Removal of Natural Organic Matter Fractions by Two Potable Water Treatment Systems:

Dual Membrane Filtration and Conventional Lime Soda Softening

Charles D. Goss* and Beata Gorczyca

Department of Civil Engineering, University of Manitoba

15 Gillson Street, Winnipeg, Manitoba, R3T 5V6 Canada

charlesgoss1@shaw.ca

Submitted to:

4th

Annual IWA Specialty Conference on Natural Organic Matter: From Source to Tap

and Beyond

July 27-29, 2011

Costa Mesa, California, USA

Acknowledgments

This group would like to acknowledge the following for financial support and technical

assistance on this project.

Financial Support

Manitoba Water Stewardship – Manitoba Water Stewardship Fund

Technical Support

Pembina Valley Water Cooperative and the Town of Morris, Manitoba

Portage la Prairie Water Treatment Plant and the City of Portage la Prairie, Manitoba

Jeff O’Driscoll and Ken Anderson (Genivar)

Victor Wei (Manager-University of Manitoba Environmental Laboratory

Abstract

The objective of this study was to investigate the removal of dissolved organic carbon

(DOC) fractions by two water treatment plants, the Portage La Prairie Water Treatment Plant

(PPWTP), which uses lime/soda softening with granular activated carbon (GAC) filtration, and

the Morris Water Treatment Plant (MWTP), a dual micro/nano membrane facility, located in

Manitoba, Canada. The study aimed to determine the cause of reportedly high trihalomethane

(THM) concentrations in plant effluent. Both the PPWTP and MWTP use surface water sources,

the Assiniboine and Red River, respectively, which are reportedly high in DOC, fluctuating from

7mg/L to 18mg/L throughout the year. As a result of the high DOC in the source water both

plants have reported high THM concentrations that have, in the past, exceeded the 100ppb

maximum limit set by the Province of Manitoba. Solid phase extraction (SPE) was used to

fractionate DOC in water samples collected during this study. The SPE method fractionated

DOC into six fractions: hydrophobic acid (HPOA), hydrophobic base (HPOB), hydrophobic

neutral (HPON), hydrophilic acid (HPIA), hydrophilic base (HPIB), and hydrophilic neutral

(HPIN).

Samples were collected from the PPWTP and Assiniboine River on November 8, 2010,

January 20, 2011 and April 2, 2011 to evaluate the DOC and DOC fraction removal throughout

the plant. Results found that the GAC filter was ineffective at removing DOC, often with DOC

concentrations increasing after the GAC filter. The HPOA fraction, largely believed to contain

the greatest THM precursors, was unaffected by GAC filter showing the potential cause for

reported high THM levels at the plant. All hydrophilic fractions increased after the GAC filter

and only the HPOB fraction was reduced by GAC filtration at the PPWTP. The recommendation

to the PPWTP from this group was to improve the coagulation process to reduce organic loads

on the GAC filter.

Samples were collected from the Red River on September 25, 2010, and fractionated, to

establish the relative composition of the river. The results found that the late summer

composition of the Red River was 45% hydrophobic and 55% hydrophilic, with 40% of the total

organic component being HPIN. On November 25, 2010 samples from the Red River and

MWTP were fractionated to establish membrane removal efficiency. The results were

unexpected finding that DOC increased from 8.7mg/L to 10.2mg/L. The HPIA and HPIN

fractions increased after the nano filter from 0.35-1.41mg/L and 2.00-4.00mg/L, respectively.

The HPOA fraction was found to be unaffected by the nano filter while the HPON, HPOB, and

HPIB faction had small decreases in concentrations. However, for samples collected in

February, 2011 DOC concentrations were reduced to <0.5mg/L by the nano filter. The reason

for the high DOC found after the nano for the November sampling period is unclear however it is

believed that (1) the samples were taken just prior to a cleaning event where filter was not

removing DOC effectively or (2) that the use of citric acid to clean the nano membrane could

have added a carbon source to the nano effluent. It is recommended that a pre-treatment process

be implemented prior to the micro/nano membranes to reduce the DOC load on the membranes

preventing both high THM concentrations and membrane fouling.

Introduction

Potable water treatment facilities in Manitoba often suffer from sources waters with high

concentrations of natural organic matter (NOM). High NOM causes concern due to the

formation of harmful disinfection byproducts (DBPs), such as trihalomethanes (THMs), which

form when chlorine reacts with NOM, during disinfection treatment (Singer, 1999). In Manitoba

water chlorine demands often exceed 5 milligrams per liter (mg/L), resulting in residuals of 0.04-

2.0 mg/L. If NOM is not removed prior to chlorination treatment the unreacted chlorine can

react with the NOM and form THMs, and other halogenated byproducts, which are potential

carcinogens (Krasner, 2009). As a result, the province of Manitoba had adopted standards set by

The Drinking Water Quality Act which requires all public potable water suppliers meet a

quarterly average of <0.100 mg/L for total THMs (TTHMs) (Manitoba Water Stewardship,

2007). Therefore, water treatment facilities are faced with improving the removal of the organic

matter from the raw water prior to chlorination in order to reduce the concentrations of THMs

and other halogenated byproducts.

