The BSTF Train Ride- A Journey from the Station to Your Own Pond Destination

Transcription

1 The BSTF Train Ride- A Journey from the Station to Your Own Pond Destination Practical Knowledge for Tailoring BMP Treatment Processes to Various Water Chemistries Integrated Engineering Solutions for Florida s Water Environments Mark J. Flint, PE and Dr. Marty Wanielista, PE

2 Today s Agenda What is the BSTF? Mass Reduction Differs from Treatment Efficiency The Treatment Train BMP Toolbox Understanding Nutrient Cycles The Challenge of Wet Detention Treatment Inter-event Treatment is a Strategic BMP Option Potential Benefits of Inter-event Treatment When do I consider Inter-event Treatment? Conclusion

3 What is the BSTF? The Briarwood Stormwater Treatment Facility (BSTF ) is an innovative management approach for improved wet detention treatment that was constructed and operated by Sarasota County Government from September, 2013 through March, Today the BSTF remains operational as a continuous stormwater treatment system. During the 18 month period of monitoring, the BSTF was found to remove an estimated 24 Tons of TSS, 1.3 tons of TN, and 129 Lbs. of TP.

4 What is the BSTF? The BSTF is an Innovative Inter-event Treatment Train known formally as the Briarwood Stormwater Treatment Facility Funded by Sarasota county and an FDEP 319 grant fund Constructed in 2011 for approximately $1.8 million BSTF began formal operations in 2013, now data in final review by FDEP BSTF treats stormwater from a +/- 65 acre wet detention system The BSTF is an inter-event treatment train that does not rely on rainfall; treatment is independent of runoff rate (flow) BSTF has capability to operate 24/7 at low steady state flow The BSTF is a text book example for meeting the challenges of enhanced wet detention treatment

5 What is the BSTF? The BSTF Demonstrates LID and Sustainability Practices in Design and Operations The BSTF includes LID practices of pervious pavements and stormwater harvesting in the train Sustainable features of the BSTF include use of many recycled materials-i.e. recycled concrete, tire crumb, and even the project property (former WWTP) is re-purposed! The 180 ft. By 8 ft. deep anaerobic zone filter is constructed from broken concrete aggregate Bold and gold media is comprised of recycled tire (tire crumb) Any existing useful site features were salvaged (i.e. An old unused power pole was re-purposed for lighting)

6 SHAMROCK RD. N BRIARWOODS LAKE BASIN VENICE FL (Approx. 650 ACRES) BRIARWOOD RD. BRIARWOOD BSTF (APPROXIMATELY 5 ACRES)

7 The BSTF treatment train is long and it is driven by high capacity, low head pumps. It features an anaerobic rock filter and up-flow media filter system

8 What is the BSTF? BSTF Influent Pumping Rate (GPM) Adjusted BSTF Daily Treatment Capacity ( MGD) Estimated BSTF Annual Treated Flow Capacity (MGY) Percentage of Treatment of Projected Annual Stormwater Runoff % 1, % 1, % 1, % 1, % The BSTF is an inter-event system that has capacity to treat 1 to 2.3 times the annual runoff, allowing for higher pollutant mass reduction.

9 What is the BSTF? THE ANAEROBIC ZONE AND UPFLOW FILTER PLAN ANAEROBIC ROCK ZONE UPFLOW FILTER (TYP.) ANAEROBIC ROCK ZONE ANAEROBIC ROCK ZONE THE UPFLOW FILTER SECTION

10 Inside the filter system (during construction)

11 Completion of the anaerobic zone rock filter

12 THE BSTF IN OPERATION (Taken 2014) PUMP STATION A (INFLUENT) PUMP STATION B (INFLUENT) STORMWATER HARVESTING/IRRIGATION N DECOMPOSTION ZONE (CATABOLISM AND DECAY) FLOATING WETLAND STORMWATER HARVESTING/IRRIGATION SETTLING AEROBIC ZONE ANAEROBIC ZONE (ROCK FILTERS) UPFLOW MEDIA FILTERS RE-AERATION ENGINEERING GROUP, INC INC..

