This invention relates to a process for water purification and to an apparatus for carrying out the process.
It is an object of this invention to provide a process of the above art that is particularly suitable for purifying waste water containing fatty acids.
In broad terms, the invention provides, in one aspect thereof, a water purification process wherein water to be purified is directed past at least two electrodes of different polarity and made of bivalent or trivalent metals. The electrodes are surrounded with a moving bed formed of solid, non-conductive particles whose specific density is greater than that of the contaminated water.
According to the process of the invention, bivalent or trivalent metal ions are released from electrolysis. The ions cause flocculation in the water to be purified. It is assumed that the floc is formed through the build-up of colloidal hydrated oxides of the separated metal ions. The floc, in turn, binds or absorbs, other impurities present in the contaminated water and thus serves as a transport medium to remove the impurities from water. The continuous production of ions for flocculation purposes is possible due to the self cleaning of the electrodes by the solid particles of the moving bed. The solid particles are kept in motion by water flowing therethrough, subject to bed characteristics.
The particles are moved at various speed in various directions against and along the surfaces of the electrodes to insure cleaning of those electrodes. An additional electrode cleaning effect results from the return motion of those solid particles which have been carried along with water and which move past the electrodes on their downward movement.
The electrodes are comprised of bivalent or trivalent metals, preferably iron or aluminum or of alloys of such metals.
In a preferred embodiment of the process of the invention, at least three electrodes are provided. The polarity of the electrodes is alternated by applying a direct current voltage. Advantageously, the polarity of each individual electrode is changed periodically, e.g. every 10 minutes, so that all the electrodes, not only those permanently positively charged, are consumed uniformly, and the above-described electrode-cleaning action takes place simultaneously.
The process of the invention is particularly suitable for purifying water containing fatty acids. Here, ions released during electrolysis combine with the fatty acids to form hydrophobic floc of metallic soap. The floc, in turn, binds or absorbs other impurities, particularly organic colloidal particles, and carries them along.
The contaminated water can be directed through the moving bed by pressure. It is also possible to blow air into the bed to intensify its motion. It is most preferred that the contaminated water be directed through the moving bed in a generally vertically upward direction.
When the electrodes are connected to a power supply, such as a direct current voltage source, the intensity of the purification process can be controlled, especially when electrodes of the same material are used, by varying the voltage of the electrodes as a function of the degree of pollution of the water to be purified. This results in energy being saved when the inflowing water is relatively clean.
Accordingly to another feature of the method of the present invention, the purification process includes the step of optically determining the degree of pollution of the water to be purified by measuring or sensing the turbidity of that water.
In another broad aspect of the present invention, apparatus is provided for purifying water. The apparatus comprises an electrolysis chamber containing a moving bed which surrounds at least two electrodes and which is composed of solid, non-conductive particles having specific density greater than that of the water to be purified. A water inlet conduit is provided at one end of the chamber, and a conically extending flocculation basin is located at the opposite end of the chamber.
Since the electrodes are located in a moving bed comprised of solid particles, the above-described self-cleaning of the electrodes is done in a simple way, and the continuity and high efficiency of the cleaning is ensured. The flow through the apparatus is slowed in the flocculation basin due to its conical shape, which also allows the solid particles carried away from the bed to return to the electrolysis chamber.
In a preferred embodiment, the electrodes are made of different metals. This results in an energy-saving arrangement. The ion release in the electrolytic process can also be accomplished without applying an external power source if the electrodes are made of suitable dissimilar metals. In case of strongly corrosive water, the electrodes can even constitute a battery cell and generate electric current.
The moving bed surrounding the electrodes can be of various kinds, especially with regard to the motion of the solid particles in the bed. In particular, the bed may be a fluidized bed, an idle bed, a loose bed, a parallel-flow bed, or a high-speed flow bed. The characteristics of the bed depend to a large degree on the properties of the solid particles, e.g. granite, sand or plastic granules as well as the number, size and arrangement of the electrodes. Granite particles are particuarly suitable as a moving bed of solid, non-conductive particles.
In accordance with a further feature of this invention, a monitoring device is provided to sense the degree of pollution of the water that is to be cleansed. This allows for an economical, simple control of the electrolytic process when the electrodes are energized from an outside source. The effectiveness of the purification of highly contaminated water can thus be increased and energy can be saved when relatively clean water is processed. The monitoring device preferably includes a light source and a light sensor reacting to variations in water turbidity.
The casing of the electrolysis chamber preferably is always negatively charged when the purification process is carried out; otherwise, the casing would corrode due to polarity reversal. The casing of the electrolysis chamber may be made, for instance, of steel.
In accordance with another feature of the present invention, a discharge conduit for purified water is installed at a distance from the upper rim of the flocculation basin.