Laboratory Study On The Nitrate Wastewater With Permeable Reactive Barrier Technology

In recent years, nitrate pollution in groundwater is increasingly serious, to remove thenitrate pollution in the groundwater has become a top priority. This paper analyzes thepresent situation and the harm of the nitrate pollution in the groundwater. Meanwhile，present remediation methods，such as physical method，chemical method and biologicmethod were compared．The permeable reactive barrier is a comparatively promisingtechnology for in-situ groundwater remediation．This paper describes the advantages and disadvantages of liquid carbon sources andsolid organic carbon sources，and compares the release of organic matter in COD whendecadent wood, corn straw and wood shavings were used as a carbon source. Throughcomprehensive comparison，corn straw was selected as activated carbon source. Becausethe small organic molecules generated by the corn straw in the water can be carbon sourceto the water anaerobic microorganisms （denitrifying bacteria）.Static experimental results show that: during corn straw in the process of soaking，theconcentration of organic matter after decomposition (permanganate index COD_Mnsaid)maintained at6to8mg/L，and this concentration can meet the nutritional carbon sourcerequired for denitrifying bacteriaï¼›The concentration of the organic matter was not high,couldn’t produce secondary pollution of groundwater; three kinds of nitrogen duringdecomposition of corn straw yield were very low, would not have a huge impact on theremoval of nitrate nitrogen;The cumulative amount of the byproducts NH₄⁺in the reactionprocess reached minimum，and the PH value range just coincide the natural undergroundwater PH value range （PH value for6-9）, the experimental simulation PRB operatingconditions can be fully applied the actual groundwater.In order to solve the problem that NH₄⁺is too high in the process of nitrate-nitrogenhandled by reduced zero-valent iron, corn straw and reduced zero-valent iron were selectedas the activity of filling material for permeable reactive barrier. In the experiment, thesimulation of the groundwater in nitrate pollutants was made in this experiment, aneffective solution was found to solve the problem of the high concentration of byproductNH₄⁺.The main processes: dissolved organic matter were generated by corn stalk during theprocess of soaking, which provided carbon source for denitrifying bacteria.In addition，pollutant nitrate could be used as a nitrogen source for the denitrifying bacteria，so thatmore of NO₃^-could converted to NO, N₂O and N₂, reducing the concentration of NH₄⁺inthe water. Sufficient carbon and nitrogen sources was provided， so that heterotroic denitrifying bacteria could occur denitrification.In dynamic experiments, the water flow rate was controlled to simulate the practicalgroundwater. Experimental results show that: using corn straw and reduced zero-valentiron as the activity of filling material for permeable reactive barrier could effective removalof nitrate pollution in groundwater, after stabilization, NO₃^-concentration in the waterwas<2.0mg/L permeable reactive barrier, which fully meet the groundwater qualitystandards （GB/T14848-93） Standard requirement （NO₃^-concentration in Class â… wateris less than2.0mg/L）, the removal rate of NO₃^-could reach more than99%; theconcentration of by-product of NH₄⁺had reduce to about6mg/L or so, the concentrationof the NH₄⁺accounted for about10%of the NO₃^-concentration which has been removed..It was found that the change of water flow had little effect on nitrate nitrogen removal.