NOM in Potable Water Treatment

Natural organic matter can be removed by both chemical and physical treatments. The

use of chemical coagulants in combination with filtration (sand or membrane) and physical

adsorption (activated carbon) are processes which treatment plants apply in order to remove

organics prior to disinfection. Although all of these processes remove NOM to some degree

each comes with their own set of drawbacks. Separating NOM laden coagulation flocs by

physical filtration either through sand or membrane filtration, or adsorption of NOM to activated

carbon filters, creates several challenges to treatment facilities. Mainly, all filtration systems

require some backwash, flushing or cleaning process in order to remove organics and other

materials built up on the surface. These cleaning procedures are often laborious and costly as it

requires the use of chemicals, water for backwashing, or physical cleaning by operators. Also,

the build-up of organics on the surface of membranes can cause reversible and irreversible

fouling and reduce the overall life of the membrane resulting in costly replacement (Agenson,

2007). The applications of adsorptive filters in situations where the NOM concentrations in the

source water are high have been used with limited success. Often these activated carbon filters

quickly reach adsorptive capacity due to size exclusion of large molecules blocking pores

thereby reducing their effectiveness of NOM removal (Amy, 1992). Therefore, these filters

require increased cleaning or flushing events and more frequent media replacement.

NOM largely consists of humic and fulvic acids which are largely believed to contain the

greatest THM precursors. Fulvic acids with high charge density, due to high carboxylic acid

moieties, are minimally affected by charge neutralization during coagulation compared to humic

acids (Musikavong et al., 2005; Amy, 1992). Although lowering the pH (pH 4-6.5) will improve

coagulation by reducing the charge density of fulvic acids as well as reduce the solubility of the

coagulant, water treatment operation at low pH ranges are difficult and costly due to high

volumes of acids required to overcome the buffering capacity of waters with high alkalinity

(Sawyer, 2003; Amy, 1992). Therefore, NOM not removed in coagulation pre-treatment has

potential to form THMs.

Natural organic matter is unique to location and therefore it is important to establish the

composition of organic matter as well as concentration (Chow, 2008). Organic carbon

fractionation studies are conducted to gain better understanding of the chemical and physical

properties of local organic matter. Studies often focus on dissolved organic matter, or dissolved

organic carbon (DOC), which is the organic carbon that is able to pass through a 0.45

micrometer (µm) filter paper, as this is typically harder to remove than particulate NOM.

Fractionation of DOC can be based on physical size through the use of filtration and size

exclusion chromatography. Likewise, chemical properties, such as hydrophobicity and charge,

can also be used to fractionate DOC. Methods developed that separate DOC on hydrophobicity

and charge were largely based upon methods originally developed by Leenheer and Aiken

(Leenheer, 1981, Aiken, 1992). Recent methods separate DOC into hydrophobic acid (HPOA),

hydrophobic base (HPOB), hydrophobic neutral (HPON), hydrophilic acid (HPIA), hydrophilic

base (HPIB), and hydrophilic neutral fractions (HPIN). The original methods used ion exchange

resins (eg. XAD-4 and XAD-8) which were often laborious to prepare and required long run

times (~24h). New methods have been developed to reduce sample preparation and run times.

One method developed by Ratpukdi et al. uses solid phase extraction (SPE) to fractionate DOC

into these six fractions (Ratpukdi, 2009). This method reduces run times to roughly 12 hours as

well as preparation times as the SPE cartridges are pre-packaged and the sample requires only

filtration and pH adjustment.

Dissolved Organic Carbon Fractions and THMs

It is largely suggested that the HPOA fraction, which is largely humic matter, has the

greatest potential to form THMs, and other by-products, due to its high aromaticity and reactivity

(Singer, 1999; Leenheer, 2003; Chow 2005). However, a review study conducted by Chow in

2005 mentions several studies that found the HPI fractions had greater THMFP while others

suggest that both HPO and HPI form THMs when chlorinated (Chow, 2005). This review, and

others, suggests that the formation of THMs is dependent on local environment and that THMFP

and organic composition are unique to that location. Therefore, caution should be taken when

estimating the potential of organic fractions to form THMs.

Objectives and Significance of Research

This study focused on the characterization of DOC and its removal in two water

treatment plants located in Manitoba that suffer from high DOC concentrations in the source

water. The first plant is located in Portage la Prairie and is a conventional softening plant with

ballasted flocculation pretreatment and granular activated carbon (GAC) filtration. The second

plant is located in Morris and is a newly constructed dual membrane (micro/nano) facility that

replaced a conventional lime soda softening plant. Both plants use surface water sources, the

Assiniboine and Red Rivers, which experience high NOM concentrations between 8 and 18

mg/L. As a result both plants have, in the past, experienced elevated THM concentrations

occasionally exceeding the Manitoba guideline of 0.100 mg/L.

