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Document No. KCJ876_01A Crescent Head Enhanced Coagulation Jar Test Trials.docx 4 January 2016
Crescent Head Enhanced Coagulation Jar Test Trials
for Kempsey Shire Council
4 January 2016
DOCUMENT ISSUE RECORD
ISSUE DATE REVISION ISSUE ISSUED TO PREPARED BY APPROVED BY
04/01/2016 A First KSC RM MB
1. Introduction
The Crescent Head Water Treatment Plant (WTP) sources raw water from two bores located at Maguires Crossing. The bore water generally has excessive levels of dissolved iron, hydrogen sulphide, organics (colour), and turbidity. The treatment processes provide only limited removal of iron and turbidity and no significant removal of organics. In the past, the organics have resulted in elevated disinfection byproducts concentrations, specifically trihalomethanes (THMs). This has necessitated use of chloramine as the primary disinfectant. Due to these factors, Kempsey Shire Council (KSC) are considering construction of a new WTP for Crescent Head.
City Water Technology (CWT) completed the report Scoping and Options for New Crescent Head Water Treatment Plant for KSC. In the report, four potential treatment processes for a new WTP were presented:
Process Option 1: Aeration, enhanced coagulation, media filtration, and chlorination
Process Option 2: Aeration, enhanced coagulation, media filtration, GAC filtration, and
chlorination
Process Option 3: Ozone, enhanced coagulation, media filtration, ozone-BAC, and chlorination
Process Option 4: Aeration, coagulation, media filtration, MIEX®, and chlorination
KSC engaged CWT to undertake a jar testing study to help evaluate each of these treatment processes with the findings presented in this report.
The observations contained within this report are based upon the results achieved by CWT during our laboratory simulations using the raw waters collected by KSC staff and on the limited subset of treated water quality parameters able to be examined.
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2. Jar Test Program
1. Measurement of current raw water properties;
2. Establishment of a jar test methodology that replicated as closely as possible the four proposed
WTP Process Options;
3. pH adjustment and aeration of sample to facilitate iron oxidation and hydrogen sulphide removal;
4. Identification of optimal alum dose and coagulation pH for organics removal (enhanced
coagulation);
5. Trial of alternative coagulant, replacing alum with aluminium chlorohydrate (ACH);
6. Following treatment with the optimal pH, coagulant type, and coagulant dose:
a. Measure baseline (Process Option 1) treated water quality;
b. Chlorination and measurement of baseline (Process Option 1) treated water THM
formation;
c. Trial activated carbon dose with 5 and 10 minute contact times:
i. Pick the best jar (lowest colour);
ii. Measure activated carbon (Process Option 2) treated water quality (colour, TOC,
UV absorbance); and,
iii. Chlorination and measurement of activated carbon (Process Option 2) treated
water THM formation;
d. Trial ozone doses with 5 and 10 minute contact times:
i. Measure ozone residual (indigo method);
ii. Quench jars and measure UV absorbance and colour;
iii. Pick the best jar (lowest colour and/or UV absorbance);
iv. Measure biodegradable dissolved organic carbon (BDOC) and bromate; and,
v. Estimate ozone-BAC (Process Option 4) DOC based on BDOC result.
e. Trial doses of MIEX® resin at supplier’s recommended contact time:
i. Pick the best jar (lowest colour);
ii. Measure MIEX® (Process Option 4) treated water quality (colour, TOC, UV
absorbance); and,
iii. Chlorination and measurement of MIEX® (Process Option 4) treated water THM
formation.
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3. Results
Note that results achieved under laboratory conditions tend to differ to those achievable in a full scale treatment plant. This is due to margins of error introduced by the small volumes involved in the bench scale investigation amplifying minor variations (such as minor deviations in dosed volumes, wall effects in jars, imperfect matching of mixing velocities and filter media pore size). As such, the trends in results reported should serve as an indication of relative performance for comparison purposes rather than a definitive indication of actual performance when applied to a larger scale.
Turbidity results in particular tend to be higher in jar tests than that achieved during full-scale production.
