Team:Lethbridge HS/Applied Design
WASTEWATER TREATMENT
Applied Design demonstrates the integration of our system to tackle real-world problems. The first possible integration for our system is in wastewater treatment plants. There are two types of wastewater treatment plants: biological and physical. Biological plants use organisms to clean household wastewater, while physical plants use both chemical and physical treatments for industrial wastewater [1]. As part of our Human Practices, we toured our local biological wastewater treatment plant and recognized the processes that occur, in addition to a potential place where we could integrate it. Integrating our system in the biological treatment plant would be useful by aiding the metal removal process; however, due to the low heavy metal concentrations in average wastewater, our system is most suitable for physical/industrial wastewater treatment plants.
Current Methods
To remove the metals from industrial wastewater, there are many current methods, such as chemical precipitation. Chemical precipitation involves the use of chemicals such as lime to convert the metal ions into solid particles. From there, chemical coagulation occurs to destabilize the solid particles to allow for their precipitation by adding a negatively charged flocculant to react with the positively charged particles; this allows for the creation of larger particle groups [2]. Chemical precipitation is efficient and generally safe. However, there are many flaws. For example, chemical precipitation produces toxic sludge, which requires additional processing to remove, increasing the cost of production. Additionally, the sludge has a low settling rate in addition to being gelatinous, which is difficult to dewater. An alternative option to chemical precipitation is electrocoagulation; however, it is unable to remove significant amounts of heavy metal[3]. Chemical precipitation also requires a very specific pH range; beyond the range, the reagent is likely to re-solubilize into the solution [4].
Comparison of Our System
Our system in comparison is more ideal because it does not produce a toxic sludge, it does not require a specific pH, and its efficiency is much higher. The sludge produced by the precipitation of the metals using our phage and bacteria does not contain chemicals. Theoretically, our phage and bacteria do not require a specific pH, although we will need to perform further tests to prove it. Furthermore, due to our system’s self-renewability, it is greater in both functional efficiency and cost efficiency. Our system is more complex in comparison to chemical precipitation, due to its requirement of heat and UV disinfection; however, our system proposes a solution that solves the issues faced with chemical precipitation in an effective manner, providing a sustainable alternative.
Incorporation
To incorporate our system into the biological wastewater treatment plant, we would put it in the secondary clarifiers as this is where metal removal occurs, according to our interview with the process coordinator of our local wastewater treatment plant, Duane Guzzi. Additionally, it would be the final process before UV disinfection, where all the organisms are killed. Currently, we are unsure as to where our system would integrate within industrial wastewater treatment plants; this will be a future direction.
Positive Impacts of Our System
The incorporation of our system into wastewater treatment plants could reduce the number of metals present in a more inexpensive manner, as it is self-renewable; doing so would help prevent heavy metals from negatively affecting the ecosystem, without the cost with chemical precipitation. Additionally, it could also be used in addition to chemical precipitation and biosurfactants for the complete removal of metals from wastewater. In biological wastewater treatment plants, the sludge made from the process is used as fertilizer for crops and soil which meet the guidelines for metallic concentration; our system could lower the concentration, allowing a greater amount of crops to benefit from the fertilizer. This reduces the amount of unnecessary sludge dumped in the landfills, increasing the reusability of waste [5]. The use of this system would be particularly ideal for places dealing with heavy metals present in wastewater, such as current industrial plants. Additionally, it can be used in places such as Flint, Michigan, where drinking water is tainted with large quantities of lead [6].
TAILINGS PONDS
Current Methods
Biosurfactants are one solution for metal removal in tailings ponds. Biosurfactants can be defined as the surface-active biomolecules produced by microorganisms with a wide range of applications [7]. Surfactants increase the solubility of hydrophilic molecules, thereby reducing both surface and interfacial tensions at oil or water interfaces, and have been studied for the removal of metals from tailings ponds. In one study, the removal of arsenic from mining tailings ponds was done by Rhamnolipid biosurfactants, which decreased the interfacial tension between contaminants and tailings, increasing the metal’s mobility and thus separating them [8].
Another current method of metal removal from tailings ponds is bioleaching. Bioleaching is the use of organisms as a catalyst to leach certain metals from their ores, by turning the metal sulphide crystals into sulphates and metal [9]. This is used to oxidize the sulphide materials left behind from mining, in addition to extracting the valuable metals from the tailings. This bacterial oxidation technology is advantageous due to its use of natural bacteria already present in the tailings and its relative simpleness. [10].
