Drinking Water Treatments, Filtration Methods, And Purification Classifications.
Let's look at the different water filtration methods, when to use them to achieve desired results, and what to expect from them in drinking water treatment.
The four predominate filtration methods used in residential, commercial and industrial water purification process are Ultra-filtration (UF), Micro-filtration (MF), Reverse Osmosis (RO), and in certain specialized cases, Nano-filtration (NF). In addition we will also discuss Distillation, UV radiation, Deionization and Ozonation. If there's any other filtration or purification method you're interested in, please email us and we'll add it to this list.
Below we will talk about filtration and purification. The difference between them has to do with the type of process of removing particles from water. Some filters work by blocking specific size particles from moving through the filter, and instead adhere to the surface or neutralize them and some work by the process of osmosis or reverse osmosis to be exact at 0.0001 micron so microscopic level.
Each filter or purifier is produced with a media or material that has specific pore sizes to "attract" or "reject" particles found in water base on their "size" to provide a desired level of filtration or rejection rate. These rejection rates also rely on size of the filter and the amount of time drinking water has contact with the media. Another two determining factors are water pressure and volume of water each filter or membrane will process daily. This is why there's often "gallons per day" (GPD) or in total included by each filter or purifying membrane.
During the filtration or purification process, filters and membranes do not distinguish between the types of particles they remove beyond the particle's ionic charge and/or its size. This is very important to understand especially when the goal is to remove, reject or retain (some or all) particles in the water such as retaining max amounts of minerals vs. rejecting max amounts of chlorine, lead, arsenic and other contaminants if present. When searching for a purifier or filter system, focus on what chemicals need to be removed, then what method will remove it best and most efficiently and effectively.
For those who are worried about systems wasting any amount of water in this process, The RO systems especially are very versatile and modular, you can add a water line and route drained water out of your house to water your garden, you can also filter it further or remineralize. Most hard contaminants: arsenic, metals, VOCs etc can not be neutralized or removed without using some water and today's purification systems turn off when tank is full or turn off valves to only process water on demand.
Often times due to matching sizes, some of these good and bad particles are similar in size or charge, so in order to produce the safest drinking water it might be best to remove as much of TDS (total dissolved solids) as possible and then add or infuse drinking water with minerals achieving maximum quality control.
There is no effective method that filters out or purifies water removing 100% of all harmful contaminants, while at the same time leaving 100% of naturally occurring minerals. All waters contain traces only, even those that are remineralized. What's more important is to eliminate tea, coffee, alcohol and other acidic liquids instead of worrying about minerals in tap water unless your water has TDS higher than 500ppm and must be distilled instead to be deemed safe to drink.
All sources of drinking water (including "natural spring water which often times gets mixed with purified tap water and gets pumped from the ground near contamination sources") contain contaminants that are regulated by the Environmental Protection Agency (EPA) or Food And Drug Administration (FDA) and must be removed prior to distribution for consumption, regardless of packaging methods. This requires companies to implement various filtration, purification and remineralizing methods to remove inorganic particles, turbidity, bacteria, viruses, asbestos, lead and other toxic heavy metals, radium, and many dissolved organics. The process will also remove chlorinated pesticides and most heavier-weight VOCs. improve alkalinity, mineral content or pH of water to meet those mandated standards to ensure water is safe to drink. Many companies add minerals and salts back into their water for improved taste.
Alkaline filters or remineralizing cartridges are available to add to your purification process if higher mineral content is desired. Modular Residential purification systems provide flexibility to customize purification or filtration stages to meet your needs.
Minerals found in water or frequently added to drinking water are responsible for the refreshing taste of water vs. a "flat" taste found in distilled water which is the actual taste of water with TDS of 0. Despite the marketing that has infiltrated the internet regarding the benefits of highly mineralized water, science points to the fact that human body derives much higher levels of minerals from nutrients and does not rely on traces of minerals found in water. The goal in drinking water purification should be removal of harmful contaminants and a balanced diet.
The chart below shows the smallest (finest) purification levels from the left gradually increasing the size of particles to the right with their cut off points. Depending on the source of your water (sea, municipal, well, ground water, surface water etc), the system may or may not have a water pump to ensure that the water flows property through each of the filtration stages for maximum contamination removal.
