ENVIRONMENTAL MICROBIOLOGY Microbial Communities Involved in Biological Ammonium Removal from Coal Combustion Wastewaters Tatiana A. Vishnivetskaya & L. Suzanne Fisher & Greg A. Brodie & Tommy J. Phelps Received: 10 August 2012 / Accepted: 6 December 2012 / Published online: 13 January 2013 # Springer Science+Business Media New York (outside the USA) 2013 Abstract The efficiency of a novel integrated treatment sys- tem for biological removal of ammonium, nitrite, nitrate, and heavy metals from fossil power plant effluent was evaluated. Microbial communities were analyzed using bacterial and archaeal 16S rRNA gene clone libraries (Sanger sequences) and 454 pyrosequencing technology. While seasonal changes in microbial community composition were observed, the sig- nificant (P=0.001) changes in bacterial and archaeal commu- nities were consistent with variations in ammonium concentration. Phylogenetic analysis of 16S rRNA gene sequences revealed an increase of potential ammonium- oxidizing bacteria (AOB), Nitrosomonas, Nitrosococcus, Planctomycetes, and OD1, in samples with elevated ammoni- um concentration. Other bacteria, such as Nitrospira, Nitro- coccus , Nitrobacter, Thiobacillus , ε -Proteobacteria , Firmicutes, and Acidobacteria, which play roles in nitrification and denitrification, were also detected. The AOB oxidized 56 % of the ammonium with the concomitant increase in nitrite and ultimately nitrate in the trickling filters at the beginning of the treatment system. Thermoprotei within the phylum Cren- archaeota thrived in the splitter box and especially in zero- valent iron extraction trenches, where an additional 25 % of the ammonium was removed. The potential ammonium-oxidizing Archaea (AOA) (Candidatus Nitrosocaldus) were detected towards the downstream end of the treatment system. The design of an integrated treatment system consisting of trickling filters, zero-valent iron reaction cells, settling pond, and anaer- obic wetlands was efficient for the biological removal of ammonium and several other contaminants from wastewater generated at a coal burning power plant equipped with selec- tive catalytic reducers for nitrogen oxide removal. Introduction Excess ammonia (NH 3 ) along with oxygen is fed into the selective catalytic reduction (SCR) systems of fossil-fueled electric utility plants to achieve greater removal of nitrogen oxides (NO X ) and increase the life of the catalyst [1]. Unreacted ammonia typically results in a discharge stream that integrates with the combustion byproduct (fly ash) handling system and ultimately enters wastewater streams. Streams from SCR sys- tems combined with aqueous fly ash handling systems may result in localized transient ammonium (NH 4 + ) concentrations approaching 4 mg/L, often in conjunction with the trace levels of other potential fly ash-related contaminants such as mercury (Hg), arsenic (As), selenium (Se), and boron (B) [2]. Ammonium, if discharged inappropriately, may negatively impact air and water quality, as well as fish and human health. The adverse impacts of NH 4 + -containing wastewaters may be mitigated by facilitating the nitrification and denitrification processes. An experimental onsite wastewater treatment tech- nology for removing SCR-derived ammonium, nitrite, and nitrate from wastewater has been developed by the Tennessee Valley Authority (TVA) [3]. The treatment system, known as Aquatic Toxicology Improvement and Control Treatment Technology (ATOXIC), also contains a separate parallel treat- ment train known as the Arsenic and Selenium Extraction Trench (ASSET) designed to treat trace elements such as Hg, As, and Se. The ASSET portion is comprised of extraction trench cells containing a mixture of zero-valent iron and lime- stone for trace contaminant removal and a settling/oxidation T. A. Vishnivetskaya : T. J. Phelps (*) Biosciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS-6036, 1 Bethel Valley Rd., Oak Ridge, TN 37831-6036, USA e-mail: phelpstj@ornl.gov L. S. Fisher : G. A. Brodie Tennessee Valley Authority, Knoxville, TN 37902, USA Present Address: T. A. Vishnivetskaya Center for Environmental Biotechnology, University of Tennessee, Knoxville, TN 37932, USA Microb Ecol (2013) 66:49–59 DOI 10.1007/s00248-012-0152-5