Biogas and the Circular Economy

Morgan Vincent

Hey everyone, welcome back to Educators Empowering Educators. I'm Morgan Vincent, and today, we’re tackling something near and dear to both my science and teaching sides—how biogas and circular economies can actually transform our approach to food security, starting right here in Pennsylvania. Joining me is Dr. Marcus Ellery, chief scientist, agrifood systems champion, and someone who truly knows what it means to bridge the world of research and the reality of farming. Dr. Ellery, thanks for being here!

Dr. Marcus Ellery

Thanks, Morgan. It’s always a pleasure to dig into these big questions with folks who care about teaching and the future of food.

Morgan Vincent

So, before we get technical, let’s set the scene. I always come back to this moment in Uganda, standing on a student-run school farm where waste wasn’t seen as, well, waste. It was this resource they could transform. That idea connects so strongly to what you work on, Marcus: not just growing food, but redesigning the system so nothing is wasted, whether you’re a smallholder in Africa or running a dairy in Pennsylvania. Could you lay out this big idea of the “circular economy” in agriculture?

Dr. Marcus Ellery

Absolutely. Agriculture is linear: you take resources, make products, and whatever’s left is waste—an afterthought. In a circular economy, we try to recapture everything in that chain. So manure, crop leftovers, even external food waste, they all become inputs again. It’s about closing loops: recycling nutrients in the soil, creating renewable energy, making the farm more resilient, and less dependent on outside fertilizers or fossil fuels. That school farm you mentioned? That’s the same logic and it works whether you’re operating on one acre or 1,000.

Morgan Vincent

Yeah, and I mean, it’s funny. I used to think of waste management as sort of the dusty back-end of farming, but the more I see projects, the more I realize it really sits at the center of food security and climate resilience. It’s global and local all at once.

Dr. Marcus Ellery

Exactly. And we’re lucky Pennsylvania’s dairy sector is leaning in here, especially with biogas systems. But I’m getting ahead of myself! Where should we go next?

Morgan Vincent

Let’s get practical for the teachers in the room. How does anaerobic digestion, the process at the heart of these biogas systems, actually work? Walk me through a way that us newcomers could understand and share in class.

Dr. Marcus Ellery

Alright, picture a giant stomach for microbes. That’s honestly the most accurate analogy. You toss in manure and sometimes food waste, from the farm. It all goes into a big, sealed tank known as the digester. Microbes there don’t need oxygen, so they go to work breaking down all the organic matter. First they kind of liquefy everything. Then another team of bacteria produces acids, and finally, special bacteria called methanogens turn those acids into biogas, which is mostly methane and carbon dioxide. That gas can power a generator or be used for heat.

Morgan Vincent

So, it’s not just about getting rid of waste. It’s creating something valuable. Can you give us a walkthrough of what happens on a real Pennsylvania farm, like Penn State’s digester? How does the manure become electricity?

Dr. Marcus Ellery

Sure. Take Penn State’s system: they scrape manure from over 350 cows in the dairy barns, then run it through a sand separator. All that separated sand gets recycled for bedding. The liquid manure goes into the digester, sometimes mixed with swine manure too. Inside the digester, the microbes work at about 95 degrees Fahrenheit, churning away for about 23 days in Penn State’s set-up. The resulting biogas gets piped over to a combined heat and power plant, which both generates electricity for the dairy complex and heats the digester to keep things running. Any leftover digestate, all those rich nutrients, gets spread on fields as fertilizer.

Morgan Vincent

And that biogas isn’t just a trickle, right? The Penn State setup produces enough to power the entire dairy operation plus supply energy back to the grid at times.

Dr. Marcus Ellery

That’s right. And systems like Reinford Farms, which we’ll talk about soon, take it another step by integrating food waste as well. It’s a closed loop, but it’s also an open door to new income streams and massive climate wins.

Morgan Vincent

Let’s talk actual numbers and impact and look at a larger scale project. You’ve been part of the WasteToWorth case study on a Pennsylvania dairy farm, a real working operation with over a thousand cows, right? What makes it an example of the circular economy in action?

Dr. Marcus Ellery

Absolutely. This farm co-digests manure from over a thousand dairy cows with off-farm food waste, think waste from the local community, things like expired milk, fruit and veggie scraps, and even dog food. Roughly 66% of the biogas they produce comes from this food waste, and that highlights just how much ‘waste’ from outside the farm can become a key energy source. They meet nearly all their fertilizer needs by recycling digestate right back to the fields, and still export surplus electricity to the local grid. During economic uncertainties or even weather shocks, that energy independence is a huge resilience factor.

Morgan Vincent

And just to clarify, by bringing in off-farm food waste, they’re actually helping reduce what might otherwise be landfill methane emissions, while boosting the on-farm nutrient supply?

Dr. Marcus Ellery

Exactly. Food waste that would’ve ended up rotting in a landfill, releasing greenhouse gases, gets turned into power, fertilizer, and soil carbon. A third of the nitrogen in the digestate comes from off-farm waste. They’re basically converting external problems into internal solutions.

Morgan Vincent

And during a time when fertilizer costs are unpredictable, using recycled nutrients is a stabilizer for budgets too, right?

