Migration And Transformation Law Of Nitrate In Unsaturated Zone And Saturated Zone

Groundwater as one of the main source of human drinking water, itspollution was concerned by the human widely. The excessive use of fertilizer in theagricultural, as well as the discharge of industrial wastewater and domestic sewageled to nitrate pollution in groundwater. unsaturated zone and saturated zone is notonly the main media when nitrate migrate to the groundwater， but also the mainplace of degradation of nitrate to prevent contamination of groundwater. Therefore,of great significance to the study of the migration and transformation of nitrate inunsaturated zone and saturated zone.Because of the sand column experiments in the study of groundwater in asuperior position, so this experiment using sand column analog migration andtransformation of nitrate. The sand column is made by plexiglass tube,high-2000mm, diameter150mm, with a outlet at the bottom, filled by washed finesand(high-1700mm)。Since the sands surface of every200mm set a sampling portsin the sand column. Study the Influence of carbon sources、 C:N、 initial pH、height ratio of unsaturated zone、 nitrate concentration and influent speed ondenitrification in sand column. The experimental results showed that:(1)Cultivation of denitrifying bacteria in sand column can be divided intothree stages. In the first stage, due to the sand column rejection and nitratereduction, concentration was reduced compared to influent nitrate concentration,and ammonia appeared. In the second stage, nitrate concentration was Increased,the intermittent influent let the environment of sand column changed from reducingenvironment and oxidizing environment， when it in oxidizing environment, thenitrification make ammonia which was absorbed in sand column in the frist stageinto nitrate, lead nitrate concentration rising. In the third stage, according to thetheory that bacteria will choose to get more energy， the reduction of the nitrateconcentration in the sand column due to the occurrence of denitrification reaction，rather than nitrate reduction.(2)Order the denitrification efficiency of different carbon source: sodiumacetate> ethanol> glucose, denitrification efficiency relate with carbon sourcesnature、 molecular weight. When glucose or sodium acetate as carbon source，deep water in the sand column was polluted by organic carbon. (3)When the height ratio of unsaturated zone and saturated zone in the sandcolumn is0, nitrate is decomposed completely at a depth of400mm, and noaccumulation of nitrite; when the height ratio of unsaturated zone and saturatedzone in the sand column is1,nitrate moves to the depths of the sand column andcauses accumulation of nitrite.(4)When the C/N of influent water is1:1, carbon source is relativelyinsufficient, which resulting in incomplete decomposition of nitrate in a sandcolumn and nitrite accumulated. When the C/N of influent water is6:1, the carbonsource is adequate, denitrifying bacteria have an effectively and completelydegradation with nitrate, in this condition, no accumulation of nitrite appear, butcause pollution of organic in the depths of sand column.(5)Order the nitrate removel efficiency of different initial pH in the sandcolumn:7.00＞6.00＞8.00＞9.00＞5.00. The stronger the denitrification in thesand column, the less the amount of nitrite accumulated， the greater the amount oforganic carbon consumed.(6)In a certain range, the higher the influent nitrate concentration, the higherthe rate of denitrification. When the influent nitrate concentration exceeds thedecomposition ability of denitrifying bacteria in sand column, denitrification ratesare no longer rising, nitrate to migrate to the sand column depths, remaining nitratemigrate to the depths of the sand column.(7) Investigated the infulence of different influent speed on the rate ofdenitrification, the slower the influent speed the better the nitrate removed in sandcolumn. but when the influent rate is too slow， nitrite will accumulated，due to thelacking of a carbon source.Under the terms of the height of the unsaturated zone is zero、 the C/N ofinfluent water is3:1、 initial pH=7.00and glucose as carbon source, denitrificationefficiency of sand column is very well; nitrate concentration was decrease to1.11mg/L at400mm height， no nitrite accumulated and not cause pollution oforganic in the depths of sand column.