In the heart of Vietnam, researchers have uncovered a promising solution to a pressing environmental challenge: the treatment of nitrogen-rich pig wastewater. Dr. Thi Minh Hoa Duong, from the Faculty of Resource Management at TNU—University of Agriculture and Forestry (TUAF), has led a study that could revolutionize wastewater management in the agricultural sector. The research, published in ‘Materials Research Express’ (translated as ‘Expressions of Materials Research’), focuses on the use of ozone-modified biochar derived from acacia wood sawdust to adsorb nitrogen from pig wastewater.
The problem at hand is significant. Pig wastewater contains high concentrations of total nitrogen (TN), ranging from 500 to 1,500 mg per liter, and ammonia, between 50 and 70 mg per liter. These high levels of nitrogen can lead to severe environmental issues, including eutrophication of water bodies, which depletes oxygen and harms aquatic life. “The need for effective and sustainable treatment solutions is urgent,” Dr. Duong emphasizes.
The study introduces ozone-modified biochar (SPO) as a potential game-changer. By treating acacia wood sawdust biochar with ozone, the researchers increased its oxygen uptake rate from 17.11% to 22.28%. This modification enhances the biochar’s ability to adsorb nitrogen. Under optimal conditions—pH 7, a dosage of 0.2 grams per 50 milliliters, and a contact time of 270 minutes—SPO achieved a maximum adsorption rate of 32.38 mg per gram and a removal rate of 46.39 mg per liter at an initial TN concentration of 279 mg per liter.
The researchers characterized the SPO using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier-transform infrared spectroscopy (FTIR). They found that the ozone modification created a porous, oxygen-rich surface with functional groups such as hydroxyl (-OH) and carboxyl (-COOH) groups. These features facilitate both chemisorption and multilayer adsorption, making SPO highly effective in nitrogen removal.
The study also delved into the kinetics and isotherms of the adsorption process. The pseudo-second-order model and the Elovich model best described the kinetic data, with R² values of 0.9310 and 0.9484, respectively. The Freundlich isotherm, with an R² of 0.9612, indicated heterogeneous adsorption, suggesting that the SPO’s surface is not uniform and offers multiple sites for nitrogen adsorption.
To further understand the factors influencing nitrogen removal, the researchers employed machine learning models. The extreme gradient boosting (XGB) model, with an impressive R² of 0.998, predicted the removal efficiency. The model identified the adsorption dose and nitrogen concentration as the main drivers of the process, with average SHAP (SHapley Additive exPlanations) values of 7.736 and 3.607, respectively.
Dr. Duong highlights the practical implications of the research: “Our findings demonstrate the potential of SPO as a sustainable and cost-effective adsorbent for nitrogen removal from pig wastewater.” The study showed that SPO could be reused over five adsorption-desorption cycles, retaining 53.27% of its initial capacity. With an estimated production cost of 0.15–0.25 USD per kilogram, SPO outperforms commercial zeolite (0.5–1.0 USD per kilogram) and activated carbon (1–2 USD per kilogram) in cost-effectiveness.
The research published in ‘Materials Research Express’ opens new avenues for sustainable wastewater treatment in the agricultural sector. As Dr. Duong notes, “This technology could be scaled up for industrial applications, providing a viable solution for managing nitrogen-rich wastewater and mitigating its environmental impact.”
The study’s findings could have significant commercial impacts for the energy sector, particularly in regions with intensive pig farming. By offering a sustainable and cost-effective solution for wastewater treatment, SPO could help reduce the environmental footprint of agricultural activities and contribute to the circular economy. As the world grapples with the challenges of climate change and resource depletion, innovations like SPO offer a glimmer of hope for a more sustainable future.