Disinfection Performance in Wastewater Stabilization Ponds in Cold - - PowerPoint PPT Presentation

Disinfection Performance in Wastewater Stabilization Ponds in Cold Climate Conditions: A case study in Nunavut, Canada

• Dr. Pascale Champagne

Lei Liu & Alan MacDougall Department of Civil Engineering, Queen’s University Kingston, Ontario, Canada

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Background

 Advantages of WSPs

• Low energy required
• Easy to operate
• Less equipment maintenance
• Economical
• Effective disinfection

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WSP facility located in Amherstview, ON, Canada

Background

 Disadvantages of WSPs

• Require more land
• Highly depend on

environmental conditions

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WSP facility located in Pond Inlet, Nunavut, Canada

Background

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• Disinfection in WSPs

– Capable of removing a wide range of pathogens

• Bacteria: 2 – 6 log unit
• Viruses: up to 5 log unit
• Protozoa: >90%
• Helminth: >90%

– Removal mechanisms/factors

• Sunlight
• pH
• DO
• Temperature
• Attachment/sedimentation
• Predation

Bolton, N. F., Cromar, N. J., Hallsworth, P., Fallowfield, H. J., 2010. A review of the factors affecting sunlight inactivation of microorganisms in waste stabilisation ponds: preliminary results for enterococci. Water Sci. Technol. 61, 885-890.

Bacteria Viruses Protozoa Helminth Pathogenic Organisms

Background

• Algal photosynthesis, pH and DO

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• H2CO3*

<-----> CO2 + H20

• Eq.1

HCO3-

• +

H2O <-----> H2CO3* + 0H-

• Eq.2

CO32-

• +

H2O <-----> HCO3- + 0H-

• Eq.3
• CO2
• O2

+ C6H12O6

Sunlight Disinfection Mechanism 1: Oxygen-Independent UV-Radiation

• E. coli cell exposed to direct UV-B light resulting in cell death

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Disinfection Mechanism 2: Endogenous Photo-

Oxidation

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Representation of endogenous photo-oxidation. E. coli cell constituent exposed to UV-B radiation, producing reactive oxygen species (ROS). The ROS damages DNA, resulting in cell death.

Disinfection Mechanism 3: Exogenous Photo-

Oxidation

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Representation of endogenous photo-oxidation. E. coli cell constituent exposed to UV-B radiation, producing reactive oxygen species (ROS). The ROS damages DNA, resulting in cell death.

Why Study Disinfection in Cold Climate WSPs?

Nunavut Water Board (NWB)

City of Toronto

• E. coli

(CFU/100mL) 104-106 200

• If environmental variables affecting

naturalized disinfection in WSPs do not meet certain threshold, disinfection can be compromised.

• Indigenous Drinking water crisis -

source water protection (SWP).

Arctic WSP in Pond Inlet, NU (top). E. coli O157:H7 bacteria under electron microscope (bottom).

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Northern, Remote and Rural Communities & Water/Wastewater Issues

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“…wastewater management, particularly sewage, is especially problematic for First Nations. This problem is not just about how others dispose of their sewage and how this affects our lands and waters, but how inadequate our own wastewater systems are on our reserves. … 75% of the 740 water treatment systems on reserves and 70% of the 462 wastewater treatment systems on reserves posed a medium-to- high risk to drinking water and wastewater quality…”

• Expert Panel report on Safe drinking water,

AFN, 2012

A typical Canadian Arctic Wastewater Treatment System

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Objectives

• To investigate the level of disinfection that is achieved for systems under

extreme climatic conditions

• To understand disinfection mechanisms in Arctic WSPs
• To conduct a comparative analysis of disinfection models using Arctic data.
• To provide guidelines for refining regulations and enhancing treatment

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WSP in Pond Inlet, Nunavut

Pond Inlet WSP

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Pond Inlet We are here! 72o42’N:77o57’W

Field Study: Pond Inlet, Nunavut

Pond Inlet Volume (m3) ~100,000 Depth (m) 1.5-3m Discharge rate (m3/day) ~104 Population 1500

