WCW24

The challenge of maintaining wastewater treatment performance during cold weather is a common problem for many biological nutrient removal (BNR) wastewater treatment plants (WWTP) across Canada, including the EPCOR Gold Bar WWTP in Edmonton. With an average treatment capacity of 310 MLD (82 MGD) and a peak capacity of 420 MLD (111 MGD) for secondary treatment, the Gold Bar WWTP faces operational hurdles when the wastewater temperature drops, leading to poor settling sludge and reduced clarifier capacity. To address this challenge, the plant has installed the inDENSE™ hydrocyclone technology on one of its eleven BNR trains. This technology uses hydrocyclones to enhance sludge settleability through selective sludge wasting and retaining well-settling sludge. Compared to other intensification alternatives like Membrane Bioreactor, inDENSE™ offers a less costly solution, potentially deferring large capital investments. Nevertheless, whether inDENSE technology is appropriate for facilities with cold wastewater is not well understood. With commissioning in Summer of 2023 and process optimization in the Fall, the system showed significant improvements in the sludge settleability by December 2023. Process optimization included the implementation of intermittent mixing and reduction in return activated sludge rates. Historically, the mixed liquor has exhibited poor settleability with SVI values over 250 mL/g in the winter. With inDENSE and the process optimization, the SVI improved dramatically, stabilizing around 150 ml/g, even as the temperature dropped from 19ºC to 14ºC over the five-month period. To further assess performance improvements, Stantec and EPCOR Gold Bar WWTP are collaborating to conduct intensive site testing through the Winter and Spring of 2024. This includes tall settling column testing, analysis of bioreactor nutrient profiles, clarifier flocculation test, sieve analysis, morphology, and kinetic rate tests. The BNR system with inDENSE technology will undergo testing where flow rates will be increased to stress the system's operational limits. These assessments will provide a comprehensive understanding of the additional flows and loads that can be managed by a bioreactor/secondary clarifier system equipped with selective sludge wasting compared to conventional treatment trains. The collected data will provide valuable insights for selective wasting, a cost-effective treatment intensification process, with a focus on cold wastewater BNR facilities across Canada.