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46 DECEMBER 2016 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 55, NO. 12 CHEMICAL TREATMENT The hose is inserted into the sewer as the float is pulled downstream by a cable winch located at a downstream manhole. The ap- plication rate of chemical is determined by the pumping rate and travel speed of the float. New Research and Development for Deactivating Sulfur- Oxidizing Bacteria Extensive research has been done on the corrodibility of sewer pipe under condi- tions that foster the development of H 2 S. 8-10 For this research, the chemistr y of H 2 S characteristics of sewer corrosion, and the use of new chemical(s) for preventing sewer corrosion must be clearly understood. It is important to know the amount of H 2 S es- cape (f lux) that transfers from the waste water to atmosphere in the sewer pipe. P rop er ties of H 2 S and bi sulf ide ion (HS – ) in dissolved sulfide fraction in waste water are a function of pH, as shown in Equation (5): = + = + log HS H S –log H log K pH – pK – 2 1 1 (5) where pK 1 ≈ 7.0 (ionization constant). Therefore, it is necessary to investigate the amount of H 2 S that can be produced and fluxed into the air space of sewer pipe at different pH levels, as shown in Equa- tions (6) through (11): ≈ + = = At pH 2.0 : [H S] [H S] [H S ] 1 1.00001 0.99999 2 2 – (6) ≈ + = = At pH 5.0 : [H S] [H S] [H S ] 1 1.01 0.99 2 2 – (7) ≈ + = = At pH 7.0 : [H S] [H S] [H S ] 1 2 0.5 2 2 – (8) ≈ + = = At pH 9.0 : [H S] [H S] [H S ] 1 101 0.0099 2 2 – (9) ≈ + = = At pH 10.0 : [H S] [H S] [H S ] 1 1001 0.00099 2 2 – (10) ≈ + = + = × ≈ At pH 13.0 : [H S] [H S] [H S ] 1 10 1 1.0 1 0 0 2 2 – 6 –6 (11) The above analyses indicate that H 2 S hardly exists in the air space of sewer pipe at a pH of 9.0 or greater. The SOB actively thrive at a pH level of approximately 2.0 and contribute to pipe corrosion. There- fore, the purpose of this research is aimed at inventing or developing chemicals that can deactivate SOB. In order to find out the amount of H 2 S in the air space at different pH levels, the rela- tionship between H 2 S, HS – , and sulfide (S 2– ) must be identified. The relationships be- tween H 2 S, HS – , and S 2– at various pH levels are shown in Figure 2. 11-12 At pH values of 7 (pK 1 ) and above, most of the reduced sul- fide exists in solution as HS – and S 2– ions, and the amount of free H 2 S is gradually re- duced toward almost zero at a pH level ≥ 13.0 (pK 2 ). A logarithmic pH concentra- tion diagram for H 2 S with ionization con- stants, K 1 = 7.0 and pK 2 = 13.0, is illustrated in Figure 2. At pH levels ≤ 7.0, the equilib- rium shifts toward the formation of non- ionized H 2 S/[aq] at –Log 3.5, which is ~54% of total sulfide (S T ). The corrosion of concrete sewer pipe depends on the following: • Production of H 2 S in sewer water (P s ) • Turbulence of flow (t f ) • Velocity of flow (V f ) • H 2 S flux from the waste water to the air space of the sewer pipe ( f s ) at dif- ferent pH levels • The fraction of H 2 S absorbed by con- crete (F H 2 S ) in terms of grams of H 2 S/ m 2 /y. The more H 2 S absorbed by the concrete surface, the greater the cor- rosion rate. • Alkalinity of the concrete surface (A), which is reversely proportional to the rate of corrosion • Other unknown factors ([K]) Therefore, the corrosion rate (C) can be formulated with Equation (12): = C P t V f [K ] F A s f f s H S 2 (12) There are also daily cycles for velocity, detention time, waste water characteris- tics, etc. The major factors in Equation (12), however, are the fraction of H 2 S absorbed by the concrete (F H 2 S ) and alkalinity (A) of the concrete crown surface. It was found through long-term research that P s and f s proportionally affect F H 2 S , while t f and V f adversely affect F H 2 S . Also, f s is dependent on the pH of waste water in the sewer pipe. TABLE 1. COMPARISON OF EXISTING AND NEW CHEMICALS Chemicals Mg(OH) 2 Alone (A) Mixture of A, B, and F Mixture of A and F Mixture of B and F Mixture of C and F Mixture of D and F Mixture of E and F % Mix 100% of A [90% of A] + [10% ± B] + [F ≤ 0.01% of A] [100% of A] + [F ≤ 0.01% of A] [100% of B] + [F ≤ 0.01% of B] [100% of C] + [F ≤ 0.01% of C] [100% of D] + [F ≤ 0.01% of D] [100% of E] + [F ≤ 0.01% of E] pH 8.5. to 9.0 13.0 or greater 13.0 or greater 13.0 or greater 13.0 or greater 13.0 or greater 13.0 or greater Chemical and % Dilution: A = [50 to 60%, by vol., of Mg(OH) 2 ] + [40 to 50%, by vol., of water] D = [50 to 60%, by vol., of Ba(OH) 2 ] + [40 to 50%, by vol., of water] B = [50 to 60%, by vol., of TiO 2 ] + [40 to 50%, by vol., of water] E = [50 to 60%, by vol., of Ca(OH) 2 ] + [40 to 50%, by vol., of water] C = [50 to 60%, by vol., of Al(OH) 3 ] + [40 to 50%, by vol., of water] F = 50% NaOH as liquid state (A) Currently Used by Public Agencies in the United States