Team:SCAU-China/Implementation

MESEG

Implementation

End users


We hope to apply the engineered Chlamydomonas reinhardtii in real environment. It could be a natural environment or sewage treatment plant. Compared with the natural environment, sewage treatment plants are more likely to be our first object. Understanding how sewage treatment plants operate is what we need to learn. At present, most sewage treatment plants serve urban sewage, so there is no special heavy metal pollution treatment tank. And most of them mainly deal with nitrogen and phosphorus pollution. The following is the brief introduction of the workflow of sewage treatment plants. At the first stage, water will be transported to the plant by pump house and get preliminary filtration by the coarse grid. Next, we can get a better water filtration result in the fine grid and swirling sand tank. Then, water will be passed the membrane grid pool into the biochemical pool and the microbial reactor pool for the digestion of organic matter. The sludge after filtration and biological reaction will be discharged into the sludge storage tank. After that, it is made into mud cakes for export through the sludge thickening and dehydration machine room. Finally, the remaining waste liquid will be recycled. The wastewater after biological reaction is disinfected by ultraviolet or disinfectant, and then discharged from the pump station (Xie, 2021).

Figure 1: Process flow of sewage treatment plant




Imagine how to use


We hope to design a pool in the sewage treatment plant to place our device. The size of the pool may be determined based on the flow rate of the sewage treatment plant, the absorption efficiency of the device and the pollution situation of heavy metals. We may also need a real-time detection device to measure the concentration of heavy metal ions at the inlet and outlet of the pool, so as to ensure the good operation of our device. Using it in the natural environment may be more complex. We need to prevent the destruction of our devices by organisms in the external environment. In the future, we hope to have electronic devices, such as Bluetooth and wireless networks, to help and remind them when they need to recycle the device and carry out the next operation.



Other challenges

Commercialization: We believe that the current device cost is not as low as other methods. We need higher cost performance to convince potential investors in the future, such as environmental protection enterprises and sewage treatment plants. The commercialized batch operation mode may bring us new opportunities.

Large-scale use: large-scale use has always been our desired direction. But due to various limitations, we did not verify it in the real world, which means that our large-scale mode may be immature. In the future, we may continue to complete this step in human practice.

Membrane contamination: With the activity of microorganisms in the device, an increasing number of microbial metabolites can form membrane contamination. Membrane contamination is formed by the accumulation of fouling colloids, organics, extracellular polymers, soluble biological products and so on. These things will attach the membrane surface to form a cake layer or adhere to the inside of the membrane to form a blockage of the membrane pores. Long residence time will also increase the amount of dissolved organic matter in the sewage and form a layer of gel outside the membrane, which will reduce the open porosity of the membrane, which will eventually affect the use of our device (Song and Yang, 2012; Liu and Zhao, 2016). Currently, the commonly adopted method is to add powdered activated carbon, which acts to absorb colloidal substances and solutes in the supernatant, but excessive dosing still increases membrane contamination and increasing costs. Flocculant is also a commonly used dosing agent which reduces the small particles in the supernatant by disrupting the stability of the mixed liquid colloids, but this method can produce by-products and cause negative effects. The choice of control methods for membrane contamination in membrane bioreactors is more inclined to membrane alteration and membrane cleaning. For example, improving the terminal hydrophilicity through surface modification enables a better control of membrane contamination. The roughness of surface was more manifested to promote the formation of membrane contamination. A more hydrophilic membrane could reduce the formation of membrane fouling (Sun et al., 2016). In the future, we may increase the stability of the device by putting an appropriate amount of activated carbon powder in the device or membrane treatment.




References

  1. Liu Y, and Zhao J. (2016). Investigation of Membrane Fouling Mechanisms in Membrane Bioreactors. Journal of Shanxi Datong University (Natural Science Edition) 32, 36-39.
  2. Sun D, Han X, and Ren T, et al. (2016). Research Progress in Membrane Biofouling Mechanism and Control in Membrane Bioreactor (MBR). Liaoning Chemical Industry 45, 504-506.
  3. Liu Y, and Zhao J. (2016). Investigation of Membrane Fouling Mechanisms in Membrane Bioreactors. Journal of Shanxi Datong University (Natural Science Edition) 32, 36-39.
  4. Xie G. Operation Comparison of Advanced Wastewater Treatment Process in Sewage Treatment Plant. Guangdong Chemical Industry 48, 137-138.
  5. Song W, and Yang Y. (2012). The analysis of mechanism and control measure of membrane pollution for MBR. The north environmental 24, 177-179.