ABSTRACT TWO YEAR CASE STUDY OF INTEGRATED FIXED FILM ACTIVATED SLUDGE (IFAS) AT BROOMFIELD, CO WWTP Mr. Ken Rutt 1, Jim Seda 1 and Mr. Chandler H. Johnson 2 1 City & County of Broomfield 2985 West 124th Street Broomfield, CO 82 2 AnoxKaldnes, Inc. The City & County of Broomfield wastewater treatment plant secondary treatment processes were upgraded to a new biological nutrient removal process described as Integrated Fixed Film Activated Sludge (IFAS) back in 23 using a moving bed plastic carrier element to help grow the biomass. This allows the existing aerobic reactors to maintain nitrification during year round operation while still operating near conventional activated sludge solids retention times (SRT) one would find in just carbonaceous treatment plants. The upgraded IFAS system includes anaerobic and anoxic reactors to help meet new effluent Total Nitrogen and Total Phosphorus limits. The performance of the entire system since July 23 averaged effluent concentrations of 2.4 mg/l for BOD, 4.2 mg/l for TSS,.3 mg/l for NH 3 -N, 8.3 mg/l for NOx-N and 1.25 mg/l for TP while operationally during this period of time the aerobic suspended MLSS SRT averaged 4 days, the MLSS concentration averaged 1,718 mg/l and the SVI averaged 12 ml/l. The plant has operated with one set point for both the RAS and WAS rates for months at a time while meeting these very consistent effluent results. KEYWORDS IFAS, municipal wastewater, nutrient removal, Moving Bed biofilm process, MBBR, nitrification. INTRODUCTION Following an expansion in 1988, the City & County of Broomfield wastewater treatment plant secondary treatment processes consisted of a roughing biofilter (Trickling Filter) followed by activated sludge for meeting discharge limits of 25 mg/l cbod and 3 mg/l TSS at a flow rate of 5.4 MGD. Due to population increases & new regulations with respect to NH 3 -N, the city needed to upgrade its facility. To further add to the design and treatment requirements, the City was also adding treatment processes to reuse a large portion of its wastewater as reuse irrigation water. The storage system for the reuse water includes converting a former water supply reservoir into a water reuse reservoir. Therefore, the added treatment requirements of lower total phosphorus (TP) and total nitrogen (TN) levels became part of the overall plan. Table 1 shows the effluent requirements the City s WWTP would have to meet for the reuse water storage standards. 225
Table 1 City of Broomfield WWTP Effluent Requirements Parameter BOD TSS NH 3 -N TIN TP Effluent Requirement <1 mg/l <1 mg/l <1.5 mg/l Summer <3. mg/l - Winter <1 mg/l <1. mg/l The City & County of Broomfield evaluated six (6) options put forward by their engineer. Each option was evaluated based on a) future expansion, b) similar treatment process, c) land usage, as the selected approach needed to leave room at the site for eventual expansion to 16 MGD and d) overall cost. The City selected an IFAS (Integrated Fixed Film Activated Sludge) type process based on free floating plastic media. The first process train was converted during the summer months of 22. Wastewater was treated through the process train in September 22 and media was first added in November 22. The second process train was converted in the summer of 23 with final media addition by fall 23. After 2 years of operation, the staff has had the opportunity to play and learn from the new IFAS system. Figure 1 - IFAS principle with biofilm carrier (K1) used at the Broomfield WWTP INTEGRATED FIXED FILM ACTIVATED SLUDGE 226