The pore size on micro-filtration membranes ranges from 0.1 – 5 um, and has the largest pore size of the four main membrane types. Its pores are large enough to filter out such things as bacteria, blood cells, flour, talc and fine dust. Because its pores are relatively large compared to other membranes, it can be operated under low pressures and therefore low energy.
Examples of micro-filtration applications are:
- Cold sterilization of beverages and pharmaceuticals
- Clearing of fruit juice, wines, and beer
- Separation of bacteria from water (biological wastewater treatment)
- Effluent treatment
- Separation of oil/ water emulsions
- Pre-treatment of water for nano-filtration or Reverse Osmosis
- Solid-liquid separation for pharmacies or food industries
Ultra-filtration has a pore size range of 0.1um to 0.01um. UF membranes reject particles such as silica, viruses, endotoxins, proteins, plastics and smog/fumes such as ZnO. Due to the decrease in pore size, the osmotic pressure required is higher than that of MF.
Ultra Filtration uses membrane technology to reject contaminants from 0.01 to 0.2 microns. UF is effective in the removal of bacteria, pyrogens, high molecular weight dissolved solids and other water contaminants without removing healthful minerals. Does not remove radioactive isotopes, viruses or salts and sugars and usually is sold with a UV filter. This level of filtration is not suitable for tap water.
Examples of ultrafiltration applications are:
- Removal of particulates and macromolecules from
raw water to produce potable water.
Filtration of effluent from paper pulp mill
- Cheese manufacture, see ultrafiltered milk
- Removal of some bacterias from milk
- Process and wastewater treatment
- Enzyme recovery
- Fruit juice concentration and clarification
- Dialysis and other blood treatments
- Desalting and solvent-exchange of proteins (via diafiltration)
- Laboratory grade manufacturing
- Radiocarbon dating of bone collagen
- Removal of particulates and macromolecules from
Nano-Filtration (NF)Nano-filtration has a pore size range of 0.001-0.01um. NF membranes can filter particles up to and including some salts, synthetic dies, and sugars, however, it is unable to remove most aqueous salts and metallic ions, as such, NF is generally confined to specialist uses.
Reverse Osmosis Purification (RO)
Reverse Osmosis technology is used by most leading water bottling plants including companies that sell spring water. Natural osmosis occurs when solutions with two different concentrations are separated by a semi-permeable membrane. Osmotic pressure drives water through the membrane; the water dilutes the more concentrated solution; and the end result is equilibrium. Reverse osmosis works much like a filter, but instead of using media that attracts contaminants, it uses pressure to force all water particles through a very small semi-permeable membrane eliminating particles as the water travels through each layer of the semi-permeable membrane, rejecting or repelling particles.
Reverse osmosis unlike UF, MF or NF is the most popular (most effective, efficient and affordable) methods of removing dissolved solids (TDS) such as salts (desalination process) sugars as well as dangerous minute particles such as arsenic, sulfur, chlorine, radioactive isotopes occurring naturally deep within the ground from residential municipal water. RO purification process was developed originally in California to desalinate salt water and quickly adopted by the military, biotech, medical and manufacturing industries and for residential and commercial use.
Reverse osmosis membrane uses ionic exclusion process where the semi-permeable membrane rejects heavily charged particles, the greater the charge, the higher the rejection rate.
The membrane rejects nearly all (>99%) strongly ionized polyvalent ions but only 95% of the weakly ionized monovalent ions like sodium.
RO has a pore size range of 0.0001 – 0.001. It is by far the finest separation material available to the industry. This purification process removes particles 500,000 times smaller than a diameter of a single strand of a human hair. RO is successfully used for desalination and purification of water (or liquids) as it rejects everything but water molecules, with pore sizes approaching the radius of some atoms in many cases. This pore size means it is the only membrane that can reliably filter out salt and metallic ions from water. The small pore size of RO membranes means that a significant amount of osmotic pressure is required to force purification.
Flow rates on RO membranes (36 GPD, 50 GPD, 75 GPD etc) are limited to certain gallons per day rating. Some systems with high volume per day require pumps or flow restrictors to control volume, water pressure and flow rate within the system for maximum effectiveness.
