COLD WEATHER NITRIFICATION OF LAGOON EFFLUENT USING A MOVING BED BIOFILM REACTOR (MBBR) TREATMENT PROCESS

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1 ABSTRACT COLD WEATHER NITRIFICATION OF LAGOON EFFLUENT USING A MOVING BED BIOFILM REACTOR (MBBR) TREATMENT PROCESS Mr. Flemming G. Wessman 1 and Mr. Chandler H. Johnson 1 AnoxKaldnes, Inc., 58 Weybosset Street, 4 th Floor, Providence, RI Since 2000, the population at Johnstown, Colorado has increased over 22%, and shows no signs of slowing down. Faced with more residents and impending year round ammonia limits, the Town of Johnstown was forced to upgrade their wastewater treatment facility. The existing treatment facility in Johnstown consisted of three lagoons, whose main purpose was to achieve settling of total suspended solids and organic matter (BOD) removal. To meet the new increase in flows and nutrient limits, the Town of Johnstown had two choices: eliminate all existing lagoons and build a new conventional activated sludge facility, or continue to utilize the existing lagoons for organic matter reduction and add a down stream post-nitrification fixed film treatment system. By choosing the latter option, the Town of Johnstown managed to save about 50% of the cost of building a whole new plant. The post-nitrification MBBR was installed during the winter of 2003/2004 and brought online in June December 2004 to mid-january 2005, the average influent water temperature was 4.2 C, the MBBR treatment system removed an average of over 40% of influent NH 3 -N. In fact, the effluent NH 3 -N decreased by 35%, 42%, and 58% in December, January, and February, when compared with the same months in the winter prior to the installation of the MBBR treatment system. Throughout the warmer months, the MBBR treatment removed an average of 85% of influent NH 3 -N while the effluent BOD has been, on average, less than 1 mg/l, making it very easy for the plant to meet its permit requirements month after month. KEYWORDS Waste water, treatment, Moving Bed biofilm process, MBBR, experiences, nitrification, Lagoon. INTRODUCTION Since 2000, the population at Johnstown, Colorado has increased over 22%, and shows no signs of slowing down. Faced with more residents and impending year round ammonia limits, the Town of Johnstown was forced to upgrade their wastewater treatment facility. Johnstown is located about 50 miles north of Denver, and during winter time their lagoon wastewater temperatures frequently dip below 40 F (4.5 C). The existing treatment facility in Johnstown consisted of three lagoons, whose main purpose was to achieve settling of total suspended solids and organic matter (BOD) removal. To meet the new increase in flows and nutrient limits, the Town of Johnstown had two choices: eliminate all existing lagoons and build a new conventional activated sludge facility, or continue to utilize the existing lagoons for organic matter reduction and add a down stream post-nitrification fixed film treatment system. By choosing the latter option, the Town of Johnstown managed to save about 50% of the cost of building a whole new plant. 4738

2 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 then being washed out during colder temperatures as a conventional activated sludge system would typically see happen. The Town of Johnstown investigated the Moving Bed Biofilm Reactor (MBBR) treatment technology for meeting its new effluent ammonia and increased flow requirements. Overall treatment requirements for the system are summarized in the table below. Month Effluent limit (mg NH 4 -N/L) January 16 February 12 Mars 5.1 April 2.9 May 1.5 June 1.3 July 1.2 August 1.2 September 1.1 October 1.1 November 2.2 December 13 Table 1. Overall treatment requirements The ability of the MBBR to be designed for a future flow capacity by sizing the tankage for the ultimate build out flow and loads was attractive as the initial investment only required media to meet the current flows and loads. Once the systems flows and loads increased the town only has to add additional media to provide the additional surface area needed for biofilm growth. DESCRIPTION OF THE MOVING BED BIOFILM REACTOR The idea behind the development of the Kaldnes Moving Bed biofilm process (MBBR biofilm process) was to adopt the best features of the activated sludge process as well as those of the biofilter process without including the worst. Contrary to most biofilm reactors, the Moving Bed biofilm reactors utilises the whole tank volume for biomass growth, as does the activated sludge reactor. Contrary to the activated sludge reactor, however, the MBBR does not need any sludge recycle, as is also the case in other biofilm systems. This is achieved by having the biomass grow on carriers that move freely in the water volume of the reactor, kept within the reactor volume by a sieve arrangement at the reactor outlet. Since no sludge recirculation takes place, only the surplus biomass has to be separated - a considerable advantage over the activated sludge process. The reactor may be used for both aerobic, anoxic or anaerobic processes, see Figure

