Experimental Study On Remediation Of Black Smelly Water And Sediments In Urban Lakes By Chemical Method

In 2015,the Ministry of housing and urban rural development in conjunction with the Ministry of environmental protection,the Ministry of water resources,the Ministry of agriculture to organize the formulation of “ Guide to the remediation of the urban black and odorous water”,and gradually pay attention to assessment and pollution prevention of the urban black smelly water.Then,Chongqing carried out a “Clear water action”,focusing on controlling the water environment protection of major rivers and their tributaries within their jurisdiction.The comprehensive monitoring and comprehensive management of urban water environment has become an important part of the improvement of urban living standards.This paper analyzes the black odor level of a typical urban lake-Xinhua reservoir,comparing with the advantages and disadvantages of rivers and lakes restoration methods at home and abroad,then put forward a pilot scheme to in situ repair of the black smelly lake by chemical method,adding calcium nitrate and calcium hydroxide.The test set up respectively 0.19,0.36,0.54,0.73,0.91,1.09 mol/m2,a total of 6 dosing gradients of calcium nitrate and calcium hydroxide,had the hourly monitoring in the short term(15d)to the overlying water pollution indicators,measured in the fresh sediments after the long(30d)test,and evaluated its repair effects,then got the following conclusions:(1)Calcium nitrate repair the overlying water: The reduction rate of ammonia nitrogen,which is one of the indicators of black odor in the water body,was the highest(compared with the pre-repair)of 86g/m2,which 15 d was 77.3%,and 30 d was 74.0%.When calcium nitrate was added to 173g/m2,the ratio of 14 d to total nitrogen was negative;30d is the largest and positive reduction in total nitrogen.Calcium nitrate to repair most of the time node in overlying water ammonia nitrogen in 3 d(measurement for the first time,the highest point)and 6d~ 8d(the highest point of the total phosphorus and total nitrogen),experimental group high ammonia nitrogen content than the blank group 4 days in advance.(2)Calcium nitrate is used for sediment repair: After adding 30 d the color of sediments turned to black yellow.The average thickness of brown sediments and water sulfate concentration is positively linear correlated with calcium nitrate dosing.Calcium nitrate had no cuts to free ammonia nitrogen and total nitrogen(compared with the blank group),with the increase of calcium nitrate dosing quantity,the stronger the sediment free nitrogen release,but less than the degree of release and molar added amount of calcium hydroxide.For heavy metals,manganese is more active and frequent than iron in the flow of water and sediment.Low doses of calcium nitrate can reduce the amount of copper in the sediment,but the amount of calcium nitrate in the sediment is less than that.(3)Calcium hydroxide repair the overlying water: the addition of 27g/m2 of calcium hydroxide,and the reduction of the above water ammonia nitrogen(compared with the pre-repair)15d is 89.6%;The maximum amount of calcium hydroxide is 14g/m2,and the maximum 30 d is 84.7%.The reduction rate of total nitrogen came to the highest,which was 38.1% and 40.7% respectively,when the amount of calcium hydroxide was maximized by 81g/m2.Considering the condition of the phosphorus release,the low amount of calcium hydroxide has a significant degradation effect on the above water.Calcium hydroxide repair black smelly in overlying water time node is the basic for 3d(the highest point of the ammonia nitrogen and total nitrogen)and 12 d stable point(total phosphorus),of the peak of ammonia nitrogen and calcium hydroxide group than the blank group 4 days in advance.(4)Calcium hydroxide is used for sediment repair: Calcium hydroxide has an improved effect on the almost unobserved characteristics of black and black deposits.30 d,free ammonia nitrogen of sediment nitrogen is the main existence form(consistent with calcium nitrate),accounted for 70% ~ 90% of the total nitrogen free,but less dosage of nitrogen in the experimental group of free form a certain degree of conversion.For heavy metals,after 30 d,the manganese and iron deposited in the water gradually deposited into the sediment as the amount of calcium hydroxide was added.The amount of copper in the sediment gradually increased to more than the filter.Zinc and lead are still less than the corresponding screening value(consistent with calcium nitrate)after calcium hydroxide.The total chromium deposits of calcium hydroxide were generally higher than that the calcium nitrate test group of the same molar concentration.Finally,in addition to the highest concentration of calcium hydroxide,calcium nitrate and calcium hydroxide were able to lower the concentration of ammonia nitrogen in 15 d and 30 d below the level of the mild black and odorous.But in overlying water within 30 d of total nitrogen is still cannot achieve the Ⅴ surface water environment quality standards.Calcium hydroxide unit water pollution index(ammonia)cut the reagent cost lower than that of calcium nitrate.In the range of reagent adding quantity and the monitoring period,the repair effect of ammonia nitrogen in the overlying water adding calcium hydroxide in a short period is obvious,however,the repair effect of sediments adding calcium hydroxide is poorer,and the long-term stability of the water nutrient remains to be further improved.Thus,calcium hydroxide can be used as a short term repair emergency plan for overlying water black smelly,and calcium nitrate can be used as a stable long-term measures to part cut black smelly sediments.