The municipality’s lagoons and wetlands system was designed for seasonal discharge (early spring and late fall) with a maximum of 700 m3 average daily flow. As of 2011, the facility was already operating at maximum hydraulic loading. An upgrade was required to meet current and future demand. In order to attain the capacity increase without constructing additional lagoons, the process was to be converted from seasonal to continuous discharge. This required the effluent quality meet permit requirements on a year round basis.
In 2014, Napier-Reid was selected to construct the housing facilities and supply the equipment for the lagoon’s aeration and chemical treatment systems as well as all the mechanical upgrades within the scope of work.
There are two lagoons; the south lagoon cell serves as a storage facility. The north lagoon cell was divided using three heavy-duty floating baffle curtains to divert flow and effectively maximize the hydraulic retention time by preventing short-circuiting. Fine bubble submerged diffused aeration was implemented in the partitioned cells to achieve improved year-round BOD5 and TSS removal through bacterial degradation and solids settling.
Napier-Reid constructed a building to house three positive displacement blowers (two duty and one standby) which supply the required oxygen demand (OD) to the aeration system. The variable frequency drives respond to the dissolved oxygen probe readings, through a common control panel.
A chemical building was also erected for the chemical addition to the discharge pumping station at the wetland cells.
The components and design approach for the Stirling wastewater treatment process demonstrates the ability to increase hydraulic capacity and provide nutrient removal in a lagoon based process. The current design also maximizes the use of existing lagoon infrastructure and maintains low operation and maintenance costs.