Due to slow flow rates and inter-substance reactions in groundwater, remediation requires the addition of materials with sustained release properties. This research uses agricultural waste and zero-valent iron (Fe0), coupling biology and chemistry, to research and develop a sustainable long-release carbon material with a synergistic physico-habitat, and to evaluate its performance, also taking into account the occurrence of nitrogen in groundwater. The material developed has a double-layer structure with an inner core and an outer shell. The core, consisting of agricultural waste, Fe0, and other raw materials, constitutes the repair layer. Agricultural waste provides a carbon source for microorganisms, and Fe0 can quickly remove nitrate via chemical reactions and reduce DO to develop an anaerobic environment in water. The shell provides a solute permeation layer and consists of primary minerals and other components. This can slow the release of TOC from the core and adsorb secondary contaminants. Physical properties testing showed that the materials core was uniformly cross-linked, and its shell exhibited a clear uniform pore structure (SEM). Favorable mechanical compression was recorded for particle strengths of up to 80-105 N. With a density of 1.1 g·cm-3, the material did not float in water. Experiments showed that the material had excellent sustained release. The amount[Max:21-25 mg·(g·L)-1] and rate[Max:0.185 mg·(g·L·d)-1] of TOC release exhibited a steady state trend, but fluctuated greatly in the case of agricultural wastes[(Max amount:53-75 mg·(g·L)-1, Max rate:0.455 mg·(g·L·d)-1]. In terms of further functional gene abundance, materials leachate was found to be conducive to denitrifying bacteria. In early denitrification and oxygen trapping experiments, the Fe0 chemical reaction was dominant for reduction of nitrogen and DO, facilitating denitrification. However, biological denitrification gradually dominated. Differences in denitrification rates between iron-free and iron-containing materials were smaller, as was the correlation between denitrification rate and iron content. These results indicate the formation of physico-habitat synergistic denitrification in the materials system.
Keywords: controlled carbon release; denitrification; groundwater remediation; physical and chemical-habitat synergistic nitrogen removal; sustainable long-release carbon material.