By Karen R. Smith
The city of Corona, California made the commitment to water reclamation several years ago, opting to treat wastewater to a level of quality where it would be suitable for a variety of beneficial non-potable uses. Recycled water is safe to use for irrigation of landscaping, playgrounds, golf courses, parks, freeway embankments and much more. Conventional water supply sources are scarce in Corona, which lies roughly 45 miles southeast of Los Angeles. Incorporated in 1896 as a small farming town, the city is now a diverse community with a population of more than 138,000.
Today, as you approach Corona from the freeway, there are construction projects in progress at every point of the compass. New housing developments, malls and recreational facilities are going up within a stone’s throw of the city’s Waste Water Treatment Plant 3. Not likely that many people will realize that fact, as there is no telltale odor to denote the facility’s presence.
Achieving Corona’s wastewater treatment goals became possible with the use of a suspended growth biological reactor integrated with a microfiltration membrane system. Membrane technology for potable water treatment was first applied in the late 1960s for brackish water desalination using RO.
Membranes are classified into four categories by the size of the materials they can remove; microfiltration is a low-pressure membrane process that removes particulate material ranging in size from 0.1 to 1.0 microns. Suspended solids and bacteria (E-coli, Cryptosporidium or Giardia) can be separated from water with this membrane.
The Corona Department of Water and Power authorized the creation of Waste Water Treatment Plant 3 specifically because of the need to treat the flows from the planned Eagle Glen community along with other anticipated commercial, retail and residential developments in the area. The plant was designed to treat reclaimed water to the state’s Title 22 standards.
California Department of Health Services (DHS) is responsible for the regulations for the use of recycled water. DHS has established water quality standards and treatment reliability criteria for recycled water under Title 22 of the California Code of Regulations. California Regional Water Quality Control Boards issue water recycling permits based on the established DHS regulations. In accordance with Title 22 requirements, the recycled water plant is designed to provide the highest possible degree of treatment under varying circumstances; recycled water is delivered through purple pipes that are completely separate from the potable (drinking) water pipes; routine inspections are conducted to ensure no cross-connection between potable water pipes and recycled water pipes has occurred and the water recycling plant and water distribution system are monitored continuously.
The recycled water is used at the Eagle Glen Golf Course, where it fills a lake-like reservoir, as well as at surrounding schools and parks. Additionally, the plant is permitted to discharge into the Temescal Wash.
The plant has three parallel trains; each with two-stage process tanks comprised of an anoxic zone followed by a fully aerobic zone. Simply stated, the process begins at the headworks, where raw wastewater is pumped to a rotary drum screen where grit and solids are removed. They are waste-pumped daily and sent to Corona’s Waste Water Treatment Plant Number 1 for further processing.
Screened wastewater flows into the anoxic zone, then into the complete mix aerobic bioreactor. The reactor contains microbes that work to decompose the organic material in the wastewater and generate organic mass. Dissolved oxygen is provided by blowers to satisfy the oxygen demand by the microbes to stabilize the organic matters and for nitrification of the incoming ammonia concentrations. The anoxic zone of each train provides a denitrification process.
In the aeration zone of the tank, water is drawn through the membrane surface (the membranes are hollow strands of porous plastic fibers which look like spaghetti) by a vacuum created by the process pump. The membrane has microscopic pores that prevent the passage of select impurities, physically blocking contaminants on the outside while collecting water on the inside. Filtration is achieved by drawing water to the inside of the membrane fiber under a low-pressure (–1 to –8 psi) suction, created by a permeate pump.
The system is modular, with individual membrane strands fabricated into multi-stranded modules and numerous modules combined to form cassettes. Each cassette is immersed directly in the raw water of the process tank. The number of cassettes is based on the desired treatment capacity. This replaces both the clarifier and granular media filters of conventional treatment systems. An additional advantage of these modular components is that municipalities can easily and inexpensively plan for expansion simply by leaving room for additional cassettes in the future.
Energy costs are low (as compared with the costs of applied pressure systems) and membrane fouling is reduced since contaminants aren’t forced into the pores of the membrane under high pressure; thus, longer membrane life and reduced membrane replacement costs.
Air keeps the surface of the membranes clean and free of particles. It is introduced from the base of the cassette and travels up the surface of the membrane fibers, scouring the surface and creating a circulation pattern in the process tank. In addition, the membranes can be manually cleaned by swapping out cassettes on a rotational basis for regular maintenance.
The treated effluent enters permeate tanks where it is chlorinated prior to entering the contact for disinfection. Then the reclaimed water pump stations send the flow to the Eagle Glen Golf Course reservoir.
The entire system is monitored and controlled by computer, allowing the municipality to achieve optimal operational performance with very few employees, all without sacrificing quality or safety.
The mission statement of the City of Corona’s Department of Water and Power defines the goal of providing customers with an adequate supply of safe, good quality water and an effective, efficient system for collecting, treating and disposing of wastewater and its by-products at a reasonable price.
For additional information, contact Zenon Environmental Inc., 3239 Dundas Street West, Oakville, Ontario, Canada L6M 4B2; tel (905) 465-3030; fax (905) 465-3050 or visit their website at www.zenonenv.com