StaRS Backwash Alternative, Fall 2014

Alberto Arnedo, Ainhoa Arribas Llona, Jorge Guevara

Abstract

The current slotted pipes being used in the backwash system of the AguaClara filtration plants have been clogging up with sand, thus posing a problem for the backwash system since the slotted pipes’s purpose is not being fulfilled. Given this issue, the Alternative Backwash without Slotted Pipes subteam will work to find an alternative pipe for the backwash system that will not clog up with sand at any point of backwash or filtration and will be easy to manufacture on site in Honduras and India given the resources available in each respective country. The team has successfully built a STaRS scale model to be used to accurately experiment with alternative pipes for both an inlet and an outlet valve. Through experimentation, it was found that the alternative tubes in the shape of a hollow rectangular prism cut in half lengthwise and placed with the interior facing down did not fill up with sand during the processes of filtration or backwash.Once the pump was turned off, however, the sand would settle underneath the outlet pipe. This led the team to two possible courses of action: the first being that the team could leave the pump running the water at a low flow rate and the second being that the team build a second alternative for the outlet pipe. Both actions would solve the issue of the sand clogging up, but the team pursued the second alternative. The new shape for the alternative was a hollow cylinder with wings that extended out tangentially from the top of the cylinder with a hole in the middle of the cylinder’s bottom. In experimentation, the new alternative outlet pipe worked well for the first trial, but filled up with sand in the subsequent trials. Through more experimentation with the current alternatives, or perhaps new alternatives, future subteams will work to find a solution that will consistently work without filling up with sand.

Fabrication - Fall 2014

Carl Talsma, Sara Sanz, Adrian Cobo

Abstract:

Make a hydraulic working scale model of the SRSF weir system for two filters to demonstrate how the weir system is used to set the flow to the filter during backwash. The hydraulics of this system are sufficiently complicated that explaining how it works is difficult and thus we need a working model for demonstration.

No final report was available for this team for this semester. The final presentation is linked below.

Foam Filtration - Spring 2015

Marlana Hinkley, Alena Hutchinson, Ethan Keller, Alicia Peters

Abstract:

The primary goal of foam filtration is to design a low cost, locally sourced, easy to operate water filtration system. Throughout the semester, backwash cleaning efficiency experiments were performed on the small-scale filter, designed in Fall 2014 to hydraulically model the full scale filter implemented in El Carpintero. The objective of these experiments was to determine an empirical relationship between backwash pore velocity and the percent mass removal of the particles from the foam during the cleaning cycle. Experimentation with different pore sizes revealed a new mechanism for filtration: the foam acts as a sedimentation tank, providing a large surface area for the flocs to settle. This is contrary to the initial hypothesis that coagulant-covered flocs stuck to the inside of the pore walls, and that a large shear force would be required to remove the flocs during backwash. Evidently, there is still much to be understood with regards to the mechanisms behind filtration and backwash. 

Apart from work in the laboratory, the team continues to analyze data collected from experiments performed on the full-scale filter in El Carpintero by AguaClara engineer, Walker Grimshaw, to understand the discrepancies between performance in the laboratory and in the field. 

Much of the semester was spent preparing for the EPA P3 Conference held on April 10th and 11th in Washington, DC. The team fabricated a small scale model of the technology, prepared a technical report, and created a poster display for the competition, and received an Honorable Mention for its efforts in creating an “Off-Grid Solution to Drinking Water Treatment.”