Case Study for Hydrogen Sulfide Odor Control
California Water Pollution Control Plant Case Study
A California WPCP contracted with U.S. Peroxide, LLC (now USP Technologies) to conduct a three-month demonstration of hydrogen peroxide in an effort to improve control of odors emanating from its headworks and primary clarifiers. Expanding the existing chlorine facilities to meet these goals would have involved major upgrades required by the newer fire codes and Process Safety Management regulations.
The WPCP is a 130 MGD tertiary treatment facility that receives sewage from three interceptors (see Figure 6). During peak PM flows, a portion of the primary effluent is diverted to a 20 MGD equalization basin, and fed to the secondary units during the low flow early AM. Chlorine is injected at two locations for odor control from April to October: at the influent to the headworks (10,000-15,000 lbs/day); and at the influent to the equalization basin (3,000-5,000 lbs/day). This corresponded to a dose ratio at the headworks of 7-8:1 (w/w chlorine:sulfide). The primary reasons for considering H2O2 in lieu of other chemical alternatives were the success of other municipalities in converting from chlorine to H2O2, and the favorable price trend for H2O2.
Figure 6. WPCP Influent Flows.
The initial baseline survey indicated that about 2000 lbs/day (or 1.8 mg/L) of sulfide was entering the treatment plant from the collection system. Another 825 lbs/day (or 0.7 mg/L) was being generated within the primary clarifiers. This explained why chlorine injection at the headworks was not controlling odors off the clarifiers. The approach taken with H2O2 was thus two-fold: 1)utilize a single injection point into each of the interceptors discharging into the headworks; and 2) provide a booster dose into the influent to the primary clarifiers. The results showed that a H2O2:S dose ratio of 1.4:1 achieved the target level of control at the headworks (< 0.5 mg/L). For the clarifiers, the combination of headworks injection (2.5 mg/L) and primary booster dose (1.5 mg/L) was shown to be most efficient, improving the cost-performance by 20% over headworks dosing alone. A significant factor in the performance of H2O2 at this facility was the use of FeCl3 in the upstream collection system (for odor control). As indicated in Figure 7 (below), the effect of 1-2 mg/L iron in the influent wastewater was to catalyze the H2O2 - Sulfide reaction, accelerating the removal of sulfide by a factor of 2-3. The conclusion was that H2O2 provided better control of H2S through the primary clarifiers than did chlorine - no treatment of the equalization basin was needed when H2O2 was added. Further, on an equal performance basis, the effective cost for H2O2 was equal to or less than that for chlorine.
Figure 7.Effect of iron on catalyzing the reaction between H2O2 and sulfide.
Keywords: Hydrogen Sulfide, Odor Control, Hydrogen Peroxide, H2O2, Collection System Odor
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