生物炭添加对曝气人工湿地脱氮及氧化亚氮释放的影响

Impact of Biochar on Nitrogen Removal and Nitrous Oxide Emission in Aerated Vertical Flow Constructed Wetland

尽管增加曝气会提升潜流人工湿地中溶解氧(DO)浓度,改善污染物去除效果,但由于湿地中氧扩散条件差,易引起DO分布不均,导致氧化亚氮(N_2O)的排放.生物炭由于孔隙率大、比表面积大,近年来逐渐被应用于传统湿地系统,实现强化脱氮和温室气体减排.为了探讨生物炭对曝气潜流湿地的影响,本实验在温室内构建曝气生物炭潜流湿地(SW),以常规曝气潜流湿地(CW)作为参照,探究生物炭投加对湿地系统脱氮性能及N_2O排放的影响.结果表明,SW系统曝气段平均DO浓度为2.66 mg·L^(-1),较CW提高了0.42 mg·L^(-1).SW系统平均出水NH_4^+-N和总氮(TN)浓度为0.17 mg·L^(-1)和1.98 mg·L^(-1),去除率分别达到99.5%和95.0%,较CW提高了5.1%和6.9%.生物炭的投加对湿地系统有机物污染去除效果无显著影响(P>0.05),出水化学需氧量(COD)稳定在25 mg·L^(-1),去除率达到94.0%.SW系统中N_2O的平均释放速率为0.27 mg·(m^2·h)^(-1),较CW系统降低了70.7%.因此,生物炭投加可作为一种有效的控制手段来强化曝气湿地系统脱氮,实现N_2O气体减排.

In an intermittent aerated vertical flow constructed wetland, the dissolved oxygen（ DO） distribution tends to be inhomogeneous because of poor diffusivity resulting in the production and emission of nitrous oxide（ N2O）. As a multifunctional environmental material with numerous porosities and a large specific area,biochar has been recently applied to enhance pollutant removal and reduce greenhouse gas emissions in traditional wetland systems. Using the conventional aerated vertical flow constructed wetlands（ CW） as the comparison,biochar-amended wetland microcosms（ SW） were built in greenhouses to investigate the influence of biochar on nitrogen removal and N2O emissions. The results showed that DO concentration in the aeration stage increased by 0. 42 mg·L^-1 in SW. Furthermore,SW achieved higher removal efficiencies for NH4^＋-N（ 99. 5%） and total nitrogen（ TN; 95. 0%） than CW. Similar removal rates of chemical oxygen demand（ COD）,close to 94%,were observed in CW and SW,indicating that no significant effects resulted from adding biochar（ P〉 0. 05）. Additionally, N2O emission fluxes of CW and SW were 0. 92 mg·（ m^2·h）^-1 and 0. 27 mg·（ m^2·h）^-1,respectively. The N2O cumulative emission in SW was 6. 58 mg·m^-2,which was significantly lower than that in CW（ 22. 03 mg·m^-2）. Biochar addition could be an effective strategy to promote nitrogen removal and reduce N2O emissions.