Isolation and characterization of nitrogen removal bacteria from sewage and fecal sludge of dairy cow farms in Cu Chi, Ho Chi Minh City, Vietnam

The bacteria that involved in the removal of nitrogen in wastewater were initially studied. Isolation media were SW-MM (artificial Seawater-Minimal Medium) and 17208 PIA (Pseudomonas Isolation Agar). The pure isolates were streaked on the SW-MM agar plates that added ammonia, nitrate, or nitrite with ascending concentrations to select the isolates had good nitrogen removal potential. The result was that 49 isolates had been collected from 11 samples of sewage and fecal sludge of dairy cow farms, in which including 6 isolates had been isolated by using specialized medium for Pseudomonas. All 49 isolates (100%) were able to grow on the SW-MM added 100 mM ammonia/nitrate or more. The ability to withstand ammonia and nitrate of the best isolates reaches 800 mM. Meanwhile, the ability to withstand nitrite had only belonged to 39 isolates (79.6%) with nitrite concentrations of 5 - 15 mM. Nine isolates were investigated the in vitro ability to reduce ammonia in the wastewater. Quantitative results of ammonia by phenol-hypochlorite method showed that the ability to reduce NH4+ of 9 isolates ranged from 27.9 – 48.9 mg/L on 10 days after inoculation. The six best isolates that had the ammonia- removing efficiency reached 88.5% - 97.5% were identified by using the MALDI Biotyper System (Germany). The identification result showed that XM3, NA6 was Bacillus megaterium, M7C1 was Bacillus pumilus, NA8 was Rhodococcus ruber, MD6 was Pseudomonas fulva, and XM5 was Pseudomonas mendocina. It is recommended to test the ability of these isolates to reduce nitrate and nitrite in the wastewater.