Note: Descriptions are shown in the official language in which they were submitted.
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Filtering plant for waste water
This invention relates to a purification plant for purification of waste water
and recycling water from a small group of households, agricultural units,
cabins and the like. If the plant receives only grey water, the plant should
purify it to such an extent that the water can be re-used for watering,
washing, flushing of toilets, etc. If the plant receives black water, the
plant
should purify the water so that it can safely be discharged into the
environment. The plant is divided into three main parts; a sludge interceptor,
a main filter with vertical unsaturated aerobic flow at the top and saturated
anaerobic flow at the bottom of the filter, and a final filter with horizontal
saturated anaerobic flow. As a final treatment the water is disinfected in
order to remove bacteria. The filtering plant is equipped with one or more
buffer zones and overflow pipes between the main parts in order to give the
plant the capacity to absorb extraordinary loads without untreated waste
water running out into the environment. The term aerobic means with access
to external oxygen, while anaerobic means without access to external
oxygen.
Background
Local conditions may give rise to various problems associated with water
consumption in households, agricultural units, cabins and the like. In some
urban areas and other areas with high population density, e.g., the water
resources may be limited, thus making it desirable to use the water several
times for different purposes, while in sparsely populated districts it is
often
expensive and impractical to build municipal/regional waste and purification
plants for the waste water. If in addition the local ground conditions have a
low drainage tolerance, earth filters and similar solutions will not
constitute a
suitable purification method for the waste water. In these cases a
purification
plant may be an acceptable solution.
Waste water contains biological and chemical components such as bacteria,
phosphorus, nitrogen and organic materials, etc. These can cause local
pollution problems such as acidification, dissemination of disease,
overfertilisation of streams and water and the like if the waste water is
discharged freely into the environment. When municipal/regional waste
water facilities are not present, therefore, the waste water should be treated
in
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order to reduce the content of, or completely remove, these components in
order to ensure that the environment does not receive excessive amounts of
the waste water's content of infectious and/or other environmentally hostile
substances. In those cases too where the water resources are scarce and the
waste water is required for watering, washing, flushing toilets, etc. in order
to reduce the household's water consumption, the waste water should be
purified before re-use.
Prior art
The use of sand and other filter materials in a reservoir is known for
purification of waste water where the water is dispersed on and/or in the
filter media and transported through the filter media. In such filters it is
known to perform the purification under either anaerobic conditions, e.g. the
filter medium is saturated with water, or under aerobic conditions where the
filter medium is not saturated with water. There are many different devices
and filter materials for such filters, but they will not normally combine
zones
with purification under both saturated and unsaturated conditions or have the
possibility of regulating the size of the different zones for optimisation of
the
purification process.
In EP 0 654 015 a purification plant is disclosed which has combined a
sludge interceptor with aerobic conditions. a second reservoir with anaerobic
conditions filled with active carbon and mineral filter medium and a third
reservoir with aerobic conditions where the water flows through a series of
filter walls filled with active carbon or mineral filter medium. Part of the
water will be recirculated back to the sludge interceptor. This plant,
however,
is not equipped with buffer zones which enable the plant to absorb
extraordinary loads, nor has it the possibility of regulating the ratio
between
the size of anaerobic and aerobic zones in the plant.
The object of the present invention
An object of the present invention is to provide a compact purification plant
which can purify grey water chemically, mechanically and biologically under
both aerobic and anaerobic conditions, from a small group of households,
agricultural units, cabins and the like to such an extent that the water can
be
re-used for watering purposes, as washing water, for flushing of toilet bowls.
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etc. If the waste water also contains water from the toilet, so-called black
water, the plant should purify the water to such an extent that it can safely
be
discharged into local earth masses or another recipient without the risk of
local pollution.
It is also an object of the present invention to provide a purification plant
which has a large buffer capacity in order to be able to absorb substantial
extraordinary loads without the risk of untreated waste water evading the
purification process, with the result that the risk of sludge escaping from
the
plant is as good as eliminated.
Another object of the invention is to provide a purification plant which can
easily regulate the recirculation of the water between the different
purification zones, the water's residence time and where it is easy to replace
filter media, thus providing the plant with a very high total purification
effect
which satisfies present day requirements for purification of phosphorus,
organic materials, nitrogen and bacteria by a wide margin.
A further object of the present invention is to provide a purification plant
which is optimised with regard to nitrogen removal, and which can rapidly be
adjusted/modified in order to maintain optimal nitrogen removal without
conversion or alterations to the filter medium according to any changes in the
operating conditions.
