Closer to Home

Ventura County biosolids, once trucked a million miles a year, now are dried to provide daily cover material for a local landfill

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When the citizens of Kern and Ventura Countiesspoke up, clean-water professionals LISTENED. Until 2009, biosolids produced in Ventura County were hauled 150 miles away from the California coast for land application in Kern County.

 

Ventura County residents weren’t happy with the miles logged hauling 8,000 tons of biosolids every month, and the residents of Kern County weren’t keen on taking material from outside their county’s boundaries.

 

So, in 2005, Ventura Regional Sanitation District (VRSD) officials began to design a new facility. In 2009, they flipped the switch. Now, rather than making a long haul, biosolids are trucked from four wastewater treatment plants, none more than 40 miles away, to the Toland Road Landfill in Santa Paula.

 

Trucking costs down

While a landfill is not usually a prime site for a biosolids facility, it made logistical sense in this case: The biosolids and the landfill have a symbiotic relationship. The landfill provides methane to power the drying system and ancillary equipment. And the end product, Class A biosolids, provides alternate daily cover at the landfill.

 

The process cuts out about one million miles of annual truck traffic between Ventura and Kern Counties, eliminating about 1,800 tons of carbon dioxide emissions. It also uses landfill methane as a valuable fuel and eliminates the purchase of some landfill cover material.

 

Greg Grant, P.E., solid waste division manager for VRSD, was involved in the design and location of the biosolids facility. “Kern County didn’t want the solids, and Ventura County didn’t want them trucked so far,” says Grant. “We were looking for a greener, large-scale, acceptable method for handling the biosolids.”

 

With a gas collection system in place and available land for equipment, the landfill is now home to the Biosolids Drying and Renewable Power Generation Facility. And the crew of landfill operators has taken on day-to-day system operations. “It’s very innovative,” says Grant. “It’s a nice-looking structure. It’s a beast of a machine, but it’s fairly hands-off.”

 

Making the trip

Ventura County operates four wastewater treatment plants: Thousand Oaks, Oxnard, Fillmore, and Ventura. Each has anaerobic digesters and belt presses that produce material at about 15 percent solids, all of it hauled in semi-trailers to the landfill.

 

With a population of 200,000, the City of Oxnard produces the most biosolids. Four trucks from there make the drive to the landfill every day. Ventura and Thousand Oaks each send two truckloads per day, and the City of Fillmore, population of 15,000, sends just one a week.

 

Dan Pfiefer, Ventura wastewater superintendent, made only slight modifications to accommodate the new dryer system. Solids from three 500,000-gallon anaerobic digesters are run through an Edward & Jones (Veolia Water Solutions & Technologies) plate and frame press.

 

One cycle of solids on the press fills one semi-trailer. When the cycle is complete, the plates open and the dewatered material drops into an open-top semi-trailer. Previously, the process operated Monday through Friday, but since the dryer came online, solids are dewatered and transferred to the landfill seven days a week.

 

Pfiefer says the costs of the new process and land application are about the same. “The tipping fee is about the same as driving the material to Kern County,” he says. “And we’re facing increases in transportation costs. Once the equipment is paid for, the cost should stabilize. We expect in five years the costs will flatten out.”

 

Chuck Rogers, superintendent at the Thousand Oaks treatment plant, appreciates having the option to take material to the dryer, but he uses that option only for backup. “My contract is different than the other treatment plants,” he says. “It’s nice that we have that option, but we dry as much of the solids here as we can.”

 

After the anaerobic digesters at Thousand Oaks, solids are dewatered using two Sernagiotto belt presses (technology purchased by Siemens in 2006) and transferred to more than two acres of drying beds, where the material can reach 80 percent solids. The dried solids go to the landfill.

 

“We want to use the least amount of energy to produce the driest cake,” Rogers says. “And when it’s raining, it’s nice we have somewhere else to take it.”

 

The four plants produce the 160 tons of biosolids treated at the landfill each day. As the semi-trailers enter the facility, they back up to a receiving hopper. The front end of the trailer is raised, and the contents are dumped out the back.

 

“We have truckers backing up to the receiving hopper anywhere from 6 a.m. to 6 p.m.,” says Grant. “The system is fairly automated, but we have to be there for unloading.” The hopper contains odor-control equipment and is kept closed — it opens only to receive solids.

 

From the receiving hopper, material is transferred automatically via auger pumps to the storage hopper, which holds 300 cubic yards (eight truckloads) of material — enough to handle what might be delivered over a weekend. Even though drying takes place only during standard business hours, an operator is always on site to oversee the deliveries.

