WASTEWATER
By Rick Lallish
In fixed-film processes, what must be reduced before nitrification can occur?
A. Organic loading rate
B. Hydraulic loading rate
C. AOB and NOB bacteria
D. Endogenous respiration
Answer: A. Higher organic loading rates (OLR) favor the growth of heterotrophic bacteria over nitrifying bacteria. In most fixed-film systems, the higher OLRs cause rapid growth of heterotrophic bacteria, forcing the weaker nitrifiers to go deeper into the biomass. This process slows their growth rates. By reducing the OLR, the heterotrophic bacteria will slow, and this prevents the nitrifiers from being overtaken. Operating the system in a series mode where the OLR is reduced after the first
