An environmentally conscious wastewater facility upgrade uses the optAER lagoon aeration with SAGR to achieve year-round non-toxicity compliance.
Location: Doaktown, New Brunswick
Project Type: Municipal Wastewater Treatment
Completion Date: December 2010
640 m3/day (0.169 MGD)
Effluent Quality Requirements:
cBOD5: 10 mg/L
TSS: 10 mg/L
Total Ammonia (Summer): 1 mg/L
Total Ammonia (Winter): 7 mg/L
Project Background & Challenges
The town of Doaktown, New Brunswick can be found in Northumberland County on the shores of the Miramichi River. Once home to one of the largest Atlantic salmon populations in North America, water from the Miramichi River eventually makes its way to the Gulf of St Lawrence. Today, the Miramichi River not only continues to support a large fishery, but the river attracts recreational fly fisherman from all over the world. In order to preserve this industry, the New Brunswick Department of Natural Resources has implemented rules and regulations for fishing.
But in order to protect life within the river, stricter limits were also placed upon the wastewater effluent that is discharged into the river. The Canadian government’s Wastewater Systems Effluent Regulations (WSER) department introduced new and lowered nutrient limits for all Canadian wastewater treatment facilities. With only one facultative lagoon servicing the needs of the plant, this meant the wastewater treatment facility (WWTF) at Doaktown would no longer capable of maintaining compliance.
Historically, lagoon systems like Doaktown were designed to meet BOD and TSS limits but were not capable of producing non-toxic effluent throughout the year. The increased federal enforcement of toxicity requirements has resulted in a greater focus on effluent ammonia levels, and the first indication of an issue is a fish kill in the receiving stream or river. For these reasons, engineers for Doaktown sought a cost-effective and reliable solution.
The Nexom Answer
In 2010, the existing wastewater treatment plant in Doaktown consisted of a single facultative lagoon. The proposed solution would utilize this existing lagoon as part of the overall upgrade, allowing the WWTF to realize cost savings in the construction, and long-term operation and maintenance of the system. The updated facility would consist of a new optAER® aerated lagoon for primary treatment, followed by the existing lagoon, which was divided into two treatment cells for secondary treatment, using a geomembrane floating baffle curtain to divert flow and effectively maximize the hydraulic retention time by preventing short-circuiting. Two SAGR® beds were then constructed to provide tertiary treatment before discharging into the Miramichi River.
Addition of a new aerated lagoon:
A brand-new lagoon was constructed west of the existing lagoon to serve as primary treatment, and aerated using Nexom’s optAER lagoon-based wastewater treatment system. In comparison to mechanical treatment facilities, optAER process-enhanced sites can be implemented at a fraction of the cost but still maintain the simplicity of a lagoon. Aeration provides internal sludge digestion, resulting in minimal solids accumulation, and extending the life of the lagoon.
Before construction began, the area underwent an archaeological study. The archaeological study determined the potential of finding archaeological artifacts or features during construction activities. A bird survey, a species at risk and a sensitive habitat survey were also conducted. While the bird survey and species at risk survey showed all species observed in the area were common, and therefore not at risk, wildlife observations showed the wood turtle species would likely to be encountered and construction personnel were directed to carefully remove them from site and place them near the river shore.
Air supply for the optAER system is provided by a 30 hp positive displacement blower, with a second blower on standby. When needed, the second blower also supports the SAGR aeration system.
Installation of optAER aeration into the existing lagoon:
The existing facultative treatment lagoon at Doaktown was first drained for sludge removal, and then expanded. It was divided into two separate cells by a geomembrane floating baffle curtain,m used to divert flow and maximize hydraulic retention time. The optAER system was then added to the two cells individually to assist with improved year-round BOD and TSS removal through bacterial degradation and solids settling.
With aerated partial mix cells, BOD is reduced to carbon dioxide, water, and inert ash via natural bacteria, which receive their oxygen supply through fine bubble diffusers. Through the slow rise of bubbles and subsequent mixing, convection cells are created between the diffusers, allowing solids to settle out between diffusers where the circulation loop is completed.
Diffusers are secured to floating laterals at the surface and suspended near the bottom of the lagoon. Marine grade suspension rope is used to hang the diffusers from the header, allowing for uniform diffuser elevations if the lagoon floor is uneven. This low location maximizes the oxygen transfer efficiency of the system, and also provides protection from ice movement in winter.
Floating laterals are secured against wind action with a stainless-steel cable system fastened to anchors in the lagoon berm and use a self-adjusting tensioning assembly. With floating laterals, cells do not have to be dewatered or taken out of service for system installation or maintenance. All maintenance can be done from a boat with a 2-person crew.
Implementation of the SAGRs:
At Doaktown, two SAGR beds were constructed after the lagoons for tertiary treatment, providing additional BOD and TSS polishing. The SAGR consists of an aerated submerged aggregate bed, with a horizontal flow distributing influent wastewater across the bed.
With the SAGR, the only moving parts are the blowers supplying oxygen to the lagoons and SAGR. A simplified control scheme manages the day-to-day operation of the blowers, maintaining the simplicity of a lagoon-based system while still meeting effluent limits. This simple process allows nitrification and polishing to be accomplished following any aerated or facultative lagoon.
One concern during the design of the Doaktown facility was low influent alkalinity, which is required for complete nitrification. However, following additional testing, it was determined that no alkalinity addition was necessary to meet the effluent limits. Operational data over the past 9 years has confirmed that the system meets the required nitrification levels reliably despite low alkalinity.
Upgraded System Performance
Following the successful completion of system construction, the upgraded WTTF at Doaktown was commissioned in December 2010, with operator training on December 20th. Since commissioning, the Doaktown facility has exceeded all effluent requirements – consistently producing low effluent concentrations for BOD, TSS and TAN.
The system was designed with simplicity in mind. The O&M requirements of the process are similar to the operation of a conventional diffused air aerated lagoon, but with no solids return to monitor and adjust, sludge management and disposal becomes a non-issue. Since commissioning, it is estimated operators of the Doaktown facility spend (an average) 30 minutes per day doing a systems check and maintenance.
One of the considerations while designing the treatment facility was the temperature of the effluent discharging from the lagoon, as warm water entering the Miramichi River was having an adverse effect on the salmon population. The system’s long retention time allows the temperature of the effluent time to drop to match environmental conditions, ensuring a safe breeding ground for the salmon.
The upgraded system in Doaktown is an example of a cost-effective and efficient solution for small and mid-sized communities. These communities face the same effluent challenges as larger communities and are now able to keep the low operational complexity and costs associated with their existing lagoon systems.
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