This study utilized the Ratpukdi et al. solid phase extraction method to fractionate water

DOC in the samples collected from the Red and Assiniboine Rivers as well as the Morris and

Portage la Prairie water treatment plants in order to establish the removal efficiency of DOC

fractions by each process. Understanding removal efficiency of DOC from each plant will

provide operators and design engineers with greater knowledge of which processes are effective

at removing DOC and which need optimizing in order to reduce the formation of THMs.

Water Treatment Plants Analyzed in this Study

Portage la Prairie Water Treatment Plant (PPWTP)

The City of Portage la Prairie has a population of roughly 13,000 people and has been

growing at a steady rate for the past several years due to the development of food processing

industries and agriculture in the region. To meet the long term water demands of the growing

community, along with the construction of a new potato processing facility in the area, the

PPWTP underwent several upgrades from 2000-2003. Upgrades to increase water production

from 18 mega liters per day (ML/d) to 34ML/d were implemented in order to meet growing

demands, as well as, improving and adding treatment processes to overcome challenges such as

high turbidity, hardness, and organic matter, along with occasional increased algal growth, often

seen in the Assiniboine River. Turbidity levels at the PPWTP were found to exceed 1500

nephelometric turbidity units (NTU) and peaks of 6000 NTU have been recorded (Table 1). The

high levels of DOC (15mg/L) found in the river resulted in THM levels that often exceeded the

0.100 mg/L guideline set by the Province of Manitoba.

Table 1: Water quality for the Assiniboine River and PPWTP for samples collected in May

1999. Guidelines presented here are according to the Canadian Drinking Water

Quality Guidelines for 2001 (Table adapted from Anderson, 2003)

Parameters Raw Water Treated Water Guideline

Hardness (mg/L CaCO3) 349 133 200*

Turbidity (NTU) 140 0.3 1

TOC (mg/L) 15 7 10**

Chloroform (mg/L) 0.0003 0.100 -

Bromoform (mg/L) 0.0010 0.001 -

BDCM (mg/L) 0.0002 0.021 -

DBCM (mg/L) 0.0002 0.031 -

Total THMs (mg/L) 0.0017 0.153 0.1

Note: * = Operational objective

**= Aesthetic guideline

To improve the removal of turbidity a John Meunier ACTIFLO® Ballasted Flocculation

Clarification system was implemented as a preclarification step (Figure 1). Pilot studies found

that raw waters with turbidity levels of 2500 NTU could be reduced to 3 NTU overcoming the

occasional high spikes in turbidity seen in the Assiniboine River (Anderson, 2003 and 2004).

Figure 1: ACTIFLO® Ballasted Flocculation system (Anderson, 2003)

Along with the ACTIFLO® system, an additional clarifier and new chemical dosing systems

were installed to increase plant flow. Improvements to the backwash system for the four dual

media sand filters were made to improve plant performance and promote organics removal.

Ozone was applied to softened and clarified water to promote biologically stable water, to

minimize chlorine demand, reduce the formation of DBPs, and to improve taste and odor. In

addition to sand filtration granular activated carbon adsorption was introduced to reduce

organics. Upgrades were made to the storage reservoirs to increase disinfectant contact time and

plant capacity. Lastly, a state of the art control system replaced the original system in order to

provide operators with complete control and monitoring of the system.

Although preliminary plant performance tests indicate that the new system improved the

removal of turbidity and hardness, tests in 2007-2008 suggest the plant may not be effectively

removing organics as THM levels were found to occasionally exceed guideline limits (Table 2).

Table 2: THM results for Portage la Prairie Water Treatment Plant from 2007-2008

Date THM concentration (µg/L)

Chloroform BDCM DBCM Bromoform Total THM

January 9, 2007 20 16 12 <1 48

May 9, 2007 17 11 8 <1 36

August 23, 2007 79 30 13 1 123

December 11, 2007 42 23 6.7 0.3 72

January 7, 2008 57 26 8.9 0.6 92.5

April 22, 2008 50 < 9.5 < 59.5

*BDCM = Bromodichloromethane

DBCM = Dibromochloromethane

< = less than detection limits

Pembina Valley Water Cooperative (Morris, MB)

The Pembina Valley Water Cooperative owns and operates the water treatment plant in

Morris, Manitoba. The original Morris water treatment plant (MWTP) was constructed in 1998

and was a typical lime soda softening plant with a flow capacity of 32 liters per second (L/s)

however it was determined that the plant would need to be expanded to meet growth in

population and industry in the area. The source for the plant is the Red River and, like the

Assiniboine, is prone to high DOC concentrations often exceeding 12 mg/L, as well as turbidity

levels ranging from 37-455 NTU. Due to the high DOC concentrations in the Red River THM

levels were also found to, at times, exceed the Manitoba guidelines (Table 3).

