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wateronline.com ■ Water Online The Magazine 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/m 2 /d at 26˚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 on page 28 present the ammonia and total inorganic nitrogen (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/m 2 /d at 27˚C. During the IFAS phase, stable ammonia and TIN removals were not achieved, which may have been 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 mixed liquor suspended solids (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/m 2 /d at roughly 25˚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/m 2 /d for COD and 1.0 g/m 2 /d for nitrogen. The COD removal from C-stage is 75 percent, and the TIN removal rate from the MBBR system is 74 percent. 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. I n s u m m a r y , deammonification is now an established and acceptable process used by many state agencies to treat sidestream BNR 101: Pilot Study 26 TCOD SCOD TSS VSS NH 4 -N NO 3 -N PO 4 -P pH T ( o C) Average, mg/L 4,226 1,988 580 267 650 7.0 10.1 8.5 24.8 Min, mg/L 1,290 1,110 110 75 140 3.8 2.9 7.6 14.5 Max, mg/L 20,600 4,900 1,180 460 1,460 10.2 19.5 10.6 29.4 Table 2. Characteristics of old leachate during the testing period C-stage Reactor C-stage Clarifi er ANITA Mox Reactor ANITA Mox Clarifi er (IFAS Phase Only) Reactor Volume, Liter 5.0 5.0 7.0 5.0 Media Volume, Liter 2.0 NA 3.0 NA Media surface area, m 2 1.6 NA 2.4 NA Return sludge fl ow NA No RAS NA 100% to 500% of infl uent Table 1. Reactor volumes, media volume, and media surface areas Figure 2. ANITA Mox system layout at Cincinnati's Mill Creek WWTP