Increasing oxytetracycline and enrofloxacin concentrations on the algal growth and sewage purification performance of an algal-bacterial consortia system.

Oxytetracycline (OTC) and enrofloxacin (EFX) pollution in surface water are very common. Using the algal-bacterial consortia system to remove antibiotics remains to be further studied. In this study, the algal growth and sewage purification performance were studied in an algal-bacterial consortia system with different concentrations of antibiotics. The enzyme activity, malondialdehyde content, chlorophyll-a content, extracellular polysaccharide, and protein content of algae were also tested. It was found that the algal growth was promoted by low-dose antibiotics, 21.83% and 22.11% promotion at 0.1 mg L-1 OTC and EFX, respectively. The nutrients and antibiotics removals of the low-dose groups (OTC <5 mg L-1, EFX <1 mg L-1) were not affected significantly. More than 70% of total organic carbon and total phosphorus, and 97.84-99.76% OTC, 42.68-42.90% EFX were removed in the low-dose groups. However, the algal growth was inhibited, and the nutrients removals performance also declined in the high-concentration groups (10 mg L-1 OTC, 5 mg L-1 EFX). The superoxide dismutase and catalase activity, and malondialdehyde content increased significantly (P < 0.05), indicating the increased activity of reactive oxygen species. In addition, the decreased chlorophyll-a content, thylakoid membrane deformation, starch granules accumulation, and plasmolysis showed that the algal physiological functions were affected. These results showed that the algal-bacterial consortia system was more suitable to treat low-concentration antibiotics and provided basic parameters for the consortia application.

The response mechanism of Hydrilla verticillata and leaf epiphytic biofilms to depth and nutrient removal.

The mechanism of morphological and physiological regulation of submerged aquatic plants (Hydrilla verticillata) is influenced by spatial and environmental changes related to water depth gradients. In the present study, changes in the aquatic microcosm were explored at the depth gradients of 0.3 m, 0.6 m, 0.9 m, 1.2 m, and 1.5 m, and the depth was recognized as a critical factor for improving water quality, especially for the removal of total phosphorus (TP) and recalcitrant protein-like molecules. At 0.9 m, the removal rates of TP and protein-like substances reached 78% and 18.67%, respectively, 1.76 times and 1.28 times the rates at 0.3 m. The maximum shoot/root growth and chlorophyll (a + b) suggest photosynthesis inhibition is minimal at 1.2 m. Fluctuations in enzyme activities imply an antioxidant response to lipid peroxidation damage under different oxidative stress. The adjusted activities of glutamine synthetase (GS) and alkaline phosphatase (APA) were an adaptive nutrient utilization strategy to different water depths. Microbiological diversity analysis of biofilms indicates that community structure changes in response to water depth. Considering the growth status and nutrient removal effects, the results indicate that the optimal planting depth for H. verticillata is 0.9-1.2 m. These findings contribute to understanding water purification mechanisms in depth gradients, and support the effective rebuilding and management of submerged macrophyte communities in natural shallow lakes.

Phosphorus characteristics and microbial community in the sediment-water-algal system during algal growth.

Phosphorus (P) characteristics in eutrophic lakes change during algal growth. Furthermore, algae have a significant relationship with the microbial communities of lake sediments. This study addressed the influence of algal growth and soluble reactive phosphorus (SRP) concentrations on P characteristics within the sediment-water-algal (SWA) system. Results indicated that the SWA system simulating a high algal bloom level (SWA-HAB) had a correspondingly high SRP concentration (258.9 µg L-1), and that algal growth promoted a high SRP concentration in the overlying water. The high SRP concentration in overlying water could support algal growth, resulting in a high chlorophyll a (Chl-a) concentration (285.23 mg L-1). During algal growth, the P release flux was high in sediments from the high-SRP SWA system, with the highest P release flux measured at 0.982 mg m-2 day-1. Furthermore, microbial community abundance had a significant relationship with Chl-a concentrations in overlying water (p < 0.05) and increases with algae growth.

Effects of modified sediments from a eutrophic lake in removing phosphorus and inhibiting phosphatase activity.

Phosphorus is one of the main limiting and strong influencing factors of eutrophication, and phosphorus controlling in lake is of great significance for eutrophication. To do this, sediment materials were taken from Dianchi Lake, a typically eutrophic lake, and modified by hexadecyltrimethylammonium bromide (CTAB) and ZnSO4 to remove phosphorus and inhibit alkaline phosphatase activity (APA). Results indicated that phosphorus removal efficiencies of sediments modified by CTAB (S-CTAB), ZnSO4 (S-Zn), and oxidized sediments (OS) were higher than that of the raw sediment (RS). Ability to absorb phosphorus varied, following the order S-Zn>S-CTAB>OS>RS. Sorption was influenced by ionic strength, with the former decreasing with the increase of the latter. Freundlich model well described the sorption isotherm, with an R2 ranging from 0.9168 to 0.9958. Furthermore, compared with the raw sediments, the maximum phosphorus sorption capacities of S-Zn and S-CTAB increased by 12.2% and 124.5%, respectively. Results of desorption studies suggest that the desorption rate of S-Zn was from 3.88 to 13.76%, lower than that of other sediment materials. APA was inhibited by S-CTAB and S-Zn at the same time, with inhibition rates from 29.6% and 61.0% when the concentrations of S-CTAB and S-Zn were 10 nmol L-1 and 0.2 nmol L-1, respectively. This study provides new insights into phosphorus removal and phosphatase activity inhibition in water treatment.