Removal Of Groundwater Nitrate By Biochar And Zero-valent Iron And Its PRB Repair Performance

Groundwater plays an important role in China’s residential water.However,groundwater pollution in northern China is extremely serious,and the groundwater nitrate content exceeds the limit in more than half of these areas,which is a great harm to humans and natural ecosystems.This project adopts zero-valent iron-biochar to remove nitrate,which is efficient and environmentally friendly.In this paper,biochar（BC）was prepared from pine sawdust as raw material at 400^oC and zero-valent iron-biochar was uesd to remove nitrate and to study the possibility of selective nitrogen conversion in the product.In addition,we also simulated the application of zero-valent iron-biochar as a filler in PRB.The main findings are as follows:（1）The optimal amount of biochar is 0.3 g,at which time the nitrate removal rate of84.51%and the nitrogen selectivity of 67.53%can be achieved.Zero-valent iron-biochar can be adapted in a wide p H range（3.0-11.0）,and the removal rate of nitrate and nitrogen selectivity are above 72.84%and 71.76%,respectively.When the initial nitrate concentration is 60 mg·L^-1,zero-valent iron-biochar has the highest removal amount of nitrate（40.61 mg）,and the nitrogen selectivity can reach 75.66%.H₂PO₄^2-can inhibit the formation rate decreased.Both the nitrate removal rate and nitrogen selectivity increased with increasing temperature（15^oC-35^oC）,the activation energy of the reaction was18.50 k J·mol^-1,and the molecular diffusion had a large effect on the reaction..（2）The removal of nitrate by zero-valent iron-biochar has the highest removal amount of nitrate conforms to second-order kinetics,with a kinetic rate constant of0.008（mg·L）^-1·min^-1.zero-valent iron-biochar has the highest removal amount of nitrate has better ability to reduce nitrate rather than nitrite,BC-Fe（Ⅱ）has stronger ability to reduce nitrite,and nitrite is more likely to be converted to nitrogen.Fe⁰-BC-Fe（Ⅱ）can realize the optimization of the reaction,with a nitrate removal rate of 99.16%and a nitrogen selectivity of 85.66%.（3）The reduction reaction of zero-valent iron-biochar to nitrate can be maintained for a long time,and the effluent always meets the water quality requirements.Zero-valent iron-biochar has an excellent performance as a PRB filler in various aspects.The loading method has an effect on the early stage of the reaction and has little effect on the final removal rate of nitrate in the reaction.The flow rate is an important factor to determine the nitrate removal rate,and the removal rate of nitrate: 0.3L·d^-1> 0.7 L·d^-1> 1.5 L·d^-1.