Walkerton Clean Water Centre Fall Small Systems Seminar. Water Quality Challenges in Small Drinking Water Systems in Southern Ontario

Transcription

1 Walkerton Clean Water Centre Fall Small Systems Seminar Water Quality Challenges in Small Drinking Water Systems in Southern Ontario Gamsby and Mannerow Limited October 25,

2 Introduction Background This presentation consists of a selection of water quality issues that have been encountered during our firm s experience with regulated small drinking water systems since new drinking water regulations emerged in 2000 following the Walkerton tragedy. Each water quality topic includes an introductory statement, background discussion of the issue, a system description, investigation of root causes, and selection of an appropriate solution(s). Selected Topics Disinfection By-Product (DBP) Control Raw Water Turbidity Technical Considerations for Implementing Membrane Treatment Taste and Odour Control 2

3 Disinfection By-Product (DBP) Control Introduction Definition : Disinfection By-Product (DBP) is a chemical that is formed unintentionally as a result of chlorine-based (typically) chemical disinfectants reacting with naturallyoccurring chemicals in water. DBP s are considered to be problematic or health concerns. Background Groundwater in some areas east of Toronto (York Region, Durham Region, Northumberland County) tends to exhibit elevated concentrations of ammonia, natural organic matter (DOC, TOC, Organic Nitrogen), methane, iron, and manganese. High doses of chlorine are required to oxidize ammonia, as well as iron and manganese, to achieve breakpoint chlorination, resulting in formation of disinfection by products (THM s, HAA s, chlorite). There are various options available for DBP control, including : Other forms of chlorine (chloramines, chlorine dioxide) Alternative oxidants for filtration prior to chlorine application Combination of chlorine-based disinfectants with UV Improved clearwell hydraulics Removal of DBP precursors (organic compounds) Advanced oxidation processes (e.g. UV plus H 2 O 2, UV plus O 3 ) 3

4 Disinfection By-Product (DBP) Control Background Information Item Description Site 1 Municipal Residential Site 2 Children s Camp Site 3 Children's Camp Location Northumberland County Durham Region Durham Region System Capacity 905 L/min. 950 people 152 L/min. 150 people 114 L/min. 70 people THM Monitoring Requirements Reg. 170/03 Schedule 13 Section 13-6 (quarterly) Not required Not required Water Source Drilled Wells (3) Drilled Well Drilled Well Well Classification Non GUDI Non GUDI Non GUDI Well Depth 208 feet (63m) 202 feet (62m) 172 feet (52m) Confining Layer(s) 148 feet (45m) clay 192 feet (59m) clay 151 feet (46m) clay Production Zone Brown Sand Black Sand Black Sand Casing and Screen Casing to ~180 ft. (55m) Screen to ~200 ft. (61m) Casing to 198 ft. (60m) Screen to 202 ft. (62m) Casing to 157 ft. (48m) Screen to 172 ft. (52m) Note : Information for the wells at Site 1 are average values for 3 production wells. 4

5 Disinfection By-Product (DBP) Control Water Quality Summary Parameter Raw Groundwater Standard Conc. (mg/l) Site 1 Municipal Site 2 Children s Camp Site 3 Children s Camp Iron (Total) AO Manganese (Total) AO Dissolved Organic Carbon (DOC) AO to Organic Nitrogen OG < no test Ammonia (TAN) ns ns 2.0 to Methane (CH 4 ) AO 3 L/m 3 6 to Bromide (Br) ns ns 315 ug/l no test no test Colour AO 5 TCU 11 <3 17 ph OG 6.5 to Nitrate (NO 3 ) MAC 10 <0.05 <0.2 <0.2 Sodium (Na) MAC 20/ Distributed Water THM s MAC to to Bromate (BrO 3 ) MAC to no test no test Chlorite (ClO 2 ) MAC to 1.70 no test no test Note : Values for Chlorite are based on experimental data. Ozone was not tested. No full scale trails were performed with ClO 2 or O 3. 5

