The effect of pH on H2S removal by P. putida CH11 is shown in FIgure 3. The H2S degradation activity at each pH level is expressed relative to the maximum removal rate. P. putida CH11 possessed high removal activity (>90%) in the range from pH 6 to 9. The ability of P. putida CH11 to remove hydrogen sulfide was less sensitive to pH than Thiobacillus thioparus. From an operational standpoint, the control of pH is avery important parameter in H2S treatment since the removal efficiency drops to 65% when the culture pH increases to 10. Hence, it is suggested that the optimum pH value for H2S treatment ranges from 6 to 8.