Enhanced Biofilter Treatment of Urban Stormwater by Optimizing the Hydraulic Reidence Time in the Media Redahegn Silehi 1, Robert Pitt 2 and Shirley Clark 3 1 Graduate tudent, Dept. of Civil, Contruction, and Environmental Engineering, Univ. of Alabama, P.O. Box 870205, Tucalooa, AL 35487; e-mail: rkilehi@crimon.ua.edu. 2 Cudworth Profeor, Urban Water Sytem, Dept. of Civil, Contruction, and Environmental Engineering, Univ. of Alabama, P.O. Box 870205, Tucalooa, AL 35487; e-mail: rpitt@eng.ua.edu. 3 Aociate Profeor, Environmental Engineering, Penn State Harriburg, 777 W. Harriburg Pike TL-105, Middletown, PA 17057; e-mail: eclark@pu.edu ABSTRACT Selecting the bet media for a pecific ituation i critical when deigning a biofilter or bioinfiltration tormwater control practice a the media affect the amount of runoff that i treated and the level of treatment that can be obtained. Appropriate hydraulic characteritic of the media, including treatment flow rate, clogging capacity, and water contact time, are needed to elect the media and drainage ytem. Thi information, in combination with the media ability to capture targeted pollutant with minimal clogging given the appropriate contact time, can be ued to predict the performance of a biofilter device. Thi paper preent a erie of tet being conducted to determine the hydraulic characteritic of and-baed filter media (having a variety of particle ize repreenting a range of median particle ize and uniformity coefficient) during pilot-cale trench tet. The drainage rate in biofiltration device i uually controlled uing an underdrain that i retricted with a mall orifice or other flow-moderating component. Thee frequently fail a the orifice are uually very mall (<10 mm) and are prone to clogging. A erie of tet TM (alo are conducted uing a newly developed foundation drain material (Capiphon referred to a SmartDrain in thi paper) ) that offer promie a a low flow control device with minimal clogging potential. A pilot-cale biofilter uing a fibergla trough 3m long and 0.6 x 0.6m in cro ection i ued to tet the variable affecting the drainage characteritic of the Capiphon TM (uch a length, lope, hydraulic head, and type of and media). The reult indicated that lope of the Capiphon TM material had no ignificant effect on the tage-dicharge relationhip wherea the length had a mall effect on the dicharge rate. The information collected during thi tudy will ait tormwater manager in the deign of biofilter needing a lowly draining device. INTRODUCTION Biofilter can be effective pollutant removal tormwater management device, and 1
can alo enhance tormwater infiltration for runoff volume reduction. Mot of the removal benefit of biofilter and bioinfiltration device are through phyical removal a the particulate-bound pollutant are trapped in the media, and through water infiltration into the natural oil urrounding the device. The preence of plant in thee device i common and ait in enhancing removal through many biological procee, uch a decribed by LeCoutumer, et al. (2008) a part of the extenive biofilter reearch conducted by Monah Univerity. Plant can enhance the treatment flow rate and time period before clogging by penetrating the urface clogging layer, allowing water to flow to deeper filter layer. Biochemical reaction may alo be enhanced near the root zone of ome plant. Evapotranpiration loe of runoff in mot biofilter are uually relatively mall though a the incoming water volume are relatively large compared to the available planted area. The effectivene of a biofilter i commonly reduced through clogging of the media, through hort-circuiting of infiltrating water through an under-drain, or by hort reident/contact time of the tormwater and the treatment media. Several tudie have demontrated the pollutant removal efficiency of tormwater biofilter (City of Autin 1988; Clark and Pitt 1999; Clark 2000; Winer 2000). With the exception of ome highly mobile contaminant (uch a chloride), they can be deigned for good pollutant removal. Figure-1. Cro-ection of a bioinfiltration tormwater treatment device. A biofilter would have an underdrain to capture much of the tormwater filtered through the media and return it to the urface flow regime (Villanova Urban Stormwater Partnerhip: http://www3.villanova.edu/vusp/bmp_reearch/bio_traffic/bio_de_comp.htm). 2
