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 1

Background  Advantages of WSPs  Low energy required  Easy to operate  Less equipment maintenance  Economical  Effective disinfection WSP facility located in Amherstview, ON, Canada 2

Background  Disadvantages of WSPs  Require more land  Highly depend on environmental conditions WSP facility located in Pond Inlet, Nunavut, Canada 9

Background • Disinfection in WSPs – Capable of removing a wide range of pathogens • Bacteria: 2 – 6 log unit Bacteria Viruses • Viruses: up to 5 log unit • Protozoa: >90% Pathogenic Organisms • Helminth: >90% – Removal mechanisms/factors Protozoa Helminth • Sunlight • Temperature • pH • Attachment/sedimentation • DO • 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: 4 preliminary results for enterococci. Water Sci. Technol. 61, 885-890.

Background • Algal photosynthesis, pH and DO � � CO 2 � � � � � � O 2� +� C 6 H 12 O 6� � � � H 2 CO 3 *� <----->� CO 2 � +� H 2 0� � � � � � � � � � � � � � Eq.1� HCO 3-� � +� H 2 O� <----->� H 2 CO 3 *� +� 0H - � � � � � � � � Eq.2� CO 32-� � HCO 3- � 0H - � +� H 2 O� <----->� +� � � � � � � � � � Eq.3� 5

Sunlight Disinfection Mechanism 1: Oxygen-Independent UV-Radiation E. coli cell exposed to direct UV-B light resulting in cell death 6

Disinfection Mechanism 2: Endogenous Photo- Oxidation Representation of endogenous photo-oxidation. E. coli cell constituent exposed 7 to UV-B radiation, producing reactive oxygen species (ROS). The ROS damages DNA, resulting in cell death.

Disinfection Mechanism 3: Exogenous Photo- Oxidation 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. 8

Why Study Disinfection in Cold Climate WSPs? • 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). Nunavut Water City of Toronto Board (NWB) E. coli 10 4 -10 6 200 (CFU/100mL) Arctic WSP in Pond Inlet, NU (top). E. coli O157:H7 bacteria 9 under electron microscope (bottom).

Northern, Remote and Rural Communities & Water/Wastewater Issues “…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 10

A typical Canadian Arctic Wastewater Treatment System 11

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 13

WSP in Pond Inlet, Nunavut Pond Inlet 72 o 42’N:77 o 57’W Pond Inlet WSP We are here! 14

Field Study: Pond Inlet, Nunavut (a) Plan view with sampling plan (b) Profile view of bathymetry of Pond Inlet WSP Characteristics of Pond Inlet WSP Pond Inlet Volume (m 3 ) ~100,000 Depth (m) 1.5-3m Discharge rate ~104 (m 3 /day) Approximated hydraulic model Pond Population 1500 Inlet WSP 14

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) 16

Field Study: Pond Inlet, Nunavut • Data Interpolation : OLS method + random noise from a normal distribution with standard deviation of the sampled data. 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 16

Results – Sunlight Attenuation 18

Results – Water Quality Parameters Trip 1 Parameter Influent Trip 1 (July) Trip 2 (August) pH 7.3 9.4 7.4 Chl-b Chl-a 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%) 19

Results – Indicator Organisms Trip 1 (July) Trip 2 (August) Influent Effluent Influent Effluent 5.1 x 10 6 8.9 x 10 5 2.5 x 10 7 1.3 x 10 6 E. coli (CFU/100ml) Fecal coliforms 1.8 x 10 7 2.8 x 10 6 1.1 x 10 8 1.1 x 10 7 (CFU/100ml) Total coliforms 2.3 x 10 7 3.7 x 10 6 1.3 x 10 8 1.23 x 10 7 (CFU/100ml) Nunavut Water Board Standard (NWB) 10 4 - 10 6 E. coli (CFU/100ml) 20

Results – comparison of Pond Inlet WSP and Clyde River WSPs Pond Inlet Pond Inlet Clyde River Effluent Primary effluent Final effluent Clyde River E. Coli (CFU/100ml) 8.9 x 10 5 / 1.3 x 10 6 5.18 x 10 6 1.61 x 10 4 Clyde River WSPs 21

How Do Past Disinfection Models Perform in Predicting Cold Climate WSP Disinfection? Parameters considered in these models: Model Parameters Marais (1974) Temperature Auer et al. Sunlight, sedimentation (1993) Curtis et al. Sunlight, pH, DO (1992) Sunlight, Xu et al. (2001) temperature Mayo (1995) Sunlight, pH A comparison of past models in predicting performance using Mortality rates predicted by the data collected from Pond Inlet, NU. models over the course of the treatment season 21

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. 23

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. 24

Potential solutions • Enlarge surface area • Implement additional pond(s) • Add coagulant • Inoculate algae • Adapt disinfection models 25

Acknowledgements Dr. Champagne’s Research Group • Lei Liu • Alan Macdougall • Meng Jin • Rami Maassarani • Christine Gan • Dr. Shijian Ge • Dr. Omar Valdez • Madeline Howell 26