Table 3: THM concentrations for two storage reservoirs supplied by the Morris water

treatment plant. Samples were collected on November 4, 2009

Parameter

THM concentration (µg/L)

Miami

(Influent)

Rosenort

(Influent)

Bromodichloromethane 21 17

Bromoform < <

Chloroform 100 44

Dibromochloromethane 2 3.8

In 2008, construction began at the MWTP to renovate the existing lime soda softening

plant into a state of the art dual membrane facility. The upgrade included Pall ARIA™ micro

membrane filtration and Pall Ultipleat High Flow nano membrane filters. According to Pall the

micro filters would remove turbidity to 0.1 NTU along with three log reduction of Giardia and

Cryptosporidium. The nano filters would remove hardness and reduce organic matter

concentrations to <0.5 mg/L. The implementation of the membrane system would expand

capacity from 32 L/s to 66 L/s with room to increase flow to 100 L/s if required. A 1,000,000 m3

retention pond was also constructed to provide the plant with more stable source water and to

ensure availability during drought. Figure 2 outlines the flow for the membrane facility in

Morris. Construction of the facility was completed in late 2009 and went online in early 2010.

Figure 2: Plant flow diagram for Pembina Valley Water Cooperative in Morris,

Manitoba (Figure supplied by Anderson, 2009)

Table 4: Water quality parameters for the Morris water treatment plant after the installation of

the membrane system. Samples were collected in March 26, 2010.

Sample

Identification Unit Raw Water Post Micro Post Nano Tap

DOC mg/L 13.5 10.5 <1.0 3.1

True Color TCU 15 15 <5.0 <5.0

TDS Calculated mg/L 743 735 <5.0 186

Turbidity NTU 0.82 0.1 <0.10 <0.01

Alkalinity mg/L CaCO₃ 316 315 3.5 74.2

The water quality parameters for the MWTP, taken after the installation of the micro and

nano membrane (Table 4), suggest that the system is capable of meeting water quality guidelines.

However, the presence of high organics found in the source water could cause significant

problems to membranes over long term use. DOC characterization can provide insight into the

potential for these organics to cause fouling preventing unnecessary replacement costs.

Research Methodology

Sample collection Portage la Prairie Water Treatment Plant and Assiniboine River

1 liter (L) water samples were collected from the Assiniboine River, via an intake in the

plant, as well as throughout the water treatment plant three times during this study; November 8,

2010, January 20, 2011 and April 2, 2011. These three sampling dates represent river water

conditions during fall (prior to snow fall), winter and spring. Figure 3 diagrams the sampling

locations at the PPWTP. November 8th

samples only tested the overall removal of DOC

throughout the plant. Samples were collected from before and after the GAC filter on January 20,

2011 to establish the DOC fraction removal efficiency of the filter. All samples collected at

Portage la Prairie and the Assiniboine on April 2, 2011 were fractionated using SPE method

(described below).

Figure 3: Sampling locations for Portage la Prairie water treatment plant. (1) Assiniboine

River (2) after ACTIFLO ballasted flocculation (3) after lime softening (4) after

recarbonation (5) after ozonation (6) after sand filtration (7) after sand filter reservoir

(8) after GAC (9) Finished water

Sample collection Morris Water Treatment Plant and Red River

1-4L water samples were collected at various times during the study from the Red River

as well as from the retention pond, post micro filter, and post nano filter effluent, prior to

blending. Samples were collected on August 11, 2010 to establish an estimate of the summer

THM and THM formation potential (THMFP) from the Red River and treated MWTP effluent.

THM concentration and THMFP analysis was conducted by ALS laboratories (ALS Laboratories

Winnipeg, Manitoba). Samples collected from the Red River on September 25, 2010 were

fractionated to establish the relative composition of the river DOC during late summer. On

November 23, 2010 and February 28, 2011 samples were collected from the river as well as the

retention pond, post micro filter and post nano filter for full fractionation study. Note that

February sampling did not include the Red River due to ice cover.

All DOC measurements were made using Standard Method 5310 with a Tekmar

Dohrmann Phoenix 8000 total organic carbon analyzer (Tekmar Dohrmann, Ohio) which was

calibrated according to the instrument manual. All DOC measurements were made in triplicate.

All samples collected during this study were filtered through 0.45µm nitro cellulose filter paper

prior to analysis except for THM and THMFP analysis conducted by ALS laboratories.

