Utilizing a modified down-flow sponge reactor for the treatment of industrial sewage sludge, offering a solution to the fertilizer crisis through agricultural applications

Untreated sewage poses severe threats to ecosystems, public health, and economies, particularly in developing nations where treatment facilities often fail due to poor maintenance. Concurrently, rising natural gas prices have escalated chemical fertilizer costs. This study evaluates an eco-friendly biological and chemical sewage sludge treatment using a modified Down-flow Hanging Sponge (DHS) reactor with organic additives at hydraulic retention times of 3 and 6 hours. The modified DHS system demonstrated high removal efficiency for organic pollutants, suspended solids (COD, BOD, TSS, VSS), oil/grease, nitrogenous compounds (NH3, NO3−), total coliforms, and toxic heavy metals (Pb,Ni,Cu,Zn,Cr,Cd,Fe). Agricultural trials on radish plants (Raphanus sativus) under identical cultivation conditions revealed significantly lower heavy metal accumulation in plants fertilized with DHS-treated sludge compared to untreated sludge. These findings confirm that modified DHS reactors offer an effective, sustainable, and cost-efficient solution to treat sewage sludge while producing a safe, nitrogen-rich alternative to synthetic fertilizers.