Expert Q&A with Harold Leverenz
Harold Leverenz has been modeling and pilot testing technologies and processes for sustainable water and waste management for the past 15 years. His studies have included analysis of decentralized and satellite wastewater reuse systems, development of natural treatment systems, audits of wastewater system based energy use, determination of greenhouse gas emissions, and analysis of source control systems for nutrient and energy recovery. Dr. Leverenz has a degree from Michigan State University in Biosystems Engineering and completed his doctorate in Environmental Engineering at University of California at Davis (UC Davis). He is a registered civil engineer in California and conducts research in the Department of Civil and Environmental Engineering at UC Davis. Harold gained attention this summer when he developed a process to convert urine to fertilizer and partnered with a local brewery that enabled him to collect urine from a latrine-like device called the “Pee Hive.”
Your undergraduate degree was in biosystems engineering. How did you become interested in applying that discipline toward decentralized wastewater treatment/reuse?
I was in an agricultural engineering program at Michigan State, where many of my classes were related to nutrient and fertilizer application on conventional farming systems. I was intrigued by the concept of integrated biological systems engineering, so I started taking classes in environmental engineering. In those classes, I learned a lot about water, wastewater treatment, and the amount of energy and effort we put into trying to get nutrients out of wastewater. It was an interesting paradox; in one class, I’d learn how to apply nutrients, and in another class, I’d learn how to get rid of nutrients. I decided then to focus on clearly understanding how these nutrient cycles work and how to close them. Before that, I didn’t have any ambition to go to graduate school, but it occurred to me that we had the ability to recycle nutrients from wastewater for use in agriculture, and ignoring this potential was a glaring oversight in our society. I started talking to professors and was directed to UC Davis, where George Tchobanoglous, the author of our wastewater engineering textbook, was a professor.
The topic of wastewater is massive. It took more than a Master’s degree to start answering the questions I had about the best ways to recover nutrients from wastewater and then recycle them back into agricultural systems, so I ended up staying for a PhD. After the PhD, I had some of the pieces of the puzzle but I still hadn’t totally figured it out. I stayed for a post-doc, but I still couldn’t answer all of these questions. Most of my work on the concept of using urine as a source of fertilizer has been self-funded and done on my own time. It has been a long journey, but I feel like I’m finally getting closer to some of the answers.
Were you the only graduate student in your program who was looking into nutrient recovery from wastewater?
I don’t know of anyone else who was thinking about nutrient recovery from wastewater except for my professor, George Tchobanoglous. He has been an advocate for this stuff all along, and I have learned a great deal from him.
Have researchers in other countries been looking in to this?
In 2008, when I started doing serious analysis of the nutrient content of urine and the impact of urine on wastewater, the only relevant literature was about stuff being done in Sweden and parts of Europe, where they were collecting urine and directly applying it to hayfields. Direct application is the state of most urine-based fertilizer systems now. They collect urine in underground tanks and the farmer pumps the tanks out and applies the urine directly to the field. There are problems with the direct application model, and that is why I set out to look for a different model.
Was one of those problems the amount of energy required to pump and move that urine?
Yes, and there is also the issue of how to collect large quantities of urine. A big issue is that urine contains a lot of salt, pharmaceuticals, chemicals, and hormones, and we don’t fully understand the fate and transport of these components and their impact on our food system. If we were going to look into fertilizing food crops with urine, we needed to address that.
I read that your interest in urine was piqued after you worked on a wastewater treatment project for highway rest areas. Can you tell me about that work?
In 2007, Caltrans, the California Department of Transportation, contacted me because they were having problems with their highway rest stops. As with most highway rest stops across the country, their wastewater systems consisted of a septic tank and a leach field. Many of these low-tech systems were installed in the 1960s and 70s. After 30 or 40 years, they get to the end of their life and need to be replaced.
The concept of on-site wastewater management in the 60s and 70s was one focused on disposal. If your toilet was flushing, and your wastewater wasn’t forming a pool on the ground, the system was working. Rest areas get a lot of urine input, and urine contains a lot of nitrogen. However, a septic and leach field system is not designed to remove nitrogen and a fraction of the nitrogen is typically converted into nitrate and ends up in groundwater. That was the first problem. The age of the systems was the second problem. Physical problems develop in these systems over time, such as corrosion of the concrete of the tanks and clogging of the leach field with solids.
