Study on the co-pyrolysis behaviors of sewage sludge and Enteromorpha prolifera and the adsorption mechanism of Cr(VI) in water using pyrolysis residue

The thermal–chemical conversion method has significant potential for the recovery of organic matter present in sewage sludge (abbreviated as SS), offering broad market prospects. In this study, a novel approach is proposed for the preparation of a composite adsorbent, named SS-EP, derived from the co-pyrolysis residue of sewage sludge and Enteromorpha prolifera. An orthogonal experiment was designed to investigate the performance of the adsorbent, and the results revealed that the optimal conditions were achieved when the SS proportion was 40%, the concentration of zinc chloride was 0.1 mol/l, the pyrolysis temperature was 500 °C, and the pyrolysis time was 30 min. Notably, the SS-EP composite adsorbent exhibited pronounced efficacy in the removal of Cr(VI) under both acidic and neutral conditions, achieving a removal rate exceeding 97%. Furthermore, the concentration of heavy metals in the leaching solution of the adsorbent was found to be significantly lower than the limit specified in the GB5085.3-2007 standard. Regeneration experiments demonstrated that even after the third regeneration, the SS-EP composite adsorbent maintained a removal rate of 70% for Cr(VI).