Microplastics are everywhere. They show up in drinking water, mountain streams, and even human blood. And while big industrial solutions are slowly rolling out for wastewater treatment plants, there’s basically nothing out there for California’s freshwater lakes and rivers, the sources a lot of communities actually drink from.
That’s the problem this project is trying to solve.
Fight waste with waste
California generates over 1.7 million tons of agricultural waste every year just from nut and grape production. A huge portion of that gets burned, which is something the state is actively trying to stop. At the same time, biochar (the carbon-rich material you get when organic matter is heated without oxygen) has been getting real attention lately as a way to pull microplastics out of water.
The connection seems obvious. What if the state’s agricultural waste could become its microplastic solution?
This project puts five locally-sourced feedstocks side by side: almond shells, pistachio shells, walnut shells, grape vine prunings, and rice hulls. The goal is to figure out which one produces the most effective and affordable biochar filter for treating freshwater.
Why biochar actually works
Biochar traps microplastics in three main ways. Physically, tiny particles get stuck and tangled in its porous structure. Electrostatically, the charged surface of biochar attracts plastic particles. And hydrophobically, non-polar plastics are drawn out of water toward the biochar surface. Recent research backs this up with removal efficiencies above 90% in lab settings, and a 2024 University of Mississippi study showed 86 to 92 percent removal from real agricultural runoff in column filter tests.
The science is there. What’s missing is data specific to California.
What makes this comparison worth doing
No published study has directly compared nut shell biochars from almond, pistachio, and walnut sources for microplastic removal. Grape vine prunings haven’t been studied for this purpose at all. This project fills a real gap, and it goes a step further by including cost-effectiveness analysis, something most academic studies skip.
The setup is rigorous: five biochar types plus a sand control, 50g of standardized biochar per column, five trials per type (30 total filtration tests), and microplastic counting under a microscope using vacuum filtration. An ANOVA test will sort out whether the differences between biochars are real or just random variation.
The cost question matters as much as the science
Good removal rates in a lab are great, but they mean nothing if the material is too expensive to use at scale. Grape vine prunings can often be sourced for free from Napa, Sonoma, or Lodi wineries. Rice hulls run about $15 to $30 per ton. Almond shells fall in the $25 to $50 range. By tracking biochar yield from each feedstock and calculating cost per 1,000 liters treated, the project aims to identify which material gives the best real-world value, not just the best lab number.
Why this matters right now
California already requires microplastic testing in drinking water and is working on new standards. The regulatory pressure is real, but practical solutions for natural freshwater systems are still largely missing. A low-cost biochar filter built from locally available agricultural waste could be exactly the kind of tool that bridges the gap between research and something you can actually deploy in the field.
This project won’t fix microplastic pollution on its own. But it might point to which feedstock deserves serious investment next.
About ACSEF
The Alameda County Science and Engineering Fair gives grade 6 through 12 students across Alameda County a chance to show what they can do in science and engineering, with top projects advancing to regional, state, national, and international competitions including the California State Science and Engineering Fair and ISEF. Atomicmind
Students from public, private, charter, parochial, and homeschool settings are all eligible, and projects can be done individually or in groups of up to three. If a student’s school doesn’t run its own science fair, they can enter ACSEF on their own. Atomicmind
At the state level, the California Science and Engineering Fair Foundation brought the fair back to an in-person format in April 2025 Csef-foundation after a transition period, and the 75th Annual California Science and Engineering Fair is set for April 11 and 12, 2026 at California Lutheran University in Thousand Oaks.
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