Method and apparatus for treating sludge, and method and apparatus for treating wastewater utilizing the same

Abstract

A method and an apparatus for treating organic wastewater and sludge which remarkably reduce the generated amount of sludge at a much lower running cost, and which reduce the size and the capacity of the solubilization tank. The method and apparatus for treating sludge employs a biological treatment system, wherein a biological treatment of wastewater is carried out, and a solid-liquid separation unit for separating a solid from a liquid in the wastewater after the biological treatment, to obtain a treated wastewater and a sludge. The apparatus has a means for obtaining a withdrawn sludge from a part of the sludge and an alkali-treatment tank, wherein an alkali-treatment of the withdrawn sludge is carried out. The apparatus also has a biological solubilization tank which solubilizes the sludge after the alkali-treatment under an anaerobic, anoxic or microaerophilic condition, and a means for recycling the solubilized sludge to the biological treatment system.

1 . A method for treating a sludge comprising the steps of: 
 (a) treating a wastewater biologically to generate a sludge;    (b) treating the sludge from step (a) by an alkali-treatment to provide a treated sludge; and    (c) solubilizing the treated sludge from step (b), biologically, under an anaerobic, an anoxic, or a microaerophilic condition.    
   
   
       2 . A method for treating a wastewater comprising the steps of: 
 (a) treating a wastewater biologically;    (b) separating a solid from a liquid in the wastewater treated biologically from step (a), to obtain a treated wastewater and a sludge;    (c) withdrawing a portion of the sludge from step (b) to obtain a withdrawn sludge;    (d) treating the withdrawn sludge from step (c) by an alkali-treatment; and    (e) biologically solubilizing and decomposing the withdrawn sludge from step (d), under an anaerobic, an anoxic or a microaerophilic condition.    
   
   
       3 . The method according to  claim 1 , wherein a pH value is 7 to 9 during treating the sludge by the alkali-treatment.  
   
   
       4 . The method according to  claim 2 , wherein a pH value is 7 to 9 during treating the sludge by the alkali-treatment.  
   
   
       5 . The method according to  claim 2 , further comprising the step of thickening the sludge before treating the withdrawn sludge by the alkali-treatment.  
   
   
       6 . An apparatus for treating a sludge comprising: 
 (a) an alkali-treatment tank for treating a sludge by an alkali-treatment, said sludge being generated from a biologically treated wastewater; and    (b) a biological solubilization tank, said biological solubilization tank being located at a downstream side of the alkali-treatment tank, said biological solubilization tank being connected with the alkali-treatment tank via a passage, said biological solubilization tank being capable of biologically solubilizing the sludge after treating the sludge by the alkali-treatment under an anaerobic, an anoxic, or a microaerophilic condition.    
   
   
       7 . An apparatus for treating a wastewater comprising: 
 (a) a biological treatment unit to biologically treat a wastewater;    (b) a solid-liquid separation unit, said solid-liquid separation unit being located at a downstream side of the biological treatment unit, said solid-liquid separation unit being connected to the biological treatment unit via a passage, said solid-liquid separation unit being capable of separating the biologically treated wastewater from the biological treatment unit and obtaining a treated wastewater and a sludge;    (c) a sludge thickening device for obtaining a withdrawn sludge from a part of the sludge;    (d) an alkali-treatment tank to treat the withdrawn sludge by an alkali-treatment;    (e) a biological solubilization tank to biologically solubilize the sludge after treating the sludge by the alkali-treatment under an anaerobic, an anoxic or a microaerophilic condition; and    (f) a means for recycling the solubilized sludge to the biological treatment unit.    
   
   
       8 . The apparatus according to  claim 6 , wherein the alkali-treatment tank is a plug flow tank.  
   
   
       9 . The apparatus according to according to  claim 7 , wherein the alkali-treatment tank is a plug flow tank.  
   
   
       10 . The apparatus according to  claim 6 , wherein the biological solubilization tank is a plug flow tank.  
   
   
       11 . The apparatus according to  claim 7 , wherein the biological solubilization tank is a plug flow tank.  
   
   
       12 . A method for treating a sludge comprising the steps of: 
 (a) biologically treating a wastewater to generate a sludge; and    (b) treating the sludge from step (a) by an alkali-treatment, by intermittently adding an alkali to the sludge at a determined interval.    
   
   
       13 . The method according to  claim 12 , further comprising a step of biologically solubilizing a sludge after treating the sludge by the alkali-treatment under an anaerobic, an anoxic or a microaerophilic condition.  
   
   
       14 . The method according to  claim 12 , wherein a retention time of the sludge in the alkali-treatment step is from 3 hours to 24 hours and a retention time of the sludge in the biological solubilization step is from 1 day to 3 days.  
   