Fractionation using Solid Phase Extraction (SPE)

Prior to fractionation all samples were filtered through 0.45µm nitrocellulose filter paper

and were brought to room temperature. The fractionation method used in this study was

developed by Ratpukdi et al. (2009). The method fractionates DOC into six fractions:

hydrophobic acid (HPOA), hydrophobic base (HPOB), hydrophobic neutral (HPON),

hydrophilic acid (HPIA), hydrophilic base (HPIB), and hydrophilic neutral fractions and is as

follows. The fractionation procedure uses three nonpolar Bond Elute ENV cartridges (Varian

Inc, Lake Forest California), one Phenomenex Strata XC strong cation exchange cartridge, and

one Phenomenex Strata X-AW weak anion exchange cartridge (Phenomenex, Torrance,

California). All SPE cartridges contained 1gram of sorbent. The fractionation procedure begins

with all cartridges being conditioned with 10mL of HPLC grade methanol (MeOH). The Strata

XC and X-AW cartridges are then conditioned with 10mL of 1.0M hydrochloric acid (HCl). All

five cartridges are then rinsed with deionized water until the effluent DOC measured <0.100

mg/L. 1L of sample was adjusted to pH 7.0 using either concentrated sulfuric acid (H2SO4) or

1M sodium hydroxide (NaOH) and was drawn through the first ENV cartridge labeled ENV-1.

The fraction collected on the ENV-1 SPE cartridge is defined as the HPON fraction. The same

sample water was then adjusted to pH of 10 using 1.0M NaOH and drawn through the second

ENV cartridge (ENV-2). The fraction retained on this cartridge is the HPOB fraction. Next, the

sample water was adjusted to pH of 2 with H2SO4 and drawn through the third ENV cartridge

(ENV-3) capturing the HPOA fraction. Following the ENV-3 cartridge the sample water was

drawn through the Strata XC cartridge without pH adjustment. The HPIB fraction was retained

on the Strata XC cartridge. Lastly, the sample water was adjusted to pH of 7 with NaOH and

drawn through the Strata X-AW cartridge which captured the HPIA fraction. The fraction of

organic matter that was not retained by any of the five cartridges is defined as the HPIN fraction.

All samples were drawn though the SPE cartridges at 10-15 mmHg vacuum pressure. After the

sample was drawn through each SPE cartridge a 40mL sample was collected to measure the

DOC concentration. Figure 4 outlines the Ratpukdi et al. method.

Figure 4: DOC SPE fractionation setup (Ratpukdi et al., 2009)

Results and Analysis

Characterization of DOC in Assiniboine River and Portage la Prairie Water Treatment Plant

On November 23, 2010 samples were collected form the PPWTP and the Assiniboine

River to establish the general removal of organics during the treatment process. As shown in

Figure 5 the incoming DOC of 16.1mg/L is significantly reduced to 5.0 mg/L after coagulation

and clarification. The coagulant that is used at the PPWTP is Alufer S25. The DOC is further

reduced to 3.8mg/L after the sand filtration; however the concentration increases after the GAC

filter to 6.7mg/L.

Figure 5: DOC removal at the Portage la Prairie Water Treatment Plant for samples

collected on November 23, 2010 (Personal communication Hooshyar, 2010)

It was suspected that the increase in DOC may be due to the GAC media being over

capacity as a result of constant high DOC source water. Organics could leach into the water

from the filter increasing the concentration. This increase could potentially provide enough

organic content to form levels of THMs that would exceed guideline limits. It must be noted that

the effluent DOC was 1.5mg/L showing a removal after the GAC filter. However, there is no

treatment process after the GAC filter that would reduce the DOC; it is unclear how the removal

occurred. More data is currently being collected at this plant to evaluate DOC removal by the

GAC filter.

Water samples were collected on January 20, 2011, from before and after the GAC filter,

to determine the dissolved organic fraction removal efficiency/ability of the filter (Table 5). It

was found that there was no DOC removed by the GAC filter, on the contrary, the DOC was

found to increase by 0.2326mg/L or 3.2% following GAC filtration.

The water samples DOC were also fractionated (Table 5) to establish which fractions

were affected by the filter. HPIB and HPIA fractions showed the greatest increase in

concentration from 0.2950mg/L to 1.1228mg/L and 0.0438mg/L to 0.3229mg/L, while HPOA

and HPIN fractions were largely unaffected by the GAC filter. The HPON and HPOB fractions

experienced the greatest reduction by the GAC filter from 0.5711mg/L to 0.1075mg/L and

0.2879mg/L to 0.0441mg/L, respectively. The mechanisms that caused the overall change in

DOC composition occurring on/near the filter was not a focus of this study therefore reasoning

for the increase/decrease of fractions cannot be fully evaluated. However, the ineffective DOC

removal by the GAC filter suggests that the filter has exceeded adsorptive capacity.

0.02.04.06.08.0

10.012.014.016.018.0

DO

C (

mg/L

)

Table 5: DOC concentration changes occurring before and after the GAC filter at the

Portage la Prairie Water Treatment Plant for samples collected on January 20,

2011.

Fraction

DOC concentration (mg/L)

Before GAC After GAC

HPON 0.51±0.1 0.1075*

HPOB 0.288±0.003 0.0441*

HPOA 2.3±0.1 2.4442*

HPIB 0.2950±0.0006 1.12±0.01

HPIA 0.04±0.05 0.32±0.03

HPIN 3.7688±0.0008 3.4585*

Total 7.2674 7.5000

*No error value could be established due to instrument carryover.