In the simplest definition, IFAS takes a conventional activated sludge wastewater treatment plant and adds into its existing aerobic basins some form of media to help the slower growing bacteria, mainly nitrification type bacteria, to inhabit the media. The overall goal is to take the investment provided in the existing system (to perform BOD removal and potentially a portion of nitrification) while simply adding to it rather then building all new tanks or unit processes. An IFAS system is a process using kinetics from a suspended growth treatment system (namely conventional activated sludge) and adding to it kinetics from a fixed film treatment system. Fixed film technologies are well known for biological treatment of ammonia in cold temperatures as the bacteria / biofilm grows on a substrate / media and are kept within the system rather than being washed out during colder temperatures as in a conventional activated sludge system would typically see happen. Thus, during the winter time operation, the majority of the ammonia degrading nitrification bacteria are found on the media and retained within the system rather than washed out due to low aerobic SRT s. Factors that affect the overall design of an upgrade are: media type, aeration system pattern & type (complete floor coverage vs. spiral roll & fine bubble vs. course bubble), operational dissolved oxygen concentration, effluent NH 3 -N concentration, basin configuration and hydraulic profiles through the basin. All are necessary design factors which are required to help create a well working IFAS treatment system. Should one of these factors not be considered or designed properly, the overall treatment system could be adversely affected. Currently there are two (2) types of IFAS media categories in the market place, fixed media and free floating media. Fixed media can be similar to trickling filter type plastic media fixed in place and submerged in the reactor, or rope type media placed in a web or cage configuration and also submerged in the reactor. For both of these types of fixed media systems, the media is static and does not move around. These types of systems are placed above the activated sludge systems aeration system and flow makes its way through the basin and though the fixed media allowing contact of the wastewater constituents with the bacteria housed inside the fixed media. Free floating media are generally small plastic buoyant media or sponges which are placed in a reactor and move freely throughout the entire aeration basin volume. Since this media is moving around freely in the reactor, screens are required to retain them inside the aeration basin so they don t escape. THE BROOMFIELD WWTP Founded in the latter quarter of the Nineteenth Century, Broomfield, Colorado began as an agrarian community. Hard-working, community-oriented families located there on the heels of adventurous gold-seekers seeking their fortunes and hoping to strike gold in Colorado s wilderness. In 1961, the city incorporated with a population of 6,. Its growth continued at a moderate pace throughout the 7 s and 8 s. In the 199 s with the development of one of Colorado s premier employment centers, Interlocken Business Park, home to Sun Microsystems, Level 3 and the Flatiron Crossing regional shopping area, Broomfield s population nearly doubled from 24,638 in 199 to over 5, today. 227