13 LILLY SURFACE COVERAGE FLOATING ISLAND BSTF DECOMPOSITION ZONE (SORPTION OF ALGAL BIOMASS, CATABOLISM AND DECAY-RELEASE OF AMMONIA AND DECOMPOSITION BYPRODUCTS)

14 Mass Reduction Differs from Treatment Efficiency Stormwater Managers and Engineers are Expected to be Focused on Removal Efficiency, Cost Effectiveness, and $/Lb. Old traditional treatment designs utilized presumptive rules and assumptions-like 80% TSS and TN removals for wet detention--yet only a small percentage of runoff is treated Research has improved modern wet detention treatment and newer treatment designs can achieve higher solids capture and nutrient reduction but still realize about 40% reduction in nitrogen-and that is considered good The USEPA NPES program is concerned about treatment efficiency and mass loading to water bodies!

15 Mass Reduction Differs from Treatment Efficiency Fact: The true effectiveness of stormwater mass pollutant reduction does not just rely on efficiency of treatment but the volume of runoff that is treated. Consideration: Although the stormwater profession has dramatically increased our understanding of the efficiency of wet detention design, old school design ponds are out there and may not function well! Consideration: Wet detention ponds accumulate organic solids; How may wet ponds are serviced every 10 years? Do they remove 10 years of solids accumulation?

16 The Treatment Train BMP Toolbox Stormwater Treatment Best Management Practices Include Traditional Approaches Dry retention and infiltration Wet detention Wet detention with exfiltration Effective nutrient BMP design requires us to understand nutrient cycles Specialized media biologically active filters (in ponds) Biologically enhanced systems (wetlands and flowways) Chemical treatment (alum) Other physical treatment (baffle boxes, hydrodynamic separators

17 Understanding Nutrient Cycles There is More to Understanding Total Nitrogen than First Meets the Eye!!! FORMS OF TOTAL NITROGEN ORGANIC NITROGEN INORGANIC NITROGEN BIOMASS ALGAL CELLS, FUNGI AND BACTERIA EMERGENT PLANTS DISSOVED ORGANIC NITROGEN "AMIDE" GROUPS, AMINO ACIDS, PROTEINS NH4 NH3 NO3 NO2 ATMOSPHERIC NITROGEN

18 Understanding Nutrient Cycles Organic Solids- Algae, Bacteria and Vegetation (Assimilation) Decomposition (Decay and Catabolism) Nitrogen Gas- Product of Denitrification (Denitrification)

19 Understanding Nutrient Cycles UNLIKE NITROGEN, PHOSPHORUS DOES NOT RETURN TO THE ATMOSPHERE

20 Understanding Nutrient Cycles How does nitrification and denitrification really work? NH 4 >>>>> NH 3 >>>>>>>>>>>>> NO 2 >>>>>>NO 3 Nitrosomas and Nitrobacter do the work in aerobic environment The process requires oxygen-lots of it Nitrification consumes alkalinity and low alkalinity can limit effectiveness Denitrification is conversion of nitrate to nitrogen gas 2 NO e + 12 H + N H 2 O Facultative bacteria reduce nitrate-acceptance of electrons Facultative bacteria need to eat Carbon is food, or alternative electron donar is needed Needs low DO to convert to anoxic reactions Annamox-yet another less understood pathway NH NO 2 N H 2 O Bacteria convert ammonium directly to nitrogen gas in aerobic environment

21 Bacteriological Nutrient Uptake is Very Complicated Nitrification occurs from genus Nitrobactor and Nitrosomas Denitrification occurs from genus Flavobacterium Many bacteria are facultativethey can change respiratory pathways between aerobic and anaerobic Biological phosphorus uptake (PO 4 ) is slower and is assimilative only Understanding Nutrient Cycles Electron microscope image courtesy University of Wisconsin, Madison

22 The Challenge of Wet Detention Treatment Wet Detention Ponds with Long Residence Periods can Cause an Unwanted Conversion of Nutrients! CONSIDER THIS SAMPLE: TN > 2.5 MG/L TP > 0.2 MG/L TSS > 40 MG/L Nitrogen + Phosphorus + Sunlight = Reacted Nitrogen (Organic N and P)

23 The Challenge of Wet Detention Treatment Sometimes Urban Lakes Become Detention Ponds! This is an example of long term stormwater nutrient loads that regenerate available nitrogen (this caused fish kills) Nitrogen + Phosphorus + Sunlight = Reacted Nitrogen (Organic N and P)

24 This is What the Intake of the BSTF Looks Like The Challenge of Wet Detention Treatment BSTF Was challenged with very bad water chemistry! Near 100 percent nutrients are reacted Total suspended solids fraction of volatile organics is near 100 percent The BSTF treatment goal was based on tough standards

