Client: Municipality of the County of Inverness
Solution: Sequencing Batch Reactor (SBR)
The rural coastal community of Port Hood, N.S. with a population of around 1300 people, like many other small Nova Scotia communities has aging municipal infrastructure. In 2011, the wastewater collection system was extended to the adjoining community of Harbourview, where an additional approximately 80 homes were connected to the wastewater collection system. Water distribution piping was also extended along with the sewer lines.
Phase 2 of the project was for the replacement of the Port Hood Sewage Treatment Plant (STP) which was originally built in 1971 with major upgrades in 1996. The STP design flow was for 225,000 USgpd with peak flows as high as 450,000 Usgpd. Effluent discharge criteria was set at 20/20 mg/l BOD/SS.
After several options for treatment technologies and site selection were considered and costed, the strategy chosen was to use the Sequencing Batch Reactor (SBR) technology on the site adjacent to the existing STP. The advantages of using this site included:
- Could intercept around 80% of the existing flows and direct it to the head of the new plant by gravity.
- Could extend the recently added Harbourview sewers (force main) up to the new headworks(15% of the flow).
- Only a small sewage pump station needed to divert around 5% of the existing flows to the head of the new plant site.
- Could make use of the existing sewage outfall.
The chosen site, while located conveniently with respect to the existing plant, had its challenges. First task was to re-locate a small residential house to a new foundation on a lot removed from the site. The site also was quite narrow and sloped towards the Port Hood Harbour. The seaward bank, situated on the Atlantic Ocean coastline, was subject to coastal erosion. Part of the project was tore-enforce the slope protection using a system of geotextiles, rip rap and armour stone.
The design of the plant made optimal use of the lot configuration. The plant configuration included an upstream concrete headworks structure where a channel grinder macerates solids and stringy materials and a parshall flume and ultrasonic transducer provided flow monitoring back to the control building.
After the headworks structure, sewage gets directed through a flow splitting structure and into a two train SBR plant constructed of reinforced concrete tankage with aluminum covers. The SBR chosen was Fluidyne’s ISAM™ - Integrated Surge Anoxic Mix SBR with flow equalization and integral sludge reduction system. This provided flow equalization storage, elimination of aerobic sludge storage tanks and power savings due to no requirement for blowers for sludge digestion. Sludge reduction and thickening is achieved in the ISAM™ process. Wastewater is introduced into the SBR into a SAM tank (Surge Anoxic Mix), where solids and floatables are captured, wastewater gets“conditioned” and anaerobic sludge digestion takes place.
For greater flexibility and ability to treat varying quantities and qualities of sewage, the two trains are interconnected and able to run independently or together. Batches may alternate from one SBR train to the other or the plant may operate in single train mode with the second train tankage available for emergency conditions or as simply equalization storage for the active train.
After the SAM tank, the wastewater gets treated in the SBR via an aerated equalization/batch tank and SBR Reactor tank. Blowers within basin air lines and SBR jet motive pumps and in basin piping with jet nozzles provides the aeration and mixing for the treatment process.
Treated effluent is decanted through a Solids excluding fixed wall decanter which is mounted on each reactor tank end wall. This end wall is a common wall with the basement wall of the control building. Effluent piping from each SBR reactor tank discharges into an in-floor channel and is directed through an in channel Ultraviolet disinfection system prior to being piped to the former STP outfall.
The facility makes use of state of the art SCADA to monitor the process and allow for remote monitoring/control. Levels in the tankage, status of the pumps/motors, influent flow, process status, mlss of the SBR contents, UV intensity, equipment timers, etc are all connected to the SCADA system.
Operation of the plant was commissioned in the Spring of 2013 and has been treating the community wastewater and meeting the regulatory discharge criteria.