TYPE: Tertiary wastewater treatment plant.CAPACITY:200,000 gallons per day (gpd).
TREATMENT PROCESSES: Comminution, activated sludge process, secondary clarification, coagulation, sand filtration, and ultraviolet disinfection.
The reclaimed water is primarily used for irrigation on the campus of Pepperdine University.
BACKGROUND
The Malibu Mesa Water Reclamation Plant (WRP) is located at 3863 Malibu Country Drive, Malibu, California. The Los Angeles County Department of Public Works operates and maintains the Malibu Mesa WRP. The plant treats domestic wastewater from 102 single family homes in the Malibu Country Estates, located in the City of Malibu, 66 condominiums on Pepperdine campus, and Pepperdine University, which is located in the unincorporated county area.
The purpose of the Malibu Mesa WRP is to reclaim the raw wastewater received in the wastewater collection system to recycle water standards in accordance with the California Code of Regulation, Title 22. The recycled water is discharged into two storage reservoirs, then used by Pepperdine University for landscape irrigation on approximately139 acres (as of 2008/2009 academic year). The Reclamation Plant also uses the reclaimed water on-site for landscape irrigation on approximately 1.6 acres.
During rare emergency situations when the storage reservoirs are unable to hold additional water and Pepperdine University is unable to irrigate because the soils are saturated, the recycled water is discharged to surface water (Marie Canyon). This National Pollutant Discharge Elimination System (NPDES) emergency discharge is regulated by the Regional Water Quality Control Board.
WASTEWATER TREATMENT PROCESSES
The Malibu Mesa WRP is designed to treat 200,000 gpd of domestic wastewater. All the wastewater generated at Pepperdine University is collected at Pepperdines flow equalization station, then pumped at an approximate constant rate to the Malibu Mesa WRP. Wastewater generated by the Malibu Country Estates flows directly to the plant. Figure 2-2 is a Flow Diagram of the treatment process. Following is a brief discussion and description of the treatment plant processes.
Figure 2-2.Flow Diagram
Preliminary Treatment
Preliminary treatment consists of an influent channel, comminutor and flow meter. The flow enters the treatment plant from a 12-inch gravity line into the influent channel and flows to the comminutor. The comminutor cuts and shreds large pieces of material into smaller pieces. This minimizes clogging and plugging problems in the downstream treatment processes. A by-pass channel with a manual bar rack is provided if the comminutor needs to be serviced. The influent flow is measured by a 3-inch parshall flume downstream from the comminutor and the bar rack.
Secondary Treatment
Secondary treatment consists of a Walker Process package unit, which includes an aeration basin, aerobic digester, and a secondary clarification basin all accommodated in a two concentric circle configuration (Photo 2-1). The inner circle serves as a secondary clarifier, while the other circle is split into two parts aeration basin and aerobic digester respectively. Flow proceeds from preliminary treatment by gravity to the aeration basin were the flow is aerated by coarse bubble diffusion. The aeration basin provides a location where biological treatment of the wastewater takes place. In these tanks, microorganisms remove organic material from wastewater and form settleable solids. After the aeration basin, the flow enters the secondary clarifier basin where the solids are settled and pumped by airlift pumps to either the aeration basin (return activated sludge) or to the aerobic digester (waste activated sludge). The aerobic digested solids are then pumped to the centrifuge for additional thickening. Thickened sludge from the centrifuge is pumped to a sludge holding tank.
Photo 2-1. Walker Process Package Unit
Tertiary Treatment
Tertiary treatment is provided through coagulation, flocculation, and filtration. Coagulation involves chemical coagulants (alum and/or polymer) addition to the secondary effluent in a rapid mix tank. The coagulant is used to destabilize the colloidal (very small) particles during rapid mixing. The flocculation tank, which is divided into two treatment trains, receives the flow from the rapid mix tank. The flow is gently mixed so that the small particles can combine into larger aggregates, this process is called flocculation. Coagulation and flocculation are an essential component of wastewater reclamation facilities to enhance the removal efficiency of the filters.
The water from the flocculation tank flows into 3 continuous backwashing filters (Photo 2-2). As the water passes through the filters sand media, the suspended matter is removed. The filters are continuously cleaned by air lifting the sand from the bottom and redistributing the sand to the top layer.
Photo 2-2. Continuous Backwashing Filters
Disinfection
The tertiary (filtered) effluent flows to the UV chamber (Photo 2-3). Disinfection is provided by the germicidal properties of the radiation emitted from the UV lamps. UV systems have the added benefits of not contributing to the formation of toxic byproducts, such as Trihalomethanes (THMs).
Photo 2-3. UV Disinfection Chamber
Sludge Disposal
Sludge generated from the plant is pumped to the centrifuge (Photo 2-4). The sludge is hauled off either after thickening with the centrifuge or without thickening in which case the centrifuge is bypassed allowing the unthickened sludge to flow directly to the sludge holding tank. The sludge is hauled in tanker trucks to the City of Los Angeles-owned Tillman WRP for treatment and disposal.
Photo 2-4. Centrifuge