Broomfield s original wastewater treatment facility was constructed in 1954 and consisted of a single treatment train of primary clarification, a trickling filter and secondary clarification. Over time as flows and loads increased, expansions took place in 1962, 1974, and 1988. As housing developments approached the treatment facility s boundaries, odor control improvements were constructed in 1996 and 1998. A Wastewater Utility Plan was completed in 1999 and contained the necessary information and direction to meet demands of providing wastewater collection and treatment service to the residents of Broomfield until the year 22. The proposed wastewater system upgrades and expansions coordinated with water system upgrades and expansions. Based on flow projections according to population, and industrial growth estimates to the year 22, the WWTP needed to be expanded to a capacity of 12 MGD. It was proposed that the expansion take place in two phases with the first phase expanding the plant to 8 MGD, including upgrades to meet the new stream standards and to control odors. FULL SCALE PLANT RESULTS The full scale design criteria for the system were based on winter wastewater temperatures and the maximum month primary effluent concentrations. Specific design criteria and a flow diagram of the treatment facility are shown in Table 2 Broomfield WWTP Design Specifications and Figure 2 Full Scale Flow Diagram, respectively. Table 2. Broomfield WWTP Design Specifications Flow Average Month 6.7 MGD Maximum Month 8. MGD Summer 6.7 MGD Winter TSS Maximum Month 6,54 lbs/day (97.5 mg/l) BOD 5 Maximum Month 9,725 lbs/day (145.8 mg/l) Soluble BOD 5 Maximum Month 6,5 lbs/day (9 mg/l) NH 3 -N Maximum Month 2,48 lbs/day (37.2 mg/l) TKN Maximum Month 2,724 lbs/day (4.8 mg/l) NO 3 -N Maximum Month 35 lbs/day (5.2 mg/l) MLSS Concentration 3,5 mg /L Solids Retention Time Suspended Growth 4.7 days Wastewater Temperature 13-25 C 228
Figure 2 - Full Scale Flow Diagram Mixed Liquor Recycle Primary Effluent To Secondary Clarifiers FEQ Return Mixed Liquor Recycle RAS from Clarifiers Flow Junction/ Splitter Box Anaerobic and Anoxic Basins (mixed liquor only) IFAS Aeration Basins (media and mixed liquor) Process Schematic of Broomfield BNR/IFAS Facilities Pre-Anoxic 12,846 ft3 (364 m3) Anaerobic 21,313 ft3 (64 m3) Anoxic 46,59 ft3 (1,319 m3) Aerobic 16,526 ft3 (4,546 m3) Figure 3 & Table 3 show in graphic form and table form, the monthly averages for the main influent characteristics of the facility. The overall flow to the facility over the past 3 years has been fairly consistent in the 4-5 MGD range, while the Figure 3 shows good variability in the concentrations for BOD, TSS & ammonia throughout the years. It should be noted that the table and graphs are only showing the influent ammonia while Organic N is not included as the facility doesn t perform TKN analysis and as such the overall nitrification load is higher. Figure 3 Monthly Average Influent Data (Flow, BOD, TSS, Ammonia, Temp) 5 Broomfield WWTP Monthly Average Influent Data 5 45 45 4 4 Flow (MGD), NH3-N (mg/l), Temp (C) 35 3 25 2 15 1 Influent Flow Influent Ammonia Wastewater Temperature Influent TSS Influent BOD 35 3 25 2 15 1 BOD & TSS (mg/l) 5 5 Jul-3 Sep-3 Nov-3 Jan-4 Mar-4 May-4 Jul-4 Sep-4 Nov-4 Jan-5 Mar-5 May-5 Jul-5 Sep-5 Nov-5 Jan-6 Mar-6 229
