LifeStraw® Family - Functioning

At the time of first use, opening the exit valve removes all the air trapped inside the hollow-fibre membrane and wets the membrane surface, allowing an optimal filtration of the untreated water. The exit valve must be closed after 3 seconds.

When untreated water is poured into the feed water bucket, the textile prefilter removes coarse particles larger than 80μm. Gravity pushes the water with particles finer than 80μm to flow down the plastic hose towards the purification cartridge. The purification cartridge, which contains an ultrafiltration (hollow-fibre) membrane of 20nm porosity, stops all particles larger than 20nm (including all microbes: protozoan parasites, bacteria and viruses). Turbidity particles are also stopped by the membrane by size exclusion. The untreated water is pushed through the ultrafiltration (hollow-fibre) membrane by gravity, i.e. by the pressure applied by the 1m long plastic hose, which corresponds to 0.1 bar pressure. This 0.1 bar pressure forces the water through the pores of the hollow-fibre membrane; particles and microbes larger than 20nm stay on the dirty side of the membrane and clean/purified water passes through the membrane. Purified water can be collected from the blue tap. When the cleaning bulb is squeezed, dirt particles on the dirty side of the membrane are lifted by backpressure and then removed by flushing through the exit valve.

Since all microbes are stopped by the 20nm membrane, the purified water complies with the US EPA requirements of LOG 6/4/3 reduction of microbes concentrations for water purifiers. The 0.1 bar pressure which allows the purification process to take place also leads to a flow-rate of 12-15L/hour of purified water.

The LifeStraw® Family filter also contains a chlorine chamber located below the top container. This chamber elutes low amounts of active chlorine, which protect the ultrafiltration membrane from fouling (small amounts of active chlorine slow down the bio film formation on the  hollow-fibre membrane). The low amounts of active chlorine protect the ultrafiltration cartridge and that way lead to an extended lifetime of the LifeStraw^® Family water purifier.

1. Feed water bucket with prefilter

2L capacity container for filling with unpurified water

2. Prefilter

the 80 micron textile prefilter removes coarser turbidity and is easy to clean

3. Halogen chamber

releases low-level chlorine to prevent membrane fouling

4. Plastic hose (one metre long)

gravity creates sufficient pressure on the membrane cartridge in order to reach a high flow rate

5. Membrane cartridge

ultra filtration takes place in the membrane cartridge – a pore size of 20 nanometre retains bacteria, viruses, parasites and fine dirt particles

6. Blue tap

outlet for purified water

7. Cleaning bulb

backwashing of the membranes is done by squeezing the bulb three times

8. Exit valve

disposes the dirt and impurities