Why We Prefer Our Method
Bioremediation is the process of using living organisms to remove toxic contaminants from soil or water (ELC). Multiple sources have mentioned that bioremediation is a successful method to clean up pollutants, with the added benefits of lower costs and less disruption of contaminated environment when compared to other clean up methods. According to Rogalla, the biological treatment of groundwater is a good alternative because of “low cost and reduced health and taste impacts”. Since bioremediation is a natural process, the public may perceive it positively, as no harsh chemicals are coming into contact with the water. In addition to this, the complete break down of targeted pollutants is possible, whereas a commercialized treatment plant cannot break down everything due to the various steps carried out.
We chose to immobilize Pseudomonas stutzeri rather than let it freely be in the wastewater because of its stimulation of cell growth, ability to be reused and continuous use as a bioreactor, and how it is able to be used at various temperatures and pHs. Free cells do denitrify well, however, they have a long lag time and slow denitrification rate. We are trying to use the cells for the San Joaquin Valley, so we want a faster reduction rate to keep up with the demands of water in agriculture.
Microbial cellulose is an ideal material to immobilize the bacteria onto due to its efficiency and effectiveness. Although microbial cellulose is an expensive material to make, the benefits outweigh the costs. There is a lower toxicity of the material and high operational stability. According to Rezaee, the immobilization of Pseudomonas stutzeri in microbial cellulose increased the adsorption capacity, decreased the cell leakage from the beads, had higher activity of the immobilized cells, and allowed better operational control.
Our group considered the use of wood chips in the bioreactor, however, the bacteria starts to turn them into toxic methyl mercury (Christianson). This raises concerns for our project because we want the wastewater to be recycled and reused on the farm; if methyl mercury is in the water, this could kill the agriculture. Other cons we found were during low temperature months, the efficiency of the system decreases (Jang). In the San Joaquin Valley, the temperature can drop to 20 degrees from November to January, posing big concerns for the farmers of the valley during these months. Another concern is that after a couple years, the wood chips can clog the machine making it unable to be used. Because of these reasons, we have decided to not use wood chips as our bioreactor medium.
Christianson, L. E., et al. “A Practice-Oriented Review of Woodchip Bioreactors for Subsurface Agricultural Drainage.” Applied Engineering in Agriculture, vol. 28, no. 6, 2012, pp. 861–874., doi:10.13031/2013.42479.
Christianson, Laura E., et al. “Denitrifying Bioreactor Clogging Potential during Wastewater Treatment.” Water Research, vol. 105, 2016, pp. 147–156., doi:10.1016/j.watres.2016.08.067.
Christianson, Laura E. and Helmers, Matthew J., "Woodchip Bioreactors for Nitrate in Agricultural Drainage" (2011). Agriculture and Environment Extension Publications. 85. http://lib.dr.iastate.edu/extension_ag_pubs/85
Jang, Jeonghwan, et al. “Denitrifying Bacteria Active in Woodchip Bioreactors at Low-Temperature Conditions.” Frontiers in Microbiology, vol. 10, Feb. 2019,
Rezaee, Abbas, et al. “Microbial Cellulose As Support Material For The Immobilization Of Denitrifying Bacteria.” Environmental Engineering and Management Journal, vol. 7, no. 5, 2008, pp. 589–594., doi:10.30638/eemj.2008.082.
doi:10.3389/fmicb.2019.00635.
Rogalla, F., et al. “Large-Scale Biological Nitrate and Ammonia Removal.” Water and Environment Journal, vol. 4, no. 4, 1990, pp. 319–328., doi:10.1111/j.1747-6593.1990.tb01400.x.
“Bioremediation.” The Environmental Literacy Council, enviroliteracy.org/environment-society/waste-management/bioremediation/.