Advanced Oxidation Process to Reduce Sulfide, Hydrogen Sulfide and Filamentous Bacteria at South Shore WRF

The South Shore Water Reclamation Facility (WRF) began operations in 1968 in the city of Oak Creek, Wisconsin. The plant receives wastewater from the southern, far western, and far northern portions of the Milwaukee Metropolitan Sewerage District (MMSD) as well as diverted waters from the Jones Island Water Reclamation Facility. In addition to residential wastewater, South Shore receives the majority of diverted industrial wastewaters in the MMSD service area. In 1974, South Shore was expanded and upgraded to provide secondary treatment utilizing an activated sludge process. The plant has conventional barscreens, grit removal tanks, primary clarification, activated sludge basins, final clarification and sodium hypochlorite disinfection. South Shore currently has a maximum treating capacity of 250 million gallons per day (MGD) and a peak flow of 300 MGD. Average flows are maintained from 65-85 MGD. Description of Problem South Shore has an extensive collection and tunnel system that creates anaerobic/anoxic conditions during warmer months. This results in elevated levels of hydrogen sulfide (2.0 mg/l - >5.0 mg/l) as well as organic volatile fatty acids (250mg/l - 400 mg/l) entering the plant. Elevated levels of soluble BOD (300mg/l -400mg/l) and COD (900-1400 mg/l) entering the plant are also typical. Ortho-phosphorous and nitrogen deficiencies are typically below the recommended BOD5:P ratio of 100:1. It is suspected that elevated ferric chloride dosing concentrations prior to the primary clarifiers designed to aid sedimentation may be contributing to this situation. It is also suspected that this overall combination of factors is leading to an overgrowth of filamentous bacteria in the activated sludge basins that further effects sedimentation in the secondary clarifiers. Since filamentous bacteria have been demonstrated to overgrow where an organic acid concentration of >100 mg/L and a sulfide concentration of >1-2 mg/L exist it is logical to assume that a reduction in these two factors may reduce filamentous growth and lead to improved settling.

Figure 1 Corrective Action Treatment Method In July of 2020, Streamline Innovations and Veolia North America partnered with Veolia Operations to perform a study to determine if a REDOX Process could reduce sulfides, and decrease filamentous bacterial populations to improve settling and reduce bulking. The REDOX process utilizes a patented liquid organically bound iron that is dosed in combination with an oxidant, in this case 50% peroxide. The REDOX reaction that takes place is as follows: Overall Reaction The hypothesis of the trial was centered on the premise that reducing total sulfide and volatile fatty acid levels using a vigorous REDOX process, filamentous growth would not have sufficient food leading to a reduction in their prevalence and improved settling of solids in the activated sludge basins and secondary clarifiers. The treatment goals were to maintain total sulfide levels at <0.8 mg/l. A Hach spectrophotometer was used to verify sulfide levels in the wastewater. H2S atmospheric levels were also monitored before and after treatment to verify gaseous reductions in hydrogen sulfide before and after treatment to further document the efficacy of the REDOX process. The detention time between REDOX chemical injection and water testing was around 1.5 hours under normally occurring flows. Total sulfide tests were conducted every 6 hours from the primary influent and 1-2 times per day from the injection manhole. An average dosage of 80 gallons per day of organically bound iron and 500 gallons per day of 50% peroxide were dosed into the headworks.

Conclusions
Sulfide levels decreased after treatment and maintained averages of 0.25 mg/l. After approximately 5 days, filamentous populations began to drop in the activated sludge basins (Averages ranging from 3.5-4.5 down to 1.5-2.0). Nuisance. Odors in the preliminary building, grit chamber and primaries were also noted to have improved. At the time of this submittal the destruction of hydrogen sulfide, a notable food source for filamentous organisms, correlates with a significant reduction in 021N and Thiothrix sp. filaments to manageable levels. A reduction in hydrogen sulfide corrosion in the front of WRF is also expected and will be studied. As of the writing of this submittal, there have been no deleterious effects to the overall operations of South Shore WRF using the described REDOX treatment approach. Since this chemistry has been used in scores of wastewater plants, none are expected. Additional research on the reduction of iron chloride use in the primary influent is ongoing and is expected to paint a more complete picture on microorganism species richness and diversity impacts and sludge volume index (SVI) metrics. Further studies to understand the organic acid concentrations before and after treatment are currently underway.