Exploration and discovery

A geomicrobiologist by background, my interest was always in the study of natural stratified microbial ecosystems. Passionate about the study of the relationship between the different biological compartments of a given ecosystem, I wanted to understand how organisms mutually adapt to their environment and how they subsequently shape their surroundings.

Whilst studying stratified microbial ecosystems, I always had in the corner of my mind the desire to create artificial complex microbial ‘ecosystems’ that could help reduce the impact of human activities on the environment. Since microbial fuel cells (MFCs) are a bio-electrochemical technology converting organic waste into electricity, this field of study immediately caught my interest.

Even thoughthe first MFCs是由m·c·波特在1911年,这项研究field only started to really develop in the 90’s. Hence, it is a relatively young area of research with a lot of opportunity for exploration and discovery!

这是如何运作的？

MFC是一项技术，微生物在其厌氧呼吸中采用电极（阳极）作为末端电子受体。这导致化学能（减少有机物）直接转化为电能，这又意味着从废水到尿液的任何物质都可以用作燃料。

The technology’s intrinsic characteristics are: low power (compared to established technologies), a wide range of organic matter (otherwise considered waste) which can be used as fuel, low fiscal and maintenance costs, durability and robustness.

将多个单独的MFC单元组装成堆栈时，可以达到可利用的功率。在这种情况下，单个MFC的规模在集体的绩效中起着重要作用。

Although units can be enlarged, this affects the power density.

Although units can be enlarged, this affects the power density. This is primarily due to diffusion limitations and sub-optimal volume-to-surface-area ratios, meaning the power density is lowered.

To date, the only way to obtain high power densities was to employ small MFCs, which maximally exploit the active surfaces where the microbial biofilms transfer electrons. To reach exploitable power however, an enormous number of units is needed.

因此，能够增加功率密度损失有限的单元的大小是将技术部署在工业规模上以外的应用程序的部署的主要障碍。

扩大而不会失去能量

为了克服由于尺寸增加而引起的功率密度损失，我们的主要目标成为增加了生物界面，作为固定比率与较小单位的比率。实际上，具有多个微环境意味着增加单位大小不会增加扩散限制，因为在电活性尺度上，所有接口和扩散距离都将保持在最低限度。

However, in order to maximize bio-interfaces within a fixed volume, a novel design of MFC was needed. Electrical power generation mainly resides in the difference of氧化还原电位between an anode and a cathode. Hence the multiplication of these redox gradients (between anodes and cathodes) was the challenge.

考虑到需要简单性和低成本的需求，我们受到了启发分层微生物生态系统。例如，当某些湖泊在夏季分层时，我们观察到，各种微生物群落沿水柱的塞/缺氧界面进行分层，具体取决于它们的特定代谢（沿着不同氧化还原状态的元素梯度）。

Following on from that observation, we recreated an environment whereby the activity of microorganisms allowed a water column (urine in our case) to self-stratify, with an oxic upper part and an anoxic bottom part.

By doing so, a difference of redox potential was created between these two liquid layers. A number of cathodes could then be placed in the upper part of the urine column whilst a number of anodes could occupy the bottom part.

The result is a novel MFC design with all its anodes and most of its cathodes submerged in the same electrolyte – without short-circuiting. The obtained simplified and inexpensive design is shown to allow scale-up with limited losses in power density. The obtained stack was also shown to be stable and powerful: the power from this design is in the high range of existing, more complicated designs.

未来会带来什么？

在过去的三十年中，MFCS的研究重点是：

1) improving the power density of individual units
2) reducing the cost of each unit
3) widening potential fuels
4）将这种生物技术实施到实际实施中

The future of this research lies in pursuing the above points. However, having MFCs which can be scaled-up to match their intended use opens new avenues in terms of applications.

The deployment of the technology can now be tested against real usage conditions: as a power source for off-grid, remote areas; as an energy efficient way of treating human organic wastes; or as self-sufficient biosensors.