Changing the nutrient source from ammonia to nitrate: Effects on heterotrophic bacterial growth in wastewater

Abstract

Bacteria can use nitrate as a nutrient for growth, but the underlying mechanisms of this pathway have not yet been identified. We investigated the effects of changing the nitrogen source from ammonia to nitrate on the properties of heterotrophic bacterial growth in anoxic and anoxic/oxic (A/O) SBRs. Both SBR types were seeded with activated sludge cultivated with ammonia and were then fed with 1,400 mg·L-1 chemical oxygen demand (COD) and 250 mg·L-1 of nitrate nitrogen. Heterotrophic bacteria had a lag period of 8-9 d and 13-14 d in terms of growth and COD and nitrogen removal, respectively, in both reactors with nitrate as nutrient. Of the influent nitrate, 15% were converted to biomass nitrogen. Compared with ammonia or organic nitrogen as a nutrient source, with the use of nitrate more energy was needed for proteins synthesis, which resulted in a lower sludge yield (0.32-0.35) and lower amounts of proteins and phosphorus compounds. Furthermore, fewer extracellular polymer substances (EPS) and more soluble microbial products (SMP) were produced, both of which also had low proteins and high polysaccharide contents. The proteins in the cells were synthesized via dissimilatory nitrate reduction to ammonia (DNRA).