   
       15 . The method according to  claim 13 , wherein the alkali-treatment is carried out at a temperature of 5° C. to 35° C. and at atmospheric pressure; and the solubilizing of the sludge is carried out at a temperature of 5° C. to 35° C. and at atmospheric pressure.  
   
   
       16 . The method according to  claim 14 , wherein the alkali-treatment is carried out at a temperature of 5° C. to 35° C. and at atmospheric pressure; and the solubilizing of the sludge is carried out at a temperature of 5° C. to 35° C. and at atmospheric pressure.  
   
   
       17 . An apparatus for treating a sludge comprising: 
 (a) an alkali-treatment tank for intermittently adding an alkali at a determined interval to a sludge generated by biologically treating a wastewater, and for treating the sludge by the alkali for a retention time of 3 hours to 24 hours;    (b) a biological solubilization tank for biologically solubilizing the treated sludge by the alkali-treatment, at a temperature of 5° C. to 35° C. and at atmospheric pressure in an anaerobic, an anoxic or a microaerophilic condition, for a retention time of from 1 day to 3 days, wherein the biological solubilization tank is located at a downstream side of the alkali-treatment tank and is connected to the alkali-treatment tank via a passage; and    (c) a means for transporting at least a part of the alkali-treated sludge into the biological solubilization tank.    
   
   
       18 . A method for treating a wastewater comprising: 
 (a) biologically treating a wastewater in a biological treatment system;    (b) separating a solid from a liquid after treating the wastewater biologically, to obtain a treated wastewater and a sludge, and to obtain a withdrawn sludge from a part of the sludge;    (c) treating the withdrawn sludge from step (b) in an alkali-treatment, by intermittently adding an alkali at a determined interval, wherein a retention time of the sludge after adding the alkali is from 3 hours to 24 hours;    (d) biologically solubilizing the alkali-treated sludge from step (c) at a temperature of 5° C. to 35° C. and at atmospheric pressure in an anaerobic, an anoxic or a microaerophilic atmosphere, wherein a retention time after adding the alkali is from 1 day to 3 days; and    (e) recycling the solubilized sludge from step (b) to the biological treatment system of step (a).    
   
   
       19 . An apparatus for treating a wastewater comprising: 
 (a) a means for biologically treating a wastewater in a biological treatment system;    (b) a means for separating a solid from a liquid in the biologically treated wastewater from step (a), to obtain a treated wastewater and a sludge;    (c) a means for obtaining a withdrawn sludge from a part of the sludge from step (b);    (d) a means for treating the withdrawn sludge from step (c) by intermittently adding an alkali at a determined interval, and for treating the withdrawn sludge by the alkali for a retention time after adding the alkali of 3 hours to 24 hours;    (e) a means for biologically solubilizing the withdrawn sludge after the alkali-treatment from step (d), wherein the biological solubilization is carried out at a temperature of 5° C. to 35° C. and at atmospheric pressure in an anaerobic, an anoxic or a microaerophilic atmosphere, wherein a retention time after adding the alkali is from 1 day to 3 days; and,    (f) a means for recycling the solubilized sludge to the biological treatment system of step (a).    
   
   
       20 . A method for treating a wastewater comprising the steps of: 
 (a) biologically treating a wastewater in a biological treatment vessel to provide a biologically treated wastewater;    (b) separating a solid from a liquid in the biologically treated wastewater from step (a) to obtain a treated wastewater and a sludge;    (c) treating a part of the sludge from step (b) by an alkali-treatment, within a pH range of from 9 to 12.5;    (d) biologically solubilizing the sludge from step (c) in an anaerobic, an anoxic or a microaerophilic condition; and    (e) returning the solubilized sludge from step (d) to the biological treatment vessel of step (a).    
   
   
       21 . The method according to  claim 20  further comprising a step of thickening the sludge before treating the sludge by the alkali-treatment.  
   
   
       22 . An apparatus for treating a wastewater comprising: 
 (a) a biological treatment tank to treat a wastewater biologically;    (b) a solid-liquid separation unit to separate the wastewater discharged from the biological treatment tank to obtain a treated wastewater and a sludge;    (c) an alkali-treatment tank to treat a part of the sludge by the alkali within a pH range of from 9 to 12.5;    (d) a biological solubilization tank, said biological solubilization tank being connected to the alkali-treatment tank, said biological solubilization tank being capable of biologically solubilizing the sludge discharged from the alkali-treatment tank under an anaerobic, anoxic or microaerophilic condition; and    (e) a means for recycling the sludge discharged from the biological solubilization tank to the biological treatment tank.