At the same time, the state was starting to implement measures to protect groundwater in response to developing regulatory standards. There was a Caltrans rest area in a desert in El Centro, CA called the Sunbeam Rest Area, that had a failing septic system. The regional water board required Caltrans to install a wastewater system that would not discharge nitrogen above the 10 mg/liter drinking water limit. Caltrans’ engineering staff did not have specific experience designing such systems, so we collaborated to identify an on-site wastewater systems for nitrogen removal.
We had limited flow and mass data, so our first step was to collect background design data. Domestic wastewater usually includes greywater, which dilutes the nutrients that are present. However, we found very high nitrogen concentrations in the rest area wastewater. We realized that these high concentrations were due to both the large quantity of urine and the lack of greywater dilution in the system. Some Caltrans rest stops have a limited water supply, and had already been using low flush toilets and waterless urinals. We did an analysis and figured out that the system would be much more reliable and better performing if we diverted urine from the waste stream using waterless urinals.
This particular site also had an RV dump, where recreational vehicles unloaded their wastewater. Caltrans was considering an option to have that RV wastewater hauled away, but a wastewater evaporation pond was found to have a lower life cycle cost.
At the time, we didn’t know of anyone in the U.S. who had done a urine diversion system like this. We weren’t exactly sure how the system would work, or what we would do with the urine after we had collected it. Wastewater treatment plants don’t necessary want it because it has such a high nutrient load. We didn’t know how to find farmers who would take it because there are no regulations in the U.S. related to how to land apply urine. We talked to the regional water boards about the possibility of changing the regulations so that urine application to fields could fit into policy, but there wasn’t much interest. However, we had the evaporation basin for the RV wastewater, so we decided to discharge the diverted urine into that. Then we had a few management alternatives to consider. The urine could be pumped out and hauled away, used by a farmer if direct land application regulations changed, or we could just let it evaporate. So the Sunbeam Rest Area became the first urine diversion system we put in, and the first such system in a public facility in the U.S. as far as I know.
How is that system working today?
It is still running and it works pretty well. We have learned a lot of lessons.
Urine has a lot of mineral content. Minerals tend to precipitate and collect in the tank, and the crystals accumulate on urine pumping systems. So we learned lessons about the design of urine collection tanks to manage the mineral build up. We also gained a lot of experience by testing different types of waterless urinals.
You have been involved in research related to sustainable water and waste management for the past 15 years. What are some outcomes of that work that have advanced decentralized wastewater treatment/reuse?
First: the concept of urine diversion from a waste stream. It had such a positive impact at Sunbeam (it takes half the nitrogen from the water) that Caltrans now considers, if not uses, urine diversion in the design of all rest area wastewater systems.
Some nitrogen is still left in the rest stop wastewater even after the urine from men’s urinals is diverted, so I also worked with Caltrans to develop treatment wetlands for enhanced nitrogen removal. Conventional treatment wetlands are a robust technology, and especially appropriate for on-site wastewater treatment, but they are not particularly effective for removing nitrogen. I started a research project with constructed wetlands where I added wood chips and organic matter to wetland media—which is usually just gravel—to allow for the de-nitrification reactions. That technology is now called anoxic treatment wetlands for de-nitrification, and it is now used in several systems.
I also worked on a project where we measured greenhouse gas emissions from on-site wastewater systems. We came up with an estimate for on-site systems that the EPA now uses for greenhouse gas emissions inventories. Most recently I have been working on decentralized water reuse systems. Most of the water in rest areas and commercial buildings is used for toilet flushing, so I have been developing low-energy, low-O&M treatment systems to recycle water within buildings for non-potable applications.
Your recent work involves transforming urine into usable agricultural fertilizer. How did you discover a process to do that, and how does it work?
In 2012, an associate of mine, Rus Adams, had been doing some work on energy recovery from organic waste. He had a client who was interested in taking nitrogen out of digestate. Digestate is the waste stream that comes out of an anaerobic digester, after methane gas is extracted from sludge at a wastewater treatment plant. Digestate contains a lot of organic matter and a high nutrient content. That nitrogen and phosphorus gets recycled back into the influent wastewater at a wastewater treatment plant, and the nitrogen in particular has a big energy and performance impact. Rus knew I was interested in nutrients so he approached me. We did some preliminary testing to see how we could take out the nitrogen, but because the nitrogen in digestate is not in a form that can be extracted easily, the methods that worked didn’t seem economically feasible.
