Performance of a Tire Chip Media Constructed Wetland Presented by William Li, PE, Stantec Consulting Inc Geoffrey Holmes, Superintendent, Fisherman Bay Sewer District, WA Pacific Northwest Clean Water Association Annual Conference, Sept 13 to 16, 2009 Boise, Idaho
Where the Facility is Located?
Plant Background Plant Influent wastewater characteristics: Septic tank effluent pumping (STEP) wastewater Low TSS (36 mg/l, average) High ammonia (58 mg/l, average) Low temperature (56 o F, average) Weak BOD 5 loading (170 mg BOD 5 /l, 157 mg CBOD 5 /l) Plant Flows: Permitted for 34,000 gpd in the summer and 23,000 gpd in the winter, current annual average flow is 16,000 gpd Treatment Process: Anaerobic pretreatment cell, aerated lagoon cell #1 and #2, settling cell #3, constructed wetland and chlorine disinfection system.
The Fisherman Bay Sewer District Wastewater Plant
Plant Aerial View
Why a Wetland is Built for the Plant? To remove high amount of algae from the lagoon effluent For easy control of chlorine dosage Improve plant effluent quality Potential reuse of the plant effluent Increase plant capacity Create a new habitat for local wildlife
Wetland Design Criteria and Data Type: Subsurface Flow System (SFS) Media: 30 deep and 31,000 cubic ft Media material: 30% of ¾ clean gravel & 70% of 2 minus shredded tire chips Porosity of Media: 0.41 (gravel), 0.57 (tire chips) HRT: 2 days Wetland basin: 12,350 sq ft, lined with 45 mil synthetic liner Design Flow: 41,424 gpd Vegetation: local cattails, bulrushes and reeds Completed construction in Sept 2006
Why Tire Chips Were Used? Gravel is not locally available, and overall cost (delivery and material) was higher than tire chips. Beneficial uses of tire chips, which are recycled waste materials. Tire chips have been successfully used in leach fields of septic system for replacing gavels. Study by Texas A&M University in 2003 showed tire chips can be used as wetland media.
The Constructed Wetland in June 2007
The Constructed Wetland in June 2007
The Constructed Wetland in 2008
The Constructed Wetland in August 2009
Fecal Coliform Removal Performance of the Wetland Fecal C olifo orm (#/100 ml) 7000 6500 6000 5500 5000 4500 4000 3500 3000 2500 2000 1500 1000 500 Influent Fecal Coliform (#/100 ml) Effluent Fecal Coliform (#/100 ml) Removal Efficiency (%) 100.0% 99.5% 99.0% 98.5% 98.0% 97.5% 97.0% 0 2/22/2009 3/14/2009 4/3/2009 4/23/2009 5/13/2009 6/2/2009 6/22/2009 Time 96.5%
Plant Effluent Fecal Before & After Wetland in Service 1600 1400 1200 F ecal (# #/100m l) 1000 800 600 400 200 0 10/28/03 5/25/04 12/21/04 7/19/05 2/13/06 9/11/06 4/9/07 10/29/07 5/12/08 12/8/08 7/6/09 Time
Plant Effluent TRC Before & After Wetland in Service 1.2 1 0.8 T R C (m g /l) 0.6 0.4 0.2 0 10/17/05 3/13/06 8/7/06 1/1/07 5/21/07 10/15/07 3/4/08 7/21/08 12/15/08 5/11/09 Time
Wetland Influent and Effluent SCBOD5 90 80 70 Influent SCBOD5 Effluent SCBOD5 SCBOD5 (mg/l) 60 50 40 30 20 10 0 11/27/06 3/27/07 7/25/07 11/22/07 3/21/08 7/19/08 Time
Wetland Influent and Effluent CBOD5 100 90 80 Influent CBOD5 Effluent CBOD5 70 CBOD5 (mg/l) 60 50 40 30 20 10 0 11/27/06 3/27/07 7/25/07 11/22/07 3/21/08 7/19/08 11/16/08 3/16/09 7/14/09 Time
Wetland Effluent SCBOD5 & CBOD5 100 90 80 Effluent SCBOD5 Effluent CBOD5 SCBOD5, CBOD5 (mg/l) 70 60 50 40 30 20 10 0 11/27/06 3/27/07 7/25/07 11/22/07 3/21/08 7/19/08 11/16/08 3/16/09 7/14/09 Time
Wetland Effluent TSS and CBOD Correlation 100 90 80 Effluent CBOD5 Effluent TSS 70 C B O D 5, TSS (m g/l) 60 50 40 30 20 10 0 11/27/06 3/27/07 7/25/07 11/22/07 3/21/08 7/19/08 11/16/08 3/16/09 7/14/09 Time
Influent & Effluent TSS Before & After Wetland in Service 90 80 Wetland Influent TSS (mg/l) Plant Effluent TSS (mg/l) 70 60 TSS (mg/l) 50 40 30 20 10 0 10/28/03 5/25/04 12/21/04 7/19/05 2/13/06 9/11/06 4/9/07 10/29/07 5/19/08 12/15/08 7/13/09 Time
TSS and CBOD5 Removal Efficiencies of the Wetland 100% 90% TS S, C B OD 5 R em oval (%) 80% 70% 60% 50% TSS Removal Efficiency CBOD5 Removal Efficiency 40% 11/12/07 1/11/08 3/11/08 5/10/08 7/9/08 9/7/08 11/6/08 1/5/09 3/6/09 5/5/09 7/4/09 Time
Summary of Wetland Performance Removed over 96% fecal coliform Reduced chlorine dosage Plant effluent fecal is significantly lower than permit limit (200 MPN/100ml) TRC is generally lower than 0.2 mg/l in the last one and half years. Eliminated nitrite effect on chlorine dosage
Summary of Wetland Performance Removed almost all particulate CBOD 5. Average CBOD 5 removal was 80% Effluent CBOD 5 is consistently less than 5 mg/l in the last 2 years Removed 88% TSS on average Effluent TSS is consistently below 10 mg/l, and generally less than 5 mg/l in the last 2 years
Lessons learned: Tire chips should be washed and cleaned prior to placing in the wetland Steel wires in the tire chips contribute CBOD 5 Operating data show that it took approximately 9 months to reduce the ferrous wires on effluent CBOD 5 Placed gravel on top of the tire chips to prevent tire chips bouncing Coarse gravel should be used at influent manifold to prevent clogging
Conclusions Shredded tire chips is a suitable and less expensive alternative media for subsurface flow wetland Appropriate designed and operated wetland is effective for TSS, CBOD 5 and fecal coliform removal in the lagoon effluent Wetland treatment of lagoon effluent can produce high quality effluent water for limited reuses The wetland has become a new habitat for local wildlife. Redwing black birds, swallows and sparrows are observed in the wetland (Probably) the first large scale field application of constructed wetland with tire chips media in North America
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