Such a method is known.

The means that are used for cleaning and disinfecting milking installations may be subdivided into cleaning means that are specifically intended for cleaning the installation, disinfecting means by means of which the installation is disinfected, combined means having both a cleaning and a disinfecting action at the same time, and acid means that are principally intended for removing any deposit that may be present. Before being used for cleaning the milking installation, these means are usually dissolved in water.

Cleaning of a milking implement takes place according to a predetermined schedule. First of all the installation is pre-rinsed while easily removable milk residues are flushed away, then the installation is cleaned and disinfected and deposit, if any, is removed, after which the installation is rinsed again and any residues of cleaning means, disinfecting means, combined means and/or acid means that may be present are removed.

From the foregoing it is obvious that considerable quantities of water are used up during cleaning and disinfecting of a milking installation, which is very expensive. This also results in a large quantity of waste water. Depending on the size and the type of the installation, the quantity of waste water amounts to approximately from 100 m3 to 500 m3 of waste water per year (Milk Production, Manual August 1996, Practical Research Cattle Sheep and Horses). This waste water contains particularly organic contamination owing to milk residues in the pre-rinsing water and chemical contamination owing to residues of the cleaning and/or disinfecting means. Consequently, the waste water constitutes a considerable burdening of the environment. Therefore, in many countries it is not allowed to

discharge the waste water directly into the surface water.

However, discharging the waste water into a slurry pit has the disadvantage that the slurry pit will soon be filled up. After spreading the manure, the pollutants will still end up in the surface water. For that reason, the waste water is often discharged into the sewer. In some countries special taxes are imposed therefor. Besides, during cleaning of the milking installation there are used large quantities of cleaning and disinfecting means, which entails considerable costs.

With the introduction of the milking robot the water consumption at the farm has strongly increased. Per milking run of an individual cow the milking robot is pre-rinsed, cleaned, disinfected and rinsed again. As cows in a herd are often milked three to four times per day, there is produced a large quantity of waste water, while also considerable quantities of cleaning and disinfecting means are consumed. Besides, the entire milking installation including the milking robot is integrally cleaned and disinfected at least two times per day.

It is an object of the invention to obviate the above- mentioned drawbacks or at least to minimize same. According to the invention, for that purpose the waste water is conveyed along a first side of a membrane, while a liquid, preferably water, is conveyed along the other side of the membrane, as a result of which from the first side of the membrane water and/or one or more waste products are conveyed through the membrane, in such a manner that there is formed a concentrate at the first side of the membrane and a filtrate at the other side of the membrane, the filtrate consisting at least of water. Depending on the pore size of the membrane and the pressures applied, the filtrate consists of water, or cleaning and/or disinfecting components and water, or parts of milk, cleaning and disinfecting components and water. Before the waste water is supplied to the membrane, it is preferably filtered by means of a conventional filter for the purpose of removing coarse particles, such as slurry and mud.

The filtrate is preferably re-used for cleaning again the installation for milking animals. Components of the waste water, such as water and/or components of cleaning and/or disinfecting means and/or acid means for removing deposit, are re-used in this manner. This results in a considerable saving of expenses and moreover in a smaller burdening of the environment by the discharge of waste water coming from the milking installation. Components of the cleaning and/or disinfecting means which have been used up during cleaning may be replenished when the filtrate is re-used for cleaning and disinfecting the milking installation. The concentrate may be discharged as waste matter. By filtering the waste water according to the above- described method the amount of pollutants to be discharged strongly decreases. The filtrate may also be discharged as waste matter. As a result of the fact that the filtrate consists substantially of water, the filtrate may be discharged directly into the surface water.

According to an inventive feature, the waste water is circulated in a circuit along one or more membranes. In this manner there is achieved a large waste water treating capacity of the filtration process, without the use of membranes with a very large area being required. Moreover, the membrane is thus prevented from easily clogging up. According to a first embodiment of the invention, during the filtration the waste water and the water are conveyed in equal directions of flow along the membrane. In this manner there is achieved a great filter efficiency. According to an inventive feature, in a preferred embodiment, the waste water and the water are conveyed in opposite directions of flow along the membrane during the filtration. The latter measure is by far the most effective way to make an optimal use of the capacity of the membrane and to prevent the membrane from being contaminated and clogged up.

