Revealing dual roles of g-C3N4 in Chlorella vulgaris cultivation

Construction of Bio-TiO2/Algae Complex and Synergetic Mechanism of the Acceleration of Phenol Biodegradation

Microalgae have been widely employed in water pollution treatment since they are eco-friendly and economical. However, the relatively slow treatment rate and low toxic tolerance have seriously limited their utilization in numerous conditions. In light of the problems above, a novel biosynthetic titanium dioxide (bio-TiO₂ NPs)-microalgae synergetic system (Bio-TiO₂/Algae complex) has been established and adopted for phenol degradation in the study. The great biocompatibility of bio-TiO₂ NPs ensured the collaboration with microalgae, improving the phenol degradation rate by 2.27 times compared to that with single microalgae. Remarkably, this system increased the toxicity tolerance of microalgae, represented as promoted extracellular polymeric substances EPS secretion (5.79 times than single algae), and significantly reduced the levels of malondialdehyde and superoxide dismutase. The boosted phenol biodegradation with Bio-TiO₂/Algae complex may be attributed to the synergetic interaction of bio-TiO₂ NPs and microalgae, which led to the decreased bandgap, suppressed recombination rate, and accelerated electron transfer (showed as low electron transfer resistance, larger capacitance, and higher exchange current density), resulting in increased light energy utilization rate and photocatalytic rate. The results of the work provide a new understanding of the low-carbon treatment of toxic organic wastewater and lay a foundation for further remediation application.

Transformation and toxicity dynamics of polycyclic aromatic hydrocarbons in a novel biological-constructed wetland-microalgal wastewater treatment process

In this study, a novel wastewater treatment process combining sequencing batch reactor, constructed wetland and microalgal membrane photobioreactor (BCM process) was proposed, and its performance on removal, transformation and toxicity reduction of polycyclic aromatic hydrocarbons (PAHs) was intensively explored. Satisfactory PAHs removal (90.58%-97.50%) was achieved and molecular weight had significant impact on the removal pathways of different PAHs. Adsorption dominated the removal of high molecular weight PAHs, while the contribution ratio of microbial degradation increased with the decrease of molecular weight of PAHs. More importantly, it was reported for the first time that substituted PAHs (SPAHs) produced by microbial degradation of PAHs would lead to increased toxicity during the BCM process. High PAHs (75.37%-88.52%) and SPAHs removal (99.56%-100.00%) were achieved in the microalgae unit due to its abundant cytochrome P450 enzyme, which decreased the bacterial toxicity by 90.93% and genotoxicity by 93.08%, indicating that microalgae played significance important role in ensuring water security. In addition, the high quantitative relationship (R² = 0.98) between PAHs, SPAHs and toxicity exhibited by regression model analysis proved that more attention should be paid to the ecotoxicity of derivatives of refractory organic matters in wastewater treatment plants.