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

• Published in: Environmental science & technology Vol. 38; no. 4; pp. 1228 - 1235
• Main Authors: Pynaert, Kris, Smets, Barth F, Beheydt, Daan, Verstraete, Willy
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15-02-2004
• Subjects: Ammonium; Applied sciences; Bacteria; Bacteria, Aerobic - physiology; Biocatalysts; Biofilms; Biological and medical sciences; Biological treatment of waters; Bioreactors; Biotechnology; Catalysis; Environment and pollution; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; General purification processes; Industrial applications and implications. Economical aspects; Nitrogen; Nitrogen - isolation & purification; Nitrosomonas; Oxidation; Oxygen; Pollution; Population Dynamics; Sludge; Waste Disposal, Fluid - methods; Wastewaters; Water treatment; Water treatment and pollution; Planctomycetales; Fixed bed reactor; Denaturing gradient gel electrophoresis; Autotrophy; Aerobe; Real time system; Biocatalyst; Biological purification; Polymerase chain reaction; Bioreactor; Anaerobe; Starting; Methanogenesis; Nitrification; Biofilm; Denitrification; Bacteria; Waste water purification; Microbial community; Rotating biological contactor
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es030081+

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, NH4 + is directly converted to N2 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 NH4 +-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 NH4 + with NO2 - as electron acceptor (maximal 434 mg of NH4 +-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.