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  The Garden - Purpose

~ The Japanese Garden at the Donald C Tillman Plant:

The Donald C. Tillman Water Reclamation Plant (DCTWRP), was designed to produce reclaimed water that will meet the requirements of the California Department of Health Services and the County Health Department for specific uses with the priority to protect public health. The main function of the plant, however, is to relieve the overburdened portions of the wastewater collection system between the San Fernando Valley and the City's main wastewater treatment facility, the Hyperion Treatment Plant, located in Playa Del Rey, (above).

The following briefly describes the treatment process:
The influent pumping facility includes four eight foot diameter enclosed screw pumps which lift sewage into the plant for the initial stages of grit, sand, and trash removal. Barminutors consisting of screens collect the coarse debris and grinders move up and down over the screens, as needed, to shred the coarse material.

Following this preliminary treatment, the wastewater flow into the primary sedimentation tanks where gravity is used to settle most of the heavy particles. A pair of continuous chains connected to wooden scrapers (flights) move settled material (primary sludge) along the bottom to a hopper for disposal to the main sewer line for treatment at the Hyperion Treatment Plant. Floatable material is skimmed off the top by the same flights and also removed to the sewer line for transport to Hyperion.

The next step is the secondary treatment process which takes place in aeration tanks. Compressed air is bubbled through thousands of ceramic domes located on the bottom of the tanks. In this biological process air provides the mixing and oxygen for particles teeming with bacteria, fungi and protozoa. These particles (what is called activated sludge) consume the organic material (pollutional load) in the wastewater, converting it to carbon dioxide, water, and new cells.

Since the activated sludge serves to remove pollutants from the wastewater, it must be maintained at a necessary concentration level. The water containing the activated sludge moves to a final settling tank so that it can settle to the bottom - excess is removed to the main sewer line and sent to Hyperion while the amount necessary for the bacterial process in the aeration tank is returned to that tank. The effluent produced in this biological process flows into rapid mix basin where coagulant chemicals are added to improve the filtration process, the next step in wastewater reclamation.

The filtration process removes a large portion of whatever suspended solids and turbidity are left through continuous backwash sand filters. This material is also returned to the sewer for treatment at Hyperion. Immediately following filtration, chlorine is added to the filtered wastewater, to provide disinfection. At the completion of the process, taking about a total of 11.5 hours, reclaimed water can be made available for reuse, with any excess being discharged to the Los Angeles River.

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