Large Particle Filtration Methods
1. Pre-coat Filters:
Filtration media is pre-coated with diatomaceous earth (non-toxic safe substance made from crushed fossils of freshwater organisms and marine life- acts as glass shards that puncture harmful insects and particles) to remove very small particulate and some bacteria.
Uses natural methods, not harmful to humans
Only practical for limited volume use
Would be expensive ($7 for 6oz)
2. Screen Filters:
Coarse screen to filter out large particles at the intake point. Commonly used to filter out physical matter such as fine sand and large inorganic debris. Typically made from metal, plastic or synthetic cloth
Simple and economical
Made from materials possibly available in area
Can be used for large scale operation
Will clog is algae is present
3. Bag Filters:
Constructed of non-woven media such as polypropylene in the shape of a bag.
Water is placed in the bag and filters through (using gravity or pressure) Once bag is clogged it can be discarded.
If tweaked design possibly re-usable
Each person could have his own
Possibly “Bag Concept” can be used in design
Polypropylene is not prevalent in Africa
If used as described wasteful
Need to search for new material that would work as well
4. Plate and Frame Filters:
Thick woven materials such as cotton or polypropylene mounted on a frame. Rows of the filters are lined up and fluid pushes through them.
Uses materials that are abundant in Africa
Can be easily broken into components for protability
May have many parts difficult to assemble
May need pressure source to filter water??
5. Sand Filters:
Position coarse sand on top, then have layers with fine sand/clay on bottom. Run water through each material, to filter out physical matter
Process large volumes
Uses abundant materials
Easy to replace
Multilayer prevents clogging
Need to allow time for materials to pack closely for better filtration
Still need to add on two part filtration
6. Active Carbon:
Remove large particles and absorb low molecular weight organics and chlorine by running through active carbon
May be able to use abundant charcoal?
Must be back washed frequently and changed periodically to avoid bacterial growth and efficiency
Not good for large scale use (possibly)
7. Depth Filters:
Most common particle filter and most suitable for majority of applications. Water flows through a thick wall filter, where particles are trapped. (Thick wall- cotton, cellulose, synthetic yarns, polypropylene) The best depth filters have lower density on the outside and higher density on the inside. This traps coarse particles toward the outside, fine particles on the inside, leading to a longer life.
Could use materials that are abundant as media
Large scale applications
Removes bulk of particles
Need to look into how to have varying screening materials in one screen