich., doesn’t always lend itself to farming, but localfarmers count on biosolids produced at the Wyoming Clean Water Plant to nourish their crops. And farmland isn’t the only destination for the biosolids: Some is also pumped to nearby Grand Rapids in a combined biosolids management program.

 

The 24 mgd (design) Wyoming Clean Water Plant joined with the 61.1 mgd (design) Grand River Wastewater Treatment Plant in Grand Rapids to form the Grand Valley Regional Biosolids Authority (GVRBA). With rising transportation costs and an unpredictable regulatory environment, the cities decided to work together to manage biosolids cost effectively.

 

The authority became official on Earth Day 2004, when the mayors signed the articles of incorporation. The project began with construction of storage tanks and a dewatering facility at Grand Rapids, and installation of two pipelines with pump stations that allow Wyoming to pump material to the dewatering site.

 

At the dewatering facility, solids are centrifuged and stored in silos before transport to the Autumn Hills landfill in Zeeland or the Ottawa County Farms landfill in Coopersville.

 

While all Grand Rapids solids (16,000 dry tons per year) are treated at the dewatering facility, Wyoming delivers 25 percent (2,000 dry tons) of the 8,000 dry tons of solids it produces. Most of the Wyoming plant’s waste activated sludge is dewatered and mixed with primary solids before being trucked to corn, bean and wheat fields.

 

“If we sent all our solids to Grand Rapids, we feel we might lose our contacts with farmers,” says Kim Hackbardt, project manager of the GVRBA.

 

A new hat

Hackbardt was named project manager of the Grand Valley partnership last January, and he works under an operating team and a four-member board with two representatives from each of the two cities. He has been a manager at the Wyoming plant, which serves 140,000 customers, and has been involved with that city’s biosolids program.

 

For well over a decade, he has been the man in the fields, meeting with farmers, inspecting fields and working with the city’s hauling contractor.

 

Wastewater at Wyoming is treated using a primary clarifier followed by aeration and phosphorus removal. Solids from the aeration basin are pumped to one of two Bird Humboldt (Andritz Separation Inc.) centrifuges that produce a product at 6 percent solids. The material then goes to one of two 160,000-gallon day holding tanks. Primary sludge at 4.5 percent solids is also pumped to those tanks. There, the solids are dosed with lime to achieve pH 12 for two hours before transfer to one of three 2-million-gallon storage tanks.

 

“It’s usually enough storage for the winter when the ground freezes over,” says Hackbardt. “We usually quit land-applying the first week in January and resume the third week in March.” When the farmland is accessible, biosolids are injected into the soil on farms up to 35 miles away. Transportation is handled by Synagro Technologies Inc. In a year, 26 million gallons of biosolids are land-applied.

 

Before the biosolids authority was formed, tank storage sometimes ran out before the ground thawed, and the Wyoming plant used two Ashbrook Simon-Hartley belt filter presses to dewater the material before transport to a landfill. Grand Rapids faced similar issues, and as the dewatering presses aged and the plants faced high costs to replace them, the cities began to discuss joining forces and share the expense of dewatering equipment.

 

Checking options

The treatment plant staffs looked at digesters and a pelletizer, but found them too costly and eventually decided on dewatering followed by landfilling.

 

Today, Wyoming solids destined for dewatering are stored in three wet wells, one for primary solids, one for waste activated and the third for either. Generally, two wet wells store waste activated sludge because at 1 percent solids it pumps faster than primary solids at 4 percent. Two 8-inch pipes, one pipe for primary solids and the other for waste activated, convey the material three miles from Wyoming to the dewatering site.

 

The Grand Rapids plant serves 265,000 customers and has an activated sludge process. It dewaters only primary solids. Magnetic flowmeters (Siemens Energy & Automation) control the flow of solids from the pipelines to the dewatering facility. Mag meters in each line sense an increase in solids from 0.5 to 1.2 percent for activated sludge or 3 to 4 percent for primary and open the valves to the appropriate tanks. Each flush of solids through the pipe is followed by wash water. Here, the mag meters sense the decrease in solids and close the valves.

 

“It takes 65 minutes for the solids to travel to the dewatering plant,” says Hackbardt. “And then the valves say, ‘The solids are here.’” Water is flushed from the pipe by pumping it back to Wyoming in a loop configuration. If it goes down the activated sludge line to dewatering, it returns through the primary pipe. The process relies on careful measurements and communication between the treatment plants.

 

Into dewatering

At the dewatering facility, the pipes empty into one of two 1-million-gallon storage tanks, one for primary and the other for waste activated sludge. When it’s time to blend the materials, they are pumped to a 10,000-gallon storage tank before heading to three Siemens Water Technologies centrifuges. The centrifuges and polymer dosing are operated through a touchscreen.

 

Initially, the addition of manic polymers caused excessive foaming. To keep the foam from making its way to the head of the plant with the centrate, spray bars were installed and a de-foaming agent used. Hackbardt hopes a switch to emulsion polymer will cure the foaming.

 

From each centrifuge, solids are transferred by an auger to a cake chute in the basement. Cake pumps then move the solids up to the 55-foot-tall storage silos. Semi-trucks back under the silos and are filled to a total of 50 wet tons. By contract, the hauler must empty each silo each week by Friday afternoon. That allows the plant to continue producing material over the weekend and have storage space for a Monday holiday if needed.

 

Cake from the silos is then trucked to the two landfills. Methane generated at the landfills from decomposing biosolids and municipal refuse is used to generate electricity.

 

Sticking with the farmers

Although the biosolids contribute to electricity generation, Hackbardt wants to keep the farmers furnished with the material. “The farmers get great results,” he says. “When I came here 16 years ago, I said I would promote land application as long as it was successful.

 

“I go out to the fields before, during and after application. I see the crops. I’ve yet to see it ever be detrimental. The only negative impact is that the trucks compact the soil, and we’re working to keep them on the road. As far as the product itself, it’s unbelievable.”

 

It’s easy for Hackbardt to push a product he believes in. “Three of our farmers said they’ve had their best beans ever,” he observes. “And two have said they got their best beans on their worst ground.”



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