25 The Challenge of Wet Detention Treatment Modern Wet Detention Utilizes Littoral Shelf Design Near the Outfall and Optimal Pond Geometry (i.e.10l x W) Wet pond depth is sufficient for storing sediments in permanent pool-not exceeding 8 ft. Some states require a fore-bay to enhance solids settling Settling relies on TSS characteristics; Organic solids are generally harder to settle Realized performance factor for non; Volatile TSS removal is 30-60% MOSTLY INERT SOLIDS Sediments Include Both Inorganic and Organic Solids

26 The Challenge of Wet Detention Treatment What if We Have an Old School Wet Pond (Designed prior to the ERP Rules?) TSS -RUNOFF Hydraulic residence time (HRT) is a key in controlling nutrient conversion Non volatile total suspended solids-- inorganic fraction (conservative pollutants) accumulate in ponds Volatile suspended solids--usually low (outside of floating vegetation solids) Literature does not report details on stormwater VSS/TSS VSS/TSS ratio can increase from algal growth to be the major source of solids NON-VOLATILE (INERT) VOLATILE (ORGANIC) TSS HRT < 14 DAYS NON-VOLATILE (INERT) VOLATILE (ORGANIC) TSS HRT> 30 DAYS NON-VOLATILE (INERT) VOLATILE (ORGANIC)

27 The Challenge of Wet Detention Treatment Long HRT Allows for Conversion of Nutrients to Algal Biomass As inert solids settle, organic solids are generated Estimates of 72,500 species of algae! Freshwater algae fall into two main groups: Blue green and Green Algae can be animated --they can move and shake Algae can be single or multi-celled, eukaryotic or prokaryotic, planktonic or periphytic Algal cells range in size from 3 microns to over 15 microns--very SMALL!! LYNGBYA-A BLUEGREEN ALGA SPIROGYRA-A GREEN ALGA

28 Inter-event Treatment is a Strategic BMP Option Continuous Inter-event Treatment Offers Several Strategic Advantages Wet pond treatment can be improved with steady state controls; This allows for lower but reliable treatment efficiency Old school wet detention systems can be retrofitted to improve performance Long term lower continuous flow option can treat 100% or more of the runoff volume and remove larger mass quantities than traditional treatment Inter-event treatment train systems can add amenities and function to enhance wet pond water quality

29 Inter-event Treatment is a Strategic BMP Option Examples of Inter-event Treatment for Wet Detention: Stormwater harvesting from wet detention pond (irrigation occurs in dry period between rainfalls) Strategically placed fountains (in deep pool) Specialty designed recirculating filters (i.e., Up-flow media filter) Mechanical filtration (i.e., Disc filtration) Chemical treatment

30 Potential Benefits from Inter-event Treatment Here is an Example of the Effectiveness of Inter-event Treatment A hypothetical TMDL requires stringent mass reduction goals as follows: Annual TSS Load < 12 tons Annual TN Load < tons Annual TP Load < 600 lbs. 500 AC RESIDENTIAL URBAN WATERSHED EXISTING REGIONAL POND EXAMPLE WATERSHED DATA Watershed Area = 500 Acres Annualized Runoff = 450 Ac-Ft CN = 78 HRT (Avg.) = 90 Days Pond Depth = 5 Ft. Annual TSS Load = 23 tons/yr. Annual TN Load = 1.3 ton/yr. Annual TP Load = 650 tbs./yr.. Existing TSS = 0.30 (75% Volatile)

31 Potential Benefits from Inter-event Treatment Estimated Monthly Runoff (CF/Month) 8,000,000 7,000,000 6,000,000 5,000,000 4,000,000 3,000,000 2,000,000 1,000,000 0 Hypothetical Stormwater Runoff and TSS Loads from 500 Acre Urban Drainage Basin MONTHLY RUNOFF (CF) TOTAL MONTHLY MASS LOADING (LBS) Total Mass Loading (lb./month) Month

32 Potential Benefits from Inter-event Treatment PROJECTED IMPROVED INTER-EVENT TSS MASS REMOVAL IN OUR EXAMPLE POND CAN MEET THE IMPOSED TMDL INCREASED TSS REMOVAL BY 9,300 LBS FLOW RATE OF INTER-EVENT TREATMENT SYSTEM (GPM) PROJECTED ANNUAL MASS REMOVAL WITH INTER-EVENT TREATMENT ADDED PROJECTED ANNUAL MASS REMOVAL WITH TRADITIONAL POND 0 5,000 10,000 15,000 20,000 25,000 PROJECTED ANNUAL TSS MASS REMOVAL (LBS) 750 GPM INTEREVENT TREATMENT AT 80% OPERATIONAL TIME IS PROJECTED TO INCREASE ANNUAL TSS MASS REMOVAL BY 9,300 LBS TO MEET TMDL AND IMPROVE EFFICENCY TO 50%

