Sewer Systems

The Comox Valley Water Pollution Control Centre (CVWPCC) is a secondary wastewater treatment facility operated by the Comox Valley Regional District (CVRD) for the communities of Courtenay, Comox and CFB Comox on Vancouver Island. The CVWPCC was first proposed in 1978 as a replacement for aging municipal and military wastewater treatment facilities. From an initial concept of collection and discharge to a long marine outfall, the design of the CVWPCC rapidly evolved to include primary and secondary treatment with aerated static pile composting of dewatered sludge.

Designed by Associated Engineering (BC) Ltd., the CVWPCC opened in March 1984 with a crew of five. At present, there are seven operators, all of whom are certified under the BC Environmental Operators Certification Program.

Flow
Five wastewater pumping stations discharge to either a 930 mm diameter 8 km long force main or a 400 mm diameter 2 km force main which join together at the plant headworks and discharge an average daily flow of 17,000 cubic metres of wastewater. Four of the stations feature FLYGT submersible pumps ranging in size from 20 to 75 HP while the fifth has three variable speed 175 HP FLYGT pumps in a dry pit configuration.

Headworks
At the headworks wastewater is screened then degritted in aerated grit chambers before entering the primary clarifiers. Primary sludge (PS) and grit are withdrawn continuously through degritting cyclones and a grit classifier. Grit is added to the dewaterd biosolids and trucked to the composting facility
Primary effluent passes into two aeration basins that can be operated in either a plug flow or step feed mode. Aeration rates are adjusted by means of in-tank DO probes which feed back via a PLC to motorized inlet valves on the aeration blowers and the tank distribution air system.
 
Aeration
Aeration tank mixed liquor flows to a pair of peripheral feed, flat bottomed secondary clarifiers and a new centre feed clarifier.  Settled sludge is returned as return activated sludge (RAS) through a three variable speed RAS pumps. WAS is withdrawn downstream of the RAS pumps and thickened in a DAF unit. Secondary effluent is discharged through a re-aeration cascade to a gravity outfall which terminates in the Strait of Georgia at a distance of 3 km offshore in 80 metres of water. There is no disinfection of final effluent.

Sludge
PS is thickened in a pair of gravity thickeners and the thickened sludge is stored at 5% solids in a sludge holding tank prior to dewatering by two Andritz high speed centrifuges. Dewatered sludge at 25% solids is transferred in screw conveyors and loaded into a tandem axle dump truck with a watertight sealed box for transport to an offsite composting facility. Thickener supernate and centrifuge centrate are returned to the headworks for treatment.

Dewatered sludge has been managed in a number of ways since the plant opened. From 1984 to 1991 sludge was composted on-site using the aerated static pile composting method.

Following an odour lawsuit in 1991,  composting was moved off-site to a regional landfill and windrow composted using a Cobey compost turner. Inclement weather at the windrow site forced the CVRD to seek additional disposal methods and a pilot land application was tried. In 2003, an enclosed aerated static pile composting facility was constructed.

Effluent
The CVWPCC has consistently met effluent discharge quality targets since commissioning, however, it has been plagued by odour complaints from local residents. A 1991 lawsuit resulted in the CVRD moving the compost operations off-site and the construction of over $2 million worth of odour control measures. These include a ferrous chloride dosing station to combat H2S formation in the force mains, tank covers, a foul air collection system, a caustic/hypochlorite wet chemical scrubber and a 40 metre tall discharge stack for treated air. With the commissioning of the scrubber system in April, 1997, odours have been dramatically reduced from previous levels.

The Comox Valley Water Pollution Control Centre is classified as a Level IV plant.