A paper titled “Ozone-functionalized acacia wood sawdust biochar for total nitrogen adsorption from pig wastewater,” published in Materials Research Express by Thi Minh Hoa Duong, Huu-Tap Van, Thi Pha Tran, Duy Hai Nguyen, Thi Cuc Luu, Diep Anh Do, Thi Bich Hanh Nguyen, and Thi Quynh Nga Luong, addresses the severe environmental problem caused by nitrogen-rich pig wastewater. This waste stream, a significant challenge for intensive livestock farming, typically contains total nitrogen (TN) concentrations ranging from 500 to 1,500 mg/L. The study focused on creating and characterizing a novel, highly efficient adsorbent, SPO (ozone-modified biochar), from locally abundant acacia wood sawdust to mitigate this pollution through adsorption.

The untreated biochar (SP600), produced by pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More, had a moderate adsorption capacity. However, the subsequent treatment with ozone gas (O3​) significantly enhanced its performance. The ozonation process successfully altered the biochar’s surface, increasing its oxygen content at the optimal ozone flow rate. This modification introduced key oxygen-containing functional groups such as hydroxyl (-OH) and carboxyl (-COOH), confirmed by FTIR and EDS analyses. These groups enhance the biochar’s hydrophilicity and create new binding sites, facilitating a hybrid adsorption mechanism involving both chemisorption (strong chemical interaction) and multilayer adsorption (physical buildup).

The study found that special ozonated biochar (SPO) works best at a neutral pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More of 7. At this level, the biochar can easily attract and capture ammonium ions, which are the main nitrogen pollutants in pig wastewater. The ideal contact time was about 270 minutes, after which the biochar became saturated and could not hold more nitrogen.

Further analysis showed that nitrogen sticks to the biochar mainly through chemical bonding. The biochar also has many different types of surface sites, allowing nitrogen to form multiple layers on it rather than just one. Machine learning supported these findings, showing that the most important factors affecting nitrogen removal are how much biochar is used and how much nitrogen is present in the wastewater. SPO is also very cost-effective to produce, costing only $0.15 to $0.25 per kilogram because it is made from cheap and abundant acacia sawdust. This makes it far more affordable than commercial products like zeolite or activated carbonActivated carbon is a form of carbon that has been processed to create a vast network of tiny pores, increasing its surface area significantly. This extensive surface area makes activated carbon exceptionally effective at trapping and holding impurities, like a molecular sponge. It is commonly More. The material can be reused as well: even after five cycles, SPO kept more than half of its original capacity, making it practical for repeated use before being converted into a useful biofertilizer.

The best dosage found was 0.6 g per 50 mL of wastewater, which removed about 60.75% of the nitrogen. Overall, SPO is an effective, affordable, and environmentally friendly option for treating pig wastewater, especially in rural or decentralized systems. The Extreme Gradient Boosting (XGB) machine learning model further confirmed the efficiency of SPO, achieving very high accuracy . It also highlighted that adsorbent dosage and initial nitrogen concentration are the key factors influencing performance. Altogether, these results show that SPO is a sustainable, scalable, and circular-economy solution that transforms waste pollution into valuable biofertilizer.

Source: Duong, T. M. H., Van, H.-T., Tran, T. P., Nguyen, D. H., Luu, T. C., Do, D. A., Nguyen, T. B. H., & Luong, T. Q. N. (2025). Ozone-functionalized acacia wood sawdust biochar for total nitrogen adsorption from pig wastewater. Materials Research Express, 12(4), 045009.