铁碳复合效应对塘床系统脱氮的强化机制研究

Tail water from wastewater treatment plants has been the main source of aquatic nitrogen pollution recently, economic and ecological methods for nitrogen removal from tail water are deeply demanded in our country. Although constructed wetlands (CWs) have the ability on advanced nitrogen removal, nitrification-denitrification as the main nitrogen removal mechanism in CWs is subject to insufficient oxygen and carbon source. In this proposal, algal pond-CW bed integrated system has been raised to enhance the carbon-oxygen level of CWs by utilizing algae photosynthesis. Simultaneously, iron-carbon composition effect composed of sponge iron-calcium carbonate compounds and iron-carbon micro-electrolysis packing has been introduced into integrated system to enhance nitrogen removal. Sponge iron-calcium carbonate compounds as growth regulators are put into algal ponds to increase algal biomass; ferric salt-biochar as micro-electrolysis packing are put into CWs to accelerate the utilization efficiency of algae organic residues by microorganisms, and electronic supply capacity of ferric salts and algae organic matters can create the synergetic denitrification effects. With the analysis of carbon-nitrogen-oxygen temporal-spatial variability, the impact of sponge iron-calcium carbonate compounds on algae physiological attribute and the effect of micro-electric field on microbial ecology and iron-carbon electron transfer, are investigated. By which, the enhancement mechanism of iron-carbon composition effect on nitrogen removal of integrated system will be revealed. Further, the key factors affecting nitrogen removal of iron-carbon coupled pond-bed integrated system will be explored. The research project will provide scientific bases and technological supports for efficient nitrogen removal of low C/N tail water from wastewater treatment plants.

污水厂尾水上升为水体氮污染的主要来源，而国内缺乏经济生态的尾水脱氮方法。人工湿地（CWs）具有深度脱氮的能力，但作为其脱氮主要过程的硝化/反硝化受到碳氧不足的制约。本项目提出由藻塘和CWs结合而成的塘床系统，利用藻类光合作用增强CWs中的碳氧水平。同时本项目利用海绵铁-碳酸钙复合物与铁碳微电解填料形成的铁碳复合效应，强化塘床系统的脱氮禀赋。海绵铁-碳酸钙复合物作为生长调节剂被投入藻塘，提高藻类生物量；铁盐与生物炭作为微电解填料被填入CWs，提高微生物利用藻类有机残体的效率，铁盐与藻类有机碳源的供电子能力产生协同反硝化效应。通过研究海绵铁-碳酸钙复合物对藻类生理属性的影响，以及微电场对CWs中微生物生态和铁碳电子传递的影响，结合碳氮氧时空变化分析，阐明铁碳复合效应对塘床系统脱氮的强化机制。深入探索影响铁碳耦合塘床系统脱氮的关键因素，为低C/N比污水厂尾水的高效脱氮提供科学依据和技术支撑。

近年来氮污染正上升为我国主要的水环境问题。由藻类塘和人工湿地结合而成的塘床系统，具有明显的生态经济效益和修复水体氮素污染中优势互补的可塑性。本研究发现：藻类塘中富含的藻菌体系可吸收降解氮素；藻类光合作用还可提高水体的氧含量，并将空气中吸收的无机碳转化为有机碳。因此，藻类有机体死亡后可向水体补充有机碳源。利用藻类塘出水可实现对人工湿地中碳氧水平的生态调控，提升湿地硝化和反硝化脱氮效率。人工湿地则通过截留、吸附并利用藻类有机残体作为碳源，去除藻类塘出水中过剩的藻类。本研究向藻类塘中投加海绵铁和碳酸钙作为生长调节剂，经研究证实海绵铁-碳酸钙复合物有助于促进藻类光合、固氮和代谢过程，藻类生物量得到明显提升，有效促进了塘床系统内的碳氧水平。本研究还通过研制一种经济高效的铁碳微电解填料，进一步增强湿地填料属性和脱氮能效。主要研究结论如下：1、铁碳微电解人工湿地中硝态氮去除率显著高于未添加铁碳填料的空白人工湿地，平均去除率提高了约35.0%；2、铁碳微电解人工湿地中COD去除率与未添加铁碳填料的空白湿地相比，平均提高了约21.0%左右；在间歇递进增氧作用方式下，污染物实现了较好的去除效果。其中，COD的平均去除率达到92.2%，氨氮的平均去除率达到63.1%，硝态氮的平均去除率达到66.0%；3、通过对铁碳微电解人工湿地和空白湿地中基质样品进行高通量测序及分析后，得出以下结论：通过向湿地内投加铁碳微电解填料，可大幅度提高其微生物多样性以及丰度，尤其是湿地内部的反硝化菌属丰度和多样性有了较大幅度的提升。利用塘床系统的生态协同机制，可经济高效地实现水体脱氮的目标。通过海绵铁-碳酸钙复合物与铁碳微电解填料形成的铁碳复合效应，强化塘床系统的脱氮禀赋。本研究通过阐明铁碳复合效应对塘床系统脱氮的强化机制以及影响铁碳耦合塘床系统脱氮的关键因素后，为低碳氮比污水厂尾水的深度脱氮提供新思路和新方法。