The R2 values included in graphs are an attempt to explain the percent of variance in the data set drawn. In its simplest application, as used here, the R2 values offer an indication of how closely data points for a set of conditions were to the trendline drawn. The closer an R2 value is to 1, the more closely the line matches the distribution of the data points. It is a useful tool in identifying outliers or deciding which trends are robust enough to draw conclusions from. A plot with a low R2 value doesn’t necessarily mean that results are worthless but rather that they varied more with less discernible trends present. R2 values are more significant when looking at larger data sets and in regards to this report, the R2 values really only serve to reinforce that despite the limited number of data points, the trends observed seem robust enough for drawing conclusions from.
Raw water 3.1
Table 1. Raw water properties
Parameter Unit Crescent Head borewater 5/11/2015
Comments
Turbidity NTU 2.83 Low turbidity.
pH 5.02 After aeration, pH increased to 5.48, likely due to CO2 being stripped out.
Apparent Colour HU 17.5 Moderate/high level of colour present, mostly dissolved.
True Colour HU 15
% true colour 85.7%
Total iron mg/L Fe 1.094 Elevated iron present in raw water is predominantly soluble. The 2.4% particulate iron is likely to have resulted from oxidisation occurring during sampling and/or transport. After aeration, Total dropped to 1.055 and Soluble 1.034.
Soluble iron mg/L Fe 1.068
% soluble iron 97.6%
Total manganese mg/L Mn 0.049 Low manganese present. Unclear whether oxidisation has occurred during sampling/transport or is naturally readily oxidisable.
Soluble manganese mg/L Mn 0.028
% soluble manganese 57.1%
Aluminium mg/L Al 0.04 Low level of natural aluminium present.
Alkalinity mg/L CaCO3 9 Very low raw water alkalinity present. Likely to prove problematic for coagulation and pH control.
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Parameter Unit Crescent Head borewater 5/11/2015
Comments
Conductivity µS/cm 132 Good/low levels of conductivity in raw water.
Temperature °C 14
Visual Apparent colour visible
Odour Unidentified odour detected
DOC mg/L C 6.1 Performed by Sydney Water Analytical Monitoring Services
THM µg/L <0.5 Performed by Sydney Water Analytical Monitoring Services
Bromide mg/L 0.10 Performed by Sydney Water Analytical Monitoring Services
Bromate µg/L <0.5 Performed by Levay & Co. Environmental Services
Alum coagulation pH optimisation 3.2
Using an estimated dose of 120mg/L liquid alum, a range of coagulation pHs were trialled.
Note that due to the very low raw water alkalinity there was minimal buffering and subsequent attempts to control coagulation pH using lime were difficult. As a result it was not possible to reliably generate results for pHs below 6.69.
In the Process Options investigated, this situation was addressed by dosing CO2 in conjunction with lime. In practice this allows precise control of coagulation pH and converts hydroxide alkalinity from the lime to bicarbonate alkalinity. Hydroxide provides no buffering of pH, whereas bicarbonate is an effective pH buffer. Unfortunately this could not be replicated under laboratory conditions.
Table 2. Alum coagulation pH optimisation
Aluminium sulphate dose (mg/L as 47% liquid alum)
Parameter Unit 120 120 120 120
Filtered Turbidity NTU 0.177 0.136 0.068 0.102
pH 6.69 6.78 6.89 6.97
Apparent Colour HU 5 5 5 5
True Colour HU 5 5 5 5
Total Fe mg/L Fe 0.067 0.010 0.053 0.058
Sol Fe mg/L Fe 0.055 0.009 0.048 0.010
Total Mn mg/L Mn 0.040 0.036 0.029 0.025
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Aluminium sulphate dose (mg/L as 47% liquid alum)
Parameter Unit 120 120 120 120
Sol Mn mg/L Mn 0.016 0.014 0.014 0.016
Total Al mg/L Al 0.02 0.02 0.05 0.27
Max floc size mm 0.5 0.7 0.9 1
Floc class A-G B B C D
Figure 1. Alum coagulation pH optimisation
R² = 0.8891
0
0.1
0.2
0.3
6.6 6.7 6.8 6.9 7
Turb
idit
y (N
TU)
Coagulation pH
Filtered Turbidity
R² = 0.5561
R² = 0.2301
0.000
0.020
0.040
0.060
0.080
0.100
6.6 6.7 6.8 6.9 7
Tota
l Iro
n (
mg/
L Fe
)
Coagulation pH
Total Fe
Sol Fe
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Figure 2. Alum coagulation pH optimisation (continued)
Observations on alum coagulation pH:
1. Floc size increased with elevation in pH; 2. Good turbidity reduction was achieved across the pH range trialled with all below ADWG target.
