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Posts Tagged: ultraviolet disinfection



Case Study- Chemical Free Iron Removal.


Author: Helmut Dresselhaus – Pacific Water Technology – Brisbane

Date: 26/08/2018




 Pacific Water Technology recently commissioned a new commercial water treatment facility for bore water to produce high quality water destined for the water bottling plants in Queensland.  The innovative technology employed is leading edge, and has delivered excellent results.   The project included the complete scope from equipment design, supply of equipment and storage tanks, as well as commissioning and process optimisation.   

 In order to ensure that the good properties of this water is maintained during storage,   the 316 Stainless Steel tanks from Select Water Tanks provided the cost effective solution.  The water bottlers require very strict water quality standards, both in regards to chemical and microbiological standards exceeding Australian Drinking Water Guidelines.  The best technology and equipment was therefore selected to ensure optimum results are delivered. A secondary concern was the formation of bromate due to the ozone oxidation of bromide. Due the low levels of bromide (less than 30 ppb) there was undetectable levels of bromate.

The table below compares the results of ozonation vs aeration of the water, both delivering results well within the required tolerances.  There was some evidence of perhaps ozone oxidation causing some manganese to go back into solution, however this can be remedied by reducing the ozone dose. In conclusion the implementation of either air or ozone in conjunction of Nanobubble technology delivered excellent results in removing iron and manganese and producing water with an excellent flavour and aesthetic profile.








IC001 Bromate mg/l <0.01 <0.01
I.619 Total Dissolved Solids mg/l 250 260
5.308 Manganese as Mn mg/l 0.013 0.001
5.308 Iron as Fe mg/l 0.0052 0.036



Rainwater Harvesting and Filtration

Rainwater  Harvesting and Filtration

Many Australians rely on rainwater as their water supply for their daily needs. The general public perception is that rainwater is safe to drink. In most areas of Australia, the risk of illness arising from consumption is relatively low, providing it is visually clear, has little taste or smell and, importantly, the storage and collection of rainwater is via a well maintained tank and roof catchment system.

Australian Households using rainwater.

Source ABS 2010


This water may be used as if it was potable water and sometimes without any filtration and disinfection.   That the water comes from the skies and is always safe to drink, is a fallacy.   As the rainwater is harvested on the roof, any organic and inorganic material including faecal matter is collected into the rainwater tank.  Live animals may also get trapped in the tank and drown providing a source of nutrients and high risk of bacterial contamination.   Algae can also grow where the water is exposed to sunlight.   Most tanks will also contain mosquito larvae which feed on the organic nutrients collected in the tank.

Odours from sediments and slimes are the most commonly reported. Sediment can accumulate in the bottom of tanks that have not been cleaned frequently enough. In warm to hot weather, anaerobic conditions can develop, leading to growth of microorganisms that produce sulphides, with a distinctive sewage or rotten egg-like smell. Listed below are some water parameters that can impact your water quality:

pH levels in rainwater are normally below 7 and considered acidic. This is because carbon dioxide from the atmosphere is absorbed which in turn converts to carbonic acid.  In plastic tanks the pH will remain acidic  and can corrode copper plumbing and brass fittings.  Also see : http://www.abc.net.au/local/stories/2010/11/24/3075218.htm

 If the rainwater is stored in concrete tanks the acidic water will cause lime from the concrete to leach into the water. 

Calcite filters are recommended for an appropriate treatment of acidic water.


Turbidity is the measure of relative clarity of a liquid. It is an optical characteristic of water and is an expression of the amount of light that is scattered by material in the water when a light is shined through the water sample. The higher the intensity of scattered light, the higher the turbidity. Material that causes water to be turbid include clay, silt, finely divided inorganic and organic matter, algae, soluble colored organic compounds, and plankton and other microscopic organisms.


Tannins are a natural organic material that can be the byproducts of nature’s fermentation process, be created as water passes through decaying vegetation in the gutters. This can cause water to have a faint yellow to tea-like colour, and can cause yellow staining on fabrics, fixtures, china and laundry.

Rainwater in its natural state, is very close to de-ionised but after passing over the  roof, conductivity levels can be elevated due to contaminants that may be dissolved in  the rain water.

In its natural state rainwater is very soft and ideal for washing and laundry and  under some conditions for hot water systems.  The water also has a low alkalinity and that combined with soft water and low pH results in the rain water causing corrosion and that includes copper plumbing .

Total Suspended Solids .

Suspended solids refers to small solid particles which remain in suspension in water as a colloid or due to the motion of the water. It is used as one indicator of water quality.  A colloid is a solution that has particles ranging between 1 and 1000 nanometers in diameter, yet are still able to remain evenly distributed throughout the solution.

