System for treating water with ozone

A water treatment system having an apparatus (2) for the intensive pretreatment of the untreated water with ozone, having a downstream filter (3) with reducing action, and also having an apparatus (4) for the post-disinfection is improved in that the excess ozone which accumulates in the upper part (17) of the filter tank and which is added to the water during the pretreatment is removed anhydrously and fed into the apparatus for the post-treatment of the filtered water. The post-treatment takes place preferably in a retention vessel (4) filled with packing material (15) in which the water comes into contact with ozone by surface contact. The water level (24) is kept constant by regulating the gas discharge from the retention vessel (4). (Illustrated by drawing).

DESCRIPTION 
The invention relates to a water treatment system having an apparatus for 
the intensive pretreatment of untreated water with ozone, having a filter 
downstream comprising a filter tank, partly filled with filter materials 
having a reducing action, through which the pretreated water flows from 
top to bottom, in which process the residual ozone contained in the water 
is decomposed, and having an apparatus for the post-treatment of the water 
with ozone for the purpose of post-disinfection. 
A preferred field of application of the invention is drinking water 
treatment, i.e. the treatment of organically and biologically contaminated 
water, for example groundwater collected near the surface of the ground, 
to produce water which can be drunk by human beings. 
Subjecting organically and biologically contaminated water to an intensive 
oxidation with ozone for the purpose of improving the quality is known. 
Depending on the degree of contamination, repeating this treatment of the 
untreated water several times by circulating the water in a loop is also 
known. This intensive ozone treatment produces the result through 
oxidation that viruses are inactivated, bacteria are killed, organic 
substances are reduced to subsidiary products, and also colloids are 
caused to coagulate and consequently rendered capable of being filtered. 
If the untreated water contains manganese, in particular in the form of 
brown manganese oxides, the latter are oxidized at high ozone 
concentration to permanganates which are soluble and cannot therefore be 
filtered out. 
The use of filters with reducing action, e.g. mixed bed filters which 
largely consist of coked coal of varied granulation, for the pretreated 
water is further known. In this case, the ozone present in the water is 
completely removed, and the dissolved permanganate is reduced to manganese 
oxides which, just like the filterable organic constituents, are retained. 
However, it has already always been observed that, in the deeper filter 
layers, bacteria colonies are formed from which microbes are occasionally 
flushed out with the pure water. Post-disinfection was therefore used as a 
prophylactic measure but an attempt was made to mineralize the organic 
substances as much as possible by an all the more intensive preoxidation. 
New discoveries have shown that it is more advantageous not to push the 
oxidation in the pretreatment stage too far so that assimilatable organic 
substances, i.e. substances suitable as nutrient for bacteria, are 
produced on a larger scale. As a result of this, there is formed in the 
reductively constructed filter bed an aerobic bacterial growth which is 
adapted to these assimilatable substances and which in turn produces a 
more extensive mineralization and, consequently, reduction of the organic 
substances. In this case the ozone in the pretreatment stage is comparable 
to a tool which only opens up the organic substances to render them 
suitable for the biological conversion in the filter bed. The pretreatment 
consequently requires less ozone. 
On the other hand, the post-disinfection acquires increased significance. 
It is to be understood as an operational disinfection. It inevitably 
eliminates the microbes possibly originating from the biomass and makes it 
possible to establish a residual oxygen content in the pure water which is 
necessary for the more extensive protection of hygiene. 
The invention is based on the object of proposing a particularly simple and 
effective system of water treatment which functions in this manner, which 
is economical to operate and which makes optimum use of the ozone 
produced. 
This object is achieved according to the invention on the basis of a water 
treatment system of the type described in the introduction, wherein the 
excess ozone which accumulates in the upper part of the filter tank and is 
added to the water during the pretreatment is fed anhydrously into the 
apparatus for the post-treatment of the filtered water. 
Although only one ozone generator is provided according to this proposal, 
ozonized gas with different ozone concentration is made available at two 
points without a pipeline system and without ozone loss, the ozone 
concentration corresponding to the particular requirement. As high an 
ozone concentration as possible is necessary for the ozone pretreatment 
since the untreated water is heavily contaminated with organic substances. 