The best was 0.068 NTU at pH 6.89; 3. Good colour removal was achieved across the pH range trialled, although there was no discernible
difference in removal between the pH values (constant 67% removal of true colour); 4. Reduction of total manganese was superior at higher pH although soluble remained comparable
across the pH range trialled; and 5. Iron results were inconsistent although adequate removal to meet ADWG values was achieved
across all pHs trialled.
R² = 0.9963
R² = 0.9981
0.000
0.010
0.020
0.030
0.040
0.050
6.6 6.7 6.8 6.9 7
Tota
l Man
gan
ese
(m
g/L
Mn
)
Coagulation pH
Total Mn
Sol Mn
R² = 0.9999
0.0
0.2
0.4
0.6
0.8
1.0
6.6 6.7 6.8 6.9 7
Max
flo
c Si
ze (
mm
)
Coagulation pH
Max floc size
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Alum dose optimisation 3.3
Using a targeted coagulation pH of 6.2 - 6.3, a range of alum doses were then trialled to identify the
optimal alum dose for organics removal (enhanced coagulation)
Table 3. Alum dose optimisation results
Aluminium sulphate dose (mg/L as 47% liquid alum)
Parameter Unit 60 80 100 120
Filtered Turbidity NTU 0.498 0.301 0.164 0.175
pH 6.28 6.32 6.29 6.26
Apparent Colour HU 5 5 5 5
True Colour HU 5 5 5 5
Total Fe mg/L Fe 0.054 0.026 0.060 0.054
Total Mn mg/L Mn 0.037 0.008 0.020 0.008
Total Al mg/L Al <0.01 <0.01 0.04 0.09
Temperature °C 18 18 18 18
DOC mg/L C 3
THM µg/L 21.4
Bromide mg/L <0.10
Figure 3. Alum dose optimisation
R² = 0.9946
0
0.1
0.2
0.3
0.4
0.5
0.6
60 80 100 120
Turb
idit
y (N
TU)
Alum dose (mg/L filter alum)
Filtered Turbidity
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Figure 4. Alum dose optimisation (continued)
Observations on alum dose optimisation:
1. Turbidity reduction improved as alum dose increased. Good turbidity reduction was achieved across the dose range trialled with the best 0.164 NTU achieved at an alum dose of 100 mg/L;
2. Good colour removal was achieved across the range of alum doses trialled, although there was no discernible difference between doses (constant 67% removal of true colour);
3. Manganese results were good with all meeting ADWG values; and 4. Iron results were good with all meeting ADWG values.
ACH dose optimisation 3.4
With alum coagulation pH and dose optimised, an alternative coagulant was trialled, replacing alum with
aluminium chlorohydrate (ACH). However even after trialling doses ranging from 5-100 mg/L as Al2O3, no
flocs developed. Further trials were subsequently abandoned.
This may be related to the very low raw water turbidity (2.83 NTU), as under some conditions ACH can fail
to initiate coagulation and flocculation.
R² = 0.2558
0.000
0.020
0.040
0.060
0.080
0.100
60 80 100 120
Tota
l Iro
n (
mg/
L Fe
)
Alum dose (mg/L filter alum)
Total Fe
R² = 0.6259
0.000
0.020
0.040
0.060
0.080
0.100
60 80 100 120
Tota
l Man
gan
ese
(m
g/L
Mn
)
Alum dose (mg/L filter alum)
Total Mn
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Additional Treatment Options 3.5
With filtrate collected from the optimised alum dose and pH conditions, the additional treatment steps in
the Process Options were then replicated.
