我国“十四五”规划和2035年远景目标纲要提出: 实施国家节水行动, 鼓励再生水利用。 再生水回用是实现水资源可持续发展的重要途径。 将再生水用于贫水区农业灌溉, 有望取得良好的经济效益、 生态效益和社会效益, 同时也符合“碳达峰碳中和”(即“双碳”)的政策导向和宏观要求。 现阶段, 我国对再生水农灌的基础性研究刚刚起步、 成果不多, 尚无法提供系统性的数据支持和理论指导。 以陕西省西安市和辽宁省沈阳市的两种污水源再生水(分别记为A水样和B水样)为研究对象, 借助紫外可见光谱(UV-Vis)、 元素分析、 三维荧光光谱(3D-EEMs)和傅里叶变换红外光谱(FTIR)比对再生水DOM性质差异, 结合特征参数剖析DOM微观信息。 结果发现: UV-Vis图谱的250~270 nm附近出现吸收平台, 源于DOM双键结构和腐殖质芳香族组分; 210~250 nm吸收带则由DOM不饱和双键共轭结构引起。 紫外可见特征参数和元素分析原子比值表明: A水样DOM腐殖化程度更高、 相对分子质量更大, B水样DOM苯环C骨架聚合度较低、 内源性更明显; 微生物活动对水样DOM的组成干扰相当关键。 两种水样DOM的3D-EEMs图谱均出现三处明显特征峰, 分别位于 E_x/ E_m=280/310 nm(类酪氨酸)、 E_x/ E_m=230/320 nm(类色氨酸)和 E_x/ E_m=250/460 nm(类腐殖质); DOM具有较强自源性, 但其总体芳香性都不高, B水样新近产生的“新鲜”DOM较多。 两种水样DOM的FTIR图谱高度相似, 均在3 460~3 420 cm^-1(—OH和—NH₂伸缩振动)、 2 925 cm^-1(—CH₂不对称伸缩振动)、 1 639 cm^-1 (C=O伸缩振动和N—H弯曲振动)和1 412 cm^-1(—CH₂剪式变形振动)等处出现特征峰, 表明两种水样DOM官能团差异很小, 类蛋白组分、 碳水化合物和芳香类有机物是DOM主要组分。 相关结果有助于深度预估农灌过程再生水DOM的环境行为和生态效应。

“Promoting the national water conservation action” and “encouraging the reutilization of reclaimed water” is officially described in “The 14th Five-Year Plan for National Economic and Social Development of China (2021——2025)” and “the Long-Range Objectives Through the Year 2035”. The reuse of reclaimed water in the water-deficient areas is important for the sustainable development of water resources. Reclaimed water-irrigated agriculture can achieve comprehensive economic, ecology and society benefits, and conforms to the national policy requirements of Carbon Peak and Neutrality (namely “Double Carbon”). The fundamental investigation on reclaimed water-irrigated agriculture is generally beginning, and the related achievements can seldom be found. Two kinds of reclaimed water samples from wastewater treatment plants in Xi’an City, the capital of Shaanxi Province in northwestern China and Shenyang City, the capital of Liaoning Province in northeastern China, were recorded as “water sample A” and “water sample B”, respectively, were used in the research, and methods of ultraviolet-visible spectroscopy (UV-Vis), elemental analysis, three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEMs) and Fourier transform infrared spectroscopy (FTIR) was applied to analyze DOM in water samples. The characteristic constants were further discussed to study the detailed information of DOM. The results show taht the absorption regions of 250~270 nm appear in UV-Vis spectra, indicating double-bond structure and aromatic components, and the absorption peaks at 210~250 nm are caused by unsaturated double-bond conjugate structure in DOM. DOM in “water sample A” shows a higher humification degree and a greater relative molecular mass, while it suggests a low polymerization degree of C-skeleton in the benzene ring and a more obvious endogenous feature in DOM from “water sample B”. The nature of DOM can be significantly affected by micro-organisms activities. The DOM fluorescence peaks appear at three locations, which are E_x/ E_m=280/310 nm (Tyrosine-like components), E_x/ E_m=230/320 nm (Tryptophan-like components) and E_x/ E_m=250/460 nm (Humus-like components), respectively. DOM in two water samples are autochthonous and of low-aromaticity, and DOM in “water sample B” is relative fresh and new generated. The FTIR spectra of the two DOM samples are similar, and the representative peaks appear at 3 460~3 420 cm^-1 (stretching vibration of —OH and —NH₂), 2 925 cm^-1 (asymmetric stretching vibration of —CH₂), 1 639 cm^-1(stretching vibration of C=O and bending vibration of N—H) and 1 412 cm^-1 (shear deformation vibration of —CH₂). Functional groups of DOM in two water samples very little, and the main elements are the protein-like components, carbohydrates and aromatic organic compounds. The achievements are significant to pre-evaluate the environmental behavior and ecological effect of DOM in reclaimed water used for agricultural irrigation.