| Resource & environmental sciences |
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| Preparation and performance study of water purification bacteria-embedded solid capsules based on texture profile analysis. |
| Wang Qingsong1, Liu Yong2, Wang Xin2, Sun Hong2, Yao Xiaohong2, Wu Yifei2, Tang Jiangwu2*, Ge Xiangyang1* |
| (1. State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China; 2. Institute of Plant Protection and Microbiology, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China) |
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Abstract The technology for microorganism immobilization originated from the immobilized enzyme technology in the 1970s. After decades of development, it has been widely used in food fermentation and environmental protection, etc. Especially, microbe-embedded capsules have drawn substantial attentions from researchers due to their significant roles in water purification and sewage treatment. However, lack of consolidated standards has impeded their applications. Texture profile analysis (TPA) has been widely used in food industry for determination of product structure and quality, while its application in non-food field is yet to be explored. Therefore, in the present study, TPA was used for the development and optimization of bacteria-embedded solid capsule systems in the purpose of water purification.
To achieve this purpose, solid capsules were prepared with different materials, such as diatomite, zeolite powder and bamboo charcoal in different blending ratios. TPA was employed to characterize these capsules in respects of hardness, cohesiveness and elastic resilience (springiness). Meanwhile, scanning electron microscopy (SEM) was adopted to investigate the sectional structure and pore size of these capsules. Furthermore, simulative experiments in both ultrapure water and sewage were carried out to examine the releasing velocity and water purification efficiency of these bacteria-embedded solid capsules. Combining with TPA and SEM, the factors influencing the internal structure of capsules including embedding/crosslinking medium, curing duration, and ingredient proportions were explored, thus providing standards and guidelines for the preparation of bacteria-embedded capsules for large-scale practical applications in the future.
The TPA data showed that a high ratio of sodium alginate in the embedding medium resulted in capsules with high strength, and polyvinyl alcohol rendered cohesiveness and resilience (springiness) to capsules. An optimal embedding medium system was established as follows: V(4% sodium alginate) ∶V(10% polyvinyl alcohol)=1∶9 for embedding medium, while the mixture of 4% boric acid and 4% calcium chloride for crosslinking medium. The optimal concentrations of various materials were determined as follows: 20%30% for diatomite, 20% 80% for zeolite powder and 20%60% for bamboo charcoal. The optimal curing duration varied from 16 to 36 h. The SEM images indicated the existence of internal microspores both at nanoscale and micron-size in the crosslinked capsules, and differences on microstructures of capsules were observed among single or combining addition of diatomite, zeolite powder and bamboo charcoal. Both specific surface area and pore volume decreased after embedding, but not for pore size. The releasing rates of bacteria in capsules in 24 h were low, from 1% to 14%. In the simulative experiments of the sewage purification, all groups, including bacteria-embedded capsule and free bacteria, showed good ammonia removal efficiency. The final concentration of ammonia was below 0.1 mg/L after 20 h, while the initial concentration was 39.3 44.7 mg/L. The bacteria-free group had the highest ammonia removal efficiency, followed by mixture 1 group (1 mL of 4% sodium alginate, 9 mL of 10% polyvinyl alcohol, 1.5 g diatomite, 0.5 g zeolite powder, 0.5 g bamboo charcoal, and 2 mL bacterial culture) and bamboo charcoal group. Meanwhile, the total nitrogen concentration decreased at a certain degree. These results confirmed that these capsules were applicable for sewage treatment.
In conclusion, the present study establishes successfully standards and guidelines for the preparation of bacteria-embedded capsules on the basis of TPA in combination with SEM and simulative experiments. This profound step can accelerate the practical application of bacteria-embedded capsules in actual sewage purification.
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Published: 20 November 2015
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基于质构量化分析的净水菌胶囊制备及其性能研究
为提高净水菌剂的应用性能，通过固定化包埋处理，以实心载菌胶囊为研究模型，以质构量化分析数据为主要筛选依据，通过不同辅料配方和制作工艺对胶囊的硬度、黏聚性和弹性恢复进行比较研究，以筛选出较佳的辅料配方和加工工艺，并对较佳配方的载菌胶囊进行断面形貌观察、孔隙率测定、菌剂释放率测定和氨氮模拟污水净化实验。结果表明：较佳成囊壁材配方为V(4%海藻酸钠)∶V(10%聚乙烯醇)=1∶9，固化液配方为4% H3BO4和4% CaCl2混合溶液，辅料硅藻土、沸石粉和竹炭的适宜添加量分别为20%~30%、20%~80%和20%~60%；胶囊为多孔结构，单独添加硅藻土、沸石粉、竹炭或三者混合添加下，胶囊微观结构存在差异，其中硅藻土、沸石粉和竹炭经包埋后比表面积和孔容均减小，孔径变化不大；24 h内胶囊中菌剂的水体释放率较低，为1%~14%；载菌胶囊在模拟污水净化实验中，20 h后各实验组氨氮质量浓度从1 h时的39.3~44.7 mg/L降低到0.1 mg/L以下，其中未经包埋的菌株直接投放组降低最快，其次为混合1组［V(4%海藻酸钠)∶V(10%聚乙烯醇)=1∶9，海藻酸钠和聚乙烯醇总体积10 mL+硅藻土1.5 g+沸石粉0.5 g+竹炭0.5 g+菌悬液2 mL］和竹炭组，同时，总氮也出现不同程度的降低。总之，该研究采用的质构量化分析方法为净水菌固定化载体研究提供了可靠的数据支撑，研究获得的优化胶囊体系在质构和净水能力方面均表现出良好的性能，在环境污染水体微生物净化治理方面具有较大的应用潜力。
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