Nitrifying community structures and nitrification performance of full-scale municipal and swine wastewater treatment plants

This study evaluated nitrification performance and microbial ecology of nitrifying sludge in two full-scale wastewater treatment plants (WWTPs) including a municipal WWTP treating 20 mg N L−1 of ammonium and a swine WWTP treating 220 mg N L−1 of ammonium. These two plants differed in both wastewater characteristics and operating parameters, such as influent COD, TKN, ammonium, hydraulic retention time, and solids retention time, even though both plants achieve >85% nitrification efficiency. By employing molecular techniques, including terminal restriction fragment length polymorphism, cloning-sequencing and phylogenetic analyses targeting the 16S ribosomal RNA and group specific ammonia-monooxygenase functional gene (amoA), microbial community structures of nitrifying sludge and their significance to nitrification performance were evaluated. The results reveal that for the municipal WWTP Nitrosomonas marina-like AOB (ammonia-oxidizing bacteria) and Nitrospira-like NOB (nitrite-oxidizing bacteria) were the ubiquitously dominant nitrifiers, while Nitrosomonas europaea-, Nitrosomonas oligotropha-, and Nitrosospira-like AOB and Nitrobacter- and Nitrospira-like NOB were the major nitrifying populations found in the swine WWTP. The observed dissimilar nitrifying populations prevailing in these two plants may be related to niche differentiation concerning ammonium concentrations, system operation, and salinity. Moreover, our results suggest that the swine nitrifying sludge, involving relatively diverse AOB and NOB populations that perform the same task but with distinct growth and survival characters, may allow communities to maintain nitrifying capabilities when conditions change such as sudden increases in ammonium concentrations as examined with nitrification kinetic batch tests.