— The journey begins when the toilet flushes. Whatever is in the bowl heads through a series of pipes and treatments that separate the solids from the water. While the travels of one's wastewater is seldom a topic of conversation, it affects virtually every San Diegan, and everyone's wastewater shares the same destiny.

Jesse Pagliaro has worked for the San Diego Metropolitan Waste Water Department for 13 years, with an additional 10 years' experience at other facilities in California and Illinois. As assistant deputy director for the Operations and Maintenance Division, Pagliaro is in charge of personnel and manages facilities that include wastewater treatment plants, water reclamation plants, pumping stations, and biosolids dewatering facilities -- the final stage in sewage treatment. "I'm a long-term wastewater treatment plant operator who's been involved with various levels of how plants are operated and maintained."

Pagliaro's laconic description of the process reinforces his air of experience. "Essentially, what leaves your home raw as sewage -- or wastewater, as the term has been renamed in the last 20 years -- comes out of your home line and goes into a 'trunk' line that may be behind your home or in the street. From the trunk, it discharges through to a main, which delivers it to the interceptors, which are larger conveyance pipes, which deliver it to a pump station. Because of the terrain of San Diego, along the way there are various pumping stations, depending on where the wastewater has to go. It's not all gravity, although it's gravity coming out of your home and gravity going down the road from you to a lift [pump] station, but at a certain point, you're going to have a lift station that pumps it up another line into a fourth force main, and it discharges by gravity until it comes into these larger mains and interceptors. From there it gets pumped from the smaller lift stations to the larger lift stations to the treatment plant." This treatment involves all the water -- from the boundaries of Del Mar to the north, Alpine to the east, and south as far as the international border. "The entire service area is 450 square miles. Within the city we are servicing approximately 3000 miles of collection system."

The collection or removal system at pump stations is another intermediate step for the water on its way to the treatment facility. "Typically, we find things at our treatment facilities and pumping stations like money, toys, occasionally jewelry. One day I found 120 dollars in the removal system."

While the thought of sundry items flowing through the water might inspire lurid images of criminal evidence afloat, Pagliaro insists that is not the case. "I once heard about a baby coming out in the screening structure of a pump station. When that happens, there are phone calls made to appropriate support in the community -- the fire department, police. There's a whole series of follow-ups that they would go through. I don't know what stage it was at or any other information." Pagliaro explains that such a horrid event is an anomaly; disposing of bodies through the sewage system is impractical. "You have to think about where you're talking about disposing. If you're talking about going through your home, what is a commode capable of transporting or discharging? It would likely be a miscarriage or something of that nature. You would have to make a serious, concerted effort to find a sanitary sewer of good enough size to transport anything of significant size. It's rare. I've heard about this one instance in my entire 23-year career."

Any items found for removal come up on a bar screen. "One of the first processes for the waste stream is preliminary treatment. That's where the waste stream comes into the plant through several channels that have racks. The rack is several bars placed closely together in rows, with an auto-raker on it. It will catch coarse debris, like sticks, rags, plastic. Then there's the occasion where you'll find money or jewelry in there. There's a myriad of things that are going to come through. It's amazing. For the most part, it's removed prior to the real treatment process, discharged into large hauling bins, and, from there, hauled to the landfill. The water is rinsed and pressed out of any materials." The collection process is fully automated. "Occasionally people will walk by the bins where stuff has accumulated, or the collections folks will have to clean out a structure, but that's it. Nobody sits there and watches it. It would be a poor waste of the employees' time to just have them sit and watch!"

The men and women who work in the collection-and-treatment systems wear protective clothing whenever exposed to the waste stream. This includes coveralls, rubber gloves, face shields, and hard hats. Personnel who are exposed to the waste stream serve a variety of functions. "There are many different jobs -- anything from plant-maintenance technicians, engineers, and electricians, to plant operators."

There are currently three operational facilities for treatment in San Diego: Point Loma, the oldest and largest plant; North City in Miramar; and San Pasqual Water Reclamation Plant. A fourth, South Bay, is scheduled to open in October, although construction problems could delay it. "Point Loma went online in 1963 and has undergone several million dollars' worth of upgrades over the past ten years or so. It treats about 180 million gallons per day on the average. It's rated at a max of 240 million gallons per day. The North City plant has been operating since April of 1997. That's a reclamation facility, so it treats the waste stream to a level where it can be used for irrigation purposes."

