Research On Screening And Identification Of Salt-tolerant Microorganism For Water Treatment And Optimization Of Compound Microbialagents

Mariculture wastewater contains a lot of harmful substances such as nitrogen,COD and suspended solid.Improper discharge will lead to eutrophication in coastal waters.The common biological treatment methods have the disadvantages of long acclimation period,poor treatment effect and so on.Therefore,it is necessary to find a kind of microbial agent with strong salt tolerance and good treatment effect.In this paper,functional microorganisms for water treatment were screened out according to the target pollutants.The compound bioflocculant and compound microbial agent for ammonia-nitrogen degradation were prepared by selecting excellent strains,and the optimum working conditions were explored.In this study,the sediment samples were collected from the offshore sewage outfall in Weihai and 179 strains were isolated by using 6 kinds of medium.The ability of flocculation,ammonia-nitrogen degradation,nitrite-nitrogen degradation,nitrate-nitrogen degradation and COD degradation of some strains were determined.Among them,17 strains with obvious effect were identified by molecular analysis,as the following 6 genera:8 strains of Pseudoalteromonas sp.,4 strains of Psychrobacter sp.,2 strains of Candida sp.,1 strain of Planococcus sp.,1 strain of Bacillus sp.,and 1strain of Pichia sp.Because the multifunctional strain S2A15（Planococcus maritimus）had the ability of flocculation and COD degradation with better treatment effect,it’s necessary to do a further exploration of it.In the flocculation aspect,the result showed that the optimum flocculation conditions were as follows:10%CaCl₂ solution of 3 mL,the flocculant dosage of 2 mL,pH of 9 and the flocculantion activity reached 77.83%.When the bioflocculant was heated at 120℃,the flocculation activity could still reach 65.41%.In the degradation of COD,the COD degradation rate of S2A15 was the highest at 28℃and the removal rate of COD was 76.9%in the wastewater with COD concentration of400 mg/L（3.3%salt concentration）.The strain could grow under the condition of4-28℃,pH 6-10 and 0-18%salinity.In this study,S2F5（Pseudoalteromonas nigrifaciens）and S2M5（Pseudoalteromonas agarivorans）were creatively constructed as compound bioflocculant-produing bacteria with the best ratio（1:2）,and the flocculation activity was increased by 4.95%and 5.42%respectively,higher than that of single strain.The optimization of formula for compound bioflocculant-produing bacteria was carried out by Plackett-Burman（PB）design and central composite design（CCD）and the result of the optimum formula was:sucrose 12.82 g/L,K₂HPO₄ 4.00 g/L,MgSO₄ 3.70 g/L,KH₂PO₄ 3.00 g/L,NaCl 33.00 g/L,（NH₄）₂SO₂ 0.52 g/L.Through central composite design（CCD）,the optimum culture condition was as follows:the pH value of 7.12,inoculation size of 4.81%and the liquid volume of 20.93 mL.The optimum flocculation conditions were determined as follows:10%CaCl₂ solution of 300μL,the bioflocculant dosage of 2 mL,and pH value of 6.5,which resulted in reaching the maximum flocculant activity at 93.56%,and the flocculation activity was increased by 20.91%than before.The compound bioflocculant was suitable for treating acid and neutral wastewater with pH value of 5.0-7.5.When the compound bioflocculant was heated at100℃,the flocculation activity could still reach 85.57%.In this study,N7（Pichia kudriavzevii）and N9（Candida tropicalis）were constructed as compound microbial agents for ammonia-nitrogen degradation with the best ratio（1:2）,and the degradation rate was increased by 13.69%and 11.85%respectively,higher than that of single strain.It could grow under the condition of pH3-9 or 0-11%salinity,and the degradation rate could reach more than 90.00%.At 30℃,the highest degradation rate was reached 96.00%.When corn leaves were used as carriers,the adsorption effect for compound microbial agents was better,and the living bacteria number could reach 1.1 x 10⁷ cfu/g.This study shows that the compound microbial agents have a great application prospect in the treatment of mariculture wastewater.