2010 Spring AguaClara Filtration Team

Abstract

The design challenge for the 2010 Spring AguaClara Filtration Team is to design a filtration system for the AguaClara water treatment plant. The filtration system must meet the following requirements: First, it must reliably treat the current AguaClara effluent water with a turbidity ranging from 5 to 10 NTU and producing effluent turbidity less than 1 NTU, The filtration technology should not require any electricity, It should make minimal use of specialized components that would be difficult to acquire in remote communities, and the system should be easy to construct and to maintain.

Currently, the filtration team has made progress in three fields: clear well backwash, foam filtration, and siphon-aided backwash. Once divided up into those three sub teams, we each conducted a literature review of existing technology and research. We then developed initial designs based on our research and proceed to test the fundamental theories behind our design. For example, the foam filtration sub team tested the effectiveness of foam in reducing the turbidity of the water while the clear well backwash team developed a bench scale model to test the empirical equations behind the design.

Method & Result and Discussions for each sub team

Siphon-Aided Backwash

Foam Filtration

Clear Well Backwash Filtration System

The Clear Well sub team developed a simple design based on placing the clear well's elevation between that of the filter beds and the effluent source of the sedimentation tank. During normal operations, gravity drives the effluent from the sedimentation tank to flow through the filter and be distributed. In order to stock up backwash water, the valve leading to the distribution lines are closed and water is allowed to accumulate in the filter beds until the head difference between the clear well and the filter bed allows the clear well to be filled up with filtered water. We based our initial design on empirical granular filtration equations from existing works on granular filtration. Our experiments involved developing a bench-scale model of our system and testing it to observe the discrepancy between the actual fluidization velocity and the calculated fluidization velocity required to achieve a target bed expansion. We noted an increasing difference between those two sets of values that prompted us to conclude that, if we were to base our design on these empirical equations, we need to implement a significant safety factor. We need to conduct further experimentations before we can conclude whether or not our design is feasible.

Future Challenges

Siphon-Aided Backwash Sub Team

We will develop a bench-scale model of the Siphon-aided system and test it for effectiveness and feasibility.

Clear Well Backwash Sub Team

We will conduct the following additional experimentation before we conclude whether or not our clear well design is feasible. We will first increase the scale of our model and see if the difference between the calculated and actual fluidization velocity decreases. If that is the case, we can conclude that wall friction was the major source of error in our experimentation and the actual plant size design is feasible. We will also test multi-layered media and test whether or not the same empirical equations are applicable.

Foam Filtration sub team

Our team will further test the filtering capacity of the 90 ppi foam when the colloidal particles are larger. To do this, we will install an alum dosing and flocculation unit to our experimental setup. Additionally, we would like to further test the effects of higher flow rates on the percentage of colloid removal, and on the time to failure of the filter foam.