6 Disinfection By-Product (DBP) Control Summary of Disinfection Strategies Method of Disinfection Description Advantages Disadvantages Free Chlorine (original strategy prior to process upgrades) Sodium hypochlorite injection to raw water. Apply sufficient dose to oxidize all constituents plus have excess ( free ) residual Well established and understood method Achieves consistent reliable level of disinfection Operational simple, no complex equipment or controls required High chlorine dosages (~ 20 mg/l) required, creating THM DBP s Elevated sodium in treated water High chemical (Chlorine) consumption Reduces service life of equipment (esp. electrical) due to ambient chlorine off-gassing Fe / Mn Filtration P Treated Water to Distribution Free Chlorine Residual Well NaOCl (high dose) Reservoir (unbaffled) Original Primary Disinfection Strategy Free Chlorine (high dose ~ 20 mg/l) 6

7 Disinfection By-Product (DBP) Control Summary of Disinfection Strategies, (cont d) Method of Disinfection Description Advantages Disadvantages Ultra-Violet Irradiation (UV) Photo chemical method using a high voltage current inside a quartz lamp to vaporize a mercury amalgam, which emits UV wavelength radiation. Typical design target dose is 40 mj/sq.cm at peak design flow Well established and understood method Effective against many water borne pathogens at low doses, including E. coli, cryptosporidium, giardia, and most viruses. Complementary strengths when used in combination with free chlorine and provides a multiple-barrier approach to disinfection Relatively small footprint Moderate level of operation and maintenance effort No residual disinfectant Pre-treatment required to achieve high UV Transmittance (UVT) No direct on-site method to validate successful disinfection since no residual created. Very high UV dose required to inactivate Adenovirus-40 Examples of Small Capacity UV Systems 7

8 Disinfection By-Product (DBP) Control Recommended Disinfection Strategy Length-to-Width Rations for Various Baffle Configurations Rating Curve with Corresponding T 10/ T Values for CT Calculations Installation of Baffle Curtains Inside an Existing Reservoir 8

9 Disinfection By-Product (DBP) Control Summary of Disinfection Strategies Method of Disinfection Description Advantages Disadvantages Alternative Oxidant with Combined Chlorine (Chloramines) and UV Use Potassium Permanganate (KMnO 4 ) for Fe/Mn filtration Combination of KMnO 4 to oxidize and filter minerals (Fe, Mn) prior to Cl injection. Leave natural ammonia unreacted in water Injection of chlorine after filtration to create chloramine residual Well established and understood method Effective method of DBP control Relatively simple process upgrade No complex equipment or controls required Very stable secondary disinfectant KMnO 4 must be very accurately dosed Chloramines are weak oxidants, require supplemental primary disinfection system such as UV under some operating conditions Increased water quality monitoring required in distribution system for early detection of nitrification P Treated Water to Distribution Fe / Mn Filtration UV Combined Chlorine Residual (Chloramines) Well KMnO4 (Alt. oxidant) NaOCl (low dose) Reservoir - Upgraded with Baffle Curtains Upgraded Primary Disinfection Strategy Combined Chlorine + UV, alternative oxidant for filtration 9

10 Disinfection By-Product (DBP) Control Recommended Disinfection Strategy Primary Disinfection Combined Chlorine (i.e. Chloramines, predominately mono-chloramine NH 2 Cl) with contact time plus ultra-violet (UV) irradiation Pre-oxidize and filter minerals (iron, manganese) with KMnO 4 prior to hypochlorite injection Leave excess ammonia in water un-reacted (addresses DBP formation) Eliminate high breakpoint chlorine doses ( ~ 20 mg/l) which often led to sodium exceedances Add UV to provide a multiple barrier approach to disinfection Install baffle curtains in existing reservoir to improve mixing and CT, reducing required Cl dose Define operation conditions (max. flows, min. reservoir levels) to achieve primary disinfection, i.e. not compromise 2-log virus inactivation with chloramines. Outside the defined operating ranges, UV required. Secondary Disinfection Combined Chlorine (i.e. Chloramines, predominately mono-chloramine NH 2 Cl) Stable residual Distributed water quality must be monitored more intensively in a chloraminated system to detect changes in water quality and avoid nitrification events. Testing programme to detect onset of nitrification may include ph, HPC, NO 2, NO 3, TAN. May revert to free chlorine for brief period (3-4 weeks annually or as required). 10

