MS Thesis Defense

The rapid infiltration (RI) land treatment process is a reliable, cost effective method for secondary and/or tertiary treatment of municipal wastewaters. When properly designed and operated, RI systems can achieve a significant level of nitrogen removal via coupled biological processes, namely nitrification-denitrification. Generally, it is believed that lower overall nitrogen levels can be achieved when influent wastewater is fully nitrified. However, at a specific RI facility located in Colton, CA higher nitrogen removals were observed when non-nitrified influent wastewaters were introduced. As a result, it was hypothesized that an abiotic mechanism, ammonium adsorption, to the soils was occurring. This hypothesis, led to conducting a previous study to determine the sorptive phenomenon that was occurring at this site. However, it was determined that ammonium adsorption was not occurring. No nitrogen removal was observed under abiotic (sterile) conditions. Nitrogen removal was observed only under biotic conditions.

This present study was conducted in an effort to confirm and better understand the biological nitrogen removal mechanisms that are occurring at the Colton RI facilty. In addition, experiments were conducted to evaluate whether nitrogen removal could be enhanced at the facility via organic carbon amendment to the influent wastewater. For design purposes, a 2:1 mass ratio of organic carbon to nitrogen is recommended for nitrogen removal in RI systems. The normal organic carbon to nitrogen ratio at the Colton RI facility is 1:3, highly organic carbon deficient. Experimental systems were amended with additional organic carbon in the form of methanol. Consistent with biological nitrogen removal mechanisms, a steady decline of nitrate throughout the soil column occurred when additional organic carbon was added to the system.