硝酸盐缓释凝胶强化生物降解地下水中甲苯研究

Enhanced Biodegradation of Toluene in Groundwater by Temperature-Sensitive Nitrate Slow-Release Gels

硝酸根作为微生物介导的厌氧还原过程中重要的电子受体,其浓度对污染物降解阶段起关键性作用。然而在未经干涉的低扰动地下水介质中,由于硝酸根的纵向补给受限,导致一旦消耗殆尽,污染物的硝酸根厌氧还原过程就会中断。本文通过调控琼脂糖与明胶的掺杂比例(1∶3、1∶1和3∶1),制备了不同孔隙大小和密度的硝酸盐缓释凝胶(Nitrate agarose gelatine,NAG,分别记为NAG_(0.25)、NAG_(0.50)和NAG_(0.75)),实现了硝酸根的长效稳定释放和定向补给。结果表明:①琼脂糖-明胶缓释凝胶具有密集连续的孔道结构,硝酸根在其中负载储藏,在15℃条件下,NAG_(0.25)可以实现硝酸盐缓释时间达3000 min。②琼脂糖-明胶缓释凝胶作为填料,可以有效补给含水层中硝酸根,并促进包括Lysobacter sp.和Massilia sp.在内的具备硝酸根还原能力的特征微生物增殖,强化甲苯的衰减。③30 d时间内,实现甲苯污染羽中心浓度衰减率达59.15%,污染羽范围大幅缩减。④修复过程中监测到硝酸盐最高浓度为10.14 mg/L,硝酸盐的补给不会对地下水构成二次污染。研究显示,基于琼脂糖-明胶构建的硝酸盐缓释凝胶具备补给地下水硝酸根、促进微生物厌氧还原甲苯的作用,为实际场地强化自然衰减提供理论支撑和经验支持。

As an important electron acceptor in the microbially mediated anaerobic reduction processes,nitrate plays a critical role in contaminant degradation.However,in uninterrupted groundwater media,limited vertical recharge of nitrate leads to a subsequent interruption of the nitrate anaerobic reduction process once it is depleted.In this study,nitrate agarose gelatine gels(NAG,denoted as NAG_(0.25),NAG_(0.50) and NAG_(0.75),respectively)with different gel pore sizes and densities were developed based on agarose and gelatin by modulating the doping ratio of raw materials(1∶3,1∶1 and 3∶1),to achieve the long-term stable release and directional recharge of nitrate.The results showed that:(1)The agarose-gelatin slow-release gel had a dense and continuous pore structure in which nitrate was loaded and stored,and the slow-release time of NAG_(0.25) was up to 3000 min under the condition of 15℃.(2)As a filler,the agarose-gelatin slow-release gel effectively recharged nitrate in the aquifer,promoting the proliferation of nitrate-reducing microorganisms,including Lysobacter sp.and Massilia sp.,thereby enhancing toluene degradation.(3)The attenuation rate of the central concentration of the toluene plume reached 59.15%,and the plume extent was significantly reduced within 30 days.(4)The highest concentration of nitrate observed during the remediation process was 10.14 mg/L,ensuring that recharge of nitrate did not result in secondary contamination of groundwater.This study demonstrates that the agarose-gelatin-based nitrate slow-release gel can effectively recharge groundwater nitrate and enhance microbial anaerobic toluene degradation.These findings provide both theoretical and empirical support for enhanced natural attenuation at actual contaminated sites.