Effect Of In-situ Remediation Of Black Smelly Sediment With Calcium Peroxide On Overlying Water Body

Malodorous water is still one of the most prominent environmental problems in China.The key and difficulty to solve the problem lies in the restoration of the sediment.In-situ remediation technology is a kind of sediment remediation technology which has attracted wide attention in recent years.Compared with ectopic remediation technology,it has the advantages of simple operation and low treatment cost,and has good prospects for development.However,there are some controversies about the safety of in-situ repair technology,and the impact of the repair process needs to be further studied.The static and dynamic simulation experiments were carried out with calcium peroxide as the main restoring agent.The effects of calcium peroxide on the restoring indexes of sediment and overlying water were discussed,and the optimum dosage of calcium peroxide under different hydraulic conditions was determined.In view of the shortcomings of repairing by adding calcium peroxide alone,the method of combining with zeolite was further adopted to optimize the repairing effect,and the optimum coverage thickness of zeolite under different conditions was determined.The main conclusions are as follows:Adding calcium peroxide can remove AVS(Acid Volatile Sulfide)from sediment,inhibit the release of ammonia nitrogen from sediment,alleviate the black odor of sediment,make the concentration of zinc in overlying water decrease rapidly,and the pH of overlying water rise.Proper dosage can improve the acidic environment of sediment.However,there are also problems that lead to the increase of ecological risk of heavy metals in sediment,accelerating the release of COD and Cu elements and phosphorus elements in sediment.When the amount of sediment is too large,it will cause the problem of excessive pH of water body,which will have a certain impact on the environment.Considering the effect of restoration and the negative impact on environment,the optimal dosage of calcium peroxide is 5g/L under static condition.At the end of the experiment,AVS in sediment is reduced by 76.69%,ammonia nitrogen in overlying water is reduced by 28.32%,zinc concentration is reduced from 0.8mg/L to 0.2mg/L,and the pH value of overlying water is stable at about 8.0.The concentration of COD,total phosphorus and Cu in overlying water can be controlled at 40 mg/L,0.2m/L,and below 0.2 mg/L.On the whole,the inhibition effect on ammonia nitrogen release was limited and the concentration of COD was on the high side.Under dynamic(t = 10d),dynamic(t = 5d)and dynamic(t = 1d),the optimal dosage of calcium peroxide was 5g/L,3g/L and 3g/L,respectively.Under dynamic(t = 10d)and dynamic(t = 5d)conditions,ammonia nitrogen and COD indices still need to be further optimized under the optimum dosage.In view of the shortcomings of adding calcium peroxide alone,calcium peroxide was combined with zeolite.Under static condition,under the premise of adding 5g/L calcium peroxide,the optimum coverage thickness of zeolite is 9mm,which can control the concentration of ammonia nitrogen and COD in overlying water below 15mg/L,the pH rises to about 7.8,and other index concentration of overlying water is controlled in a lower range.Under dynamic condition(t=10d),under the premise of adding 5g/L calcium peroxide,the optimum coverage thickness of zeolite is 3mm,and the concentration of ammonia nitrogen and COD in overlying water can be controlled below 12.30mg/L and 20mg/L respectively,and the pH rose to about 7.8.The concentration of other indicators in overlying water is very low.Under dynamic(t=5 d)conditions,under the premise of adding 3g/L calcium peroxide,the optimum coverage thickness of zeolite was 3 mm,which could control ammonia nitrogen concentration and COD concentration of overlying water below 12.30 mg/L and 20 mg/L respectively,and pH rose to about 7.3,while other index concentrations of overlying water were extremely low.Combined remediation can further reduce the concentration of ammonia and nitrogen in overlying water and solve the problem of rapid increase of COD concentration caused by adding calcium peroxide alone.At the same time,when the concentration of copper and total phosphorus in overlying water is at low concentration,the combined remediation still has a certain reduction effect,which is better than adding calcium peroxide alone.