IT202300004089A1 - FILTER FOR PURIFICATION OF POLLUTED WATER - Google Patents

Description

FILTER FOR PURIFICATION OF POLLUTED WATER

Premise

Polluted waters with both solid particles and dissolved pollutants are wastes that are difficult to dispose of. An example of this is the olive vegetation water produced by oil mills following grinding cycles and subsequent centrifugation of the ground olives with the addition of water. The polluting load of waste water contains a quantity of suspended organic solids in the order of about 80g/L as well as approximately 20g of dissolved organic substances, among which phenolic and quinonic substances abound, giving the water a brownish color. Suspended solids are difficult to settle and therefore separable through simple decantation processes. They represent the major problem for the disposal of the water itself, as the quantities are such that it is not possible to convey the waste water to common civil water purification plants. The elimination of these substances is also complex even when industrial microfiltration methods are taken into consideration due to the ease with which the filters themselves become clogged. The present invention concerns the development of filters in which the filter element is made up of natural plant fibre powder ground to micrometric sizes ranging from 50 to 500 microns in size. Another example is well water extracted from soils containing fine silts. Finally, industrial water containing colloidal particles of both organic and inorganic type can be mentioned. Although there are many filtering systems on the market that are suitable for purifying water polluted by the most varied types of particles, the same filtering systems are however attributable to categories of non-biodegradable materials that are difficult to recycle when the filters are disposed of. The present patent concerns a type of water filter based on the use of natural biodegradable and recyclable materials both in the form of feed for livestock and as compost to be used in agriculture.

State of the art

Filters with aquatic plants have been used to purify polluted water. An example is described in CN107434301, however these types of filters require large surfaces. To overcome these disadvantages and to obtain other advantages, the present filter was invented.

Description of the invention

The filters which are the subject of the present invention consist of a container in which support elements are placed at a suitable height on which a layer of filtering material consisting of natural plant fibre powder is placed, with a grain size between 50 and 500 microns, and a thickness preferably between 2 and 20 cm.

In the case where the water is to be purified mainly from suspended solids, the filter material should preferably rest on an underlying funnel-shaped support structure. The entire lower part of the container, including the funnel-shaped cavity, must be able to be maintained in a vacuum condition. The air suction for creating the vacuum will take place from a position in the lower part of the filter such that the filtered water exiting the funnel that accumulates uniformly on the lower part of the filter is not sucked up by the vacuum pump. The upper part of the filter can be kept open so that adequate quantities of water to be filtered can be deposited above the plant material filter. During the creation phase of the filter layer, the perfect and compact deposition of the plant material can be obtained by dispersing the adequate quantity of dust in an aqueous environment and then exposing the surface of the filter to the vacuum obtained by suction of air from the lower part of the filter itself. The upper part of the filter can be closed so as to apply an adequate pressure above the plant material filter and create a pressure gradient from 0.01 to 25 atm. During the creation phase of the filter layer, the perfect and compact deposition of the plant material can be obtained by dispersing the adequate quantity of powder in an aqueous environment and then exposing the filter surface to the vacuum obtained by suction of air from the lower part of the filter itself. The construction of the filter is not subject to any type of specific geometry of the structure, it can be made with a cylindrical geometry as shown in figure 1, or with a rectangular geometry as shown in figure 2. The upper part of the filter can allow the gradual removal of the solids that are deposited during filtration by means of appropriate blades rotated or translated by means of appropriate motors as will be described in the following examples.

If the water to be purified does not contain mainly suspended solids but only dissolved substances, the typology of filters is simplified as described in example 10, since it is not necessary to remove solids accumulated on the filter surface during the filtration process. In this case, it will be preferable to use thicker filters to exploit the chemi-absorbent power of the natural plant fibers used, compared to the pollutants dissolved in water.

In all respects, the filter which is the object of the present invention offers the following advantages compared to other industrial filters which use membranes or other types of filter material:

1) Extremely economical filter material which can be obtained simply by grinding natural plant fibres such as straw, wheat bran, rice bran, fast-growing fibrous plants such as broom, cane, ferns, pruning waste from plants or other plants constituting the Mediterranean herbivorous flora; The compaction of this material in a filter layer in the manner described above generates interstitial spaces between the particles separated by porous channels whose diameter falls within the micrometric range. The exact size of the pores can be governed by the size of the powders obtained by grinding the plants themselves. Obviously, to obtain increasingly finer porosities, it will be necessary to grind the powders constituting the filter more finely by varying the output sieves of the powder mills between 100 and 500 microns. The porosity can be varied from dimensions ranging from 1 micron to 10-20 microns, therefore there are no limitations in the possibility of using the filter. to adopt micrometric filtering systems suited to the size of the solid particles that need to be filtered.