3.5.1 Process Option 1: Base (optimised alum dose and coagulation pH only)
Filtrate was chlorinated with 5mg/L sodium hypochlorite.
3.5.2 Process Option 2: Granular Activated Carbon (GAC)
Filtrate was soaked in a GAC bed for 5 and 10 minute durations, then filtered and chlorinated with 5mg/L
sodium hypochlorite.
3.5.3 Process Option 3: Ozonation
Filtrate was sent to Research laboratory Services (RLS) for external ozonation using 1 and 2 mg/L O3 for contact times of 5 and 10 minutes.
3.5.4 Process Option 4: MIEX®
Following the procedure and advice provided by IXOM, the filtrate was dosed with the proprietary MIEX® product at rates of 2000 (0.5 mL resin per litre) and 400 (2.5 mL resin per litre) bed volumes and stirred for 15 minutes. The beads were then magnetically settled and the supernatant collected and chlorinated with 5mg/L sodium hypochlorite.
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3.5.5 Results
Table 4. Comparison of additional treatment options.
Parameter Unit Raw Base GAC 5 min
CT
GAC 10 min
CT
MIEX 2000 BV, 15 min
CT
MIEX 400 BV, 15 min
CT
OZONE 1 mg/L, 5 min CT
OZONE 1 mg/L, 10 min
CT
OZONE 2 mg/L, 5 min CT
OZONE 2 mg/L, 10 min
CT
DOC mg/L 6.1 3 0.8 0.9 3.1 1.5 2.4 2.4 2.4 2.4
DOC after 8 day biological contact
mg/L 1.5
BDOC (8 day) mg/L 0.86
Estimated DOC post BAC filtration
mg/L 2.0
THM µg/L <0.5 21.4 0.8 0.5 22.7 8.8
Bromide mg/L 0.1 <0.10
Bromate µg/L <0.5 1.8
Ozone residual mg/L O3 <0.01 <0.01 0.18 0.1
UV254 Abs/cm 0.049 0.050 0.050 0.043 0.042
% UV254 reduction vs Base % 22.9 22.3 29.6 30.9
True Colour PtCo 2 0.6 0.5 0.4 0.3
% true colour reduction vs Base 63.4 66.6 76.7 80
NOTE: Estimated DOC post biologically active carbon (BAC) filtration is based on an estimated 50% reduction in BDOC.
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4. Conclusions
Enhanced coagulation using an alum dose of greater than 100 mg/L liquid alum produced acceptable treated water results for turbidity, colour, iron, and manganese. There was no discernible difference for apparent and true colour values between doses with all 5 HU.
Coagulation pH appears to have less impact on treated water quality than coagulant dose with acceptable results achieved across the range trialled. Note that the very low raw water alkalinity present made control of pH problematic.
GAC produced the best reduction in DOC and THM formation compared to the base case.
The MIEX® product when applied at 400 bed volumes provided a moderate reduction in DOC and THM formation compared to the base case. It was observed that after magnetic settling a considerable portion of the beads remained in suspension.
DOC removal by ozone alone was not as effective as that achieved with GAC or the 400BV MIEX.
Filtration through biologically active carbon (BAC) post ozone treatment could potentially provide similar DOC removal and THM formation to the 400BV MIEX®.
RLS’ conclusions from their ozone study were that:
2 mg/L O3 dose with a 10 minute contact time provided the best UV254 and colour reduction.
However significant reductions in UV254 and colour were observed even at the lower 1mg O3 dose and shorter 5 minute contact time.
Ozone had no significant impact on DOC.
Even at the higher 2 mg/L dose and longer Ct, bromate formation was low and well below the ADWG.
Ozonation increased BDOC concentration of the water suggesting a strong potential for DOC reduction through biological activated carbon after ozonation.
The report provided by RSL has been included in the Appendix.
5. Appendix
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