The removal of oluble form of many tormwater pollutant i dependent on the reidence time of the tormwater in the media, the tormwater characteritic, and the media type. However, Clark (2000) found that failure of thee ytem i motly caued by clogging, which can occur well before the contaminant removal capacity of the media i exceeded. Outlet control can be more conitent in providing the deired reident time needed for pollutant control. However, mot outlet control (underdrain) are difficult to ize to obtain long reidence time. Perforated pipe underdrain hort-circuit natural infiltration, reulting in decreaed performance. Orifice outlet control that allow long reidence time uually are very mall and clog eaily. We are tudying a foundation drain material (Capiphon TM ) that can be applied to biofiltration device and provide another option for outlet control. A typical biofilter that i 1 m deep, 1.5 m wide and 5 m long would require about 8 hour to drain uing the Capiphon TM material a the underdrain. Thi i a ubtantial reidence time in the media and alo provide ignificant retention of tormwater before being dicharged to a combined ewer ytem. In addition, thi low drainage time will allow infiltration into the native underlying oil, with minimal hort-circuiting to the underdrain. Even andy-ilt loam oil frequently ued in bioretention device can reult in extended urface ponding, requiring an underdrain. Conventional underdrain (perforated pipe) reduce ponding, but alo decreae infiltration opportunitie. Capiphon TM alo reduce the ponding time but doe not allow a much hort-circuiting of the infiltration water. Capiphon TM operate under laminar flow condition (Reynold number of 100 to 600). The Capiphon TM ha a low ediment carrying capacity due to the low Reynold number and therefore ha a reduced clogging potential by the fine that are in the tormwater. It ha 132 micro channel about 1 mm in diameter that are connected to the bottom of the 200 mm wide trip with maller lot. Thi arrangement reult in very mall dicharge rate (Figure 2). The pilot cale tet being conducted are determining the drainage characteritic of the Capiphon TM material (uch a length, lope, hydraulic head, and type of and media) under a range of typical biofilter condition. A and filter media purchaed from a local upplier in Tucalooa, Alabama i being ued for the tet etup to meaure the hydraulic characteritic of the Capiphon TM drainage material. The filter and ha a median particle ize ( D 50 ) of about 700 µm and a uniformity coefficient ( Cu) of 3.3. The particle ize ditribution of the and filter media and the US Silica Sil-Co-Sil 250 ground ilica material (manufactured by U.S. Silica Company) that i being ued during the clogging tet are hown in (Figure3). 3
Figure2. Capiphon TM material howing the microchannel on the underide of the 200 mm wide trip. 4
Figure3. Particle ize ditribution of the and filter media material (coare material on graph) and the U.S Sil-Co-Sil 250 (fine material on graph) ued for the clogging tet. MATERIALS and METHODS The firt phae of the experiment wa conducted uing a pilot-cale biofilter that conit of a fibergla trough 3 m long and 0.6 x 0.6 m in cro ection. The outlet end of the Capiphon TM wa inerted into a lit cut in the PVC collection pipe and ecured with crew and ilicone ealant (Figure 4(a)). The Capiphon TM material i intalled with the microchannel on the underide of the trip. The Capiphon TM direct the collected water into the PVC pipe, with a everal inch drop to enhance a iphoning action. The Capiphon TM wa intalled on top of a 100 mm layer of the drainage and, and another 100 mm layer of the and wa placed on top of the Capiphon TM (Figure 4(b)).The PVC pipe i 50 mm in diameter and i placed at the bottom of the trough. The pipe outlet i located o the flow can be meaured and water ample collected for analye. During the tet, the trough i initially filled with clean water to a maximum head of 55 cm above the center of the pipe and then allowed to drain, reulting in head v. dicharge data. A hydraulic jack and block are ued to change the lope of the trough (Figure 4(c)). Different length of the Capiphon TM were teted for a range of lope. Each tet wa alo repeated everal time and regreion analye were conducted to obtain equation coefficient for the tage- dicharge relationhip for thee different condition. 5