3 a. Aerobic reactor b. Anoxic and anaerobic reactor c. The biofilm carrier (K1) Figure 1 - Principle of the MBBR biofilm technology and shape of the original biofilm carrier (K1) In aerobic processes, the biofilm carrier movement is caused by the agitation set up by the air, while in anoxic and anaerobic processes a mixer keeps the carriers moving. In the aerobic reactors a special medium bubble aeration system has been developed. This type of aeration system is very robust and will not require any maintenance or replacement. The oxygen transfer rate (OTR) is high due to the presence of the biofilm carriers. Tests have shown that the OTR is equal to what you achieve with fine bubble aeration systems (membrane aerators) in activated sludge reactors (Hem, 1999 & Hem, 2002). The carriers are kept within the reactor by an outlet sieve. This may be vertically mounted, rectangular mesh sieves, but lately the sieve is more often shaped as a cylindrical bar sieve, vertically or horizontally mounted. The agitation in the reactor is so arranged that the carrier elements are constantly being moved upwards over the surface of the sieve. This action creates a scrubbing effect that prevents clogging. 4740

4 Figure 2 - The moving bed biofilm reactor The original and mostly used biofilm carrier (K1) is made of high density polyethylene (density 0,95 g cm -3 ) and shaped as a small cylinder with a cross on the inside of the cylinder and fins on the outside (see Figure 1c). The cylinder has a length of 7 mm, and a diameter of 10 mm (not including fins). One has later introduced various carriers of other sizes and shapes, but the K1 carrier is still the one mostly used (Ødegaard et al., 1994 & Ødegaard et al., 1999). a) Principal drawing b) MBBR at Johnstown WWTP Figure 3 System components 4741

5 The filling of carrier elements in the reactor may be decided for each case, giving considerable flexibility in the specific biofilm surface area. A maximum filling of about 70%, based on empty reactor volume corresponds to a specific growth area of biofilm of about 350 m 2 /m 3. The reactor volume is totally mixed and consequently there is no dead or unused space in the reactor. Different reactor shapes can be used and the MBBR process is ideal for upgrading of overloaded activated sludge plants or for converting unused tankage into biofilm reactors. As in every biofilm process, diffusion of compounds in and out of the biofilm plays a key role. Because of the importance of diffusion, the thickness of the effective biofilm (the depth of the biofilm to which the substrates have penetrated) is significant. Since this depth of full substrate penetration is normally less than 100 μm, the ideal biofilm in the moving bed process is thin and evenly distributed over the surface of the carrier. In order to obtain this, the turbulence in the reactor is of importance, both in order to transport the substrates to the biofilm and to maintain a low thickness of the biofilm by shearing forces. As demonstrated in Figure 3, much less biomass is growing on the outside of the carriers than on the inside. This is probably caused by the fact that abrasion, caused by carrier collisions, is limiting growth. Various investigations have shown that the typical biomass concentration when calculated on reactor volume, is in the order of 2-5 kg SS/m 3 (Rusten et al., 1994, 1995a, 1998), about the same as in activated sludge reactors. Since the volumetric removal rate, however, has been demonstrated to be several times higher in the moving bed process (Rusten et al, 1995a), the biomass of this process must be much more viable than in similar activated sludge processes. Description of the plant The post-nitrification MBBR was installed during the winter of 2003/2004 and brought online in June Installed in the upgrade were two parallel MBBR process trains, each consisting of two concrete reactors in series, creating a total footprint of just 60 ft X 60 ft, and a total volume of 43,200 ft 3. The new reactors were placed between Lagoons 2 and 3. A by-pass around lagoon 2 for winter time operation is also included. This was done to minimize the temperature loss in Lagoon 2 so in this case effluent from Lagoon 1 flows directly into the MBBR Also included in the upgrade was a dissolved air flotation (DAF) device for high-rate solids separation and phosphorus removal. 4742

