Guide to water treatment and filtration.

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Selecting water treatments specially for rural water supplies is challenging because there is rarely a single solution. Many people make the mistake of adopting one technology and assuming it will do the whole job. This is rarely the case because water varies so much in its characteristics and no two situations are the same. It is sometimes useful to think in terms of progressive barriers. This means slowly treating water by removing contaminants in a sequence of steps. Sometimes the first step is to change the pH or oxygenation level.

Many water treatments include a filtration step using a mechanical filter like a fast sand filter, a large cartridge filter or a DE filter because most filter setups do require some type of sediment filter.

For a domestic supply some treatments are best before the water enters the house. Now you will probably want to disinfect your drinking water. Do this with a UV steriliser or a reverse osmosis system at the point of use or perhaps earlier using chlorination. Now way back where you collect or store your water this may be a good place for some aeration and perhaps use of a flocculant followed by time to settle. Somewhere in between you will want to treat some specific problems - if you've got them, like too much Manganese, or organic chemicals that might possibly be in your water.

It's a good idea to get a water test before you choose a filter because there are many subtleties you need to know about so your filters will actually work after you pay out your money. Now if all this sounds just too confusing don't worry you can ask your own lab or Apps Labs how the different water treatments work. In the meantime here is a summary of some of the main water treatment methods.

1. Chlorination Chlorination is mainly used as a control for microorganisms. It also breaks down organic matter in water and removes some metals by making them less soluble. In our lab at Gembrook we've found that around 10 ppm chlorine can dramatically reduce the humic brown yellow colours common in many surface waters. Chlorination is carried out by adding chlorine gas or sodium hypochlorite to water (use pool chlorine not the bleach that contains sodium hydroxide). The levels have to be monitored to ensure adequate exposure time as well as safe drinking levels. It is mainly used for large scale disinfecting so don't try this at home folks! Well actually you can do this at home. The Victorian Govt Department of Human Services says you can use chlorine to disinfect tanks so that's good enough for me. If you ring 03 59 681 401 first, Apps Labs will help you figure out how much Chlorine to use, whether your pH is right for disinfection and how to know when you can resume drinking your water. Nowdays people are getting alarmed because chlorination actually produces some water nasties - so always use a carbon filter if your water has been chlorinated.

2. Filtration

2a. Sediment filtration Water can contain all sorts of sediment from rust to insects, dirt, algae and bits of washed in plant matter. Particle filters come in various grades - mesh or pore sizes. If water is very contaminated start with a coarse filter then add a finer filter. Use a sediment filter first before passing water through either a carbon filter or a reverse osmosis process. A standard for household supplies is the 1 micron pore size filter cartridge. These are cheap and effective. Some coarser filters are washable for example pleated sediment cartridges. Try a 0.5 micron filter if you are concerned about disease microorganisms. Some carbon cartridges can filter microorganisms. Ceramic cartridges can filter out approximately 99.99% of bacteria.

2b. Activated carbon filtration Activated carbon filters are good for removing the chemicals which cause tastes and odours. They can remove a very wide range of organic compounds which makes them almost essential for treating drinking water. Luckily convenient filters which use activated carbon are readily available for household use and are relatively cheap. Here is a summary of the types of chemicals they can reduce: toxic by products of chlorination (trihalomethanes), Polynuclear Aromatic Hydrocarbons (some carcinogenic compounds), most of the Phase I and Phase II organics regulated under the US Safe Drinking Water Act.

2c. Slow Sand filtration Sand filters have been used for a long time for treating drinking water. Their great advantage is that they are cheap, low tech and effective. Water is passed slowly downward through a container of sand which is organised from large to small particle sizes (upwards). The water moves slowly by gravity only. They are specially good for removing organic matter, fungi, bad bacteria and even some viruses. Sand filters can also be used to treat recycled water. The media can also be lightweigh material like rockwool.

2d. Fast Sand filtration. This is a commonly used method. The water is passed upwards through fine sand. This is done under pressure so the filter is sealed. Most filters can be set to automatically perform a backwash to clean themselves. It's possible to put different types of media or combinations of media in these filters for example sand and anthracite.

2e. Settling. Just let the water stand if you have suspended particles which will settle by themselves. Use a clear container to test a small sample. Some of the particles from natural surface waters for example may take a little while to settle.

2f. DE fitration. DE stands for diatomaceous earth. Its a powder which is just about inert and packs down to trap right down to very small dirt and algae. The best setup for a DE filter is to use it to continuously or frequently cycle water from a tank, through the filter and back into the tank. This way the filter works to keep the water clean. Use a small electric pump to push water through the filter. Inside the filter there are a lot of porous plates. The idea is that you mix up a DE slurry and poor it into the filter chamber. Just let the water cycle through the filter for a while so that the DE coats the porous plates. Now it will do it's work until the little guage on top says the filter is getting clogged up. Just turn a tap to change direction of the flow and you'll flush out all the old DE. DE filters can trap Giardia and Cryptosporidium spores so for this reason alone they are worth looking at for rural water supplies. And what's really good is that they are one of the best ways to trap that nuisance algae so common in farm water supplies.

These single celled algae are about 4 microns x 7 microns. They are difficult to remove from water specially if there are a lot of them because they may quickly clog a filter. Try a DE filter. This can be backwashed and replenished when it reaches it's capacity.

2g. Microfiltration, ultrafiltration and nanofiltration. These are newer technologies that show improved possibilities for removing particles between 1/2 micron and the ions that are removed by reverse osmosis. Ultrfiltration can remove viruses and colloids and nanofiltration can remove the larger ions that cause water hardness.

