04 December 2013

Creating Better Flocs Through Measurement and Mixing

A tool that allows for the analysis of flocs would aid AguaClara’s current research significantly. Flocs are the masses formed by particles in the water after having been dosed by coagulant. Conclusions drawn from the analysis of these flocs for attributes such as size distribution have implications especially for our laminar and turbulent tube floc teams. For example, the laminar tube floc team is currently working to see if breaking flocs up somewhere during the flocculation process will create better flocs and thus cleaner water. A member of the AguaClara team, Tiago Viegas, is currently conducting research that will hopefully allow them to analyze the results of their experiments more precisely.

Tiago’s design for the floc size measurement tool consists of a square tube called the flow cell, and a camera. The flow cell’s square shape is meant to minimize distortion. The camera, specially suited for capturing accurate images of the flocs, will provide high-quality images from which we will be able to obtain information about flocs in a variety of different situations. With these images, for example, we would be able to find the most efficient floc size distribution by feeding the sedimentation tank with different distributions and analyzing each one accordingly.

For analysis of the images, it was determined that LabVIEW would be best for managing the images and data provided by the tool’s measurements.

We’re currently looking to find the most suitable camera for the job, and we’re also working with a glassworks company to create a flow cell with dimensions that match the pipes of our flocculators.

Integral to the floc formation that Tiago’s tool will analyze, however, is our coagulant, polyaluminum chloride, otherwise known as PACl. PACl is delivered to raw water through the stock tank. As of right now, PACl is distributed to the raw water and stirred manually. While this method is acceptable, the coagulant sometimes isn’t evenly distributed throughout. Alyx Cheng and Apoorv Gupta of our Stock Tank Mixing subteam are trying to devise a method for mixing the two that will ensure even distribution of PACl.

Much of the team’s past work has been empirical; Alyx and Apoorv are working off a system built in past semesters. This semester, however, they’re more concerned with the theory and calculations behind the mixing. They’ve been able to find a uniform relationship between density and concentration of PACl with the help of a hydrometer, a tool used to measure the density of a given solution.

One of their main challenges this semester is to determine the relationship between pump speed and life height of the coagulant, taking into consideration watts of power of the human arm, potential energy, and drag force. Through their calculations so far, the team has discovered large discrepancies between their theory and their lab results concerning the relationship between energy used and lift height.

The continuous lines on the left-hand side of the graph above show the relationship between the two variables yielded through calculations, while the plots on the right show the results of actual experimentation. The baffle denoted in the legend refers to a slab of plastic that was installed in the stock tank in an attempt to make the system more efficient.

Thanks to the baffle, the team was able to conclude that the error was not just the result of an accident during testing. 

A diagram denoting the variables used in calculations.
The main issue now is that while their experimental results are consistent with each other, they're not consistent with the theoretical calculations. In order to resolve this, the team is working to make their model stock tank as efficient as possible. Design changes include the addition of a t-joint to stabilize the pump at the bottom and planks to stabilize it at the top. The direction of the output of the coagulant was also changed. 

All calculations are made to ensure that any results yielded from their model will translate well to the larger sized version used in the field. Their most important goal right now is to determine the relationship between total power required and flow rate of solution out of the arm, as that will reveal the ideal distribution of the coagulant.

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