Table 3 Broomfield Monthly Average Influent Data Raw Influent Characteristics Month, Year Influent Total Alkalinity Flow TSS BOD5 NH3-N NO3-N NO2-N Total P PO4-P (as CaCO3) Temp (MGD) mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l ( C) July-3 4.73 349.7 185.3 3.71 2.57 2.17 7.2 1.39 246. 2.63 August-3 4.85 321.81 195.86 32.15 2.74 2.42 6.62 1.66 238. 21.61 September-3 4.76 337.59 22.32 33.61 2.81 2.17 7.38 1.39 245.2 21.11 October-3 4.48 464.5 221.38 35.16 3.44 2.75 8.38 1.78 244.25 19.98 November-3 4.35 337.33 218.9 33.85 3.81 2.8 7.32 1.27 23.75 17.8 December-3 4.9 322.13 216.83 33.76 3.8 2.77 7.12 1.79 229.4 15.93 January-4 4.28 38.1 26.86 34.88 4.18 2.88 7.36 2.64 24.25 14.62 February-4 4.34 286.71 22.38 35.88 4.36 3.18 7.35 1.57 214.5 14.21 March-4 4.25 376.22 217.35 37. 4.9 3.3 7.72 2.27 225.4 15.32 April-4 4.52 46.29 223.5 34.83 3.44 2.71 8.56 1.81 234. 16.18 May-4 4.59 422.77 221.23 36.39 2.99 2.31 8.39.93 241. 17.91 June-4 4.58 421.5 187.73 32.92 2.23 2.1 7.7 1.1 245. 19.5 July-4 4.9 42.32 188.24 28.41 1.96 2.19 7.12.82 242. 2.77 August-4 5.6 37.22 192.5 29.66 1.72 1.81 6.91.92 244.25 21.51 September-4 4.93 368.82 224. 32.27 1.72 2.4 6.95 1.18 243.33 21.2 October-4 4.93 299.29 226.62 34.48 2.21 1.84 7.66 1.37 249. 19.8 November-4 4.56 39.82 2.45 36.48 2.57 3.1 7.67 1.86 242.2 17.11 December-4 4.49 315.23 217.14 36.52 2.97 3.45 7.29 1.98 254.5 15.25 January-5 4.37 374.32 21.27 4.43 3.17 3.45 8.24 3.87 297. 14.27 February-5 4.38 368.21 214.53 4.59 3.25 2.63 9.66 5.5 283. 14.13 March-5 4.41 38.12 199.6 39.7 3.25 2.88 8.61 3.67 284. 14.87 April-5 4.75 323.2 169.5 44.3 2. 1.72 7.9 4.29 274.5 15.85 May-5 4.89 375.57 189.57 34.29 1.87 2.38 9.97 4.67 31. 17.3 June-5 5.18 372.9 23.32 39.46.6.12 9.86 4.75 33.4 18.59 July-5 4.83 379.29 197.57 31.8.11.15 9.5 3.79 254.5 2.81 August-5 5.25 428.22 24.57 29.46.6.8 8.74 3.1 246.6 21.58 September-5 5.7 419.41 21.82 3.1 7.58 3.8 251.25 21.26 October-5 5.53 344.74 185.65 31.12 7. 2.89 262.5 19.75 November-5 5.1 292.9 213.36 34.89 9.4 4.93 296.8 18.6 December-5 4.93 285.26 22.43 37.88 1.56 6.77 273.5 15.68 January-6 4.75 375.76 232.29 38.27 12.38 7.22 255.75 15.16 February-6 4.49 373.37 218.1 35.5 8.69 3.51 25.75 14.9 March-6 4.31 313.82 221.91 41.88 9.6 4.25 256.6 14.35 April-6 4.47 375.76 229.17 39.2 9.98 5.11 258.5 15.83 Figure 4 Monthly Average Influent Data (Flow, BOD, TSS, Ammonia, Temp) TSS, BOD, NH3-N, NOx-N, TP (mg/l) 14 12 1 8 6 4 2 Broomfield WWTP Monthly Average Effluent Data Effluent TSS Effluent BOD Effluent NH3-N Effluent NOx-N Effluent Total P Jul-3 Sep-3 Nov-3 Jan-4 Mar-4 May-4 Jul-4 Sep-4 Nov-4 Jan-5 Mar-5 May-5 Jul-5 Sep-5 Nov-5 Jan-6 Mar-6 23
The IFAS system at Broomfield has performed & operated very consistently over the past 3 years and average monthly effluent data is presented in Figure 4 & Table 4 for BOD, TSS, NH 3 - N, NO x -N & Total P. Table 4 Broomfield Average Monthly Effluent Final Effluent Characteristics Month, Year Total TSS BOD5 NH3-N NOX-N Total P PO4-P Temp mg/l mg/l mg/l mg/l mg/l mg/l ( C) July-3 2.37 2.58.25 7.16.15.1 2.63 August-3 2.74 1.6.17 6.8.74.48 21.61 September-3 2.55 2.23.18 5.78 1.69.99 21.11 October-3 2.96 2.66.25 6.33 1.53.9 19.98 November-3 2.63 1.62.22 7.7 1.12.56 17.8 December-3 4.11 1.88.25 8.62 1.42 1.1 15.93 January-4 5.73 2.75.77 1.48 1.37 1.15 14.62 February-4 4.96 2.33.95 9.28 1.17.55 14.21 March-4 3.25 2.24 1.2 9.33 2.15 1.45 15.32 April-4 5.58 2.36.32 6.78 1.25.8 16.18 May-4 4. 1.85.23 7.2.18.1 17.91 June-4 3.64 1.72.16 7.2.29.8 19.5 July-4 3.7 1.78.26 6.15.24.3 2.77 August-4 2.85 1.91.16 5.79.23.5 21.51 September-4 3.12 1.62.17 5.77.16.3 21.2 October-4 2.22 1.68.14 5.93.58.38 19.8 November-4 3.33 1.67.16 7.55.48.29 17.11 December-4 4.48 2.13.17 7.65.78.46 15.25 January-5 4.93 2.19.17 8.21 1.4.71 14.27 February-5 5.91 2.66.25 8.26 2.63 2.3 14.13 March-5 4.85 2.21.25 7.2 1.18.87 14.87 April-5 4.92 2.34.41 8.3.79.46 15.85 May-5 4.8 2.51.26 8.37 1.48 1.19 17.3 June-5 2.57 2.43.14 11.56 1.33 1.11 18.59 July-5 2.54 2.1.18 1.89 1.54 1.5 2.81 August-5 3.32 2.1.16 11.7 1.17.92 21.58 September-5 3.9 1.88.11 1.78.44.38 21.26 October-5 3.76 1.93.1 11.42 1.31 1.34 19.75 November-5 4.87 3.33.19 12.85 2.43 2.6 18.6 December-5 6.2 3.57.21 1.8 1.81 1.18 15.68 January-6 5.87 3.94 1.21 1.83 1.31 15.16 February-6 5.36 3.58.4 11.2 1.79 1.42 14.9 March-6 8.17 4.33.52 11.78 3.12 2.38 14.35 April-6 7.3 3..18 12.28 2.5 1.68 15.83 231
