Soil-less Soils, A THREAD

 
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Below is our recent Tweet thread about Soil-less Soil in long form for easy reading:

FACT:

In 2015, landfills received approximately seven million tons of MSW glass. This was 5.1 percent of all MSW landfilled that year. (EPA https://www.epa.gov/facts-and-figures-about-materials-waste-and-recycling/glass-material-specific-data)

FACT:

Sand is one of the most heavily used materials in major construction projects…and we’re running out.

Let’s get to the bottom of this. #thisisolinlabs

We must first credit this thread to our @OLIN_Labs research team and the great work of recent @Penn Master of Environmental Studies @PennLPS graduate Anqi Zhang, who took on this study as her capstone research project. Read her full report here: https://repository.upenn.edu/mes_capstones/78/

And huge thank you’s also to @AeroAggregates for supplying data on glass processing and Christoph Koffler from @thinkstep for his critical review—give him a follow at @LifeCycleGeek.

Now, onto the report!

Let’s start with the challenges at hand.

FIRST: The Sand Crisis

Like naturally occurring soil, manufactured or designed soil is comprised of a mix of organic and inorganic materials, with the inorganic components often being mined from stone or sand quarries.

But with construction booming worldwide, demand for resources like sand is increasing, dangerously straining our supply, and amplifying health and environmental impacts. Erosion, habitat destruction, and hazardous pollutants generated by industrial mining, just to name a few.

NEXT: The Glass Crisis

In the US, there is a surplus of waste glass. Some colored glass and small pieces can’t be recycled, and recent shifts in the global markets have dramatically reduced demand for recyclable materials…which means they end up in landfills.

BONUS: the cost to municipal recycling programs to recycle this glass (that nobody wants) has risen dramatically, further disincentivizing cities from sorting and processing the glass they do collect.

But in the midst of these dueling environmental crises, we had a thought: isn’t glass MADE of sand??

…so if we took this glass…and ground it back down into sand…could we solve both of these problems together?

This was the hypothesis that became @OLIN_Labs Soil-less Soil Project. We wanted to understand not only if post-consumer glass could be a suitable sand replacement in designed soils, but if other environmental benefits could result. Enter Anqi and her research.

Anqi examined the many factors which go into the harvesting, processing, and transportation of waste glass and the resulting glass fines which would be our sand substitute. The results were striking.

Nearly across the board, from fossil fuel consumption to greenhouse gas emissions to human toxicity, the negative environmental impacts from the glass processing were dramatically lower than sand mining.

 

LET’S GET SPECIFIC

It is estimated that about 93.24 kg of CO2 is produced during the production of 1 ton of aggregates from quarry sand…but producing the same amount of recycled aggregates only yields about 30.1 kg of CO2—almost a 70% reduction!

 

“But what about terrestrial acidification?!?” you’re probably asking, and we don’t blame you. The more acidic the soils around us are, the harder it is for plant life to grow, meaning losses in biodiversity across the whole ecosystem.

 

We measure terrestrial acidification in terms of SO2/kg emission. Nearly 82% more terrestrial acidification potential measured as SO2 equivalents is seen when producing 1 ton of sand aggregates compared to producing 1 ton of glass aggregates. 82%!!!

 

Now to human toxicity. We’re going to keep it simple, because Anqi’s report uses the word “dichlorobenzene,” which we’re pretty sure may blow up Twitter’s servers. In short, glass aggregate production reduces human toxic exposure by 95% versus sand aggregate processes.

 

Now we did uncover an increase in potential negative impacts, so let’s dive into that side and examine potential mitigation strategies.

 

For example, the production of glass fines causes 61% more ozone depletion potential than the production of conventional sand. 52% of that increase is caused by the sorting process, so Anqi recommends special waste air treatment for that part of the production cycle.

So how feasible would a glass for sand swap be in practice? Well from a cost standpoint, with the current challenges in the municipal recycling markets and the abundance of low-value waste glass, the cost of the two materials is more or less a toss-up, and diverting waste from the landfill is an economic and environmental win.

 

THE CONCLUSION?

While  regional and international differences in the collection and recycling process may change the environmental impacts and material availability, the replacement of mined sand with post-consumer glass fines would start a ripple effect of environmental - and economic - benefits.

Let’s think about the impact in terms of a single tree pit, which on average tree pit contains up to 2 tons of sand, which through the mining process produces 186.3 kg of greenhouse gasses… while the process to use recycled glass fines only produces 60.2 kg—that’s a savings of 126.1 kg, the equivalent of driving a car for nearly 5 hours straight!

But this LCA research is just the beginning.   We’ve seen the environmental benefits of replacing sand with glass, but how will this waste material perform in topsoil? This summer will be spent in the greenhouse with our friends from @PennDesign @GreenPenn and @TempleUniv assessing plant growth in a variety of glass and natural sand soil mixes.

If we can home in on a designed soil mix that supports healthy plants, reduces greenhouse gas emissions, protects natural resources, closes a municipal waste loop and saves money for cities… well let’s get it done!

We can’t wait to see where the Soil-less Soil Project will take us next! Thanks for reading and stay tuned to olinlabs.com for much more on this vital topic.

THE END…for now! 😉