Nutrient Management: Heterotrophic Nitrification

Background

The removal of nitrogen in the form of ammonia from wastewater is an important yet expensive step in treatment often done in two stages, typically by different autotrophic nitrifiers:

  • Nitrification: Ammonia is converted to Nitrite and Nitrate.
  • Denitrification: Nitrate is converted to nitrogen gas (N2)

Heterotrophic nitrifiers like Alcaligenes faecalis are able to perform both processes and reduce the two step treatment process to one.

Previously, experiments were performed on Alcaligenes faecalis in a synthetic wastewater environment to determine the kinetic constants for a substrate-dependent ammonia removal rate (Michaelis Mentin Kinetics).

KM=2.09mg/L VMAX0.088 mg/L-min

Growth Method Development

The ammonia removal performance of A. faecalis in exponential phase was compared between three growth methods using sythetic wastewater media: suspension culture, rope substrate, and MBBR substrate. The various substrates were used to test for possible biofilm developments.

graph of results from the growth method experiment

Biofilm Growth Test

A three-week growth test was run to determine if Alcaligenes faecalis is capable of forming a viable biofilm on MBBR (Moving Bed Bioreactor) plastic media and test the ability of A. faecalis to perform in a competitive community environment. Cultures were grown in both synthetic and real wastewater. The MBBR was tested for biofilm presence at the end of the three-week growth period.

ammonia removal of MBBR biofilm growths
Ammonia removal for various biofilm growths; only the wastewater growth samples showed consistent ammonia removal within 9 hours. Microscopy of gram-stained scrapings taken from MBBR pieces. A) Wastewater growth sample; biofilm-evident structure implies symbiotic relationship between A. faecalis (gram-negative) and an organism present in the wastewater sample. B) Synthetic growth sample; some structures are present.

Growth Flasks with MBBR Media

Synthetic growths after 3-week period Synthetic growths after 3-week period Wastewater growths after 3-week period. Wastewater growths after 3-week period. Wastewater and Synthetic growth MBBR in new media for ammonia removal test Wastewater and Synthetic growth MBBR in new media for ammonia removal test

Notable Results

  • A. faecalis can take up ammonia, removing it from solution, at a zero order reaction rate for typical ammonia levels in wastewater (>5 mg/L NH4-N). This is supported by the low KM value of 2.09 mg/L found by a previous senior design group; for most of the NH4-N concentration range, the bacteria are performing at VMAX.
  • Although it is unclear whether or not A. faecalis is able to grow a biofilm on its own, preliminary results seem to suggest that it can form a symbiotic relationship with other organisms found in wastewater in order to grow a biofilm (see figure 3A).

Future Work

  • More experimentation on biofilm capabilities could be done to find if A. faecalis is able to form a biofilm on its own, given time and ideal conditions for biofilm formation.
  • Research to better understand what temperature ranges are optimal for A. faecalis' removal of ammonia.
  • Experimentation to determine the kinetic constants for ammonia removal by A. faecalis in wastewater, to compare to previous work done in synthetic wastewater.

People

Team Members

  • Zac McClellan
  • Jaden Storrer
  • Anna Scribner
  • Jayce Bradley

Project Sponsor

  • Kirsten Sims - WesTech

Academic Mentor

  • Dr. Ronald Sims