2) The type of filter with an open upper structure allows for the gradual removal of solids that accumulate on the filtering surface by simple scraping using special mechanical systems. This eliminates the inconveniences caused by the slowing down of the filtration speed due to the accumulation of material already filtered, which sometimes takes on a compact structure that prevents further penetration of the water to be filtered.

3) At the end of each working day, the filter itself can be easily removed from its base so that it can be renewed the following day. The filtering system will therefore not need other types of maintenance that cause waste of time and generate production costs.

4) The vegetal nature of the filter material can be edible.

If the filtered material is of an organic nature and is equally edible, suitable mixtures of the filter and the filtered material can form the basis for highly nutritious feed. Another possibility of using mixtures of filter and filtered material can be achieved by sending the composite materials to suitable composting processes.

5) The ease of construction of the filter will allow its use even in situations of wastewater production in widespread agronomic environments where the adoption of more complex industrial systems appears to be at the very least very difficult.

To achieve a main purpose of the present invention, a filter for the purification of polluted water is provided, characterized in that the filtering material is made up of natural vegetable fibres, ground to sizes between 25 and 500 microns, supported by support elements having holes whose dimensions are smaller than the dimensions of the particles of the filtering material.

Another feature is given by the fact that the support elements include a perforated technical sheet and a rigid support.

Another feature is given by the fact that the filter includes an apparatus for the removal of solids gradually deposited on the surface of the filter during filtration.

Another feature is given by the fact that it includes pumps that generate a pressure gradient between the upper surface and the lower surface of the filtering material that ranges from 0.01 to 25 atm.

Another feature is given by the fact that the filter materials are obtained from fibres coming from agro-industrial waste.

Another main purpose is achieved by a filtration process using a filter according to claims 1 to 5, characterised in that a layer of filter material consisting of natural vegetable fibres, ground to sizes between 25 and 500 microns is spread on a support held in a container.

Another feature is given by the fact that a pressure gradient ranging from 0.01 to 25 atm is created between the upper surface and the lower surface of the filter material layer.

Other features and advantages will be clear from figures 1 and 2 given as examples and not as limitations.

Examples of embodiments of the present invention

Example 1

The filter was assembled as shown in fig. 1. The filter's load-bearing structure (1) was made using a steel cylinder with a diameter of 1.2 m and a conical bottom (2) 0.3 m deep. The filtering sector (3) was set up at a depth of half a metre from the top of the cylinder. This sector was placed on a metal ring transversal to the cylinder and welded to it. A circular section structure was screwed onto this ring. It consisted of a peripheral ring inside which a metal mesh with a mesh size of half a centimetre on each side was welded. On this ring was placed a technical nylon sheet with a circular shape, with a square mesh size of 120 microns on each side. Its perfect flatness and immovability were ensured by an additional circular ring, placed on the edge and screwed onto the lower ring. A perfect seal against lateral percolation of liquid was achieved. was created using special gaskets between the various circular rings. The cylindrical part of the filter (4) underneath the filtering section (3) had a height of 1.3m. The funnel-shaped internal part (5) underneath the filtering section was always made of steel and its lower end was positioned at a height of 40cm from the bottom. The structure was equipped with suitable support feet (6). The vacuum suction tap (7) on the lower part of the filter was placed at a distance of 20cm from the filtering section. The vacuum in the lower part of the filter was created using the pump (8) capable of generating a pressure gradient between the upper and lower filtering surfaces of 0.9 atm in a time of 10sec, in the presence of water above the filter. The filtering material was created by grinding clean dry straw to a size of 500 microns using a special mill. Above the filtering section by means of the motor (9), blades (10) have been placed which are suitably shaped in such a way as to remove, during rotation, the solids filtered from the purified water, through the opening of the door (11).

All the processing phases of the filtering system have been managed in an automated manner. In particular, automation has been managed for:

1) periodic entry and blocking of the entry of the water to be filtered in the upper part of the filter, by controlling the pump (12)

2) opening of the discharge hatch for the discharge of the filtered solids (11),

3) rotation and locking of the blades for removing the filtered solid materials, by controlling the motor (9)

4)drain the filtered water from the lower part of the filter.

5) activation and closing of the pump (8) to restore or cease the vacuum during the water discharge phase, in the lower part of the filter.

The process activities were timed for appropriate software control, by the operator, based on the quantity and quality of suspended solids. The system allowed the filtration of olive mill vegetation water, eliminating approximately 60 grams of suspended organic solids per liter of water and obtaining an output COD of 20,000. The filtration capacity was found to be 4 tons/hour.