Dr. Marcus Ellery

Totally. They’re meeting about 78% of their nitrogen requirements from in-house sources, meaning less spending on pricey synthetic fertilizers. Plus, they actually use their own bedding made from digested solids, driving costs even lower.

Morgan Vincent

And now I want to dive in further on those nutrients for a second. There’s a lot of optimism about digestate as a soil amendment, reducing pollution and costs. But managing those nutrients, specifically the nitrogen and phosphorus, it’s not all sunshine and rainbows, is it?

Dr. Marcus Ellery

Yeah, it’s a double-edged sword. Digestate is rich in plant-available nutrients, mostly ammonium nitrogen and phosphorus, so you reduce your need for synthetic fertilizer. So, that’s great for water quality. The less runoff, the less risk to watersheds like the susquehanna river, for example. But in a system like our Pennsylvania case study, phosphorus in particular can build up over time. Too much, and you risk pollution through runoff or leaching, especially as soils reaches phosphorus saturation.

Morgan Vincent

So what can farms do to manage that responsibly?

Dr. Marcus Ellery

Injecting digestate into the soil instead of spraying it on the surface is one best practice. Less ammonia lost to the air, more roots getting the nutrients. Pair that with no-till farming and stream setbacks for fertilizer application, and you’re stacking wins. Our case study farm is even participating in a digestate injection trial right now, looking to maximize nitrogen retention and minimize environmental impact. But honestly, not matter what the farm is doing, ongoing monitoring is crucial. If excess nutrients start to build up, it could be an opportunity for farms to process and sell their surplus digestate as commercial fertilizer, for example.

Morgan Vincent

That’s a real systems-thinking approach. Not just closing the loop, but tweaking the loop along the way.

Morgan Vincent

Now, I want to zoom out a bit, because this isn’t just about one farm. When you start scaling biogas across Pennsylvania’s dairies and bring in food waste and crop residues, what does that mean for the state’s energy future?

Dr. Marcus Ellery

So, our modeling shows that if you combined manure, food waste, and crop byproducts statewide, Pennsylvania could offset about 3% of its total electricity use with biogas systems, which is roughly 3,300 gigawatt-hours a year. That’s a serious chunk of renewable energy. Plus, most farms would cover all their own on-site electricity and heat needs, and potentially have surplus to sell back to the local grid.

Morgan Vincent

And it’s not just about energy, right? It’s resilience. When energy prices spike, these farms will feel less pain. And you’ve mentioned before the positive impact on rural economies.

Dr. Marcus Ellery

Right. Biogas systems can create and keep energy dollars local and provide new revenue streams like food waste tipping fees and carbon credits. It all adds up to stronger communities, not just cleaner power.

Morgan Vincent

Let’s bring this home for our educator audience. If you’re a teacher, where does this “circular economy meets biogas” story fit in your classroom? What are some realistic entry points, Dr. Ellery?

Dr. Marcus Ellery

First off, this connects across disciplines: science, agriculture, social studies. In science, you can have students run classroom waste audits. The students could think about where the food waste coming from and where could it go? In agriculture classes, try building small biogas models. Think soda bottles, some food scraps, a balloon for gas collection. It’s hands-on and directly relevant. For systems thinking, you can analyze nutrient flow diagrams which shows how carbon, nitrogen, energy, and water move through the farm.

Morgan Vincent

In my experience, field trips are a gold mine too. Seeing digesters at places like Penn State or Reinford Farms, students can connect the abstract ideas to real-world practices. And using local case studies makes the science feel less distant in theory and more practical. “This is what your neighbors are doing.” If you want inspiration and practical examples, these are tailor-made for student-driven inquiry and even project-based learning.

Morgan Vincent

Let’s close by looking ahead. What are the real roadblocks for farmers or communities who want to build biogas systems, and what new innovations should we have on our radar?

Dr. Marcus Ellery

The biggest barriers right now are economic and technical. Biogas systems are expensive and they work best for larger farms. There’s a need for financing, strong policy support, and skilled operators. Smaller dairies in Pennsylvania need more affordable options. But we’re seeing exciting innovations: co-digesting multiple feedstocks like crop residues and food waste, upgrading raw biogas into renewable natural gas that can be sold on the grid, and new digester types like “fixed film” systems that reduce size and costs. Policy incentives, workforce training, and collaborative models are going to be critical for scaling and making these systems more equitable.

Morgan Vincent

So, we should not see circular farming and biogas as exceptions or experiments, but as the new rule. We need all hands: classroom, farm, and lab, to make this the norm. Marcus, any final words for our educators before we wrap up?

Dr. Marcus Ellery

Just this: every classroom visit, every student project, every farm that tries something new, it all adds up. Biogas and circular farming aren’t silver bullets, but they’re powerful tools. If you’re listening, you’re already part of creating that future. Keep asking questions. Stay curious. Keep building those bridges between science and real life.

Morgan Vincent

Perfect place to end. Dr. Ellery, it’s always a joy. Thanks for sharing your wisdom and, honestly, for making the science feel hopeful. Alright, that’s it for today, folks. We’ll see you next time on Educators Empowering Educators. Take care, everyone!

Dr. Marcus Ellery

Thanks, Morgan. Take care, everyone.