Degree Type


Date of Award


Degree Name

Master of Science


Civil, Construction, and Environmental Engineering

First Advisor

Say Kee Ong

Second Advisor

Tim Ellis

Third Advisor

Thomas Loynachan


Regulation of the discharge of biological nutrients into the environment continues to increase in order to protect sensitive bodies of water. One promising new technology is the membrane bioreactor, which combines the activated sludge process with membrane filtration. The focus of this study was to determine the best anaerobic and anoxic hydraulic retention time (HRT) for biological nitrogen and phosphorus removal. A randomized experimental design of fourteen different HRT runs was tested with the anaerobic HRT varying between 0.5 and 3 hours and the anoxic HRT varying between 1 and 5 hours. Essentially complete nitrification was achieved with an average ammonia removal of 98.8 ± 0.2%. Total nitrogen removal varied from a low of 76 ± 1.2% to 88.7 ± 0.3% and showed a positive correlation with increases in anoxic HRT from 1 to 4 hours. High anaerobic HRTs (3 hours) slightly decreased nitrogen removal. Phosphorus removal varied from 40.3 ± 2.2% to 81.7 ± 0.8% and showed strong positive correlation with increases in anaerobic HRT from 0.5 to 2 hours and a negative correlation with increases in anoxic HRT. In general, phosphorus removal appears to be more sensitive to changes in HRT than nitrogen removal. Optimization of the system requires balancing the conflicting needs of higher anoxic HRT for nitrogen removal but negative impact on phosphorus removal and higher anaerobic HRT for phosphorus removal. A prediction model was developed to estimate nitrogen and phosphorus removal given the anaerobic and anoxic HRT. In addition, a study was conducted to determine the influence of various SRTs on biomass phosphorus concentrations and bacterial floc sizes in an aerobic MBR system. Phosphorus uptake by the biomass increased with increased SRT from 10 to 50 days and decreased from 50 to 75 days. This finding has implications for the operation of aerobic MBR systems at high SRTs. A statistical analysis indicated that the bacterial floc diameters were statistically similar from 10 to 50 day SRT and significantly larger for 75 day SRT. The results did not follow the trend of decreasing floc size with increased SRT reported in other studies, although the floc sizes were generally similar to those reported in other studies.



Digital Repository @ Iowa State University,

Copyright Owner

Patrick Anderson Brown



Proquest ID


OCLC Number


File Format


File Size

159 pages