Removal of nitrogen and phosphorous from blackwater via an integrated nature-based system: hybrid-vertical flow constructed wetland, upflow anaerobic fixed biofilm reactor, and granular activated charcoal column along with in situ electrochlorination disinfection

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The hybrid vertical-flow constructed wetland (H-VFCW) sequenced with an upflow anaerobic fixed biofilm reactor (UAFBR) was developed to treat blackwater for single households. The H-VFCW filter bed layer's redox zonation and hydraulic retention time (HRT) were designed optimally with the potential of simultaneous nitrification, denitrification, and enhanced biological phosphorous removal. The UAFBR optimisation for residual nitrate removal was based on the carbon -nitrogen ratio, HRT, and biofilm growth on carriers. Complete disinfection was achieved by optimised in situ electrochlorination by dosing 0.16% sodium chloride, with 20 min of electrolysis and 44.48 Am⁻² of current density. The power consumption was 1.81±0.14 KWhm⁻³. Ammonia volatilisation was studied on a granular activated charcoal column (GACC) column to remove residual TAN as the final treatment. The integrated treatment system removed 98.63 ± 0.15% chemical oxygen demand (COD), 97.09 ± 0.19% total nitrogen (TN), 93.96 ± 0.34% nitrate (NO₃⁻), 97.92 ± 0.2% TAN, 99.62 ± 1% orthophosphate (PO₄³⁻), 87.49 ± 0.36% total suspended solids (TSS), and 100% Coliform, with the final effluent pH of 8.4 ± 0.08. The microbial and functional annotation diversity of the UAFBR biofilm was studied. The treatment systems achieved the Central Pollution Control Board (India) effluent discharge standards.