Advanced Phosphorus Removal with Woven Cloth Filters: Full Scale Experience

INTRODUCTION Across the world, eutrophication problems are still being addressed through the implementation of phosphorus removal technologies at water resource recovery facilities. As effluent phosphorus limits become increasingly strict, numerous treatment technologies have been developed. One such technology, woven cloth media filtration, has been successfully used for decades in effluent polishing applications. More recently, this versatile technology has been integrated with chemical pretreatment as an advanced tertiary treatment system, allowing facilities to meet low (<0.3 mg P/L) and ultra-low (<0.075 mg P/L) effluent phosphorus concentrations. In order to update the wastewater industry on the phosphorus removal capabilities, treatment reliability, and important operating and design parameters of the technology, three filter installations were evaluated. OBJECTIVES The objective of this study is to present the performance data and operational insights from three installations: Arvidstorp (Sweden), Sun Prairie (Wisconsin USA), and Nenäinniemi (Finland). An evaluation of each installation's effluent quality will be presented, as well as other key design parameters such as hydraulic and/or solids loading rates, backwash requirements, and chemical (coagulant/polymer) consumption. Best practices for the operations, such as automated chemical dosing, enhanced media cleaning requirements, and operational costs, will be presented. FINDINGS Arvidstorp WWTP, Sweden In the summer of 2014, the Arvidstorp WasteWater Treatment Plant (WWTP) commissioned an advanced tertiary system for phosphorus removal. Between 2014 and 2018, the plant was operated with a designed peak flow of 2,700 m3/h. In 2018, the filter units were upgraded (via installation of more discs) to increase the treatment capacity to 3,600 m3/h. The maximum influent design Total Suspended Solids (TSS) concentration is 100 mg/L. The target effluent performance is to reach Total Phosphorus (TP) < 0.3 mg/L as a monthly average. The configuration at Arvidstorp is unique in that it allows for 50% of the influent to bypass the secondary treatment steps and to be routed directly to the advanced tertiary treatment system (see Figure 1). Testing was performed with and without chemical dosing. Results of testing during dry weather and wet weather conditions were as indicated in Table 1. The testing results demonstrated the tertiary treatment system's ability to meet and exceed the effluent demands. Sun Prairie WPCF, Wisconsin USA The Sun Prairie Water Pollution Control Facility (WPCF) in Sun Prairie, WI commissioned an advanced tertiary system for phosphorus removal in the summer of 2022. The site needs to meet a seasonal low TP limit of < 0.075 mg/L and TSS limit of 5 mg/L. Three (3) traveling bridge sand filter basins were repurposed with chemical conditioning tanks (rapid mix tank, coagulation tank, & flocculation tank) and two (2) filter units. The system is designed to treat an average flow of 945 m3/h and a peak flow of 1,460 m3/h. The influent design concentrations for suspended solids and phosphorus are summarized in Table 2. Performance testing was successfully completed in July 2022. Throughout the following year (July 2022 through July 2023), the facility achieved the seasonal effluent TP limit of < 0.075 mg/L due to the system's consistent performance, even during peak influent loading (see Figure 2). Nenäinniemi WWTP, Finland Located in Jyväskylä, Finland, the Nenäinniemi WWTP has a permit limit of TP<0.3 mg/L on the effluent. An advanced tertiary treatment system was commissioned in 2017. The system's design basis was for a peak capacity up to 4,220 m3/h with influent TSS and TP concentrations of 60 and 1 mg/L respectively. Sampling and testing from 2020 through 2021 demonstrated the system's ability to achieve levels below the <0.3 permit requirement (see Table 3). A positive experience at the Nenäinniemi WWTP has been the site's ability to maintain performance while also optimizing the chemical dosing and thus reducing operating costs. Initially, the facility used a manual adjustment methodology to control the dosing of coagulant and polymer. In 2021, the facility implemented automated control of the chemical dosing via online instrumentation and PLC. By implementing a combination of feed forward and feedback control loops, the facility was able to reduce coagulant dosing by ~70% and polymer dosing by ~35%, while also improving the effluent TP concentrations by ~20% (see Table 3). CONCLUSIONS The experiences and data shown at the Arvidstorp, Sun Prairie, and Nenäinniemi facilities demonstrate the long-term treatment capabilities of advanced tertiary treatment systems integrating woven cloth media filtration with chemical pretreatment. Design practitioners will gain a better understanding of critical design parameters to achieve low and ultra-low phosphorus concentrations, while operators will learn best practices for long-term success. In summary, effective system design (including chemical pretreatment) and implementation of best management practices make woven cloth media filtration technology a reliable alternative to achieve low and ultra-low phosphorus concentrations.