title: Impact of Limited Organic Carbon Addition on Nitrogen Removal in a Mainstream Anammox Moving Bed Biofilm Reactor
Creators: name: Godwin, Johnnie Wayne
Publisher: name: Old Dominion University Libraries
Year: 2015

description: Excessive nitrogen compounds are a growing problem in the world and are leading to further environmental degradation. For future nitrogen pennit limits, conventional water treatment processes tend to not meet the requirements to drive these concentrations to low levels, and if they do, it can be rather costly. However, in mid 1990s a new bacterium was discovered that has allowed for nitrogen removal to occur at a considerably reduced cost. The use of anaerobic ammonia oxidizing bacteria (anammox or AMX) is well established in sidestream deammonification (partial nitritation and anammox). However, as of late there has been discussion of applying anammox in mainstream wastewater treatment to decrease the cost of nitrogen removal, with respect to energy, chemicals, and reactor volume.

This pilot-scale study describes how limited supplemental carbon addition to a fully anoxic anammox moving bed biofilm reactor (MBBR) following a two-stage mainstream adsorption/nitrite shunt bio-oxidation process (A/B process), producing a blend of ammonia, nitrite, and nitrate, can enhance nitrogen removal at 20°C. Anammox bacteria have been shown to use acetate as an electron donor to reduce nitrate to nitrite; however, this can lead to competition with ordinary heterotrophic organisms (OHO). With low dose acetate addition, nitrate removal of 1.5-2.5 mg NO3- -N/L occurred in the MBBR; however, in most cases nitrate production would have been expected given the loading of ammonia (NH4-) and nitrite (NO2-). Based on mass balance, a portion of the nitrate must have been reduced to NOf, which was then used with NH4- by anammox. Previous work by Holgate (2014) demonstrated this anammox capability with limited acetate addition to the anammox MBBR

The objective of this project was to quantify the contribution of the observed nitrate reduction that was due to suspended solids (SS) in the B-stage effluent containing OHO, OHO growing on the biofilm carriers, or anammox growing on the biofilm carriers. To test this, MBBR SS were removed, existing MBBR SS were tested, and SS were added to the MBBR, while only dosing nitrate, ammonia, and acetate.

Results suggested that OHO and anammox coexist on the biofilm, and demonstrated that anammox performed organotrophic reduction of nitrate to nitrite. In the biofilm, anammox performed 3-25% of nitrate reduction and OHO performed 38-65%. The percent contribution by each bacterial group was dependent on MBBR TSS concentrations which varied from 0-200 mg/L. Based on nitrite production rates of B-stage mixed liquor of 0.39 and 1.07 mg NO2--N/gVSS/hr, it was concluded that B-stage effluent TSS may play an important role in the observed N removal as a result of partial denitrification. The mixed liquor OHO probably have a mass transfer advantage in terms of substrate availability compared to the biomass existing on the carriers. Also, keeping a low COD added/Influent NO3-N of 0.3-2.0 allowed for anammox to contribute to nitrate reduction. As expected, excess acetate addition (COD added/Influent NO3-N = 3.5-5) led to full denitrification by OHO. The combination of high TSS and COD allowed for more nitrate reduction to be performed in the suspended solids.