| As shown in Figure 1, the sulfate ion (SO42-) naturally occurs in water supplies and in sewage as well. Sulfates are reduced to sulfideand to hydrogen sulfide (H2S) by bacteria under anaerobic condition of sewer pipe. The H2S is then biologically oxidized to sulfuric acid (H2SO4), which is corrosive to sewer pipes and consequently can lead to collapse of sewer pipes. Magnesium hydroxide [Mg(OH)2], using “Crown Spray Process”, is the currently adopted technology. Spray coating of magnesium hydroxide alone on the internal surface of the sewer pipe can prevent corrosion of sewer pipe, but it lasted only less than 6 to 8 months. The pH of 50 to 60 % Mg(OH)2, i.e., 40 to 50 % water mix, by volume, is 8.5 to 8.8. By adding a negligibly small amount, less than 1 %, by volume, of 50 % conc. sodium hydroxide (NaOH) and 10 % more or less, by volume, of titanium dioxide (TiO2) to Mg(OH)2, the pH of the three (3) chemical mix suddenly increased the pH to 13.0 or greater. In fact, experiments showed that an addition of only 0.3 %, by volume, of NaOH to mixed slurry of Mg(OH)2 and TiO2 increased the pH to 13.0 or greater. Consequently, the life time of the spray coating to prevent sewer corrosion can be extended to 16 to 18 months, i.e., it lasted more than two (2) times of Mg(OH)2 coat alone. Alternatively, a mixture of Mg(OH)2 with less than 1% of NaOH, by volume, also suddenly increased its pH to 13.0 or greater and it lasts 15 to 16 months, i.e., it also lasted two times more than that of Mg(OH)2 coating alone. Alternatively, a mixture of TiO2 with less than 1 % of NaOH, by volume, also suddenly increased its pH to 13.0 or greater and it lasted surprisingly long up to between 20 and 24 months, i.e., it also lasted three times more than that of Mg(OH)2 coating alone. Due to this invention, the economic benefits and time saving for long-run could be astronomical. In addition, expectancy of life time of coating, based on new invention, can be extended 2 to 3 times or longer. |
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