Vertical flow red beds.
The chemists talk of long chain molecules of carbon and nitrogen being broken up as the water passes through the various reed bed stages. Nitrogen eventually is released safely back into the atmosphere. Carbon is given off as carbon dioxide or is taken up in a small way in the reeds as Biomass. Oxygen must be made available to treat ammonia. Vertical flow beds are necessary for this.
In these the effluent passes vertically downwards through the gravel and reed roots. The bacteria in these beds use oxygen from the aerobic environment. Without an aerobic stage, ammonia, which is a constituent of sewage, would remain untreated. Most fish and caddis fly larvae cannot live in high levels of ammonia. Caddis fly larvae are biological indicators of clean water. From the point of view ammonia reduction the horizontal bed must be preceded by a vertical aerobic stage.
Ideally Herr Ltd would like to work with people seeking the highest standard of water treatment. In the past for various reasons inadequately treated water was allowed into larger water bodies. Dilution was seen as the solution to pollution. Larger numbers of our lakes now have low levels of pollution, whereas in the past there was relatively little pollution present at all present. Some sections of our coastline have no Blue Flag beach at present. Herr Ltd would prefer to go the extra mile to install systems that treat to high standards, to be reliable, passive, requiring no pumps, compressors or maintenance. Please let us know if phosphates are of particular concern.
Horizontal flow reed beds.
In these the flow passes horizontally through the bed. Oxygen is limited and so nitrates and nitrites are broken down at this stage. Any ammonia present will not get treated. Where there is no fall on the site a horizontal bed alone can be used. Without a vertical flow reed bed stage, this will undoubtedly be a simpler system. It does require however a much larger area of reeds, up to 80 square meters for a domestic house. As already stated horizontal beds alone cannot reduce all the elements that can cause water pollution.
In both stages the polluting power or “BOD” is reduced. Assuming the area of the reed beds have been adequately sized this BOD measure will be low enough to discharge safely. The local authorities will be generally happy with effluent of a clear appearance and low BOD. This will not necessarily be adequate for fish, as high levels of ammonia, a toxin, may still be present.
Slope and fall on site.
For Ammonia treatment there needs to be a down hill slope of 2 to 3.4 meters after the septic tank to allow movement of the water by gravity through the vertical flow reed bed stages. Having a slope on the site is ideal since there is no dependence on pumps or electricity. Consider living in the first floor of your house with the sewer pipes leaving the house a 8 feet above normal ground level. Provide an artificial hill for the vertical flow beds. Having this arrangement eliminates the need for pumps. The wastewater is then directed to a dosing box that stores the water until ready to give a full flush over the full surface of the first stage reed beds.
During the few minutes that the bed is being dosed there can be a slight sewage smell immediately at the first beds. Remember this water has just come from a septic tank. Some 95% of visitors to such sites don’t notice the smell until it is pointed out to them. There are however some 5% of people who would be put out by it. It’s not noticeable at all when 10 to 15 feet away. Except that you are very aware of scents and odours generally this will not be a problem. Whenever there is no dosing there is no odour at all.
The roots of the reeds provide a beneficial environment for the bacteria that eat the sewage. The sewage is spread over the full surface of the vertical flow bed and trickles down through the gravel and root network. The bacteria in these beds need air. Careful attention is needed for the choice of gravel to ensure adequate drainage and full aeration of the reed bed bottom.
The water passes through three stages of reeds. The last bed is permanently flooded. This is the horizontal flow stage. The bacteria eating the sewage at this stage work in the absence of air. This completes the basic treatment process. Some 80 to 90% of the polluting power of the sewage will now have been removed. Herr Ltd will attempt to design for high tertiary water treatment standards.
During the few minutes that the bed is being dosed there can be a slight sewage smell immediately at the first beds. This is so if this water has just come from a septic tank. Some 95% of visitors to such sites don’t notice the smell until it is pointed out to them. There are however some 5% of people who would be put out by it. It is not noticeable at all when 10 to 15 feet away. Except that you are very aware of scents and odours generally this will not be a problem. Whenever there is no dosing there is no odour at all.
With a solids seperator at the front end, however the possibility of smells is greatly reduced as the organic matter will not sit in a septic tank for a few days.