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Optimisation of granular media filtration: impact of chemical conditioningCon Pelekani & Loreline Kerlidou SA Water & Allwater
Wednesday, 27 May 2015
PRESENTATION OUTLINE
• CONTEXT & OBJECTIVES• TEST METHODOLOGY• KEY ISSUE 1: Impact of pre‐chlorination • KEY ISSUE 2: Impact of pre‐chlorination for manganese removal• KEY ISSUE 3: Impact of filter aid polymer• KEY ISSUE 4: Biological Filtration• CONCLUSIONS
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Project Context and Objectives
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Pilot Filter Project Investigation details
Previous Study (May 2012)
Determination of optimum filtration media for Happy Valley Filters
Phase 1(June 2013‐February 2014)
Impact of filtration rate, backwash sequence, filter resting and slow start on filter performance
Phase 2(Mars‐August 2014)
Impact of pre‐chlorination on filtration performanceImpact of pre‐chlorination/pH on Mn removalImpact of filter aid polymer dosing on filter performanceImpact of combined pre‐chlorination and polymer‘Biological’ filtration: hydraulic and treatment performance
Pilot Plant Configuration
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Key Issue 1: Impact of pre‐chlorination on filtration performance
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Columns 3 and 4 Dosage stabilityVarious chemical conditions
Cl2=0.5mg/l Range: 0.38 – 0.55mg/l
Cl2=1mg/l Range: 0.94 – 1.14mg/l
Cl2=1.5mg/l Range: 1.46 – 1.66mg/l
Chlorine dosed as NaOCl (12.5%)
13m/hChemical Dosage (mg/l)Chlorine 0.5
Chlorine 1
Chlorine 1.5
Chlorine Dose Chlorine ResidualTurbidity removal C3&C4 compared to
C1
Particle counts removal C3&C4 compared to C1
Chlorine (mg/l) Chlorine (mg/l) % Removal % Removal
0.5 0.1 +13% +37%
1 0.3‐0.4 +16% +50%
1.5 0.8 +15% +52%
Key observations 1: Impact of pre‐chlorination on filtration performance• Filtered water quality achieving KPI
– <0.1 NTU 90% of run time– <0.15 NTU 95% of run time
• Pre‐chlorination demonstrated improvement:o + 15% relative improvement for turbidityo + 46% relative improvement for particle counts
• Low sensitivity of filtrate turbidity to chlorine doses tested (0.5‐1.5 mg/l)• Greater sensitivity of particle counts (2‐15 m) to chlorine dose
o For Cl2 = 0.5 mg/l + 35% improvement o For Cl2 = 1 – 1.5 mg/l + 50% improvement
• Simultaneous monitoring of filtrate turbidity and particle counts beneficial in pilot plant environment
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Key Issue 2: Impact of Pre‐chlorination Dose on Manganese Removal
• Trial 1: Low manganese dose (0.05 mg/l)
• Trial 2: High manganese dose (0.1 mg/l)
• Trial 3: Impact of pH (7.2 vs. 7.6) on manganese removal (0.1 mg/l)
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Key Issue 2: Impact of pre‐chlorination dose on Manganese removal
Test Conditions• Mn dosed as soluble MnCl2
– WTP settled water Mn residual ~ 0.02 mg/l• Sampling time: 30 min, 2h, 4h and 6h• Quantify total and soluble Mn removal
Filtration Performance• Excellent filtrate turbidity: < 0.10 NTU • Particle Counts (2‐15 m): 170 – 350 /ml
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Impact of filter pre‐chlorination on Mn removal
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Columns 3 and 4 Dosage stabilityVarious chemical conditions
Mn=0.1 mg/l Range: 0.088 – 0.15 mg/l
Cl2=0.5 mg/l Range: 0.42 – 0.61 mg/l
Cl2=1 mg/l Range: 0.74 – 1.41 mg/l
Cl2=2 mg/l Range: 1.68 – 2.20 mg/l
13 m/hChemical Dosage (mg/l)ManganeseChlorine
0.10
ManganeseChlorine
0.10.5
ManganeseChlorine
0.11
ManganeseChlorine
0.12
Key observations for ‘high’ manganese challenge tests
• For low chlorine doses (0, 0.5 and 1 mg/l)o No consistent Mn removalo Low removal of soluble Mn (≤ 10%)o Lowest soluble Mn in filtrate = 0.088 mg/lo No observable catalytic removal