Pagliaro makes it clear that the reclamation treatment at the North City plant is not the same as "gray water." "Gray water has significantly less treatment. Gray water is essentially water that comes out of your laundry and not the bathroom facilities of your home. It's not contaminated with human waste. The level of treatment provided by the North City facility makes it better than the water that comes straight out of the Colorado River. There's treatment facilities all up and down the Colorado River that treat the secondary standards, then discharge into the river. That's why we have water-treatment facilities in San Diego, because they pull raw water from the river and from the aqueduct to the north, and they treat it, and remove any of the solids inherent in the raw water -- a different function altogether." The South Bay plant will also serve as a reclamation facility.

The treatment process is labyrinthine; it ends in a simulation of animal digestion. "As a result of the treatment process, you remove solids that are discharged, whether human waste or any other materials. The water is a conveyance system to remove the waste from your household, and this water used for transport is essentially 99.9 percent water and only .1 of 1 percent solids. So the amount of solids that people in the community have in their water is really minuscule. Next to nothing. In order to meet the treatment needs at the reclamation plants, there is nothing left in the water, and if it ends up at Point Loma, we remove anywhere from 83 to 95 percent of the particulates. The suspended particulates form a mass called 'sludge' or 'raw sludge.' The facilities, Point Loma in particular, take the raw sludge and they pump it through anaerobic digesters. Anaerobic digesters digest the organic materials in the raw sludge that we call 'volatile matter.' Raw sludge is typically 75 to 80 percent volatiles. There's bacteria or 'anaerobes' in those digesters that utilize the solids as a food source and also for respiration. There's a large amount of sulfates and sulfites carrying the sulfates, carrying particulates; they break those down and remove the oxygen and release the sulfite.

"The first stage is called acid formation. All digesters carry two types of bacteria: acid-forming bacteria and methane-forming bacteria. The first order of business, when you feed it with a slug of raw sludge, is that those bacteria that are acid-formers will break that material down and essentially form acids that are similar to vinegar. The methane-formers will utilize those acids and break that material down to release CH4 [methane gas]. The end result is reduced solids. You have water with fixed solids left, with a little bit of organic solids left, but mostly broken-down material or 'bio-solids' and methane in the water."

After going through the treatment plant, any water containing solids is pumped back to Miramar's Metro Biosolids Center, or MBC, near the Miramar Landfill. "Those solids are dewatered, then hauled to landfill. Very soon we'll be going to land application as well, and the land application will serve as a supplement for nitrogen, phosphates -- that type of thing, but mostly nitrates. The product is fairly rich in nitrates."

Little of the product is wasted; even the treatment process is used to generate energy. It might be more appropriate to label our waste as "fuel."

"Those digesters -- and they're fairly large units -- produce a mixture of methane and CO2 [carbon dioxide] that's a natural part of the digestion process. We operate the digesters at 98.6 degrees to about 99 degrees Fahrenheit. Essentially, what we're trying to do is extend the digestion process that begins in the human body. We want to reduce these solids to next to nothing. One of the side-products, digester gas -- a combination of 65 to 67 percent methane with CO2 and some trace gasses -- is being used at Point Loma to produce electricity. We use the digestive gas to operate two large engine generators that produce electricity on the order of 2.258 megawatts per unit.

"It's essentially potential energy that we're talking about. Point Loma puts out about 4.56 megawatts of electricity and only uses about 2 megawatts of that power at the facility. The remaining two and a half megawatts are sold back to the utility. So the community is being provided additional service by the production of electricity. Besides the 2.258 megawatts provided by the methane, there's a small hydroelectric facility because of the location of the discharge. It has to go through a drop-structure and spins a turbine. That produces another megawatt to 1.35 megawatts. When you total it all up, a lot of the time we're pushing as much as 3.85 additional megawatts of electricity from Point Loma -- enough to operate approximately 3800 homes. There's also a cogeneration facility at MBC, but they're using a combination of digester gas and landfill gas. They use a small portion and the rest is marketed to the public utility. But that generation facility is owned and operated by a private firm. North City also has a cogeneration facility next to the plant. So we use the waste in a digestion process, which produces electricity. It's not just a waste stream, as many would think; it's also a source of energy."

Share / Tools

  • Facebook
  • Twitter
  • Google+
  • AddThis
  • Email

More from SDReader


Log in to comment

Skip Ad