Extracellular polymeric substrates of Chlorella vulgaris F1068 weaken stress of cetyltrimethyl ammonium chloride on ammonium uptake.

This study investigated the influences of cetyltrimethyl trimethyl ammonium chloride (CTAC), an emerging pollutant quaternary ammonium compound (QAC) in municipal effluents, on the transfer and uptake of NH4+ by Chlorella vulgaris F1068 cells removed EPS artificially (EPS-R) and coated EPS naturally (EPS-C) under different scenarios (e.g., the presence or absence of CTAC, different photoperiod sequences (light 12 h: dark 12 h or dark 12 h: light 12 h)). The results showed that the removal of EPS increased the transfer and uptake of NH4+ but the presence of EPS caged NH4+ and effectively weakened the stress of CTAC (<0.5 mg/L) on NH4+ uptake. The main mechanism was considered that CTAC in the concentration range from 0.1 to 0.5 mg/L induced an increased amount of polysaccharide and protein in EPS and thus protected algal normal physiological functions (including cell membrane permeability and glutamine synthetase activity) from the damage of CTAC (0.1 to 0.5 mg/L) regardless of the photoperiod sequences. Thereby, the findings of this study provided an insight into the role of algal EPS in transfer and uptake of nutrients under the coexisted toxics for the future algae-based sewage treatment application.

Importance of controlling pH-depended dissolved inorganic carbon to prevent algal bloom outbreaks.

This study investigated effects of pH-depended inorganic carbon (IC) species and pH on algal growth in the sewage simulation system, and fruitfully discussed the relationships among IC, pH and algal growth by the Monod kinetics. Results showed HCO3(-) significantly increased algal growth by 3.17-6.52 times than that of CO3(2-) and/or glucose when the value of pH was in the range of 8.0-9.5, and also the preferentially utilized indicated by the affinity coefficient (Kp) of HCO3(-), CO3(2-) and glucose (0.17, 15.14 and 31.22, respectively). Meanwhile, the same pH range facilitated HCO3(-) to become a dominated species (e.g., 48.80-93.19% of total IC). More importantly, good linear correlations pairwise existed among pH, IC species and algae growth. These results suggested pH plays a critical role in regulation of IC species and algae growth, which would be an efficient method to control the IC discharge from sewage effluents and weaken bloom outbreak.

Nutrient removal by Chlorella vulgaris F1068 under cetyltrimethyl ammonium bromide induced hormesis.

Toxicants are generally harmful to biotechnology in wastewater treatment. However, trace toxicant can induce microbial hormesis, but to date, it is still unknown how this phenomenon affects nutrient removal during municipal wastewater treatment process. Therefore, this study focused on the effects of hormesis induced by cetyltrimethyl ammonium bromide (CTAB), a representative quaternary ammonium cationic surfactant, on nutrient removal by Chlorella vulgaris F1068. Results showed that when the concentration of CTAB was less than 10 ng/L, the cellular components chlorophyll a, proteins, polysaccharides, and total lipids increased by 10.11, 58.17, 38.78, and 11.87 %, respectively, and some enzymes in nutrient metabolism of algal cells, such as glutamine synthetase (GS), acid phosphatase (ACP), H(+)-ATPase, and esterase, were also enhanced. As a result, the removal efficiencies of ammonia nitrogen (NH4 (+)) and total phosphorus (TP) increased by 14.66 and 8.51 %, respectively, compared to the control during a 7-day test period. The underlying mechanism was mainly due to an enhanced photosynthetic activity of C. vulgaris F1068 indicated by the increase in chlorophyll fluorescence parameters (the value of Fv/Fm, ΦII, Fv/Fo, and rETR increased by 12.99, 7.56, 25.59, and 8.11 %, respectively) and adenylate energy charge (AEC) (from 0.68 to 0.72). These results suggest that hormesis induced by trace toxicants could enhance the nutrient removal, which would be further considered in the design of municipal wastewater treatment processes. Graphical abstract The schematic mechanism of C. vulgaris F1068 under CTAB induced hormesis. Green arrows ( ) represent the increase and the red arrow ( ) represents the decrease.