Controlling internal nutrients loading at low temperature using oxygen-loading zeolite and submerged macrophytes enhances environmental resilience to subsequent high temperature.

Nutrients releasing from anoxic sediment can be enhanced in summer because the dissolved oxygen (DO) consumption, nitrogen (N) and phosphorus (P) migration are susceptible to temperature. Herein, we proposed a method to hinder the aquatic environmental deterioration in warm seasons through consecutive application of oxygen- and lanthanum-modified zeolite (LOZ) and submerged macrophytes (V. natans) at low temperature scenario (5 °C, with depleted DO in water), and the effect was examined with drastic increasing the ambient temperature to 30 °C. The investigation was conducted in a microcosm scale including sediment cores (with a diameter of 11 cm, height of 10 cm) and overlying water (with depth of 35 cm). During the 60 days experiment, application of LOZ at 5 °C facilitated slower releasing and diffusion of oxygen from LOZ and the growth of V. natans. Thereby, when the temperature was increased to 30 °C and maintained for 35 days, the DO reached 10.01 mg/L, and the release of P and N from the sediment was reduced by 86% and 92%, respectively. This was achieved from the joint efforts of adsorption, biological conversion, chemical inactivation, and assimilation. Also, the LOZ inhibited 80% N2O, 75% CH4, and 70% CO2 emissions primary by promoting V. natans growth and reshaping microbiota. Meanwhile, the colonization of V. natans benefited the sustainable improvement in the water quality. Our results addressed the time that the remediation of anoxic sediment can be applied.

Potassium supplement enhanced cadmium removal in a Microcystis aeruginosa photobioreactor: Evidence from actual and simulated wastewater.

In this study, a Microcystis aeruginosa-based photobioreactor (M. aeruginosa-based PBR) was developed for the removal of cadmium (Cd2+) from diluted actual mine wastewater (DW) and Cd2+-contained simulated wastewater (SW), with a uniform Cd2+ concentration of 0.5 mg/L. For the DW and SW, both K+ -abundant (DWA & SWA) and K+-insufficient (DWB & SWB) treatments were conducted. It was found that continuous supplementation of K+ benefited Cd2+ removal. The Cd2+ removal efficiency in SWA reached 70% during the 41 days of operation, which was 20% higher than that in the SWB. The K+ addition triggered great higher Cd2+ removal efficiency (90%) in the DWA in comparison to the SWA. The Cd2+ assimilation by M. aeruginosa and Cd2+ retention on M. aeruginosa surface were the primary processes involved in the PBR system. The K+ starvation triggered a 45% and 43% loss of M. aeruginosa biomass in the DWA and the DWB, respectively. Hence, the Cd2+ removal efficiency in DWB increased significantly, and this was attributed to the increased abundance of non-living cells and enhanced bioretention of Cd2+. The results revealed that continuous K+ supplementation enhanced the Cd2+ removal efficiency in the M. aeruginosa-based PBR jointly by prompting algal cell growth, Cd2+ assimilation and biosorption, as well as Cd2+ retention on the algal cells.

Potassium regulates cadmium toxicity in Microcystis aeruginosa.

Microcystis aeruginosa (M. aeruginosa) was found to be capable of cadmium (Cd2+) assimilation. Potassium (K+), an essential factor in transmembrane transport, can possibly manipulate the interaction between Cd2+ and M. aeruginosa. In this study, the effect of available K+ levels on Cd2+ toxicity in M. aeruginosa is examined. The results showed that the K+ level was positively linked with toxicity of Cd2+ to M. aeruginosa. And with respect to the M. aeruginosa incubated in K+ = 460 µM treatment, the release of extracellular polymeric substance was augmented, which benefited the retention of Cd2+ on the M. aeruginosa surface. In addition, the assimilation of Cd2+ showed a 3.42-fold increase in comparison to that without K+ supplement. Moreover, the enhanced K+ level caused the up-regulation of the Cd2+ transporting protein and down-regulation of the Cd2+ efflux protein, associated with the positive energy metabolism response. These results documented that the K+ availability could influence the toxicity of Cd2+ to M. aeruginosa jointly through the manipulation of Cd2+ assimilation, excretion, and the biological response. These findings may attach importance to the effects of K+ level on Cd2+ assimilation by M. aeruginosa and shed a degree of light on the enhanced Cd2+ removal using algal-based technology.