Figure 6: Overall DOC removal at the Portage la Prairie Water Treatment plant. Samples were

collected on April 2, 2011(Hooshyar, 2011)

Figure 6 shows the overall removal of organics at the PPWTP for samples collected on

April 2, 2011. The removal of organics is largely done by the lime softening and recarbonation

processes removing 10mg/L, combined. Note that the ACTIFLO system was not active during

this sampling period. An increase in DOC from 7.0mg/L to 9.5 mg/L is seen after ozonation.

Sand filtration reduces the concentration of DOC down to 6.9mg/L however the GAC filter is

again ineffective at removing any organics showing an increase in DOC concentration to

7.2mg/L.

Fractionation of all samples collected on April 2, 2011 was conducted to determine how

each process within the plant affects DOC fraction removal (Figures 6 and 7). The fractionation

results for samples collected from the river and the PPWTP show that nearly all fractions were

reduced by lime softening and clarification with the HPOB fraction having the greatest reduction

of nearly 92%. After the ozonation process all fractions increased, except the HPIB fraction, by

15-50%. Similar results were seen in a study conducted by Śweitlik et al. (2004) where it was

found that after the application of ozone there was an increase in HPIA, HPIN and HPON, with a

small increase in HPIB (Śweitlik, 2004). Śweitlik et al. suggests that the application of ozone

will also increase the biodegradable organic carbon (BDOC) fraction (Śweitlik, 2004). Higher

0.02.04.06.08.0

10.012.014.016.018.0

DO

C (

mg

/L)

concentrations of BDOC could cause an increase in microbial populations in the system

potentially causing another source for the increase in organics seen in the PPWTP. Further

research on the effect of ozone and the increase in microbial populations is currently being

conducted to better understand if the presence of microbes influences the formation of THMs.

Sand filtration reduced all fractions by 21-42% except for HPIB which increased 97% after sand

filtration. The HPON fraction was unaffected by the sand filtration process. The GAC filter was

found to have similar results to the January 20, 2011 results which found the HPIN fraction to be

largely unaffected with only a small decrease in concentration of 0.5mg/L. The HPOA fraction

increased by 24% from1.6mg/L to 2.1mg/L, likewise the HPIB and HPIA fractions increased by

54% and 45%, respectively. Only the HPON and HPOB fractions were reduced by the GAC

filter with a removal of 64% for HPON and 100% for HPOB. These results clearly show that the

GAC filter is ineffective at removing all organic fractions. The GAC filter can be seen as an

unfavourable process as organics, especially the HPOA fraction, increase after the filter. In turn,

there is a large presence of HPOA in the finished water for this sampling period, and throughout

this study, suggesting there is potential to form THMs based on the high reactivity of the these

compounds noted in literature. However, there is some controversy as to the fraction of DOC

that contains the largest THMFP. Therefore, further analysis into the THMFP of organics found

in the Assiniboine River and PPWTP effluent is required. Currently, THMFP analysis for the

river and treatment plant is being conducted by this group. The results lastly show an increase in

HPIN, HPOA, HPOB and HPON fractions in the finished water while the HPIB and HPIA

fractions decreased. Although it is unclear why there is an increase in DOC in the system from

the GAC to finished water, this increase poses an issue for THM control. Further study into the

increase seen after the GAC to the finished water is ongoing.

Figure 7: Removal of DOC fractions from the Assiniboine River and Portage la Prairie Water

Treatment plant. Samples were collected on April 2, 2011.

0.000

1.000

2.000

3.000

4.000

5.000

6.000

7.000

DO

C (

mg

/L)

HPON HPOB HPOA HPIB HPIA HPIN

One suggestion to address the problem with high THMs at the PPWTP would be to

optimize the coagulation process prior to the GAC filter. If the coagulation process is optimized

for DOC removal the GAC filter will experience low concentrations allowing greater time before

the filter reaches capacity and no longer removes organics. The use of a more effective type of

GAC media is another possible solution to improve the removal of DOC. Cheng et al.

demonstrated that modified activated carbon such as iron impregnated or modification with

helium or ammonia significantly improved the removal of DOC over virgin activated carbon

(Cheng, 2005). Further investigation into a more effective type of carbon media is being

conducted by this group.

Characterization of DOC in Red River and Pembina Valley Water Cooperative (Morris,

Manitoba)

On August 11, 2010 samples were collected from the Red River and the Morris water

treatment plant to establish the THM concentrations as well as THMFP of the Red River and the

treated effluent (Tables 6 and 7). The results show that the THM levels for plant effluent are

below the guideline limits of 100ppb (Table 6), however the THMFP of the pond is significantly

higher than the guideline suggesting there is potential to for THM levels that exceed the 100ppb

limit. Likewise, the THMFP of the nano effluent also shows potential to form THM levels that

are greater than 100ppb. Although the Morris plant is seemingly controlling THMs there is

evidence that high DOC feed water can negatively impact the performance and lifetime of

membrane filters (Cho, 1999).

