| Summary: | While research is conclusive that the membrane bioreactor process performance in removing the carbonaceous and phosphorus constituents of wastewater is superior or equivalent to a conventional gravity separation process, there have been conflicting reports regarding its ability to achieve nitrification rates comparable to the conventional process. In this long-term study conducted at University of British Columbia’s (UBC’s) wastewater treatment pilot plant facility, the specific nitrification activity of a membrane enhanced biological phosphorus removal (EBPR) process was compared to that of a conventional EBPR process operating under identical conditions to identify factors that influence the relative nitrification rate of the processes.
The specific nitrification rate measured from batch experiments showed a natural variation between the processes. There were periods where the specific nitrification rate of the membrane process was either consistently high or consistently low, relative to the conventional process. Average rates were nearly equal, however, the membrane process showed less variability in the individual rates.
Nitrifier decay rates measured during the various performance periods conformed to the variation observed as rates for the membrane process were lower relative to the conventional process during periods where the specific nitrification rate for the membrane process was higher and vice versa. The presence of rotifers caused an increase in the decay rate of the conventional process. These organisms were absent in the membrane process. Vigorous coarse bubble aeration did not affect the decay rate.
Terminal restriction fragment length polymorphisms (T-RFLP) analysis showed that ammonia-oxidizing (AOB) communities differed for the two processes, however the nitrite-oxidizing bacteria (NOB) communities as represented by the genus Nitrobacter and Nitrospira were similar for both processes. Temperature effects were significant for both AOB and NOB communities, but the effect was greater for the AOB community. Community shifts for the AOB were observed to occur during plant operation.
Quantification of the nitrifiers by a real time polymerase chain reaction assay indicated similar quantities of AOB, Nitrobacter and Nitrospira in the two processes with Nitrospira being the most abundant of the nitrifiers present in the systems. AOB and Nitrobacter quantities correlated with the relative nitrification rate of the processes.
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