Figure 4. Capiphon TM intallation procedure in a fibergla trough 3m long and 0.6 x 0.6m in cro ection. Phae two of the experiment wa conducted to examine the clogging potential of the Capiphon TM. U.S Sil-Co-Sil 250, having a median particle ize of about 45 µm, wa mixed with the tet water at a concentration of about 1,000 mg/l. A tall Formica-lined plywood box 0.90 m by 0.85 m in cro ectional area and 1.20 m tall wa ued to verify the tage-dicharge relationhip for deeper water and ued for the clogging tet. The box wa filled with tap water uing a hoe to produce a maximum head of 1.20 m above the center of the pipe.. Figure4. Capiphon TM intallation procedure in a fibergla trough 3m long and 0.6 x 0.6m in cro ection. RESULTS and DISCUSSION Variable affecting the drainage characteritic of the and filter Five replicate for each of the five different length (2.9 m, 2.2 m, 1.6 m, 0.95 m and 34 cm) were conducted to tudy the variable affecting the drainage characteritic of the material a a function of length, lope, and hydraulic head. Two different length of the Capiphon TM (2.9 m and 2.2 m) were teted for five different lope (0%, 3%, 6%, 9%, and 12%) and three different length of the Capiphon TM (1.6 m, 0.95 m and 6
34 cm) were teted for three different lope (0%, 3%, and 12%). Flowrate meaurement are manually obtained at the effluent of the biofilter at 25 to 30 minute interval until the clean water wa completely drained from the trough. The flow were meaured by timing how long it took to fill a 0.5 L graduated cylinder. Stage-dicharge relationhip plot (Figure 5) are hown for five different length of Capiphon TM material. Linear regreion analye were ued to determine the intercept and lope term of thee tage v. dicharge relationhip. The p-value of the etimated coefficient were ued to determine if the coefficient were ignificant ( ). All of the five length teted for the given lope howed that coefficient were tatitically ignificant ( ), while many of the intercept term were not found to be ignificant on the tage-dicharge relationhip. The phyical lope of the Capiphon TM had no ignificant effect on the tage-dicharge relationhip, while length only had a mall, but ignificant effect. Figure 5 alo how tage-dicharge relationhip for three very mall orifice (2.5, 5, and 6.5 millimter) uperimpoed on the Capiphon TM drainage characteritic. The Capiphon TM tage-dicharge relationhip are repreented by firt-order linear equation and have flow generally in the range of orifice in the ize range of 2.5 to 5 millimter for typical head condition. Figure 5. Stage-dicharge relationhip plot for five different length of Capiphon TM (0.34m to 2.9m) teted for five different lope uing a fiber gla trough 3 m long 7
and 0.6 x 0.6 m in cro-ection. The tage-dicharge relationhip plot hown for the clean v. dirty water tet had a Capiphon TM length of 38 cm. Thee tet were conducted in a formica-lined plywood box 0.90 m by 0.85 m in area and 1.20 m tall. Examining the clogging potential of the Capiphon TM Flowrate meaurement were taken from the effluent of the device at 25-30 minute interval until the water completely drained from the 1.20 m tall lined box ued to verify the tage-dicharge relationhip for deeper water. Only a moderate reduction in flow rate wa oberved with time, even after 38 kg/m 2 load (the total US Sil-Co-Sil 250 loading in kg per quare meter of the biofilter area) on the biofilter (2 to 4 time the typical load oberved before clogging for mot biofilter media). Turbidity meaurement of the effluent were alo obtained at 25 to 30 minute interval at the ame time a the flowrate meaurement until the water completely drained from the tank. The turbidity (NTU) meaurement rapidly decreaed with the head of water in the tank (and effluent flow rate). The initial turbidity level were about 1,000 NTU in the tank at the beginning of the tet (and with imilar effluent water turbidity at the beginning of the tet), but with ignificantly decreaing effluent turbidity value a the tet progree and the flow rate decreae. Figure 6 Sil-Co-Sil 250 load (kg/m 2 ) v. equation lope coefficient for the clogging 8