While we were doing that research, I encouraged Rus to think about the concept of not just taking the nitrogen out, but converting it into a product like fertilizer so that we’d actually be recycling the nutrients. We were able to do it, but it wasn’t easy and it wasn’t clear how it could be economically viable. I convinced him that instead of digestate, we should look at urine, because urine has a much higher nitrogen content. The characteristics of nitrogen in urine are different than nitrogen in digestate, so I thought that it might be easier to extract from urine. He agreed to that to humor me, I think.
You’ve got to start somewhere, so we began collecting urine in buckets. When urine sits, its chemistry changes, so we studied the chemistry of urine and how it changes over time. Every weekend, we’d take the urine we collected that week and do experiments with it. We tested all kinds of technologies and approaches for nutrient recovery. We tried vacuum stripping, air stripping, zeolite absorption, absorption through other resins, and others. Eventually we got to steam distillation, which was the most effective approach by far for removing ammonium. Then we took the waste stream and looked at different ways to take the phosphate out. There is one way of doing that which everyone agrees on: phosphate precipitation with magnesium.
Our first innovation was to put these two processes together. No one had ever done that. Then, we had to try different configurations to determine the best way to sequence these reactions. We ended up configuring the system to first break down the urea to ammonium and raise the pH, distill out the ammonium, and then add magnesium to precipitate the phosphate. That is the process we are working on now, and we think it has commercial potential for use in buildings.
We have never had any funding for this project, so we have been doing it on our own time with our own resources. It takes time to learn lessons about how chemistry works, especially when you are dealing with biology.
Can you describe the end products of this process?
One product is a solution of ammonium bicarbonate, a high purity liquid fertilizer that contains about 10% nitrogen. The other product is a phosphate mineral: the struvite precipitate, which is also a fertilizer. Then, there is the “depleted urine stream,” which doesn’t have any nitrogen or phosphorous left in it but still contains salt, pharmaceuticals, and chemicals. All three products get sterilized in the distillation process, but what to do with the depleted urine stream is a research question. It seems to me that with its high concentration of chemicals, pharmaceuticals, and salt, the depleted urine stream presents an opportunity to manage that waste appropriately. With typical domestic wastewater systems, these components are more diluted by greywater. There is a possibility that there are other things in that depleted urine stream that we can recover. We haven’t gotten to the point of developing a technology to do that yet.
As you said, you had to use your own resources for all of this research—including the collection of urine. Two men and their friends can only produce so much urine. What gave you the idea to partner with a local brewing company (Sudwerk Brewing Co.) for urine collection?
It all started with Jessica Hazard, a graduate student. Jessica’s thesis is on this concept and process, and she was worried we wouldn’t have enough urine for her to graduate. She was very motivated to figure out where we could find enough urine for our research. The civil engineering department at UC Davis often has socials at the brewery. Jessica, who is more tuned into the social scene than I am, had the idea that the brewery would be a good place to collect urine. There a lot of craft breweries out here in California, and from the brewery’s perspective, anything you can do to set you apart is positive. They saw this as an opportunity to do something that had never been done before while also contributing to our project.
The question of how to collect urine is a project in itself, and we had already been working on that for a couple of years. If not properly collected and stored, reactions can occur in urine that can cause ammonia to evaporate. We also had to address challenges such as making sure the collection system wouldn’t clog, overflow, or stink. We also had to consider aesthetics. Over that time, we learned what equipment to use and how to collect urine and maintain its quality.
The Pee Hive concept [the urine collection system designed for the brewery] was the culmination of all of our past urine collection efforts, along with the further challenge of coming up with something that could work in a public dining area. The Pee Hive is essentially a urinal in which the urine drains into a pump that pumps it into a large tank. [The Pee Hive is a six-sided, outhouse-like structure made of corrugated sheet metal. The urinal is made out of a sawed-off keg from the brewery.]
How do women urinate in the Pee Hive?
Many women simply squat over it, but I also bought silicone funnels that women can use to urinate standing up, which the brewery offers to all women who purchase a beer.
The “Pee Hive” has gotten a lot of media attention. Did you have that potential “buzz” in mind when you chose to partner with Sudwerk Brewing Co., or were you purely looking for a urine source?
It is unfortunate that I didn’t have the vision to think that partnering with the brewery would be a good business move. For me, the driving force was that we just needed a huge amount of urine! Jessica was the one who definitely recognized the potential.
