摘要
To address the environmental and health hazards of nitrate(NO_(3)^(-))in water,a denitrification advanced reduction process(ARP)using only formic acid(HCOOH)activated by ultraviolet(UV)light was proposed.The efficiency,influencing factors,mechanism,and kinetics of the reduction were investigated through component analysis and radical detection.Results show that,after 90 min of UV illumination,the reduction and gas conversion ratios of 50 mg/L NO_(3)^(-)-N reach 99.9%and 99.8%,respectively,under 9 mM of C_(0)(HCOOH),pH=3.0,and N_(2) aeration.Meanwhile,96.7%of HCOOH is consumed and converted into gas.The NO_(3)^(-)-N conversion process includes the transformation to NO_(2)^(-)-N,followed by a further reduction to gas and a direct conversion into gas,introducing small amounts of nitrite and ammonia.The carbon dioxide anion radical(·CO_(2)^(-))from HCOOH/HCOO^(-)is the principal cause of NO_(3)^(-)-N reduction by UV/HCOOH/N 2 ARP.In contrast,·CO_(2)^(-)production is caused by the hydroxyl radical(·OH).The NO_(3)^(-)-N reduction efficiency is enhanced by the increase in the light intensity,considerably affected by the initial pH,and less affected by inorganic anions,including Cl^(-),H_(2)PO_(4)^(-),and HCO_(3)^(-)/CO_(3)^(2-).The initial HCOOH concentration and light intensity are the main factors that influence the NO_(3)^(-)-N reduction rate.
为解决水中硝态氮引发的环境和健康问题,提出了一种以甲酸为还原剂、以紫外光为活化手段的硝态氮还原(ARP)方法.通过组分分析和自由基测定研究了体系的还原效能、影响因素、反应机理及反应动力学.结果表明:在C_(0)(HCOOH)=9mmol/L、初始pH=3.0和N_(2)曝气条件下,紫外光照90min后50mg/L硝态氮的还原率和气体转化率分别达到99.9%和99.8%,同时96.7%的甲酸被消耗并转化为气体.该体系还原硝态氮的反应中不仅存在首先生成亚硝态氮再进一步被还原为气体的过程,还存在硝态氮直接转化为气体的过程.硝态氮的还原主要由活化HCOOH/HCOO^(-)产生的二氧化碳自由基(·CO_(2)^(-))实现,而羟基自由基(·OH)是·CO_(2)^(-)的前体物.硝态氮还原率随光照强度增加而提高,初始pH值对还原效果影响较大,而Cl^(-)、H_(2)PO_(4)^(-)和HCO_(3)^(-)/CO_(3)^(2-)等无机阴离子的影响则较小.甲酸初始浓度和紫外光强是还原速率的主要影响因素.
基金
The National Major Science and Technology Project(No.2017ZX07202-004-005)。
