Overview
Wastewater treatment and energy recovery are becoming global concerns with the increase of human activities and substantial consumption of fossil fuels. Even in Antarctica, the biggest untouched wilderness on our planet, wastewater treatment are urgently needed with the presence of 44 permanently manned research stations[1]. However, ordinary biological filtration devices are typically designed with rigid structures and sizes. This inflexibility leads to high cost and great challenges in satisfying the vast and various demands of wastewater treatment in remote and off-grid areas, because of the lack of infrastructure, limited funding or difficulty in implementing and maintaining facilities. For example, transferring devices to Antarctica is not easy due to unusual constraints of remoteness, isolation, tough weather and other local conditions. Therefore, most countries have chosen processes that use biofilms[2].
In today's wastewater treatment industry, different kinds of contemporary biofilm reactors have been created. However, they still have some limitations. The fluidized bed biofilm reactor (FBBR), for instance, consumes substantial energy due to the frequent collisions of its biofilm-coated particles. And the membrane biofilm reactor (MBfR) is more susceptible to contamination, which can lead to a shortened lifespan[3].
插图 FBBR MBfR ,找现成的,给出出处
Our team is concerned about all these limitations and come up with our own solution using carbon nanotubes (CNTs). CNTs possess unique physicochemical and morphological characteristics, excellent adsorption capabilities, and permeability, showing significant potential in wastewater treatment[4]. We designed an innovative fiber structure based on carbon nanotubes, which can not only carry and nourish our engineered bacteria but also be woven into any required shape and size according to actual needs. In practical application scenarios, we load the engineered bacteria onto our designed fibers and weave them into a form that perfectly matches the target device. With this fiber structure deployed in the treatment device, we can effectively achieve the recovery and purification of heavy metals such as nickel.
Compared to traditional biological filtration devices and modern biofilm reactors, our customized fiber boasts considerable benefits. The reversibility of the fiber weaving process allows for recycling and reuse, effectively extending the product's lifespan and release the environmental burden. The fibers are available in laboratories and provide great convenience for research. Futhermore, the fiber's construction is characterized by low energy consumption. Our customized fiber serves as a platform that bridges our project to practical applications and offers an efficient, environmentally friendly new facility for wastewater treatment.
Design of aCNT
Our fiber uses carbon nanotubes as a skeleton and agarose gel are wrapped around the nanotubes. Subsequently, we assemble several carbon nanotubes into bundles through a spiral extrusion method, fixing the carbon nanotube-agarose gel (aCNT) composite fiber, which provides a growth platform for our engineered bacteria. We referenced the method for preparing graphene composite microwires 参考文件不够,这里要链接去Koo的实验室 by Professor Hyung-Jun Koo 哪个单位[5] and the method for preparing high-performance fiber electrodes by Professor Peng Huisheng in Fudan[6]. We also made appropriate adjustments so that our composite fibers have good performance while carrying engineered bacteria. We used a 40mg/50mL agarose gel, andadjusted the ratio of the two components in the solution to allow more agarose gel to encapsulate the carbon nanotubes, making it easier for the engineered bacteria to attach. The aCNT composite fiber works as a carrier that allows the bacteria to perform normal life activities and engage in recovering nickel (Figure 1).
Additionally, we designed application forms for different scenarios, which are demonstrated in our "Multi-Application Scenarios" part. 具体是什么样的adjustments,取得了什么样的good performance 呢?
Section 1: Constructing aCNT Composite Fibers
Laboratory Preparation
- Heat a 2.0g suspension of multi-walled carbon nanotubes (MWNT) (3% by weight in water, purchased from Nanostructured & Amorphous Materials, Inc.) to approximately 100 degrees Celsius. Stir continuously for 5 minutes.
- Add 40mg/50ml of agarose (Acros) to the solution and stir for 30 minutes while maintaining the temperature.
- Transfer the hot liquid suspension containing MWNT and agarose into a 5 mL syringe equipped with a needle, and form hydrogel threads by extruding through the needle with a 0.5 or 1 millimeter diameter hole (Tygon; Saint-Gobain Corp.).
- Dry the hydrogel threads at room temperature for 12 hours to form aCNT composite fibers (Figure 2) [7].
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Industrial Preparation
We propose to use the apparatus shown in Figure 3 to produce sCNT in large scale. The apparatus contains agarose gel solution. The multi-walled carbon nanotube pass through the apparatus. We could control the diameter of the inlets and outlets to control the diameter of the fibers. The size and shape are adjustable according to real world needs. Then heat the carbon nanotube to approximately 100 degrees Celsius and cool it down quickly to solidify the agarose gel on the surface of the carbon nanotube.
Section 2 : Assembling the Fiber-Bacteria System
Use a spinning machine to spiral our composite fibers into bundles and weave them into the desired size and shape.
Soak the woven fiber material in bacterial solution. Stand for 30 minutes to facilitate the adsorption of engineered bacteria onto the surface of fiber. The agarose gel provides certain nutrients, ensuring the survival of bacteria on the fibers for a period of time. Therefore, we successfully constructed our fiber-bacteria system (Figure 4).
Section3 Multi-Application Scenarios
Our aCNT composite fibers can be used in multiple scenarios. In industrial environments, the complete composite fiber-engineered bacteria system can be placed inside the wastewater treatment device. Engineered bacteria on the fiber absorb and reduce nickel ions as the wastewater flows through the fiber mesh. In natural water bodies, we can weave the fiber into nets similar to fishing nets. Once fixed to the banks of rivers or wooden poles in the water, the fiber nets can naturally hang into the water and achieve purification.
Testing
We purchased 50 grams of pure multi-walled carbon nanotubes (MWNT) from ___ and prepared a 3% suspension. We then followed the protocol from the article to create the aCNT composite fiber. However, our initial product failed to obtain the desired toughness and exhibited a uneven texture and thickness. We suspected that the this outcome was due to insufficient stirring and inconsistent application of force during the extrusion process.
Therefore, we decided to stir the mixture for a full three hours and used a pump to apply a steady force during the extrusion process. These adjustments led to a more homogeneous texture in the fiber, but the issue of toughness persisted.
After reviewing related literature, we concluded that the suspension ratio required optimization.
Feedback
Summary
Our hardware design serves as a carrier for synthetic biology applications. Carbon nanotube-agarose gel composite fibers are an efficient and sustainable facility for wastewater treatment technology. Traditional biological filtration devices often have fixed structures and single shapes, making it difficult to adapt to the diverse needs of wastewater treatment. In response to this disadvantage, we have designed macro-amorphous composite fibers that can be woven according to actual needs and can carry engineered bacteria, making biological recycling available. The device not only recovers nickel but can also be applied to the recovery of other heavy metals and wastewater purification. Its strong plasticity enables a wide range of application scenarios. aCNT composite fibers provide an efficient, environmentally friendly new way for wastewater treatment and metal recovery as well as innovative solutions for the sustainable development of future bioenergy and green chemical industries.
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