Reusable Perforated Plastic-Ball Bulking Agent for Decentralized Food Waste Composting: Maturity Validation, Nutrient Retention and Machine Learning-Based Process Interpretation

Every day, millions of tons of food scraps are thrown away, often ending up in landfills where they rot without air. This rotting process releases bad smells and greenhouse gases, while the valuable nutrients inside the food are lost forever. A better way to handle this waste is composting, a natural method where microbes break down organic matter into rich soil fertilizer. For this to work well, the pile needs oxygen. Without enough air, the process stalls, the pile gets too wet and compacted, and the beneficial bacteria cannot do their job. Traditionally, people mix in bulky materials like sawdust or wood chips to keep the pile loose and airy. However, these natural materials break down themselves during the process, eventually losing their ability to hold air and requiring constant replacement.

Researchers have been looking for a solution that keeps the pile open without disappearing. They are also interested in using data to understand exactly how these composting piles change over time, moving beyond simple guesses to precise predictions. The goal is to turn high-moisture food waste into a stable, safe, and nutrient-rich product quickly, especially for places like schools, hotels, or neighborhoods that generate waste daily but lack the space for massive industrial facilities.

In a controlled laboratory setting, a researcher at MIT Art Design and Technology University in Pune, India, tested a new approach to this problem. The study focused on using reusable plastic balls, specifically perforated ones, as a permanent stand-in for the traditional wood chips. These plastic balls act as a scaffold, creating tiny tunnels for air to flow through the wet food waste without breaking down themselves. The researcher mixed food waste collected from a university canteen with a few helpful additives: biochar to hold nutrients, lime to balance acidity, neem powder to control unwanted microbes, and jaggery to feed the bacteria. To see how much of the plastic scaffold was needed, four different batches were prepared. One batch had no plastic balls at all, serving as a control. The other three batches contained 2%, 4%, and 8% plastic balls by weight, mixed into the food waste.

The experiment ran for thirty days inside a specially designed metal reactor that could control temperature and air flow. The machine kept the pile warm and supplied oxygen in cycles, mimicking the conditions of a large-scale composting system. Throughout the month, the researcher measured how hot the pile got, how the acidity changed, and how the chemical makeup of the waste evolved. The key measure of success was the ratio of carbon to nitrogen, a standard indicator of whether compost is ready to use. A high ratio means the material is still raw and unstable, while a lower ratio indicates the compost has matured into a safe, soil-like product.

The results showed a clear difference between the batches. The control pile with no plastic balls struggled to stay hot and only reached a peak temperature of 40 degrees Celsius. It never stayed in the high-heat zone long enough to fully sanitize the waste or break it down efficiently. By the end of the month, this pile was still not fully mature, with a carbon-to-nitrogen ratio that remained too high for safe use. In contrast, the batches with plastic balls performed much better. The batch with 8% plastic balls reached a peak temperature of 58 degrees Celsius and stayed hot enough to kill pathogens for eleven days. This heat helped the microbes work faster, and the pile matured significantly sooner. By day eighteen, this batch had already reached the target range for maturity, and by day twenty-four, it was fully stable. The other batches with 2% and 4% plastic also improved, but the 8% batch showed the most consistent performance.

Beyond just speed, the plastic balls helped the compost keep its nutrients. When organic matter breaks down, valuable elements like phosphorus and potassium can easily wash away or escape. The study found that the batch with 8% plastic balls retained the most phosphorus, holding onto 45.65% of it, compared to only 24.44% in the control batch. It also kept more potassium, retaining 22.96% versus just 7.69% in the control. This means the final product was not only ready to use sooner but was also richer in the minerals plants need to grow. The final compost from the 8% batch was classified as top-quality, safe for agriculture and free of heavy metal risks, while the control batch remained of lower quality.

To understand exactly which factors were driving these changes, the researcher used computer models to analyze the data. One model looked at all the measurements taken over the month to figure out what mattered most. It found that the amount of nitrogen in the pile, the acidity level, and the moisture content were the main drivers of how quickly the compost matured. Another model, designed to track changes over time, successfully predicted how the carbon-to-nitrogen ratio would drop as the days went by. These tools confirmed that the plastic balls did not just add bulk; they created an environment where the right chemical reactions could happen faster and more reliably.

The study suggests that using these reusable plastic balls could be a practical solution for decentralized composting systems. Unlike sawdust or wood chips, which are consumed and need to be bought again and again, these plastic balls can be removed from the finished compost and used in the next batch. This could make composting more efficient and less expensive for institutions that generate a lot of food waste every day. While the experiment was conducted on a small scale in a lab, the findings point toward a method that accelerates the breakdown of waste, preserves nutrients, and produces a high-quality fertilizer without the need for constant replacement of bulking materials. The research highlights that with the right physical structure and a bit of data-driven insight, turning food scraps into soil can be faster, cleaner, and more effective than previously thought.