Removal of Cr(Ⅵ)by glutaraldehyde-crosslinked chitosan encapsulating microscale zero-valent iron:Synthesis,mechanism,and longevity

Microscale zero-valent iron(mZVI)has shown great potential for groundwater Cr(Ⅵ)remediation.However,low Cr(Ⅵ)removal capacity caused by passivation restricted the wide use of mZVI.We prepared mZVI/GCS by encapsulating mZVI in a porous glutaraldehydecrosslinked chitosan matrix,and the formation of the passivation layer was alleviated by reducing the contact between zero-valent iron particles.The average pore diameter of mZVI/GCS was 8.775 nm,which confirmed the mesoporous characteristic of this material.Results of batch experiments demonstrated that mZVI/GCS exhibited high Cr(Ⅵ)removal efficiency in a wide range of pH(2-10)and temperature(5-35℃).Common groundwater coexisting ions slightly affected m ZVI/GCS.The material showed great reusability,and the average Cr(Ⅵ)removal efficiency was 90.41%during eight cycles.In this study,we also conducted kinetics and isotherms analysis.Pseudo-second-order model was the most matched kinetics model.The Cr(Ⅵ)adsorption process was fitted by both Langmuir and Freundlich isotherms models,and the maximum Langmuir adsorption capacity of m ZVI/GCS reached243.63 mg/g,which is higher than the adsorption capacities of materials reported in most of the previous studies.Notably,the column capacity for Cr(Ⅵ)removal of a mZVI/GCS-packed column was 6.4 times higher than that of a mZVI-packed column in a 50-day experiment.Therefore,mZVI/GCS with a porous structure effectively relieved passivation problems of mZVI and showed practical application prospects as groundwater Cr(Ⅵ)remediation material with practical application prospects.

微米铁复合生物碳源对地下水中1,2-二氯乙烷的高效去除

1,2-二氯乙烷(1,2-DCA)是一类地下水中常见的难降解饱和氯代烃,为探究厌氧条件下零价铁(ZVI)协同生物作用对其降解规律,采集北京市某氯代烃污染场地地下水及含水层土壤,利用微宇宙实验体系,通过添加由微米级零价铁(mZVI)、生物碳源及营养组成的复合药剂,考察不同条件下1,2-DCA的去除效果,并对地下水理化参数的变化进行长期监测.结果表明:复合药剂添加量为3%时,恒温、避光、匀速振荡的反应条件下,15 d内地下水中的1,2-DCA即可降至低于检出限.中性pH及SO_4^(2-)的存在更有利于1,2-DCA的脱氯降解. 30 d后仅检测到体系中明显的乙烯产生,推测双脱氯消除为1,2-DCA在该体系内的主要降解途径.此外,复合药剂加入后,地下水可长时间维持较低的氧化还原电位(-100～-300 m V)、溶解氧(<0. 5 mg·L^(-1))以及适宜的pH值(6. 5～7. 5),利于厌氧微生物活性的维持及脱氯反应的进行.

微米零价铁对剩余活性污泥和餐厨垃圾厌氧联合消化的加强效果及机制

针对剩余活性污泥和餐厨垃圾厌氧联合消化产气效率不高的问题,通过投加微米零价铁,研究其对厌氧联合消化的强化效果及作用机制.结果说明,零价铁的添加强化了厌氧联合消化的产甲烷阶段,但对溶解、水解及酸化阶段没有明显影响.当零价铁的投加量为10 g·L^(-1)时,经过15 d的厌氧消化,累积甲烷产量(以VS计)达到238.68 mL·g^(-1),相比于空白组提高了20.05%.机制分析表明:零价铁提高了系统的电子传递体系(ETS)活性,当零价铁投加量为10 g·L^(-1)时,最终的ETS活性(以INTF/TS计)达到21.50 mg·(g·h)^(-1),而空白组仅为13.43 mg·(g·h)^(-1).此外,零价铁还强化了细菌和产甲烷菌之间的直接性种间电子传递(DIET),微生物群落的变化显示DIET相关的微生物,例如Syntrophomonas、Methanosarcina和Methanobacterium,在有零价铁添加的条件下显示出更高的丰度.