SIMPLE FILTER CAPPING APPROACHES FOR ENAHANCED BIOLOGICAL FILTRATION PERFORMANCE. Andrew WT Wong, EIT, University of Waterloo*

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1 SIMPLE FILTER CAPPING APPROACHES FOR ENAHANCED BIOLOGICAL FILTRATION PERFORMANCE Andrew WT Wong, EIT, University of Waterloo* Monica B Emelko, Ph.D., University of Waterloo Timothy Walton, A.Sc.T., Region of Waterloo *Department of Civil and Environmental Engineering, University of Waterloo, 200 University Ave W, Waterloo, Ontario, N2L 3G1 Water Services Division, Region of Waterloo, 150 Frederick St., Kitchener, Ontario N2G 4J3 BACKGROUND A biologically active filter (BAF) employs the metabolic capacity of bacteria that are attached to a support matrix in the form of a biofilm to oxidize biodegradable organic matter (BOM), and use it as a carbon source. It has been well documented in literature that there are a number of benefits to using biological filtration, such as: removing of disinfection by-product precursors, taste and odour compounds, iron, manganese, ammonia, nitrate, and improving the biological stability of the finished water. A filter is considered biologically active when no residual disinfectant is measured in its effluent (Evans, 2010). The filter media selection and configuration of a biologically active filter are important design parameters to consider as they have cost, performance, and operational implications (Urfer, et al., 1997). Anthracite, granular activated carbon (GAC), and sand are typically used as the support matrix for BAF. Previous studies have demonstrated that expanded clay aggregates (ECAs) can be used for BAF (Melin & Odegaard, 1999; Persson, et al., 2006). Studies investigating the use of plastic media as a biological carrier element in fixed bed bioreactors (Min et al., 2004) and moving bed biofilm reactors (Ødegaard, 2006) for water and wastewater treatment, respectively. However, the use of non-adsorptive media as a capping material, such as ECAs and plastic media, combined with adsorptive media, such as GAC, in a deep bed BAF has not been previously reported. Recently, the concept of nutrient amendments has gained popularity in the drinking water industry. There are a variety of different stoichiometric carbon, nitrogen, and phosphorous (C:N:P) ratios that have been presented as being ideal for biological treatment; however, a C:N:P ratio of 100:10:1 is often referenced to improve BAF operation and performance (Lauderdale, et al., 2012; LeChevallier, et al., 1991). Lauderdale, et al., (2012) observed an improvement in the head loss development of their biological filters while amending the influent phosphorous concentrations. Over the course of 17 consecutive filter cycles, each lasting 18

2 hours, from the 12 th filter cycle onward that was a noticiable change in the head loss development (FIGURE 1). FIGURE 1: COMPARISON OF NUTRIENT-ENHANCED (PO 4 -P) AND BIOFILTER CONTROL HEAD LOSS PROFILES (LAUDERDALE ET AL., 2012) The purpose of this project is to demonstrate some of the benefits of biological filtration while assessing the impact of capping material selection and nutrient amendments on operational filter performance, and the removal of BOM. MATERIALS AND METHODS A series of five pilot scale BAFs containing coal-based GAC, a combination of ECA and GAC, and a combination of a plastic media and GAC were set-up at the Mannheim Water Treatment Plant (MWTP) to allow for the comparison of the different filter media combinations. The influent water for the pilot filters comes directly from the full scale plant following chemical coagulation and flocculation, clarification, and ozonation. The overall height of the media in the filter bed is 1.3 m, which includes a 0.3 m layer of support sand at the bottom of each filter. The capped filters have 0.2 m of GAC media replaced with a larger diameter ECA or plastic media. The effective size of the GAC and ECA media are 1.3 mm and 1.7 mm, respectively. The plastic medium has a diameter of 2.5 cm. The filters were operated at a loading rate of 8.5 m/h and were backwashed on a schedule of approximately hours. Each filter was backwashed with its own filtrate using a collapsed pulse backwash (described by Amirtharajah (1993)) followed by a high rate water wash.

3 FIGURE 2: PILOT PLANT FILTER COLUMNS AND MEDIA CONFIGURATIONS The performance of the BAFs has been assessed through measurements of effluent turbidity, head loss, filter run time, removal of dissolved organic carbon (DOC), ammonia (NH 3 -N), total phosphorous (TP), and soluble reactive phosphorous (SRP). Analyses were conducted at both warm ( 10 C) and cold (< 10 C) water conditions, when possible. RESULTS Operational data (effluent turbidity, head loss, and filter run time) were collected from 2 August, 2013 to 16 March, Nutrient data were collected from 30 October, 2013 to 16 March, These results include brief period of warm water conditions, a transitional temperature period, and cold water conditions. Additional cold water data are being collected, and warm water data will be collected this spring and summer. Capping Material Selection Following filter ripening, excellent effluent turbidities equal to or less than 0.1 NTU were achieved from each filter media configuration. As the temperature decreased turbidity breakthrough was observed in all filters. It has been observed that using the ECA as a capping material offers some improvement in the effluent turbidity, while using the plastic media is slightly worse, compared to the GAC filter. Work is being done to confirm these results by examining the relative error of the turbidity instruments due to calibration. Across all temperature ranges, replacing a 20 cm layer of GAC media with a larger diameter media reduced the rate of head loss development. Terminal head loss was reached in the ECA and plastic media capped filters up to a day after the

4 GAC filter. During warm water conditions, material accumulation was observed at the top of each of the filter media beds. A thin layer of material accumulation, approximately 0.5 cm thick, was observed at the top of the media bed of the GAC filter (FIGURE 3). In contrast, in the plastic media capped filter, an accumulation of material around each plastic element was observed for its full 20 cm depth (FIGURE 4Figure 4). It is speculated that the improvement in the head loss development is related to the larger media size. FIGURE 3: GAC FILTER MEDIA BED FIGURE 4: PLASTIC MEDIA CAPPED FILTER BED The filter run time data was analyzed separately for at three temperature ranges: C, 5-15 C, and < 5 C, presented in TABLE 1, Table 2, and Table 3, respectively. At the warmest operating temperature, it was found that the filter run times for the ECA and plastic media capped filters were both significantly different than the GAC filter. The filter run times were extended up to one day. However, as the operating temperature decreased, no significant difference was observed in the filter run times between the capped and GAC filters.

