Growth Stress Of Cu²⁺on Microalgae And Adsorption Of Cu²⁺by Microalgae Waste

In recent years,heavy metal pollution and proliferation of microalgae have become two major environmental issues faced by natural water.Heavy metals not only become toxic to aquatic organisms,but also pass through the food chain threatening human survival after entering water.Microalgae,as a primary producer in the aquatic environment,produces a sensitive reaction to heavy metals and is the preferred test substance for heavy metal biotoxicity assessment and toxicological studies.Copper is a typical heavy metal contaminant in sewage.Chlamydomonas microsphaera and Microcystis aeruginosa are common microalgae species in natural water.Exploring the effects of copper ions on the growth and physiological characteristics of two species of microalgae can provide theoretical basis of toxicological studies of copper.On the other hand,the ability of microalgae to adsorb heavy metals in water has been confirmed,and the collected microalgae can be used as heavy metal adsorbent.Polyaluminum chloride as a flocculant can more efficiently collect microalgae in water.However,few studies have focused on the adsorption of heavy metals by flocs of polyaluminum chloride and microalgae.In this paper,the flocs of Chlamydomonas microsphaera and Spirulina platensis collected with polyaluminum chloride were made into dry powders.The adsorption performance and mechanism of heavy metal copper ions on two kinds of floc powders were studied.and it was carried out with pure algae powder of two kinds of algae.For comparison,The effect of flocculation on Cu²⁺adsorption was evaluated by compared with two kinds of pure microalgae powder.Through the study of the interaction between microalgae and Cu²⁺,the following results have been obtained:?1?After the stress of Cu²⁺for 96 h,the growth inhibition rate of Chlamydomonas microsphaera increased with the increase of Cu²⁺concentration.Cu²⁺promoted the growth of Microcystis aeruginosa at low concentrations?less than 0.01 mg/L?and inhibited its growth at high concentrations?greater than 0.1 mg/L?.The EC₅₀ of Cu²⁺on Chlamydomonas microsphaera and Microcystis aeruginosa decreased with the passage of time.The EC₅₀ at 96h was 0.74 and 0.70 mg/L respectively,indicating that the tolerance of Chlamydomonas microsphaera to Cu²⁺was slightly higher than Microcystis aeruginosa.With the increase of Cu²⁺concentration,the photosynthetic activity of both microalgae decreased.Meanwhile,the increase of superoxide dismutase,malondialdehyde,and soluble protein contents of two microalgae respectively indicated that Cu²⁺stimulated the antioxidation reaction of microalgal cells;caused the lipid peroxidation reaction of the microalgal cells to intensify and destroyed the membrane system;Cu²⁺stimulates the synthesis of soluble proteins in microalgal cells and is due to the self-defense of Cu²⁺toxicity.?2?Chlamydomonas microsphaera collected by PAC flocculation?PCM?and Spirulina platensis collected by PAC flocculation?PSP?both have a good adsorption effect on Cu²⁺in water.With the increase of the dosage,the adsorption rate of Cu²⁺on the two adsorbents also gradually increased,and the unit adsorption amount gradually decreased.Concentration of 0.5g/L was the appropriate dosage and the adsorption equilibrium was achieved within 1 h.The addition of PAC did not change the adsorption mechanism of Cu²⁺by single microalgae powder,but changed the adsorption performance of Cu²⁺by single algae.As for pure Chlamydomonas microsphaera powder?CM?and pure Spirulina platensis powder?SP?,the adsorption process of Cu²⁺by PCM and PSP conformed to the second-order kinetic model.The most suitable pH adsorption conditions were 5.0 to 6.0.Similar to CM and SP,the amount of Cu²⁺adsorbed by PCM and PSP was not affected by the coexistence of Na⁺and Ca²⁺,but was easily disturbed by coexisting Fe³⁺.The isothermal adsorption process conformed to the Langmuir and Freundlich model.Scanning electron microscopy and elemental energy spectrum analysis directly confirmed the adsorption of Cu²⁺by PSP and PCM.Fourier-infrared spectroscopy analysis showed that CM and PCM mainly adsorb Cu²⁺with hydroxyl and carboxyl groups contained therein,while PSP and SP adsorb Cu²⁺mainly depends on the carboxyl groups.The maximum Cu²⁺adsorption capacity(Q_max)of PSP is slightly lower than SP,while the Q_max of PCM is obviously higher than CM,indicating that PAC can promote the adsorption of Cu²⁺by CM.It can be seen that the microalgae waste collected by PAC flocculation can be used as a Cu²⁺adsorbent to purify heavy metal-contaminated water.?3?Compared with other adsorbents studied,PCM and PSP have a strong adsorption capacity of Cu²⁺in water,and its Q_max exceeds most of the adsorbents.There are TOC residues in the waters produced by PCM and PSP,but the residual TOC content is far less than CM and SP,indicating that PAC can significantly reduce the TOC contamination risk of microalgae powder adsorbents to the water.The content of TOC was positively correlated with the amount of algae powder.Concentration of 0.5 g/L was the safe amount of PCM and PSP used.At this concentration,PCM and PSP also had good adsorption removal rate of Cu²⁺.Therefore,0.5 g/L was the appropriate amount of removal of Cu²⁺from water by PCM and PSP.