What does Home Gardens Sanitary District Do?

How does Home Gardens Sanitary District Provide Wastewater Service?

1. Collects the Sewage

The District owns many miles of sewer pipeline located underground within streets and easements throughout the Home Gardens community. Connected to the pipelines within the streets and easements, are smaller pipes called “laterals” that are extended to the edge of the property line of each property the District serves. Customers connect drain plumbing from the home or business to the lateral. This provides a continuous way to convey the wastewater that goes into drains within the house to the pipelines in the street. Customers may notice manhole covers within the streets. These manholes are access points the District uses to periodically clean grease and debris that builds up in the pipelines, so the pipelines do not plug and cause overflows into the streets.

The Wastewater Treatment Process

Treatment of wastewater at WRCRWA is accomplished using primary, secondary and tertiary processes with part focused on treating the water and the other on removing and handling of the solids. Below is a brief overview of the treatment process:

1. Primary Treatment: This is where wastewater enters the treatment plant. The goal of primary treatment is to remove the bulk of the solids from the water.

• a. Headwork: Water enters the headwork and flows through screens that remove solids down to approximately one eighth of an inch in size. Solids removed at the headworks go into covered bins that are emptied at landfills.
• b. Primary Clarification: Water flows from the headwork to large tanks where smaller solids can physically settle to the bottom of the tank. Settled solids are sent to digesters for biological treatment as part of the solids handling process.
• c. Flow Equalization: Primary clarified water flows to another large tank that is used to equalize flow. Sewer flows fluctuate during a day with largest flows generated in the morning as customers start their day, and in the evenings when customers return from work. Lower flows occur during the day and late night. The equalizing tank provides storage to hold high flows so a steady flow can be maintained for the biological processes.

2. Secondary Treatment: With most of the solids removed from the water through primary treatment the next step is to use biological treatment to remove suspended solids and nitrogen.

• a. Oxidation: From the equalization tank, flow enters an oxidation ditch where over a period of 16 to 24 hours organic suspended solids and nitrogen is biologically treated. Treatment is accomplished through control of oxygen, population of bacteria, and supply of suspended solids. The oxidation ditch has areas within it where there is substantial dissolved oxygen in the water, while others there is little to no oxygen present. Where oxygen is present (aerobic condition), bacteria multiplies and consume the organic suspended solids. Where little oxygen is present (anaerobic condition), bacteria use oxygen from nitrogen molecules which results in lowering of overall nitrogen present.
• b. Secondary Clarification: Once the biological process has had enough time to remove the organics and nitrogen, the water then goes to secondary clarifiers. These are large tanks that physically allow the bacteria and solids to settle to the bottom of the tank where it is collected and sent to digesters for further biological treatment as part of the solids handling process.

3. Tertiary Treatment: To enable use of the water as recycled water for non-potable purposes such as irrigation and groundwater recharge, the water goes through two more “polishing” treatments to ensure clarity and disinfection.

• a. Filtration: Water coming from the secondary clarifiers is pumped through very fine (10 micron) filter membranes. This is a mechanical process. The filtered water is very clean and clear of solids.
• b. Disinfection: After filtration water then enters a large chlorine contact basin where chlorine is introduced to disinfect the water of any remaining bacteria or viruses that may have survived through the treatment processes. After being fully disinfected, a de-chlorination chemical is added so the finished water can either be used for non-potable purposes, such as irrigation or groundwater recharge, or be discharged to the Santa Ana River. Testing is done daily to confirm lack of bacteria and chlorine prior to discharge of the recycled water.

4. Solids handling: Solids that have settled within the primary and secondary clarifiers are sent to digesters for additional treatment to reduce quantity and to enable the material to be hauled off for use as soil amendment.

• a. Digestion: the material going into the digester from primary and secondary clarification is approximately 2% solid and 98% water. The digester tank is kept in an anaerobic state (no oxygen) which promotes growth of a bacteria that thrive in anaerobic conditions. As these bacteria consume the solids, they produce methane gas. Methane gas is captured and used to fire boilers that keep the digester temperature at around 98 degrees.
• b. Dewatering of solids: After digestion, the material is now approximately 4% solid and 96% water. To reduce costs of hauling off solids, the next step is to remove as much water from the solids as possible as water is heavy. The digested material goes to a thickener and then centrifuging. Centrifuging spins water out of the biosolids like how a washer machine removes water in spin cycle. After centrifuging the biosolids are approximately 17 to 22% solid.
• c. Dryer: The centrifuged biosolids enter a large football field sized greenhouse structure and is spread thinly across the floor. Within the building the temperature can get upwards of 140 degrees and become quite humid as water evaporates from the biosolids. To control humidity and temperature, air exchanges are made. Odors are controlled before air is released to the atmosphere. Once dried, the biosolids are approximately 80% solid and 20% water. Dried biosolids are automatically loaded into 25-ton trucks and hauled off to Arizona to be used as soil amendment.

Environmentally Friendly

The District as a member of WRCRWA fosters use of technology and methods that supports sustainability and are efficient. This is exemplified by:

1. Use of energy producing solar panels to generate electricity. A 9-acre, 1 mega-watt solar panel array is located at the WRCRWA Plant that produces approximately 25% of the entire plant’s energy demand. This system produce power without emissions and have provided a cost stable energy source.
2. Use of generated methane gas. To maintain a 98-degree temperature within the digesters, methane gas produced within the digestion process is captured and used to fire boilers that heat water. The use of methane gas offsets the need to buy as much natural gas.
3. Creation of recycled water. The plant currently produces approximately 3 billion gallons per year of recycled water that can be reused for non-potable purposes such as irrigation and groundwater recharge. This conservation and reuse reduce the amount of imported water from Northern California or Colorado River that needs to be imported to meet regional water demands.
4. Beneficial use of biosolids. The biosolids are used as soil amendments rather than put to landfill.
5. Public Health Benefits. Collection, treatment and disposal of wastewater is a necessity for the health and welfare of the community to maintain sanitary conditions.
6. Supports the Santa Ana River Environment. High quality recycled water discharged to the Santa Ana River supports riparian habitat that provides protected species places to live such as various fish, animals and birds.