Techno-economic evaluation of decentralised multi-nutrient biofilters using agro-waste: a preliminary computational screening framework

Decentralised, nature-based biofiltration is vital for industrial nutrient remediation, yet scalability is constrained by hydrochemical variation and spatial logistics. This study simulated the large-scale performance and life-cycle costs of five unmodified agro-waste matrices: spent tea waste (STW), rice husk (RH), sawdust (SD), roasted groundnut shell (RGS), and sugarcane bagasse (SB) at sugar mill nala (Meerut, India) under strict Central Pollution Control Board limits. The multi-ion interferences tracked in this framework represent a qualitative bounding analysis and theoretical interpretation of performance boundaries rather than a dynamic mechanistic layout. Monovalent nitrate capture was crippled by outer-sphere electrostatic shielding and valency competition from divalent sulphates. For SD, this forced an unfeasible daily peak mass allocation of 99.90 kg and an expansive volumetric bed footprint of 346.71 L m−3 effluent, driving the 5-year Life-Cycle Cost to an unviable ₹43,32,74,062.50 ($4,590,740.23). Conversely, co-located SB bypassed market shocks, logging logistics costs of ₹0.00 via on-site waste-recovery loop. Biochemically, SB formed covalent, inner-sphere coordination complexes via ligand exchange with phosphate groups, resisting background salinity and pH drops. Mass-energy modelling confirmed thermal recovery of spent SB in co-generation boilers, upcycling captured nutrient into slow-release fertiliser.