Two types of novel municipal sewage sludge (SS) combined TiO ₂ photocatalysts (ST ₁ and ST ₂ ) were synthesized through calcination treatment under different atmospheres (air and N ₂ ). The morphology, structure, and chemical states of photocatalysts were characterized by SEM, XRD, EDS, FT-IR, Raman UV–Vis, BET, and TG-IR. The results showed that ST ₂ consisted of a mesoporous graphene-like structure (20.02 nm) displayed exhibited better visible light photocatalytic performances and the highest BET surface area and pore volume (92.97 m ² g ⁻¹ and 0.46 cm ³ /g). The doping of Carbon and transition metals (Al, Mg) in TiO ₂ strengthened visible-light response by lowering the band gap. The photocatalytic ability is evaluated in the degradation of tetracycline, which is a typical antibiotic in the aquatic environment. The ST ₂ photocatalytic efficiency under visible light than that of ST ₁ and TiO ₂ . The enhancement is formed together by porous surface and lower band gap of ST ₂ , which could offer more active sites and facilitate faster electron-hole pair separation. In addition, the sludge-TiO ₂ calcination in N ₂ (ST ₂ ) has the potential to reduce CO ₂ emission while recovering more energy from the sludge, which turned out to be a more cost-effective way to reutilization of sewage sludge compared with that of calcination in air.

Three identical pilot-scale flat-sheet membrane-coupled aerobic digesters for simultaneous sludge thickening and reduction (MSTR) were performed in parallel under a hydraulic retention time (HRT) of 14.6 h for 15 days. In the first 8 days, the stepwise destruction of waste activated sludge (WAS) flocs, i.e., dispersion from the outer to inner part, was observed likely due to the variation of dissolved oxygen concentration (Step 1: from 7.0 to 2.5 mg/L, Step 2: from 2.5 to 0.5 mg/L). During the process, the concentration of extracellular polymeric substances (EPS) first decreased from about 170.0 to 140.8 mg/g volatile suspended solids (VSS), then from 140.8 to 67.7 mg/g VSS, resulting in the much higher concentration of soluble organic matters and small particles (1–20 lm) in Step 2. Meanwhile, the ratio of protein like substances to humic acids in the EPS first increased from 0.5 to 0.7, then decreased from 0.7 to 0.4. After 8 days, the regroupment of sludge fraction and successive increase in fine particle could also correspond to the slight change of EPS concentration. Moreover, the degree of humification of the supernatant could well correspond to the reduction degree of the sludge.