Client: Portugal Cove, St. Philip's, Newfoundland
Solution: ISAM™ Integrated Surge Anoxic Mix
The Town of Portugal Cove-St. Philip’s, Newfoundland Labrador --- The public works superintendent and his consulting engineer here report successful operation of a special activated sludge wastewater treatment plant (WWTP) for St. Philip’s since the end of 2003, with a similar and larger plant scheduled to start up for Portugal Cove later this year.
The currently operating plant, with design average flow of 7.7 liters/second. and peak flow of 28.5 liters/second, has consistently met effluent standards for biochemical oxygen demand (BOD), total suspended solids (TSS), total nitrogen (TKN), phosphorus (P), and fats/oils/grease (FOG). It has required only minimal, routine, maintenance-class operator attention, and has converted 99.999% of influent solids to landfill disposable sludge. The larger plant is to handle design average flow of 15.2 liters/second and peak of 34.2 liters/second.
The ISAM™ Integrated Surge Anoxic Mix System, manufactured by Fluidyne Corp. of Cedar Falls, Iowa, is specially designed to provide for lower amounts of sludge production compared to other activated sludge processes. Here, the system has processed over 129,000,000 U.S. gal. of raw sewage since startup, and to date only about 15,000 U.S. gal. of sludge has been removed. Fluidyne indicates similar results have been realized at numerous installations in the U.S. and Canada. The company’s local rep firm, ENG Environmental Technologies Inc. of Halifax, NS and St. John’s, NL, participated in system design, was on-site throughout installation, and remains committed to ongoing service as needed.
The St. Philip’s WWTP was the first treatment system for the town. The second system, presently under construction on the Portugal Cove side of town, is a direct result of the success of the first installation. The projects represent fulfillment of the joint local government’s 2002 commitment to proactive environmental protection for their pristine harbor, on behalf of both local residents and a growing tourism industry. The commitment not only includes exceeding all present guidelines, but also more stringent guidelines that are pending---without the use of chemical additions.
At St. Philip’s, where sewage for the 300 residences(850 PE) and a few commercial operations was previously handled via septic tanks, WWTP influent levels are BOD, 200 mg/L; TSS, 250 mg/L; TKN, 50 mg/L, and FOG, 50 mg/L.
The Provincial Dept. of Environmental and Conservation for Newfoundland/Labrador presently requires effluent treatment levels for BOD of 20 mg/l and TSS of 30 mg/l, with reduction to 10 mg/l for both parameters by both provincial and federal regulators considered possible within a few years. The new plant has consistently met the 10 mg/l level, with less than 5 mg/l measured more than 90% of the time.
TKN and FOG are also both consistently below 10 mg/l. Phosphorus has been recognized as consistently reduced to the 1 mg/l limit or below, and has often been non-detectable. Fecal and total coliform counts in the influent, at >10,000 cfu/ml, has been reduced to non-detectable.
“We’ve seen rapid growth here, especially since the late 90’s, and had moved from individual wells for drinking water to hooking up with the St. John’s Regional Water Supply,” said Roy C. Burry, Superintendent of Public Works for Portugal Cove-St. Philip’s. “But construction to also hook up regionally for wastewater would have been physically threatening to the drinking water system, and it was far too expensive as well. We worked with our engineers to consider alternatives for our own treatment facility to receive flow from a new local pipeline network we installed in our rocky and hilly terrain, and the SBR alternative we selected to receive input from that network has provided excellent service.”
“We had been impressed during visits to other sequencing batch reactor (SBR) plants that their effluent was good even though they were only being taken care of from time to time,” he continued. “That’s also been our experience, with a maintenance class operator taking sufficient care of it with only three visits a week, 3 hours each. The effluent is so clean and odorless, that if you put a glass of it next to a glass filled from the potable system, you can’t tell the difference. ”
Design limitations for the new WWTP that were established by the towns’ engineering firm included location on pristine oceanfront property; placement within residential development, as close as 60m to a residence; available footprint of only 1200 sq.m; and service for a small community that did not have a large, trained WWTP staff available, and needed a simplistic and economical plant to operate and maintain.
During initial scope, alternative technologies considered included lagoon, engineered wetland, oxidation ditch, rotating biological contact (RBC), and SBR.
“The engineered wetland and lagoon options were ruled out early in the selection process because of the large footprint they required, with the lagoon concept also having the disadvantage of open basins in a residential area,” recalled Darryl Mills, Project Engineer, and Group Manager, Municipal Engineering for Newfoundland and Labrador Consulting Engineers, Ltd. (NLCEL) of St.Johns, NL.
“Oxidation ditches are also open processes, and were challenged to provide the same level of treatment and technical effectiveness as RBC and SBR, which therefore became finalists.”
