Valorization of sludge materials after chemical and electrochemical treatment
Rumky, Jannatul (2022-10-24)
Lappeenranta-Lahti University of Technology LUT
Acta Universitatis Lappeenrantaensis
School of Engineering Science
School of Engineering Science, Kemiantekniikka
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Wastewater sludge requires effective dewatering, lower metal content, retention of nutrients, and biological stability prior to use for other applications. This thesis presents a comprehensive sludge treatment study by chemical and electrochemical processes to develop alternative scope for sludge usage. Firstly, Fenton-ultrasonication was applied to treat anaerobically digested sludge (ADS) by optimizing three process variables (Fe2+, H2O2, and sonication time). 36 mM of Fe2+, 320 mM H2O2 with 30 min of sonication showed the best performance for total organic carbon (TOC), extracellular polymeric substances (EPS), and heavy metals. Secondly, pressure-driven electro-dewatering (EDW) was assessed by a lab-scale device 5, 15, and 25V. After EDW, dry solid content increased up to 56%, and EDW did not show remarkable effects on heavy metals and E.coli quantification. Thirdly, the effect of inorganic coagulant PTS combined with organic Ce-CTA was investigated on EPS, heavy metals, and nutrient contents in ADS at different levels of pH. pH 3 and 9 showed promising results after coagulation-flocculation and suggested the production of various sludge-based materials (adsorbents, catalysts, building materials, etc.). Finally, sludge beads were prepared for recovery of rare earth elements (REEs) from aqueous effluents. Among the REEs studied, Fenton and hydrochloric acid-treated sludge beads demonstrated a higher affinity towards Sc3+ and Sm3+ ions, displaying the maximum adsorption capacities of 2.80 to2.83 mg/g and 4.03 to 4.16 mg/g. To perform an economic evaluation of Fenton and electro-dewatering systems, chemical costs and required energy were calculated and the electrochemical system found them to be more appropriate for sludge treatment than Fenton.
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