Description of the invention
The objects of the invention are achieved with a purification plant consisting
of several well-tried filtering techniques which are assembled in a specific
combination:
Sludge interception with denitrification and prefiltering, dispersal of water
over a main filter medium for purification under aerobic unsaturated
conditions, followed by purification in a final filter medium with saturated
anaerobic conditions and finally disinfection by means of UV radiation or
another disinfection method, such as sodium hypochlorite, ozone, etc. In
addition both the sludge interception chambers and the final filter are
equipped with buffer zones and connected to each other by one or more
overflows in order to ensure that non-disinfected water does not escape
during periods of extraordinary loading of the plant.
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The sludge interceptor removes suspended materials and is divided into three
chambers, two sedimentation chambers and a coarse prefilter. The
sedimentation chambers are designed in such a manner that they have a large
volume and so that the water is forced to take a long path. The sedimentation
chambers should preferably be designed in such a manner that the water is
forced to make a 180° turn in order to enter the second sedimentation
chamber. This increases the residence time and thereby the sedimentation in
the first sedimentation chamber. The removal of suspended material is
further ensured by the fact that the sludge interceptor has a prefilter. The
prefilter will form a biofilm which removes some of the content of organic
material and bacteria in the waste water while some of the phosphorus
content will be chemically bound to the filter medium. The first
sedimentation chamber is also used for denitrification of water recirculated
from the main filter.
After sludge interception the water will be pumped into a dispersal system
which comminutes the water on the upper surface of the filter medium in the
main filter in such a manner that the water will be passively enriched with
oxygen. Passively means without the injection of air into the filter. In the
main filter the water will undergo purification under vertical unsaturated
aerobic flow conditions as it percolates downwards in the filter medium. In
this process phosphorus will be chemically bound to the filter medium by
means of adsorption, organic material is removed mechanically and
bacterially by means of an active bioskin, and the nitrogen content of the
water will be nitrified into nitrate ions. Bacteria will also be retained in
the
filter medium. This is the largest filter, and the size will cause this step
to
represent the principal purification of organic material, phosphorus and
bacteria. In the bottom of the main filter there is located a collecting pipe
which passes water to a pump chamber. The height of the collecting pipe's
outlet can be adjusted, thus causing a water surface to be formed in the lower
part of the main filter. The bottom part of the filter medium thereby becomes
saturated with water, thus creating anaerobic conditions in this area. Under
anaerobic conditions the nitrate ions will be converted bacterially to
nitrogen
gas (denitrification), while the removal of organic material, bacteria and
phosphorus will be conducted at approximately the same rate as for the
aerobic part of the filter. The height adjustment of the water surface allows
the ratio between aerobic and anaerobic filter media to be adjusted by a
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simple movement for optimisation of the nitrification and denitrification
processes.
As mentioned above, after having passed through the main filter, the water is
transported in a perforated pipe which is placed along the bottom of the
filter
5 to a pump chamber. The pump will pass some of the water back to the first
sedimentation chamber for denitrification and the rest to the final filter for
final purification via a distribution pipe. The distribution of the water
between the final filter and the sludge interceptor can easily be adjusted by
means of valves mounted on the distribution pipe. In the final filter the
water
will pass horizontally through the filter medium under anaerobic saturated
conditions, thus causing the water to be denitrified. The final filter will
also
remove residual organic material, bacteria and phosphorus.
The object of recirculating some of the water from the main filter back to the
first sedimentation chamber is to utilise the high incidence of carbon in the
chamber for the denitrification process. It is well known that carbon is
necessary for the denitrification process, and an area with a high incidence
of
carbon will therefore enhance the removal of nitrogen in the plant. In
addition there are two other zones in the plant which also contribute to the
removal of the nitrogen content. This gives the plant a very high total
purification effect on nitrogen.
After the water has passed through the final filter it is passed through a
disinfection unit for further removal of bacteria. The water is then
discharged
into local earth masses or another water recipient, or collected in tanks for
re-
use.
The plant is designed to be able to accept a larger volume of water than that
which is the average water consumption per day for the user units. This is
due to the fact that the plant has a fixed through-flow area on the throughput
connections between the different chambers. However, both the sludge
interceptor and the final filter can increase the water level in order to
absorb
sudden extra loads if the plant is loaded with more water than that which can
run through the throughput connections per time unit. Even though the water
level rises, however, all the water will still pass through the filters, thus
creating buffer zones. In addition a guarantee is obtained that if the water
level rises too much in the sludge interceptor an overflow will pass the water
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to the pump chamber for the main filter, while for the final filter chamber a
second overflow will pass water back to the sludge interceptor if its buffer
zone is exceeded. A guarantee is thereby obtained that the entire plant will
absorb extra loads before untreated water will escape. This gives the plant a
very large total buffer zone, thus essentially eliminating the risk that
sludge
and/or untreated water will escape.
