Chlorine Contact Reactors in Wastewater Treatment Plant Tracer Study
Conducted at the Graton Community Services District WWTP, this tracer study evaluated the modal contact time for a purge tank and serpentine concrete basin operated in series, with a focus on chlorine contact reactors. The results, including modal contact time and hydraulic residence time, provide valuable insights for optimizing the treatment process.
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Graton Community Services District SN 4990011 Wastewater Treatment Plant Sonoma County, CA Modal Contact Time (Tmod) Tracer Study #1 May 30, 2018 by Guy Schott, P.E. Water Resources Control Board, Division of Drinking Water Guy.schott@waterboards.ca.gov 707-576-2732 Revised on July 30, 2018; basin volume.
Chlorine Contact Reactors in Series Plain View Chlorine Contact Chamber Channel width: 2.75 ft Channel length: 28.5 ft Channel opening: 2.75 ft Operating depth: 4 ft Operating volume: 12,000 gal L:W = 52 Purge Tank 8 ft diameter 9 ft height 6 ft inlet height 150 degree inlet/outlet 2,800 gallons operating volume Chlorine Contact Basin Tracer Flouride 120 gpm Pipeline 30 ft x 6 in dia. pipe 30 ft x 4 in dia. pipe 150 ft x 6 in dia. pipe 280 gallons 120 gpm Purge Tank Tracer Flouride (slug) Graton Community Services District 250 Ross Ln, Sebastopol, CA 95472 707-823-1542 Revised Contact Rectangular Basin from 10,800 to 12,000 gallons
Final Results Test Date: May 30, 2018 Test by: GCSD & WRCB, Division of Drinking Water Tracer Test Method: Slug-Dose using Fluoride Reactors Tested: Purge Tank, pipeline & Serpentine Contact Basin (in series) Total Operating Volume: 15,080 gallons Operational Flow: 120 gpm (steady-state) HRT: 126 minutes (hydraulic residence time) Tmod: 112 minutes (Modal Contact Time) Modal Baffling Factor: 0.89 (Tmod/HRT)
Operating Parameters Based on Tracer Test Modal Minimum Chlorine Residual (C), mg/L Flow gpm HRT min Contact Time (T), min CT mg/L min 450 450 450 450 450 450 450 120 125 130 135 140 145 149 126 121 116 112 108 104 101 112 107 103 99 96 93 90 4.0 4.2 4.4 4.5 4.7 4.9 5.0 Working Volume: 15,080 gallons HRT: Hydraulic Residence Time (Vol/Flow) Modal Baffling Factor (BFmod): 0.89 (T/HRT), based on tracer test Modal Contact Time (T): HRT BFmod = HRT 0.89
Tracer Study Overview 1 On May 30, 2018 a single tracer study was conducted at the Graton CSD WWTP. This test was to evaluate the modal contact time for the 3,000 gallon purge tank and 12,000 gallon serpentine concrete basin operated in series including pipe volume between the two reactors. The modal contact value (Tmod) is that time at which the slug- dose curve is at its peak concentration. The modal contact time was 112 minutes. The HRT was 126 minutes.
Tracer Study Overview 2 Tracer Method: Slug-Dose Injection Point of Tracer: Pipeline to Purge Tank Sample Point: Overflow weir at end of serpentine contact basin. Tracer Analysis: Ion Selective Fluoride Probe Sampler: Graton CSD Operators Analyses by: Guy Schott, Division of Drinking Water
Tracer Material Overview Tracer Material: Hydrofluorosillicic Acid (H2SiF6) Tracer Bulk Density: 10.3 lbs/gal Tracer Product Strength: 24% as H2SiF6 Molecular Weight: 144.09 g/mole (H2SiF6) Fluoride Concentration: 79.11% (144 g/mole) H2SiF6 Tracer Added: 406 mL (neat) Fluoride (F) Tracer Added: 94 grams Method of Injection: Slug-Dose (< 20 sec)
3,000 Gal Purge Tank Inlet Inlet Tracer Tracer Injection Point Outlet to 12,000 gallon chlorine contact basin
12,000 Gal Contact Basin Sample
Tracer Field Results Elasped Time, min Tracer Conc., mg/L Elasped Time, min Tracer Conc., mg/L Elasped Time, min Tracer Conc., mg/L Elasped Time, min Tracer Conc., mg/L Sample # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Sample # 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 Sample # 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Sample # 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 0 0.000 76 0.013 136 1.86 240 0.197 5 0.000 79 0.040 139 1.73 250 0.107 10 0.000 82 0.221 142 1.57 260 0.127 15 0.000 85 0.423 145 1.45 270 0.079 20 0.000 88 0.580 148 1.42 280 0.082 25 0.000 91 0.983 151 1.32 290 0.071 30 0.000 94 1.11 154 1.16 300 0.042 35 0.002 97 1.45 157 1.05 310 0.063 40 0.019 100 1.77 160 0.896 320 0.036 43 0.001 103 2.10 165 0.755 330 0.040 46 0.013 106 2.63 170 0.699 340 0.027 49 0.025 109 2.64 175 0.622 350 0.028 52 0.004 112 2.75 180 0.509 360 0.032 55 0.028 115 2.37 185 0.437 370 58 0.005 118 2.40 190 0.435 380 61 0.006 121 2.40 195 0.384 390 64 0.006 124 2.34 200 0.322 400 67 0.011 127 2.23 210 0.227 410 70 0.000 130 2.11 220 0.215 420 73 0.022 133 1.97 230 0.196 430
Flow: 120 gpm Graton CSD - May 30, 2018 3.0 112, 2.75 2.8 2.6 2.4 2.2 2.0 1.8 FLUORIDE (mg/L) 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 Modal Conatact Time:112 minutes HRT: 126 minutes ELASPED TIME (MINUTES)