6 Figure 4. Flow diagram of Johnstown WWTP The overall design concept is to allow wastewater to flow via gravity from the existing lagoons directly to the MBBR system. The existing lagoons will provide organic removal and the MBBR system will provide additional organic removal and nitrification of ammonia nitrogen. The design for the initial flow rate of 0.75 MGD is based on filling the MBBR reactor to 26% its liquid volume with media to treat an average BOD load of 194 lb/day and an NH 3 -N load of 126 lb/day. When the wastewater flow increases over time to the build out design flow of 1.5 MGD, the design is based on a filling degree in the MBBR reactor of 56% its liquid volume and treat an average BOD load of 800 lb/day and an NH 3 -N load of 275 lb/day. Since the maximum filling capacity of an MBBR is 70% of liquid reactor volume, the overall treatment capacity of the MBBR can be upgraded by just adding media to the reactor and extra air to the existing aeration grid system. 4743

7 The design is based on the following influent wastewater characteristics and effluent requirements. Design Flow of 0.75 MGD Effluent Limit Inf. BOD Inf. TKN Temp BOD Load TKN Load (mg/l) (mg/l) (mg/l) C (lb/day) (lb/day) January February March April May June July August September October November December Design Flow of 1.5 MGD Effluent Limit Inf. BOD Inf. TKN Temp BOD Load TKN Load (mg/l) (mg/l) (mg/l) C (lb/day) (lb/day) January February March April May June July August September October November December Table 2. Design figures 4744

8 The month of November for both design options (0.75 MGD and 1.5 MGD) is the month requiring the maximum amount of surface area for treatment of BOD and NH3-N to the levels of < 10 mg/l & < 2.2 mg/l respectively. This month is therefore used as design basis. Below is a summary of the design during the month of November for both the initial design flow and the future design flow with reactor dimensions. Number of Basins Basin Dimensions Aeration Type Initial Design Flow Future Design Flow Peak Hydraulic Flow Initial Influent BOD 5 Future Influent BOD 5 Initial Influent TKN Future Influent TKN Temperature Media Percent Fill 4 (2 Trains of 2 Basins in Series) 30 ft Width by 30 ft Length by 15 ft Depth (12 ft SWD) Engineered Orifice System with complete floor coverage = 0.75 MGD Daily Average = 1.5 MGD Daily Average = 4.5 MGD = 31 mg/l (193.9 lb/day) ** Month of November = 64 mg/l (800 lb/day) ** Month of November = 20.2 mg/l (126.3 lb/day) ** Month of November = 22 mg/l (275.2 lb/day) ** Month of November = 4.9ºC Initial Design; 6.3 ºC Future Design = 26% Basin Volume Initial Design Conditions = 56% Basin Volume Future Design Conditions Air Requirements: Initial Design Flow = 1,303 SCFM Future Design Flow = 3,772 SCFM Blower Pressure Required losses)) = 6.37 psig (4.87 psig (water pressure) psig (for line 4745

9 RESULTS AND DISCUSSION The plant has been extensively followed up since the start up in June The source of data that is presented below is from the Board of health and the operator log sheet. Overall performance As the graph below illustrates, the plant has achieved the effluent ammonia limit every month since the MBBR reactors were installed. 30 MBBR Operational Since 6/2004 0, ,6 Effluent Ammonia & Limits (mg/l) January-04 February ,4 11,5 14 Figure 5. Results March-04 April-04 May-04 June-04 July-04 August-04 September-04 October-04 November-04 6,5 7, December-04 January-05 February ,4 March-05 April-05 Date 11, ,5 Eff Ammonia 30-day Avg Monthly LIMIT Inf Flow 7,5 7 9 May-05 June-05 July-05 August-05 September-05 October-05 November-05 December-05 January-06 February ,5 18 0, ,4 0,3 0,2 0,1 March-06 0 Influent Flow (MGD) From December 2004 to mid-january 2005, the average influent water temperature was 4.2 C, the MBBR treatment system removed an average of over 40% of influent NH 3 -N. In fact, the effluent NH 3 -N decreased by 35%, 42%, and 58% in December, January, and February, when compared with the same months in the winter prior to the installation of the MBBR treatment system. Throughout the warmer months, the MBBR treatment removed an average of 85% of influent NH 3 -N while the effluent BOD has been, on average, less than 1 mg/l, making it very easy for the plant to meet its permit requirements month after month. 4746

