In a recent study published in ACS Omega, authors Khandgave Santosh Sopanrao and Inkollu Sreedhar developed a new, cost-effective material to combat heavy metal contamination in wastewater. The article, titled “Novel Phosphoric Acid-Modified Biochar-Chitosan Nanocomposite for an Efficient and Cost-Effective Multimetal Removal from Wastewater,” introduces a phosphoric acid-modified biochar-chitosan nanocomposite (PGB-CS) designed for the removal of copper (Cu2+), nickel (Ni2+), and zinc (Zn2+) from industrial wastewater.

The presence of heavy metals in water has significant consequences for human health and aquatic ecosystems, leading to serious health problems such as neurological disorders, kidney damage, and cancer. While several methods exist for treating heavy metal contamination, adsorption is widely used due to its economic viability and ease of regeneration. The new PGB-CS adsorbent is a sustainable and efficient solution for this ongoing problem.

The PGB-CS adsorbent was synthesized at an optimal 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 temperature of 550∘C for two hours. This process created a mesoporous material with a high surface area of 167.98 m2/g and a pore diameter of 9.18 nm. The material’s structure, low crystallinity, and thermal stability, along with an abundance of surface functional groups like amine, carboxylic, and hydroxyl, were key to its success. These properties contributed to a low production cost estimated at $8.13 per gram (Rs. 682.14/g), with chitosan accounting for over 80% of that cost.

Using a systematic three-level optimization approach, the researchers determined the optimal conditions for maximum metal removal. Through a Box-Behnken design of response surface methodology, the study achieved maximum adsorption capacities of 221.56 mg/g for Cu2+, 175.47 mg/g for Ni2+, and 127.46 mg/g for Zn2+ under optimal conditions. Further 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 optimization improved these capacities to 249.78 mg/g for Cu2+, 191.48 mg/g for Ni2+, and 145.91 mg/g for Zn2+. The adsorption process was rapid, with equilibrium times of 36 minutes for Cu2+ and 20 minutes for both Ni2+ and Zn2+. The process followed a pseudo-second-order kinetic model, indicating that chemisorption was the primary rate-limiting step. The adsorption was also confirmed to be a monolayer process by the Langmuir isotherm model.

The study also tested the PGB-CS adsorbent on real industrial effluent from a battery manufacturing facility. The adsorbent, with a dosage of 1 g/L and a contact time of 20 minutes, achieved removal efficiencies of 83.19% for Cu2+, 61.94% for Ni2+, and 52.34% for Zn2+. The PGB-CS adsorbent showed a higher affinity for copper ions compared to nickel and zinc ions, which was attributed to copper’s higher electronegativity and smaller ionic size. The PGB-CS material maintained its stability and reusability over eight regeneration cycles, retaining desorption efficiencies of 53.17%, 51.97%, and 51.07% for Cu2+, Ni2+, and Zn2+, respectively. The regeneration process used H2​SO4​, HNO3​, and HCl as eluting agents. The adsorption mechanisms were identified as a combination of surface complexation, ion exchange, and electrostatic attraction.

Overall, the study demonstrated that PGB-CS is a promising material for treating heavy metal-contaminated industrial wastewater due to its effectiveness, low production cost, and reusability. Further research is suggested to focus on column studies to evaluate long-term operational feasibility, address challenges like pressure drop and bed compaction, and explore cheaper alternatives for chitosan to further reduce costs.

Source: Sopanrao, K. S., & Sreedhar, I. (2025). Novel Phosphoric Acid-Modified Biochar-Chitosan Nanocomposite for an Efficient and Cost-Effective Multimetal Removal from Wastewater. ACS Omega.