Water purification technology
The purpose of water treatment is to remove unwanted contaminants in the water, such as micro-organisms, particles, dissolved organic and inorganic materials, odours and colour, and to make it clean and safe to drink. Various methods exist to treat polluted and contaminated water, each with their own capabilities and limitations. Not all of those are suitable for autonomous drinking water supply. Those that are, have different pro's and con's with respect to efficacy, efficiency, cost, energy consumption, yield, use of chemicals, sustainability, robustness and maintenance requirements.
For our solutions we have only selected technologies that
are very efficient, robust, and proven in harsh conditions,
have a continuously high yield of very high quality drinking water, thanks to the automatic back washing of filters, to prevent fouling and clogging,
have a long life, resulting in a very low cost per cubic meter of safe water,
require very little maintenance, and the required maintenance is easy and straightforward,
do not require chemicals to disinfect the water, except for automatic or scheduled cleaning cycles of the equipment itself. The chemicals used are low-cost readily available and eco-friendly, like acidic acid, citric acid and chlorine dioxide.
Sediment filtration is the first water treatment step in the filtration process. Sediment filters or strainers mechanically sieve out solid particles (sediment and debris) from by preventing them to pass through a surface with small holes of a defined size. This (pre-)filtration step is indispensible to prevent damage, or clogging of subsequent finer, more sensitive and more expensive filtration equipment. The type of strainer, the filter media used, the size of the holes or pores and the water quality determine how easily strainers get clogged. A floater or a fixed suspension should be deployed to avoid that a strainer gets too close to the sediment layer at the bottom of the water. At Filtraide, we exclusively apply high grade screen/mesh sediment filters that can easily be cleaned and descaled and thus maintain excellent performance and yield for years.
Hollow Fiber Membrane Filtration
Hollow Fiber Membranes are tiny tubes made from polymer. They are semi-permeable, which means that the walls of the tubes have small pores. The pore size determines which particles can pass and which particles are rejected. Hollow fibre membranes are used to filter the smallest particles from a fluid. Pore sizes vary from 1 nm for nano filtration (NF) to about 100 nm for micro filtration (MF). In between those two UF (ultra filtration) makes up a very important and widely used category, as it has the perfect pore size to block micro organisms like bacteria and viruses.
Another special type of membrane filters are those used for reverse osmosis (RO).
To create a filter assembly, a high number of hollow fibres are packed into a cilindrical cartridge.
Ultrafiltration (UF) is a very effective, efficient and sustainable method to remove small particles, bacteria and viruses from water. It is therefore often used in the professional treatment of surface water, well water and harvested rain water.
UF only needs a relatively low differential pressure on the water to function (the difference in pressure between the two sides of the membrane). Important minerals like calcium and magnesium are small enough to still pass the membrane.
Widely applied UF membranes have a pore size of approximately 20 nm (0.02 μm). Of all micro-organisms, viruses have the smallest size. The virus SARS-Cov-2 that causes Covid19 for example, has a size of approximately 100 nm.
NF is often used to reduce the salt contents of brackish water.
RO is used to remove enough salts from sea water to make it potable.
As filtered particles and micro-organisms are collected inside the membrane filter units, they have to be regularly cleaned to prevent clogging of the pores. In Filtraide systems this is automatically performed by a high pressure backwash process that kicks out all this debris through a separate flushing hose.
Activated carbon (AC) is a form of carbon (charcoal) that is processed to have a huge number of very small pores. These pores create a very large surface area in a small amount of carbon: up to 3000 square meters per gram. Through a process called adsorption polluting molecules in the water can be trapped in these pores. Active carbon filters are highly effective for removing taste, odour, volatile organic compounds from pesticides and chlorine. They are in general not suitable for the removal of minerals, salts, and dissolved inorganic compounds. If water is stagnant inside an AC filter for longer periods of time, micro-organisms may grow inside the activated carbon. Therefore we place the AC filtration step after the Ultrafiltration step, so the input water to the AC filter is free from micro-organisms.
UV radiation is an effective way to combat microbial contamination in water. Microbes must be exposed to a sufficient dose of UV-C light (wavelength 100 – 280 nm) in order to effectively disinfect the water. The disinfection is a result of the destruction of the genetic material in the micro-organisms by the UV radiation.
Particles in water can create shadow areas, which can shield micro-organisms from the UV radiation. UV disinfection should therefore only be applied as a treatment step after the complete removal of particles.
As UF already removes all micro-organisms, UV radiation is usually not required when our systems are used on a daily basis. It is therefore in general only proposed by Filtraide when filtered water is stored in retention tanks for extended periods of time.