Full Scale Trial of a Low-Hazard Buffered Iron Product (SulFeLox®) to Control Hydrogen Sulfide Odors at The City of Portland, OR

BACKGROUND The City of Portland serves over 600,000 customers and about 100 sewage pumping stations and more than 2,500 miles of sewer pipes conveying to the Columbia Boulevard Wastewater Treatment Plant. Focusing on one of the major stations; 86AV and Fanno Basin (FABA) pumping station consists of two pump sets designed to operate at all times. 86AV the 'LEAD' pumping facility for base flows up to 15 MGD (23 cfs) and FABA will operate during 'wet' season to increase flow to 30 MGD (46.5 cfs). Historically 86AV and FABA is equipped with a chemical feed system injecting calcium nitrate into the wetwell. 86AV and FABA discharge to two 30-inch force mains, referred to as Line A and Line B, each approximately 16,000 feet in length with a retention time of 4 – 8 hours. The Burlingame Trunk Sewer (BTS) conveys the flows from the 86AV and FABA FM discharge structure to the Southwest Parallel Interceptor (SWPI) along Taylors Ferry Rd and SW Virginia Ave. The Taylors Ferry Ventilation odor control facility (ARQ452) extracts foul air from the sewer system at SW Virginia Avenue at Taylors Ferry Road via a 24-inch odorous air duct. The City of Portland receive numerous odor complaints along the BTS and SWPI, particularly along SW Custer St and SW Virginia Avenue. These complaints have correlated to the force main discharge odor migration from 86AV and FABA FM discharge. The City attempt to control these odors with calcium nitrate, which is injected at 86AV PS wetwell. Odor from the 86AV and FABA FM discharge continues to cause odor complaints at the FM discharge and downstream gravity segments with addition of calcium nitrate. The City of Portland and Carollo Engineering requested evaluation of an alternative low hazard chemical dose approach to effectively address odor release at the 86AV and FABA force main discharge and reduce vapor and liquid H2S migration downstream along the gravity segments. USP Technologies along with the City of Portland and Carollo Engineers conducted a 6-week field demonstration comparing cost and performance efficiency of a low hazard buffered -Fe product (SulFeLox®) feeding at 86AV and FABA PS in the fall of 2020 to compare to the current calcium nitrate program. Extensive sampling and monitoring took place during the 6-week field demonstration looking at performance, usage rate, and cost comparing SulFeLox® to calcium nitrate at the force main discharge structure and downstream gravity interceptor. OBJECTIVES Compare performance efficiency of low hazard buffered iron (SulFeLox®) to historical calcium nitrate for hydrogen sulfide odor control along the 86AV and FABA Pumping Station FM discharge and impact downstream of the gravity interceptor segments. The trial focused on the following: - Reduce hydrogen sulfide odor generation at the 86AV and FABA Pumping Station force main discharge and downstream along the gravity segments of the interceptor - Document and log odor complaints during the duration of the trial and compare to historical odor complaints logged - Determine treatment cost and chemical usage at equal and improved performance to calcium nitrate at the 86AV and FABA Pumping Station discharge and downstream gravity segments of the interceptor METHODOLOGY Both vapor and liquid H2S were collected throughout the trial period. Data loggers (OdalogTM) were used and deployed at two main control points 1) 86AV and FABA Pumping Station FM discharge and 2) gravity segment at 1.5 miles downstream from the FM discharge point. Liquid samples were also grabbed at the two locations listed above. Liquid grabs were taken every day once during the AM and PM periods. Each liquid sample were analyzed on the spot for the following: - Total and dissolved sulfide - Liquid and ambient temperature - pH - Total and soluble iron The City of Portland and Carollo Engineers provided historical vapor and liquid data based on calcium nitrate feed in 2020 and the data collection provided would yield valid comparison between the two technologies. FINDINGS The calcium nitrate treatment level of 72 gpd was followed by a SulFeLox® rate of 98 gpd for six days which translated to three days of treatment on each force main due to the operations practice of alternating between the FM each day. A 55% reduction in H2S vapor levels were observed at the force main discharge, and a 95% reduction in H2S vapor levels at the downstream interceptor monitoring point during the conditioning phase when compared to calcium nitrate. Following the conditioning-period, SulFeLox® dose was reduced to 72 gpd to match the calcium nitrate dose. At the same dosage of 72 gpd, SulFeLox® showed a 63% and 96% vapor reduction when compared to calcium nitrate at the FM discharge and downstream gravity segment respectively. (Table 1, Figures 2 & 3) The City of Portland requested to use 144 gpd of calcium nitrate as the optimized feed rate for upcoming rate comparisons. Three different SulFeLox® rates were tested during the trial: 72 gpd, 48 gpd, and 37.5 gpd. Below are vapor percent reduction when compared to 144 gpd of calcium nitrate (Table 2, Figures 4, and 5): - 77 GPD SulFeLox® – 42% and > 99% respectively at the FM discharge and downstream gravity interceptor. - 48 GPD SulFeLox® – 27% and > 99% respectively at the FM discharge and downstream gravity interceptor. - 38 GPD SulFeLox® – 4% and 84% respectively at the FM discharge and downstream gravity interceptor. RELAVANCE Iron salts are an inexpensive solution, their hazardous nature constrains use outside the treatment plant, particularly for smaller pump stations in commercial districts and residential communities. Chemicals with lower hazard levels, such as calcium nitrate, are thus the odor control technology of choice for many such applications (Jiang, 2009). SulFeLox® is a low-acidity form of iron salt, having a pH of approximately 4.0-4.5 which contributes to its low skin irritation potential and carrying an NFPA placard of 1-0-0. Having a low hazard iron product option, as an alternative to e.g., calcium nitrate and magnesium hydroxide, allows agencies to access the inherent benefits of iron for controlling sulfide levels in sewer lines that pass through residential neighborhoods and commercial districts. Based on the trial at the City of Portland, the SulFeLox® technology provided equal to better performance when compared to calcium nitrate at the 86AV and Fanno Basin (FABA) pumping station FM discharge and downstream gravity interceptor segments. Results clearly validated that a reduction in chemical feed by 74% (37.5 gpd SulFeLox® vs 144 gpd calcium nitrate) and 60% (29 gpd SulFeLox® vs 72 gpd calcium nitrate) during the fall and winter seasons respectively. This would result in reduce chemical delivers and overall annual chemical expenditure of 25% for the City of Portland.