3. Distillation Distillation means boiling water and collecting and condensing the steam. This is really good for removing metals and salts. Use distillation with care if the water contains more than a little organic matter or organic compounds as these may find their way back into the condensed water.

4. Reverse osmosis Reverse osmosis uses water pressure to push the water through a very fine membrane. This membrane stops nearly everything except very small molecules. A good household system has a sediment pre filter, a reverse osmosis membrane and then a final activated carbon filter to clean up small organic molecules. Apart from removing most bacteria and viruses, reverse osmosis will remove typically up to 95 - 99% of salts and metal ions. It's probably one of the best ways to remove salts and pathogens but your water has to be reasonably clean beofre going through the RO unit otherwise it will clog up too quickly.

5. Ultraviolet irradiation With this method you'll need to buy an ultraviolet steriliser. Water is passed in clear tubes between ultraviolet lights. Ultraviolet light is effective against bacteria, fungi and protozoan cysts incl Giardia and Cryptosporidium. Some units are quite neat and will give you more confidence about your water quality. The water needs to be very clear so the UV can be effective. A UV sterilizer is usually the final step in treating drinking water.

6. Ion exchange resins A large number of different ion exchange resins are available to reduce particular contaminants. They are usually recommended for specific problems. They have been used to reduce hardness, iron, manganese and many other ions in water. Ion exchange cartridges are available for household use and some are even combined into a single cartridge with activated carbon.

7. Acid neutralisation Various chemicals are added to water to reduce the acidity and the tendency for corrosion of metal particularly in pipes. These include sodium bicarbonate. The choice depends largely on the existing hardness and alkalinity of the water. For home use its better to install a calcite cartridge filter. The calcite slowly dissolves as you use the water, but it is better before the water comes into contact with any Copper pipes.

8. Water softening Lime Calcium hydroxide and soda ash (Sodium carbonate) are often used to remove hardness and scale forming compounds in water. Calcium and Magnesium can also be removed by ion exchange.

9. Aeration Aeration is basically speeding up the rate of air mixing with water. Oxygen breaks down organic compounds converting them to less harmful forms compared to what happens if there is low oxygen. Aeration works for iron because the iron which is usually dissolved in water reacts with the oxygen to form less soluble compounds. These settle if the water is left to stand or they can be filtered. The simplest way to aerate water is to pump it through a venturi aerator which forces air bubbles into the water stream. There are a number of other technologies designed to increase the efficiency of aeration like diffusers, spraying, bubblers, towers, and surface agitators.

10. Boiling Boiling reduces pathogens like bacteria and some microorganisms.

11. Ozonization Ozone is like oxygen but more effective. It works by efficiently oxidizing organic matter or metals or killing many microorganisms. It needs a special ozone generator and a diffuser to go in the water. It may under certain conditions be a good alternative to chlorine. Here are some of the things it reduces: kills bacteria and viruses, kills algal and fungal spores, precipitates heavy metals, removes excess iron, manganese and sulphur, removes colour and odour, reduces scale build up.

12. Flocculation. This method is good for water which is discoloured by colloids. These are very small particles that don't settle and can't be filtered. Usually a flocculant chemical such as aluminium sulphate is added by a dosing pump which adds a small amount of flocculant to the water as it is being mixed or circulated in a tank. The aluminium part makes the colloids clump together so they settle. This may take a while so you will need a good sized tank. Afterwards run the water through a fast sand filter or a large cartridge filter. If you get a test done on your water by a good lab eg Apps Labs! How to get a water test you can find out how much flocculant to use. That way all the aluminium will be used up in settling out the colloids and very little will end up in your finished water.

13. Constructed wetlands. As strange as it may seem, wetlands can improve water quality specially by removing nutrients like nitrates and phosphates. And this is achieved through natural processes. So constructing an artificial wetland makes sense both for improving the quality of a water supply, for treating waste water before discharge or even in recycling. Phosphates are usually removed through binding to sediments whereas nitrates are removed by conversion to harmless nitrogen gas through a process called denitrification. Wetlands can also reduce the organic loading in water by allowing bacteria to consume organic matter in the water.

Treatment options: This list may not include all possible contaminants, problems or treatments and doesn't mean that a given treatment will completely solve a particular problem. Remember there are no right and wrong ways to treat water only guidelines, good data and common sense.

Problem Cause / example Treatment Commercial solution
Algae, suspended material   2a (may clog), 2c, 2f, 11  
Bacteria from effluent discharge E. coli, Aeromonas

1, 2b (bacteriostatic), 2c, 2f (partial), 3, 4, 5, 10, 11

Protozoan parasites Giardia and Cryptosporidium spores 2f traps spores, 1 (may not be fully effective), 5  
Heavy metals incl copper, lead 3, 4, 11  
Taste, discolouration Iron and manganese 8, 11  
Nitrate   3, 4, 6, 13  
Viruses   2g (Ultrafiltration)  
Colloids   2g (Ultrafiltration)  
Salt, tendency to corrode Chloride 3, 4  
Hardness Carbonates 8, 2g (Nanofiltration)  
Smells Hydrogen sulphide 1, 9, 11  
Corrosion low pH 7, 9  
Discolouration Colloids eg clays 12, 1 for humic material  
  Synthetic organic compounds 9, 2a but with pretreatment  
Volatile organic compounds   Mainly 9 but 2a in conjunction with 9  
Tastes / odours Organic compounds 1, 2b. 11  

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