Table 6: THM concentrations for samples collected from the Red River and Morris water

treatment plant on August 11, 2010. Samples were analysed by ALS Laboratories

(Winnipeg, MB).

Sample Location

THM concentrations (mg/L)

Chloroform Bromoform Dibromochloromethane Bromodichloromethane

Red River <0.00050 <0.00050 <0.00050 <0.00050

Retention Pond <0.00050 <0.00050 <0.00050 <0.00050

Post Micro <0.00050 <0.00050 <0.00050 <0.00050

Post Nano 0.0280 <0.00050 0.00097 0.0062

Table 7: THMFP for samples collected on August 11, 2010 from the retention pond and post

nano effluent at the Morris water treatment plant. Samples were analysed by ALS

Laboratories (Winnipeg, MB).

Sample Location THMFP concentrations (mg/L)

Chloroform Bromoform Dibromochloromethane Bromodichloromethane Total

Retention Pond 0.495 <0.00050 0.00711 0.0627 0.565

Post Nano 0.1400 <0.00050 0.00153 0.0145 0.156

Samples collected from the Red River on September 25, 2010 were fractionated to

establish the relative composition of the river during late summer (Table 8). The results show

that the Red River is 45% hydrophobic and 55% hydrophilic, with 40% of the total organic

composition being HPIN. Although the concentrations of THMs at Morris are low (Table 6)

there is a large HPOA fraction of nearly 22% suggesting the potential to form THM upon

chlorination.

Table 8: Fractionation results for the Red River collected on September 25, 2010

Fraction DOC (mg/L) % DOC

HPON 2.47 22

HPOB 0.21 <2

HPOA 2.47 22

HPIB 0.21 <2

HPIA 1.46 13

HPIN 4.49 40

Total 11.3 100

Samples collected from the Red River and Morris water treatment plant on November 23,

2010 were fractionated to determine the removal efficiency of the micro and nano filter

membranes (Figure 8). The results obtained from this sample set deviated from what was

expected. It was suggested by the Pall Corporation that the nano membranes would be able to

reduce DOC concentrations to <0.5mg/L, however the results from this sample set found that

the DOC concentration increased after the nano filter from 8.7mg/L to 10.2mg/L. The HPIA and

HPIN fractions increased after the nano filter from 0.35-1.41mg/L and 2.00-4.00mg/L,

respectively. The HPOA fraction was unaffected by the nano filter while the HPON, HPOB, and

HPIB faction had small decreases in concentrations. It must be noted that shortly after this

sampling period the Morris plant reported unexpected levels of THMs in the distribution system

ranging from 75-86ppb (Fehr, 2010). Although the levels are still below the required 100ppb

guideline the increase is of concern since the maximum allowable THMs concentration are

rumoured to be reduced to 80ppb in the near future. The increase in THMs may have resulted

from the poor removal of organics seen during the November 23rd

sampling period. The reason

for the increase in DOC is not fully understood however there it is suggested that the sampling

event may have taken place just prior to a cleaning event where DOC rejection was not

efficiently occurring. Another potential cause is the use of citric acid as a cleaning agent for the

nano membranes. If the citric acid was not fully rinsed after the cleaning cycle it could have

caused the increase in HPIA. Further investigation into the relationship between membrane

cleaning cycles, citric acid as a possible organic source, and organics removal is suggested.

Figure 8: Fractionation results for Red River and throughout the Morris water treatment

plant. Samples collected on November 23, 2010

0

1

2

3

4

5

Red River Pond Post Micro Post Nano

DO

C (

mg

/L)

HPON

HPOB

HPOA

HPIB

HPIA

HPIN

Samples were collected on February 28, 2011 from the retention pond and at the Morris

water treatment plant for DOC and fractionation analysis. Note samples could not be collected

from the Red River due to ice cover. The DOC results found during this sampling period

resembled the expected results with the overall DOC being reduced from 9.00mg/L to 0.42mg/L

after nano filtration (Figure 9). Due to the low DOC in the nano filter effluent the sample could

not be fractionated. Pond water and post micro filter water fractionation results (Figure 10)

found that the change in overall DOC concentration was not significant after micro filter,

however there were noticeable changes in the overall composition of DOC following micro

filtration. There was a roughly 50% decrease in HPON (1.1mg/L to 0.53mg/L) and about a 50%

increase in HPIA (1.37mg/L to 2.46mg/L). This could be related to microbial growth on the

clean side of the nano-membrane surface or membrane surface-DOC interactions changing the

chemical properties of the compounds. The fractionation results also show there is a large

HPOA component in the post micro membrane filter effluent. This effluent is blended with nano

treated water at a 20-30% blend rate. This is done to increase hardness and alkalinity in the final

effluent that is removed by the nano filter. However, with the HPOA fraction being 35% of the

total DOC in the micro effluent caution should be taken when increasing this blend rate to ensure

organic concentrations do not increase to where THM levels are exceeding guidelines.

