By Wendy Wert
On April 26, 2007 the Los Angeles Basin Section (LABS) of CWEA held officer installations during a training meeting at Ports O’Call Restaurant in San Pedro. Slavica Hammond of MWH discussed their experiences during design and construction of a major nitrogen removal program at the City of Los Angeles’ upstream plants.
The Donald C. Tillman (DCT) (located in the Sepulveda Basin in Van Nuys) and Los Angeles-Glendale (LAG) (located in the vicinity Colorado Blvd. and the I-5 Freeway) Water Reclamation Plants are being converted for nitrogen removal using the eMLE (enhanced Modified Ludzack Ettinger) process.
The Los Angeles/Glendale Water Reclamation Plant was designed for conventional activated sludge treatment in the late 1960’s and built in the mid 1970’s. Nitrogen limits are a relatively new requirement from the Regional Water Quality Control Board. The purpose is to remove nitrogen from the waters of the Los Angeles River to provide a more healthful environment for aquatic life. Studies show that the effluent from LAG and DCT is a source of the LA River’s nitrogen. Certain nitrogen compounds, such as ammonia (NH3) in elevated concentrations exhibit toxic effects on aquatic life. The Los Angeles River has the ability to assimilate a portion of these compounds. It is anticipated that removing additional nitrogen compounds (i.e., ammonia, nitrates, nitrites) may enhance the water quality and habitat of the LA River.
Costs for the program were $15 million for LAG and $87 million for DCT. In addition to the initial investment it is anticipated that O&M costs will increase. For example power costs will increase due to the added energy needed to produce higher dissolved oxygen levels in the aeration tanks. Chemical costs will increase due to the addition of polymer to control foam. Disinfection costs of the Plant’s final effluent may increase due to chemical reactions in the absence of ammonia, i.e., no chloramines will be formed.
The main treatment process unit of each plant, Secondary Treatment, were each designed for conventional activated sludge treatment of sewage. Each needs to be converted to a nitrification/denitrification (aerobic and anoxic) set of sections to comply with the nitrogen removal requirements. This will result in a significant modification of the Secondary Treatment processes at the plants. This operational scheme has been shown to increase foaming in the “biological filtering” section of the process. Excessive foaming can cause odors. The addition of chemicals (polymer) has shown promise in reducing foam.
The amount of flow that is treated may have to be reduced to achieve the higher performance standard. This retrofit may result in a decrease in plant capacity to accommodate the higher treatment level. During the upgrade, throughput (flow) at the plants will have to be de-rated by as much as 40% to 50%.
Due to reduced capacity of these upstream plants, a larger volume wastewater required routing to Hyperion Treatment Plant, the downstream sewers had to be adequate to accommodate the increased flow. Therefore, the City worked with the Regional Board to improve downstream sewer capacity prior to the installation of nitrogen removal at the upstream plants.