Solving for the Unknown

So to start off, I have been waiting for a Yale net ID for what is going on 2 weeks now. This has severely impacted my participation in the lab because I have not yet been able to complete the lab safety training and therefore can not work in the lab independently. A certain level of bureaucracy exists that the registration form has to make its way through. As a result, I have been shadowing the (soon to be Dr.) Humberto Jaramillo during his routine tasks and experiments in the lab. To my benefit, instead of going off and doing things on my own, I have been receiving a wealth of knowledge about each step and procedure as they are performed (plus I wouldn’t say that I am completely incapacitated, but my participation has still been minimal). Thankfully, Humberto is a top notch mentor, and goes out of his way to make me feel comfortable and well informed.

The lab PI, the famed Menachem Elimelech, who happily took me under his wing this summer, has been out of town this week, but seems to be a more hands-off type of mentor to his graduate students. Last week, I attended a meeting with Humberto, Changhe (a fellow researcher with a similar research topic), and the very own Dr. Elimelech in the flesh. It consisted of Humberto detailing his current progress and future endeavors accompanied by data to support the basis of his plans. Elimelech was very direct and blunt with his opinions and directions, quickly weeding out what he deemed unnecessary and lacking quantifiable backing. He’s a busy man and there’s a certain feeling I get throughout the lab that he is pushing for as many papers to be published as quality allows. That’s not to say that he is a respectful and intellectually considerate mentor that allows his students to figure out many lessons of grad school on their own (to their advantage of course).

Furthermore, in that quick meeting, Humberto outlined some of his goals. Another part of his research involves running a reverse osmosis system using the control and modified membranes. That means that he has the system running almost 24/7 in a unit that he constructed with the help of the lab technician, Evy. Two plates sandwiching a membrane act as the center of the system. A feed source containing calcium chloride and sodium sulfate is pressurized through a pump and pushed into the bottom plate and through the membrane’s active layer. The concentrated feed is left behind while filtered water is fed through the top plate and through a flux meter where the flow (mL/min) is gauged. Ideally, we run the system until a 40% reduction in flux occurs, which takes approximately 12 hours. The first few hours of runtime is known as the induction period, which is the initial slow, steady stage of crystallization of gypsum. The remaining time consists of rapid surface crystallization on the membrane surface that inhibits the flow.

We have been running the reverse osmosis (RO) system under varying conditions, but currently, the parameters have included a temperature of about 25°C (the chiller has been broken for weeks), a pressure of between 300 and 400 psi (we want an initial flux of about 1.7 mL/min), and a feed stock with a concentration of 0.019M for both calcium chloride and sodium sulfate to give us a conductivity (slightly above saturation) of approximately 6.1 mS (microsiemen). All of these factors affect how much salt is dissolved in the solution because we don’t want bulk crystallization in the feed that could damage the pump and be confused with surface crystallization if deposited on the membrane surface. Pressure affects the flux. Intuitively, as the pressure increases, the flux increases but scaling also occurs more quickly. Pressure is also important because, on an industrial scale, higher pressures means more input energy and therefore higher operational and capital costs, so we want our modified membranes to have higher fluxes at lower pressures.

Presently, only our control commercial membranes for brackish water have been tested in the system, so the next step is to modify membranes based on results from the self-assembled monolayers (SAMs). We used a goniometer to measure the contact angles of three known liquids on our newly modified monolayers on which the acid, amino, and alcohol were grown through wetting experiments. The surfaces of the three different monolayers were tested with drops of water, glycerol, and diiodomethane. Currently, we are working on calculating the van der Waals and acid-base interaction forces for the surface using complicated derivations of Young’s equation (the complex, grad-level equation). The contact angle and the known Lifshitz-van der Waals surface tension, electron-acceptor, and electron-donor components of each liquid (two of which must be polar) can be used to determine the different surface energy components of the solid (membrane or SAM). The results from the wetting experiments will then be used to justify how the different modifications of the membrane work to reduce fouling.

We are in the stage of experimentation, which involves a lot of trial and error, especially when running the RO system under varying conditions for optimal results. Wish us luck on our endeavors as we face uncertainty head on and stay updated to learn more about our finding!

 

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