From Waste to Value: Developing Catalytic Materials and Bio-oil from Waste for Use in Green Processes

The concept of turning waste into value has been a guiding principle for sustainable development, but in today’s world, it has taken on new urgency. As we strive to meet the increasing demand for greener solutions, the challenge is no longer just about waste management; it’s about reimagining waste as a resource that can drive sustainable progress. Traditionally, organic waste—food scraps, agricultural residues, and even everyday items like eggshells—has been considered a low-value byproduct, often ending up in compost or, at best, serving as feedstock for bioenergy. But what if we could take this a step further? What if this waste could be a catalyst—literally—for innovation?

It was with this idea that researchers from the Indian Institute of Petroleum and Energy (IIPE), Visakhapatnam, began investigating the production of catalytic materials from waste products. In a new study published in Biomass Conversion and Biorefinery, a research team—including Assistant Professor Ravi Kumar Sonwani from IIPE—has developed calcium oxide catalysts for pyrolysis using eggshells and seashells to convert organic wastes (i.e., sugarcane bagasse) into bio-oil and biochar. Pyrolysis is a process in which an organic material, like biomass, is heated to around 400–600°C in the absence of oxygen to produce energy products, such as bio-oil. Typically, the products of pyrolysis are upgraded to more energy-dense products using catalysts. The researchers used calcium oxide catalysts to upgrade sugarcane bagasse to three products: bio-oil, gas, and bio-char.

“Our study investigated the use of waste materials, namely eggshells and seashells, to produce calcium-enriched materials, which were later employed as catalysts in pyrolysis reactions,” explains Dr. Sonwani. As part of their study, the researchers conducted three types of pyrolysis experiments—without catalyst, with in situ catalyst—where the catalyst was placed along with the biomass, and with ex situ catalyst—where the catalyst was placed in a separate bed from the biomass. They also examined three different catalysts: commercial-grade calcium oxide, eggshell-derived calcium oxide, and seashell-derived calcium oxide. The products of all these experiments were analyzed both qualitatively and quantitatively. The research team further optimized the pyrolysis process using a technique called response surface methodology (RSM), which is a powerful technique that not only allows the optimization of individual variables (temperature, biomass size, etc.) but also accounts for the interaction of different process variables.

“We found that the theoretical predictions from the RSM-optimized model and the actual experimental responses under optimized conditions were in high agreement, indicating the accuracy of the optimization process,” says Dr. Sonwani. While the yield of bio-oil via non-catalytic pyrolysis and catalytic pyrolysis was almost similar, the catalytic process improved the calorific value (i.e., energy density) of the bio-oil. Even more significantly, the gas produced via catalytic pyrolysis had a calorific value of up to 30% higher than the non-catalytic process. “The moisture and acidity control of the bio-oil produced in our experiment holds promising implications for storage stability and use in engine combustion,” adds Dr. Sonwani. Overall, this study highlights how biomass upgradation using an organic waste-derived catalyst offers a new synergy in the waste-to-value process.

While this study is an example of how waste-derived catalysts can be used to produce oil, the opposite process is also an intriguing possibility. In another study, a research team from IIPE—including Dr. Sonwani, Dr. Kumud Malika Tripathi, and Mr. Diwakar Patel—has investigated how waste frying oil can be used for waste remediation. In a new study published in ACS Omega, the researchers evaluated how waste frying oil can be used to produce adsorbent materials for the treatment of dye-contaminated wastewater. “Synthetic dyes are used in a wide variety of industries—from textiles to leather to even pharmaceuticals,” explains Dr. Sonwani. “Some of these dyes, like methylene blue, are resistant to degradation and can pose a significant health risk to both humans and the environment. Finding a way to treat dye-contaminated water is, thus, an urgent need.”

In their study, the team produced carbon nano-onions (CNOs) from waste frying oil—a cooking by-product that is normally disposed of down the drain or in water bodies, causing further pollution. Dr. Tripathi elaborates, “CNOs have a unique multi-shelled structure, much like their namesake, the onion. This structure greatly increases their surface area, which makes them powerful adsorbent materials.” The research team synthesized CNOs from waste frying oil using a ‘cotton wick combustion technique’ followed by treatment at 600°C for two hours to remove any unburnt residual oils. These CNOs were then placed into a dye solution and the rate of adsorption was studied. They found that 99.78% of the dye was removed from the contaminated water within 20 minutes of addition.

The research team then investigated the kinetics of the adsorption process, as well as the adsorption capacity of the CNOs. They found that 1 gram of CNOs had the capacity to adsorb around 43 mg of dye. They also investigated the regeneration potential of the CNOs. “Regeneration and reusability are crucial for adsorbents because it not only brings down the overall cost of the process, but it also makes the process more environmentally sound,” says Dr. Tripathi. They found that regenerated CNOs achieved a dye removal efficiency of 99.6% over three cycles. Characterization studies were also carried out on the CNOs. Finally, phytotoxicity studies were conducted on the treated water. “A phytotoxicity study essentially looks at whether the treated wastewater has any adverse effects on plants,” says Mr. Patel, “and helps us explore if the treated wastewater can later be used for the irrigation of agricultural crops, etc.” The research team found that mustard seeds watered with treated dye-contaminated water showed better growth than those watered with untreated dye-contaminated water, indicating the environmental sustainability of the process.

Overall, these findings indicate that CNOs derived from waste frying oil show high potential as an effective, economical, and eco-friendly means to remove dye from wastewater. Both these studies underscore that the concept of waste-to-value transcends traditional waste management. The approaches outlined in the papers and the subsequent findings not only provide an opportunity to enhance resource efficiency, but also open new pathways for environmental and economic benefits. As we continue to explore and refine these methods, we move closer to a future where waste is not just managed but actively contributes to a greener, more sustainable world. We congratulate the researchers on their exemplary work and eagerly anticipate their future advancements in this transformative field.