| The pickled industry not only brings economic benefits but also produces a large amount of wastewater,which contains massive salt,nitrogen,phosphorus,and organic matter.Pickled wastewater is harmful to the environment.At present,there is no suitable method for treating pickled wastewater.In this dissertation,we used salt-tolerant microorganisms as research objects to explore the reutilization of pickled wastewater.Firstly,the salt-tolerant Haloarcula sp.and Dunaliella sp.were successfully screened and domesticated from the wild.Then,we studied the optimal growth conditions of Haloarcula sp.and Dunaliella sp.and the influence of environmental factors on the physiological and biochemical characteristics of bacterium and algae.On this basis,the purification effects of algal system,bacterial system and mixed system on different concentrations of pickled wastewater were studied.Under the optimal conditions,we judged the feasibility of recycling degradation products,which is based on the analysis of water quality characteristics,the production of biological byproducts,and the quality of crystalline slat.Finally,we obtained the nitrogen-phosphorus transformation mechanism of Haloarcula sp.and Dunaliella sp.by studying the changes in the adsorption and absorption capacity of Haloarcula sp.and Dunaliella sp.,which were under different nitrogen-phosphorus concentration.The main conclusions are as follows:(1)By using salt stress and streak plate method,two salt-tolerant microorganisms,which can survive at the concentration of 250 g/L NaCl,were successfully isolated from a coastal salt field in Lianyungang.According to the morphological observation,16 S rDNA sequencing and 18 S rDNA sequencing,the strains were Haloarcula sp.and Dunaliella sp..Modified Johnson medium was used to cultivate bacterium and algae,which can improve bacterium and algae adaptability to the high concentration of nitrogen,phosphorus and organic carbon.The results showed that the growth cycle of Haloarcula sp.and Dunaliella sp.were about 14 days under the experimental conditions,and Dunaliella sp.contains β-carotene that means this alga has great commercial value.(2)The optimal growth conditions of Haloarcula sp.and Dunaliella sp.were determined by single factor experiment.The Haloarcula sp.optimal growth condition was pH=6.0,salinity 200 g/L and glucose 5 g/L.The Dunaliella sp.optimal growth condition was 24hL:0hD,pH=8.0,salinity 50g/L and glucose 10 g/L.In addition,the study found that environmental factors had a great influence on the biochemical composition of Dunaliella sp..The alkaline,high-salinity and high organic carbon concentration environment was beneficial to the accumulation of β-carotene and total sugar in Dunaliella sp..The short-light,alkaline and high-salinity environment was beneficial to the accumulation of protein in Dunaliella sp..The short-light,acidic and high-salinity environment was beneficial to the accumulation of total lipids in Dunaliella sp..(3)Under the optimal conditions,the purification ability of the mixed system to different concentrations of pickled wastewater was greater than the algal system and bacterial system.Comparing the algal system and the bacterial system,it can be found that the algal system had a higher COD removal rate when the wastewater concentration is lower.When the concentration of the pickled wastewater is higher than 40%,the bacterial system had a better purification effect on the organic pollutants of the pickled wastewater.Besides,the algal system,bacterial system and mixed system all had obvious purification effects on nitrogen and phosphorus pollutants.Under the conditions of different concentrations of pickled wastewater,the removal rate of TP by the three systems was more than 60%.(4)The experimental results show that it is more feasible to use Haloarcula sp.and Dunaliella sp.to degrade the pickled wastewater and recycle its degradation products.The Haloarcula sp.and Dunaliella sp.had a good effect on the purification of certain pollutants,but aromatic compounds,organic halide and alkane compounds still existed in the effluent of the three systems.If we want to use effluent for reuse,we need to combine with other water treatment technology to process pickled wastewater.In addition,compared with other systems,the mixed system had the highest production of high-value biological byproducts.The protein yield was 0.417 g/L,the total sugar yield was 0.431 g/L,the total lipid yield was 0.787 g/L,and the β-carotene yield was 5.430 mg/L.Moreover,the quality of the crystalline slat from the mixed system was the best.Compared with the raw water,the purity of sodium chloride in the mixed system was increased by 8.9%.The physical and chemical indicators of crystalloid salt from the mixed system met the secondary standard of industrial salt other than the concentration of calcium-magnesium ions and insoluble matter.(5)In the experiment of exploring the mechanism of nitrogen-phosphorus transformation by Haloarcula sp.and Dunaliella sp.,it was found that compared with nitrogen-phosphorus deficiency,Haloarcula sp.and Dunaliella sp.grow better under high nitrogen-phosphorus conditions.In the environment of high nitrogen-phosphorus conditions,Haloarcula sp.and Dunaliella sp.can adsorb a large amount of nitrogen and phosphorus.From the perspective of individual Dunaliella sp.cells,the adsorbed nitrogen content accounts for 56.7% and the adsorbed phosphorus content accounts for 53.2%.From the perspective of Haloarcula sp.,the adsorbed nitrogen content accounts for 71.4% and the adsorbed phosphorus content accounts for 80.8%.However,when Haloarcula sp.and Dunaliella sp.were exposed in low nitrogen-phosphorus concentration environment from a high nitrogen-phosphorus concentration environment,Haloarcula sp.and Dunaliella sp.were dissolved some nitrogen and phosphorus,which used to adsorb on the surface of cells.The change of nitrogen-phosphorus concentrations will not change the molecular structure of the Haloarcula sp.and Dunaliella sp.,but only change the conversion efficiency of biochemical components. |
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