Updated: July 2002

1. Introduction

Environmental control including deodorization can be accomplished in many ways - physical, chemical, mechanical, and biological. The final choice from among these must be made from a comprehensive point of view taking into consideration the efficiency of treatment, relative economy, the need for the secondary treatment of post-treatment by-product, and so on. The objectionable odor produced from the sewage disposal plant, etc. has thus far been eliminated mainly by the acid/alkali washing method and activated carbon adsorption process. In recent years, however, R&D has been gaining impetus in pursuit of a biological deodorization system because of its relative advantage in terms of running and maintenance costs. With eyes on the saddle type ceramics used in the distillation column and reactor vessel in many chemical plants and having excellent engineering properties, Nippon Steel Corporation has successfully developed and put into commercial use a new biological deodorization process and equipment in which an inexpensive carrier made from iron-making by-products is used to remove odor-evolving components.

2. Deodorization Efficiency

3. Features and Advantages

The biological deodorization process in which blast furnace slag-based saddle type ceramics in use as a stabilizing carrier offers many advantages, including:
1) The blast furnace slag as the feedstock of the saddle type ceramics contains Fe, Mg, and many other trace nutrients and is porous - a habitable condition for microorganisms. This means that the carrier can stabilize microorganisms at high efficiencies.
2) The saddle type structure provide a high efficiency of gas-liquid-solid contact and hence a high stability of deodorizing treatment.
3) Very low resistance to gas passage - an advantage that makes this new deodorization system energy efficient.
4) High-speed deodorizing treatment permits a compact system configuration.
5) Simple in construction, easy to operate, and hence easy to maintain. The running cost is only 1/8 to 1/3 that required with the previous processes.

4. Principles

Biological deodorization is used to eliminate odor by decomposing odor constituents by biological oxidization. In operation, sulfides are deodorized according to the decomposition reactions below.

S^2- -> S⁰ -> S2O3^2- -> S4O6^2- -> S2O6^2- -> SO3^2- -> SO4^2-

Thiobacillus microorganisms contribute most to this decomposition. Ammonia, on the other hand, is decomposed and deodorized by nitrosomonas and nitrobacteria as follows.

NH4⁺+3/2O2 -> NO2^-+H2O+2H (nitrosomonas)
NO2^-+½O2 -> NO3^- (nitrobacter)

5. Flow Sheet

6. Installations

Biological deodorization system for sewage disposal plants and sewage pumping stations.