10 Loss of nitrification During the first winter there was a ph excursion to 9 while the wastewater temperature dropped to less then 3C. Figures 6-8 show the progression of the system losing nitrification when the ph increased to 9 and temperature dropped to less then 3C (Figure 6), to a slight recovery in nitrification even though the wastewater temperature was still below 5C (Figure 7) to a complete recovery in nitrification when the ph and temperature recovered to normal levels (Figure 8). 35,0 30,0 Johnstown WWTP Ammonia Profile Through 2 Stage MBBR With Temperature and ph /8 Temperature Influent NH3-N Reactor 2 Effluent ph 12,0 11,0 10,0 25,0 9,0 Ammonia (NH3-N) (mg/l) 20,0 15,0 10,0 8,0 7,0 6,0 5,0 Temperature ( C) & ph 4,0 5,0 3,0 0,0 2, Date Figure 6 Ammonia Profile with ph & Temperature vs. Time Loss of Nitrification 4747

11 45,0 40,0 Johnstown WWTP Ammonia Profile Through 2 Stage MBBR With Temperature and ph - 12/8-1/11 Temperature Influent NH3-N Reactor 2 Effluent ph 12,0 11,0 35,0 10,0 Ammonia (NH3-N) (mg/l) 30,0 25,0 20,0 15,0 10,0 9,0 8,0 7,0 6,0 5,0 4,0 Temperature ( C) & ph 5,0 3,0 0, Date ,0 Figure 7 Ammonia Profile with ph & Temp. vs. Time Slight Nitrification Recovery 40 Johnstown WWTP Ammonia Profile Through 2 Stage MBBR With Temperature and ph - 1/17-3/ Temperature Reactor 2 Effluent Influent NH3-N ph Ammonia (NH3-N) (mg/l) Temperature ( C) & ph Date 2 Figure 8 Ammonia Profile with ph & Temp. vs. Time Complete Nitrification Recovery 4748

12 Flotation. Dissolved air flotation (DAF) device for high-rate solids separation and phosphorus removal were installed after Lagoon 3. The MBBR and DAF combination have successfully been installed at numerous plants around the world (Wessman F et. al 2005). Since the MBBR requires no sludge return the TSS (mg/l) in the MBBR effluent is approximately the same as TSS (mg/l) in the influent, making the DAF an excellent solution for particle separation. The operating result of the DAF during the first year is demonstrated in the table below. Parameter DAF influent DAF Effluent Range Average Range Average Turbidity, NTU BOD mg/l TSS mg/l Table 3. Design figures CONCLUSION The new MBBR at Johnstown WWTP has successfully operated through the first year with wastewater temperatures below 2 C. Effluent concentrations were well below the discharge limits. Throughout the warmer months, the MBBR treatment removed an average of 85% of influent NH 3 -N while the effluent BOD has been, on average, less than 1 mg/l. REFERENCES Hem, L. (1999) Oxygen transfer rates in Kaldnes Moving Bed biofilm reactors at two Norwegian wastewater treatment plants. Aquateam report (99-058). Hem, L. (2002) Measurement of oxygen transfer rates in clean water and domestic wastewater. Aquateam report (02-009). Hem, L., Rusten, B., Ødegaard, H. (1994) Nitrification in a moving bed biofilm reactor. Water Research, Vol. 28, No 6, pp Rusten, B., Hem, L., Ødegaard, H. (1995b). Nitrogen removal from dilute wastewater in cold climate using moving bed biofilm reactors. Water Environm. Res., Vol. 67, No1, pp 65-74,

13 Ødegaard, H., Rusten, B., Wessman, F.(2004) State of the art in Europe Of the Moving Bed biofilm reactor (MBBR TM ) Process, WEFTEC 2004 Ødegaard, H., Rusten, B., Siljudalen, J. (1999) The development of the moving bed biofilm process from idea to commercial product. European Water Management, Vol.2, No. 2. Ødegaard, H., Rusten, B., Westrum, T. (1994) A new moving bed biofilm reactor- Applications and results. Wat. Sci. Tech. Vol. 29, No 10-11, pp Wessman F, Nielsen I, Bungum S. (2005) Nitrogen Removal in Moving Bed TM Biofilm Reactor Plants IWA specialized conference proceedings 4750