ABSTRACT
Effective dewatering is vital for both sludge treatment and resource recovery. This study focuses on converting post-anaerobic digested sludge into biochar to enhance sludge dewatering. The sludge-derived biochar is further modified with polyacrylamide (PAM-ADBC) and applied with sulfuric acid-modified montmorillonite (HMTS) for better performance. Significant advancements in dewatering were noted, even at reduced HMTS (0.1 g/g DS) and PAM-ADBC (25 g/kg DS) dosages. These improvements resulted in a remarkable 41.96% enhancement in capillary suction time (17.2 s) and a notable 20.26% reduction in moisture content (66.33%), respectively, all while maintaining a stable pH level. HMTS, with leached cations, improved dewatering by decomposing the extracellular polymeric substance structure through electro-neutralization to release the internal bound water within sludge flocs. Simultaneously, PAM-ADBC coagulated decomposed sludge particles into larger flocs to form a skeletal structure with itself to discharge internal water in compression dewatering. This study introduces a resource recovery method for anaerobically digested sludge and highlights its potential for sustainable utilization.
ABSTRACT
In this work, a novel heavy metal chelating agent (DTC-SDS) containing dithiocarbamate (DTC) was synthesized using sodium dodecyl sulfate (SDS), formaldehyde, and carbon disulfide. DTC-SDS has excellent trapping performance under pH 1-7 and initial concentrations 100-500 mg/L. With the increase in adsorbent dose, the adsorption amount of DTC-SDS increases and then decreases, and the optimized dosage of DTC-SDS is 0.02 g. The DTC-SDS adsorbent exhibits superior adsorption capacity (191.01, 111.7, and 79.14 mg/g) and high removal rates (97.99%, 98.48%, and 99.91%) for Mn2+, Zn2+, and Pb2+ respectively, in wastewater. Such remarkable adsorption performance could be attributed to the strong trapping effect on heavy metal ions by the C-S bond of DTC-SDS. The liquid adsorbent was in full contact with heavy metal ions, which further enhanced the complexation of heavy metal ions. The adsorption isothermal model showed that the adsorption process was typical of Langmuir monomolecular layer adsorption. Kinetic studies showed that the pseudo-second-order kinetic model fits the experimental adsorption data better than the pseudo-first-order kinetic model. In the ternary metal species system (Mn2+, Zn2+, and Pb2+), DTC-SDS preferentially adsorbed Pb2+ due to its highest covalent index. The main controlling step is the chemical interaction between the active groups of DTC-SDS and the heavy metal ions. This work provides valuable insights into the adsorption of heavy metal ions onto dithiocarbamate, which could guide the development of other heavy metal chelating agents and be beneficial for developing novel treatments of wastewater contaminated with heavy metals.
