Optimisation of granular media filtration: impact of chemical conditioning Con Pelekani & Loreline Kerlidou SA Water & Allwater

Transcription

1 Optimisation of granular media filtration: impact of chemical conditioning Con Pelekani & Loreline Kerlidou SA Water & Allwater Wednesday, 27 May 2015

2 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 27/05/2015 Page 2

3 Project Context and Objectives Pilot Filter Project Previous Study (May 2012) Phase 1 (June 2013 February 2014) Phase 2 (Mars August 2014) Investigation details Determination of optimum filtration media for Happy Valley Filters Impact of filtration rate, backwash sequence, filter resting and slow start on filter performance Impact of pre chlorination on filtration performance Impact of pre chlorination/ph on Mn removal Impact of filter aid polymer dosing on filter performance Impact of combined pre chlorination and polymer Biological filtration: hydraulic and treatment performance 27/05/2015 Page 3

4 Pilot Plant Configuration 27/05/2015 Page 4

5 Key Issue 1: Impact of pre chlorination on filtration performance Turbidity removal Particle counts Columns Chlorine Dose 3 and 4 Chlorine Residual C3&C4 compared Dosage to stability removal C3&C4 C1 compared to C1 Various chemical conditions Cl 2 =0.5mg/l Range: mg/l Chlorine 13m/h (mg/l) Chlorine (mg/l) % Removal % Removal Chemical Dosage (mg/l) Cl 2 =1mg/l Range: +13% mg/l +37% Chlorine % +50% Chlorine Cl 2 =1.5mg/l Range: +15% mg/l +52% Chlorine 1.5 Chlorine dosed as NaOCl (12.5%) 27/05/2015 Page 5

6 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 o + 15% relative improvement for turbidity + 46% relative improvement for particle counts Low sensitivity of filtrate turbidity to chlorine doses tested ( mg/l) Greater sensitivity of particle counts (2 15 m) to chlorine dose o o For Cl 2 = 0.5 mg/l + 35% improvement For Cl 2 = mg/l + 50% improvement Simultaneous monitoring of filtrate turbidity and particle counts beneficial in pilot plant environment 27/05/2015 Page 6

7 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) 27/05/2015 Page 7

8 Key Issue 2: Impact of pre chlorination dose on Manganese removal Test Conditions Mn dosed as soluble MnCl 2 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): /ml 27/05/2015 Page 8

9 Impact of filter pre chlorination on Mn removal Columns 3 and 4 Various chemical conditions Chemical Manganese Chlorine Manganese Chlorine Manganese Chlorine Manganese Chlorine 13 m/h Dosage (mg/l) Dosage stability Mn=0.1 mg/l Range: mg/l Cl 2 =0.5 mg/l Range: mg/l Cl 2 =1 mg/l Range: mg/l Cl 2 =2 mg/l Range: mg/l 27/05/2015 Page 9

10 Key observations for high manganese challenge tests For low chlorine doses (0, 0.5 and 1 mg/l) o No consistent Mn removal o Low removal of soluble Mn ( 10%) o Lowest soluble Mn in filtrate = mg/l o No observable catalytic removal For higher chlorine dose (2 mg/l) o o o Consistent removal for both C3 & C4 Soluble Mn removal 50% (from 2 h run time) No treatment improvement with filtration time Mn removal performance is strongly related to oxidant concentration 27/05/2015 Page 10

11 Impact of ph on manganese removal Columns 3 and 4 Various chemical conditions 13m/h Chemical Dosage (mg/l) ph Manganese 0.1 Chlorine Manganese 0.1 Chlorine Manganese 0.1 Chlorine Dosage stability Mn=0.1mg/l Range: mg/l Cl 2 =2mg/l Range: mg/l Cl 2 =3mg/l Range: mg/l ph=7.2 Range: ph=7.6 Range: /05/2015 Page 11

12 Key Findings: Impact of ph on Mn removal Under ambient ph: coating of MnO 2 on sand grains Results confirm relative importance of ph and chlorine dose High ph and chlorine dose promote faster Mn oxidation kinetics improved removal 27/05/2015 Page 12

13 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 cometabolism 27/05/2015 Page 13

14 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 27/05/2015 Page 14

15 Filter aid polymer test conditions Trial Number Poly Dose Chlorine Dose (mg/l) ph (mg/l) /05/2015 Page 15

16 Impact of filter aid polymer Polymer Dose Turbidity removal C3&C4 compared to C1 Particle counts removal C3&C4 compared to C1 Polymer (mg/l) % Removal % Removal % 11% % +52% 27/05/2015 Page 16

17 Impact of filter aid polymer with pre chlorination 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 % +21% % +56% % +81% 27/05/2015 Page 17

18 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) 27/05/2015 Page 18

19 27/05/2015 Page 19

20 Key Issue 4: Could Effective Biological Filtration be established? Hydraulic Performance Filter operating conditions (Column #2) o Days 1 32: 5 m/h o 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 27/05/2015 Page 20

21 Headloss profiles for biological and control filter columns 1 Step 1: Water 5min@20m 3 /m 2 /h Step 1: Air 1min@50Nm 2 3 /m 2 /h Step 2:Water 5min@20m 3 /m 2 /h Step 1: Air 1min@50Nm 3 /m 2 /h 3 Step 2:Combined Air 7min@50Nm 3 /m 2 /h Water 7min@20m 3 /m 2 /h Step 3: Water 5min@40m 3 /m 2 /h 27/05/2015 Page 21

22 Biological Filter: General Water Quality Performance 27/05/2015 Page 22

23 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 27/05/2015 Page 23

24 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 27/05/2015 Page 24

25 MIB/Geosmin Spiking Trial Results No significant removal of MIB and Geosmin 27/05/2015 Page 25

26 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) 27/05/2015 Page 26

27 QUESTIONS? 27/05/2015 Page 27

28 27/05/2015 Page 28

29 ORP ph Diagram for Manganese 7.6 o Laboratory tests: conditions to favour MnO 2 (s) formation ph=7.2 ORP>700mV Cl 2 =2 mg/l ph = 7.6 ORP>600mV Cl 2 =2 3 mg/l Effects of increasing ph increased soluble Al possible reduction in Cl 2 disinfection capability possible increase in THM formation in product water decreased product water corrosivity Need for ph optimisation 29

30 Summary: Cl 2 and Mn Trials Summary on Chlorine and Manganese Trials Chlorine condition Cl 2 = mg/l Cl 2 =2 mg/l Cl 2 =2 mg/l Cl 2 =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 Particle counts (C3 C4 %Removal compared to C1) Similar Turbidity Performance: NTU 0.5 mg/l: 11% 1 mg/l: +3% +7% +20% +29% 30

31 Polymer Trial Results Summary Trial Number Test Conditions Polymer (mg/l) Chlorine (mg/l) ph C Mean Turbidity (NTU) C3/C % Difference 35.5% 48.5% 43.1% 61.2% 52.8% 17.4% 18.2% Mean Total Particle Count (cts/ml) C C3/C % Reduction 10.6% 51.3% 55.7% 81.5% 79.7% 17.9% 21.1% Time to Terminal Headloss (hr) UFRV (m) C3/C Not Reached Not Reached C3/C

32 Slide 31 CP10 Good layout Con Pelekani, 30/10/2014