This study investigated the symbiotic structure relationship between mixed algae and activated sludge while treating high-load printing and dyeing wastewater under natural light. The effects of hydraulic retention time (HRT) (12 h, 16 h and 20 h) and aeration rate (0.1–0.15, 0.4–0.5 and 0.7–0.8 L/min) on algal–bacterial symbiosis (ABS) and conventional activated sludge (CAS) systems. Experimental results showed that the ABS system exhibited the best removal performance for chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N) and total phosphorus (TP), which was increased by 12.5%, 23.1% and 10.5%, respectively, and reduced colour 80 times compared with the printing and dyeing wastewater treatment plant. Algae growth could be promoted under lower dissolved oxygen (DO), and the addition of algae could provide more DO to the ABS system. The particle size distribution of sludge in the ABS system was stable, which guaranteed a stable treatment effect. In addition, the COD and colour could be further degraded under the conditions of no external carbon source and longer HRT. It is expected that the present study will provide a foundation for the practical application of the ABS system, and new insights for the treatment of printing and dyeing wastewater.

In this study, an oil-producing freshwater microalgae Chlorella sorokiniana XJK was identified and used for the degradation of disperse blue 2BLN. According to the decolorization rate, the optimal conditions were found to be as follows: initial dye conc. = 60 mg L⁻¹, initial biomass density = 8 × 10⁶ cell per mL, initial pH = 4, light intensity 470 μmol (m² s)⁻¹ and CO₂/air (v/v) ratio = 1%. The decolorization rate reached up to 83% in 6 days cultivation with Chlorella sorokiniana XJK, which also obtained 570 mg L⁻¹ of biomass and 43% of lipid content under the optimum conditions. Moreover, the enzyme activities (laccase and manganese peroxidase) in XJK were determined to be 3.89 U mL⁻¹ and 4.86 U mL⁻¹, respectively, which played a significant role in dye decolorization. The degradation products of the dye were analyzed by UV-vis, FTIR and GC-MS methods. This revealed that the major chromophore group was broken down and disperse blue 2BLN was converted into several low-molecular compounds including dibutyl phthalate, ethylbenzene and ethyl acetate during the microalgae-based treatment. This indicated that XJK shows a potential for dye degradation and providing materials for biofuel.

The microbial fuel cell (MFCs) has dual functions, capable of achieving dye decolorization and synchronous power generation. Despite these advantages, the MFCs have faced challenges related to low electron transfer efficiencies and limited dye treatment capacity in wastewater applications. This work introduces an innovative approach by employing reduced graphene oxide-modified carbon cloth (TP-RGO@CC) anodes, utilizing tea polyphenols as the reducing agent. This modification significantly enhances the hydrophilicity and biocompatibility of the anodes. The MFC equipped with the TP-RGO@CC anode demonstrated a remarkable increase in the maximum power density, reaching 773.9 mW m⁻², representing a 22% improvement over the plain carbon cloth electrode. The decolorization rate of methyl orange (50 mg L⁻¹, pH 7) reached 99% within 48 h. Biodiversity analysis revealed that the TP-RGO@CC anode selectively enriched electrogens producing and organic matter-degrading bacteria, promoting a dual mechanism of dye decolorization, degradation, and simultaneous electro-production at the anode. This work highlights advanced anode materials that excel in effective pollutant removal, energy conversion, and biomass reuse.