The end of the pipe solution means ending the pipe, says Dr. David Sedlak, but he warns newer wastewater treatment processes do present challenges
Increasing demands for water in recent years have led to a greater appreciation of the value of municipal wastewater as a source of water, resources and energy. Coinciding with this change in attitude, much of the Bay Area's wastewater infrastructure has reached the end of its useful like, while other area treatment plants are vulnerable to sea level rise. As the Bay Area readies to replace its aging and vulnerable wastewater infrastructure, these facilities will likely be replaced by state-of-the-art resource recovery facilities that will extract water, energy and fertilizer from sewage, and the effect of this new infrastructure on San Francisco Bay is uncertain. At the State of the Estuary conference last fall, Dr. David Sedlak spoke about the challenges and opportunities this new infrastructure presents.
Dr. David Sedlak began by recalling that he grew up in a town called Oyster Bay on the northern shore of Long Island. “As a child growing up, I realized that I wanted to protect, restore, and study Oyster Bay and Long Island Sound and so I went to college with that in mind,” he said. “Somewhere along the lines, I got seduced by engineering and this idea that engineers are better respected and better paid by society. And somewhere along the line, I also learned that engineers are also the ones who advise the decision makers who build the infrastructure that has the greatest impact on pollution in these systems that are so near and dear to me.”
“So today, I want to try to use some of these experiences to tell you about the three phases that our relationship to SF Bay have gone through, and the coming new phase and the way we can understand the investments in infrastructure that are likely to occur and their likely effect on the Bay itself,” he said.
Dr. Sedlak turned to the three phases they have already been through with the Bay. The first phase was the pre-development phase when there wasn’t a lot of people here. That was followed by the development phase was when there was population growth and the Bay was used to dispose of wastes, such as cannery waste, industrial waste, and sewage – a legacy we are still dealing with today, he noted. During the third phase, the Clean Water Act phase, society woke up to the problems of dissolved oxygen depletion, nutrients, and contaminants going into the Bay, and major investments in wastewater treatment infrastructure were made.
“The events of the last decade have shown me that we’re about to enter a fourth phase, and that fourth phase is going to involve major investments in infrastructure and lead to a fundamental change in the way we interact with the Bay,” he said. “There are unresolved questions, and there are issues for people who are interested in studying, understanding, and protecting the Bay that they have to be aware of that come from this world of engineering that I’m now part of.”
Dr. Sedlak pointed out that the word ‘wastewater’ is made up of two words: waste and water. “One of the first things we teach young engineers when they go to college is that waste is a really interesting concept,” he said. “To a chemical engineer, the difference between waste and profit is being able to sell all the stuff that comes out of a manufacturing process to someone to use in the next phase of their process, and what that material doesn’t have enough economic value, it becomes waste and it affects the economics of your whole system.”
“The reason that things become waste is because no one has a good use for it, the uses that there are don’t command enough money to make it worthwhile to do, or there hasn’t been an external event that causes you to rethink your treatment process to improve the quality of the material that’s coming out of your process such that someone would want to use it,” he continued. “As society develops and we think more about sustainability and pollution control, and we have more competition for resources on the planet, the idea of waste is going to apply to fewer and fewer things that we deal with.”
The second part of wastewater is water, and it’s kind of a funny word, he said. “The stuff that comes out of sewage treatment plants is 99.99% water; it has trace amounts of other things in it,” he said. “We have technologies that can turn that into valuable water. In some places such as Singapore, the stuff that comes out of the sewage treatment plant gets treated so much that it’s used in semiconductor manufacturing and in the manufacturing of pharmaceuticals, so this stuff that comes out of our wastewater treatment plants is primarily water and we have the means of removing those contaminants; we just have to set our minds to it.”
Dr. Sedlak said with that in mind, he would talk about three lessons from the last decade and the way in which he thinks they’ll apply to San Francisco Bay:
Lesson #1: Don’t waste water. “Well that’s obvious to everyone here,” he said, presenting a picture of dry Folsom reservoir. “This feeds into this idea of waste. This water is becoming more and more valuable, and in this current drought, no matter how bad El Nino is this year, this is coming back again because the predictions that we have from climate change models of the effects on our snowpack, the predictions are of long-term droughts being more common than we ever thought.”
“This water is going to become more and more valuable and Northern California has to take lessons from Southern California where they’ve been aware of the value of water and the insecurity of their imported water supply for at least two decades longer than we’ve been thinking about it, so that’s the first lesson – we’re not going to waste water in the future.”
