Abstract:
A method for removing metal compounds from waste water comprising the steps of adjusting the pH of the water to from 5 to 12 and preferable 6 to 9; aerating the waste water; adding a flocculating agent to the water and allowing floccules including metal compounds to form; and separating said floccules including metal compounds from the water. An apparatus for carrying out this method is also disclosed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of application Ser. No. 09/268,465 filed Mar. 16, 1999, now U.S. Pat. No. 6,117,314 which is a continuation-in-part of application Ser. No. 08/714,510, filed Sep. 16, 1996, now U.S. Pat. No. 5,882,513 which is continuation of application Ser. No. 08/348,581, filed Dec. 2, 1994, now abandoned, which is a division of application Ser. No. 08/072,418, filed May 25, 1993, now U.S. Pat. No. 5,370,800. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to the treatment of waste water, and, in particular, to the treatment of water to remove various precipitated or suspended metal compounds therefrom. 
     Runoffs from a number of industrial operations such as electrical power plants, steel plants and mines are known to be contaminated with various metal compounds including iron, manganese, aluminum, zinc, copper, lead, arsenic and chromium. Such contaminants may pose a serious environmental problem. Methods heretofore used to remove such contaminants have included the additional lime, soda ash or other neutralizing agents and the use of holding ponds or clarifying tanks. Such methods have not, however, been entirely satisfactory because of the lengthy periods of time, which they would generally be required to effect treatment. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an improved method and apparatus for removing precipitate or suspended metal compounds from waste water. 
     In this method, the pH of the water is first adjusted from 6 to 10. Preferred neutralizing agents are sodium hydroxide, and anhydrous ammonia when the waste water is overly acidic or sulfuric acid or hydrochloride acid when it is overly basic. The water is also aerated to a dissolved oxygen concentration of from 0.01 lb./hr to 70 lb./hr. Neutralization and aeration may preferably be done simultaneously. A polymeric flocculating agent is then added to the water. The metal compounds are then flocculated, and the flocculated metal compounds are separated from the water by means of a rotary drum thickener clarifier or other suitable means. A preferred flocculating agent is an anionic or cationic polymer wherein the use of an anionic polymer would be preferred for primary clarification or setting purposes while the cationic polymer would be preferred for dewatering purposes. The flocculated metal compounds are then further dewatered in a belt filter press or other suitable apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is further described with reference to the accompanying drawing in which: 
         FIG. 1  is a schematic drawing of apparatus used to carry out one preferred embodiment of the method of the present invention; 
         FIG. 2  is a schematic drawing of apparatus used to carry out another preferred embodiment of the method of the present invention; 
         FIG. 3  is a schematic drawing of apparatus used to carry out a third preferred embodiment of the method of the present invention; and 
         FIG. 4  is a schematic drawing of apparatus used to carry out a fourth preferred embodiment of the method of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , the raw water source is shown at numeral  10 . Waste water is removed from this source in line  12 . Neutralizing agent tank  14  is connected by line  16  to reaction neutralizing agent, aerated and agitated. A preferred embodiment of the reaction tank  18  is described in U.S. Pat. No. 4,749,497, although it has now been found that in some cases, the apparatus disclosed in that patent may be advantageously modified by the removal of its baffles and the relocation of the aeration mixing unit to a 45° angle to the vertical plane of the reaction tank. The rate of aeration would normally be from about 0.10 lbs./hr to about 70 lbs./hr for a metals concentration of 50 mg/l to 1,000 mg/l at a raw water input flow rate of 50 gal/min to 500 gal/min. The pH of the water is adjusted to between 5 and 12 and preferably to between 6 and 9. It will be understood that for regulatory reasons, if the pH is adjusted to above 9, it will ordinarily be necessary to reduce the pH to below that level on completion of the process described herein. The water is then removed in line  20  to rotary drum thickener  22 . A flocculating agent from polymer tank  24  is also moved in line  26  to line  20  to be mixed with the water in rotary drum thickener  22  where the metal compounds are flocculated and separated. Such polymers, which are used for primary clarification purposes are anionic polymers. NALCO 7767 is a suitable commercially available anionic polymer. Cationic polymers may be used for dewatering purposes and may be selected from the following commercially available polymers: PERCOL AC 737 and UNIFLOC 630. Water from the rotary drum thickener is removed in line  28  to polishing pond  30  from where outfall is removed in line  32 . Water and flocculated metal compounds are removed from the rotary drum thickener in line  34 . Additional polymer from polymer tank  36  is moved in line  38  to be mixed with water and flocculated metal compound in line  38 , which are then moved to belt filter press  40  where the flocculants are dewatered and from which water is removed to the polishing pond in line  42 . An equivalent thickening means such as a gravity belt filter or a vacuum belt filter may be substituted for the rotary drum thickener. An equivalent water removal means such as a screw press or a plane and frame press may be substituted for the belt filter press. Other equivalent polishing means may be substituted for the polishing pond. Such equivalent polishing means would include a settling clarifier, which would have a rake to move suspended solids, a settling tank, or a filter that could be a ceramic filter, a DACRON filter, a fiberglass filter, a sand filter or a micro-filter. 