33 Potential Benefits from Inter-event Treatment Hypothetical Inter-event Treatment Scheme: Install Recirculating Upflow Media Filters and Floating Vegetation as Pre-filtration 7 HP low head pumping system (750 20ft) 200 LF serviceable up-flow filter system Install floating vegetation zone ahead of filter (pre-sorption) Install fountain for aeration FLOATING VEGETATION ZONE UPFLOW FILTER CELLS AND PUMP (TYP 2 FILTERS AT SHORELINE) AERATED FOUNTAIN EXAMPLE TREATMENT SYSTEM FEATURES This is a single Treatment BMP Serviceable up-flow filters can be checked and maintained annually!

34 Potential Benefits from Inter-event Treatment How Effective is Interevent Treatment in This Example? Inter-event treatment system required no additional land for construction This 750 GPM example met the TMDL challenge with a single project vs. multiple ones that treat only small fractions of the runoff. FLOATING VEGETATION ZONE UPFLOW FILTER CELLS AND PUMP (TYP 2 FILTERS AT SHORELINE) EXAMPLE TREATMENT RESULTS MET TMDL WITH ONLY 20% EFFICIENCY IN UPFLOW FILTER Annual TSS Load =11.4 Tons Annual TN Load = Tons Annual TP Load = 600 Lbs. (Note only 10% Reduction in TP)

35 Potential Benefits from Inter-event Treatment Inter-event Treatment Relies on Both Physical and Biological Processes; In our Example Media Filters: Settling: Inorganic solids settle more readily Organic TSS removal by adsorption mechanism Adsorption: The Physical sticking of organic solids to other plants, media, and rock Rock and up-flow filter is biologically active Electron microscope image courtesy of University of Central Florida

36 Potential Benefits from Inter-event Treatment There are Many Types of Media Processes (I.e., Bold and Gold Media) That Hold Promise for Continued Advancement in Control of Organic Solids Sorption sites have limitations Solids capture and biological growth require occasional cleaning and removal after time See UCF Stormwater Management Academy for more research data; This is a typical column study

37 When Do I Consider Inter-event Treatment? Consider Inter-event Treatment When Old School Wet Detention Fails to Achieve Desired Reduction in Pollutant Mass Wet detention ponds are older than 30 years TMDL or other regulations require higher level mass removal than possible from traditional wet detention pond When wet detention pond has HRT > 30 days Pond geometry and morphology are not conducive to good solids capture (i.e., Pond is too shallow) When nutrients are reacted and organic (high chlorophyll)

38 When Do I Consider Inter-event Treatment? When Source Control BMP s May Not Make Sense, Inter-event Treatment Might be an Option Multiple smaller upstream points of BMP treatment may not be feasible Community demographics are not amenable to public education A regional wet detention pond receives stormwater with a single point of discharge (opportunity to control discharge at a single point)

39 When Do I Consider Inter-event Treatment? When Low Impact Development (LID) is Not Enough to Meet TMDL s When higher volume watershed discharges can be only partially diverted for effective treatment by LID When implementation of LID practices can be very costly to retrofit and not produce the expected results When it is not possible to effectively maintain LID When the public will not accept LID practices (such as bioswales in urban areas)

40 When Do I Consider Inter-event Treatment? Inter-event Treatment Requires Responsible Maintenance Consider our example: With treatment 13,790 lbs. Of TSS still accumulates in the treatment system each year! Solids and nutrient management requires a plan for removal Intakes, pumps and controls require routine checks Media up-flow filters offer lower maintenance if design incorporates methods for ease of removal-recommended filter cleaning and servicing annually

41 Conclusion The BSTF is an Important Demonstration of Inter-event Treatment for Mass Pollutant Reduction Since it s operational inception, the BSTF has met the challenge of high mass reductions in TSS and TN BSTF cost data include construction and documented O&M costs to achieve reasonable and reliable mass pollutant reductions with media based treatment Inter-event treatment BMP options should include a customized design approach for each water quality situation The inter-event treatment option could be an option coming to your old school pond