“Choosing between the finalists, we recognized SBR as a far more forgiving technology for a situation where there was no storm sewer, and no separate system underground for groundwater and rainwater runoff,” he continued. “There was a high potential for infiltration that could cause the flow rate to the WWTP to jump to 7-10 times the average, and we saw RBC as struggling with that scenario. It would have to go into a bypass mode and potentially wash off its biomass, thereby causing loss of treatment that could take as long as two weeks to restore, where the SBR in such a scenario could be back within a day or day and a half, with very little decrease in treatment efficiency.”
NLCEL had been given the mandate in the fall of 2002 to provide the appropriate WWTP, and the new SBR plant began receiving sewage in December of 2003---about 14 months after project inception. The initial technology evaluation took about 4-6 weeks. After SBR was selected, visits were arranged to six existing SBR sites, representing several different manufacturers.
“We wanted to know what the operators liked and didn’t like, and what they would have done differently,” Mills recalled. “Key issues that emerged included process reliability from a controls perspective; user-friendliness of controls and technology; and personnel requirements. SBR had always been considered the process that achieved the highest levels of treatment, but it was also one of the most complicated, and until the advent of the programmable logic controller (PLC), huge labor input was required.”
“We found the selected vendor had combined a strong process background with good programming people to develop a good controller for the operating plant,” he noted. “What was previously very complex for operators was now very simplified. We also learned that SCADA was essential, and that we wanted it for every piece of equipment, so that everything was on the operator’s screen in his office, and changes could be made from his desktop.”
Mills added that service availability was also a key consideration.
“The plant site is located on east limits of Canada, on the island of Newfoundland, and can often be considered isolated regarding a time frame for any spare parts and technical expertise that might be needed,” he explained. “We found this vendor had also done a good job finding strong, competent local service people. We didn’t want a manufacturer who was going to install and then forget about it after a few months. It was a small project to some, but to us, it was large. The vendor’s local rep was there throughout the design and construction stages, and remains on call. It’s one thing to sell a process, and quite another to find long-term service.”
Mills said five SBR manufacturers were reviewed, three were finalists, and Fluidyne was the low bidder of the two that bid during the tendering stage. The tender had included a requirement for established Newfoundland representation, and also noted stipulations regarding particular equipment.
“We wanted to use high-level equipment for all system components, to promote maximum reliability for a long-term commitment beyond warranty,” he said. “This has helped the realization of little on-site presence required for reliable and continuous operation. The operator has been needed on site only for an hour or so every three days, versus an original estimate of an hour to an hour and a half every day.”
For the first four years of operation, the plant has removed about 60,000 liters of sludge to landfill. The second and larger WWTP, for Portugal Cove, is designed to mirror the successful St. Philip’s WWTP, with minor improvements.
In particular, a special piping system will allow for easy transfer of the sludge blanket from one treatment train to another. Both projects have two treatment trains, with one of them redundant at a given time.
“At the request of the superintendent, if the active train gets a peak load, and the biology is killed off due to contaminant shock loading or infiltration, they’ll be able to quickly seed the disturbed train with the undisturbed train just by opening a valve and turning on a pump,” Mills said.
Fluidyne describes its Integrated Surge Anoxic Mix (ISAM™) system as a single-train type, with a constant-level anaerobic selector chamber followed by a surge/anoxic/mix (SAM™) tank, and then one or more SBR basins. It is designed to incorporate BOD, TSS, and nitrogen removal with sludge reduction, in an integrated process.
The system has consistently demonstrated 0.15-0.25 lbs of sludge production per lb. of BOD removal, compared to 0.5-0.6 for other SBR systems, and an average daily conversion of influent wastewater to sludge of about 0.1%, compared to a typical conversion rate for other biological processes of about 2%.
In operation, all influent flow enters the anaerobic chamber, where solids settle in the manner of a primary clarifier. Elimination of primary solids at that stage is said to allow for much smaller SBR basins, at equivalent SRT, than with conventional SBR’s.
The anaerobic selector is noted as creating soluble carbon as a food source for biological nutrient and phosphorous removal, through conversion of settleable BOD to soluble BOD, while forcing the release of phosphorous by subjecting the recirculated biomass to anaerobic conditions.
Influent then continues to the SAM™ surge basin, also known as the influent equalization basin. This part of the system is said to provide flow and nutrient equalization that allows for optimization of treatment at the full range of flows and loadings.
Mixed liquor is maintained in the SAM™ tank for immediate reaction with flow from the anaerobic chamber, in order to suppress odors, and also initiate and accelerate carbon and nitrogen reactions. In addition, mixed liquor is recycled from the top of the SBR tank, for removal of scum by a proprietary flow and scum control sub-system.
Nitrates are recycled to the SAM™ tank for denitrication, with reactions said to be accelerated in the presence of unreacted carbon from the raw sewage entering that tank. Aeration and energy requirements are said to be reduced, as nitrates are fully reduced to nitrogen gas there.
In addition to WWTP applications like the St. Philip’s installation, Fluidyne says its ISAM™ has also been used as a stand-alone system to thicken and destroy organic sludge from other biological treatment plants, as a means for significantly reducing sludge disposal volume.