The Cranbrook Wastewater Treatment Plant Upgrade: An Example of Sustainability

The City of Cranbrook (British Columbia, Canada) upgraded its wastewater treatment system (WWTS) in 2010-2011 in response to an Environmental Appeal Board's decision to decrease the storage volume in one of its storage lagoons (Storage Pond 2) and because the system was reaching its maximum capacity. The City of Cranbrook had to decide between keeping the existing lagoon system and developing a new mechanical activated sludge treatment system. The City of Cranbrook decided to upgrade the lagoon system because it was the more sustainable upgrade option with benefits to the population and the environment. The lagoon system was upgraded to achieve “zero discharge” most or all of the time within the next 30 years. The upgraded WWTS produces a high quality nitrified effluent of which most or all is used for irrigation. If future treated sewage flows exceed the irrigation requirements, due to an event such as excessive rainfall, disinfected treated effluent may have to be discharged to the Kootenay River. The following challenges had to be overcome to achieve the desired sustainable approach to upgrading the system:• Additional storage capacity for effluent reuse• Treatment and storage (variable level pond 2): new aeration system upgrade• Canadian cold climate nitrification in ponds• Phosphorus removal in lagoon treatment system• Wastewater reuse and water conservation.The approaches taken to overcoming these challenges and upgrade the lagoon wastewater treatment system are discussed in this paper.