Team:NFLS/Description
Inspiration— Why do we choose our project?
As high school students under fierce pressure of education system, all our team members possess hundreds of test paper and textbooks, which pile up in the corner of our houses with no perfect treatment. We investigated the present situation of waste paper disposal and found it not environmentally benign. To be specific, the main way of waste paper processing is to recycle it. As raw material of papermaking, waste paper goes through several technological processes like pulping, deslagging and deinking, and finally manufactures new paper products. However, some paper cannot be recycled because recycling low quality paper may potentially leads to accumulation or un-intended spreading of chemical substances contained in paper. Paper that doesn’t reach the standard of being recycled is burned or buried, polluting the environment and threatening people’s health.
At the same time, one of our team members took part in an agricultural knowledge trainee at Nanjing Ecology Agriculture Base, studying eco-agriculture and communicating with local farmers, who pointed out that they were confronted with the disposal of large amount of agriculture waste like straws. Precisely, a large number of straws are burned by farmers to be fuels, polluting the air and causing compaction of the soil as well. Though the local governments in some advanced areas do introduce regulations to limit the burning of straws, only a tiny proportion of them are reutilized to develop stockbreeding, while most of the straws are heaped up in the fields and left alone to decay [1]. The numerous rotten straws produced in rural areas every year are a huge waste of resources since they contain ample cellulose.
In conclusion, the disposal of either waste paper or straws is imperfect. As both of them are composed mainly of cellulose, we decided to fuse the two ideas into one project and devise an environmentally friendly way to process them.
Our solution— a system degrading cellulose and generating electricity
Overview：
Since the main composition of both waste paper and straws are cellulose, we use engineered Escherichia coli (E.coli) to degrade cellulose into glucose and use Microbial Fuel Cell (MFC) to convert this chemical energy into electrical energy.
Why E.coli?
MFCs rely on electrochemically active bacteria to capture the chemical energy contained in organics and convert it to electrical energy [2], while E.coli is one of the most commonly used electrochemically active bacteria.
Why genetic engineering?
There are already cellulose-decomposing microbes, why do we genetically engineered E.coli? According to an essay [3], the complete extracellular hydrolysis of celluloses has several critical barriers in biomass technology and the intracellular cellobiose assimilation is an alternative bioengineering strategy. The most efficient way of degrading cellulose is to degrade cellulose into cellobioses extracellularly and degrade cellobioses into glucose intracellularly. Accordingly, we genetically engineer the E.coli to secrete endoglucanases and exoglucanases outside to respectively degrade cellulose to oligosaccharides and then to cellobioses. Cellobioses get into E.coli through transport protein and are degraded into glucose by β-glucosidases. During this process, countless E.colis are working in the MFC as fuels to generate electricity.(view more in Design)
References
[1] 宋成琼. 秸秆综合利用的现状与对策. 农民致富之友. 1003-1650(2014) 11-0104-01
[2] Suzanne T Read, Paritam Dutta, Phillip L Bond, Jürg Keller & Korneel Rabaey. Initial Development and Structure of Biofilms on Microbial Fuel Cell Anodes. BMC Microbiol. 2010 Apr 1;10:98.
[3] Vinuselvi Parisutham, Sathesh-Prabu Chandran, Aindrila Mukhopadhyay, Sung Kuk Lee, Jay D Keasling. Intracellular cellobiose metabolism and its applications in lignocellulose-based biorefineries. Bioresour Technol. 2017 Sep;239:496-506
