Waste Systems

Closing the Poop-loop: The Biogeochemistry of Sanitation

Humans have direct control over large portions of the global methane and nitrous oxide budget. That means there are significant opportunities for climate mitigation in managed and coupled human-natural systems. Biogeochemical flows associated with sanitation systems are particularly poorly quantified globally, while their mismanagement underlies a global public health crisis affecting almost half the Earth’s population and contributing to > 800,000 deaths annually from preventable illness.

The McNicol Lab joins research in ecosystem science with sustainable development via a collaboration with the internationally-recognized NGO Sustainable Organic Integrated Livelihoods (SOIL) Haiti. SOIL serves communities in Port-au-Prince and Cap Haitien, employing locals to provide an innovative sanitation service that recovers compost from waste. To date, we have estimated scalable greenhouse gas emission factors for SOIL’s thermophilic composting treatment method, finding that waste diverted from slum pit latrines globally could mitigate 13-44% of wastewater sector methane emissions. We published the first paper from this work in June, 2020, in the journal Nature Climate Change. Here is a short reflection on this work:

Sanitation and climate: Sustainability in the broadest possible sense  

We quantify the climate change dimension of a sustainable development synergy between public and planetary health in the sanitation sector.

“Deye mon, gen mon,” (beyond mountains, there are mountains) is a Haitian provèb, possibly inspired by the country’s unrelenting terrain, or by the vertiginous immediacy of daily life in the poorest country in the Western hemisphere. However, I think it may also contain some perspective for sustainability: that appreciation of distant challenges depends on first ascents. Climate change may seem to the (relatively) affluent to be a towering massif on the not-so-distant horizon, but that it is so clearly visible may be a privilege of elevation.

When you can’t take a poop in private (that is, you lack any safe sanitation options), climate change seems, not just glacial, but tectonic. Yet, as global environmental priorities coalesce around a climate emergency, sanitation access continues to lag behind as an international development objective. In Haiti, about 30% of the population lacks access to improved sanitation and about 10% rely on open defecation, meaning they have literally nowhere to go. These statistics mirror the global sanitation crisis. Though exact numbers are unclear, likely 1-2 billion people have no toilet whatsoever, while 3-5 billion lack a safe sanitation system.

Fresh from a PhD at Stanford University, one of my collaborators, Sasha Kramer, was motivated by these realities to improve sanitation access in Haiti. In 2006, Sasha co-founded the non-governmental organization Sustainable Organic Integrated Livelihoods (SOIL). SOIL is now a bright light among a constellation of international research and development enterprises designing new sanitation systems that will work in low resource settings. Innovations they explore broadly reflect recent transformations in the waste sector, namely, to value human excreta as a resource, rather than merely disposing of it as waste. When nutrient and energy recovery, or even more distal environmental benefits such as climate regulation, become a part of the service value chain, they make essential reductions to the prohibitive costs of sanitation.

SOIL’s circular design uses the combination of container-based toilets, that enable easy containment, collection, and transport of poop, with off-site thermophilic composting, a treatment method to neutralize pathogens and recover a sellable product. As a biogeochemist, Sasha envisions a repaired nutrient cycle in Haiti, where dependency on foreign imports is moderated by upcycling waste into compost. The externalities here are both economic and positive; SOIL has grown from a focused service attending the devastation of the 2010 earthquake, to an operation employing over 30 local recruits from the coastal city of Cap-Haïtien.

As I finished my own PhD in 2015, I was searching for a way to apply what I’d learned about the greenhouse gas balance of wetlands, to a more immediate sustainability challenge, ideally with development intersections. I first met Sintana Vergara, a new UC Berkeley postdoc joining from the World Bank, who turned my attention to waste, a very large greenhouse gas source sector over which we have direct control. Then a chance reunion at the Ecological Society of America 2015 meeting had me explaining my new interests to Rebecca Ryals, who, by extraordinary coincidence, was already collaborating with SOIL. In a series of papers with our shared PhD advisor Dr. Whendee Silver, Rebecca had previously shown that compost generated from green waste in the Bay Area, California, could sequester carbon when applied to rangeland soils. A later lifecycle analysis underscored an enormous methane mitigation potential for diverting organic waste away from landfill.

In Haiti, Becca had been surveying greenhouse gas emissions from different human waste (poop) fates, such as anaerobic lagoons and open sewers, and comparing it with SOIL’s composting treatment. The early work indicated lower methane emissions from SOIL’s composting treatment process, but much more data were needed. Becca and I therefore spent a year collecting flux measurements with SOIL, becoming a biogeochemical extension of SOIL’s multifaceted research efforts. The essential vehicle for this work was our climate and compost fellows; several cohorts of local agronomy students, led by our co-authors Julie Jeliazovski and François Junior-Jules, a French environmental engineer and Haitian agronomist, respectively.

Clarence Golueke, also of UC Berkeley, once said he hoped to take the witchcraft out of composting and replace it with rationality. With this work we begin to augment the wealth of compost engineering knowledge with a global biogeochemical insight: composting, as an aerobic microbial transformation, can treat human waste with relatively low greenhouse gas emissions. There is still so much to do to understand the biogeochemistry of composting, and the sanitation systems it could become integral to. However, we are in ideal position to do this work. Parallel research at SOIL has described the evolution of the compost microbiome over time, a compelling application of the metagenomic capabilities developed in the last decade.

Sustainability synergies are built on mutually reinforcing, but not necessarily reciprocal, objectives. We believe that the sanitation and climate synergy is such an example. Concern for climate change is often congratulated for it’s a moral elevation, but we should be humbled by the fact that so many people around the world are still making the climb. Our work with SOIL is about finding a way to lighten the burden on those dedicated traversers, and we should prioritize doing so, because they are bringing us vital supplies for the next ascent.