The plant has three chambers which employ filter media. Any kind of
material may be employed which satisfies the requirements regarding
permeability, porosity, specific surface, ability to form bioskin and the
capacity for binding phosphorus given in Table 1. No requirements are
placed on the bottom and the wall materials of the plant apart from the fact
that they have to be capable of withstanding water and the pressure
conditions in the plant, both externally and internally.
Examples of preferred embodiments
The invention will now be described in more detail with reference to two
examples of preferred embodiments of the purification plant and with
reference to the accompanying drawings of the embodiments.
Figure 1 is a plan view seen from above of a first preferred embodiment of
the purification plant according to the invention. 'The arrows indicate the
direction of flow of the water.
Figure 2 is a side view of the first preferred embodiment illustrating the
second sedimentation chamber and the pretilter chamber.
Figure 3 is a new side view of the first preferred embodiment illustrating the
prefilter chamber and first pump chamber. This view is perpendicular to the
view presented in figure 2.
Figure 4 is an interrupted side view of the main filter, second pump chamber
and first sedimentation chamber in the first preferred embodiment.
Figure 5 is a side view of the final filter and the I7V unit in the first
preferred
embodiment.
Figure 6 is a plan view seen from above of a second preferred embodiment of
the plant according to the invention.
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Example 1: First preferred embodiment
From figure 1 it can be seen that the first preferred purification plant is
rectangular and composed of 7 chambers. The first sedimentation chamber is
indicated by reference numeral 1, the second sedimentation chamber by 2,
the prefilter chamber by 3, the first pump chamber by 4, the main filter
chamber by 5, the second pump chamber by 6, the final filter chamber by 7
and the UV chamber with outlet by reference numeral 8.
Table 1: Preferred requirements for filter materials
Chamber Phosphorus binding Permeability Structure~J
Prefilter No requirements > 1500 m/day 4 - 20 mm
Main filter > 5 kg/m3 > 100 m/day 0.2~ - 7 mm
Final filter > 5 kg/m3 > 1000 m/day 0.25 - 7 mm
1 ) The shape of the filter material can be both round or angular.
The first sedimentation chamber has a wet volume of 1.6m3 (wet volume
refers to the amount of water in the chamber at lowest normal water level).
Waste water enters the chamber through inlet 1 l, flows through the chamber
and on into the second sedimentation chamber 2 via a 110 mm transition pipe
which is located in the middle at 2/3 the height (measured from the bottom)
on the short partition between the sedimentation chambers (not shown). The
chamber is designed in such a way that the water has to make a 180°
turn
before entering the second sedimentation chamber. As mentioned, water from
the main filter will be returned to the first sedimentation chamber for
denitrification. This is carried out by means of a perforated pipe 66 which
distributes and mixes water from the second pump chamber 6 with the water
in the chamber (see also ftgure 4).
The second sedimentation chamber 2 has a wet volume of 0.8 m3, and is a
pure sedimentation chamber. In figure 2 it can be seen that the water flows
out of the chamber through a 110 mm transition pipe 21 which is located at
1/3 of the height from the bottom. The transition pipe 21 is located at the
opposite end of the chamber relative to the transition pipe between chambers
1 and 2, and is connected to a vertically perforated 75 mm distribution pipe
31 which is located in the prefilter's filter medium. The distribution pipe 31
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will distribute the water over the entire height of the filter medium. In the
event that the perforation should be clogged by suspended material, the
distribution pipe 31 is extended so that it reaches higher than the filter
medium and is equipped with an overflow 33. In the figure the water level in
the event of maximum utilisation of the buffer volume is indicated by the
arrow 32.
The prefilter chamber 3 has a wet volume of 0.8 m3, and is filled with a
filter
medium consisting of Leca Lettklinker (light clinker) or a similar material
with a diameter of 4-20 mm. The water will flow horizontally through the
filter medium under anaerobic saturated conditions. After the water has
passed through the filter it will be collected in a 7~ mm perforated
collecting
pipe 34 which flows into the first pump chamber 4 (see figure 4). The end of
the collecting pipe 34 may be equipped with transitional end pieces 35 in
order to regulate the water through-flow. This offers the possibility of
increasing the water's residence time in the sludge interceptor and thereby
increasing the sedimentation and denitrification. In periods of extraordinary
loading the water level in the sludge interceptor will rise. In order to
prevent
flooding, the partition between the prefilter chamber and the first pump
chamber is equipped with a 110 mm overflow 36 immediately above the
water level which corresponds to the maximum utilisation of the buffer
volume.
