December 2008, Vol. 20, No.12
City of Penticton (British Columbia) Advanced Wastewater Treatment Plant
Startup date: 1960; upgraded in 1971 and 1991
Service population: 35,000
Number of employees: 10
Design flow: 4.8 mgd (18,200 m3/d)
Average daily flow: 4.0 mgd (15,000 m3/d)
Peak flow: 4.5 mgd (17,000 m3/d)
Annual operating cost: $1.4 million
In addition to treating the flow from its 35,000 customers, the staff and management at the City of Penticton (British Columbia) Advanced Wastewater Treatment Plant also find new ways to do more with less. For example, in 2007 alone, they designed a methane-gas scrubber that enabled the time between boiler cleanings in the cogeneration system to triple, installed two new suspended-solids meters on their bioreactor to help reduce the daily lab routine and provide insight on how suspended solids fluctuate throughout the day and night (grab samples were always collected at the same time), and installed a washer and dryer to clean uniforms, resulting in a $3000 to $4000 annual savings.
In fact, one of the city’s projects may have led to a reduction in flow reaching the plant. In 2007, the plant received 1.31 billion gal (4.95 million m3/d) of influent from the sanitary sewer system, compared to the 2006 influent flow of 1.34 billion gal (5.1 million m3/d). This decrease in flow may be the result of the City of Penticton’s initiative in water conservation. The 2007 average daily influent flow rate was 3.6 mgd (13,600 m3/d), and the average influent flow rate per person was 105 gal/d (0.4 m3/d) per person, based on the 2007 Penticton population estimate of 34,002 people.
to the anaerobic zone. This process biologically removes both nitrogen and phosphorus, and reduces the effects of nitrates on the anaerobic stage.
The Penticton plant is an activated sludge facility that uses the modified University of Cape Town configuration — that is, the wastewater passes through an anaerobic zone, two anoxic zones, and an aerobic zone, respectively, and then is clarified. Return activated sludge is pumped from the clarifier to the first anoxic zone, and mixed liquor is recycled from the aerobic zone to the second anoxic zone and from the first anoxic zone
All staff at the Penticton Advanced Wastewater Treatment Plant participated in a 2-day safety course. Here, Dillon Bucknell and Korey Birch practice chlorine-leak response training. (Photo by Randy Craig)
Before reaching the biological nutrient removal process, the flow passes through a vertical bar screen and a vortex degritter in the headworks. Settling occurs in five rectangular primary clarifiers. Liquids then enter two equalization basins, while the solids move on to two fermenters for volatile fatty acid production, which later aids in phosphorus removal.
Two secondary clarifiers serve the biological nutrient removal process and are followed by three low-head sand-media filters with automatic backwashing. Next, the water is disinfected with gaseous chlorine and flows through three contact tanks, followed by dechlorination with gaseous sulfur dioxide.
The treated effluent has less than 0.15 mg/L total phosphorus, less than 5.0 mg/L biochemical oxygen demand and total suspended solids, less than 1.0 mg/L ammonia as nitrogen, and fecal coliform counts lower than 2.2 MPN per 100 mL. This quality of effluent is required to protect and preserve both the highly valued trout and kokanee spawning resource and the recreational value of the Okanagan River channel.
Penticton’s effluent is then either discharged to the Okanagan River outfall or stored in two emergency retention basins for later reuse. In 2007, the plant discharged 1.2 billion gal (4.4 million m3) of effluent to the Okanagan river channel. The average effluent discharge rate in 2007 was 3.2 mgd (12,100 m3/d), compared to an average effluent discharge flow rate of 2.9 mgd (11,000 m3/d) in 2006.
The treated effluent can be stored in two emergency onsite 9.5-million-gal (36,000-m3) storage basins for reuse (specifically, for irrigation). Irrigating with the effluent is accomplished using three 60-hp (44.7-kW), eight-stage vertical turbine pumps.
Maximum pumping capacity is approximately 26 gal/s (1 m3/s). In 2007, 159 million gal (602,000 m3) were used for irrigation, accounting for 12.2% of the total plant flow. The city currently irrigates the Penticton Golf and Country Club’s 71.9 ac (29.1 ha) and King’s Park’s 12.6 ac (5.1 ha).Solids
Primary solids are fermented and then treated by anaerobic digesters. The methane gas produced by the digesters is used to heat plant buildings and the solids process. Mixed liquor suspended solids are thickened in a settling tank to 2% solids, then gravity-belt thickened to 6%, and belt-filter press dewatered to 13% solids before being composted at the city’s compost site. Composting is by static-pile aeration method, which produces a Class A compost. This resulting biosolids product is used by city parks, landscapers, the public, and orchards for agriculture use.
Optimization at the Penticton plant also goes beyond the processes into staffing matters. In 2007, the plant reorganized the staff structure to create a foreman’s position to aid in attracting and retaining employees, as well as to define more clearly the management hierarchy. That reorganization also created two operator III positions.
The plant also is in the third year of its staff training program that helps to promote and retain individuals; 100% of the staff completed the 2.4 continuing education units needed to stay current with the Environmental Operators Certification Program, the British Columbia certification program.
The plant also brought in outside consultants for a 2-day course in confined-space entry and rescue, hazard identification and risk assessment, and chlorine-leak response training. All plant staff participated in these training sessions.