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Welcome to The Executive Exchange, a premier podcast series for on-the-go senior executives. Each episode features short, impactful podcasts where industry leaders share key insights and experiences from the water industry.
[00:00:00] Piers Clark: Welcome to the Exec Exchange, 15 minute podcast, in which a leader from the water sector shares a story to inspire, educate, and inform other water sector leaders from around the globe.
[00:00:09] Piers Clark: My name is Piers Clark and my guest today is Rob Thompson, General Manager at OC San in California. Now we've heard from Rob twice. Once about a year ago, and last time a few weeks ago. A year ago he was talking about asset management, and a few weeks ago he was talking about their incredible groundwater replenishment system.
[00:00:30] Piers Clark: Today we're going to be talking about biosolids. Rob, brilliant to have you join us again. Thank you. You are the first person to be on the Exec Exchange podcast three times.
[00:00:41] Rob Thompson: I'm honored. Thank you.
[00:00:42] Piers Clark: Well, of course the flip side of being on the Exec Exchange three times is it means that I have to find a different opening question for you. So we've done your background. For those who don't know, Rob has spent 30 years in OC San working up from the lower ranks to becoming general manager.
[00:00:58] Piers Clark: And last time we talked about his management style and what he'd learned from that. He's quite a detailed man. This is what happens when you have a technical person making it through to the top of the organization.
[00:01:10] Piers Clark: I wanna go a bit personal on this question this time, and I wanna ask you about your home life work balance, because being general manager of a utility is a tough job.
[00:01:19] Piers Clark: You are constantly on call. How do you balance your home life?
[00:01:24] Rob Thompson: I am 24/7, 365, OC San. It really is a big part of my life. It wasn't always that way, obviously. It's just my wife and I now, my kids are up and grown. A lot of what we used to do on vacations, we'd be driving along looking at infrastructure, whether it's power lines or aqueducts or pipeline systems, and I'd be explaining to my kids, and I'm happy to say, they bought into it. They appreciate their geeky dad, my oldest daughter's in fact, a civil engineer working for an electrical utility here in the area, and she went back and got her electrical PE just like her dad. So we're both double PEs civil and electrical. I don't separate them very well but I hope it's not too burdensome for my wife to drive down and look at construction projects in the service area.
[00:02:15] Rob Thompson: We live here and I think it's an important ethic for people to understand. It's part of being a part of a community. Taking care of the community is important.
[00:02:24] Piers Clark: And for those people who dunno what a PE is, a PE is a Professional Engineer, which, in other parts of the world is often called a chartership. So you are both chartered, Civil and Electrical Professional Engineer. Brilliant, Rob.
[00:02:36] Piers Clark: Now the topic we're going to go into today is biosolids, and I'd like to start with you actually painting me a picture of the biosolids management challenges that you've got in Southern California, before we get into the actual technology that you are using.
[00:02:51] Piers Clark: So can you just set that tone for me?
[00:02:54] Rob Thompson: Biosolids for agricultural reuse is really the bulk of where all of our biosolids are used here at OC San. We ship some of them to Arizona, which is an eight hour round trip truck drive. And the other parts go to the Central Valley of California, big agricultural areas there where they're composted and then reused.
[00:03:15] Rob Thompson: Like everyone else, I think we're under pressure. People are worried about PFAS. People are worried about microplastics. I will tell you in California, methane is also under a little bit of attack. So we've used digesters to stabilize, part of that is to make methane and burn it in a power plant.
[00:03:33] Rob Thompson: So even that reuse idea is under strained. People want that green powerful greenhouse gas limited. I'm not sure what will be the nail in the coffin for our current system, but I believe as you look out into the distance, our current systems, one way or another will be limited by regulation.
[00:03:54] Piers Clark: And that is a universal problem that people are seeing around the world with microplastics and PFAS and the yuck factor to do with sewage sludges being spread on land. There is of course, a very strong argument that is the best and most environmental thing to do with it, but it's a battle that you are fighting with the public and if you are trucking your sludge four hours each way to get it to spread that economically, it's probably no longer making much sense.
[00:04:19] Rob Thompson: Especially when you're talking electric trucks.
[00:04:22] Piers Clark: Yeah. They probably have to stop and charge halfway along the way.
[00:04:25] Rob Thompson: Yes. At least halfway.
[00:04:28] Piers Clark: Now, we first met about 20 years ago because I was chairing a TAG meeting, a Technology Approval Group meeting, which is where we were showcasing new types of technology. And there was one of the technologies at that meeting called Supercritical Water Oxidation from a Swedish company called AquaCritox.
[00:04:45] Piers Clark: I seem to recall presenting it saying, well, here's a new technology. It's very early stage and it's probably the sort of thing that in 30 years time will be being used on the manned mission to Mars.