tet. There wa about a 25% reduction in flow rate after about15 kg/m 2, compared to the initial flow rate, and thi reduced flow continued to the end of the tet with no further reduction in flow rate oberved. Table-1 linear regreion analyi reult for clogging tet.about 0.95 kg of Sil-Co-Sil 250 wa added at each trial, for a total of about 30kg applied during the complete tet erie. The experimental procedure remained the ame for all trial. The cumulative Sil-Co-Sil 250 loading on the biofilter i the only variable changing throughout the trial. Trial-1 Trial-2 Trial-3 Coefficient P-value Coefficient P-value Coefficient P-value 0 #N/A -0.008 0 #N/A Slope 0.080 0.083 0.0741 Trial-4 Trial-5 Trial-6 Coefficient P-value Coefficient P-value Coefficient P-value 0.001 0 #N/A 0.006 Slope 0.073 0.072 0.064 Trial-7 Trial-8 Trial-9 Coefficient P-value Coefficient P-value Coefficient P-value 0 #N/A 0.0026 0 #N/A Slope 0.068 0.0620 0.071 Trial-10 Trial-11 Trial-12 Coefficient P-value Coefficient P-value Coefficient P-value 0 #N/A 0.0011 0 #N/A Slope 0.0705 0.0615 0.0613 9
Trial-13 Trial-14 Trial-15 Coefficient P-value Coefficient P-value Coefficient P-value -0.0025 0 #N/A 0.00561 Slope 0.0664 95 019 Trial-16 Trial-17 Trial-18 Coefficient P-value Coefficient P-value Coefficient P-value 0.0024 0 #N/A -0.0013 Slope 78 0.0658 0.0646 Trial-19 Trial-20 Trial-21 Coefficient P-value Coefficient P-value Coefficient P-value -0.0045-0.0030-0.00280 Slope 0.0706 0.0646 0.06084 Trial-22 Trial-23 Trial-24 Coefficient P-value Coefficient P-value Coefficient P-value -0.0020-0.0039 0 #N/A Slope 0.0622 0.0634 77 Trial-25 Trial-26 Trial-27 Coefficient P-value Coefficient P-value Coefficient P-value -0.0105-0.0060-0.0027 Slope 0.0742 85 54 Trial-28 Trial-29 Trial-30 Coefficient P-value Coefficient P-value Coefficient P-value 10
-0.0087 Slope 0.0645-0.0071 0.0660-0.0109 0.0678 Trial-31 Trial-32 Coefficient P-value Coefficient P-value -0.0038-0.0046 Slope 86 0.0625 CONCLUSIONS The reult from the experiment conducted to tet the variable affecting the drainage characteritic of the filter media indicate that the lope of the Capiphon TM material had no ignificant effect on the tage-dicharge relationhip, wherea the length had a mall effect on the dicharge rate. Effluent turbidity (NTU) meaurement decreaed rapidly with time, indicating ignificant retention of ilt in the tet biofilter. Thee preliminary tet indicate that the Capiphon TM material provide an additional option for biofilter, having minimal clogging potential while alo providing very low dicharge rate. We have tarted further tet to invetigate biofouling of the Capiphon TM material. We expect to continue thee tet through the coming warm eaon. REFERNCES City of Autin, Texa, 1988. Deign Guideline for Water Quality Control Bain Environmental Criteria Manual Clark, S. and R. Pitt. Stormwater Treatment at Critical Area, Evaluation of Filtration Media for Stormwater Treatment. U.S. Environmental Protection Agency, Water Supply and Water Reource Diviion, National Rik Management Reearch Laboratory. Cincinnati, Ohio. 1999 EPA/600/R-00/010 July 1999. Clark, S.E., 2000, Urban Stormwater Filtration: Optimization of Deign Parameter and a Pilot-Scale Evaluation, Ph.D. Diertation, Univerity of Alabama at Birmingham. Le Coutumer, S., T.D. Fletcher, A. Deletic, and M. Potter. Hydraulic Performance of 11
Biofilter Sytem for Stormwater Management: Leon from a Field Study. Facility for Advancing Water Biofiltration, Department of Civil Engineering, Intitute for Sutainable Water Reource, Monah Univerity, Melbourne, Vic., 3800, Autralia. April 2008. http://www.monah.edu.au/fawb/publication/fawb-biofilter-field-infiltrationtudy.pdf Winer, R. 2000. National Pollutant Removal Performance Databae for Stormwater Treatment Practice: 2nd Edition. Center for Waterhed Protection. Ellicott City, MD 12