Lesson #2: Don’t waste energy. “California is getting serious about solving the greenhouse gas problem,” Dr. Sedlak said. “There are a lots of places that society is going to have to change in response to climate change and reducing greenhouse gas emissions. In terms of the stuff that comes out of those things we used to call wastewater treatment plants, we’re going to look to make those more energy efficient in the future … The operators of those treatment plants are going to look towards the organic matter that’s in the wastewater and turn it into energy.”
“This figure shows that our current aerobic wastewater treatment plants use about a half a kilowatt hour per cubic meter to treat water, but if we go to anaerobic treatment processes and using the nitrogen in the wastewater for energy and producing biogases, we can make those actually energy positive,” he said. “We’re going to see a lot more pressure to do that kind of thing.”
Lesson 3. Don’t waste an opportunity. The Sunnyvale Wastewater Treatment Plant and the San Francisco Water Treatment Plant demonstrate two different problems. “The first is that our treatment plants are obsolete,” he said. “The Sunnyvale treatment plant is a mechanical treatment plant with an algal pond system and it is clearly obsolete. It was built a long time ago and if we want to meet the new standards we’ve come to expect, we have to just knock it down and replace it with something else. We have an opportunity to not build the things that we know don’t work so well. We have the opportunity to implement new technologies that are going to help us realize our goals of this new type of water relationship that we’re going to have with the Bay.”
The San Francisco Wastewater Treatment Plant is an example of wastewater infrastructure in the front lines of sea level rise and flooding, he pointed out. “We’re going to have to march our wastewater infrastructure away from the Bay and in the process, there’s going to be an opportunity to build something different,” he said.
Dr. Sedlak then took those lessons and spoke about how they apply to the San Francisco Bay.
He presented a map showing where wastewater goes into the Bay, noting that he didn’t think anywhere near the same volume of water will flow into the Bay in 30 years. Some of it is being reused right now in purple pipe for landscape irrigation. “That process just takes the water out of the bay and all the contaminants and salts out of the bay too, so if someone in Dublin San Ramon has a purple pipe project and they do landscape irrigation, that is water that used to go into the bay that doesn’t go there anymore. When we look at the EBDA pipeline, we can see decreases in the flows in the summertime because more and more of that water is being recycled.”
But the purple pipe approach is not going to keep growing in the future. “All signs are that we’re going to value that wastewater to such degree that we’re going to use it for potable water reuse, and when you do potable water reuse, you use reverse osmosis membranes that produce a brine concentrate,” he said. “They take everything out of the water – the salts, those emerging contaminants you’ve heard about, the nutrients that people are starting to worry about; then you have this concentrate that has to be disposed of in some way. The logical place to put that is back into the bay, and so now we might be actually reducing the dilution water that would lower the concentrations of contaminants.”
He then presented a map of the lower South Bay below Dumbarton Bridge, noting that this part of the Bay is particularly susceptible to the effects of contaminants because there is very little dilution. He noted said the three cities that discharge their wastewater to the area south of the Dumbarton Bridge. Recently the Silicon Valley Advanced Water Purification Plant was completed. “They want to use the water from the San Jose treatment plant as a drinking water supply, and when they are done with it, they want to put the concentrate back in the Bay, so that is an issue that we need to think about and anticipate.”
“Let me just give you one example of what this could mean,” he said, presenting a slide showing copper and nickel present in effluent versus concentrate. “Remember how copper and nickel in the South Bay was an issue at these meetings until we made a site specific criteria? The dark colored bars are the concentrations of copper and nickel going into the bay from the south bay treatment plants now, and compares them to the site specific water quality objective that we have for saltwater discharges. If those cities succeed in water recycling in recycling 80% of the water that’s now wastewater, that’s what’s going to happen to their concentrations? The same mass loading of metals will occur, but the concentrations will be higher. Is this an issue? Do we need to deal with this? Do we need to force those cities to build a pipe to go north of the bridge and dilute the water? Because if we do that, that project might not happen at all, so we need to think about what numbers make sense.”
“The same applies to everything else in the wastewater,” he continued. “The nutrients are going to be concentrated, the steroid hormones are going to be concentrated, contaminants are going to be concentrated – we haven’t resolved that issue yet.”
