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.

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The pyrolysis characteristics and kinetics of pre-dried dewatered sewage sludge under different heating rates (10, 20, and 30 °C/min) were investigated by thermogravimetric analyzer-fourier transform infrared analysis (TG-FTIR) and differential scanning calorimetry (DSC), and a heated tubular reactor. The thermal analysis results showed that four weight loss zones (<165, 165–400, 400–600, and >600 °C) were observed in TG curve, and a higher heating rate led to the increase of the maximum devolatilization rate and the higher temperature corresponding to the peak. The activation energy of different heating rate (10, 20, and 30 °C/min) was 70.0, 60.6 and 65.0 kJ/mol, respectively. The FTIR analysis of gaseous products indicated the concentrations of CO₂ and CO increased steadily with the increased heating rate, while the concentration of CH₄ first increased then decreased. Moreover, the yield of gaseous products and bio-oil increased with the increasing of the heating rate. Finally, the surface structure of chars and the chemical properties of bio-oil obtained were characterized using nitrogen adsorption, scanning electron microscopy, elemental analysis and gas chromatography–mass spectrometry. Overall, the results highlighted that pre-dried dewatered sewage sludge can be effectively converted into biofuel and porous material.

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Anaerobic digestion has been widely applied throughout the world for lignocellulosic biomass treatment and energy recovery. However, the solid digestate from anaerobic digestion still contains a rather large fraction of poorly anaerobic degradable lignocellulosic fibers due to inhibition of lignin, which deeply limits the bioenergy production from lignocelullosic biomass. Therefore, a novel fungal pretreatment method using P. sajor-caju and T. versicolor was investigated to advance the solid-state fermentation of solid digestate and improve the production of fermentative volatile fatty acids (VFAs). The results showed that a maximum VFA yield of 240 mg COD/g VS was obtained from solid digestate pretreated by P. sajor-caju in 6 weeks, which was 1.17-fold and 1.24-fold higher than that of the autoclaved group and raw substrate, respectively. The mechanisms indicated that these fungal strains could grow on the solid digestate and secrete ligninolytic enzymes such as laccase and manganese peroxidase to degrade lignin in different extents. Besides, fungal pretreatment substantially changed the solid digestate characteristics such as cellulose/lignin ratio and the presence of specific functional groups. Moreover, fungal pretreatment using P. sajor-caju effectively damaged the structure and increased surface area and pore size of the solid digestate, which is beneficial to further VFA production.

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Biomimetic mineralization has emerged as a novel tool for generating excellent supports for enzyme stabilization. In this work, protamine was used to induce titanium (IV) bis(ammonium lactato) dihydroxide (Ti-BALDH) into titania nanoparticles. This biomimetic titanification process was adopted for laccase immobilization. Laccase-biotitania biocatalyst was prepared and the effect of different parameters (buffer solution, titania precursor concentration, protamine concentration, and enzyme loading) on the encapsulation efficiency and recovery of laccase were evaluated. Compared with free laccase, the thermal and pH stability of immobilized laccase were improved significantly. In addition, laccase loaded on titania was effective at enhancing its storage stability. After seven consecutive cycles, the immobilized laccase still retained 51% of its original activity. Finally, laccase-biotitania biocatalysts showed good performance on decolorization of malachite green (MG), which can be attributed to an adsorption and degradation effect. The intermediates of the MG degradation were identified by gas chromatography-mass spectrometry (GC–MS) analysis, and the most probable degradation pathway was proposed. This study provides deeper understanding of the laccase-biotitania particles as a fast biocatalyst for MG decolorization.

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Azo dyes are very resistant to light-induced fading and biodegradation. Existing advanced oxidative pre-treatment methods based on the generation of non-selective radicals cannot efficiently remove these dyes from wastewater streams, and post-treatment oxidative dye removal is problematic because it may leave many byproducts with unknown toxicity profiles in the outgoing water, or cause expensive complete mineralization. These problems could potentially be overcome by combining photocatalysis and biodegradation. A novel visiblelight-responsive hybrid dye removal agent featuring both photocatalysts (g-C₃ N₄ -P₂₅ ) and photosynthetic bacteria encapsulated in calcium alginate beads was prepared by selfassembly. This system achieved a removal efficiency of 94% for the dye reactive brilliant red X-3b and also reduced the COD of synthetic wastewater samples by 84.7%, successfully decolorized synthetic dye-contaminated wastewater and reduced its COD, demonstrating the advantages of combining photocatalysis and biocatalysis for wastewater purification. The composite apparently degrades X-3b by initially converting the dye into aniline and phenol derivatives whose aryl moieties are then attacked by free radicals to form alkyl derivatives, preventing the accumulation of aromatic hydrocarbons that might suppress microbial activity. These alkyl intermediates are finally degraded by the photosynthetic bacteria.

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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. @en