It is suggested by Fan et al. that hydrophobic polyvinylidene fluoride (PVDF)

membranes, such as those at the Morris plant, are fouled largely by HPIN and HPOA fractions

(Fan, 2001). These two fractions constitute nearly 52% of the total DOC entering the plant

suggesting there is a potential for fouling of the membranes.

Figure 9: Overall DOC removal at Morris water treatment plant. Samples collected February

28, 2011

Figure 10: DOC fraction removal at Morris water treatment plant. Samples collected

February 28, 2011

0

2

4

6

8

10

Pond Post Micro Post Nano

DO

C (

mg

/L)

0

1

2

3

4

Pond Post Micro

DO

C (

mg

/L)

HPON

HPOB

HPOA

HPIB

HPIA

HPIN

The evaluation of the organics removal at the Morris water treatment plant found that

although the membranes were effective at reducing the DOC concentrations and in turn control

the formation of THMs, there are points in time that the membrane is not effectively removing

DOC. The reasons for the increase in organics seen in the November samples is inconclusive

although there is evidence to suggest there may be a relation to cleaning events and/or the use of

citric acid in the cleaning of the membranes. It is recommended that the relationship between

cleaning events and increases in DOC should be investigated.

High concentrations of HPIN and HPOA, suggested by Fan et al., could cause organic

fouling to PVDF membranes. Therefore it is recommended that Morris re-implement a

pretreatment that will remove organics before entering the membranes. Initially the engineers

that designed the membrane upgrade used an existing clarifier from the original lime softening

plant as a coagulation tank to reduce the organic load seen by the membranes. However, this

process was not optimized and in turn unreacted coagulant (alum) was able to pass the micro

filters causing the nano filters pressure to dramatically increase to risky levels in a short time

(<24h). It was recommended by the engineers that the pretreatment be stopped due to the

potential damage of the nano membranes. If this pretreatment step were optimized (mixing

times, coagulant types, coagulant dose) the overall organic load would be reduced without the

risk of damaging the membranes. This could extend the life of the membranes, as well as reduce

the number of cleaning cycles, reducing the operation costs for the plant due to costly membrane

replacements. Optimization of the coagulation process for removal of targeted DOC fractions is

being currently investigated by Water Research Group at the University of Manitoba.

Conclusions and Recommendations

The objective of this research was to characterize the dissolved organic carbon and its

removal efficiency in two potable water treatment plants located in Portage La Prairie and Morris

(Manitoba, Canada). This study also aimed to establish the organic composition of the two river

sources for each plant, the Assiniboine and Red Rivers, and to evaluate the concentration of

fractions suspected to form THMs and foul membranes.

The first plant located in Portage la Prairie, which uses the Assiniboine River as a source,

is a lime softening plant with ballasted flocculation and granular activated carbon filtration. DOC

removal results from all sampling at the Portage la Prairie water treatment plant during this study

found that the granular activated carbon filter was ineffective at removing DOC, often with

concentrations increasing post GAC filter. The HPOA fraction, suspected to largely contain

THM precursors, was unaffected by the GAC filter and nearly all fractions, especially

hydrophilic compounds, increased after the GAC filtration.

The Morris plant is a newly designed dual membrane (micro/nano) facility that, like the

Portage plant, experiences source water high in DOC (Red River). Two sampling periods were

conducted on the Red River and at the Morris plant to evaluate DOC faction removal:

November, 2010 and February 2011. Results from the November, 2010 sampling found that the

nano membrane was not removing DOC effectively. Specifically the HPOA fraction and all

hydrophilic fractions were not removed by the nano filter. The results obtained in February,

2011 were very different than the November results as the nano membranes were found to

reduce DOC levels to <0.5mg/L. The reason for the high DOC found after the nano for the

November sampling period is unclear however it is believed that (1) the samples were taken just

prior to a cleaning event where filter was not removing DOC effectively or (2) that the use of

citric acid to clean the nano membrane could have added a carbon source to the nano effluent.

Further analyses are currently being conducted at the Morris plant.

Results obtained at both plants indicate that the major DOC fractions present in both raw water

supplies (Red and Assiniboine Rivers), ie. HPOA, HPIN, HPIA and HPIB are not effectively

removed by the treatment processes utilized. It is believed that the high concentration of the

HPOA fraction could lead to increased THM concentrations after chlorination.

The following recommendations can be made from this study:

Due to the uncertainty as to which fraction contains the greatest potential to form

THMs, a THMFP study of fractions collected from the Assiniboine River water

intake be conducted to establish which fractions in the local environment from

most THMs.

Optimize coagulation process and GAC filtration for removal of the targeted

DOC fractions.

Identify DOC fraction with the highest nano-filter fouling potential.

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