Coliform Colony Counts 
The most basic test for bacterial contamination of a water supply is the test for total coliform bacteria. Total coliform counts give a general indication of the sanitary condition of a water supply

Prevention is better than cure

There are a number of steps that can be taken by the householder to ensure good quality rainwater.

Gutter Guard

Gutter Guard or mesh can help prevent  leaves and other organic  matter from reaching the rainwater tank.

First Flush diverters

Are readily available from hardware stores, or can easily made up yourself.

Regular tank cleaning and inlet screen filter maintenance.

Effective filtration and disinfection.

Effective filtration and UV Disinfection will provide you with safe drinking water

The filtration steps should comprise at  least of a 10 micron sediment filter, followed by an antibacterial silver impregnated activated carbon filter and final UV disinfection step.

For higher flow rates we recommend automated backwash filters. Zeolite and activated glass media filters are very effective in removing suspended solids.  Activated Carbon filters can remove dissolved organics and any bad odours and taste. An occasional backwash will ensure that any colloidal or organic material is removed It is very important to use silver impregnated carbon or antibacterial carbon, as organics trapped in the organic matrix can aggravate the problem. 

Environmental factors

Environmental Factors should also be considered.  Any dust that is blown onto your roof may end up in your water tank.  This  may include dust from a mine ,  agricultural activity that could include pesticides and fertilisers.  If the water runs off old asbestos roofing, or is in contact with plumbing that contains lead solder are factors that should be considered as well.

Water Testing

Water testing should be carried out at least once a year to see what contaminants are present. There are easy DIY test kits which can provide an indication of whether your rainwater is not contaminated.

complete water testing for your home


Rainwater harvesting has become an important factor in conserving our most precious resource. More than ever, Australians are relying on rainwater as their potable water supply.  Preventative Maintenance is an important factor in ensuring a safe water supply. Preventing organic and inorganic matter from getting into the tank can reduce the risk of bacterial contamination, algae growth and reduce the amount of suspended and colloidal material in your water tank. Sediment and carbon filtration  followed by ultraviolet disinfection are highly recommended to ensure a safe source of drinking water. Calcite filter should also be considered to ensure that the water is not corrosive, and will cause corrosion to your plumbing.


The dangers lurking in dam, river or other untreated water supplies

A large proportion of Australians rely on untreated or minimally treated water supplies,  for their daily water requirements.   Recent events have highlighted the dangers of untreated water supplies, even when the water is not consumed.  Naegleria infects people by entering the body when water containing the amoeba goes up the nose. This may occur when people swim, dive or fall into warm freshwater containing Naegleria.  Also see Australian Story .

The dangers lurking in stagnant waters

The dangers lurking in stagnant waters-Source: Wikipedia

Infections have occurred following domestic bathing, for example when young children fall or slip in a bath of water containing Naegleria. The amoebae travel up the nose to the brain where they infect and destroy brain tissue. Naegleria fowleri, also  known as the “brain-eating amoeba“, is a species of  free-living, bacteria-eating amoeba that can be pathogenic, causing a ) brain infection.This microorganism is typically found in bodies of warm freshwater, such as ponds, lakes, rivers, and hot springs. There is no reason why this bacteria could not also be encountered in rain water tanks.

There are other water borne bacteria and viruses as well, and some people may build up some level of immunity  against some of these potentially lethal microbes.    Legionella is just another example of a bacteria, that thrives in warm stagnant water. Rain water that falls from the skies is perceived safe to drink,  and provides a false sense of security- the same applies to dams and rivers that may be located in prestine environments.   Others in the community in particular older people and children may not have the same level of immunity – and it just is not worth it to roll the dice .   The best way to ensure your water supply is safe is to have some levels of filtration and ultraviolet disinfection. UV radiation affects microorganisms by altering the DNA in the cells and impeding reproduction. UV treatment does not remove organisms from the water, it merely inactivates them. The effectiveness of this process is related to exposure time and lamp intensity as well as general water quality parameters.  

Used alone, UV radiation does not improve the taste, odour, or clarity of water. UV light is a very effective disinfectant, although the disinfection can only occur inside the unit. There is no residual disinfection in the water to inactivate bacteria that may survive or may be introduced after the water passes by the light source.  It is therefor necessary to treat the water immediately after it is pumped from the water source, and prior to consumption. Water for recreational use should also be treated. The percentage of microorganisms destroyed depends on the intensity of the UV light,  the contact time, raw water quality, and proper maintenance of the equipment.  Any stagnant water like  inflatable pools may also require supplementary disinfection like chlorination.


The natural way to disinfect without chemicals

Contact your local PWT specialist and we can recommend the most suitable disinfection solution for your water requirements.


For more on our range of UV disinfection systems : 

Brochure pacific-water-uv-guard-slt-series-brochure