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Approximated hydraulic model Pond Inlet WSP (a) Plan view with sampling plan (b) Profile view of bathymetry

• f Pond Inlet WSP

Characteristics of Pond Inlet WSP

Methods

• Parameters

– Sunlight intensity (Jaz spectrometer) – pH & Temperature (Hydrolab) – Selected indicator organisms (membrane filtration)

• E. coli
• Fecal coliforms
• Total coliforms

– Nutrients (Hach Kits)

• COD
• Total Phosphorus (TP)
• Total Nitrogen (TN)

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Field Study: Pond Inlet, Nunavut

Figure 8.a) pH, DO and temperature values with interpolation between trip 1 and trip 2 b) Synthesized surface irradiance at the surface of the WSP

• Data Interpolation:

OLS method + random noise from a

normal distribution with standard deviation of the sampled data.

Results – Sunlight Attenuation

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Results – Water Quality Parameters

Parameter Influent Trip 1 (July) Trip 2 (August) pH 7.3 9.4 7.4 Temperature (°C) 22 17.5 7 TN (mg/L) 41 N/A 26 (37%) TP(mg/L) 63 38 (40%) 39 (38%) COD (mg/L) 650 378 (42%) 492 (24%)

Chl-a Chl-b

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Trip 1

Results – Indicator Organisms

Trip 1 (July) Trip 2 (August) Influent Effluent Influent Effluent

• E. coli (CFU/100ml)

5.1 x 106 8.9 x 105 2.5 x 107 1.3 x 106 Fecal coliforms (CFU/100ml) 1.8 x 107 2.8 x 106 1.1 x 108 1.1 x 107 Total coliforms (CFU/100ml) 2.3 x 107 3.7 x 106 1.3 x 108 1.23 x 107

Standard Nunavut Water Board (NWB)

• E. coli (CFU/100ml)

104 - 106

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Results – comparison of Pond Inlet WSP and Clyde River WSPs

Pond Inlet Clyde River Effluent Primary effluent Final effluent

• E. Coli (CFU/100ml)

8.9 x 105/ 1.3 x 106 5.18 x 106 1.61 x 104 Clyde River WSPs

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Pond Inlet Clyde River

Parameters considered in these models:

How Do Past Disinfection Models Perform in Predicting Cold Climate WSP Disinfection?

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A comparison of past models in predicting performance using data collected from Pond Inlet, NU. Model Parameters

Marais (1974)

Temperature

Auer et al. (1993)

Sunlight, sedimentation

Curtis et al. (1992)

Sunlight, pH, DO

Xu et al. (2001)

Sunlight, temperature

Mayo (1995)

Sunlight, pH

Mortality rates predicted by the models over the course of the treatment season

How Do Past Disinfection Models Perform in Predicting Cold Climate WSP Disinfection?

• Overprediction of disinfection performance likely caused by

two factors:

• 1. Extrapolation outside of the parameter ranges (pH, DO,

temperature etc.) for which the model was designed.

• 2. The use of surface irradiance for quantifying the effect of

sunlight rather than depth-averaged irradiance.

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Conclusions

• Pathogen removal in Arctic WSP systems is likely driven by a combination of

mechanisms and factors

• Elevated pH coupled with sunlight may contribute to the minimal disinfection in

Pond Inlet’s WSP

• Elevated pH is attributed to the presence of algae. Therefore, algae’s presence in

natural wastewater treatment systems may contribute to disinfection.

• Single celled WSP in Pond Inlet inconsistently effective indicator organism removal

according to Nunavut Water Board’s guidelines.

• Current disinfection models are unable to replicate disinfection performance in

Pond Inlet’s WSP. WSP disinfection model for Polar climates should be developed to aid design and modification of WSP systems.

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Potential solutions

• Enlarge surface area
• Implement additional pond(s)
• Add coagulant
• Inoculate algae
• Adapt disinfection models

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Acknowledgements

• Dr. Champagne’s Research Group
• Lei Liu
• Alan Macdougall
• Meng Jin
• Rami Maassarani
• Christine Gan
• Dr. Shijian Ge
• Dr. Omar Valdez
• Madeline Howell

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