Ultraviolet (UV-C) Radiation / Germicidal Irradiation
Ultraviolet radiation has been used as a germicidal treatment for water. Mercury low pressure lamps generating 254 nm UV light are an effective means of sanitizing water. The adsorption of UV light by the DNA and proteins in the microbial cell results in the inactivation of the microorganism. UV are an effective sanitization method but will not remove particles, colloids or ions.
To disinfect microbiologically unsafe water. UV can be added to all RO systems when used for well water. Great at removing viruses. Many bottled water companies use UV process to destroy microbes in drinking water, unfortunately, this process is not as thorough as chlorination and often times e-Coli and other bacteria are present in drinking water.
Distillation is one of the most expensive ways to purify water. Because it uses electricity, it is very costly. Distillation is a slow process and not recommended for high volume of water. It also produces "flat" tasting water due to removal of all TDS (total dissolved solids including minerals and salts). To improve flavor, remineralizing filters are used which should be replaced every 6-12 months.
Not recommended for drinking water as it's not practical. Often used by laboratories, deionization utilizes a series of ion exchange resins, but to produce pure water, deionization must be combined with other purification systems, as while this method removes dissolved solids and gases, many other impurities remain.
Nature's natural sterilizer. Ozone is the strongest oxidant available for the disinfection of air and water. Ozone is used to purify a high percentage of the world's drinking water, including bottled and municipal water.
Ozone acts over 3000 times faster than chlorine, with the ability to kill 99% of all waterborne bacteria, germs, viruses, and most pesticides by rupturing the cells of micro-organisms or destroying odors and chemicals by oxidation. Ozone has a fairly short life of about 20 minutes, naturally changing back to O2.
The use of ozone for most drinking water systems is unnecessary and impractical due to municipal chlorination which is more thorough and cost-effective.
Additional Water Treatments
Water softeners and conditioners are alternative whole house water treatments for you. It is not recommended to use water purification such as RO on the entire house so most often clients install RO to purify drinking water and a water softer or conditioner to treat water in their bathrooms.
Used to soften "hard" water using ion-exchange technology that exchanges magnesium and calcium with sodium or potassium and in the case of conditioners, adds . Water softeners are not designed to purify water that is microbiologically unsafe. These systems replace or suspend mineral ions with salt or potassium ions they do not filter or purify meaning "clean water".
Water softening systems consist of a resin bed that captures hardness causing minerals and a cleaning system that purges trapped minerals, flushing them out the drain.
Contact us if you need water softeners, conditioners or replacement components or medium.
Water conditioner changes the composition of water to stop crystals from scaling on your pipes and fixtures, conditioners do not exchange or remove ions.
Carbon filtration water conditioners: Contain activated carbon that absorbs a series of chemicals dissolved in water. These water filters are particularly useful in removing organic compounds such as sulfur and chlorine from well or city water. Carbon filtration also removes foul tastes and odors, making tap water more pleasant for drinking and cooking. Most water filter pitchers and water dispensers use carbon filtration to improve the quality of the water.
Electromagnetic water conditioners: Use either wire wrapped around the pipes or magnets placed on your tubes to create molecular agitation in water. The agitation breaks and blends the particles of carbonate salts with the water, reducing the concentration of calcium and magnesium ions in the liquid. Through this process, these water conditioners reduce scaling, although they don’t soften the water in the real sense of the word. However, they also purify water, removing most chemical contaminants. These devices can only treat small amounts of water at a time, and water treated with such a device should be consumed.
- Catalytic media water conditioners: Are often referred to as salt-free water softeners. These water filters use template-assisted crystallization (TAC) to change the hardness of mineral crystals in water so that they won’t adhere to surfaces. Although they represent an excellent water conditioning system for well water, catalytic media conditioners don’t reduce the actual hardness of the liquid.
The main difference between water conditioners vs. water softeners is the quality of water. If you only want to reduce water hardness (caused by minerals) and have no concerns regarding water quality then a water softener is your best bet.
Water conditioners, on the other hand, filter water and remove impurities such as chlorine, fluorine, sulfur, carcinogenic disinfectant byproducts, pesticides, herbicides, but they don’t remove water hardening minerals such as calcium and magnesium.
