Studies On The Operating Parameters Selection And Process Optimization Of Passivation Dredging Technology

With the slowing of water velocity, it is not optimistic about the problems of eutrophication and sediment deposition in the Three Gorges Reservoir. In order to meet the requirements of waterway transportation, dredging is imperative. However, the pollutants in deposited sediments will be re-released into the water during the process of dredging, thus the secondary pollution will increase the problem of eutrophication which caused by the re-release of pollutants in sediments. Based on this situation, it is necessary to reduce the secondary pollution by taking appropriate measures for different conditions of pollutants in sediments during dredging.It is an integrated technology which taking chemical passivation into dredging. By adding chemical passivation into water to remove or converted into other nontoxic and relatively stable material, so as to reduce the secondary pollution caused by disturbance of dredging and reach the purpose of dredging and water environmental protection. In view of the diversity and complexity of pollutants in sediments, it requires a lot of preliminary researches before using the chemical passivation technology during dredging. In this experiment, using the sediment at Chongqing Li jia tuo river area in The Three Gorges Reservoir as the research object, it studies the impact of environmental factors on the release of pollutants from sediment, the impact of environmental factors on chemical passivation repair and the parameters optimization of dredging-passivation based on Orthogonal Experiment with laboratory simulations.The research results of the impact of environmental factors on the release of pollutants from sediment shows: At different levels of dissolved oxygen, the release amounts of COD, TP, ammonia and TN are decreased along with the decreasing of dissolved oxygen. At different levels of pH, the release law of TP, ammonia and TN showed a U-shaped, they released least under the conditions of neutral and a lot under the conditions of acidic and alkaline, and increased along with the increasing of acidic and alkaline. Moreover, it released more obviously under the condition of alkaline than acidic; The release law of COD also showed a U-shaped and increased along with the increasing of acidic and alkaline, but it released more obviously under the condition of acidic than alkaline. Under different disturbance levels, the release mount of COD, TP, ammonia, TN and the turbidity are increased along with the increasing of disturbance intensity.The result of the impact of environmental factors on chemical passivation shows: At different levels of dissolved oxygen, passivating agents PAC has obvious inhibitory effect for the release of phosphorus, but the inhibitory effect of the passivating agents PAC is hardly affected by the level of dissolved oxygen.At different levels of pH, passivating agents PAC has different inhibitory effects for the release of COD, TP, ammonia, and TN and PAC’s effect obviously affected by PH.At different levels of pH, PAC has some inhibitory effects for the release of COD, TP and TN, but almost no impact on ammonia. PAC’s effect is decreased along with the increasing of acidic and alkaline, PAC’s effect is equivalent under the condition of pH at 6-8 and has the best effect under the condition of alkaline. Under different disturbance levels, passivating agents PAC has some inhibitory effects for the release of COD, TP and TN, and obviously inhibitory effect for the turbidity, but almost no impact on ammonia. PAC’s effect is decreased along with the increasing of disturbance intensity.The result of the parameters optimization of dredging-passivation based on Orthogonal Experiment shows: Base on the inhibitory effect of the release of phosphorus finds that the optimal operating parameters are: select PAC as Passivating agents, DO is controlled at the level of 3 mg / L, pH is controlled between 6 and 8, and the disturbance is controlled at the level of 100 r / min. Base on the inhibitory effect of the release of ammonia finds the optimal operating parameters are:select Ca(NO3)2 as Passivating agents, DO is controlled at the level of 5mg / L, pH is controlled between 6 and 8, and the disturbance is controlled at the level of 100 r / min. Base on the inhibitory effect of the release of TN finds the optimal operating parameters are: select PAC as Passivating agents, DO is controlled at the level of 5 mg / L, pH is controlled between 6 and 8, and the disturbance is controlled at the level of 100 r / min. Base on the inhibitory effect of the release of organics finds the optimal operating parameters are: select PAC as Passivating agents, DO is controlled at the level of 3 mg / L, pH is controlled between 6 and 8, and the disturbance is controlled at the level of 100 r / min. Base on the inhibitory effect of turbidity finds the optimal operating parameters are: select PAC as Passivating agents, DO is controlled at the level of 1 mg / L, pH is controlled at 6, and the disturbance is controlled at the level of 100 r / min. On the whole, the optimal choice are: select PAC as Passivating agents, DO is controlled at the level of 5 mg / L, pH is controlled at 6, and the disturbance is controlled at the level of 100 r / min.