5 TABLE 1: FILTER RUN TIME AT C Filter Media Configuration Average Run Time (h) Standard Deviation (h) GAC Plastic + GAC Expanded Clay + GAC TABLE 2: FILTER RUN TIME AT 5-15 C Filter Media Configuration Average Run Time (h) Standard Deviation (h) GAC Plastic + GAC Expanded Clay + GAC TABLE 3: FILTER RUN TIME AT < 5 C Filter Media Configuration Average Run Time (h) Standard Deviation (h) GAC Plastic + GAC Expanded Clay + GAC The collection of samples for DOC analyses began under cold water conditions. A summary of the DOC removal is presented in TABLE 4. The DOC removal achieved in the GAC filter was higher than either the plastic or ECA media capped filters. However, the differences in DOC removal between the capped and the GAC filters, respectively, were not significant. TABLE 4: COLD WATER DOC REMOVAL Filter Media Configuration Average DOC Removal (mg/l) Standard Deviation (mg/l) GAC Plastic + GAC Expanded Clay + GAC Nutrient Amendments In the literature, there are number of nutrient (carbon, nitrogen, and phosphorous) ratios that are referenced as being optimal for biological water treatment processes. In the drinking water literature, the most widely referenced C:N:P stoichiometric ratio is 100:10:1 (Lauderdale et al., 2012; LeChevallier et al., 1991). Over the course of 11 filter cycles each lasting three days, the nutrient concentrations were amended to the prescribed C:N:P ratio of 100:10:1. The nutrients were injected into the top of the filter column in the form of ammonium chloride (NH 4 Cl) and phosphoric acid (H 3 PO 4 ). During the course of nutrient

6 amended filter runs, the operating temperature was 1 C. No significant changes were observed in head loss development, filter run time, or DOC removal. TABLE 5: FILTER RUN TIME COMPARISON WITH NUTRIENT AMENDMENTS (C:N:P = 100:10:1) Filter Media Configuration Average Filter Run Time (h) GAC GAC + Nutrients Plastic + GAC ECA + GAC ECA + GAC + Nutrients Standard Deviation (h) TABLE 6: DOC REMOVAL COMPARISON WITH NUTRIENT AMENDMENTS (C:N:P = 100:10:1) Filter Media Configuration Average DOC Standard Removal (mg/l) Deviation (mg/l) GAC GAC + Nutrients Plastic + GAC ECA + GAC ECA + GAC + Nutrients PRELIMINARY CONCLUSIONS Based on the results observed to date at the pilot plant, the following preliminary conclusions have been drawn: - The larger plastic and expanded clay media have extended the filter run time without any change in effluent water quality. - These benefits in filter run time seem to diminish at lower operating temperatures; however, there are no negative impacts on filter performance, and there is still an energy benefit. - Preliminary results suggest that there are no benefits to amending the C:N:P ratio to 100:10:1. Nutrient amendment experiments are still being conducted at the pilot plant under cold water conditions. These experiments will be performed at warm water conditions to determine if the prescribed 100:10:1 C:N:P ratio is significant. ACKNOWLEDGMENTS This project would not have been possible without the help and partnership of several organizations and individuals. The authors would like to acknowledge and thank the Region of Waterloo for all of their help and support as well as the co-op

7 students, graduate students, and employees at the University of Waterloo, who have made this research possible. This research was also funded by an NSERC CRD grant, without which, this research would not have been possible. REFERENCES Amirtharajah, A. (1993). Optimum backwashing of filters with air scour: a review. Water Science & Technology, 27(10), Evans, P. (2010). Nature works biological treatment methods yield high-quality water. Opflow, 36(7), Lauderdale, C., Chadik, P., Kirisits, M. J., & Brown, J. (2012). Engineered biofiltration: Enhanced biofilter performance through nutrient and peroxide addition. Journal - American Water Works Association, (4215), LeChevallier, M. W., Schulz, W., & Lee, R. G. (1991). Bacterial nutrients in drinking water. Applied and Environmental Microbiology, 57(3), Retrieved from mcentrez&rendertype=abstract Melin, E. S., & Odegaard, H. (1999). Biofiltration of ozonated humic water in expanded clay aggregate filters. Water Science & Technology, 40(9), Min, B., Evans, P. J., Chu, A. K., & Logan, B. E. (2004). Perchlorate removal in sand and plastic media bioreactors. Water Research, 38(1), doi: /j.watres Ødegaard, H. (2006). Innovations in wastewater treatment: the moving bed biofilm process. Water Science & Technology, 53(9), doi: /wst Persson, F., Heinicke, G., Uhl, W., Hedberg, T., & Hermansson, M. (2006). Performance of direct biofiltration of surface water for reduction of biodegradable organic matter and biofilm formation potential. Environmental Technology, 27(9), doi: / Urfer, D., Huck, P. M., Booth, S. D. J., & Coffey, B. M. (1997). Biological filtration for BOM and particle removal: a critical review. Journal - AWWA, 89(12),