In a preferred embodiment, the waste water is conveyed along the membrane with such a speed that the flow of the waste water is laminar. In case of a laminar flow of the waste water the membrane operates most efficiently. The waste water may be

heated up before it is conveyed along the membrane. In this manner the filtration process is accelerated so that it will be more effective.

In accordance with a particular inventive feature, the waste water is supplied from a milking robot to the membrane.

Depending on its size, a milking installation produces approximately 500 litres of waste water per milking. As a result thereof, installations provided with membrane filters will frequently have to be sufficiently dimensioned for being able to treat these quantities of waste water coming from regular milking installations. Therefore, the invention is particularly appropriate to the filtration of waste water which is supplied from a milking robot to a membrane. As the milking robot produces a relatively small quantity of waste water per milking, a compact membrane filtering installation still having sufficient capacity will suffice.

The invention also relates to an implement for milking animals provided with one or more filtering installations which are suitable for applying a method as described above. For that purpose the filtering installation comprises one or more filters provided with one or more membranes, as well as one or more cutting-off means and conveying means for conveying waste water, water, filtrate and concentrate. The cutting-off means may comprise valves or controllable valves that may be remotely controllable. The conveying means comprise lines or tubes and one or more pumps.

In accordance with a further inventive feature, the filters are provided with at least one membrane having such a pore size that it is suitable for performing reverse osmosis.

The pore size of a membrane that is suitable for performing reverse osmosis is smaller than 10 4 Sm. In the situation of reverse osmosis the filtrate consists substantially of water.

One or more filtering installations may also be provided with at least one membrane having such a pore size that it is suitable for performing nano-filtration. The pore size of a membrane that <BR> <BR> <BR> is suitable for performing nano-filtration is larger than 10-4

Sm and smaller than 10-3 au. In the case of nano-filtration the filtrate consists substantially of water and minerals, such as components of the cleaning and/or disinfecting means and/or means for removing deposit. According to another inventive feature, the pore size of the membrane is larger than 10 3 as and smaller than 10*/m. In that situation it concerns a membrane which is chosen so as to be suitable for ultrafiltration. In that case the filtrate consists of water, minerals and components of milk, such as lactose. The pore size of the membrane may also be larger than 10 1 su and smaller than 10/mi. In that case the filtrate consists of water, minerals, lactose and/or proteins and other components, if any, of the waste water. The filtering installation may comprise an assembly of membranes having different pore sizes.

In accordance with an inventive feature, the filtering installation is provided with means for heating up the waste water. In this manner it is possible to influence the velocity and the effectiveness of the filtration process. For that purpose the filtering installation may comprise a heat exchanger. At one side of the heat exchanger waste water is supplied, while at the other side of the heat exchanger filtrate is supplied. The waste water is heated up by the filtrate which cools down as a result thereof, the waste water is heated up further by means of a heating element and the filtrate is cooled down further by means of a cooling element.

According to an inventive feature, the filtering installation is provided with one or more buffer tanks for storing waste water. Thus it is achieved that the filtering installation is able to treat the waste water continuously, while a large supply or a small supply of waste water does not affect the operation of the installation. The filtering installation may also be provided with one or more reservoirs for storing the filtrate and/or concentrate. In this manner it is achieved that there is no need for discharging the filtrate and/or concentrate immediately.

In a preferred embodiment, the filtering installation is provided with an automatic control unit for controlling the filtration of waste water. In this manner it is possible for the installation to operate continuously without the presence of an operator being required. This is in particular advantageous if the filtering installation is applied in combination with a fully automated milking installation, such as a milking installation comprising a milking robot.

At last the invention also consists of a filtering installation for the filtration of waste water, which is suitable for performing a method as described above in an implement for milking animals as described here. For that purpose the filtering installation comprises one or more filters provided with one or more membranes, as well as one or more cutting-off means and conveying means for conveying waste water, water, filtrate and concentrate.