Example 2

The filter was constructed as in example 1, except for the use of straw ground to a diameter of 50 microns and a support sheet with a mesh of 25 microns, which also allowed the elimination of part of the soluble COD present in the water. A COD of 8000 was thus obtained in the output water.

Example 3

The filter was constructed as in example 1, except for the use of dried broom ground to a size of 500 microns as the filtering plant material. The COD output was approximately 23,000.

Example 4

The filter was constructed as in example 1, but using as plant material dry cane (Arundo Donax) ground to a size of 100 microns and a plant material support sheet with a 25 micron mesh.

Example 5

The filter was constructed as in example 1, but using rice husks ground to a size of 500 microns as plant material. The output COD was found to be 17,000.

Example 6

The filter was constructed as in example 1, but using rice husks ground to 100 microns with a 25 micron support cloth as the plant material. The COD at the outlet was found to be 7000.

Example 7

The filter was constructed as in example 1, but using 100 micron ground wheat chaff as the plant material with a 25 micron support sheet. The COD at the outlet was found to be 6890.

Example 8

The filter was constructed as in example 1, using as plant material straw ground at 500 and 100 microns mixed in equal parts, with a 25 micron support sheet. The COD at the outlet was found to be equal to 6000.

Example 9

The filter which is the subject of the invention has been assembled as illustrated in fig.

2. The filter supporting structure (16) was made using a steel parallelepiped with a height of 2.1 m, a width of 0.8 m, a length of 1.5 m and a pyramidal base (17) 0.3 m deep. The filtering section (18) was created at a depth of half a metre from the upper end of the parallelepiped. This section was placed on an internal metal edge transverse to the parallelepiped and welded to it. A structure with an equally rectangular section was screwed onto this edge, consisting of a peripheral edge inside which a metal mesh was welded, with a mesh size of half a centimetre on each side, supported not only on the welding edge but also by two steel crosspieces welded perpendicularly to each other and in turn welded to the peripheral frame, in such a way as to ensure that the support mesh could not bend. The filtering system was was completed by placing a rectangular nylon technical sheet, with a 120 micron square mesh on each side, over the steel mesh, ensuring its perfect flatness by overlapping an additional rectangular frame screwed to the underlying frame on its edge. A perfect seal against lateral percolation of liquid was achieved using special gaskets. The part of the filter underneath the filtering section had a height of 1.3m. The funnel-shaped pyramidal part (19) underneath the filtering section was always made of steel and its lower end was positioned at a height of 40cm from the bottom. The structure was equipped with suitable support feet (20). The vacuum suction tap (21) on the lower part of the filter was placed at a distance of 20cm from the filtering section. The vacuum in the lower part of the filter was was created using a pump (22) capable of generating a pressure gradient between the upper and lower filter surfaces of 0.9 atm in a time of 10 seconds, in the presence of water above the filter. The filter material was created by grinding clean dry straw to a size of 500 microns using a special mill. Above the filter section, a system of circulating belts (23) was created as shown in the figure using pulleys welded onto the filter frame, carrying four transverse blades (24) capable of removing the solids gradually deposited by the filtered water on the filter surface. An inclined plane (25) was welded onto one of the edges of the rectangular structure, on whose surface the circulating blades push the suspended solids, causing them to fall into a tank (26) below. The movement of the belts is obtained by means of the motor located at the top (27). All the processing phases of the filter system were managed in an automated manner. In particular, the automation was was managed for:

1) periodic entry and blocking of the entry of the water to be filtered in the upper part of the filter, by controlling the pump (28)

2) rotation and locking of the blades for removing the filtered solid materials, by controlling the motor (27)

3)draining of filtered water from the lower part of the filter, by controlling the pump (29)

4) activation and closing of the pump (22) to restore or cease the vacuum during the water discharge phase, from the lower part of the filter.

The process activities were timed for appropriate software control, by the operator, based on the quantity and quality of the suspended solids.

The system allowed the filtration of olive mill vegetation water, eliminating approximately 60 grams of suspended organic solids per liter of water. The filtration capacity was found to be 4 tons/hour.

