Many of humanity's significant issues in the twenty-first century are due to wastewater-related water quantity and water quality issues1. Industrial wastewaters can account for a significant portion of municipal wastewaters and must be considered for proper wastewater treatment plant operation 2–4. Hence execution of an effective treatment solution remains a challenge1. As a result, wastewater treatment is necessary to protect the environment and public health. Consequently, hazardous chemicals found in wastewater must be converted into secure end products that can be safely disposed of in domestic waterways5 (Bhargava 2016). It is also critical to recycle and recover the valuable components found in wastewater in compliance with the country's legal standards6.
To treat contaminants in chemical wastewater, technological advances are continuously being explored. Recently, wastewater treatment with Bio Char (BC) has emerged as a new technology due to it several unique characteristics that set it apart from other alternatives. BC is a carbon-rich material made of different biomasses7. The BC manufacturing process relies on the thermal breakdown of basic materials. The pyrolysis process is the most frequent thermal decomposition technique. For bio charproduction, the pyrolysis method is usually carried out at different temperatures of 300 and 500°C8. The pyrolysis process' relative yield is determined by operating parameters such as time, heating rate, temperature, nitrogen flow, and so on9,10. Furthermore, the type of biomass feedstock and its water content substantially impact on the structure and properties of BC, and hence its adsorption capacity9. Several chemical, physical, and molecular changes occur during the pyrolysis process, resulting in the adsorption and immobilization of the target pollutant11. Adsorption is influenced by the physical and chemical properties of BC (surface area, porosity, surface charge, functional groups, and mineral content)12. BC as a filter medium to treat water and wastewater is getting popular with unique physical and chemical properties13. When compared to conventional soil and sand filtration systems, employing BC as a medium for wastewater treatment can improve treatment efficiencies and minimize the spread of contamination from hazardous chemicals in treated flow streams13,14.
For BC modification, many engineering methods have been developed and employed. BC engineering is the process of producing activated or modified forms of BC15. Activation is necessary to improve BC's physical properties (specific surface area and pores) and its absorption capacity. A physical activation method or a chemical activation method can be used to complete the process10. BC can be activated physically or chemically to produce activated carbon with the desirable properties. Chemical activation is a heat treatment method in which BC combines with a chemical activating substance at 450 to 900°C10. Chemical activation agents for BC activation in the industry include Zinc Chloride (ZnCl2), Sulphuric acid (H2SO4), Phosphoric acid (H3PO4), and Potassium Hydroxide (KOH)16,17. Chemical activation has many advantages over physical activation, including a larger surface area, lower temperature, higher carbon yield, quantitative and qualitative micro porosity, and higher efficiency. Chemical activation is more effective than physical activation because of these advantages10.
BC's surface is characterized by heterogeneity, which permits a range of sorption processes to occur. With the nature of the contaminants and the chemical properties of the adsorbent surface of BC, the adsorption mechanism differs18. The adsorption mechanisms of organic pollutants are characterized by electrostatic attraction, π-π electron-donor acceptor interaction, hydrogen-bonding, complex adsorption, and hydrophobic interactions 18,19. The adsorption mechanisms of inorganic contaminants such as heavy metals are addressed by surface precipitation under alkaline conditions, ion exchange, complexation, and cationic and anionic electrostatic attraction. Due to the dissociation of oxygen-containing functional groups such as carboxylic, hydroxyl, phenolic (hydroxyl), and carbonyl, groups on the surface of BC are generally negatively charged, producing electrostatic attraction between BC and positively charged molecules19,20. BC's high price limits it from being used as an adsorbent in wastewater treatment and other applications21. To develop a sustainable waste removal technology, BC must be produced from abundant and inexpensive waste materials.
The primary sources of feedstock for BC are biowaste from agriculture, the food sector, and forestry22. Wood chips and pellets, tree cuttings, bagasse, distiller grains, oil and juice press cakes, rice husks, and crop residues are among the most used substrates23. Also, Sewage sludge, poultry litter, excrement, bones, dairy manure can be used to prepare BC24.
Currently, researchers have been focusing their research on invasive plants in terms of developing BC as a value-added product and an environmentally safe and cost-effective solution for a wide range of applications, including pollution remediation 25,26.
Invasive plants are rapidly expanding over the worldwide, posing a growing danger to natural ecosystems27. They cause watercourse obstruction, dissolved oxygen depletion, water chemistry changes, and environmental contamination, rendering prospective water sources useless for economic purposes 28. As a result, developing new and cost-effective techniques to manage invasive species is crucial. Recent advancements in biochar technology enable the creation of a new strategy for controlling invasive plants by turning them into value-added products. Pyrolysis technology can thus be used as an alternative and cost-effective management technique to prevent their invasion29. During the pyrolysis process, biomass undergoes a variety of physical, chemical, and molecular changes, which consequently contribute to the adsorption and immobilization of the relevant pollutant30. Compared to other biomass waste, the application of aquatic invasive plants as BC feedstocks is more cost-effective and readily accessible31. As a result, aquatic invasive plant species could be a potential feedstock for BC manufacturing while also providing extra ecosystem benefits. Invasive plant resource utilization has proven to be a practical approach for controlling and managing invasive plants, not only because it reduces costs of prevention and control but also because it transforms waste into a useful resource. The research work focuses on the production of BC using a common invasive aquatic plant in Sri Lanka. In addition, this study aims to propose a sustainable strategy for the management of invasive aquatic plants.