Start-up of Autotrophic Nitrogen Removal Reactors via Sequential Biocatalyst Addition

Abstract

A procedure for start-up of oxygen-limited autotrophic nitrification-denitrification (OLAND) in a lab-scale rotating biological contactor (RBC) is presented. In this one-step process, NH 4 + is directly converted to N 2 without the need for an organic carbon source. The approach is based on a sequential addition of two types of easily available biocatalyst to the reactor during start-up: aerobic nitrifying and anaerobic, granular methanogenic sludge. The first is added as a source of aerobic ammonia-oxidizing bacteria (AAOB), the second as a possible source of planctomycetes including anaerobic ammonia-oxidizing bacteria (AnAOB). The initial nitrifying biofilm serves as a matrix for anaerobic cell incorporation. By subsequently imposing oxygen limitation, one can create an optimal environment for autotrophic N removal. In this way, N removal of about 250 mg of N L -1 d -1 was achieved after 100 d treating a synthetic NH 4 + -rich wastewater. By gradually imposing higher loads on the reactor, the N elimination could be increased to about 1.8 g of N L -1 d -1 at 250 d. The resulting microbial community was compared with that of the inocula using general bacterial and AAOB-and planctomycete-specific PCR primers. Subsequently, the RBC reactor was shown to treat a sludge digestor effluent under suboptimal and strongly varying conditions. The RBC biocatalyst was also submitted to complete absence of oxygen in a fixed-film bioreactor (FFBR) and proved able to remove NH 4 + with NO 2 -as electron acceptor (maximal 434 mg of NH 4 + -N (g of VSS) -1 d -1 on day 136). DGGE and real-time PCR analysis demonstrated that the RBC biofilm was dominated by members of the genus Nitrosomonas and close relatives of Kuenenia stuttgartiensis, a known AnAOB. The latter was enriched during FFBR operation, but AAOB were still present and the ratio planctomycetes/ AAOB rRNA gene copies was about 4.3 after 136 d of reactor operation. Whether this relates to an active role of AAOB in the anoxic N removal process remains to be solved.

Microbial and Physicochemical Characteristics of Compact Anaerobic Ammonium-Oxidizing Granules in an Upflow Anaerobic Sludge Blanket Reactor

“…1, bright-red anammox granules were apparent within 140 days. The start-up time in this work was similar to that of those seeded with activated sludge (23) and anaerobic digestion sludge (150 days) (3) and was significantly faster than the reactors inoculated with nitrifying (250 days) (13) or denitrifying (392 days) (25) sludge.…”

Propionate Oxidation by and Methanol Inhibition of Anaerobic Ammonium-Oxidizing Bacteria

“…Knowledge of the potential for mixotrophic growth might facilitate cultivation and microbiological study in the future (29). In wastewater treatment, it is important to know the responses of anammox bacteria to the presence of organic compounds because the target wastewaters sometimes contain organic acids and alcohols resulting from incomplete or suboptimal fermentation (1,3,15,16,23,34). The present study has documented that organic compounds can both inhibit and be converted by anammox bacteria.…”

“…Even low concentrations of methanol lead to the immediate, complete, and irreversible inhibition of the anammox process. In practice, this would mean that an anammox reactor would have to be restarted from scratch, which takes at least 100 to 200 days if no anammox seed is available (1,15,16,34). This observation is highly relevant, because methanol is often used to remove nitrate in postdenitrification or to compensate for pH effects in partial nitrification (4,5).…”

Identification and evaluation of SND in a full-scale multi-channel oxidation ditch system under different aeration modes

“…Traditional BNR process is a two-step reaction to remove total nitrogen (TN) involving aerobic nitrification of ammonia (NH 4 + -N) to nitrite (NO 2 À -N) and nitrate (NO 3 À -N) followed by anoxic denitrification of the NO x À -N to nitrogen gas (N 2 ) [3,4].…”