Abstract:
A method of purifying raw water comprises the steps of supplying the raw water to a generally vertical, open-ended inlet cylinder ( 23 ) in a reservoir ( 20 ), exposing the water in the inlet cylinder ( 23 ) to air for accomplishing oxidizing of matter, such as iron, manganese, and hydrogen sulphide in the water and/or agitation of the water, allowing the oxidized matter to fall down by gravity to the bottom of the reservoir ( 20 ), allowing the purified water to flow upwards past the inlet cylinder ( 23 ) and through a distribution disc ( 24 ) in the reservoir ( 20 ), and removing the purified water from the upper part of the reservoir ( 20 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a method of purifying raw water. It also relates to a water purification plant comprising a reservoir for receiving raw water to be purified into pure water. 
       BACKGROUND OF THE INVENTION 
       [0002]    Raw water may be purified into pure water or drinking water in a variety of ways. Besides removing unwanted matter from raw water by a number of filtering methods, it is known to remove for example iron, manganese, and hydrogen sulphide by an oxidation process by means of air introduced in the water, so that oxidized matter can simply be allowed to fall to the bottom of the reservoir in which the water is treated. It is likewise known to remove organic material from sea water and stream water by adding a flocculating agent and removing the formed flocks from the water. 
         [0003]    The end result reached in many ways may be satisfactory, but often the used processes may be complicated and involve many steps, whereas the equipment used may be intricate, costly and/or difficult to manage. 
         [0004]    The main objects of the invention are thus to reach a water purification method, which is as simple as possible, but which nevertheless gives a satisfactory end result, and to provide a water purification plant, which is simple, effective and low-cost. 
       THE INVENTION 
       [0005]    A method according to the invention of purifying raw water comprises the steps of 
         [0006]    supplying the raw water to a generally vertical, open-ended inlet cylinder in a reservoir, 
         [0007]    exposing the water in the inlet cylinder to air for accomplishing oxidizing of matter, such as iron, manganese, and hydrogen sulphide, in the water and/or agitation of the water, 
         [0008]    allowing the oxidized matter to fall down by gravity to the bottom of the reservoir, 
         [0009]    allowing the purified water to flow upwards past the inlet cylinder and through a distribution disc in the reservoir, and 
         [0010]    removing the purified water from the upper part of the reservoir. 
         [0011]    The water in the inlet cylinder may also be exposed to a flocculating agent for accomplishing flocculation of for example organic matter in the water, the flocculated matter being allowed to fall down by gravity to the bottom of the reservoir. 
         [0012]    A water purification plant according to the invention comprises a reservoir for receiving raw water to be purified into pure water and is characterized by 
         [0013]    a generally vertical, open-ended inlet cylinder in the reservoir for receiving raw water, 
         [0014]    a nozzle device for supplying air from an air line to the water in the inlet cylinder, 
         [0015]    a bottom of the reservoir for receiving matter heavier than water, 
         [0016]    a generally horizontal distribution disc, provided with openings and dividing the space inside the reservoir and outside the inlet cylinder into an upper and a lower compartment, and 
         [0017]    means for removing purified water from the upper compartment. 
         [0018]    The plant may be provided with a flocculating agent line for supplying flocculating agent to the water in the inlet cylinder. 
         [0019]    A sludge pump may be arranged at the bottom of the reservoir for occasionally removing the sludge from the reservoir. 
         [0020]    The means for removing purified water may comprise a pure water pump connected to a pure water line. 
         [0021]    For improving the water quality under certain conditions, a further filtering means may be arranged in the pure water line. 
         [0022]    For improving the mixing of the flocculating agent with the raw water, the flocculating agent line may open into a mixing cyclone, through which the raw water flows. 
         [0023]    The distribution disc is preferably provided with openings with a size and distribution for accomplishing an even water flow over its area. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0024]    The invention will described in further detail below under reference to the accompanying drawings, in which 
           [0025]      FIG. 1  is a schematical top view of a water purification plant according to the prior art, 
           [0026]      FIG. 2  is a schematical side view of the same plant, 
           [0027]      FIG. 3  is a schematical top view of a first embodiment of a water purification plant according to the invention, 
           [0028]      FIG. 4  is a schematical side view of the same plant, 
           [0029]      FIG. 5  is a schematical top view of a second embodiment of a water purification plant according to the invention, and 
           [0030]      FIG. 6  is a schematical side view of the same plant. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0031]      FIGS. 1 and 2  show a conventional water purification plant, mainly for purification of raw water with too high contents of iron, manganese and hydrogen sulphide. 
         [0032]    Raw water  1  is pumped into an oxidation tank  2 . An air compressor  3  supplies air to a nozzle device  4 . The oxidation process may be enhanced by addition of a strong oxidation agent, such as potassium permanganate, from a dosing pump  5 . Depending on the contents of iron, manganese and hydrogen sulphide in the raw water, the staying time for the raw water in the oxidation tank may normally be in the order of 20-30 minutes. 
         [0033]    Due to the forceful agitation in the tank  2  by the air supplied through the nozzle device  4 , particulate oxidation products of for example iron and manganese are prevented from sedimenting in the tank. These oxidation products will instead follow the water through a line  6  to the upper part of a filtration tank  7  containing a filter bed  8 , through which the water passes by gravity, leaving the particulate matter in the filter bed  8 , especially its upper part. Purified water leaves the lower part of the filtration tank  7  through a line  9  to a reservoir therefore. 