Example 10

A further example of a filter presented in this patent was created using a cylinder with a radius of 0.6m and a height of 30cm as the central body. The filter material was deposited on the lower face of the cylinder using systems similar to those used in example 1, thus supporting it through a technical sheet with holes with a diameter of 15 microns, which in turn was supported by a steel plate perforated on 50% of its surface, welded to a ring that could be locked onto the supporting cylinder, supported not only on the welding edge but also by two steel crosspieces welded perpendicularly to each other and in turn welded to the edge of the ring, in such a way as to guarantee that the support plate could not bend. The filter material was created with straw ground to a grain size of 50 microns and deposited in a compact manner on the technical support sheet to a height of 20cm. The central cylinder was The filter was closed at the bottom and top with two spherical caps with a base diameter equal to that of the cylinder and a depth of 5 cm. The upper and lower caps were connected to the central cylinder by means of flanges hinged on one side to the corresponding flange of the central cylinder, and hermetically closable through special screw closure systems on the opposite end of the hinge so that they could be opened like real doors through the use of extendable pneumatic arms. The perfect vacuum seal inside the filter was achieved by means of appropriate gaskets interconnected between the flanges of the caps and those of the central cylindrical body. The filter was completed with a feed pump having a prevalence of 25 atm and a flow rate such as to guarantee the flow through the filter of water to be purified equal to approximately 600 L/h. The system was therefore able to operate under a pressure gradient of 25 atm. The filter was was used to purify olive oil mill vegetation water previously filtered in the filter of example 1, and having a COD of approximately 20,000. The final filtrate was found to have a COD of approximately 5000.

Example 11

The filter was constructed as in example 1, except for the absence of the mechanical removal apparatus for the solids gradually accumulated on the filter, using 500 micron ground straw as natural fibre, with a 25 micron support sheet. The filter was used to filter well water containing suspended solids with an average grain size of between 10 and 50 microns. In this case, the filtration process was performed without the aid of pressure gradients between the surfaces of the filter material. The filtered water was found to be completely free of suspended solids.

Example 12

? a longitudinal filter was created by inserting the filter material into the gap between two concentric perforated stainless steel cylinders, the first having a diameter of 10 cm and the second having a diameter of 30 cm in such a way that the thickness of the intermediate gap was 10 cm. The surface perforated with 2 mm holes was equivalent to approximately 70% of the entire surface of the cylinders, the internal faces of each of the cylinders were covered with a technical polyamide sheet with a mesh size of 25 microns. Straw powder ground to a size of 100 microns in diameter was used as filter material, the filter powder was inserted wet into the gap between the two cylinders and was compacted in such a way that the final density of the wet material was approximately 0.6 kg/L. The two filter cylinders were inserted into a further cylinder of equal length having a diameter of 40 cm carrying the outlet tap for the filtered water. The ends of the three cylinders, all equally 1.5 m long, were closed with special caps. The caps were connected to the various cylinders in order to isolate the environment of each cylinder and avoid both the leakage of material from the filter and the exchange of fluids between the various circular sectors. This was achieved by means of special flanges present on the edges of all the cylinders and special gaskets inserted in them, and also in the circular sectors of the caps. Perfect adhesion between the flanges of the caps and the cylinders was achieved by means of special connecting screws inserted in the external flanges of the caps and corresponding flanges of the outermost cylinder of the filter. The closing caps respectively carry the inlet pipe of the water to be filtered and the outlet pipe of the retentate in the centre. The filter was completed with a feed pump having a head of 25 atm and a flow rate such as to guarantee the flow through the filter of 800 L/h of water to be purified. The system is therefore was able to operate under a pressure gradient of 24 atm. The filter was used to purify olive oil mill vegetation water previously filtered in the filter of example 1, and having a COD of approximately 20,000. The final filtrate was found to have a COD of approximately 3000.

Claims (7)

Claims 1) Filter for the purification of polluted water, characterised in that the filter material is made up of natural plant fibres, ground to sizes between 25 and 500 microns, supported by support elements having holes whose dimensions are smaller than the dimensions of the particles of the filter material. 2) Filter, according to claim 1, characterised in that the support elements comprise a perforated technical sheet and a rigid support. 3) Filter, according to claim 1, characterized in that said filter comprises an apparatus for the removal of solids gradually deposited on the surface of the filter during filtration 4) Filter, according to claim 1, characterized in that it includes pumps that generate a pressure gradient ranging from 0.01 to 25 atm between the upper surface and the lower surface of the filter material. 5) Filter, according to any preceding claim, characterised in that the filter materials are obtained from fibres originating from agro-industrial waste. 6) Filtration process using a filter according to claims 1 to 5, characterised in that a layer of filter material consisting of natural vegetable fibres, ground to sizes between 25 and 500 microns is spread on a support held in a container. 7) Filtration process using a filter according to claim 6, characterised in that a pressure gradient ranging from 0.01 to 25 atm is created between the upper surface and the lower surface of the filter material layer.