Method and apparatus for the treatment of particulate biodegradable organic waste

Abstract

A method for treating particulate biodegradable organic waste includes adjusting the pH as necessary to provide an acidic pH prior to introducing the waste to a thermal hydrolysis reactor and hydrolyzing the waste at a temperature of about 130° C. or greater and a pressure greater than the saturated water vapor pressure to produce a slurry including solubilized organic material and residual solids. The solubilized organic material is separated from the residual solids using a liquid/solid separator and the solubilized organics are subjected to anaerobic digestion to produce a methane gas. The method may further include preheating the particulate biodegradable organic waste with latent heat of the separated solubilized organic material prior to thermal hydrolysis.

1 . A method of treating particulate biodegradable organic waste comprising: 
 a) adjusting the pH of the biodegradable organic waste as necessary to provide acidic pH;    b) subjecting the particulate biodegradable organic waste with an acidic pH added to thermal hydrolysis at a temperature above about 130° C. and a pressure at about or above the saturated water vapor pressure to produce a slurry including solubilized organic material and residual solids;    c) separating the solubilized organic material from the residual solids; and    d) subjecting the solubilized organic material to anaerobic digestion to produce a methane rich gas.    
   
   
       2 . The method of  claim 1  wherein in step b) the temperature is between about 170°-225° C. and the pressure is between about 120-370 psig.  
   
   
       3 . The method of  claim 1  further comprising prior to step d), diluting the concentration of the solubilized organic material with water.  
   
   
       4 . The method of  claim 3  wherein the water is a secondary wastewater treatment plant effluent.  
   
   
       5 . The method of  claim 1  further comprising exchanging latent heat from the solubilized organic material with the particulate biodegradable organic waste prior to step b) to preheat the particulate biodegradable organic waste.  
   
   
       6 . The method of  claim 1  further comprising: 
 a1) before step b), mixing the particulate biodegradable organic waste with the separated solubilized organic material of step c) to heat the particulate biodegradable organic waste;    a2) removing liquid, including the solubilized organic material, from the heated particulate biodegradable organic waste; and    subjecting the removed liquid of step a2) to the anaerobic digestion of step d).    
   
   
       7 . The method of  claim 1  further comprising: 
 subjecting the residual solids to composting.    
   
   
       8 . The method of  claim 1  further comprising, prior to step a), sizing the particulate biodegradable waste to between 0.25-2.0 inch particles.  
   
   
       9 . The method of  claim 1  wherein in step b) the hydrolysis is at a temperature of between about 130°-225° C.  
   
   
       10 . The method of  claim 1  wherein the anaerobic digestion of step d) is an upflow anaerobic sludge blanket process.  
   
   
       11 . The method of  claim 1  wherein step c) further comprises subjecting the residual solids to washing/elutriation.  
   
   
       12 . The method of  claim 1  wherein the heat for the thermal hydrolysis is provided by steam.  
   
   
       13 . The method of  claim 12  further comprising recycling residual steam from the thermal hydrolysis step to the particulate biodegradable organic waste prior to step b) to preheat the particulate biodegradable organic waste.  
   
   
       14 . The method of  claim 1  wherein the thermal hydrolysis at 170° C. or greater lasts at least 15 minutes.  
   
   
       15 . The method of  claim 1  wherein the gas of step d) is at least about 50% or more methane.  
   
   
       16 . The method of  claim 1  wherein in step b) the particulate biodegradable organic waste has a pH of 5.15 or less.