Diagnosis of biological wastewater treatment instabilities using molecular methods

Nitrification is a natural nutrient removal process carried out by two distinct groups of chemolithotrophic nitrifying bacteria: (1) the ammonia-oxidizing bacteria (AOB) that oxidize ammonium (NH4+) to nitrite (NO2-), and (2) the nitrite-oxidizing bacteria (NOB) that oxidize nitrite to nitrate (NO3-). Due to the high sensitivity of AOB and NOB to different environmental parameters as well as toxics, nitrification is often plagued by instabilities and inadequate nutrient removal.

Traditionally, strategy for tackling upset events has been based solely on results gathered from chemical analysis, such as increase in ammonia concentrations in the effluent. Although such an approach often provides useful data on the performance of the system, it does not offer any information on the dynamics of the microbial communities in the treatment process. Obviously, studies that bridge the gap between the microbial community and stability of the system will be crucial for devising strategies for efficient process control.

With the advancement of new molecular tools, it becomes possible to carry out routine monitoring of microbial community structure and function within bioreactors.  In this forensic study at the Palo Alto Regional Water Quality Control Plant (PARWQCP), we apply these tools to diagnose factors that contribute to unstable nitrification.   Weekly samples from the aeration basin at the PARWQCP are subjected to community analyses. Terminal restriction fragment length polymorphism (T-RFLP) assays, qPCR, and clone libraries are used for establishing the basic understanding of the AOB population in the basins. By correlating microbial community data with process conditions, we expect to derive the principles that affect nitrification stability thus permitting stable and robust design and operation.

Professor Chris Francis, Department of Geological & Environmental Sciences is Co-PI on this project

Click here for a list of researchers working on this project.