Food Plant Expansion Prompts Addition of Orenco AdvanTex System

Large tankage, and wood chip denitrification and alkalinity augmentation help efficiently handle effluent for the Oregon commercial system

Food Plant Expansion Prompts Addition of Orenco AdvanTex System

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A food processing plant in eastern Oregon was growing and needed a new wastewater system. Brian Rabe had designed the previous system installed in 2013 and was called back for the expansion.

When he designed the expansion he was managing soil scientist at Valley Science and Engineering in Albany, Oregon. Now he is semi-retired with his own company, Elkhorn Consulting, based in Baker City, Oregon.

The 2013 system was essentially an oversized residential system intended for a maximum work force of 167, he says. The new system is good for up to 500 workers, employs different technologies including a pair of wood chip beds, but keeps the same drainfield.

That drainfield had originally been slightly oversized and was capable of absorbing 1 gallon of effluent per linear foot per day, Rabe says. Advanced treatment in the new system increases dosing to 3 gallons per linear foot per day.

The system

From the processing building, wastewater flows through a 4-inch pipe into a two-compartment 13,000-gallon Xerxes tank from Shawcor. The first half of the tank is used to settle solids. One feature of this tank, Rabe says, is an inlet that has no sanitary tee and is placed 4 inches above the outlet. This is something he learned from Dan Bush, one of his mentors, and he uses it to keep the inlet clear.

In the usual tank arrangement with a sanitary tee and an inlet set 2 inches high, incoming wastewater loses a lot of energy when it hits the wall of the tee, he says. Solids float and build up around the tee. Remove the sanitary tee and raise the inlet to 4 inches, and the energy of the incoming water pushes floating solids away from the inlet.

The previous system for the food plant proved the point, he says. “With the conventional sanitary tee in a concrete tank, they were having a pump truck out every week to help pull solids out of that tank.”

Next in the treatment chain are three 3,000-gallon concrete tanks saved from the previous system upgrade in 2013. These now provide additional settling, equalization, and primary treatment. The second tank has a 12-inch Orenco Biotube filter on its outlet. All tanks are from Waite Concrete Products of Canby, Oregon.

Next is a new set of three 3,000-gallon tanks. Outlets from the tanks are set low and use horizontal tees that draw water from tank corners. Without this, water can flow through the centers of tanks without much mixing, Rabe says.

The first of the new tanks is divided into one 2,000-gallon compartment and one 1,000-gallon compartment. Effluent flows from the first set of three tanks into the 2,000-gallon compartment. By gravity it flows into the next 3,000-gallon tank and along the way picks up alkalinity from a basin. (High nitrogen sources often require supplemental alkalinity to facilitate complete nitrification.)

Rabe says he’s used the alkalinity basin design before. It’s a 30-inch diameter PVC tank from Orenco. In the bottom installers build a square using 1-inch PVC pipe and fittings and drill holes in the pipe. The operator fills the tank as needed with calcium hydroxide powder from a hardware store. When the pump in a nearby basin turns on, water jets through the holes at 3 to 4 psi and dissolves the calcium hydroxide. A concentrated solution forms on top of the powder, and it flows by gravity through an outflow and into the wastewater stream from the second tank.

The third tank has four pumps, each dedicated to one of the four AdvanTex AX100 pods in the secondary treatment train. A thermostatically controlled heater warms air for the AX100s if the ambient temperature falls below 40 degrees.

Wastewater from the AX100 pods flows through a splitter basin that recirculates 40% of water to the Xerxes tank. The rest flows into the 1,000-gallon compartment of the first new 3,000-gallon tank. One pump here pushes some treated water through the alkalinity basin at 10 gpm and into the treatment flow.

Also in the 1,000-gallon compartment is another pair of pumps pushing effluent through 1 1/4-inch Schedule 40 PVC pipe to two wood chip beds for denitrification. Each bed is 30 feet long, 9 feet wide, and 7 feet high. Beds are uncovered and built with dimensional lumber and PVC membrane liners. Floats inside the beds control dosing.

Pumps in PVC basins on the end of each bed send treated water to the drainfield through 1 1/4-inch PVC pipe. Each bed feeds half the drainfield. Two six-way splitters dose 12 looped cells holding a total 2,484 linear feet of double bundle EZflow (1202H).

All pumps in the system came from Orenco, and an Orenco programmable panel with cellular telemetry manages the system and allows remote control by the operator, who is about a four-hour drive from the site. The control panel and other equipment are located in a small shed.

To do the job, a crew from Bruce Johnson Construction in Boring, Oregon, primarily used a Volvo EC160 excavator. In tight spaces they used a Volvo EC35 mini-excavator. Material was moved with a Volvo L60 wheel loader. The Xerxes tank was set with the EC160, but the three 3,000-gallon concrete tanks needed an 80-ton crane. Aside from some 100-plus-degree days, which the crew handled by starting very early, the job went smoothly, says Doug Johnson from the construction company.

Nitrogen problems

“Since the sewage generated by the facility is almost exclusively from restrooms, it has a substantially higher nitrogen content than your typical residential source,” Rabe says.

With modern low-flow fixtures, it is not uncommon for facilities like this to have total nitrogen concentrations in septic tank effluent between 135 and 230 mg/L, he says. A typical residence is likely to have about 60 mg/L nitrogen. Recirculation can do only so much. Start with 150 mg/L of nitrogen, and recirculation with additional residence time for passive pre-anoxic denitrification can drop that to about 40 mg/L, Rabe says.

It is likely the chips in the beds won’t have to be replaced for many years, Rabe says, but when that happens, the use of two beds means one can be taken out of service without interrupting treatment. Early designs placed wood chips inside tanks, he says, but replacing chips through a 30-inch-diameter access hole is difficult, and you need a truck with a strong vacuum because the average pump truck cannot suck up used wood chips.

“So I thought, that’s labor intensive and complicated. Let’s make these open vessels where we can manage the liquid level. In this case we are plumbed out the bottom of these lined beds. If we need to, we can pump the bed down, dewater it without having to get a pump truck in, and then, with a backhoe, reach in there and scoop the spent material out,” he says.

Open beds aren’t a problem in Ontario, Oregon, because it has a very dry climate, he says. For a couple of projects in wetter areas, Rabe says, he specified that chip beds be covered with the same PVC membrane used in the liner.

The food plant operates six to seven days a week year-round except for a two-week maintenance shutdown. After about a year of operation, the system effluent showed BOD of less than 7 mg/L, TSS less than 2 mg/L, total Kjeldahl nitrogen of 0.99 mg/L, and nitrate-nitrogen of 0.05 mg/L. Permit limits are 20 mg/L for all parameters.


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