Table 3 & 4 along with Figures 3 & 4 show a facility operating very consistently. The data provided in Figure 5 & Table 5 show how the facility operated on an average monthly basis with respect to aerobic suspended MLSS SRT, Total aerobic SRT (suspended + fixed), Total Suspended SRT (Anoxic + Aerobic), Sludge Volume Index (SVI) and the operating MLSS & MLVSS concentrations. The Broomfield WWTP has been operating in typical carbonaceous removal SRT ranges, in the 3 4 day range, having the average temperature of the wastewater range between 22C during the summer time and 14C during winter operation, while still meeting baseline effluent ammonia concentrations. Figure 5 Broomfield Average Monthly Operational Information Broomfield WWTP Monthly Operational Data 8. Aerobic SRT 18 MLSS (g/l); Aerobic SRT (d); NH3-N (mg/l) 7. 6. 5. 4. 3. 2. 1. Aerobic MLSS Effluent NH3-N SVI 16 14 12 1 8 6 4 2 SVI (ml/l). Jul-3 Sep-3 Nov-3 Jan-4 Mar-4 May-4 Jul-4 Sep-4 Nov-4 Jan-5 Mar-5 May-5 Jul-5 Sep-5 Nov-5 Jan-6 Mar-6 232
Table 5 Broomfield Average Monthly Operational Information Operational Characteristics Month, Year Total SRT Aerobic SRT Aerobic SRT TSS VSS (susp.) (susp.) (susp.+ fixed) SVI (MLSS) (MLVSS) Temp d d d ml/g mg/l mg/l ( C) July-3 9.99 6.62 98.87 2,51 1,887 2.63 August-3 8.4 5.56 12.71 2,181 1,667 21.61 September-3 7.23 4.79 125.72 1,86 1,389 21.11 October-3 6.76 4.48 138.51 1,864 1,534 19.98 November-3 6.15 4.7 5.16 154.91 1,96 1,54 17.8 December-3 5.59 3.7 5.99 15.53 1,738 1,48 15.93 January-4 5.31 3.52 6.72 135.73 1,627 1,33 14.62 February-4 5.78 3.83 7.65 117.22 1,944 1,45 14.21 March-4 6.35 4.21 8.44 15.88 1,917 1,511 15.32 April-4 5.43 3.6 6.13 112.47 1,974 1,673 16.18 May-4 6.29 4.17 6.46 114.1 2,56 1,637 17.91 June-4 6.5 4.1 6.92 116.1 1,745 1,323 19.5 July-4 6.69 4.43 6.47 112.2 1,641 1,251 2.77 August-4 6.19 4.1 5.2 95.86 1,73 1,31 21.51 September-4 5.5 3.65 4.76 13.5 1,893 1,462 21.2 October-4 5.73 3.79 4.99 16.33 1,78 1,377 19.8 November-4 5.76 3.82 5.56 115.21 1,648 1,272 17.11 December-4 5.19 3.44 6.8 119.47 1,633 1,313 15.25 January-5 5.44 3.6 6.39 123.64 1,764 1,412 14.27 February-5 4.91 3.26 6.1 134.76 1,532 1,278 14.13 March-5 5.31 3.52 6.63 13.15 1,78 1,352 14.87 April-5 5.14 3.41 6.49 121.45 1,792 1,417 15.85 May-5 5.7 3.78 7.2 12.2 1,691 1,333 17.3 June-5 5.18 3.43 6.21 17.96 1,748 1,542 18.59 July-5 5.19 3.44 6.32 115.56 1,49 1,146 2.81 August-5 4.69 3.11 5.53 12.78 1,528 1,21 21.58 September-5 5.22 3.46 5.94 12.88 1,488 1,261 21.26 October-5 6.97 4.62 7.74 19.67 1,665 1,387 19.75 November-5 4.82 3.19 7.2 112.43 1,293 1,39 18.6 December-5 4.46 2.96 6.51 111.28 1,41 1,98 15.68 January-6 4.13 2.74 6.33 16.8 1,431 1,184 15.16 February-6 4.7 3.11 7.49 19.95 1,45 1,165 14.9 March-6 1.13 6.71 18.39 99.21 1,357 1,217 14.35 April-6 7.83 5.19 14.58 112.96 1,473 1,22 15.83 The following set of figures show all the data in either 7 day average or daily data points to illustrate how consistent the overall treatment plant really operates. Figure 6 shows the stability of the IFAS process with plastic media with respect to the Solids Retention Time (SRT) of the aerobic MLSS expressed as both suspended MLSS SRT and suspended MLSS + Fixed SRT. The effluent NH 3 -N concentration from the secondary clarifiers was consistently below 1 mg/l even though the temperature of the system was as low as 14C and the aerobic MLSS SRT were between 3 4 days. The media provides the additional biomass and surface area for growing of the nitrification bacteria and retains them in the system rather than being washed out. 233
