Stacked Rapid Sand Filtration

Introduction

A stacked rapid sand filtration unit is preferable to a conventional rapid sand filtration unit as it requires less water to back wash since the filters are stacked, and use the same water for all filter layers to back wash. In addition, a stacked filtration system requires a much smaller footprint to achieve the same level of filtration.

A vertically stacked filtration system meets many of the AguaClara Project constraints. Both normal filtration and back wash operations are gravity driven and require no electricity. In additon, it is an open system. The required construction materials(PVC pipes, sand, concrete, brick, and rebar) are relatively cheap and available in Honduras. Most importantly, stacked rapid sand filtration is proven to consistently lower the effluent to below 1 NTU.

For more information, please see the explanation of stacked rapid sand filtration theory and unit design and the General Filtration Page.

Learn about the Stacked Filtration Team and our Challenges.

Current Research

Bench Scale Model
This is our current experimental apparatus.

Backwash
We need to prove the ability to clean the stacked rapid sand filter by backwashing. In order to prove backwashing works, we need to fully fluidize the filter and settle it to continue filtration.

Head Loss Measurement
The head loss across the filter over time is the governing factor that determines the filtration cycle time. The build up of head loss ultimately determines how often the filtration unit will require backwashing.

Filtration Unit Design
It is necessary to design a filtration unit that can be built at our existing water treatment plants and be incorporated into future plant designs. This includes a hydraulic analysis to calculate the critical elevations in relation to how the filter fits in with the sedimentation tank effluent weir and the distribution tank. This analysis must be done using the approach for the design tool with correctly named variables, and with the standard inputs of flow rate and then automated design of the filter system. This automated design must include full hydraulic design of all of the piping required.

Performance Study
A number of parameters will need to be studied in order to find the optimal design conditions for a filtration unit. The variables to be studied experimentally include diameter of sand grains, depth of each filter layer, horizontal spacing between pipes, and filtration velocity. A robust study of all these variables will require a long period of time, and it is thus recommended that we proceed with the design and installation of a filtration unit with conservative design parameters. Once full-scale performance can be analyzed, we can proceed with an exhaustive performance study to further optimize the stacked rapid sand filtration unit design.

Future Research

Field Scale Testing
We plan to build a stack rapid sand filter as an addition to an existing plant that uses AguaClara technology.

Past Research

Summer 2010 SRSF Research
Built initial bench scale model and initialized proof of concept.

Spring 2010 SRSF Research
The SRSF concept was developed through extensive academic research and planning.