[00:04:56] Piers Clark: And the reason I wanted us to talk about this today is because this is something that OC San is doing. That gem of an idea that we talked about 20 years ago is now something that you are looking at and building the world's largest full scale installation.
[00:05:11] Rob Thompson: So my familiarity with it actually started a little earlier when I was at Parsons the engineering company doing oil work. A different facet of their company did chemical weapons disposal. And they use this same technology to get rid of everything from nerve gas to mustard gas because it does truly destroy about anything it touches.
[00:05:34] Rob Thompson: The idea of Supercritical Water Oxidation is that you use the fourth state of water which is this super critical phase.
[00:05:43] Rob Thompson: If you pressurize water and heat it, you enter this end phase where you can pass the phase lines and not have the penalty like you would in drawing sludge. To drive off water you have that latent heat effusion, huge thousand times penalty in energy to dry the stuff so then you can burn it.
[00:06:03] Rob Thompson: The idea here is that you flip water's properties on their head. It's super critical and suddenly oil and water mix. Another of those lies you were told. Oil and water don't mix. They do, just at super critical temperatures and pressures.
[00:06:19] Piers Clark: Let's pin down those numbers there. So super critical temperatures and pressures.
[00:06:23] Piers Clark: What are those temperatures and pressures?
[00:06:25] Rob Thompson: At 374 degrees centigrade and 221 bars, or 3,200 PSI, that's where you pass that super critical threshold. Anything hotter or more pressurized than that and you're gonna enter that phase.
[00:06:41] Rob Thompson: When you do that, you can mix your biosolids or raw sludge and completely in one step oxidize those materials so you end up not with complex sludge compounds. You get very simple carbon dioxide, water, calcium fluoride, and nitrogen.
[00:07:01] Rob Thompson: Any other metals that were in there will form salts. So if you're thinking of your periodic table, anything on the left side's gonna make a salt with something on the right side. They all tend to be super benign. That's where source control continues to come into it. Make sure you don't have heavy metals or toxins in your sludge, but whatever you get, there will be no viruses, no bacteria, just good clean salts. Good clean water.
[00:07:29] Piers Clark: I just wanna make sure, because I wanna bring the audience with us on this journey. So you'd start with a nasty, smelly, biosolids, organic material with humus inside it. It's black, it's nasty.
[00:07:39] Piers Clark: You put it through a supercrit reactor. And what comes out will be water that if you let it settle then the inorganic fraction, these salts and minerals drop out and you've then got crystal clear water. This is why people talk about it as being potentially the technology that will be used on the manned mission to Mars.
[00:07:58] Piers Clark: Now of course the challenge here is there'll be a lot of people listening going, yeah, but Rob, how do I get to those temperatures and pressures that's going to cost me huge amounts of energy and machinery building the process plant to be able to get to those temperatures and treat huge volumes of sludge is prohibitive.
[00:08:16] Rob Thompson: That's where this company that we're tied up with 374Water comes in. In the past they would take their sludge and they would pressurize it and then heat it and then mix it with oxygen. And that caused some issues because the sludge turned into a gummy mess. When the properties flipped, you would end up coating all your heat exchangers with calcium and whatever other salts were there because water's no longer the universal solvent, and it just became problematic.
[00:08:44] Rob Thompson: The thing that makes 374 different is they flipped it on its head and said, "Hey, how about if we just mix superheated air with pressurized sludge and instantly take that sludge to super critical pressure and temperature", especially the temperature piece, and then suddenly you're in business. Their machine looks like one air compressor, if you go to Home Depot or some local hardware store, you can get a pressure washer to pump water at that pressure no problem.
[00:09:13] Rob Thompson: The heat exchanger is a very complex structure in our environment called pipe. You may be familiar with the term of pipe. I'm being sarcastic again, it's simple piece of pipe.
[00:09:24] Rob Thompson: One air compressor, one sludge pump. We have the same sludge pumps that pump our biosolids to our trucking plant.
[00:09:31] Rob Thompson: So no crazy new equipment.
[00:09:34] Piers Clark: No moving parts inside. It's just about getting the right temperature and pressure and keep it at a residence time and get it through the reactor.
[00:09:40] Rob Thompson: And the reactor is a piece of pipe and the heat exchangers are pipes inside of pipes. So it's really easy to construct. Very simple to operate.
[00:09:49] Piers Clark: Now I do wanna spend a few seconds just talking about the company 374 Water because it's actually been backed by the Gates Foundation and it's come from a US university.
[00:09:59] Rob Thompson: Duke did a lot of research with Bill and Melinda Gates, that's where they got started. 374 kind of spun out of there and they are now a publicly traded company.
[00:10:09] Rob Thompson: We are the first six ton per day unit. The unit has been in Orlando, Florida for about really a year, perfecting it, trying some new orientations and new software and how they do the mixing and how they do the heat exchanging.