Figure 6 Effluent NH 3 -N, Aerobic MLSS SRT & Temperature Profile vs. Time Effl. NH 3 -N conc. (mg/l), or aerobic SRT (d) 14 12 1 8 6 4 2 Kaldnes HYBAS plant, Broomfield, CO Effluent NH3-N, mg/l Aerobic SRT (suspended), d Aerobic SRT (susp. + attached), d Temperature, deg. C 7-day running averages 25 23 21 19 17 15 13 7/7/23 9/7/23 11/7/23 1/7/24 3/7/24 5/7/24 7/7/24 9/7/24 11/7/24 1/7/25 3/7/25 5/7/25 7/7/25 9/7/25 11/7/25 1/7/26 3/7/26 Temperature (deg. C) 11 Figure 7 shows the daily results of overall nutrient removal capability of the system with influent inorganic nitrogen concentrations increasing over time from 4-45 mg/l in 24 to 45-5 mg/l in 25 while still providing a consistently low effluent inorganic nitrogen concentration of less then 1 mg/l during winter time and less then 7 mg/l during summer time. All the denitrification was occurring in the pre-denitrification zone and utilized the influent carbon source for meeting these effluent limits. Based on mass balance of total nitrogen and the RAS and internal recycle rates, there is some type of simultaneous nitrification / denitrification occurring in the facility. The data indicates that the simultaneous nitrification / denitrification is not consistently year round and more research is being conducted to further explain these results. 234
Figure 7 Total Inorganic Nitrogen Profile with Temperature vs. Time 6 Kaldnes HYBAS plant, Broomfield, CO 4 Influent TIN (mg/l) 55 5 45 4 35 3 25 2 15 1 5 Influent TIN, mg/l Temperature, deg. C Effluent TIN, mg/l 35 3 25 2 15 1 5 Temperature (deg. C) Effluent TIN (mg/l) 7/1/23 9/1/23 11/1/23 1/1/24 3/1/24 5/1/24 7/1/24 9/1/24 11/1/24 1/1/25 3/1/25 5/1/25 7/1/25 9/1/25 11/1/25 1/1/26 3/1/26 Figures 8 & 9 show the daily BOD and daily TSS profile and demonstrates a very stable secondary clarified effluent concentrations with BOD s less then 5 mg/l and TSS less then 1 mg/l during winter time operation and less then 5 mg/l during summer time operation. The reasoning for the increase in effluent BOD and TSS during 26 is due to the lower MLSS concentrations of 14 15 mg/l that the facility is currently operating under. During 24 & most of 25, the system was operating at 1,8 1,9 mg/l. This loss of suspended biomass affected the aerobic SRT and as the SRT dropped, the effluent TSS increased, which likely is a reason for the increase in the effluent BOD. Effluent NH 3 -N during this period of time still meets <.5 mg/l. 235
Figure 8 Influent & Effluent BOD Profile with Temperature vs. Time Infl. BOD 5 conc. (mg/l) 33 3 27 24 21 18 15 12 9 6 3 7/1/23 9/1/23 11/1/23 1/1/24 3/1/24 5/1/24 Kaldnes HYBAS plant, Broomfield, CO Influent BOD5, mg/l Temperature, deg. C Effluent BOD5, mg/l 7/1/24 9/1/24 11/1/24 1/1/25 3/1/25 5/1/25 7/1/25 9/1/25 11/1/25 1/1/26 3/1/26 24 22 2 18 16 14 12 1 8 6 4 2 Temperature (deg. C) Effl. BOD 5 conc. (mg/l) Figure 9 Influent & Effluent TSS Profile with Temperature vs. Time 8 7 6 5 4 3 2 1 Kaldnes HYBAS plant, Broomfield, CO Influent TSS, mg/l Temperature, deg. C Effluent TSS, mg/l 7/1/23 9/1/23 11/1/23 1/1/24 3/1/24 5/1/24 7/1/24 9/1/24 11/1/24 1/1/25 3/1/25 5/1/25 7/1/25 9/1/25 11/1/25 Infl. TSS conc. (mg/l) 1/1/26 3/1/26 24 22 2 18 16 14 12 1 8 6 4 2 Temperature (deg. C) Effl. TSS conc. (mg/l) 236
