🌟 **Optimizing PFAS Removal in Drinking Water Treatment: Efficiency, Cost, and Operational Strategies for Granular Activated Carbon Filters**...
Published on by Hossein Ataei Far, Deputy Manager of the Research, Technology Development, and Industry Relations Center at NWWEC
### 🌍 **Introduction: **
This study examines the removal efficiency of 15 per- and polyfluoroalkyl substances (PFASs) at the Bäcklösa drinking water treatment plant (DWTP) in Uppsala, Sweden, over two years (2015-2017). PFAS contamination in Uppsala’s groundwater was first detected in 2012. Some affected wells show total PFAS concentrations up to 250 ng/L. Following process modifications, Bäcklösa DWTP began treating water from two contaminated wellfields in April 2015 using ten granular activated carbon (GAC) gravity filters. PFAS concentrations were monitored throughout the treatment process, which included aeration, softening, sand filtration, GAC filtration, and disinfection. The study aimed to: i) investigate PFAS removal efficiency in a full-scale DWTP, ii) evaluate the long-term performance of GAC for PFAS removal, iii) assess the impact of GAC age and flow rate on PFAS removal, and iv) estimate the operational costs of PFAS removal using GAC under various treatment scenarios.
### 🌍 **Key Findings: **
➡️ **1. Efficiency of GAC Filters: **
- 🔹 PFAS removal efficiency was high (92-100%) with "young" GAC filters but decreased significantly (7-100%) with "old" filters as they approached 357 operational days or treated 29,300 bed volumes.
- 🔹 GAC filters were more effective at removing long-chained PFASs compared to short-chained ones. Perfluoroalkyl sulfonic acids (PFSAs) were removed more effectively than perfluoroalkyl carboxylic acids (PFCAs).
➡️ **2. Impact of Flow Rate: **
- 🔹 Adjusting the flow rate through two full-scale GAC filters of different operational ages revealed that lower flow rates, resulting in higher empty bed contact time (EBCT), improved PFAS removal.
- 🔹 The "young" GAC filter was less affected by changes in flow rates, while the removal efficiency of the "old" GAC filter increased substantially with decreased flow.
- 🔹 Reducing flow rates by 10 L/s increased PFAS removal efficiency by 14% in "old" filters and by 6.5% in "young" filters.
- 🔹 The study suggests that reducing the flow rate from the conventional 39 L/s to 18 L/s after reaching a treatment goal of 11 PFASs < 50 ng/L in the outgoing water could nearly double the service life of the GAC filters.
➡️ **3. Cost Analysis: **
- 🔹 The study highlights the cost implications of different GAC operation scenarios, showing that lowering flow rates after achieving treatment goals can reduce costs by 26%.
- 🔹 Unit costs varied depending on the treatment goals, ranging from 0.08-0.10 €/m³ for strict goals (10 ng/L) to 0.020-0.025 €/m³ for less stringent goals (85 ng/L) for 11 PFASs.
- 🔹 Lowering Sweden's current regulatory guideline from 90 ng/L to 50, 25, or 10 ng/L would increase annual operational costs at the DWTP by 21%, 135%, and 314%, respectively.
- 🔹 Regeneration costs are the dominant factor in PFAS treatment expenses at the Bäcklösa DWTP. Adopting a strategy of lowering flow rates at the end of the GAC filter's service life could help reduce operational costs.
### 🌍 **Results: **
The study confirmed that conventional treatment techniques are not effective for PFAS removal in full-scale DWTPs. However, GAC filters are a reliable method for PFAS removal, being straightforward to operate and benefiting from a competitive GAC market that helps minimize operational costs. The removal efficiency of GAC filters was higher for long-chained PFASs than for short-chained ones, with PFSAs removed more effectively than PFCAs. Adjusting the flow rate through GAC filters showed a positive correlation between PFAS removal and lower flow rates (higher EBCT). The "young" GAC filter was less affected by flow-rate changes, while the removal efficiency of the "old" GAC filter increased substantially with decreased flow. Based on six months of data from six GAC filters, the study suggests that the service life of GAC filters could be prolonged by nearly half if the flow rate were reduced from the conventional 39 L/s to 18 L/s after reaching a treatment goal of 11 PFASs < 50 ng/L in the outgoing water.
The cost analysis indicated that treatment goals significantly impact unit costs. Lowering Sweden’s current regulatory guideline from 90 ng/L to 50, 25, or 10 ng/L would increase annual operational costs at the DWTP by 21%, 135%, and 314%, respectively. Regeneration costs were identified as the dominant factor in PFAS treatment expenses at the Bäcklösa DWTP. Prolonging the service life of GAC filters by lowering flow rates at the end of their service life could reduce operational costs.
Please keep in mind that the effectiveness of GAC treatment is greatly influenced by water quality. It is important to conduct empirical studies for each raw water source when assessing GAC filters in full-scale DWTPs. Nevertheless, the tools and methods outlined in this study can be applied to other full-scale operations, providing valuable insights for drinking water providers worldwide.
### 🌍 **Implications: **
The study provides valuable insights into optimizing GAC use for PFAS removal, balancing efficiency and cost-effectiveness in drinking water treatment. It confirms that conventional treatment techniques are ineffective for PFAS removal in full-scale DWTPs, while GAC filters offer a practical and reliable alternative. Nonetheless, GAC treatment performance is highly dependent on water quality, and empirical studies are necessary for each raw water source to effectively compare GAC filters in full-scale DWTPs.
### 🌍 **Future Research: **
Future research should focus on monitoring GAC filter performance to ensure high PFAS removal efficiencies and should quantify the influence of EBCT, incoming PFAS concentrations, and water quality parameters like organic matter concentrations for better performance and GAC service lifetime predictability. The tools and methods presented in this study can be applied to other full-scale operations, providing valuable insights for drinking water providers worldwide.
📚 **Reference: **
[1] Belkouteb, N., Franke, V., McCleaf, P., Köhler, S., & Ahrens, L. (2020). Removal of per- and polyfluoroalkyl substances (PFASs) in a full-scale drinking water treatment plant: Long-term performance of granular activated carbon (GAC) and influence of flow rate. *Water Research*, 182, 115913.
**Figure 1** illustrates the conceptual scheme of the Bäcklösa drinking water treatment plant in Uppsala, Sweden. The figure depicts three main areas of investigation:
i) **Full-scale treatment efficiency** (represented by circles),
ii) **The influence of flow rate on PFAS removal** (represented by squares), and
iii) **The long-term performance of granular activated carbon (GAC)** (represented by triangles).
Key components include:
- **SF** = Dual media filtration
- **GAC** = Granular activated carbon
- **STAD** = Region of Stadsträdgården
- **SUN** = Region of Sunnersta