The invention also relates to a method of separating waste water containing one or more waste products with the aid of separating means, which waste water comes from an implement for milking animals, such as cows, in which method one or more components are separated from the waste water. In this manner it is possible to separate the waste water in a particularly advantageous and efficient manner into different components without the use of membranes being required. The separating means may comprise e. g. biofilters or chemical separating methods, such as an ion exchanger or filtering out of precipitates. According to another inventive feature, one or more separated components of the waste water are suitable for being re-used for cleaning again the installation for milking animals. One or more separated components of the waste water may also be discharged as waste matter. Finally, the waste water may be supplied from a milking robot to the separating means.

The invention also relates to an implement for milking animals which is provided with one or more separating means that are suitable for applying a method as described above.

The invention will now be explained in further detail with reference to an embodiment as shown in Figures 1 and 2.

Figure 1 shows a filtering installation to be applied in combination with an installation for milking animals, the latter installation preferably comprising a milking robot.

Figure 2 shows a detail of a heat exchanger to be applied in an installation as shown in Figure 1.

The filtering installation consists of a buffer tank 2, one or more filters 5, a reservoir 15, an automatic control unit 8 for controlling the filtration process and conveying means 1, 3,4,6,7,9,10,16. The conveying means are constituted by the lines 1,3,4,6,7,16 and the pumps 9,10. The buffer tank 2, the filters 5 and the reservoir 15 are connected to each other via the lines 3,4 and 7 in which the controllable valve 20 and the pumps 9 and 10 are disposed. The supply line 1 is connected to the buffer tank for the supply of waste water. The discharge line 6 with the controllable valve 13 is connected to the ring line 4 around the filters 5 and is used for the discharge of the concentrate. The discharge line 7 is connected to the reservoir 15 and is used for the discharge of the filtrate. The reservoir comprises a line 14 for air supply and a controllable valve 12. Moreover, the reservoir is provided with a discharge line 16 and a controllable valve 11 by means of which the filtrate is discharged from the reservoir. The automatic control unit is connected to the pumps 9 and 10 and the controllable valves 11,12,13 and 20.

The operation of the filtering installation as shown in Figure 1 is now described.

The waste water coming from an installation for milking animals is supplied via the line 1 to a buffer tank 2 so that fluctuations in the supply of waste water can be compensated and the filtering installation can operate continuously. Via the pump 9 and the supply line 3 the waste water is brought to circulate in a circuit in which membrane filters 5 are included, while the circuit is constituted by the ring line 4 and the pump

10. The membrane filters 5 comprise several membranes whose pore size may vary. By applying several separate membrane filters it is achieved that defective filters can easily be replaced without the need of stopping the entire filtration process. By means of the controllable valve 13, an amount of concentrate is discharged periodically from the circuit via the discharge line 6. Via the discharge line 7 the filtrate is discharged to a reservoir 15. This reservoir 15 is emptied periodically by supplying compressed air to the reservoir via the supply line 14 in which the controllable valve 12 is included. Via the controllable valve 11 and the discharge line 16 the filtrate may be returned to the milking installation for the purpose of being re-used for cleaning the installation. The entire process is controlled by the automatic control unit 8 to which the controllable valves 11,12,13 and 20 and the pumps 9 and 10 are connected.

The filtration of waste water coming from a milking installation may be performed more efficiently when the waste water is heated up with the aid of heating up means before it is supplied to the membrane filters 5. The heating up means may comprise a heating up element, a cooling element and a heat exchanger. Figure 2 shows a heat exchanger 17 in which the waste water is heated up and the filtrate is cooled down. The heat exchanger is provided with a heating element 18, a cooling element 19, a line 3 for the waste water and a line 16 for the filtrate. In a preferred embodiment, the heat exchanger is disposed in the line 3 between the pump 9 and the valve 20.

Via the supply line 3 and the pump 9 the waste water flows through the heat exchanger 17, while the filtrate flows through the heat exchanger 17 via the discharge line 16, so that the filtrate gives out its warmth to the waste water, the filtrate cools down and the waste water is heated up. The waste water is subsequently heated up further by means of the heating element 18, while the filtrate is cooled down further by means of the cooling element 19. In this manner it is possible to heat up the waste water and to cool down the filtrate while effectively limiting the energy consumption.