Alum Treatment System

Alum Treatment System - 3.3.9 Alum Treatment System Limited...

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Unformatted text preview: 3.3.9 Alum Treatment System Limited Application Structural Stormwater Control Description: Chemical treatment of stormwater runoff entering a wet pond by injecting liquid alum into storm sewer lines on a flow-weighted basis during rain events. REASONS FOR LIMITED USE • Intended for areas requiring regional stormwater treatment from a piped stormwater drainage system • High maintenance requirements STORMWATER MANAGEMENT SUITABILITY Water Quality Channel/Flood Protection KEY CONSIDERATIONS • Requires no additional land purchase • Reduces concentrations of total phosphorus, total aluminum and heavy metals • Dependent on pH level ranging from 6.0 to 7.5 during treatment process • High capital and operations and maintenance costs SPECIAL APPLICATIONS Pretreatment High Density/Ultra-Urban Other: Regional Treatment Residential Subdivision Use: Yes General Description The process of alum (aluminum sulfate) treatment provides treatment of stormwater runoff from a piped stormwater drainage system entering a wet pond by injecting liquid alum into storm sewer lines on a flow-weighted basis during rain events. When added to runoff, liquid alum forms nontoxic precipitates of aluminum hydroxide [Al(OH)3] and aluminum phosphate [AlPO4], which combine with phosphorus, suspended solids and heavy metals, causing them to be deposited into the sediments of the receiving waters in a stable, inactive state. The alum precipitate formed during coagulation of stormwater can be allowed to settle in receiving water or collected in small settling basins. Alum precipitates are stable in sediments and will not redissolve due to changes in redox potential or pH under conditions normally found in surface water bodies. Laboratory or field testing may be necessary to verify feasibility and to establish design, maintenance, and operational parameters, such as the optimum coagulant dose required to achieve the desired water quality goals, chemical pumping rates and pump sizes. Construction costs for existing alum stormwater treatment facilities in Florida have ranged from $135,000 to $400,000. The capital construction costs of alum stormwater treatment systems is independent of watershed size and depends primarily on the number of outfall locations treated. Volume 2 (Technical Handbook) Georgia Stormwater Management Manual 3.3-47 Estimated annual operations and maintenance (O&M) costs for chemicals and routine inspections range from approximately $6,500 to $25,000 per year. O&M costs include chemical, power, manpower for routine inspections, equipment renewal and replacement costs. Pollutant Removal Capabilities Alum treatment has consistently achieved a 85 to 95% reduction in total phosphorus, 90 to 95% reduction in orthophosphorus, 60 to 70% reduction in total nitrogen, 50 to 90% reduction in heavy metals, 95 to 99% reduction in turbidity and TSS, 60% reduction in BOD, and >99% reduction in fecal coliform bacteria compared with raw stormwater characteristics. The following design pollutant removal rates are conservative average pollutant reduction percentages for design purposes derived from sampling data, modeling and professional judgment. • • • • • Total Suspended Solids – 90% Total Phosphorus – 80% Total Nitrogen – 60% Fecal Coliform – 90% Heavy Metals – 75% Design Criteria and Specifications Alum treatment systems are fairly complex, and design details are beyond the scope of this Manual. However, further information can be obtained from the Internet and by contacting local municipalities and engineers who have designed and implemented successful systems. The following are general guidelines for alum treatment systems: Injection points should be 100 feet upstream of discharge points. Alum concentration is typically 10 µg/l. Alum treatments systems may need to control pH. For new pond design, the required size is approximately 1% of the drainage basin size, as opposed to 10 to 15% of the drainage basin area for a standard detention pond. No volume requirement is required when discharging to existing lakes. Inspection and Maintenance Requirements Table 3.3.9-1 Typical Maintenance Activities for Alum Treatment (Source: Harper, Herr, and Livingston) Activity • • • Perform routine inspection. Monitor of water quality and pH. Perform maintenance of pump equipment, chemical supplies and delivery system. Schedule Monthly As Needed 3.3-48 Georgia Stormwater Management Manual Volume 2 (Technical Handbook) Figure 3.3.9-1. Alum Treatment System and Injection Equipment Volume 2 (Technical Handbook) Georgia Stormwater Management Manual 3.3-49 This page left intentionally blank 3.3-50 Georgia Stormwater Management Manual Volume 2 (Technical Handbook) ...
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This note was uploaded on 05/25/2010 for the course CE 798 taught by Professor Hunter during the Spring '10 term at Morgan.

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