Study On The Treatment Of Heavy Metal Simulated Wastewater By Tibetan Desmodesmus Sp. And Its Mechanism

The Qinghai-Tibet Plateau is the highest plateau in the world,with an average altitude of over 4000 m and unique geographical environment and climate characteristics.There were large and small lakes distributed in different elevation gradients,and microalgae played a key role in maintaining the water quality of these lakes.Because the traditional sewage treatment technology has limited ability to treat organic and inorganic pollutants,it has some shortcomings,such as high energy consumption,excessive greenhouse gas emissions,excessive sludge emissions and waste of resources,so it is necessary to develop modern,economical,safe,efficient and green technologies to solve these problems.As a wastewater treatment method,microalgae has the characteristics of regeneration,economy and environmental friendliness,and has become a research hotspot of wastewater biological treatment.Microalgae can use pollutants in wastewater to meet their own growth needs,and microalgae has great potential for biological purification of wastewater from different sources.Therefore,on the basis of consulting literature,this paper selected Tibetan Desmodesmus sp.to treat simulated industrial zinc-copper mixed heavy metal wastewater,and explored the mechanism of treating heavy metal wastewater by Tibetan Desmodesmus sp.through non-parametric transcriptomics,non-targeted metabonomics and the correlation analysis of transcriptomics and metabonomics.The main results are as follows:（1）R²of Tibetan Desmodesmus sp.concentration（10⁶/m L）and absorbance（689 nm）was 0.9981,and R²of Tibetan Desmodesmus sp.concentration（10⁶/m L）and turbidity was 0.9951,indicating that there is a good linear relationship between Tibetan Desmodesmus sp.concentration and turbidity and between Tibetan Desmodesmus sp.concentration and optical density.（2）In the experiment of treating simulated zinc-copper mixed heavy metal wastewater by Tibetan Desmodesmus sp.,the total removal efficiency of mixed heavy metals reached 90.90%at the concentration of10 mg/L in 3 h;At the concentration of 30 mg/L,the total removal efficiency of mixed heavy metals reached 69.33%in 4 h;At the concentration of 50 mg/L,the total removal efficiency of mixed heavy metals reached 42.46%in 4 h.（3）The comparative analysis of transcriptomics of Tibetan Desmodesmus sp.before and after the treatment of simulated heavy metal wastewater showed that the differential genes were significantly enriched in ribosome,oxidative phosphorylation,ubiquitin mediated proteolysis,photosynthesis-antenna proteins and other signal pathways,indicating that the pathways of Tibetan Desmodesmus sp.participating in energy metabolism were significantly enriched in the treatment of zinc-copper mixed heavy metal wastewater,which provided energy support for microalgae in heavy metal wastewater treatment.（4）The comparative analysis of non-targeted metabonomics of Tibetan Desmodesmus sp.before and after the treatment of simulated heavy metal wastewater showed that the pathways with the most significant enrichment of differential metabolites were aminoacyl-t RNA biosynthesis in positive ion mode and phenylalanine metabolism in negative ion mode,and up-regulation of salicylate metabolism in the pathways could improve the stress resistance of Tibetan Desmodesmus sp.in the extreme environment of heavy metal salts.The results showed that when Tibetan Desmodesmus sp.were stressed by zinc and copper,the key metabolites in the corresponding metabolic pathways were adjusted to deal with salt stress,and the removal effect of heavy metals was further achieved.（5）In the correlation analysis of transcriptomics and metabolomics,it was found that the pathways in which differential genes and metabolites were enriched were arginine and proline metabolism in positive ion mode,and the pathways in which differential genes and metabolites were simultaneously enriched were arachidonic acid metabolism and linoleic acid metabolism in negative ion mode.Metabolites d-octopine,l-arginine can improved the stress resistance of Tibetan Desmodesmus sp.to heavy metal salts;The down-regulation of linoleate,arachidonate,PGD₂and PGJ₂can improved photosynthesis,nucleic acid metabolism,protein metabolism,and the permeability of cell membrane.The results of joint analysis show that when Tibetan Desmodesmus sp.were stressed by zinc and copper heavy metal ions,the corresponding genes and metabolites can be adjusted to deal with the stress of heavy metals,heavy metal sewage was further removed by Tibetan Desmodesmus sp..