With respect to the energy issue, Oakland’s East Bay MUD has done a remarkable job converting their treatment plant so it’s energy positive, Dr. Sedlak said. “They use their excess anaerobic digester capacity to turn organic matter into biogas, methane essentially, and they can use this to generate electricity. The chart shows you the percentage of East Bay MUDs electricity that they’ve been able to generate through this program in the last ten years. One of the tricks to doing this is to invite people to bring their waste to East Bay MUD to put in the digesters, and when they do that, they are inviting chicken blood and winery waste and waste from the food industry into their digesters and that’s often very proteinaseous in nature which means it has a lot of nitrogen, and so over time you see the nutrient levels in the effluent creeping up. So if everyone starts treating their wastewater treatment plants to maximize the energy recovery by bringing in materials, we might see an increase in nutrient concentrations.”
“Alternatively, we might start applying some of the newest developments in wastewater treatments to make full scale, full anaerobic wastewater treatment plants,” he said. “They are able to treat wastewater without bubbling air into it like we currently do today and to produce energy. That raises some interesting questions as we rebuild our wastewater infrastructure, if we want to do this to maximize energy, how do these new treatment plants perform with respect to removing the contaminants that we’re worried about?”
About a year ago, the concentrations of pharmaceuticals were studied in a pilot scale anaerobic treatment plant, he said. “What we saw in all cases is that SAFMBR plant achieved much better removals of contaminants that the conventional activated sludge plant that was running side by side, so there might be an added benefit of these new kinds of treatment plants in terms of removing the contaminants of emerging concern that we’re interested in studying now.”
“Remember when we used to say the end of the pipe solution and we meant that we put all of our waste out of the pipe and that was the solution?,” he said. “Well, now the end of the pipe solution means ending the pipe. That is, in the future, when we think about sea level rise and its effect on our infrastructure, we may just want to get rid of those discharge pipes completely.”
He presented a map from EBDA that looked at what the discharges to the Bay look like today versus predevelopment times. “The idea here is that we might be able to use this opportunity of rebuilding our wastewater treatment plants to use this water as part of our restoration efforts, instead of discharging to the center of the bay and hoping dilution takes care of all our contaminants.”
He then presented a slide of the Oro Loma project, which is a horizontal levee project. “This is the idea of building a horizontal levee or a living levee in front of the existing flood control levees, bringing in bay sediments and then keeping those wetlands alive by running municipal wastewater effluent through the subsurface. In the process, you protect the levees from storm surges, you create terrestrial habitat, you polish the wastewater effluent, and you remove any residual contaminants,” he said. “This approach could also be applied to treating that concentrate that’s likely to come flowing out of the south bay treatment plants and any other kinds of materials we’re going to put in the bay, because we’re not worried about the salt concentration; we’re worried about all those other contaminants that are there. The Oro Loma project is getting ready to be built and we’re really looking forward to learning about these systems and helping them to actually work for us to remove contaminants and be part of this vision of a new kind of margin of the bay.”
Dr. Sedlak then shared his final thoughts. “I only had a few minutes to talk about this but I hope I got you thinking about how the infrastructure could be really important to the way the Bay is managed in this new era,” he said. “First of all, the era of wastewater is ending. We’re not going to call them wastewater treatment plants because they are not. They are really resource recovery facilities, and the resource that we’re most interested in recovering is water. Water reuse is the future in the bay area because our imported water supply is in jeopardy due to climate change.”
“Energy and resource recovery, even though it’s not a huge amount of energy, the way the institutions are set up, they are going to go after that biogas and they are going to make it, and that’s going to be a motivation for them to bring more material in and perhaps to explore new types of treatment processes that might either improve or diminish the quality of water going into San Francisco Bay,” he said.
“There’s this need to rebuild our obsolete treatment plants and relocate them due to the effects of sea level rise, and it would be a tragedy if we built what our grandparents built when we replace them,” he said. “There are so many improvements in technology and we know so much more about the problems we’re going to face, I hope our shovel ready solutions are not just dusting off the plans from 40 years ago.”
“So we need to anticipate the effects of these investments in infrastructure on the bay,” said Dr. Sedlak. “Will concentrate replace wastewater effluent? It’s a yin-yang good thing bad thing, the bad thing is maybe the concentrations go up; the good thing is the volume is smaller, so we have opportunities to treat it.”
“Will energy recovery affect water quality? Maybe the ammonia levels go up, maybe the trace organics go down, or maybe we have unexpected things that we haven’t been focusing on yet because we don’t have a lot of experience with anaerobic wastewater treatment? I think the overarching question that we need to pay attention to is, can our next generation of infrastructure benefit San Francisco Bay? I sure hope so.”
“Thank you very much for your attention.”
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