纳米乳化油修复地下水硝酸盐过程中产气及微生物增殖代谢对多孔介质堵塞的模拟评估

Simulated assessment of gas production and microbial proliferation and metabolism on porous media clogging in groundwater nitrate remediation by nano emulsified vegetable oil

为有效评估纳米乳化油原位处理地下水硝酸盐过程中,产气及微生物增殖代谢对含水层多孔介质的堵塞作用,以纳米乳化油为碳源,采用市售反硝化菌剂接种微生物进行硝酸盐降解批实验研究,探讨产气及微生物增殖代谢的动态变化及特征,并基于Kozeny-Carman(K-C)方程、Clement、Pham及Kozeny Grain(KG)模型,对假定含水层一维流模拟柱,预估产气及微生物增殖代谢造成的渗透性损失,识别堵塞过程及主导因素.结果显示,反硝化菌降解效果良好,硝氮总去除率达90.23%.CO2及N2为主要产气成分,降解1 mg硝氮对应的平均CO2产气量为0.71 mL,平均N2产气量为0.14 mL;微生物代谢产物胞外聚合物以蛋白质及多糖为主,降解1 mg硝氮平均蛋白产量为0.64 mg,平均多糖产量为0.16 mg.在含水层不与外界交换气体的假设前提下,K-C方程预测显示产气可在2个周期内造成渗透性完全损失,Clement、Pham及KG模型评估的微生物增殖代谢造成中、细砂渗透性损失分别为10.87%~31.10%、12.77%~48.32%,分析认为初期细胞生物量是导致渗透性骤降的关键因素,后期为细胞生物量和胞外聚合物共同作用.此外,封闭体系中产气是堵塞的主导因素,随着含水层开启程度增加,产气的贡献占比会下降,微生物的贡献占比提高.因此,对于相对封闭的含水层系统,探索增强其开放状况是缓解堵塞的有效途径之一.

Batch experiments were carried out to study the dynamic changes and characteristics of gas production and microbial proliferation and metabolism on porous media clogging during in-situ remidation of nitrate pollution with nano-emulsified vegetable oil. The reaction system was inoculated by commercial denitrifying bacteria and nano-emulsified vegetable oil was used as carbon source. Meanwhile, based on assumed aquifer conditions, the permeability loss of one-dimensional simulated column caused by gas production and microbial proliferation and metabolism was predicted by using Kozeny-Carman(K-C) equation, Clement, Pham and Kozeny Grain(KG) models. The clogging processes and the leading factor of clogging were also determined. The results indicate that denitrifying bacteria shows a good degradation performance with a removal efficiency of 90.23% nitrate nitrogen. The average CO2 and N2 production corresponding to the degradation of 1 mg nitrate nitrogen were 0.71 mL and 0.14 mL, respectively. The extracellular polymeric substances of microbial metabolites were mainly composed of proteins and polysaccharides. The average content of proteins and polysaccharides produced 0.64 mg and 0.16 mg per mg of nitrate, respectively. Assuming that the aquifer does not exchange gases with the outside, the prediction results of K-C equation show that the gas production can result in complete permeability loss in two cycles. The predicted results of Clement, Pham and KG models indicate that the permeability losses of medium sand and fine sand caused by microbial proliferation and metabolism were 10.87%~31.10% and 12.77%~48.32%, respectively. It is concluded that the biomass of microbial cells was the key factor leading to a sudden decrease of permeability in the early stage. In contrast, the permeability loss of porous media in the later stage was a comprehensive function of biomass and extracellular polymeric substances. In addition, gas production was the leading factor of clogging in the closed system, and with the increase of aquifer opening degree, the contribution of gas production in permeability loss gradually decreased, while that of microorganisms gradually increased. Hence, for a relatively closed aquifer system, exploring the ways to enhance its opening condition is one of effective ways to alleviate the clogging.