ABSTRACT
Offshore aquaculture's explosive growth improves the public food chain while also unavoidably adding new pollutants to the environment. Consequently, the protection of coastal marine eco-systems depends on the efficient treatment of wastewater from marine aquaculture. For the sulfamethazine (SMZ) of representative sulfonamides and total organic pollutants removal utilizing in-situ high salinity, this work has established an inventive and systematic treatment process coupled with iron-electrode electrochemical and ultrafiltration. Additionally, the activated dithionite (DTN) was being used in the electrochemical and ultrafiltration processes with electricity/varivalent iron (FeII/FeIII) and ceramic membrane (CM), respectively, indicated by the notations DTN@iron-electrode/EO-CM. Quenching experiments and ESR detection have identified plenty of reactive species including SO4·-, ·OH, 1O2, and O2·-, for the advanced treatment. In addition, the mass spectrometry (MS) and the Gaussian simulation calculation for these primary reaction sites revealed the dominate SMZ degradation mechanisms, including cleavage of S-N bond, hydroxylation, and Smile-type rearrangement in DTN@iron-electrode/EO process. The DTN@iron-electrode/EO effluent also demonstrated superior membrane fouling mitigation in terms of the CM process, owing to its higher specific flux. XPS and SEM confirmed the reducing membrane fouling, which showed the formation of a loose and porous cake layer. This work clarified diverse reactive species formation and detoxification with DTN@iron-electrode/EO system and offers a sustainable and efficient process for treating tailwater from coastal aquaculture.
ABSTRACT
Microplastics (MPs), an emerging pollutant, have been increasingly raising concern due to the potential impacts on aquatic organisms. Moreover, the environmental aged MPs always exhibit different environmental behavior and interaction effect with organic pollutants from virgin MPs. In this work, the single and combined toxicity impact on Chlorella pyrenoidosa, a symbiont representative, has been investigated between MPs (e.g., polyamide microplastic (PA6), 75 µm) and organic pollutants (e.g., sulfamethoxazole (SMX) and dicamba (DCB)). Growth inhibition, chlorophyll accumulation, superoxide dismutase (SOD), malondialdehyde (MDA), and catalase (CAT) were investigated with the primary or UV-aged PA6. Above 0.5 g/L PA6 (primary or UV-aged) inhibited cell growth and chlorophyll accumulation after 96 h cultivation as compared with the control. Besides, the inhibition impacts have enhanced as the UV-aging time extending in the single PA6 systems. The algae growth inhibition rate after 96 h cultivation in both the system i.e., single (PA6: 6.9%) and combined (PA6-SMX: 14.2%, PA6-DCB: 14.9%) was slightly lower than that of exposing in organic pollutants alone (SMX: 23.9%, DCB: 25.0%), while the chl. b concentration in 60 days UV-aged PA6 combined with SMX (1.19 mg/L) or DCB (1.40 mg/L) systems were higher than in single SMX (1.04 mg/L) or DCB (1.33 mg/L) system. In addition, there were several differences of the cellular oxidative stress in the combined system of SMX and DCB. Specially, it was not noticeable of three enzymatic activities for SMX exposing in the presence of primary or UV-aged PA6. While SOD, CAT, and MDA activities was obviously increasing after exposing in PA6 and DCB combined system, indicating the significant synergistic effect on algae cells damage. This research verified the remarkable combined toxicity between UV-aged MPs and organic pollutants on microalgae.