Figure 1 shows the biofilm characteristics over time and how the biofilm on the media in each of the reactors grows during winter time operation and decreases during summer time operation. This effect of the biofilm growing and sloughing is just part of the normal operation. When the MLSS concentration started a steady decline in March 25 to April 26, the overall biofilm thickness didn t show the dramatic winter vs. summer effects as the overall MLSS system was being stressed and allowed more biofilm to grow on the fixed media. During the winter of 26, the biofilm in reactor 1 showed similar g TS/m 2 of biomass as was seen during the winter of 24. From a design standpoint, one can see that it would be very difficult to say the biomass on the media is consistent; rather the only consistent value in the IFAS system is the amount of surface area. Thus, full scale designs shouldn t count MLSS suspended biomass + biomass on the media. It should be MLSS suspended biomass + surface area kinetics which control the overall design of IFAS systems. Figure 1 MLSS Conc., Media TSS Reactor 1, Media TSS Reactor 2 & Temp. vs. Time MLSS (mg/l) 3 27 24 21 18 15 12 9 6 3 Kaldnes HYBAS plant, Broomfield, CO HYBAS MLSS, mg/l Attached biomass HYBAS 1, g TS/m2 Attached biomass HYBAS 2, g TS/m2 Temperature, deg. C 3 27 24 21 18 15 12 9 6 3 Temperature (deg. C) Attached biomass (g TS/m 2 ) 7/1/3 9/1/3 11/1/3 1/1/4 3/1/4 5/1/4 7/1/4 9/1/4 11/1/4 1/1/5 3/1/5 5/1/5 7/1/5 9/1/5 11/1/5 1/1/6 3/1/6 Figure 11 shows the potential of the effect of simultaneous nitrification and denitrification (SND) occurring within the aerobic zone and the biofilm on the plastic media. In this figure the red line is the actual denitrification occurring in the system by monitoring the influent and effluent inorganic nitrogen. The blue line is a theoretical % removal of nitrogen based on the internal recycle rate and return activated sludge rate (i.e. 1% RAS + IR = 5% Nitrogen Removal). As can be seen in the graph, during periods of warmer weather the blue line is above the red line, indicating the potential for SND. The data from May 25 to current is missing influent NOx-N data and thus the evaluation during this period of time is incomplete. 237
Figure 11 Potential Simultaneous nitrification and denitrification (SND) 1 Kaldnes HYBAS plant, Broomfield, CO 8 Primary effl. C/N, g BOD 5 /g TIN DN rate, mg NOx-N/g MLSS/h Effluent NH 3 -N, mg/l 9 8 7 6 5 4 3 2 1 Effl. NH3-N TIN-removal 7-day running averages Temp r/(r+1) 7 6 5 4 3 7/7/23 9/7/23 11/7/23 1/7/24 3/7/24 5/7/24 7/7/24 9/7/24 11/7/24 1/7/25 3/7/25 5/7/25 7/7/25 9/7/25 11/7/25 1/7/26 3/7/26 2 TIN-removal in bioreactors, % r/(r+1), % 1 CONCLUSION The full scale IFAS system operating at the City & County of Broomfield s WWTP has demonstrated over the past three (3) years a very consistent operating and stable effluent system, which operates at low solids retention times and that the Hybrid MBBR process is effective in removing NH 3 -N to below the effluent requirements of 1 mg/l on a consistent basis. Based on the results obtained from this pilot study it is recommended that the full scale treatment system look at running a two stage aerobic system with media to help increase the nitrification capacity of the existing treatment system. ACKNOWLEDGEMENT The authors gratefully acknowledge the dedication of the City & County of Broomfield s operational staff at the wastewater treatment plant. Without their efforts the information presented would not be available. They also wish to thank the personnel at the Broomfield WWTP for all their help in gathering all the data for this report. 238
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