City of Tolleson WWTP
Tolleson, Arizona
The City of Tolleson, Arizona operates a 44.7 cubic meter per hour (m3/hr) [17 million gallon per day (mgd)] capacity, wastewater treatment plant (WWTP). Several residential and commercial developments have been built within ½ kilometer of the Plant and odor complaints have increased. The Plant-wide odor control study was initiated in 2006 to determine the best long-term odor control approach. The initial results of the odor study, plus the urgency of the situation with adjacent neighborhoods, required immediate odor mitigation efforts – specifically by implementing an aggressive chemical addition program utilizing ferric chloride plus hydrogen peroxide. The most significant results and findings of this project were:
• High sulfide concentrations are primarily due to high BOD5 influent in Tolleson interceptor and sludge thickening in the primary clarifiers.
• High dissolved sulfide concentrations in the primary effluent cause high H2S release at the top of the trickling filters.
• Ferric chloride alone provides the majority of sulfide control. Hydrogen peroxide produces an additional 10 to 15 percent dissolved sulfide in the PCs. Hydrogen peroxide provide some additional H2S control at the TFs, however, ferric chloride is the more predominate odor control chemical.
• Chemical dosages are relatively high and will cost the City several hundred thousand dollars per year. Thus, the planned, long-term odor control improvements should be implemented. Faster sludge withdraw and air phase odor control at covered primary clarifiers will greatly minimize the need to add chemical at such high dosages. The cost of operating biological scrubbers will be much less than continued chemical addition.
• Maintaining chemical addition capability is appropriate. The trickling filters cannot be economically covered, and therefore, odor control from the filters must rely on process improvements plus the ability to add chemical as needed.
• This project has clearly demonstrated that chemical addition can be beneficial to TF odors and is a viable means to achieve lower TF odor emissions. Source: WEFTEC 2009 Proceedings
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Posted: August 27th, 2010 | Filed under: Waste Water Treatment | Tags: Improved Neighbor Relations, Odor Control | No Comments »
91st Avenue Wastewater Treatment Plant
Phoenix, Arizona
The implementation of centrate nitrification as part of the 91st Avenue WWTP’s conversion from Class B to Class A biosolids has achieved the dual benefits of nitrogen removal and odor control. A significant expansion in biological reactor capacity and/or methanol addition has been avoided and preliminary results indicate that the City may be able to avoid a $40 million (US) capital expenditure to cover the twelve existing 43 m diameter primary sedimentation basins and treat the foul air in wet chemical scrubber systems.
• Nitrogen Removal- The centrate nitrification facility is achieving 50 percent ammonia oxidation to nitrite-nitrate without the addition of supplemental alkalinity, resulting in a 9% reduction in the primary effluent nitrogen concentration to the main activated sludge facilities. A return of approximately 1,300 kg/d of nitrite-nitrate to the headworks is resulting in 2.5 mg/L as N of oxidized nitrogen at the current WWTP influent flow rate of 5.9 m3/s.
• Odor Control- A 70 percent reduction in measured gaseous H2S concentrations in the plant headworks odor control scrubber influent from 17 to 5 ppm has resulted in a 67 percent reduction in odor control wet scrubber chemical (sodium hydroxide and sodium hypochlorite) costs, from $460 to $150 (US) per day. A reduction in the H2S emissions from an uncovered primary sedimentation basin were demonstrated in the center well (11 ppm to 1 ppm) and effluent weir (12 ppm to 6 ppm) with the discharge of oxidized nitrogen to the headworks from the centrate nitrification facility. Source: WEFTEC 2009 Proceedings
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Posted: August 27th, 2010 | Filed under: Waste Water Treatment | Tags: Environmental Impact, Odor Control, Optimize Digestion Capacity | No Comments »
City of Fargo WWTF
Fargo, North Dakota
Historically, ferrous chloride (FeCl2) injection has been utilized to successfully control odors and corrosion within the sanitary sewer collection system of Fargo, North Dakota. However, increased odor complaints prompted an evaluation of the odor conditions present in the sanitary sewer system. Study results indicated that the current FeCl2 dosing rate was insufficient to control odors. In response, a number of liquid phase odor control treatment alternatives were evaluated. Due to the existing FeCl2 injection program, iron regeneration and improved odor control were realized through the innovative use of hydrogen peroxide. A program was initiated to demonstrate the efficacy of the proposed treatment strategy on a full-scale level. In response to improved sulfide treatment, reduced FeCl2 injection rates, and economic benefits realized during the demonstration program, the City of Fargo elected to incorporate PRI-SC as part of their upcoming collection system improvements. Variable dosing strategies for FeCl2 and H2O2 were incorporated for efficient odor control. The injection rates will fluctuate based on diurnal and seasonal sulfide loadings to prevent overdosing and reduce overall chemical costs. Hydrogen peroxide injection will be utilized to regenerate spent FeCl2 at a new 151,410 m3/d (40 mgd) sanitary lift station located in north Fargo. The PRI-SC technology will serve to reduce odors and corrosion in the 750 mm (30 inch) diameter forcemain from the new lift station and at the forcemain discharge at the WWTF headworks. While PRI-SC was found to be beneficial for the City of Fargo, any liquid phase technology should be evaluated for effectiveness based on site specific conditions. Source: WEFTEC 2009 Proceedings
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Posted: July 6th, 2010 | Filed under: 100K-500K, Waste Water Treatment | Tags: Cost Savings, Innovative Approach, Odor Control | No Comments »