stormwater treatment - neil alongi, maul foster alongi
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ELEC WASHINGTON STORMWATER CONFERENCE
STORMWATER TREATMENT AND
TECHNOLOGY
Neil Alongi, P.E. – Maul Foster & AlongiFebruary 7, 2011
Hierarchal approach to compliance Large and small site challenges Characterization Treatment BMPs: Selection
Considerations Cost of compliance- Reasonably
attainable? Thoughts about the future of Treatment
BMPs
DISCUSSION OVERVIEW
Treatment BMPs = Capital + Operational Costs e.g. Active Treatment
Structural BMPs = Capital costs e.g. materials isolation
Operational BMPs e.g. Pavement sweeping
BMP HIERARCHY APPROACH
STRUCTURAL BMP EXAMPLE
Large site = High volumes and flow rates Flow attenuation a critical factor Complexity of contaminants challenging
TREATMENT BMPs – SITE SIZE
Site space limitation usually results in additional costs to manage & treat
May force facilities underground Operations personnel may be limited
SMALL SITE STORMWATER CHALLENGES
Sites with little available space = underground storage + high rate treatment system Underground storage = high cost Shifts costs to high rate treatment
systems Cost balance between these two
components
QUANTITY CONTROL
UNDERGROUND STORAGE
Like any site, must first characterize contamination and understand goals Check permit parameters Check parameters that may impact
treatment, e.g. dissolved metals Internal monitoring
Diverse contamination types May mean more than one type of
treatment to meet permit benchmarks
CHARACTERIZE FIRST
Most problematic contaminant types Metals, especially dissolved metals High turbidity from colloidal
particles Chemical Oxygen Demand (COD) Biological Oxygen Demand (BOD) Nutrients (Phosphorus, Nitrate,
Nitrite)
TYPICAL CONTAMINATION
PASSIVE EXAMPLES Created wetland Bioretention filtration
ACTIVE EXAMPLES Polymer – enhanced filtration Cartridge Filtration Adsorptive Filtration Electrocoagulation Multi-stage treatment
TREATMENT TECHNOLOGIES
Treatment dependant on detention/travel Low cost option TSS, oils/grease, some metals removal Space intensive
PASSIVE - CREATED WETLAND
Treatment and infiltration Low cost option Site and soil conditions critical Preferred SW
management approach
PASSIVE - BIORETENTION FILTRATION
Treatment and discharge Biomass retention of pollutants Natural and manufactured media Adsorptive
filtrationmediaapplication
e.g., Filterra –Ecology GULD
BIORETENTION FILTRATION
Most commonly used is chitosan TSS and turbidity High treatment capacity
POLYMER-ENHANCED FILTRATION
Mixed media cartridge inside vault TSS, P, turbidity and some metal Typical Zn removal efficiency of 45%
and 38% for total and dissolved Typical Cu removal efficiency of 50%
and 40% for total and dissolved Life of cartridge highly dependent on
site conditions e.g. Bayfilter – Ecology Conditional Use
Filtration – Cartridge Filters
Reactive media with targeted contaminant removal
May first need pretreatment for pH or to remove larger particles
Media for metals, coliform, nutrients
Adsorptive Filtration
Dual media gravity filtration Adsorptive filtration for metals Multi-stage treatment available e.g. StormwateRx
Adsorptive Filtration
ADSORPTIVE MEDIA
Effective for a variety, but not all, contaminants
High capital, moderate O& M Metal removal rates around 90% Treatment train can include pH,
settling, filtration e.g. WaterTectonics, Oil Trap
ELECTROCOAGULATION
ELECTROCOAGULATION
Single-stage advanced treatment is expensive
Multiple stage treatment more so
Multi-stage approach driven by either low effluent limits or a wider variety of contaminants
MULTIPLE STAGE TREATMENT
Example of advanced treatment system designs includes Pre-settling pH adjustment Electrocoagulation Settling Pressure Sand Filtration Micron-level cartridge filtration
MULTIPLE STAGE TREATMENT
MULTIPLE STAGE TREATMENT
Receiving Water Bodies Direct discharge
Diffuser outfall for enhanced dilution
DISPOSAL OPTIONS
Municipal Storm Sewer – potential dilution
Municipal Sanitary Sewer – potential higher limits
Infiltration – potential for no monitoring except bypass
DISPOSAL OPTIONS
Implications of stormwater permit requirements starting to set in
Development of new technology driven by demand
Pacific NW - leading role in R & D Capital and O & M costs will be
closely analyzed Need for guidance on “Reasonable”
TRENDS FOR THE FUTURE
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