         [0034]    After a certain time the upper part of the filter bed  8  will be clogged by the particulate matter. Such matter is removed by reverse flushing. Relatively large amounts of flush water under pressure are needed for accomplishing the desired cleaning of the filter bed  8 . An outlet valve  10  in the line  9  is closed, and a reverse flush pump  11  is started supplying flush water to the lower part of the filtration tank  7  through a flush water line  12 . 
         [0035]    The water level in the filtration tank  7  rises from the normal level  13  to a higher level  14  from which the flush water with the flushed away particulate matter can enter an outlet trench  15  for further transport through an outlet line  16  to discharge. 
         [0036]    The frequency of the reverse flushing is determined by the amount of particulate matter and the fineness of the filter material in the filter bed  8 . 
         [0037]    A further filter stage is often needed. 
         [0038]    This purification plant is not suited for water containing organic material to be removed, such as sea or stream water. 
         [0039]    A water purification plant according to the invention is shown as two embodiments in  FIGS. 3 and 4  and  FIGS. 5 and 6 , respectively. The two embodiments have much in common, and like numerals are used for like parts. The first embodiment is fully described, whereas the second one is only described to the extent necessary for a full understanding of the differences. As will be understood, the two embodiments may be combined. 
         [0040]    Reference is first made to  FIGS. 3 and 4 . The water purification plant shown therein has a reservoir  20 . As indicated by a ground level line  21 , this reservoir may—if desired—be placed underground. The reservoir  20  may be manufactured of a suitable plastic material, but also the use of concrete for the reservoir is possible. The reservoir may preferably have a generally cylindrical cross-sectional shape. In the shown case it is inwardly tapering towards its lower end and has a cupola-shaped cover or upper end. It is provided with a neck  22 , preferably opening above the ground level. 
         [0041]    The reservoir  20  is internally provided, preferably centrally, with an inlet cylinder  23  with open ends both upwardly and downwardly. The upper end of the inlet cylinder  23  is above the water level in the reservoir  20  at all times. 
         [0042]    A generally horizontal distribution disc  24  provided with openings divides the space inside the reservoir  20  and outside the inlet cylinder  23  into an upper and a lower compartment  25  and  26 , respectively. 
         [0043]    Unpurified raw water can be supplied to the inlet cylinder  23 , for example through an inlet line  27 , for example at a level above the distribution disc  24 . 
         [0044]    One or more nozzle devices  28  can be arranged in the inlet cylinder  23 , for example at a level below the distribution disc  24 . Air under certain pressure can be supplied to the nozzle device  28  through an air line  29 . The purpose of the air supplied to the water through the nozzle device  28  is to agitate the water and/or to cause oxidation of such impurities in the raw water as iron, manganese and hydrogen sulphide. 
         [0045]    If desired, the process may be enhanced by the addition of for example potassium permanganate as an oxidation agent through a line  30 . 
         [0046]    By the supply of new raw water, treated and aerated water will flow downwards through and out of the inlet cylinder  23 . The precipitated materials, such as metallic iron or manganese, and other possible particles in the water will fall to the bottom of the reservoir  20 , if the flow rate does not exceed 1 m 3 h per m 2  hydraulic load area of the distribution disc  24 . 
         [0047]    The precipitated materials can be removed from time to time from the bottom of the reservoir  20  as sludge by a sludge pump  31  through a sludge line  32 . 
         [0048]    The purified water will after leaving the inlet cylinder  23  downwards raise through and above the distribution disc  24 , wherefrom it may be pumped away by a pure water pump  33  through a pure water line  34 . The pure water pump  33  may be housed in a pump well  35  integrally mounted on the outside of the inlet cylinder  23 . Alternatively, the water may be removed from the well  35  by gravity. 
         [0049]    A further filtering means  36  may optionally be provided for the pure water supplied from the plant. This filtering means may be arranged to deliver its residue products to the sludge line  32 . The flow rate may hereby be increased to some 1.5 m 3 h per m 2  hydraulic load of the distribution disc  24 . 
         [0050]    The size, number and distribution of the openings in the distribution disc  24  are determined such that a desired and evenly distributed flow through the plant over its entire cross-sectional area outside the inlet cylinder  23  is obtained and that oxidized matter is allowed to sink to the bottom of the reservoir  20  and is not carried along with the purified water. 
         [0051]    It may be determined that with a diameter of 3 m for the reservoir  20  and a diameter of 1.5 m for the inlet cylinder  23 , a capacity for the plant may be some 3 m 3 /h of purified raw water. 
         [0052]    A second embodiment of a water purification plant is shown in  FIGS. 5 and 6 . This plant is mainly designed for purifying water containing organic material, such as humus in sea water or stream water.  FIGS. 5 and 6  are only provided with numerals to the extent necessary for understanding the differences in relation to the first embodiment shown in  FIGS. 3 and 4 . 
         [0053]    For removing the organic material from the supplied raw water, a suitable flocculating agent is added to the water in the inlet cylinder  23 . This addition may preferably be arranged in a mixing cyclone  40 , through which the raw water flows and to which the agent is supplied though a flocculating agent line  41 . The raw water and the flocculating agent is effectively mixed and supplied to the inlet cylinder  23 . 
         [0054]    The treated water flows out of the inlet cylinder  23  and further though the distribution disc  24  as in the first embodiment. The formed flocks sink to the bottom, if the flow rate does not exceed 1 m 3 h per m 2  hydraulic load area of the distribution disc  24 . 
         [0055]    The second embodiment of the water purification plant shown in  FIGS. 5 and 6  may be provided with an aeration system in the inlet cylinder  23  in accordance with the first embodiment. For the flocculating process to be optimally effective, it may be necessary not to supply too much air or to supply air only intermittently. 
         [0056]    Modifications are possible within the scope of the appended claims.