Wastewater: A dirty little climate opportunity

By: Daly Wettermark

This is a bi-weekly newsletter about climate solutions. To receive the Gigaton in your inbox each week, subscribe here:

---

Gigaton Potential

Expanding access to safe wastewater treatment and improving our existing systems could reduce at least 0.5 GT of CO2-equivalent greenhouse gasses per year by 2030, or cumulatively about 15 GT by 2050.

For reference: in 2019, the world emitted 51 gigatons of CO2-equivalent greenhouse gasses. Project Drawdown estimates we need to cumulatively eliminate 1,000 GT from 2020-2050 to keep global warming below 2 degrees Celsius.

You Might Be Interested If...

• You’re drawn to infrastructure challenges

• You care about global health, especially access to clean water and sanitation

• You’re a bio-chem nerd - wastewater is an ecosystem!

• You’re a finance nerd - utilities need creative business approaches!

What You Should Know

Did you know that our human life expectancies have doubled in the past 200 years? It happened because of public health investments which we easily take for granted: vaccine campaigns, clean water infrastructure, and the subject of this article, sanitation. 

“Sanitation” refers to the methods we use to avoid contact with our wastewater, for example by using piped sewers or septic systems. Despite encouraging global trends, nearly half of the world still lacks access to safe sanitation, creating an inequitable and avoidable disease burden.

Wastewater, whether treated or untreated, also produces greenhouse gasses. And no matter how “green” we live, we all have to poop! This necessitates being thoughtful in how we design public sanitation systems, to minimize their climate and environmental impacts.

How is wastewater treated?

For areas with sanitation systems, most wastewater is transported through sewers to centralized treatment plants which:

1. Remove large solids, using coarse screens and gravity-based settling

2. Remove dissolved organic compounds, using biological or chemical processes

3. Remove smaller solids, including bacteria, using fine filters or gravity-based settling

4. Disinfect the remaining water, using chemicals, UV light, or ultra-fine filtration

5. Sterilize solids, using chemical or high-temperature processes

6. Return cleaned water and solids to the environment or new uses

You can learn how a typical system, like Figure 1, works in this video.

Figure 1: Typical wastewater treatment plant. (Wikimedia Commons)

This ongoing expansion of sanitation systems, plus a need to replace aging, existing systems, is driving a 6% annual growth rate for the $200+ billion wastewater treatment market.

How does wastewater generate emissions?

Wastewater management today accounts for around 2% of global emissions, which can be categorized as:

⚡ Indirect Energy Emissions

Half of the world’s wastewater is centrally treated, using 1% of global electricity (0.6 GT CO2e). The most energy-intensive processes are typically transportation, biological treatment, and disinfecting water.

💨 Direct Process Emissions

As wastewater is broken down, bacteria in the water belch out about:

• 0.3 GT CO2e as nitrous oxide, mostly from treatment plants

• 0.4 GT CO2e as methane, mostly from untreated sewage

• 0.2 GT CO2e as carbon dioxide

Nitrous oxide and methane are greenhouse gasses with higher global warming potentials than carbon dioxide. All emissions values in this article estimate global, annual CO2-equivalent.

Key Players

The wastewater sector is made up of an ecosystem of organizations, shown in Figure 2.

Figure 2: The wastewater innovation ecosystem.

Utilities

Wastewater utility companies are at the frontline, implementing solutions across more than 16,000 treatment plants in the US, and more globally. Many have research divisions carrying out decarbonization projects, including several in the San Francisco area.

Companies

Companies, both generalized and specialized, build treatment technologies. A few examples are Suez/Veolia’s waste-to-energy solutions, Xylem’s efficient pumping and metering, DuPont’s filtration for water recycling, and Evoqua’s nutrient recovery technologies.

Consultants and Engineering Firms

Most utilities hire consultants for major engineering projects, so it is crucial for consultants to buy-in to decarbonization strategies and recommend progressive designs.

Research Organizations

Research organizations, academic institutions and technology incubators build utilities’ and consultants’ trust in novel technologies by supporting pilot-scale validation projects.

Opportunities for Innovation

💰  Financing for Quick Wins

→ 0.4 GT CO2e could be mitigated by 2030 through energy optimization, nitrous oxide optimization, and onsite renewables 

Efficiency-improving measures for wastewater treatment can be cost-neutral in the long-term, but require sizable upfront investments. Creative programs are needed to unlock the potential savings. For example, the consultancy Isle Utilities developed a “trial reservoir” finance model to help water utilities adopt decarbonization strategies quickly.

🏘️Small-Scale Solutions

→ 0.2 GT CO2e could be mitigated by 2030 by adding treatment

A third of our sewage is not collected or treated, especially in rural areas. Alternatives to centralized sewage treatment like on-site composting and urine-diverting toilets provide sanitary solutions while reducing methane emissions. Still, affordability gaps, cultural barriers, and the logistics of deploying decentralized solutions remain challenges.

♻️ Synergies with Agriculture

→ 0.3 GT CO2e could be mitigated by recycling sewage resources, some by 2030

Utilities and the private sector can partner in a circular economy, illustrated in Figure 3, by recycling wastewater’s ingredients:

• Fertilizers. Capturing ammonia from urine could offset emissions from synthetic ammonia fertilizer production. Removing ammonia also reduces nitrous oxide emissions. (0.17 GT CO2e)

• 99% water. Using recycled water for irrigation can offset some demand from surface or groundwater. (Limited CO2e quantification)

• Carbon. Wastewater could generate carbon credits, sequestering carbon via biochar or microalgae which can then be repurposed in soil or animal feed. (0.07 GT CO2e)

• Energy. Sewage can produce methane biogas to power its own treatment. However, methane leakages can negate the benefits, so monitoring is critical. Other promising waste-to-energy products include syngas and waste heat. (0.08 GT CO2e)

Technology cost poses a challenge, but many utilities are already piloting resource recovery. Each tactic is a small contributor. But when considered collectively, reducing wastewater treatment’s greenhouse gas intensity while also protecting public health is a powerful opportunity to multiply impact.

Figure 3: Wikimedia Commons

About the Author:

Daly Wettermark spends the productive portion of her time working on product development at Xylem, studying environmental engineering at Stanford, engaging in climate activism, and attempting to non-annoyingly introduce people to delicious vegan foods.