以10种农业废弃物为基料的地下水反硝化碳源属性的实验研究

为了选择理想的农业废弃物作为优质碳源,同时作为生物膜载体应用于可渗透反应墙(PRB),通过反硝化作用去除地下水中的硝酸盐.选择小麦秸秆、玉米秸秆、稻秆、大豆秸秆、玉米棒、稻壳、甘蔗渣、杨树枝、木屑、芦苇共10种农业废弃物进行元素分析实验、浸溶实验和长效浸出实验研究.元素分析实验结果显示,10种农业废弃物的C、N、H元素含量分别为38%~48%、5%~7%、0.5%~2.5%.短效浸出实验表明,甘蔗浸出液的总有机碳(TOC)浓度最高,均值可达38.66 mg·g~(-1),大豆秸秆、水稻秸秆、玉米秸秆、稻壳、杨树枝和小麦秸秆为8.04~15.30 mg·g~(-1),其他均值约为2.36~6.33 mg·g~(-1).但是,大部分农业废弃物均释放一定量的含氮物质.其中,硝酸盐及亚硝酸盐释放量均低于0.05 mg·g~(-1),氨氮释放量低于0.30 mg·g~(-1),凯氏氮除木屑、玉米棒、杨树枝释放量较低,其余均高于0.80 mg·g~(-1),最高可达1.65 mg·g~(-1).同时,秸秆类材料浸出液具有一定的色度,其中稻杆的色度最高,其值为1025.选择浸出液TOC浓度较高的甘蔗渣、玉米秸秆、稻壳、小麦秸秆及凯氏氮浓度较低的玉米棒和木屑作为理想碳源材料,进行长效浸出实验.结果表明,6种材料的TOC能迅速达到高位平衡状态,且溶出速率稳定,浸出液的高效液相色谱(HPLC)和气-质谱联用仪(GC/MS)分析表明,其主要成分为有机酸、糖类、含氮有机物和酯类等物质.其中,有机酸主要为甲酸、乙酸、草酸、富马酸等小分子有机酸、糖类主要为纤维二糖、葡萄糖、果糖和木糖.脱氮效能实验表明,6种农业废弃物硝酸盐去除率均达到80%以上,脱氮速率均达到1.00~2.00 mg·cm~(-3)·d~(-1)(以N计).综上,这6种材料均可作为地下水硝酸盐污染原位修复的理想碳源填充材料.

The characteristics of carbon sources for denitrification in groundwater from ten kinds of agricultural wastes

The purpose of this study was to select ideal agricultural wastes as biofilm carriers for the application of permeable reactive barrier (PRB), to remove nitrate from groundwater via denitrification. Ten kinds of agricultural wastes (including wheat straw, corn straw, rice straw, soybean straw, corn cob, rice husk, bagasse, poplar branch, sawdust and reed) were studied in elemental analysis experiments and leaching experiments, and some of them were further investigated in long-term leaching experiments. The results of elemental analysis show that the content of C, N and H were 38%~48%, 5%~7%, 0.5%~2.5%,respectively. The leaching solution of bagasse had the highest concentration of TOC with the mean value about 38.66 mg·g^-1, and average TOC concentrations in leaching solutions of soybean straw, rice straw, corn straw, rice husk, poplar branch and wheat straw ranged from 8.04 to 15.30 mg·g^-1, while the others ranged from 2.36 to 6.33 mg·g^-1. On the other hand, most agricultural wastes released a certain amount of nitrogenous substances. Both nitrate and nitrite concentrations were lower than 0.05 mg·g^-1, and ammonia was below 0.30 mg·g^-1. The concentrations of Kjeldahl nitrogen in leaching solutions were higher than 0.80 mg·g^-1(maximum 1.65 mg·g^-1) in all samples except sawdust, corn cob and poplar branch. Meanwhile, the straw-type leaching solutions had certain chrominance, and the highest chroma was in rice straw leaching solution (up to 1025). According to these results, high-TOC-release wastes (bagasse, corn straw, rice husk and wheat straw) and low-nitrogen-release wastes (corn cob and sawdust) were selected as potential ideal carbon sources, and were further investigated for long-term leaching. The results indicate that the TOC concentration in the chosen materials reached the high-level equilibrium quickly, and the dissolution rates were stable. Furthermore, analysis of the leaching solutions from the chosen wastes through High-Performance Liquid Chromatography (HPLC) and Gas Chromatography-Mass Spectrometer (GC/MS) reveales that the main components were organic acids, carbohydrate, nitrogenous organics and esters. The main organic acids included formic acid, acetic acid, oxalic acid, fumaric acid and other small molecular organic acids. The carbohydrates mainly consisted of cellobiose, glucose, fructose and xylose. It is found that nitrate removal rate of all six kinds of agricultural wastes reached 80% or higher, and the nitrogen removal rate reached 1.00~2.00 mg·cm^-3 ·d^-1. Our results indicate that the selected six kinds of agricultural wastes can be used as ideal carbon source for in-situ remediation of nitrate pollution in groundwater.