Phosphorus removal and flow maximization in the Kamloops rapid infiltration system
Creators: name: Bakker, Gillian
Publisher: name: University of British Columbia
Year: 2009

description: A proposal concerning its rapid infiltration system at the wastewater treatment plant was submitted to and accepted by the City of Kamloops. A project was therefore undertaken to study the basins as they currently operate as well as how they have done so in the past. To date, only half of the design throughput is realized by the basins. Also to be examined was the phosphorus removal capability of the basin sand, in the hope that it would be sufficient to cease or curtail the practice of chemical phosphorus removal using alum. The phosphorus removal capability of the sand was studied by means of a number of column tests performed using influents of varying phosphorus concentrations. The columns were packed with basin sand of varying depths. An appropriate sand depth and influent phosphorus concentration were chosen as a result of the column tests. It was concluded that a depth of 120 cm and an influent phosphorus concentration of approximately 3.5 mg/L were suitable for further testing. These subsequent experiments revealed that this influent P concentration can only be adopted if accompanied by substantial changes to the current system. These changes include either the occasional re-routing of basin effluent to spray-irrigation or the expansion of the wetlands pilot project. To ensure the propriety of the recommended changes which resulted from the column tests, numerous analyses were performed on the RI basins. It was discovered that the basins have saturated flow; the flow was previously assumed to be unsaturated and therefore all throughput problems had always been linked to surface phenomena. This change in outlook with respect to basin operation allows for a number of alterations to be made. It is recommended that the current sand depth of 220 cm be reduced by 100 cm to 120 cm. This decrease in sand depth will decrease flow resistance by 45%; the accompagnying increase in head will further increase the throughput capability. A discrepancy between in-situ permeability (0.5 x 10⁻⁵ m/s on average) and design permeability (5 x 10⁻⁵ m/s) was discovered and attributed to an error in basin construction. This information changes the view thus far maintained that the basins have never worked according to their design; this can now be altered by substituting the actual permeability for the design permeability into performance expectations. Differences in throughput between the east and west basins, which have always been evident, are attributed to a difference in surface area between the basins and to a small difference in permeability. The west basin is 21% larger than the east. Finally, it was discovered that the basins are indeed capable of removing and retaining phosphorus from wastewater, as was seen by analyzing historical basin data. Most of this retention occurs in the organic-rich surface layer. This result further supports the cutting away of 1 m of sand, since phosphorus removal does not depend on depth. More importantly, this straitforward fact implies that the RI basins are a worthwhile process within the Kamloops treatment plant. Included in the report are numerous recommendations which include changes to the current basins, design of future basins as well as suggestions regarding current basin operation and maintenance. No opinion by the author was given concerning alum cessation or reduction, although various options were provided. The use of fewer chemicals would be appreciated both monetarily and publicly; however this would necessitate increased attention to the RI system by City staff and would leave the basins more susceptible to operational failure, which could result in failure to comply with discharge permits. The recommendations are offered by the author, but the decisions are suitably left to the City of Kamloops.