Apparatus for treating exhaust gases containing nitrides

Abstract

There are provided a process and apparatus for biologically treating an exhaust containing nitrides without requiring a large amount of water by treating a circulating water containing ammonia in the treating system, preferably by which clogging of the packed layers can be prevented. The first embodiment of the present invention relates to a process for treating an exhaust gas containing nitride by passing it through a microbial carrier packed layer while cyclically spraying circulating water thereon, which comprises nitrating the circulating water containing ammonia formed therein, reducing the nitrated water to effect denitrification, and cyclically using the resulting water as the circulating water. The process of the second embodiment of the present invention comprises dividing the microbial carrier packed layer into a former stage and a latter stage, carrying out the spray treatment of the former stage with a circulating water having a weak alkalinity of pH (8) to (9), mixing the circulating water withdrawn from the former stage with that from the later stage to form a circulating water having a pH of (6.0) to (8.0), and carrying out the denitrification treatment with the obtained circulating water.

What is claimed is:  
     
         1 . A process for treating an exhaust gas containing nitrides by passing it through a microbial carrier packed layer while cyclically spraying circulating water thereon, which comprises nitrating the circulating water containing ammonia formed therein, reducing the nitrated water to effect denitrification, and cyclically using the resulting water as the circulating water.  
     
     
         2 . The process for treating an exhaust gas containing nitrides of  claim 1 , wherein the nitration of the circulating water is carried out by spraying the ammonia-accumulated circulating water having a pH regulated to not more than 7.5 on to the microbial carrier packed layer.  
     
     
         3 . The process for treating an exhaust gas containing nitrides of  claim 1 , wherein the nitration and the denitrification of the circulating water is conducted while the pH of the circulating water is regulated to 6.5-7.5.  
     
     
         4 . An apparatus for treating an exhaust gas containing nitrides comprising an exhaust gas treating tower having a microbial carrier packed layer through which an exhaust gas is passed with a mechanism of cyclically spraying circulating water on to the packed layer, a circulating water tank to store the circulating water, a nitration mechanism to nitrate the circulating water, and a denitrification tank to reduce the nitrated water to effect denitrification, and each tank being connected by a line.  
     
     
         5 . The apparatus for treating an exhaust gas containing nitrides of  claim 4 , wherein plural of the microbial carrier packed layer with a mechanism of cyclically spraying water are provided in series, and a circulating water circulation line is connected with the mechanism of cyclically spraying water of the packed layer at the most upstream to constitute the nitration mechanism to obtain a nitrated water.  
     
     
         6 . A process for treating an exhaust gas containing nitrides by passing it through a microbial carrier packed layer while spraying a circulating water thereon and withdrawing the circulating water to effect denitrification treatment, which comprises dividing the microbial carrier packed layer into a former stage and a latter stage, carrying out the spray treatment of the former stage with a circulating water having a weak alkalinity of pH 8 to 9, mixing the circulating water withdrawn from the former stage with that from the later stage to form a circulating water having a pH of 6.0 to 8.0, and carrying out the denitrification treatment with the obtained circulating water.  
     
     
         7 . The process for treating an exhaust gas of  claim 6 , wherein the microbial carrier packed layer is a gas scrubbing column of the dropping type or bubbling type.  
     
     
         8 . The process for treating an exhaust gas of  claim 6 , wherein the mixing of the circulating water withdrawn from the former and latter stages is carried out by mixing the circulating water withdrawn from the latter stage with the denitrification treated water, allowing the mixed water to stand to thereby carry out precipitation of sludge, and mixing the sludge separated by the precipitation treatment with the circulating water withdrawn from the former stage.  
     
     
         9 . The process for treating an exhaust gas of  claim 6 , wherein the denitrification treatment is carried out while measuring the pH of the denitrification treated solution and feeding hydrogen donors when the treated solution is acidified and stopping feeding the hydrogen donors when the treated solution is neutralized or alkalized.