Most people are so disconnected from their waste streams. What you are doing at the brewery seems to hold potential for helping to rebuild that connection.
There has been a huge amount of public support. We have done fundraising events at the brewery which have helped pay for the construction of the Pee Hive, and they have been wonderful. People are definitely interested in what we are doing.
Are there any plans to use the fertilizer made from urine collected at the brewery for crops used in the production of beer?
Barley used to be grown for beer making in northern California. [In the 1960s, barley production declined in California due to competition from higher value crops, and an industry shift to uniformity in barley varieties.] I actually brew my own beer, and I had the idea to try to grow barley in this area again. We planted some test plots and fertilized them with some of the products we were making. We had a very rigorous experimental design to grow barley with different nitrogen and phosphorous proportions. It was going well, but then my sheep ate the entire field.
We are interested in doing some kind of public art installation with Sudwerk Brewing Co. There is a group in Montreal that does public art installations using hops that they grow with urine in a hydroponic system. I’m hoping to work with them to develop an art installation where we can grow hop vines using some of the products created with urine from the brewery.
If we get some funding, the next move is to take our fertilizer products and do some greenhouse studies to compare our fertilizers to commercial fertilizers with different vegetables. I would also like to look into the possibility of getting it certified as an organic fertilizer. It is of such high purity and it doesn’t contain any of the salts, pharmaceuticals, and chemicals that biosolids would have. That is all research that needs to be done.
What other research do you (or your students) have underway related to wastewater treatment/reuse that you’re excited about?
There are a couple of things. I’m currently working with NWRI, an organization that sponsors and coordinates research related to water, on developing a regulatory framework for non-potable water systems. We have all of these different sources of water available: greywater, rain water, black water, and stormwater. What is the right framework to permit using any or all of these sources as non-potable water supply? The first step is looking at how we use it as non-potable supply for things like irrigation, laundry, and other uses. A future extension of that is how we can use it as water supply in general.
Other projects include the development of a high performance, low-energy biofilter for wastewater treatment; a rainwater system that I am evaluating as a potable water supply; and the potential to recover energy and potable water from wastewater.
If you had limitless funding and resources, what research related to decentralized wastewater/reuse would you want to tackle right away?
We really want to do technology demonstrations. We’d like to find some projects with a school, green building, or commercial building, where we could implement the nutrient recovery process in a building. We are confident this can be done and hopeful that somebody will take this on.
What are some of the most promising decentralized WWT systems being studied, tested or implemented in other parts of the world?
One is the concept of anaerobic treatment, which is treating wastewater passively without any aeration or energy input. A lot of innovation in this area seems to be happening in Vietnam and India, where they do not have reliable energy supply. They have been using anaerobic baffled reactors and anaerobic filters to do a lot of wastewater treatment with no energy input. They usually connect those systems with constructed wetlands for polishing, and we have adopted some of their research in anaerobic systems into our own research in wastewater treatment.
Another interesting thing I saw in India was local, decentralized groundwater recharged with rainwater. They are setting policies in urban areas that every building in every development needs to collect rainwater and use it to recharge groundwater.
There is an organization in Kenya called Sanergy, which has a very successful container-based sanitation system. They are collecting human waste and then trying to recover products from these waste streams. They have an extensive program going, and I’m hoping to work with them to apply the concept of nutrient extraction from the urine they’re collecting.
The Human Needs Project recently finished construction of a community center in Kibera, Nairobi that provides safe drinking water, recycled water for non-potable sanitation systems, and a number of other resources for the local community.
Does any of your research address industrial wastewater, or is it mostly related to domestic wastewater?
Yes. A good example is another project I did with Caltrans. Caltrans is responsible for putting salt on roads for de-icing. We worked on a way to collect and purify the salt from the waste stream that is generated when the salt trucks are washed, and then recycle it for de-icing.
How would you describe the state of decentralized WWT/reuse research today? How much do we really know? How much more is there to know?
A lot of robust technology has been established and is available. I think the problem with on-site, decentralized water systems is really with operation and maintenance. We put in these systems but there is not always long-term care for them, so they can end up not functioning as they should. Then what ends up happening is the regulators and public opinion is that these things don’t work.
There is also a need to change cultural norms, because people get very attached to legacy infrastructure. How do we change the perception that there is an alternative? How can we get people to change their concept of a toilet or how water can be used? I think the challenges are really social, not technical.