     Referring to  FIG. 2 , waste water from a raw water source  110  is removed in line  112  to be mixed with neutralizing agent from tank  114  moved in line  116  to reaction tank  118 . The neutralized, aerated and agitated water is then removed in line  120  to clarifier  122  to which flocculating agent from polymer tank  124  through line  126  is mixed. Water is removed from the clarifier in line  128  to polishing pond  130  from where outfall is released from line  132 . Flocculated metal compound along with water is removed from the clarifier in line  134  from where it is mixed with additional polymer from polymer tank  136  and line  138  and then dewatered in belt filter press  140  where additional water is removed and transported to the polishing pond in line  142 . 
     Referring to  FIG. 3 , waste water from raw water source  210  is removed in line  212  and neutralizing agent from tank  214  is removed in line  216  to reaction tank  218  from where it is removed in line  220  to clarifier  222  after being mixed with flocculating agent from polymer tank  224  moved through line  226 . Water from the clarifier is removed in line  228  to polishing pond  230  from where outfall is removed in line  232 . Flocccules containing metal compounds are removed with water from the clarifier in line  234 . Additional polymer from polymer tank  236  is removed in line  238  to be mixed with the floccules which are then introduced to rotary drum thickener  239  and are then introduced to belt filter press  240  after being mixed with additional polymer form tank  241  which is removed in line  243  and mixed with water form the rotary drum thickener removed through line  245 . Water from the belt filter press is removed in line  242  and transformed with water from line  244  from rotary drum thickener  239  to the polishing pond. 
     Referring to  FIG. 4 , waste water from waste water source  310  is removed in line  312  and mixed with neutralizing agent from tank  314  and line  316  in reaction tank  318  from where water is removed in line  320  to settling pond  322 . Flocculating agent is introduced from polymer tank  324  through line  326 . Water is removed from the settling pond in line  328  to polishing pond  330  from where outflow is removed in line  332 . Floccules containing metal compound along with water are removed in line  334  and are mixed with additional polymer from tank  336  and introduced through line  338  and then dewatered in belt filter press  340  from which water is removed to the polishing tank in line  342 . Alternatively, portions of the floccules, water and polymer mixture in line  334  are also diverted to borehole  344  and drying bed  346 . 
     The method and apparatus of the present invention is further described with reference to the following example. 
     EXAMPLE 
     350 GPM of waste water having a pH of 2, having dissolved metal concentrations of 10,000 ppm was first pumped from a collection area to a reaction vessel where is was aerated and agitated at a dissolved oxygen concentration of 3 lb./HP hour. Sodium hydroxide was added automatically as the neutralizing agent, at juxtaposition to the waste water, aeration and agitation point, to an adjusted pH of 8.5. The neutralized waste water is transferred to a flocculator reactor where a UNIFLOC 630 cationic polymer is added at a rate of 2 GPM. The instantaneous agglomeration of the neutralized waste water was transferred to a rotary drum thickener where water was filtered from the metal hydroxide sludge, where supernate water was removed to a polishing pond at a rate of approximately 300 GPM. Metal hydroxide sludge was removed from the rotary drum thickener at a rate of approximately 50 GPM to a felt filter press where a cationic polymer was added at a rate of 1 GPM. After processing through the belt filter, press cake solids were recovered at a 15% to 40% dry solids. Water leaving the polishing pond consistently had a metal ion concentration below EPA permitted limits. 
     Although the invention has been described with a certain degree of particularity, it is to be understood that the present disclosure has been made only as an example and that the scope of the invention is defined by what is claimed hereafter.