A new application of algae-grass biomass within watersheds: Employing hydrochar to control dye pollutant emissions

Suitable filter media can enhance the removal performance of refractory pollutants in constructed wetlands. In this study, locally available fibrous Alternanthera philoxeroides (AP) and protein-rich cyanobacterial (CB) biomass were used to prepare hydrochar materials with high adsorption and retention capacities for characteristic pollutants in printing and dyeing wastewater. A peak H 2 -rich gas yield of 4.57 mol kg −1 was achieved under the optimal feedstock ratio. The resultant hydrochar (CPB-II) demonstrated superior adsorption capacity (51.55 mg g −1 ) for emerging organic contaminants like Congo red (CR), attributable to its high mesoporous-dominated surface area, oxygen-rich functional groups, and structural stability. Adsorption mechanisms involved synergistic pore-filling and chemisorption processes. Systematic evaluation of bypass wetland operational parameters revealed that CPB-II extended breakthrough time to 6.5 h (53.95 % removal) under optimal conditions (9 cm bed height, 0.51 m 3 (m 2 h) −1 hydraulic loading), with breakthrough behavior effectively modeled by the Yoon-Nelson equation. The hydrothermal preparation process enabled simultaneous regeneration, and the hydroxyl radical-oxidized CPB-II maintained 97.45 % of its initial adsorption capacity after five cycles, thus verifying its robust structural stability. This study provides an economically viable alternative to traditional filter media and avoids the secondary pollution issues associated with conventional regeneration. • Hydrochar Filters from Aquatic Waste for Water Pollution Control. • Hybrid Biomass Boosts HGE 2.81 % with Peak Gas Yield. • Extended Breakthrough to 6.5h: 9 cm Media with 0.51m 3 /(m 2 -h) Loading. • ·OH-Mediated CR Mineralization into CO 2 and Water Hydrothermally.