SHORT #9: A City, Powered by Poop

Could cities be powered by human waste? In Japan, one city is trying.

This week’s text and illustration work is based on a visit some years ago to a wastewater treatment facility in Kobe, Japan. There are two parts. First a story, and second, a kind of detailed geek-out about how that story relates to the real world. Hopefully you’ll enjoy both.

It is 2032, and a poo-powered city bus glides to a stop at Motomachi. A young woman steps off. Her feet land on a street made of recycled poop bricks. Every several paces, a different tree grows skyward, some of them several stories high. All of the trees are watered with reclaimed water which—like the bus fuel and the street bricks—are products of the city’s wastewater treatment plant.

The woman is meeting a friend for lunch, at the kind of restaurant that we might call a “local farm-to-table” joint. In Motomachi however, local food restaurants are so common, they don’t use the term ‘farm-to-table’ anymore. They just call it a restaurant.

The food at this particular restaurant is grown with the help of a special local fertilizer from, yes, the city’s watewater treatment plant. The woman and her male friend sit down at a table near the kitchen, asking the chef for two of the day’s menu, “Sausage Rice Bowl.” The man asks for his to be well done, and as he looks up, the eyes of the chef lock intensely with his. The chef thrusts her hand around his sausage and drops it into the pan. Then, she winks, and shouts. “You like flames?”

A bit startled, the man friend answers awkwardly. “Uh. Yeah. Love flames.”

“Great!” the chef answers. She smiles, turns up the gas range, dashes some wine onto the sausage. Do you know the sound of a big sausage doused in wine catching fire? Well, that is the sound. But the unexpected part is not the sausage handling, or the flames, but the source of the flames. Although, I suppose by now, you can guess what that source is. Yes, the chef is cooking with poop gas, or to be more accurate, a reclaimed natural gas captured from wastewater.

The setting of this all is Kobe, Japan, a coastal city that, in the process of treating wastewater, finds ways to use nearly all of the byproducts of that treatment process productively. As sewerage is processed through the city’s anaerobic digesters, gas is produced that runs directly to a city bus fueling station. A portion of that gas is further refined and pumped directly into the city’s municipal gas supply.

One could say then, that poop literally heats the homes and fires the gas ranges in the city. Several other byproducts extracted from the city’s wastewater include organic compounds like phosphorus, used as fertilizers for local farms, and other solid material used in the production of experimental sidewalk bricks.

The final twist? None of this technology is from the future. All of these processes are in fact taking place right now, at the Higashinada Waste Water Treatment Plant in Kobe, Japan.

Now, if you are ready to get a bit geeky, read on.

Why it Matters

Most cities with modern wastewater treatment facilities do some or all of what the above story suggests. While a water treatment plant is one example of capturing and using methane as Biogas or Renweable Natural Gas (RNG), it is certainly not the only source of this gas. Methane is created naturally in decomposing organic material at landfills, in compost piles, at dairy farms, and in other livestock and agriculture operations.

If all of these possible sources of RNG were able to be captured and used, the United States could likely fulfil much of our current residential natural gas requirements without resorting to fracking, all while simultaneously reducing greenhouse gas emissions. But we’d also have to change how we use that gas, shifting from a focus on generating electricity, to more direct uses.

How the Heck is Burning Gas a Good Thing?

When it comes to the climate, we have a pretty myopic obsession with carbon emissions, but methane is up to 80-times more potent at warming the atmosphere when compared to carbon dioxide. Methane is a powerful greenhouse gas, and human activity releases a lot of it into the atmosphere. In the United States, landfills alone are responsible for 15% of methane emissions, releasing the greenhouse gas equivalent of 21.6 million automobiles.

However, if this methane that would otherwise be leaked into the atmosphere, is instead captured and used as natural gas—as illustrated by the bus and the chef in the story—it would reduce greenhouse gas emissions, and offer us a carbon neutral source of primary energy.

It is important to note here, that while all natural gases are made primarily of methane, where this methane comes from differs greatly. Most natural gas is considered a fossil fuel. Like oil, it took millions of years to develop, it is non-renewable, and it is acquired through drilling and fracking. RNG however, did not spend millions of years forming underground, and it is not drilled or fracked for. The methane in RNG is formed rapidly through the process of anaerobic digestion (decomposition of organic waste in the absence of oxygen).

In other words, natural gas = fossil fuel, and RNG = a carbon neutral, renewable energy source. This is part of the reason why the U.S. EPA has a program to capture methane from various sources, helping farms and urban utilities to make it happen.

Today, most of us are already beneficiaries of some form of natural gas, whether it is the renewable or fossil fuel kind. There are two main ways that we burn natural gas:

1. For Electricity Generation — About 40% of electricity in the United States comes from burning natural gas, and most of this is unfortunately from drilling and fracking, not RNG. We burn this gas to heat water in large power plants, where it makes steam, turns giant turbines, produces electricity, and then is distributed to homes through the power grid. Unfortunately, burning natural gas for electricity is only about 30% efficient, meaning that nearly 70% of the primary energy is wasted by the time it gets to your home. That waste gets even larger once we account for inefficiencies in home wiring systems and our electrical appliances.

2. For Direct Use — Natural gas is also used directly, as a primary energy source. It is the gas found in your city gas lines, used in homes and businesses, and is also used to fuel some vehicles, much of which are from RNG sources. When used directly as a heating source, natural gas is extremely efficient. According the the U.S. Dept. of Energy, using natural gas directly in a condensing heater can be up to 98.5% efficient, meaning that almost all of the primary energy goes directly to heating your home. Depending on the case, using natural gas directly as a primary energy source can be far more efficient than using it to make electricity.

Regardless of the efficiency however, capturing methane and using it as RNG inherently reduces the amount of greenhouse gases entering the environment. As a bonus, when facilitated at the local level, RNG can bring energy generation and distribution back into the hands of people and municipalities, rather than energy conglomerates.

Wait! What About Electrifying Everything?

None of this is meant to dissuade us from electricity, but to help us think critically about where our energy comes from, and where it is used most effectively. Local power generation and neighborhood micro-grids can be liberating, and we are just on the cusp of making them work. But a full-electrification of our entire lifestyles is not always the best solution for every person, place, and task.

Our transition to better energy needs to be paired at times with shifting away from electric use in cases where other, more simple, less technical, non-electric methods make more sense. These other methods can include RNG biogas, or even better, non-electric design innovations and passive design methods, as well as designing our homes together with nature, sun, wind, trees, water, and our local environments, as inspired by traditional knowledge and the study of nature-based solutions.

Ultimately, the truly regenerative aim is to find as many ways as possible to work together with our local environments, rather than against them. Figuring out better ways to use our poop is just one alley to walk.

Thanks for reading The Possible City. I’m Patrick, and every week or so I produce a short like the one you just read. I’m also arts editor at The Nature of Cities, and director of City as Nature, where I help us imagine more equitable, resilient, regenerative cities through art.

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