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Wastewater Creates Energy, Products – and More

Sebastien Tilmans, director of operations at the William and Cloy Codiga Resource Recovery Center at Stanford University, says wastewater should be viewed as a raw material and important resource, instead of a hazardous waste. And he tells us how it can be used to create water, energy and materials.

Written by Tara Lohan Published on Read time Approx. 6 minutes
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Historically, we’ve treated wastewater as something to be treated and dumped – a liability and not a resource. But Sebastien Tilmans may change our minds about that. Tilmans is the director of operations at the William and Cloy Codiga Resource Recovery Center at Stanford University.

The center is working to accelerate the path to commercialization of wastewater technologies. California’s drought has helped to highlight growing interest in wastewater reuse to provide water resources for drinking water and nonpotable uses such as flushing toilets and irrigation. But wastewater has other embedded resources besides water – including energy, nutrients and materials.

Some of the technologies already exist to utilize this resource, but many others are still being developed and that’s where the Resource Recovery Center comes in. It creates a space that enables researchers to plug and play with three different grades of wastewater to test different kinds of technologies. So, for example, if you want to test a new reverse osmosis process you would plug into the secondary effluent. If you want to test a new membrane bioreactor you would plug into the primary effluent.

Water Deeply recently spoke to Tilmans about how the center is providing a critical intermediate testing ground for technologies, how we can understand the value of wastewater and what the future of water recycling looks like.

Water Deeply: The most obvious resource recovered from wastewater is water; what are some of the other resources?

Sebastien Tilmans: The traditional mentality has always been that wastewater is a hazardous waste that we need to mitigate. But we view it as an ore. If you were at an iron mine you’re not getting pure iron, you’re getting iron ore and you need to take out the impurities before you have something valuable that you can sell.

And wastewater is the same – it’s got water, it’s got energy, nutrients and material. You can produce high-end materials from it; you just have to take out the impurities.

Specifically you have nitrogen and phosphorus, which are fertilizers. Production of nitrogen fertilizer actually consumes a tremendous amount of energy and produces a lot of greenhouse gas emissions globally. But in wastewater we have a free supply of nitrogen and phosphorus that we could be recovering in a safe way.

There is a process that has been developed in labs at Stanford and now is a startup company, where you can take the methane, the biogas produced from the anaerobic treatment of wastewater, and turn that into a biodegradable plastic.

What’s great about it compared to regular plastics is that at the end of its life you can recycle it or it can be sent to a landfill or anaerobic digester and turned right back into methane gas and you can make more plastic with it.

You can create these closed-loop, virtuous cycles of materials.

Water Deeply: This is actually being done commercially?

Tilmans: Yes, there is a startup company called Mango Materials that is commercializing that technology to produce bioplastic from that methane.

There is even research coming out of Europe that shows that this bioplastic can be used as a supplement in aquaculture (fish, prawns, crabs) and it boosts yields up to 20 percent. It increases the organism’s resistance to different bacterial infections. You can increase yields and reduce the amount of antibiotics that need to be used.

We’re only scratching the surface of the value that can be generated from this raw material.

Water Deeply: Energy is of course another resource?

Tilmans: Yes, and energy takes many forms. You get this biogas and then you can use that to produce electricity and heat using a conventional turbine that’s in any gas-fired power plant. But you can also purify it to pipeline-grade natural gas and put it back into PG&E’s pipelines potentially or compress it and use it as a vehicle fuel.

We also have a system for what’s called secondary treatment to remove all the dissolved organics and it yields a water that is very, very high quality. But what’s really cool is that it can achieve that while still being a net energy producer. And cutting in half or less the amount of residual solids that get produced by conventional processes.

Water Deeply: How do you do that?

Tilmans: Conventional systems use biological processes; they are typically aerobic biological processes, which means they use oxygen. The process of aerating the water consumes a lot of energy because water is a bad reservoir for oxygen. We use anaerobic processes that do not use oxygen. The bacteria that consume the organic material in the water, instead of consuming it and turning it into carbon dioxide, they turn it into methane and you can harvest that methane gas and turn it into electricity. It’s the main component of natural gas.

Water Deeply: What kinds of researchers or organizations would be able to test their technology at your facility?

Tilmans: Any group can bring in mobile units and connect to the right kind of wastewater. It could be a company like Veolia, a multinational water company. Or it could be a municipality working with a consultant who wants to test-drive a new technology in a controlled environment.

We would also work with researchers at Stanford and other places that are working with technology in the lab, which may be being tested on only a gallon or two a day and now they want to test at thousands of gallons a day to advance the technology.

Water Deeply: So your lab would create a space that would help researchers really take their technology from the small-scale test phase to the next level to see how viable it is?

Tilmans: Yes, it is a space where you have access to thousands of gallons a day to test at the intermediate scale and in a controlled environment where it won’t pose a risk to the environment or public health.

Then, once it is validated, they can next take it out of our facility and do field demonstrations.

This size of testing is also relevant for decentralized systems. San Francisco has a new ordinance that every new building [of more than 250,000 square feet/23,000 square meters] is going to need to have an alternative source of water besides the city water. They can use stormwater collected from the street but they can also recycle wastewater in the building itself.

Localized water recycling we think is going to become part of the mix for water reuse.

Water Deeply: It’s much more feasible to have water recycling at that scale than for the home. Why is that?

Tilmans: There are couple of reasons for that. One is the capital cost of building the system and the other is the operating cost of running and maintaining and monitoring the performance of this system.

We have a sensor testing station to plug in new sensors into each grade of water to test the monitoring equipment. Developing new sensors and testing them is as important as the treatment systems. We test and validate both.

Water Deeply: Do you think we will see much more wastewater reuse by municipalities or onsite systems being developed on business campuses and new buildings?

Tilmans: I think there is no shortage of municipalities across the state looking for new water supplies. Recycled water is actually one of the cheapest and most reliable new water supplies out there.

The technology absolutely exists. The real obstacles of getting [onsite reuse systems] installed today is regulatory – building inspections, codes, things like that – and of course public education. Making sure that not just the public, but regulators and building inspectors, are on board with water reuse and trust it to be safe.

Water Deeply: Ten years from now, where do you hope we’ll be in our thinking about wastewater?

Tilmans: In a place like California we are so droughtstricken we can’t afford to waste the waste anymore. Here in Silicon Valley we use the water once and it goes in the ocean. In 10 years or a little longer, I’d like to see us recycling all our wastewater. And I think we can be recycling water in an energy-neutral way.

I’d love to see our broader society view wastewater as another water supply and a raw material to be used for the highest and best use.

Top image: Michael Ruiz, of Donald C. Tillman Water Reclamation Plant, reads out the activated sludge line meter at the Los Angeles Sanitation plant where millions of gallons of wastewater are purified each day in Van Nuys, Calif. Wastewater is increasingly being recognized as a resource that can provide water, nutrients and energy. (Damian Dovarganes, Associated Press)

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