Types Of Filters And Membranes For Drinking Water, And Their Effectiveness In Removing Specific Contaminants.
The drinking water treatment technologies used in a majority of water purifying or filtering systems include using one or more of the following methods or media types:
Ranging from 1 to 20 microns are normally used as a pre-filter to protect and extend the life of other filters. These filters remove larger particles such as dust, sand, rust and other visible to the naked eye debris you don't want to consume.
Here's a sediment filter that was used for 12 months filtering drinking water in San Diego, CA. The top one is the new sediment filter and bottom (yellow) is how it looks like after 12 months of use. These filters should be replaced every 6-12 months depending on the volume used.
Granulated Activated Carbon (GAC), Carbon Block, and Catalytic Carbon – Standalone, or combined with other technologies remove chlorine, chloramines, VOCs, MTBE, and a wide range of contaminants including lead and mercury.
Activated Carbon Block Filter
Here's a carbon block filter that was used for 12 months filtering drinking water in San Diego, CA. On the left is a new carbon filter and on the right is how it looks like after 12 months of use at 50 GPD. These filters should be replaced every 6-12 months depending on the volume used. Replacing filters extends the life of your reverse osmosis membrane.
BASF ATS Media
Originally developed by Englehard Corp. (purchased by BASF), ATS Media removes lead and heavy metals. As with KDF media, there is a synergistic effect when ATS is combined with activated carbon as the two materials result in an effective method of reducing contaminants, heavy metals and chlorine.
Reverse Osmosis Membrane (RO)
RO uses a semi-permeable membrane filter (Thin Film Composite or TFC), very pure water is produced but still retains traces of minerals. RO systems utilize a series of filters (sediment, granulated activated or block carbon), the TFC membrane. As chlorine can damage the TFC membrane, all RO systems have effective carbon pre-filters, and most use a carbon post-filter to improve the taste of drinking water.
Here's a RO membrane that was used for 12 months filtering drinking water in San Diego, CA. The one on the right is a used RO membrane. These membranes should be replaced every 24-36 months depending on the volume used and water quality.
RO uses a semi-permeable membrane that has pores large enough to allow water molecules to pass through but small enough to block other types of molecules at such fluoride, chlorine, heavy metals, nitrates, nitrites, silver, aluminum, arsenic, cadmium, copper, iron, nickel, zinc, lead, chromium, barium, hydrogen sulfide, radon, selenium, trihalomethane, manganese, mercury, chloroform, trichloroethane, lindane, pesticides, radioactive isotopes, sugars, salts, pyrogens, fungicides, bad tastes and odors.
When pressure is applied to water on one side of the membrane, water molecules are forced through to the other side of the membrane, producing purified water. Contaminants are essentially filtered out by the process. RO removes .001 micron size contaminants. RO does drain some water in order to separate and remove dangerous contaminants from water completely.
Zinc-copper alloy with a wide range of contaminant removal. Usually combined with Granulated Activated Carbon. KDF does not remove fluoride and requires a special fluoride filter.
Using a process of electrochemical oxidation known as “redox” (Oxidation-Reduction), KDF media is a zinc-copper alloy that removes 95-97% of free chlorine, heavy metals, nitrates, nitrites, silver, aluminum, arsenic, cadmium, copper, iron, nickel, zinc, lead, chromium, barium, hydrogen sulfide, radon, selenium, trihalomethane, manganese, mercury, chloroform, trichloroethane, lindane, pesticides, fungicides, bad tastes, and odors. KDF media significantly extends the life of granulated activated carbon (GAC), controls and inhibits the growth of microorganisms, and outperforms silver-impregnated carbon filters.
Alternative to germicidal UV-C for filtration of bacteria. With a .5 to .9 micron rating, Ceramic filters are effective for filtering microbes such as E.coli, cysts, and sediment. Most ceramic filters do not remove viruses effectively.
Specifically designed to remove fluoride and arsenic by adsorption. Activated alumina is manufactured from aluminum hydroxide by dehydroxylating it in a way that produces a highly porous material; this material can have a surface area significantly over 200 m²/g. The compound is used as a desiccant (to keep things dry by absorbing water from the air) and as a filter of fluoride, arsenic and selenium in drinking water.