[00:10:24] Rob Thompson: I think they've really started to nail it. We expect to see that delivered here and operating very, very soon.
[00:10:31] Piers Clark: I love the idea that it's a bit like the story you told a few weeks ago with the groundwater replenishment system. You were very fast on following the city of Los Angeles with what they'd been doing. Learning from there, standing on the shoulders of giants, which is of course what you have to do in the utility sector. You've gotta see what other people are doing and work out what your step can be.
[00:10:50] Piers Clark: Now, when are you hoping the plant will be turned on ?
[00:10:53] Rob Thompson: We're hoping that it will start here in January. We should have received it in December.
[00:10:59] Piers Clark: And it's worth noting that we are recording this in Q4 of 2025. So hopefully we'll be able to have an update.
[00:11:08] Piers Clark: Now, I'd like to cover deep well injection because you are not just being innovative around your PFAS and microplastic strategy with supercritical, you've got another string to your bow. So, tell me about the deep well injection.
[00:11:20] Rob Thompson: We always believe for something as critical as a main process like biosolids or sludge treatment, you have to have more than one option. So we are looking into deep well injection. It's something we actually studied with the city of Los Angeles back in 2008.
[00:11:36] Rob Thompson: For those of you that heard the prior podcast, we were also launching the groundwater replenishment system for water reuse in 2008. So we had a bit of a marketing problem where we were gonna tell people, trust us, we're gonna put your drinking water in the ground over here, and we're gonna put your biosolid sludge in the ground over there. Trust us, this will all work out. So we decided not to go forward at the time because of that education and making sure we had a clear message.
[00:12:07] Rob Thompson: City of LA on the other hand, did go forward with deep well injection at their Terminal Island Treatment Plant. They inject biosolids directly into an expired oil field that hasn't been in production for a while, the Wilmington Oil Field, about 5,000 feet deep, and a nice layer of sandstone between layers of shale. They directionally drill down and across, inject their biosolids into that layer and it's stuck there for a millennium. The ground will act like a digester. It's about 130 degrees Fahrenheit, so the solids down there will digest over time. So you'll turn into an air bubble, which is methane carbon dioxide.
[00:12:48] Rob Thompson: Part of the advantage and the reason we're looking at both supercritical water oxidation and deep well is the mixture of carbon sequestration and energy production. We didn't talk about it but SCWO, supercritical water oxidation can also long term be an energy source 'cause you're gonna have lots of extra heat from all of those burned or combusted biosolids. But you're gonna release all that CO2 basically in the atmosphere.
[00:13:14] Rob Thompson: By sequestering carbon deep underground, we can get to carbon neutral. My back of the napkin calculation was something like 250,000 tons of carbon dioxide if we put all of our solids in the ground.
[00:13:27] Rob Thompson: Big positive impact taking all those trucks off the road again. And if we find a critical flaw with either technology, we still haven't put all eggs in one basket. We have either ground injection or we have super critical destruction.
[00:13:45] Piers Clark: It is absolutely brilliant, Rob. And you know what? I know you say it's carbon neutral. I actually think it's probably gonna be carbon negative, which is something I can probably say, but you can't confirm because you'll get into all sorts of trouble. But it's going to be carbon negative, especially when we think about the fact that a lot of the organics that's arriving at your works isn't coming from fossil fuel sources, it's coming from the food chain. You are then locking up the carbon that's come from a rapid recycling loop in the carbon cycle.
[00:14:13] Piers Clark: Very exciting. Unfortunately we're running outta time. The last time you were here, I asked you a couple of cheeky questions at the end, and I'm gonna ask you a couple of new ones now. So I'd like to start with when you were a young boy, what did you want to be?
[00:14:31] Rob Thompson: I wanted to be an engineer. My grandfather on my mom's side was a machinist, and I watched all my uncles working old machining products. My dad was a hot rodder, so I grew up looking at engines and motors and machine parts and boats and wanted to know how everything worked, and engineers were the way to figure that out.
[00:14:53] Piers Clark: You are just having the time of your life, aren't you living the dream. My last question, when did you last cry and why?
[00:15:01] Rob Thompson: The last time I cried was at my daughter's wedding. My youngest daughter was getting married, walking her down the aisle. I must confess to being a bit misty-eyed giving my daughter away to a fine young man, but still my little girl was stepping away. So that was probably the last time I cried.
[00:15:20] Piers Clark: You have been listening to the Exec Exchange with me, Piers Clark, and my guest today has been Rob Thompson, General Manager at OC SAN in Southern California, and we've been talking about their biosolid strategy in particular, deep well injection and supercritical water oxidation.
[00:15:38] Piers Clark: Hope you can join us next time. Thank you.