Case Study of Anaerobic, High Strength Wastewater Treatment System for City of Portage la Prairie, MB, Canada

The City of Portage la Prairie lies 50 miles west of Winnipeg, in the heart of Manitoba's farming belt. As the global population increases, food processors increase production to meet the global demand, which subsequently generates more wastewater. To meet pre-treatment requirements associated with existing food processors in the aera increasing production and new food processors developing new plants in the area, the city of Portage la Prairie needed to build a new anaerobic treatment system prior to their existing aerobic treatment system to handle wastewater from different food processors, such as potato and peas. In 2017, the city decided to partner with Evoqua (now Xylem) to build an anaerobic wastewater treatment system to replace an existing BVF reactor previously operating on-site. This treatment system was designed to treat 8,400 m3 of wastewater per day from potato and pea processing plants, totaling 32,800 kg/d of COD. Pairing an anaerobic system with a downstream aerobic system minimizes the energy consumption of the overall wastewater treatment plant, which algins with global sustainability efforts aimed at reducing carbon footprint. Not only does the anaerobic system reduce electricity consumption associated with aeration, mixing, and sludge dewatering in the aerobic system, but it also generates biogas from industrial wastewater, providing renewable energy for the wastewater treatment plant. For this anaerobic wastewater treatment system. Evoqua decided to use a low-rate anaerobic treatment system which consists of a lead ADI-BVF reactor, followed by a lag ADI-BVF reactor to clarify the effluent to meet pretreatment requirements. The entire anaerobic wastewater treatment system (i.e. BVF reactors) significantly digests the soluble COD, BOD, and TSS, and coverts the biodegradable organics into valuable biogas. As part of a future project, biogas will be utilized in a dual fuel boiler to meet heating demands around the plant. Technology Description The anaerobic ADI-BVF(R) reactor is an earthen basin with a concrete perimeter wall lined with a geomembrane liner. Specially designed influent piping evenly distributes incoming wastewater throughout the front-end of the reactor, where the majority of the biologically degradable organics are digested and converted to biogas. A supernatant recycle (SREC) pump is used to mix clarified liquid from near the top of the reactor through the influent distribution system, and a return anaerobic sludge (RANS) pump is used to periodically return settled sludge from the back end (sedimentation zone) of the reactor to the front-end. The lag BVF reactor is also an earthen basin covered with a geomembrane system (same material as lead BVF reactor cover). Further anaerobic pre-treatment and solids clarification is conducted in the lag BVF reactor. The lag BVF reactor has the ability to withdraw RANS and return settled solids to the lead BVF reactor influent and sludge blanket using the RANS pumps. The supernatant from the lag BVF reactor flows by gravity to the existing aerobic system. The BVF reactors are covered with a multi-layered, flexible, insulated geomembrane cover which allows for the reactor to operate under a slight vacuum. Biogas generated in the system migrates to the reactor cover perimeter, and speed-controlled blowers transmit the biogas to a waste gas incinerator. The wastewater treatment plant has been operational for 4 years since its commissioning in January 2020. The BVF reactors have effectively treated the incoming wastewater and produce high quality effluent. The ADI-BVF reactors have consistently removed over 95% of the wastewater COD load, discharging anaerobic effluent with an average COD concentration under 200 mg/l, and an average TSS concentration under 100 mg/l.