A low ozone concentration is, on the other hand, adequate for the 
post-treatment since the filtered water is almost clean and, consequently, 
uses up only a small amount of ozone. The use of all the generated ozone 
of high concentration for the pretreatment covers the requirement at this 
point, while the residual ozone of low concentration, which accumulates in 
the upper part of the filter tank is adequate for the post-disinfection. 
The invention is of particular practical importance if the ozone generator 
is immersed in the process water as a result of the construction and forms 
a structural unit with a mixer, all the generated ozone gas being 
introduced directly into the water. In this case there would be 
considerable difficulties in tapping off a part of the ozone for the 
post-disinfection, quite apart from the ozone losses due to decomposition 
in the length of pipe. According to the invention, on the other hand, the 
ozone excess present in any case is utilized for the post-disinfection. 
The excess ozone should be removed from the upper part of the filter tank 
anhydrously, i.e. separated from water, and if necessary, mixed with air. 
This is necessary because the contamination constituents retained by the 
filter accumulate at the removal point and, consequently, the water is 
heavily contaminated. The removal of anhydrous gas is achieved by a system 
wherein, at the top of the filter tank, a removal pipe is connected for 
the ozone-containing air located there and wherein a level probe which 
shuts off the removal pipe by means of a regulating valve if the water 
level rises above a certain limit value is incorporated in the filter 
tank. 
This ensures that a gas cushion of adequate height continues to be 
maintained in the filter tank and no contaminated water can enter the 
removal pipe. 
A system is proposed wherein, as apparatus for the post-treatment of the 
filtered water, an elongated retention vessel is provided which is filled 
with chemically resistant packing material having a small volume and a 
large surface and wherein the filtered water is introduced into the 
retention vessel at the top and removed at the bottom so that it trickles 
over the packing material and the ozone-containing air is introduced into 
the retention vessel and the exhaust air is removed via an active charcoal 
filter. The ozone-air mixture can be introduced directly into the 
retention vessel or shortly beforehand into the pure water which flows or 
is preferably sprayed into the retention vessel at the top so that as long 
a residence time as possible in the ozone-containing air results. For the 
same reason, the water level in the retention vessel is kept constant by 
means of a level regulating valve which shuts off the exhaust air pipe 
from a certain water level upwards. 
A further object of the invention is to circulate the untreated water in 
the pretreatment apparatus several times and to transfer the excess 
ozone-air mixture introduced to the filter tank. This is expediently 
achieved by a system wherein the apparatus for the pretreatment of the 
untreated water comprises a reaction vessel which has a mixer in the upper 
part and, about half way up, an outlet for the water-ozone-air mixture 
flowing to the filter tank, while the water from the bottom of the 
reaction vessel flows via a return branch to a circulating pump feeding 
into the mixer. During operation, a gas blanket develops in the reaction 
vessel down to the outlet connection pipe and excess gas is entrained by 
the water flowing out to the filter.

The untreated water is removed from a well (1), fed to a pretreatment 
apparatus (2), filtered in a mixed-bed filter (3), post-treated in a 
packed column (4) and then collected in a storage tank (5). 
The pretreatment apparatus (2) contains an ozone generator and a 
ozone/water mixing chamber which are combined in one module (6). The 
continuously adjustable ozone generator delivers up to 55 g of ozone per 
hour. The achievable ozone concentration in the gas phase before 
introduction into the water is up to 50 g of ozone per normal cubic meter 
of air. The ozone generator is constructed in a stack structure of 
horizontal plates and is suspended on the cover of the reaction vessel. 
The mixing apparatus is located beneath it. 
