Krishna's Blog - Reaction Kinetics of Emerging Contaminants

Introduction

Hello, I am Krishna Boppana, a rising senior, and currently I am working with Dr. Mengyan Li’s lab group at NJIT. Dr. Li’s Lab specializes in Chemical and Environmental Engineering and is currently developing and identifying new methods that can be used to treat a class of emerging contaminants from wastewater. Emerging contaminants are contaminants that result from a change in global dynamics such as advancement in technology or medicine. These classes of emerging contaminants include: Analgesics, Antibiotics, Antiepileptics, ß-Blockers, and Blood Lipid Regulators.

06/26/2017- 07/05/2017

For the first week and a half, my professor wanted me to conduct a literature review so that I would be familiar with the research already being done in water remediation. Currently, there are many methods that can be used to remove contaminants from water. However, the process in which Dr. Li and his lab group have been researching is the bio-degradation of emerging contaminants. Bio-degradation implies using a living culture of organisms as a system to separate contaminants from water and metabolize them into smaller and less harmful compounds. In most water water treatment plants there is a stage in which in-fluent(untreated) water enters a containment system that has a bacterial solution known as Activated Sludge:

Activated sludge consists of a large diversity of bacterial populations. These bacteria are suspended and mixed with wastewater in an aerated tank. The bacteria metabolize the organic pollutants to maintain homeostasis and reproduce by using the pollutants as a source of energy, CO2 and new cell material. This system is effective for contaminants that are in high concentration in the waste water. However, many emerging contaminants are in low concentrations and are rarely removed in Activated Sludge systems.

A relatively new and more advanced treatment process that has shown potential in degrading recalcitrant emerging contaminants is Biologically Active Filtration:

Biologically Active filtration is essentially using any sort of granular film/media to grow microbes such as algae and bacteria in a high concentration. When grown on a film, bacterial cells stick together and form a matrix that is efficient at absorbing and breaking down contaminants through diffusion. Due to the relatively higher concentration of bacteria in BAFs (biologically active filters) than in an Activated Sludge System, Dr. Li’s lab has chosen to research the potential of BAFs in emerging contaminant degradation. After conducting my literature review, Dr. Li and and I discussed and set up a project for me to research the reaction kinetics of antibiotics, a specific class of emerging contaminants, through a community of bacteria which can be integrated into a film. I will be specifically researching the compound Sulfamethoxazole (SMX), which is an indicator molecule that shares many characteristics with the antibiotic contaminant class.

One important quality of compounds in antibiotics, like those shown in the diagram above, is that they have low LogKow values. Kow, the octanol/water coefficient, is defined as the ratio of the compound concentration in the octanol phase to is concentration in the aqueous phase of a two phase octanol/water system. Octanol is a hydrophobic liquid while water is a hydrophilic liquid. Low Kow values equate to lower concentration of a compound in the octanol phase than in the water phase. Antibiotics like sulfamethoxazole have low Kow values making them more hydrophilic and soluble than other contaminants. This property makes it harder for traditional treatment methods such as absorption or filtration to remove antibiotic components from waste water. However, by using a biologically active filter (BAF), significant process can be made in the bio-degradation of soluble contaminants.

Overall, during the time I am researching, I will have to determine the reaction rate of SMX degrading through a bacterial community, determine whether adding an additional carbon source to the nutrient media will help bacteria degrade SMX (co-metabolism), track changes in the bacterial communities population structure through DNA extraction and sequencing, and propose a possible biochemical pathway for which SMX is broken down in specific bacterial species.

7/10/2017-7/14/2017

Most of my time this week was taken up by lab safety sessions and getting adjusted to the lab. In Dr. Li’s lab, I am working with Dr. Deng, a post doctoral researcher, and Fei Li, a PHD student. Below are pictures are of my work areas. Because I will be dealing with bacteria, most of my labs will be conducted in the biological safety cabinet (bottom right).

To set up the experiment I created 5 concentrations of SMX (1mg/L, 5mg/L, 10mg/L, 15 mg/L and 20 mg/L) and put each of those solutions into the micro-plate. The micro-plate was then hit with light waves (265nm) so that the photo-spectrometer can gauge each solutions' absorbance. After running the experiment multiple times and testing SMX in different solutions such as water and R2A (bacterial nutrient broth) we were able to create the calibration curve for SMX:

In the future, when I am trying to determine the concentration of SMX in a solution, I can put a sample of that solution in the photo-spectrometer and then find the absorbance value. This absorbance value can then be inputted into the equation(on graph) and the concentration can be solved for.