• For higher chlorine dose (2 mg/l)o Consistent removal for both C3 & C4o Soluble Mn removal 50% (from 2 h run time)o No treatment improvement with filtration time
• Mn removal performance is strongly related to oxidant concentration
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Impact of pH on manganese removal
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Columns 3 and 4 Dosage stability
Various chemical conditions Mn=0.1mg/l Range: 0.079 – 0.141mg/l
Cl2=2mg/l Range: 1.59 – 2.2mg/l
Cl2=3mg/l Range: 2.7 – 3.5mg/l
pH=7.2 Range: 7.12 – 7.35
pH=7.6 Range: 7.52 – 7.68
13m/hChemical Dosage (mg/l) pHManganeseChlorine
0.12 7.2
ManganeseChlorine
0.12 7.6
ManganeseChlorine
0.13 7.6
Key Findings: Impact of pH on Mn removal
• Under ambient pH: coating of MnO2 on sand grains
• Results confirm relative importance of pH and chlorine dose
• ‘High’ pH and chlorine dose promote faster Mn oxidation kinetics → improved removal
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Mn removal: control versus chlorinated filters• Higher average (but
variable) Mn removal for reference column
• Performance deteriorated with filter run time
• Possible biological removal pathway? Oxidation via co‐metabolism
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Key Issue 3: Impact of filter aid polymer
• Trial 1: Polymer
• Trial 2: Polymer with pre‐chlorination
• Trial 3: pH variation (7.2 vs. 7.6) w/ and w/o pre‐chlorination
• Polymer: – LT22S (BASF, Australia)– Low toxicity, high molecular weight polyacrylamide
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Filter aid polymer test conditions
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Trial Number Poly Dose(mg/L)
Chlorine Dose (mg/L) pH
1 0.1 0.0 7.2
2 0.4 0.0 7.2
3 0.1 2.0 7.2
4 0.4 2.0 7.2
5 0.4 0.0 7.6
6 0.08 2.0 7.6
7 0.02 2.0 7.2
Impact of filter aid polymer
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Polymer DoseTurbidity removal C3&C4 compared to
C1
Particle counts removal C3&C4 compared to C1
Polymer (mg/l) % Removal % Removal
0.1 +36% ‐11%
0.4 +48% +52%
Impact of filter aid polymer with pre‐chlorination
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Polymer Dose Chlorine dose
Turbidity removal C3&C4
compared to C1
Particle counts removal C3&C4
compared to C1
Polymer (mg/l) Chlorine (mg/l) % Removal % Removal
0.02 2 +19% +21%
0.1 2 +43% +56%
0.4 2 +61% +81%
Key Findings: Filter aid polymer
• Polymer addition resulted in measurable reductions in turbidity and particle counts• No apparent negative interaction between LT22S and chlorine for the range of doses tested• Very high polymer dose did not result in near complete removal of particles
– Active mechanism not related to charge neutralisation but improved bridging and media grain collector efficiency (‘stickiness’)– Polymer doses ≤ 0.1 mg/l yielded acceptable filter productivity and headloss– High doses not appropriate for long‐term filter operation sustainability
• Clarified water quality disturbances propagate through media filters– Not effectively attenuated by filter pre‐chlorination and polymer addition– Optimisation of upstream coagulation and flocculation processes more critical than filter conditioning treatments
• Elevated filter pH operation: – inconclusive results– Filtered water aluminium residuals remained below 0.2 mg/l (ADWG aesthetic limit)
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Key Issue 4: Could Effective Biological Filtration be established?Hydraulic Performance• Filter operating conditions (Column #2)
o Days 1‐32: 5 m/ho Day 32‐ present: 10 m/h
• Optimisation of backwash sequence necessary• Significant algae growth observed in filter underdrain
