How Does Anammox Bacteria Perform On Industrial Waste Streams?
By Ting Lu, Biju George, and Hong Zhao
In recent years, single-stage deammonification technology combining partial nitritation and anammox has rapidly become an emerging technology for cost-effective autotrophic nitrogen removal in sidestream centrate. The sidestream has high ammonia concentration, low C: N ratio, and warm temperatures that provide the ideal condition for anammox bacteria to covert ammonia under anoxic condition (with nitrite) to nitrogen gas. The benefit of this technology in comparison to conventional nitrification/denitrification includes reducing aeration energy, eliminating carbon dependency, reducing alkalinity consumption, and reducing sludge production — all of which have potential to significantly reduce operational costs for nitrogen removal.
At Metropolitan Sewer Department of Great Cincinnati (MSDGC), there are more than 200 significant industrial users that discharge industrial wastes into the treatment plant. In order to save energy and operation cost, MSDGC initiated many innovative technologies to treat high-strength wastes more cost effectively. This paper shows the case study of integrating innovative deammonification technology to treat landfill leachate.
The regular-strength leachate (old leachate) is characterized by its low ratio of BOD/COD and fairly high NH4-N (i.e., low biodegradable COD to N ratio). Nitrogen removal from old leachate usually involves autotrophic nitrification and heterotrophic denitrification. There are very few studies reporting the use of deammonification process to treat landfill leachates, especially in the U.S. The objective of this study is to conduct an eight-month pilot project to study the feasibility of nitrogen removal of old leachate using ANITA™ Mox, a single-stage deammonification process. The outcome of this study is significant because it indicates whether the deammonification process is a viable alternative for treating leachate, and it provides some criteria for full-scale design. In addition, it provides significant understanding of what chemicals would inhibit anammox bacteria and how to optimize its performance. The project also offers valuable information for alternative landfill leachate pretreatment processes.
Materials And Methods
ANITA Mox grows biofilms on moving carriers in a mixed reactor and can be designed in two configurations — moving bed biofilm reactor (MBBR) and integrated fixed-film activated sludge (IFAS). The biofilm on the MBBR carriers consists of multi-layers, where anammox bacteria grow on inner layers and ammonia oxidizing bacteria (AOB) grow on the outer layers to achieve single-step deammonification. In IFAS configuration, AOB is grown as suspended mixed liquor, where anammox bacteria is the dominant species on the biofilm carriers. Studies of the IFAS system have shown that effectively integrating return sludge that includes AOB will improve single-stage biofilm deammonification process performance due to less mass transfer resistance.
Figure 1. Flow diagrams of bench scale reactor system — MBBR and IFAS phases
Figure 2. ANITA Mox system layout at Cincinnati’s Mill Creek WWTP
The feasibility study consisted of three phases — start-up (May 20 to June 16, 2013), MBBR (June 17 to August 4), and IFAS (Aug. 5 to Oct. 21). As shown in Figure 1, the flow diagram of the bench-scale reactor system, a carbon removal stage (a MBBR reactor with clarifier) was added before the ANITA Mox stage to ensure influent with a low biodegradable COD concentration coming to the ANITA Mox stage. Both C-stage and ANITA Mox reactors were started with 100-percent-seeded carriers (AnoxKaldnes K5 plastic media carrier), which were obtained from the ANITA Mox pilot plant in Denver, CO. Figure 2 shows the actual system layout in the plant. The C-stage reactor was located on the shelf and the ANITA Mox reactors were located on the table. Table 1 summarizes the reactor volumes, media volumes, and media surface areas in the bench scale reactor system. The feed was the old leachate that was delivered from the Rumpke Sanitary Landfill on a weekly base. Table 2 summarizes the feed characteristics during the testing period. The characteristics indicate a variation of a factor of 10 between the maximum and minimum values on COD, TSS, and ammonia with a pH range from 7.6 to 10.6. For both the MBBR and IFAS phases, the influent flow rate was adjusted to achieve relatively stable performance. Nitrogen components (ammonia, nitrate, and nitrite), COD, TSS, and alkalinity were measured daily in each reactor for influent and effluent. The operating conditions (e.g., DO, temperature, pH, and intermittent aeration cycles) were monitored by online probes, and DO was controlled manually with adjustment of airflow.