Comparison of Our System
Biosurfactants
Our system of recovering heavy metal ions from tailings ponds is more effective than biosurfactants in a couple different ways. The removal of metals by ionic biosurfactants is thought to occur in the following order: the sorption of the biosurfactant to the soil surface and complexation with the metal; the detachment of the metal from the soil to the solution; and the association with micelles. Heavy metals are trapped within the micelles through electrostatic interactions and can be recovered through precipitation or membrane separation methods[11]. Our system is more beneficial than biosurfactants because it is more self-sustaining with our phage infection system; additionally, biosurfactants are affected by the slightest change in temperature and pH levels. They also require a higher concentration of carbon and nitrogen for growth and production. All these factors combined give us insight to the possible benefits our system compared to biosurfactants.
Bioleaching
In comparison to bioleaching, our system is more favourable. One benefit is that our system does not produce heat. The sulphide oxidation present in bioleaching is an exothermic process, which releases large quantities of heat, therefore requiring a cool environment in order to prevent the bacteria from dying. Our system would not require this. In addition, our system is self-renewable, which demonstrates the potential for greater metal removal efficiency. Our phage capsid display technology is complex, yet it provides a potential alternative for the extraction of metals from tailings ponds.
Incorporation
In order to efficiently integrate our system into the removal of metals from mining and oil sands tailings ponds, we propose a solution using multiple cisterns. It would not be feasible to implement our system directly into the tailings ponds, due to the addition of synthetic organisms into nature, and the difficulty of metal extraction at the end. The concentration of heavy metals will decrease as the effluent travels through the cisterns until a certain amount has been removed. From there, the water can be released back into the tailings or moved to a different area to be processed further.
Positive Impacts of Our System
Our system’s self-renewability and efficiency has the potential to improve the removal process of metals in comparison to currently existing systems. Our method would provide a solution to the problems faced in places such as the Athabasca oil sands and the Berkeley Pit, where heavy metal removal is valuable, in addition to extracting toxins out from the oil sands.
REFERENCES
1. Physical Water Treatment Methods. (2018). Retrieved October 14, 2018, from http://www.waterprofessionals.com/learning-center/articles/physical-water-treatment/
2. Hung, H. (2016, October 19). Current Methods for Removing Heavy Metals from Industrial Wastewater. Retrieved October 13, 2018, from https://www.manufacturing.net/blog/2016/10/current-methods-removing-heavy-metals-industrial-wastewater
3. Kurniawan, et. al, (2006). Physico-chemical treatment techniques for wastewater laden with heavy metals. Chemical Engineering Journal, 118(1-2), 83-98.
4. BrbooTI, Et. al. (2011). Removal of Heavy Metals Using Chemicals Precipitation. Engineering and Technology Journal, 29(3), 595-612. Retrieved from https://www.semanticscholar.org/
5. (Kirchmann, Et. al. (2017). From the agricultural use of sewage sludge to nutrient extraction: A soil science outlook. AMBIO: A Journal of the Human Environment, 46(2), 143-154. doi:10.1007/s13280-016-0816-3
6. Flint Water Crisis Fast Facts. (2018, April 8). Retrieved October 14, 2018, from https://www.cnn.com/2016/03/04/us/flint-water-crisis-fast-facts/index.html
7. S. Vijayakumar and V. Saravanan, 2015. Biosurfactants-Types, Sources and Applications. Research Journal of Microbiology, 10: 181-192
8. Wang, S., & Mulligan, C. N. (2009). Rhamnolipid Biosurfactant-enhanced soil flushing for the removal of arsenic and heavy metals from mine tailings. Process Biochemistry, 44(3), 296-301.
9. What is Bioleaching? (2013). Retrieved October 16, 2018, from http://www.innovateus.net/earth-matters/what-bioleaching
10. Bioleaching. (2018). Retrieved October 16, 2018, from https://www.bactechgreen.com/bioleaching/
11. Santos DK, Rufino RD, Luna JM, Santos VA, Sarubbo LA. Biosurfactants: multifunctional biomolecules of the 21st century. Int J Mol Sci. 2016;17:401.