Filtration Performance• Turbidity consistently < 0.2 NTU
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Headloss profiles for biological and control filter columns
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1 Step 1: Water 5min@20m3/m2/h
2 Step 1: Air 1min@50Nm3/m2/hStep 2:Water 5min@20m3/m2/h
3Step 1: Air 1min@50Nm3/m2/h Step 2:Combined Air 7min@50Nm3/m2/h ‐Water 7min@20m3/m2/hStep 3: Water 5min@40m3/m2/h
‘Biological’ Filter: General Water Quality Performance
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Key Observations: Biological Filtration
• Backwash sequence is critical for effective operation of ‘biological’ sequence– Filtrate quality improved (better than reference column C1) once
backwash sequence optimised
• No general water quality improvement– ‘wrong’ microbiology?– Insufficient contact time? (EBCT < 8 min)
• Assess algal metabolite removal capability
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Methodology for MIB & Geosmin Spiking Trial
• Super‐chlorinate Control Filter to create abiotic conditions• Backwash Control and Biological Filters prior to test• Install chemical dosing point for Column 2 (Biological)• Maintain chilled MIB/Geosmin stock solution on‐site to
minimise volatilisation• Target MIB/Geosmin dose ~ 150 ng/L• Sampling of filter inlet/outlet over 4 hour dosing period
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MIB/Geosmin Spiking Trial Results
No significant removal of MIB and Geosmin27/05/2015 Page 25
Project Conclusions• Filter pre‐chlorination and polymer addition enhance particle removal• Chlorine does not impair polymer performance• Filter pre‐conditioning cannot fully attenuate upstream disturbances• Optimisation of coagulation & flocculation critical• Removal of dissolved manganese is controlled by oxidant dose• Manganese oxidation kinetics enhanced by increasing pH• ‘Biological filtration’
– use of air, water and combined air/water necessary to achieve effective headloss control
– not chlorinating filters does NOT necessarily result in effective biological treatment for target micropollutants (e.g. algal metabolites)
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QUESTIONS?
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ORP‐pH Diagram for Manganese
29
o Laboratory tests: conditions to favour MnO2(s) formation• pH=7.2 ORP>700mV Cl2=2 mg/l• pH = 7.6 ORP>600mV Cl2=2 – 3 mg/l
Effects of increasing pH• increased soluble Al• possible reduction in Cl2 disinfection
capability• possible increase in THM formation in
product water• decreased product water corrosivity Need for pH optimisation
7.6
Summary: Cl2 and Mn Trials
30
Summary on Chlorine and Manganese Trials
Chlorine condition Cl2=0‐0.5‐1 mg/l Cl2=2 mg/l Cl2=2 mg/l Cl2=3 mg/l
pH condition pH=7.2 pH=7.2 pH=7.6 pH=7.6
Soluble Manganese removal ≤ 10% ≈ 50% ≈ 50% ≈ 80%
Turbidity Similar Turbidity Performance: 0.08 – 0.12 NTU
Particle counts (C3‐C4 % Removal compared to C1)
0.5 mg/l: ‐11%1 mg/l: +3% +7% +20% +29%
Polymer Trial Results SummaryTrial Number 1 2 3 4 5 6 7
Test Conditions
Polymer(mg/L)
0.10 0.40 0.10 0.40 0.40 0.08 0.02
Chlorine(mg/L)
0.0 0.0 2.0 2.0 0.0 2.0 2.0
pH 7.2 7.2 7.2 7.2 7.6 7.6 7.2
Mean Turbidity(NTU)
C1 0.182 0.141 0.139 0.179 0.222 0.271 0.288
C3/C4 0.117 0.073 0.079 0.069 0.105 0.224 0.236
% Difference 35.5% 48.5% 43.1% 61.2% 52.8% 17.4% 18.2%
Mean Total Particle Count
(cts/mL)
C1 1716 666.7 509.0 1004 2588 2882 2203
C3/C4 1897 315.2 225.7 186.0 524.7 2365 1738
% Reduction ‐10.6% 51.3% 55.7% 81.5% 79.7% 17.9% 21.1%
Time to Terminal Headloss
(hr)C3/C4 26.2 8.2 30.6 15.5 5.5 Not Reached Not Reached
UFRV(m)
C3/C4 303 101 345 217 69 ‐ ‐
Slide 31
CP10 Good layoutCon Pelekani, 30/10/2014
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