Treatment Of High-concentration Organic Wastewater By Immobilize Algae-bacteria With Chitosan And Alginate

In this study,Chlorella pyrenoidosa and aerobic activated sludge were immobilized by alginate. In self-made fluidized photobioreactor,the symbiosis of algae and bacteria,immobilization and fluidization technology were combined to achieve efficient treatment of high concentration organic wastewater.The improvement of traditional alginate immobilization method by use of barium chloride instead of part of calcium chloride as fixative,and the immobilized beads coated by chitosan were studied. It was found that the mechanical strength and stability of alginate immobilized beads was improved after coated with chitosan , while the removal efficiency of COD, nitrogen and phosphate was not influenced.Then, impacts of the concentration and pH value of chitosan solution ,and coated time on the removal efficiency of pollutants were studied. The result shows that the removal efficiency of pollutants decreased with the increase of the concentration of chitosan solution and coated time, increased with the increase of pH value of chitosan solution,while the stability of immobilized beads changed in the opposite direction.Considering the stability of immobilized beads and treatment effect of pollutants, the optimal concentration and pH value of chitosan solution ,and coated time are: 1%, 5.5, 15min.The diameter of immobilized beads can influence its mass transter efficiency. Impacts of three different particle size of immobilized beads on removal efficiency of pollutants was investigated. The result shows that the immobilized beads with the particle size about 4mm had the best removal efficiency of COD, nitrogen and phosphate ,The removal efficiency were 74.8%, 83.4%, 71.7% respectively.By testing the the concentration of DO and CO2,it was found that the concentration of DO increased faster than CO2 in immobilized bacterial and algal system, which indicated that algae's photosynthesis occupy the dominant position. After a certain time, the concentration of DO and CO2 can achieve a dynamic equilibrium ,which can meet the demand of bacteria and algae.The nutrient ratio of wastewater has some influence on removal efficiency of pollutants. In this study,it was found that the system achieved the best removal efficiency of nitrogen ,when the ratio of nitrogen and phosphorus was 4.6:1.Then the removal efficiency of nitrogen decreased evidently with the increase of the ratio of nitrogen and phosphorus,but the total removal increased.The immobilized bacterial and algal system has high tolerance of pollutants,the total removal of pollutants reached the maximum when the ammonia concentration was 154.3mg / L ,and the algae and bacteria grew well.The relationship between expansion degree of immobilized beads and the circular flow of liquid in photobioreactor can describe the expansion behavior of fluidized bed,which is the basis of the design of photobioreactor.By testing the expansion degree of immobilized beads in different flow of liquid ,the relationship can be expressed by Q=62.127Ln(x)+149.68.The removal rate will decrease when the expansion of immobilized beads is large or too small.The effect of invalid volume on removal efficiency of pollutants was also studied. It was found that the invalid volume of fluidized photobioreactor system should be minimized,which not only improves the degradation rate of pollutants ,but also can reduce the cost of the photobioreactor system.