Technical Papers

Anaerobic Digester Hydrogen Sulfide Removal

Manatee County, FL Southwest Water Reclamation Facility

This paper presents results of a full-scale trial initiated in May 2006 by the Manatee County Southwest Water Reclamation Facility and examines the impacts of peroxide regeneration of spent iron salts on the removal of hydrogen sulfide (H2S) from anaerobic digesters. Dissolved sulfide levels in the primary digester dropped throughout the course of the trial biogas H2S concentrations were reduced by 90% on average. Additional positive changes were noted in the volume and quality of biogas produced, and in finished biosolids quality.

Reprinted with permission from Proceedings of WEFTEC®.07, the 80th Annual Water Environment Federation Technical Exhibition and Conference, San Diego, CA, October 13 - 17, 2007. Copyright © 2007 Water Environment Federation, Alexandria, Virginia.  

Bio-Solids Process Enhancements Resulting From the Use of Hydrogen Peroxide for Hydrogen Sulfide Odor Control

The San Antonio Experience

This paper presents results of a trial initiated in February 2004 by the San Antonio Water System to quantify the impacts of hydrogen peroxide injection prior to dissolved air flotation thickening of wastewater sludges. The use of hydrogen peroxide has performed beyond expectations since its introduction for odor control of the Leon Creek WRC sludge transferred to the Dos Rios facility. It has also resulted in significant increases in digester gas production, and some improvements in sludge dewaterability.

Reprinted with permission from Proceedings of WEFTEC®.06, the 79th Annual Water Environment Federation Technical Exhibition and Conference, Dallas, TX, October 21 - 25, 2006. Copyright © 2006 Water Environment Federation, Alexandria, Virginia.

The Use of Peroxide Generated Iron-Sulfide Control (PRI-SC)® for Long Duration Collection System Control

Regional Municipality of York

Corrosion of collection system piping and components has become a big problem for many municipalities balancing growth and the maximum service life for existing collection system infrastructure. This paper presents the results of a trial initiated in August 2005 by The Regional Municipality of York (York Region) to quantify the impacts of PRI-SC® for control of hydrogen sulfide (H2S) in a long retention time section of the collection system. PRI-SC® technology enabled significant reductions of H2S over a 12 hour retention time section of the collection system.

Cost Savings and Performance Improvement of Large System Iron Salt Use for Integrated Sulfide Control and Chemically Enhanced Primary Treatment by Using Peroxide Regenerated Iron Technology

San Diego's Point Loma WWTP 

San Diego's Point Loma WWTP is a 160 MGD (240 MGD permitted), 100% advanced primary treatment plant that has historically used iron salts for collection system sulfide control and chemically enhanced primary treatment. Beginning in 2006, a PRI-SC® (Peroxide Regenerated Iron - Sulfide Control) program was implemented by adding H2O2 at the intermediate pump station PS2 (in place of the FeCl3), and again to the plant influent (ahead of FeCl3 addition for CEPT). The application of PRI-SC® in the Point Loma system was designed to provide at least $685/day in cost savings, to be achieved through reduced ferric chloride use at PS2 and Point Loma, while improving sulfide control and CEPT performance. Since integrating the PRI-SC® program full-time in 2008, SDMWD is realizing savings of approximately $4,700 per day (~$1.72 million/yr) compared to the 2007 baseline iron salts program. At the same time, both sulfide control and CEPT performance has improved. The cost savings were helped by the hedging aspect of the PRI-SC® program - iron salt price volatility in 2008 and 2009 was upwards of 45%. The PRI-SC® program has reduced the total iron salt use from the 2007 baseline rate of 32.5 dry tons per day to approximately 19.3 dry tons per day in 2009, with the core savings coming from an overall reduction in ferric chloride use at PS2 and the treatment plant.

Significantly, ferric chloride use at PS2 was eliminated and, for CEPT, it was reduced from 24 mg/L to 10 mg/L (16.6 to 6.8 dry tons per day) with no loss in performance. In addition, total sulfide removal has improved over baseline levels, and average CEPT performance exceeds the permit levels at 89% for TSS and 65% for BOD, and effluent water quality has improved (with 60% less spent iron (as FeS) present in the ocean discharge). For the most part, digester biogas H2S levels were maintained below the permit requirement of < 40 ppm, but required approximately twice the baseline FeCl2 feed rate. Even so, the overall program has maintained the stated savings benefit.

Reprinted with permission from Proceedings of WEFTEC® ‘10, the 83rd Annual Water Environment Federation Technical Exhibition and Conference, New Orleans, LA, October 2 - 6, 2010. Copyright © 2010 Water Environment Federation, Alexandria, Virginia.

PRI-SC® Sulfide, Phosphorus and UV Fouling Improvements

Raleigh, NC

The City of Raleigh has been using ferrous sulfate (FeSO4) for years in their collection system for hydrogen sulfide and plant phosphorus control. Several years ago the Neuse River wastewater treatment plant upgraded their ultraviolet disinfection (UV) system to a higher intensity lamp technology. Although the UV system was equipped with mechanical wipers, manual cleaning by plant personnel was required due to the elevated iron levels carrying over to the disinfection stage coupled with the lamp sleeve's higher temperature. In 2008, the City of Raleigh implemented Peroxide Regenerated Iron Sulfide Control (PRI-SC®) as a means to improve collection system sulfide control and maintain plant phosphorus removal while reducing the amount of iron salts in the collection system. PRI-SC® chemical savings were found to be $80,300 per year. Manual UV sleeve cleaning frequency was reduced from 2 weeks to 2 months, saving 32 man hours per cleaning or $25,600 per year.

Reprinted with permission from Proceedings of WEFTEC® ‘10, the 83rd Annual Water Environment Federation Technical Exhibition and Conference, New Orleans, LA, October 2 – 6, 2010. Copyright © 2010 Water Environment Federation, Alexandria, Virginia.