PEROXIDE REGENERATED IRON-SULFIDE CONTROL (PRI-SC)^™: INTEGRATING COLLECTION SYSTEM SULFIDE CONTROL WITH ENHANCED PRIMARY CLARIFICATION BY ADDING IRON SALTS AND HYDROGEN PEROXIDE

ABSTRACT

Iron salts are used by municipalities worldwide to control hydrogen sulfide within collection systems and to enhance primary clarification at treatment plants. However, the two uses are not synergistic: the product of the sulfide reaction is predominantly ferrous sulfide (e.g., FeS), a tightly-bound black precipitate that does not enhance flocculation. Further, dissolved sulfide present in the plant influent can scavenge free iron added to enhance clarification. Adding supplemental iron salt for both purposes would increase costs and potentially cause problems associated with e.g., higher volume solids production, reduced alkalinity, elevated salinity levels, and depleted dissolved oxygen. This paper presents the results of a field trial conducted at the Orange County Sanitation Districts using a novel technology to moderate these shortcomings – Peroxide Regenerated Iron – Sulfide Control (PRI-SCTM, patent pending). The combination treatment involves adding an iron salt at the upper reaches of the collection system and hydrogen peroxide at points downstream. The process may be viewed as an oxidant (H₂O₂) regenerating the spent iron salt (FeS) in-situ – yielding ferrous / ferric iron and colloidal sulfur. The study involved three major interceptors and the results show the PRI-SC technology met the control objectives at a significantly lower cost than other commonly used chemical technologies. Further, much of the ferrous salt added in the collection for sulfide control was shown to converted to hydrous ferric oxide at the treatment plant for enhanced clarification purposes. OCSD has since extended the field test into a full year evaluation.

KEYWORDS Hydrogen sulfide, odors and corrosion, iron salts, hydrogen peroxide, enhanced clarification

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