The water level in the sludge interceptor may be increased by 15 cm, which
corresponds to a buffer volume of 330 1.
After the prefilter chamber the water enters a first pump chamber which is
equipped with a float switch-controlled pump 41 which will intermittently
pass water into a dispersal system 51. The dispersal system distributes tjle
water over the main filter's 54 upper surface (see figure 1 ). The float
switch
has been given reference numeral 42. The chamber has an area of 0.50 m x
0.35 m. The main filter consists of Leca Lettklinker (light clinker) or a
similar material with a diameter of 1-4 mm and has an area of 5 m2. The
dispersal system 51 consists of a rectangular pressure pipe equipped with five
spray nozzles (not shown) which will disperse the water evenly over the
entire filter surface while saturating the water with oxygen. The water will
percolate vertically down through the filter medium under aerobic
unsaturated conditions until it meets a water surface at approximately 1/3 of
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the height from the bottom. From there and down to the bottom of the main
filter, the water will be purified under anaerobic saturated conditions. As
mentioned, the water's nitrogen content will be nitrified into nitrate under
aerobic conditions, and denitrified into elementary nitrogen gas under
anaerobic conditions. The main filter has the capacity to convert virtually
the
entire nitrogen content of the water to nitrate, but can only convert parts of
the nitrate formed into elementary nitrogen. In addition the main filter has
the capacity to purify around 90% of the water's content of phosphorus and
organic material. After the water has passed through the filter medium, it
will
be collected in a 32 mm perforated collecting pipe 52 which is located
diagonally along the bottom of the main filter and will flow into the second
pump chamber 6. The end of the collecting pipe 52 is in the form of a
gooseneck 53 (see figure 4). The gooseneck can be rotated about the
attachment point of the collecting pipe, thus enabling the height of the
discharge point on the gooseneck to be raised and lowered in order to alter
the height of the water surface, thus permitting the ratio between the aerobic
and anaerobic zones in the main filter to be adjusted according to
requirements.
As mentioned, water which enters the second pump chamber 6 will contain a
large amount of nitrate ions. In order to exploit the favourable conditions
for
denitrification in the sludge interceptor, some of the water is .recirculated
back to the first sedimentation chamber by a float switch-controlled pump 61
passing water into a double-branched pipe 63 which is connected at one end
to a perforated lead-in pipe 66 in the sedimentation chamber (see figures 1
and 4) and at the other end to a vertical distribution pipe in the final
filter.
The volume of water which is recirculated to the first sedimentation chamber
can be easily regulated by means of valve 65. In order to achieve the best
possible purification effect, as much water as possible should be recirculated
to the first sedimentation chamber, but of course there must be a balance
between ingoing and outgoing water in the plant.
In order to further increase the plant's denitrification capacity-and to
ensure
that phosphorus and organic material are adequately removed, the remainder
of the water entering the second pump chamber 6 is passed to a final filter 7
for post-purification via the second branch of pipe 63 which is connected to a
75 mm perforated distribution pipe 71 which is located vertically in the final
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filter's filter medium 72 in a corner of the final filter chamber 7 (see
figure
1 ). The final filter employs the same filter material as the main filter. The
volume of water passed to the final filter can be easily regulated by means of
a valve 64. The water will flow horizontally through the final filter's filter
5 medium 72 to a 75 mm perforated collecting pipe 73 which is located in the
opposite corner to the distribution pipe 71. As mentioned, the purification is
carried out in the final filter under anaerobic saturated conditions. The
collecting pipe 73 is connected to an overflow 74 which passes the water to a
UV unit 8 for further removal of bacteria (see figures 1 and 5}. The overflow
10 74 is equipped with a valve 75 for regulating the volume of water which
flows through the UV unit. The UV unit is connected to a submerged outlet
sump 81 with outlet 82. The outlet sump 81 has the capability of sampling
water (not shown). The chamber 7 has two safety overflows. In the event of
extraordinary loading chamber 7 can have 10 cm extra capacity before the
water will be returned by means of gravity to the f first sedimentation
chamber
1 via an overflow 76. This ensures a greater purification effect while at the
same time utilising the buffer capacity of the sludge interceptor. If the
water
level in chamber 7 rises further, the water will be conveyed past the UV unit
8 and down into the outlet sump 81 via overflow 77. This may arise in the
event of extreme loading, but will probably not occur. The object of the
overflow 77 is to ensure that the plant obtains satisfactory operating
stability.
