THE EFFECT OF BIOFILM CARRIER LENGTH ON NITRIFICATION IN MOVING BED BIOFILM REACTORS: AN EXAMINATION OF MIXING INTENSITY, SHOCK LOADINGS, AND PH CHANGES

Biofilms grown on free-floating attachment surfaces, as in integrated fixed film activated sludg (IFAS) and moving bed bioreactors (MBBRs) are commonly used in wastewater treatment, but little is known about how media geometry affects the biofilms and process performance. The objective of this study was to compare nitrification and growth of biofilms grown on different length media in bench-scale MBBRs. The carriers were cut from high density polyethylene tubing with one media type one-third the length of the other, but with inner and outer diameter dimensions identical. Each bioreactor was continuously operated with coarse bubble aeration and provided with a high ammonium loading to promote greatly active nitrifying communities. Biomass measurements were taken regularly to observe growth. A series of variable velocity gradient (G) batch tests was executed to determine the effect of mixing on mass transfer through the biofilms of each media type. High ammonium and variable pH batch tests were also conducted to assess inhibition effects on nitrifiers. Greater biomass was consistently measured on the longer media despite both media types having similar ammonia uptake during continuous operation. Lower G values consistently produced greater ammonia utilization in the short media biofilm than in the long media biofilm. However, at mid to high range G values, ammonia consumption was similar between both biofilms. Ends of media typically had greater biomass and greater nitrate production than middle sections, while ammonia consumption was similar along carrier length. Abrupt changes in ammonium concentration and pH produced significantly greater inhibition effects in the short media biofilm than in the long media biofilm, suggesting greater protection in the biofilm grown on the longer media.UNM's Center for Water and the Environment: Centers of Research Excellence in Science and Technology (National Science Foundation).Master of Science Civil EngineeringMastersUniversity of New Mexico. Dept. of Civil EngineeringSchuler, AndrewHowe, KerryCerrato, Jos