The reaction vessel is largely filled with packing material (8) which has 
been punched from stainless steel sheet and crumpled together to produce a 
spherical external shape of about 5 cm diameter. About half way up this 
layer of packing material there is situated, on the casing of the reaction 
vessel, an outlet connecting pipe from which a pipe leads to the mixed-bed 
filter (3). A circulating pump (7) forces the untreated water from below 
into the module (6), at the circumference of which it emerges again. The 
water then sinks dwwnwards through the layer of packing material (8) and 
passes through cutouts (9) at the lower edge of an inner cylinder, from 
which point it is returned again to the circulating pump (7) by a return 
branch (10). The delivered output of the circulating pump (7) remains 
constant. The throughput of the pretreatment apparatus is determined by 
the delivered output of the pump in the well (1) and by the setting of the 
throttle valves which are disposed upstream and downstream of the 
pretreatment apparatus. 
The ozone-containing air added to the circulated water in the module (6) 
allows the water level in the reaction vessel to sink roughly to the 
height of the outlet connecting pipe during operation. Further gas is 
entrained by the outlet pipe to the filter (3). The throughput of the 
pretreatment apparatus and the ozone output are so adjusted that the 
desired pure water quality is achieved with the available untreated water 
quality being taken into account. If the untreated water quality varies, 
the redox potential of the pure water can be registered metrologically and 
regulated to a certain value by altering the throughput and/or the ozone 
generator output. 
The upper filter layer (11) of the mixed-bed filter (3) comprises a mixture 
of granular material of different types of coked coal having a particle 
size of 0.8 to 1.6 mm. The middle filter layer (12) comprises a quartz 
sand having a particle size of 0.3 to 0.8 mm, and a further layer of 
coarse gravel (13) is disposed above the bottom of the filter. The 
inclusion of coking coal produces the necessary reducing environment for 
removing ozone completely, reducing permanganates back to filterable 
manganese oxides and making possible a permanent growth of aerobic 
bacteria. 
After being filtered, the water is fed via a pipe (14) into the packed 
column (4). Here it trickles over a layer (15) of packing material of the 
same type as the packing material (8) of the pretreatment apparatus (2). 
From the lower part of the packed column (4), the water is forced upwards 
via a riser (16) and then fed to the storage container (5). 
As a consequence of the low flow velocity in the mixed-bed filter (3), a 
blanket of excess ozone-air mixture (17) of low ozone concentration forms 
in the upper part thereof. This gas is introduced via a connecting pipe 
(18) into the pipe (14) shortly upstream of the packed column (4) and is 
then introduced into the upper part of the packed column (4) together with 
the water. The water level in the mixed-bed filter (3) is kept constant by 
influencing a regulating valve (19) contained in the pipe (18) by means of 
a level probe (20) so that no contaminated water can infiltrate into the 
pipe (18). 
The exhaust gas from the packed column (4) is fed through an active 
charcoal filter (21) which completely removes the ozone contained in the 
gas to form carbon dioxide. The gas discharge can be so regulated by means 
of a float valve (22) that the water level (24) in the packed column (4) 
is kept constant at the height drawn. With this low water level, the 
trickling path and, accordingly, the contact time between water and ozone 
are relatively long. Optionally, instead of the float valve (22), a more 
highly disposed float valve (23) can be put into operation. As a result of 
this, the water level is placed higher and the trickling path and contact 
time are shortened. Consequently, the effect of the ozone post-treatment 
can be coarsely adjusted by the choice of the water level. The fine 
adjustment takes place at the ozone generator. 
To back-flush the mixed-bed filter (3), pure water is removed from the 
storage tank (5) and forced from the bottom upwards by means of a 
back-flushing pump (27) through the filter tank. For this purpose, the 
valve (25) in a pipe (26) leading from the upper connection of the 
mixed-bed filter (3) to the sewer is opened and a back-flushing pump (27) 
is put into operation. As a result of this, a 3-way valve (28) in the pipe 
(14) automatically switches over. A check valve (29) in the connecting 
pipe from the oxidation apparatus (2) to the mixed-bed filter (3) closes. 
As a result of this, the contaminants detached from the filter body 
discharge into the sewer through the pipe (26). 
The water velocity during back-flushing should be adjusted with care, 
namely, so that, on the one hand, although the contaminants are detached 
and flushed out, the bacteria cultures adhering firmly to the coke 
particles remain largely intact so that the biological action of the 
filter can immediately start up again to the full extent when it is put 
into operation.