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44 DECEMBER 2016 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 55, NO. 12 CHEMICAL TREATMENT S It is a natural phenomenon that sulfate ions in sewage are biologically re- duced to hydrogen sulfide (H 2 S), which moves from waste water to the sewer atmosphere and is oxidized to sulfuric acid (H 2 SO 4 ) by oxidizing bacteria. H 2 SO 4 corrodes sewer pipe, which eventually collapses or explodes. Numerous methods for the preven- tion of sewer corrosion are currently available. These methods include in- jection of oxidizing chemicals or a spray coating of sodium hydroxide (NaOH) or 50 to 60% magnesium hy- droxide [Mg(OH) 2 ] slurry, but these methods are temporary and only last for two to eight months. A newly in- vented and U.S.-patented chemical, along with chemical theories and equations, can semipermanently pre- vent corrosion. Sulfide corrosion of sewer pipe due to biogenic acid production is not only a serious problem in the United States, but also a worldwide phenomenon. Sewer Corrosion Theories and Conventional Technology As shown in Figure 1, 1-2 the sulfate ion (SO 4 2– ) naturally occurs in water supplies and in sewage as well. Sulfates are reduced to sulfide and to hydrogen sulfide (H 2 S) by bacteria under the anaerobic conditions in sewer pipe. The H 2 S is then biologically oxi- dized to sulfuric acid (H 2 SO 4 ). 3-4 This process is illustrated in Equations (1) through (4): + → SO [organic matter] H S 4 2– Anaerobic condition Bacteria 2 (1) + → H S 2O H SO thiobacillus 2 2 Bacteria, H S oxidizing 2 4 2 (2) ↔ + + In gas stage: H S HS H 2 – (3) ↔ + + In gas stage: HS H S – 2 – (4) In s e w ers m a d e of m at eri al s su ch as concrete, iron, or steel, the acid forma- tion can lower the pH to 2.0 and lead to corrosion and destruction of the sewer crown and eventually the sewer pipe will collapse. The bacteria that produce sulfide are strict anaerobes and, consequently, live be- neath the water surface in gravity sewers and on the pipe walls in force mains. In order to produce sulfide compounds, the bacteria require a source of sulfur and a food supply. SO 4 2– , generally abundant in waste water, is usually the common sulfur source, although other forms of sulfur, such as organic sulfur from animal wastes, can also be reduced to sulfide. Deactivating Bacteria to Prevent Sewer Corrosion and Collapse Choonghee Rhee, Standard Testing and Engineering, Inc., Compton, California