The water level in the final filter can be increased by 10 cm, giving a buffer
volume of 130 1. The total buffer volume for the plant will be 460 1,
corresponding to approximately 1 day's consumption for a detached house.
In order to ensure that the waste water passes through the plant as expected,
the pumps in the first and second pump chambers should be equipped with an
alarm in case of pump failure, and a spare pump should be available. The
sedimentation chambers should be emptied of sludge once a year. The same
applies to the filter medium for the prefilter. The filter medium for the main
and final filters is expected to last for 5 years before having to be
replaced.
All materials which are watertight in the long-term and have sufficient load-
carrying capacity to resist the water pressure can be employed for the plant's
walls and bottom (concrete, fibre glass-reinforced polyester. etc.).
As mentioned, the plant is composed of several known purification
techniques. To date no measurements have been taken of the plant's total
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purification effect, but full-scale tests have been carried out on individual
purification steps in the plant. On the basis of these results the
purification
effect for the remaining steps and a total purification effect for the whole
plant under optimised conditions have been stipulated, both with regard to
purification of grey water and black water. The values are given in Table 2.
The stipulation is a theoretically anticipated purification effect calculated
on
the basis of each chamber's dimensions, process technical details,
composition and design. Included in the calculation is the fact that 50% of
the water in the second pump chamber is recirculated to the first
sedimentation chamber. This will give a dilution effect which will be
transmitted on to the other chambers. This dilution effect was not present
during the measurements on the individual purification steps, with the result
that the documented values in Table 2 will be slightly too high.
Example 2: Second preferred embodiment
The second preferred embodiment is constructed in a similar manner to the
first preferred embodiment, but in a round shape instead of a rectangular
shape. A round shape is favourable with a view to mechanical strength and
production costs.
In this form the plant is composed of a circular main filter chamber 5 with
the other chambers extending successively along the main filter chamber's
outer wall (see figure 6). The total diameter of the plant is 4 m.
The area of the main filter is the same as the main filter in example l, while
the base of the other chambers has a slightly different size to the
corresponding chambers in example 1. As can be seen in figure 6, there is no
180° "bend" between the first and second sedimentation chambers.
Otherwise
the only change compared to example 1 is that the water level in the sludge
interceptor can only be raised by 10 cm, thus giving a buffer volume of 316 1.
As in example 1, the water level in the final filter can be raised by 10 cm,
thus giving a buffer volume of 204 1. The total buffer volume is 519 1.
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Table 2 Stipulated values for anticipated purification effect for the first
preferred embodiment of the plant according to the invention.
The stipulated values are calculated on the basis of
documentedl) values from tests on single-chamber filters
corresponding to individual chambers in the plant.
Chamber PurificationDocumentedStipulatedDocumentedStipulated
parameters2)values values values values
Grey waterGrey waterGrey + Grey +
black waterblack water
1. and P (mg/l) 1.3 0.9 - -
2.
sediment- N (mg/1) 13.3 9.3 -
ation BOF7 (mg/I)176 123 - -
chamber TKB > 1 mill. < 1 mill. - -
(#/100m1)
Prefilter P (mg/I) - 0.8 9.8 7
N (mg/1) - 8 90.6 63
BOF7 (mg/l)- 100 161 113
TKB - < 1 mill. > 1 mill. > 1 mill.
(#/1 OOmI)
Main filterP (mg/1) 0.1 1 0.08 1.3 0.9
N (mg/I) 6.5 4.55 - 40
BOF7 (mg/I)7.7 5.4 - 1 ~-20
> 3000 < 3000 > 1 mill.
TKB -
(#/ 1 OOm
l )
Final filterP (mg/1) - 0.05 - 0.5
N (mg/I) - 2 - 20
BOF7 (mg/I)- 3 - 12
TKB - 0 - < S 0
(#/ 1 OOm
I)
1 ) Documented values are taKen rrom ~orarorsKrappor~ene ~carm n~~~a~ w n~N~l
«~, ~ ~ ~~ ~ ~ ,
140/97 and 144/97, and from the periodical Vann (Water) no. l, 1996.
2) BOF, is the amount of organic material measured for biological oxygen
consumption and
TKB is thermostable koliform bacteria.
Even though the invention is described with reference to two preferred
embodiments, it should be understood that the invention is not restricted to
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these. Alternative designs with separate free-standing chambers, chambers of
other shapes etc. are within the scope of the invention.
