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Questions and Answers: Wastewater | Environment

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Questions and Answers: Wastewater
Environment, Life
Questions and Answers: Wastewater

What is secondary and tertiary wastewater treatment? There are several phases of wastewater treatment. In preliminary treatment, screening and grit removal occurs. Primary treatment includes the processes of sedimentation and floatation. Secondary treatment—also known as conventional secondary treatment—includes biological, chemical, and physical processes for the removal of suspended and dissolved solids prior to disinfection. Tertiary treatment is a more costly form of advanced wastewater treatment that produces a high level of wastewater quality by filtering the wastewater just prior to disinfection. It helps remove the finer particles that conventional secondary processes cannot remove. At our El Dorado Hills wastewater facility, our tertiary system also includes the removal of algae.

What is biological nutrient removal (BNR)? BNR is an advanced secondary wastewater treatment that removes nutrients (nitrogen and phosphorus) from the waste stream. Excess quantities of nitrogen and phosphorus can be toxic to aquatic organisms and this is of concern since our wastewater is released back into streams. This treatment requires a large amount of oxygen in the process and uses a large amount of power. Because of the high power requirements, the costs associated with BNR are expensive.

What is disinfection? Disinfection of wastewater is a regulatory requirement. The District uses an ultra-violet (UV) light system for disinfection. UV light inactivates the DNA of bacteria to prevent further growth and reproduction of diseasecausing pathogens. The cost of UV can be higher than the costs of chemical disinfection depending on the utilities’ power costs. Parts and maintenance required for UV disinfection are estimated at $300,000 annually, not including the labor.

Who sets the rules as to what contaminants are required to be removed from any particular wastewater treatment plant? Those rules are set by the State Regional Water Quality Control Boards, but governed by federal law. There are nine regional boards in California. EID is in region five, also known as the Central Valley Regional Water Quality Control Board. It is bound by the Sacramento-San Joaquin Basin Plan, which contains the water quality objectives for protection of beneficial uses for those waters. This is a requirement of the federal Clean Water Act.

What are some of the benefits of the District’s recycled water program? There are several benefits, the foremost being that the recycled water that we produce is a drought-proof water supply that our customers can use for non-potable purposes. We produce about 1,200 million gallons of recycled water annually. Currently, about 4,000 customers use this recycled water to irrigate their front and back yards, commercial landscapes, street medians, and a golf course. Water recycling is a key element of our water portfolio, as it helps to provide sustainable water supplies that will help us meet future planning. In addition, the treatment requirements for wastewater and recycled water are essentially the same. At our El Dorado Hills reclamation facility, we recycle 100 percent for five to six months and eliminate all effluent discharge. By eliminating effluent discharge to the stream, we save about $12,000 per month in laboratory testing costs.

Why is my sewer bill higher than my water bill? Sewer charges are higher than water costs for a number of reasons. Wastewater is especially costly to transport in the varied topography of our service area. The District operates and maintains 64 pump stations to get wastewater to one of our treatment plants. Another big factor is the cost of treating wastewater to meet increasingly stringent environmental regulations over the past few decades. At the turn of the twentieth century, wastewater treatment might have only included screening out large objects and then discharging to the nearest creek. Over the last 50 years,wastewater treatment has become much more sophisticated, including biological systems for removing organic materials, and improved filter technology and disinfection methods. These modern systems are costly to build and operate, adding to the overall cost of wastewater treatment.

Environment, Life

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