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AFM in Tertiary Sewerage Treatment |
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back to applications |
| AFM is being used for the tertiary treatment of sewerage effluent. Under normal operating conditions if sand is used for the treatment
of sewerage effluent, the sand will rapidly become colonised and blocked by bacteria. However the smooth micro structure and self sterilisation
properties of AFM, allows AFM to be used in standard pressure filters or rapid gravity for the treatment of sewerage effluent. The performance
achieved is almost as good if not better than membrane systems. AFM will remove solids from the water down to approximately 5 microns. AFM will also
remove even smaller particles and adsorb organic molecules by surface adsorption. This performance can not be achieved by membranes. In addition,
membranes result in the development of high concentrations of phosphates, which can cause major problems.
NoPhos can be used as a flocculent
before AFM to improve solids removal performance, and remove phosphates at the same time. AFM filtration is achieved using relatively simple,
low cost pressure filters at a fraction of the cost of membranes.
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Quality of effluent |
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AFM filtration will remove virtually all of the solids from
sewage effluent. Systems are installed in Thames Water and
Scottish Water as well as many systems around the world
If you need to reduce you solids load from over 100mg/l to less
than 10, or even 1mg/l. AFM filtration can achieve this task.
Also because the media does not biofoul, you will not have
coagulation problems and bed fouling which is common in all types of
sand filters, including moving bed filters.
AFM solves the problem of the tertiary treatment of sewage effluent
at around 20% of the cost of any alternative system.
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Operational criteria |
| The AFM mode of application in effluent treatment is covered by patent. The loading on the filter is extremely high, we therefore recommend a water
flowrate of no more than 5 to 8 cubm/hr per square meter of filter bed surface area. Back-flush frequency normally ranges from 3 to 6 hours,
back-flush flowrate is 40 cubic metres per hour per square meter of filter bed surface area for 2 to 5 minutes. The back-flush water is directed
back to the beginning of the works. Air purging of the bed prior to back-flushing will reduce the amount of back-flush water, but it is
not required order to keep the bed of AFM running |
 The
above graph presents the results from a sewage works showing the
suspended solids level in the discharge from the percolating filters.
The water then enters the humus tanks, and the water quality results
for the works discharge from the humus tanks is presented. The
AFM filter receives its water directly from the percolating
filters ( AFM influent) but before the humus tanks. The AFM
effluent data gives an average value of approximately 7mg/l from an
influent of around 70mg/l. 90% solids removal efficiency is
achieved |
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Performance benefits |
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Under the above conditions you can expected a very high level of solids removal, levels less than 5mg/l suspended solids and 80% plus, reduction
on BOD. Bacterial floc and some individual bacteria will be removed by the filter. The back-flush water is directed back to the beginning of
the works. This means that the bacterial cell biomass and in particular the autotrophic nitrifying bacteria are captured and recycled. Nitrification
performance and ammonium removal efficiencies can be dramatically increased. We have also found that the AFM filter is able to capture herbicides and
pesticides, and minimise or prevent their discharge into the environment..
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Small
AFM
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AFM and systems installed in United Utilities
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