Background

In order to cater the demands of the growing population, production of the goods in the manufacturing units increases day by day. The industries also produce effluents along with the desired products. The effluents are required to be discharged into the water bodies but the most crucial factor to consider is the removal of toxic components prior to discharge[5]. Heavy metals are persistent pollutants in waste water and these trace elements are released into the water bodies from various industries. It gives birth to several environmental and health impacts[3][2].

Project Curlim focuses on scavenging cadmium ions from the industrial effluent. Cadmium is a heavy metal that can cause disastrous effects on the ecosystem with its toxic properties. When the effluent containing the heavy metal encounters the sea water, the toxic component from the discharge can be transferred from lower trophic level to higher trophic level within the food web due to biomagnification[1].

Aim of the Project

To construct Moving bed biofilm reactor in the pilot scale and remove the cadmium ions from the industrial discharge with the help of our engineered bacteria CURLIM.

Objectives

  • To genetically modify an Escherichia coli strain to produce acid phosphatase enzyme.
  • To build a lab scale model of a Moving Bed Biofilm Reactor to achieve optimum conditions for biofilm formation
  • To achieve the bioprecipitation of cadmium in the form of Cadmium Phosphate for successful removal from wastewater effluents.

Theory

In a Moving Bed Biofilm Reactor, an aeration tank with special structures called biocarriers are added. These carriers act as a substratum to which the microbes adhere and form biofilms. Usually, these carriers are less dense than water hence can be easily suspended in wastewater or media. Biofilm formation is promoted with the help of curli proteins[4]. The biofilm should be attached to the biocarriers and the biofilm formed should be sufficient and strong enough to express suffused phosphate enzymes.

Challenges

  1. We have chosen E.coli K 12 strain which is a poor biofilm forming strain.
  2. Acid phosphatase enzymes should be present on the cell surface of the bacteria so that the enzyme can bind with the phosphate substrate and give free phosphate ions as the product.

Plan of Action For Project CURLIM

Curlim bacteria has been engineered to perform two major functions:-

  1. To enhance biofilm formation by dual expression of csgD and OmpR234.
  2. To express acid phosphatase enzymes on the cell surface. This is achieved with the help of a cell surface tag (OmpA with Linker).

Curlim bacteria will be allowed to form biofilm on the biocarrier. These biocarriers will be introduced into the reactor. Upon addition of the phosphatase substrate, acid phosphatase enzyme will be dephosphorylated. The free phosphate ions available will bind to cadmium in the effluent and form metal phosphate. The metal phosphate is insoluble in aqueous solution and it leads to bioprecipitation of cadmium ions and hence cadmium can be removed easily from the industrial discharge.

Advantages

Future Perspective

We plan on developing an industrial scale version of our bioreactor to scale up the bioremediation process. The E.coli strain that is genetically engineered by Team REC-CHENNAI can be efficiently applied for Wastewater treatment due to its low toxicity level and pathogenicity. The MBBR can be used in the remediation of other heavy metals as well. Acid phosphatase is known to bio precipitate other heavy metals such as Cobalt, Lead and Ferrous along with our metal of interest, Cadmium. Due to its low energy consumption and material requirements, our proposed solution provides a cost-efficient mode of heavy metal removal.

References

  1. Ali, H., & Khan, E. (2019). Trophic transfer, bioaccumulation, and biomagnification of non-essential hazardous heavy metals and metalloids in food chains/webs—Concepts and implications for wildlife and human health. Human and Ecological Risk Assessment: An International Journal, 25(6), 1353-1376.
  2. Hutton, M. (1983). Sources of cadmium in the environment. Ecotoxicology and environmental safety, 7(1), 9-24.
  3. Idrees, N., Tabassum, B., Abd_Allah, E. F., Hashem, A., Sarah, R., & Hashim, M. (2018). Groundwater contamination with cadmium concentrations in some West UP Regions, India. Saudi Journal of Biological Sciences, 25(7), 1365-1368.
  4. Olsén, A., Wick, M. J., Mörgelin, M., & Björck, L. (1998). Curli, fibrous surface proteins of Escherichia coli, interact with major histocompatibility complex class I molecules. Infection and immunity, 66(3), 944-949.
  5. Ravera, O. (1984). Cadmium in freshwater ecosystems. Experientia, 40(1), 1-14. Infection and immunity, 66(3), 944-949.
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