Comprehensive effects of microplastics on algae-laden surface water treatment by coagulation-ultrafiltration combined process: Algae cultivation, coagulation performance and membrane fouling development.

In coastal areas, the surface water has been simultaneously exposed to the algae blooms caused by eutrophication and the microplastics (MPs) pollution originating from active human activities. As a practical alternative to address these issues in drinking water plant, coagulation-ultrafiltration combined process is still confronted with the limited understanding about the comprehensive effects of MPs on algae-laden surface water (ASW) treatment. Considering the migration of MPs in nature environment and drinking water treatment process, this study first aims to systematically investigate the influence of MPs on algae cultivation, coagulation performance and membrane fouling development. The results of algae cultivation indicate that MPs stimulated the algae activity by 58 % and then constantly suppressed the secretion of protein-like, humic-like and polysaccharide-like metabolites. The variation of particle size distribution and zeta potential confirm that MPs acted as nuclei to facilitate the development of large coagulation flocs with an increasing average size from 82.6 µm to 107.6 µm, during which the negatively charged pollutants were neutralized and removed from ASW. According to the SEM images, MPs could destroy the structure of fouling layer on 50 kDa membranes during the filtration of ASW coagulation effluent. Its synergistic effect with the enhanced coagulation performance and the suppressed EOM secretion contributed to the alleviation of membrane fouling caused by overlapped large-sized foulants. However, the interaction between the enriched organic foulants by MPs and the deposited coagulants on 300 kDa membranes facilitated the development of cake layer, leading to the deterioration of membrane permeability. This study emphasizes the importance in concerning the existence of MPs during the treatment of ASW by coagulation-ultrafiltration combined process and their exact influence in water purification efficiency.

Enhanced electrooxidation/electrocoagulation-ultrafiltration membrane process with S2O42- for saline algae-containing surface water treatment: Purification and membrane performance.

The surface water in coastal areas involving algae, is often affected by saline and emerging contaminants caused by saltwater intrusion, and expanding aquaculture industry. Therefore, it is necessary to conduct studies to address the issues that affect ecological safety and health of aquatic environments. This study presents the development of an enhanced electrooxidation/electrocoagulation-ultrafiltration (EO/EC-UF) membrane process using S2O42- (DTN@EO/EC-UF) for the treatment of saline water containing algae. Our results have shown that significant removal of NH3-N (95.1 %), UV254 (89.4 %) and algae (75.7 %) was achieved with the addition of S2O42- (DTN). Additionally, an optimal DTN dosage of 40 mg/L was used in the DTN@EO/EC process to enhance water purification, utilizing reactive species such as SO4·- and ·OH. After coupling with the ultrafiltration (UF) process, optimal operating conditions (DTN: 40 mg/L, current density: 4.65 mA/cm2, electrolysis: 60 s) were applied to treat the saline algae-containing surface water. The generated free chlorine, including NHCl2, accounted for approximately 22 % (0.14 mg/L). In addition, DTN significantly improved the ceramic membrane's permeability and anti-fouling characteristics, with a maximum increasing specific flux from 0.76 to 0.93, mainly attributing to the reduced the irreversible fouling resistance. Furthermore, we discovered that common membrane cleaning using acid or base enhanced the DTN@EO/EC-UF process. In conclusion, this study established an innovative DTN@EO/EC-UF process with excellent performance in terms of water purification and membrane self-cleaning. The results provided a promising alternative for treating saline algae-containing surface water.

Salt tide affecting algae-laden micropolluted surface water treatment and membrane performance based on BDD electro-oxidation coupled with ceramic membrane process.

Harmful algal blooms pose an emerging threat to freshwater ecological security and human health, necessitating further study in offshore areas. In this work, boron-doped diamond electro-oxidation (BDD/EO) coupled with a ceramic membrane filtration was employed aiming to assess the salt tide affecting algae-laden water treatment involving with various natural organic matters (e.g., HA, SA, and BSA). The results have demonstrated that BDD/EO remove chlorophyll from the algae-laden water effectively due to the inactivation of algal cells. Moreover, considering the influence of salt tide, NH3-N would be mainly oxidized through the in-situ generated active chlorine at the electrode-liquid interface. In addition, in three kinds of salt tide affecting algae-laden water, TOC content in BSA group was decreasing remarkably after BDD/EO with TOC removal efficiency above 80%; while those in HA and SA groups had no obvious reducing due to the more algae cells breakage synchronous with HA and SA removal. Based on the fluorescent characteristics and particle size distribution, the generated small molecular organics after electro-oxidation might raise the pore blockage probability and the hydrophobic organic and fluorescent substances were preferentially oxidized in BDD/EO process being beneficial to reducing membrane fouling. Besides, the membrane special flux in three groups were decreasing significantly and the irreversible fouling resistance in SA group accounted for a larger proportion of the total resistance than those of HA and BSA. At last, in BDD/EO-CM process, macromolecular substances degradation rate was greater than that of small molecules based on the molecular weight distribution in three groups of salt tide affected algae-laden water treatment. In a word, this work provides effective and innovative strategies for the harmful algal bloom control and contributes interesting insights of membrane fouling performance of electrochemical coupled ultrafiltration membrane process.