Research For Immobilization Of A Type Of Pseudomonas Strains And It’s Denitrification Effect With The Combination Of Submerged Plant

The long-term efficient application conditions of an efficient aerobic denitrifyingbacteria(Pseudomonas stutzeri) and the denitrification effect with the combination ofsome submerged plant were investigated in this study. Since the free bacteria is easyto loss in the water and the ability of the resistance to impact load is poor, a kind ofimmobilized material with high mechanical strength and stable performance waschosen to immobilize the efficient aerobic denitrifying bacteria isolated by ourlaboratory. Additionally, the immobilized aerobic denitrifying bacteria and thesubmerged plant (Vallisneria natans and Ceratophyllum oryzetorum) were combinedto treat different wastewater, and the denitrification effects under artificial controlconditions and simulated natural conditions were analyzed respectively. The mainresults are summarized as follows:(1) With comprehensive comparison of mechanical strength, stability,denitrification activity, immobilized costs and other factors, the combination ofpolyvinyl alcohol (PVA) and the loofa sponge is more suitable for immobilizing theaerobic denitrifying bacteria. Since the bacteria immobilized by the traditionaladsorption method are easy to fall off and unstable, and using PVA alone toimmobilize the bacteria can impede the mass transfer and lower the microbial activity,the combination of PVA and the loofa sponge could effectively solve these problems.(2) When five sponge cubes were used per100ml medium and five milliliter ofthe bacteria with concentration at9.15×105cfu/mL were inoculated, the immobilizedbacteria have the higher nitrate removal efficiency. Therefore, the concentration of theimmobilized bacterial suspension were9.15×105cfu/mL eventually, and the ratio ofthe volume of bacterial suspension, the volume of the PVA solution and the quality ofthe loofa sponge is2mL:13mL:320mg.(3) Compared with the free aerobic denitrifying bacteria, the immobilizedbacteria can resist the environmental disturbance and the impact load obviously. Atthe11th hour of the experiment, the nitrate removal efficiency of the immobilizedbacteria reached92.66%with little nitrite accumulation concentration, while the freebacteria reached62.49%and the nitrite accumulation concentration was14.56mg/L because of the incomplete denitrification.(4) The results of the repeated utilization and low temperature storage stabilitytests showed that after reused by seven batches, the percentage of NO3-N removalrate by immobilized aerobic denitrifying bacteria was still very high (about95.56%),and when stored at4℃for five months, the nitrate removal efficiency even reached90.32%. The SEM photos of the immobilized bacteria also proved that thecombination of PVA and the loofa sponge can immobilize the aerobic denitrifyingbacteria well. So the immobilization methods used in this study is feasible and hascertain actual application value.(5)The denitrification effect of the immobilized aerobic denitrifying bacteriaassociated with submerged plant were investigated under the condition that the watertemperature at20-25℃and the concentration of the dissolved oxygen at6-9mg/L.The results shows that when the initial nitrate concentration was about3.5mg/L, thedenitrification effect of the combination of Vallisneria natans and the immobilizedbacteria was the best, which can reach98.21%at the18th day of the experiment.Consequently, the application prospects of using the immobilized aerobic denitrifyingbacteria and the submerged plant to treat the nitrogen wastewater together was good.When the growth of aquatic plants is affected by the external environment, theimmobilized aerobic denitrifying bacteria can also have some effects.