Table 1 – Reactor Volume, Media Volume, And Media Surface Areas
Table 2 – Characteristics Of Old Leachate During The Testing Period
Results And Discussion
Figure 3 presents the COD removal performance for both the MBBR and IFAS phases. During the MBBR phase, the C-stage was capable of removing a majority of the influent COD and not much COD was left to the ANITA Mox stage. On average, the influent COD was about 4,000 mg/L and the effluent of the C-stage was less than about 1,000 mg/L. A COD surface removal rate (SRR) was estimated to be about 15 g/m2/d at 26 degrees C based on a feed flow rate of 8 L/d. During the IFAS phase, the COD removal in the C-stage was not complete, and about 500 to 1,000 mg/L of COD was removed in the ANITA Mox Stage. The incomplete COD removal was probably due to a lack of mixing, which resulted in media settling in the C-stage reactor. Figures 4 and 5 present the ammonia and TIN profiles in each reactor for both the MBBR and IFAS phases. At the beginning of the MBBR phase (Figure 4), the C-stage converted most of the influent ammonia to nitrite because the seeded media in C-stage contained AOBs. After about 20 days of operation (July 7), the nitritation capability in C-stage was decreased and most of the influent ammonia was removed in the ANITA Mox Stage. As shown in Figure 5, the majority of influent TIN was removed in the ANITA Mox stage after July 9. Since there was not much COD removal in the ANITA Mox stage during this same period, the TIN removal was attributed to the activity of anammox. Based on the influent flow rate of 8 L/d and average feed and effluent TINs of 483 mg/L and 158 mg/L, the average nitrogen SRR was estimated to be about 1.1 g/m2/d at 27 degrees C.
Figure 3. COD profiles in each reactor during MBBR and IFAS phases
Figure 4. Ammonia profiles in each reactor during MBBR and IFAS phases
Figure 5. TIN profiles in each reactor during MBBR and IFAS phases
During the IFAS phase, stable ammonia and TIN removals were not achieved, which may be caused by the large variation of influent ammonia load, lack of aeration control, incomplete COD removal in the C-stage, and inability to build-up MLSS in the process. Although the performance was not stable, significant ammonia and TIN removals (200 mg/L to 500 mg/L) were observed in the ANITA Mox stage for this phase. The above ammonia and TIN removals were much higher than the nutrient requirement for heterotrophic growth, and were therefore attributed to AOB and anammox activities. At an average flow rate of 7.0 L/d and an average TIN removal of 300 mg/L, the TIN SRR was estimated to be about 0.9 g/m2/d at roughly 25 degrees C.
Summary And Conclusions
This bench-scale feasibility study has clearly demonstrated that the two ANITA Mox configurations (MBBR and IFAS) were capable of removing COD and nitrogen from old leachate at SRRs of 15 g/m2/d for COD and 1.0 g/m2/d for nitrogen. The COD removal from C-stage is 75 percent, and the TIN removal rate from MBBR system is 74 percent, respectively. The MBBR test has been very successful and meets the design criteria from the vendor perspective. The relatively unstable performance from IFAS was caused by many factors as discussed above, which opened the door for more mechanical optimization and future pilot work. There is no noticeable inhibition from the old leachate that inhibit the anammox activity.
In summary, deammonification is now an established and acceptable process by the many state agencies to treat sidestream centrate to reduce nitrogen load. Process control (DO, pH, temperature, and free ammonia) is key to maintaining the right microbial population and structure to maximize performance. For an industrial waste stream, the deammonification process still requires a pilot to validate the effectiveness of the technology. In the pilot study at MSDGC, the ANITA Mox technology was capable of removing COD and nitrogen from landfill leachate. The deammonification process provides a cost-effective alternative to the landfill leachate pretreatment processes. This is valuable information for MSDGC during their process in evaluating the construction of a new wastewater treatment plant. On another deammonification pilot project, significant inhibition on bacterial activity was found when treating combined wastewater from a tannery and a pig slaughter house.
Dr. Ting Lu is currently an environmental scientist at Black & Veatch, formerly at MSDGC. She received a Ph.D. degree at University of Cincinnati and is a member of the Water Environment Federation and the Ohio Water Environmental Association.
Biju George, P.E., has served as the deputy director of the Greater Cincinnati Water Works & Metropolitan Sewer Department (GCWW) since December 2013, and first joined the Metropolitan Sewer District of Greater Cincinnati in 1991. He is responsible for the day-to-day and strategic direction of the GCWW operating divisions. (Image credit: Global Water Summit 2013, Seville)
Hong Zhao graduated with Ph.D. degree in Environmental Engineering from the University of British Columbia in Canada. He has been a process engineer at Kruger, a Veolia Water Technologies company, for more than 15 years.