UV-B Irradiation Effect on Microalgae Performance in the Remediation of Effluent Derived from the Cigarette Butt Cleaning Process

Abstract

In this study, the potential of ultraviolet B (UV-B) radiation to alleviate the effects of pollutants in cigarette butt wastewater (CBW) was investigated using different Chlorella sorokiniana strains (F4, R1 and LG1). Microalgae were treated with UV-B (1.7 W m^-2) for 3 days prior to their exposure to CBW and then incubated for 4 days in the absence or presence of UV-B. UV-B-untreated microalgae were used as the control. Comparative physiological responses, including photosynthetic pigments and non-enzymatic antioxidants, as well as nicotine and nicotyrine removal, were evaluated in 7-day cultures. UV-B treatments did not negatively impact algal chlorophyll or carotenoid production. UV-B acclimation was strain-dependent, correlating with native environment adaptations and genetic constitutions. UV-B as a pretreatment had long-term positive effects on non-enzymatic antioxidant capacity. However, LG1 needed more time to readjust the pro-oxidant/antioxidant balance, as it was the most UV-B-sensitive. Phenolic compounds played an important role in the antioxidant system response to UV-B, while flavonoids did not contribute to the total antioxidant capacity. Although cross-resistance between UV-B and CBW was observed in F4 and R1, only R1 showed nicotine/nicotyrine catabolism induction due to UV-B. Overall, the results suggest that UV-B activates defense pathways associated with resistance or tolerance to nicotine and nicotyrine.

Keywords: Chlorella sorokiniana; flavonoids; nicotine; nicotyrine; non-enzymatic antioxidants; phenolic compounds; photosynthetic pigments; ultraviolet light.

Figure 1

Effect of UV-B on photosynthetic pigments in microalgae subjected to cigarette butt (CB)-derived wastewater treatment. (A) Chlorophyll a (Chla), (B) chlorophyll b (Chlb), (C) carotenoids (Car) and (D) the ratio of Chla to Chlb (Chla/b) were determined in each microalgal strain (F4, R1 and LG1) in 7-day cultures. Microalgae were exposed to wastewater and sequential (3 d UV-B) or parallel (7 d UV-B) UV-B treatments. The UV-B exposure level was set at 1.7 W m⁻² and supplemented with 70 μmol m⁻¹ s⁻¹ photosynthetically active radiation (PAR) for 20 min each day. The control microalgal group only received PAR (No UV-B). For more details, see Section 4. Different letters represent significant differences (p < 0.05) between UV-B treatments within the same strain. Data are expressed as means of 4 different replicates ± standard error (SE).

Figure 2

Effect of UV-B the non-enzymatic antioxidants in microalgae subjected to cigarette butt (CB)-derived wastewater treatment. (A) Total antioxidant capacity (TAC), (B) phenolic compounds and (C) flavonoids were determined in each microalgal strain (F4, R1 and LG1) in 7-day cultures. Microalgae were exposed to wastewater and sequential (3 d UV-B) or parallel (7 d UV-B) UV-B treatments. The UV-B exposure level was set at 1.7 W m⁻² and supplemented with 70 μmol m⁻¹ s⁻¹ photosynthetically active radiation (PAR) for 20 min each day. The control microalgal group only received PAR (No UV-B). For more details, see Section 4. Different letters represent significant differences (p < 0.05) between UV-B treatments within the same strain. Data are expressed as means of 4 different replicates ± standard error (SE).

Figure 3

Effect of UV-B on the microalgal removal capacity of main toxic pollutants in cigarette butt (CB) wastewater. The relative abundance of (A) nicotine and (B) nicotyrine was determined in the wastewater after microalgal-based remediation by 7-day cultures. The abundance is expressed in % (kcounts/kcounts) and was obtained by its comparison with the abundance in the respective untreated wastewater (without microalgal cells), which represented 100%. Microalgal strains (F4, R1 and LG1) were exposed to wastewater and sequential (3 d UV-B) or parallel (7 d UV-B) UV-B treatments. The UV-B exposure level was set at 1.7 W m⁻² and supplemented with 70 μmol m⁻¹ s⁻¹ photosynthetically active radiation (PAR) for 20 min each day. The control microalgal group only received PAR (No UV-B). For more details, see Section 4. Different letters represent significant differences (p < 0.05) between UV-B treatments within the same strain. Data are expressed as means of 4 different replicates ± standard error (SE).

Figure 4

Multiple factor analysis (MFA) of physiological and analytical data on microalgal-based remediation of wastewater from a cigarette butt (CB) cleaning process, coupled with UV-B treatment. B: No UV-B irradiation; 3d: 3-day UV-B treatment; 7d: 7-day UV-B treatment; Chla.b: ratio of Chla to Chlb; a, b, c and d indicate replicates.

Figure 5

Experimental design of the study. All treatments were carried out under PAR. UV-B irradiation was applied either before (3 d UV-B) or in parallel to (7 d UV-B) a 4-day wastewater treatment. The control microalgal group only received PAR (No UV-B). Another parallel untreated wastewater group (no microalgae) was included, and it was exposed to each UV-B treatment (No UVB, 3 d UV-B and 7 d UV-B). Sampling was performed in 7-day cultures. See Section 4.2 and Section 4.3 for details of treatment conditions. CB; cigarette butt.