A major kitchen addition to a traditional English pub in Carp, Ontario, required a review of the 1,200 gpd onsite system. Although there was no evidence of effluent break out, the sand mound was clogged with biomat and displaying signs of distress.

Terry Davidson, director of regulations at the Ottawa and Mississippi-Rideau Septic System office, ordered the owners to cap the system and use the septic tank as a temporary holding tank until the system was upgraded or replaced.

Eric Draper, owner of The Septic Store in Osgoode, offered a solution involving a submerged buoyant-media aeration system designed for high-strength waste and pre-plumbed and wired, fully assembled treatment packages with textile media filters.

The owners approved provided the pub would be allowed to remain open. Draper worked with Matt Rainville of Houle Chevrier Engineering in Ottawa to design the replacement system. “We had a space about 85 by 75 feet behind the building that abutted busy roads to the east and south and a property line with trees and utilities to the west,” says Draper. “It was your typical shoe box situation.” The system just fit.

 

Site conditions

Soils are sand to sandy silt with a loading rate of 0.5 gallons per square foot per day. The seasonal water table is about 5 feet below grade, and bedrock is 6 to 7 feet below grade.

 

System components

Rainville designed the system to handle 2,000 gpd at a waste strength of 1,300 mg/L BOD per day. The major components are:

2,000-gallon concrete grease interceptor. All tanks made by Armtec, formerly Boucher, Precast Concrete, Ottawa.

4,000-gallon two-compartment septic tank.

4,000-gallon single-compartment concrete surge tank with duplex alternating 1/3 hp pumps from Goulds Water Technology.

4,000-gallon treatment tank with 18 Nibbler SBP (square backflush pods) from Aqua Test.

3,000-gallon clarifier-recirculation tank with 1/3 hp Goulds effluent sludge return pump and effluent filter from Orenco Systems in the first compartment, and Orenco Biotube duplex 30 gpm high-head pump vault in the second riser.

Two 20-square-foot AdvanTex AX20 Orenco secondary treatment fiberglass filter pods with room for a third.

2,000-gallon dose tank with duplex 30 gpm, 1/2 hp high-head Orenco pumps.

50- by 32-foot sand mound with 10 laterals of 3-inch PVC perforated pipe with 1/2-inch holes drilled at 4, 8 and 6 o’clock positions.

VeriComm Web-based Orenco monitoring system and control panels. Components supplied by The Septic Store, Osgoode.

 

System operation

Kitchen waste flows through the grease interceptor and into the septic tank. Wastewater from the restrooms has a separate lateral to the tank. Laterals and plumbing are 4-inch PVC pipe.

Liquid drains into the surge tank where pumps run 27.7 seconds every 30 minutes, sending 23 gallons (1,200 gpd) to the Nibbler SBP treatment tank. “Influent analysis averaged 1,000 to 1,300 mg/L BOD5, 500 to 1,000 mg/L CBOD, 100 to 150 mg/L TSS, and 50 to 75 mg/L FOG,” says Draper. “We wanted to bring the BOD down to residential strength before sending it on for treatment. The Nibblers have done that.”

Each 27-inch-square pod treats 0.81 pounds per day BOD5 and FOG. Inside the pod, microorganisms cling to 3.5-inch media spheres. The dynamics are such that within seconds of effluent entering the tank, it is thoroughly mixed with the liquor.

“This is not your typical aeration system,” says installer Mike Coady of Ketch Construction in Carp. “It’s much more robust. Lift the lid and the action resembles an old washing machine. If FOG slows down, it clings to something or settles, so the liquor is agitated by introducing 6.5 cfm of air into each Nibbler pod.”

Wastewater detention time is 36 hours. An outlet baffle extending down to the central clear zone of the tank allows liquid to gravity-feed to the clarifier-recirculation tank. Aerobic organisms die within 12 hours of entering the clarifier and are pumped to the inlet side of the grease interceptor. Liquid in the clarifier flows through the effluent filter and into the recirculation tank.

Run times on the pump in the recirculation tank fluctuate based on flow data averaged over 30 days by the control panel. When activated, the pumps send 18 gallons in 30 seconds to the AdvanTex filter pods, then rest for 4.5 minutes. As liquid trickles through sheets of synthetic textile in the units, microorganisms digest the remaining impurities so completely that nothing remains to form a biomat in the drainfield.

Effluent collecting at the bottoms of the pods gravity-flows to the recirculation tank and keeps recirculating until the compartment is full. As liquid flows from the tank, a splitter valve alternately doses the dose tank, feeding the sand mound, and recirculation tank. “The combination of treatment technologies enabled us to reduce the size of the drainfield by almost 60 percent,” says Draper. “That’s the only way we had room for it.”

 

Installation

Coady’s crew spent more than a week beating out the rock with two excavator buckets. “It was a delicate situation because the stone building is a historic landmark protected by the Ontario Heritage Act,” says Coady. “Vibrations from our work could have damaged the foundation or cracked walls. It made life very stressful.”

His crew excavated the hole for the septic tank first, added 8 inches of screened 3/4-inch stone, then set and plumbed the septic tank to activate it. Its larger capacity reduced the frequency of pumpouts.

Mark Fricke, regional sales manager from Aqua Test, and Ted Kulongoski, international account manager from Orenco, arrived in early December to supervise installation of their components. “There was snow on the ground, but it wasn’t bitterly cold,” says Coady. “We were lucky. The weather cooperated and we stayed on schedule.”

After removing the existing drainfield, workers roughed up the soil in the 50- by 32-foot bed, poured and leveled 30 inches of washed sand, and shaped the upslope and sides to a 3:1 grade. “The big challenge was limiting disturbance and not compacting the mound basal area,” says Coady.

The crew added six inches of stone, then laid 10 laterals 45 feet long in one zone. Workers covered the piping with two inches of gravel, rolled geotextile fabric over it, and cut slits to install inspection ports on either end of the drainfield. They topped the fabric with six inches each of silt loam and topsoil, also sloped to promote drainage.

“We didn’t fence the system because customers won’t see it from the parking lot on the other side of the building,” says Coady. The system meets effluent quality requirements of 15 mg/L BOD and 10 mg/L CBOD and TSS.

 

Maintenance

Rideau Valley Septic Services in Ottawa holds the service contract. A technician checks the system quarterly and draws samples twice a year. When the media spheres in the Nibbler SBP pods develop an excessive biomass, the maintenance provider closes the valve providing aeration to the interior of the unit and opens the valve directing air to the underside of the pod. The air velocity scours the media, sending biomass to the bottom of the tank. The system will be pumped as needed.