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

Abstract

Provided are a method and an apparatus for treating organic wastewater and sludge, which remarkably reduce the generated amount of sludge at much lower running cost, and which get the size smaller the capacity of the solubilization tank. The method and apparatus for treating sludge has: an biological treatment system, which applies biological treatment to wastewater, a solid-liquid separation unit for separating a solid from a liquid in the wastewater after treating the biologically, to obtain a treated wastewater and a returned sludge. And the apparatus has means for obtaining a withdrawn sludge from a part of the returned sludge, an alkali-treatment tank, which applies alkali-treatment to the withdrawn sludge. The apparatus, also, has a biological solubilization tank, which solubilizes the sludge after treating the alkali-treatment under an anaerobic, anoxic, or microaerophilic condition, and a means for returning sludge to recycle the solubilized sludge to the biological treatment system.

What is claimed is:  
     
         1 . A method for treating a sludge comprising the steps of: 
 treating a wastewater biologically to generate a sludge;    treating the sludge by an alkali-treatment; and    solubilizing the treated sludge by the alkali-treatment, biologically, under an anaerobic, an anoxic, or a microaerophilic condition.    
     
     
         2 . A method for treating a wastewater comprising the steps of: 
 treating a wastewater biologically;    separating a solid from a liquid in the wastewater treated biologically, to obtain a treated wastewater and a returned sludge;    withdrawing the sludge from a part of the returned sludge to obtain a withdrawn sludge; and    treating the withdrawn sludge by an alkali-treatment; and    solubilizing and decomposing the withdrawn sludge, biologically, under an anaerobic, an anoxic, or a microaerophilic condition.    
     
     
         3 . The method according to  claim 1 , wherein a pH value is less than 9 during treating the sludge by the alkali-treatment.  
     
     
         4 . The method according to  claim 2 , wherein a pH value is less than 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 The method according to  claim 2 , further comprising the step of thickening the sludge before treating the withdrawn sludge by the alkali-treatment.  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: 
 an alkali-treatment tank for treating a sludge by an alkali-treatment, generated in the biologically treated wastewater; and    a biological solubilization tank, located at downstream side of the alkali-treatment tank, connected with the alkali-treatment tank via a passage, to biologically solubilize 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 biological treatment system to treat a wastewater biologically;    a solid-liquid separation unit, located at downstream side of the biological treatment system, connected with the biological treatment system via a passage, to separate the biologically treated wastewater in the biological treatment system and to obtain the treated wastewater and the returned sludge.    a sludge thickening device for obtaining a withdrawn sludge from a part of the returned sludge;    an alkali-treatment tank to treat the withdrawn sludge by the alkali-treatment;    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    means for returning the solubilized sludge for recycling the solubilized sludge into the biological treatment system.    
     
     
         8 . The apparatus according to  claim 6 , wherein the alkali-treatment tank is a tank of plug flow type.  
     
     
         9 . The apparatus according to according to  claim 7 , wherein the alkali-treatment tank is a tank of plug flow type.  
     
     
         10 . The apparatus according to  claim 6 , wherein the biological solubilization tank is a tank of plug flow type.  
     
     
         11 . The apparatus according to  claim 7 , wherein the biological solubilization tank is a tank of plug flow type.  
     
     
         12 . A method for treating a sludge comprising the steps of: 
 treating a wastewater biologically to generate the sludge; and    treating the sludge by an alkali-treatment, by intermittently adding the alkali to the sludge at a determined interval.    
     
     
         13 . The method according to  claim 12 , further comprising the step of solubilizing a sludge biologically 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 held from for 3 hours to for 24 hours and the retention time of the sludge in the biological solubilization step is held from for 1 day to for 3 days.  
     
     
         15 . The method according to  claim 13  further comprising the step of: 
 treating the sludge by the alkali-treatment under the normal temperature and the normal pressure; and  
 solubilizing the sludge biologically, under the normal temperature and the normal pressure.  
 
     
     
         16 . The method according to  claim 14  further comprising 
 treating the sludge by alkali-treatment under the normal temperature and the normal pressure;  
 solubilizing the sludge biologically, under the normal temperature and the normal pressure.  
 
     
     
         17 . An apparatus for treating a sludge comprising: 
 an alkali-treatment tank for intermittently adding the alkali at a determined interval to the sludge generated by treating a wastewater biologically, and for treating the sludge by the alkali with holding a retention time of from for 3 hours to for 24 hours;    a biological solubilization tank for solubilizing biologically the treated sludge by the alkali-treatment, at a normal temperature and a pressure in an anaerobic, an anoxic, or a microaerophilic condition, with the retention time of from for 1 day to for 3 days, wherein the biological solubilization tank being located at downstream side of the alkali-treatment tank and being connected with the alkali-treatment tank via a passage; and    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: 
 treating a wastewater biologically in a biological treatment system;    separating a solid from a liquid after treating the wastewater biologically, to obtain a treated wastewater and a returned sludge, and to obtain a withdrawn sludge from a part of the returned sludge;    treating the withdrawn sludge in an alkali-treatment, by intermittently adding the alkali at a determined interval, with holding a retention time after adding the alkali from for 3 hours to for 24 hours;    solubilizing the alkali-treated sludge biologically at the normal temperature and the pressure in an anaerobic, an anoxic, or a microaerophilic atmosphere, with holding a retention time after adding alkali, from for 1 day to 3 days; and    returning the solubilized sludge to the biological treatment system.    
     
     
         19 . An apparatus for treating a wastewater comprising: 
 means for treating a wastewater biologically in a biological treatment system;    means for separating a solid from a liquid in the biologically treated wastewater, to obtain a treated wastewater and a returned sludge;    means for obtaining a withdrawn sludge from a part of the returned sludge;    means for treating the withdrawn sludge by intermittently adding an alkali at a determined interval, with holding a retention time after adding the alkali from for 3 hours to for 24 hours;    means for biologically solubilizing the withdrawn sludge immediately after the alkali-treatment, wherein the biological solubilization is achieved at the normal temperature and the pressure in an anaerobic, an anoxic, or a microaerophilic atmosphere, with holding a retention time after adding the alkali from for 1 day to 3 days; and    means for returning the solubilized sludge to the biological treatment system.    
     
     
         20 . A method for treating a wastewater comprising the steps of: 
 treating a wastewater biologically;    separating a solid from a liquid in the biologically treated wastewater to obtain a treated wastewater and a returned sludge;    treating a part of the return sludge by an alkali-treatment, within a range of pH value from 9 to 12.5;    solubilizing the sludge biologically immediately after treating the sludge by the alkali-treatment, in an anaerobic, an anoxic, or a microaerophilic condition; and    returning the solubilized sludge to the biological treatment system.    
     
     
         21 . The method according to  claim 20  further comprising the step of thickening the sludge before treating the sludge by the alkali-treatment.  
     
     
         22 . An apparatus for treating a wastewater comprising: 
 a biological treatment tank to treat a wastewater biologically;    a solid-liquid separation unit to separate the wastewater discharged from the biological treatment tank to obtain a treated wastewater and a returned sludge;    an alkali-treatment tank to treat a part of the returned sludge by the alkali within a range of pH value from 9 to 12.5;    a biological solubilization tank, connected to the alkali-treatment tank, to biologically solubilize the sludge discharged from the alkali-treatment tank under an anaerobic, anoxic, or microaerophilic condition; and    means for returning the sludge discharged from the biological solubilization tank to the biological treatment tank, to recycle the sludge.