 

Quick studies

When the decision was made to put the biosolids facility at the landfill, operators had to get up to speed. They became quick studies in biosolids and the handling equipment. “My background is in solid waste,” Grant says. “I know the solid waste management side really well, but biosolids was new. We did a lot of research and worked with vendors.”

 

They settled on an indirect dryer manufactured by Fenton Environmental Technologies Inc. The system comes skid-mounted along with landfill gas treatment, air treatment, and electric power generation. “Indirect drying is much safer than direct drying,” says Grant. “With direct drying you’re actually heating the air. Organic dust is explosive. Indirect drying is almost like cooking on the stove.”

 

Thermal fluid — a paraffin-based oil — is heated to 450 degrees F, in turn heating the drying chamber, which contains a hollow-disc rotor that turns the biosolids. The process dries the solids and kills pathogens, producing a Class A material. The facility has two drying units on site, each operating at 80 tons per day. There is room for two more if an expansion is needed.

 

“Because you don’t use hot air, there’s not as much exhaust with indirect drying, only steam,” Grant says. “And when you condense the steam, the particulates fall out.”

 

Mechanical system

Exhaust from the unit is run through a biofilter, a carbon filter, and a HEPA filter before discharge to the atmosphere. Condensed water removed from the exhaust is treated in a reclaimed water system, included as part of the Fenton package.

 

As condensate is removed from the exhaust gas, polymer is injected, and the solids are settled out. Effluent — recycled water — is stored on site and used for dust control at the landfill as needed. The amount of solids that settle out are almost negligible, and that material is hauled in slurry form to the Hills Canyon wastewater treatment plant.

 

Overall, the system is designed to be fully automated, but Grant stresses that it is still in the startup phase. The ultimate goal is to operate around the clock. “It’s not fully automated, so if it’s running, someone is watching it,” says Grant.

 

Grant is confident that his crew is up to the task of running the drying facility because there are no biological systems to manage. “It’s more of a mechanical system,” Grant says. “We don’t have to work with a digester or trickling filter. We keep the gas clean and the oil hot, we make sure the augers and pumps are feeding at the right speeds. And the burners can flame out, so we have to monitor that at the PLC or SCADA.”

 

But that doesn’t mean the operators are just sitting back and watching a screen. They collect samples at different process steps and tweak the operations. “Turbidity and coliform are tested in the recycle water to make sure the polymer and alum dosing is accurate,” says Grant. “There is routine sampling of the air for odor, ammonia, sulfur, and ROC (reactive organic compounds). And there is junk in the biosolids. Sometimes we’ll find a miscellaneous part, like a bow that’s used to hold the tarp up on the truck.”

 

For now, one operator is responsible for keeping an eye on the system. Usually, that’s an engineer, but operators rotate through to assist and to become more familiar with the facility.

 

Powered by methane

Power to run the hoppers and pumps, heat the oil for the dryer, and operate all the other equipment in the drying facility comes from methane generated as waste decomposes in the landfill. The methane is collected through 75 vertical wells drilled into the waste. The wells are valved and operate in sections across the landfill.

 

Grant and his crew must balance the flow from the wells to ensure that the right gas-to-air ratio is pulled from the landfill and pumped to the biosolids facility. “We have to go to each wellhead and balance it about every two weeks,” says Grant.

 

Once collected, the methane is treated to remove liquid, sulfur, and siloxanes, found in personal-care products. Then the gas is compressed and converted to electricity using nine low-emission 250 kW microturbines (Ingersoll Rand). About one-third of the power generated goes to the biosolids facility, and the rest is sold to the utility grid.

 

Once the biosolids are dried, they are conveyed by an auger pump to a dried-product receiving station. Here, solids are dropped into an open-top semi-trailer in one of three bays. Biosolids are primarily used on site for daily cover, but the county is negotiating contracts for its use as fuel or fertilizer.

 

Under cover

Solid waste is delivered to the site at about 1,200 to 1,500 tons per day. It is placed in a daily cell, usually about 100 feet long by 50 feet wide, and 12 inches deep. Regulations require that earthen material be placed over the waste at the end of every working day to control odors, vermin, flies, and scavenging. Instead of soil, a landfill can propose an alternate daily cover.

 

At the Toland Road Landfill, biosolids were approved for use as daily cover, but with some caveats. “Some regulators are concerned primarily with stormwater runoff,” says Grant. “So we have specific stormwater requirements in our permit that are weather-dependent.” For example, if rain is expected, biosolids cannot be used as cover.

 

The facility also uses soil, tarps, and green waste for cover material. Biosolids make up about 10 to 20 percent of the site’s cover material. “The biosolids work just fine,” says Grant. “They are just supplements along with the other alternate daily covers.”

 

Like the drying equipment itself, the dried solids have become just part of the process at the Toland Road Landfill.



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