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.

In order to improve the efficiency of anaerobic sludge digestion, alkaline and high pressure homogenization (HPH) were combined to pre-treat the excess activated sludge. The effect of HPH operating parameters, including homogenization pressure and cycle number, on the performances of anaerobic sludge digestion was studied. The results demonstrated that the performances of sludge disintegration and anaerobic digestion were markedly enhanced by increasing the homogenization pressure. After pretreatment at a homogenization pressure of 60 MPa with one homogenization cycle combined with an alkaline dosage of 0.04 mol/L, the sludge TCOD, VS removal and cumulative biogas production in a mesophilic anaerobic digestion system increased by 24.68%, 18.95% and 95.81%, respectively, in comparison with that with the alkaline pretreatment alone. But the sludge disintegration and biogas production only slightly increased with the increase of homogenization cycle. Considering biogas production and energy-saving, the suitable homogenization operation was selected as homogenization pressure of 60 MPa with once cycle. Relationships between methane yield and sludge disintegration showed that the improved methane production was mainly attributed to the sludge disintegration resulted from combined sludge pretreatment.