11 Disinfection By-Product (DBP) Control Recommended Disinfection Strategy Examples of Greensand Filtration Systems using Potassium Permanganate as an Oxidant 11

12 Raw Water Turbidity Introduction Definition : Turbidity is a measure of suspended particles in water. The commonly accepted threshold between suspended and dissolved particles is 0.45 microns (um). Turbidity is a physical indication of raw water source quality as well as effectiveness of a filtration processes in a treatment plant. Turbidity impacts effectiveness of disinfection. Background Elevated raw water turbidity can exist in both groundwater and surface water supplies. Causes of elevated turbidity may be attributed to a variety of causes, requiring a site specific investigation of root causes and implementation of an appropriate solution. Approaches to address elevated raw water turbidity ranged from a direct approach of adding higher-level filtration, to operational changes, to changing the method of water delivery within the system, to improved instrumentation care and maintenance. 12

13 Raw Water Turbidity Example 1 Problem Elevated turbidity in raw groundwater Turbidity spikes on pump start-up Typical benchmark is less than 100 particles/ml >10 um Approach Raw water quality analysis, characterization. Collect representative samples, conduct particle size distribution analysis. Gradation across range of micron sizes at low range. Solution Direct approach - Upgrade filtration process Example of Particle Size Distribution Test Results 13

14 Solution Raw Water Turbidity High portion of suspended particles smaller than 1 um Upgrade filtration process with higher level filtration Micro-filtration (MF) NSF-53 certified cysts rated filter housings and elements for cartridge filters Ultra-filtration (UF) membranes (e.g. GE-Zenon Homespring, Aquacore) Ultra-filtration with blending to minimize investment in membrane equipment On-Line Turbidity Analyzer Ultra-Filtration Membranes Nominal pore size rating = 0.02 um) 14

15 Raw Water Turbidity Example 2 Problem Raw surface water turbidity tends to exhibit dynamic and unpredictable ranges. Approach Several alternative treatment and operational strategies available to manage and adapt to the reality of dynamic and unpredictable raw water quality. Solutions Improve location of water intake, away from sources of sediment such as streams, above lake bottom but well below wave action at surface, typically in deeper water with stable bottom is preferable. Backwashable micro-screening or media filtration (high solids removal capacity, low fouling potential, no disposable or consumable elements, can be manually backwashed more frequently when required during storms, seasonal lake turnover Exhausted Cartridge Filters Media Filters (20 um) Micro-Screen (100 um) 15

16 Raw Water Turbidity Example 2 (cont d) Solutions Low-lift pumping through treatment train to storage, high-lift pumping of treated water from storage to distribution. Offers operational flexibility, allows use of stored or hauled water on temporary / emergency basis Multiple raw water tanks in series for sedimentation Raw Water Tanks in Series Inside of Tanks Raised Outlet 16

17 Raw Water Turbidity Example 3 Problem Turbidity spikes detected by on-line raw water turbidity analyzer on well pump start-up Approach Convert control of raw water pumping from level to pressure Turbidity Analyzers Improvised Air Release Devices 17

18 Raw Water Turbidity Example 3 (cont d) Solution Unpressurized systems have to evacuate air column during each pump start-up cycle, creating air bubbles which are detected by on-line instrumentation as turbidity. Convert to pressurized low-lift side of system. Also allows raw water sampling at will. Main benefit keeps system pressurized to prevent de-pressurization and potential groundwater intrusion. Add pressure tanks for smooth hydraulics, reduce water hammer on pump start-up Open Inlet Pipe to Reservoir Reservoir Filling Hydraulic Float Valve 18

19 Raw Water Turbidity Example 4 Problem Consistently elevated turbidity measured by on-line instrumentation. Portable instruments and lab results indicated lower turbidity results. Treatment process was working properly. Approach Improve care and maintenance of instrumentation Measuring Cell of Turbidimeter Solution Regular inspection and cleaning of optical surfaces inside measuring cell of the analyzer. Cleaning Mechanism 19

20 Technical Considerations for Implementing Membrane Treatment Introduction In recent years, as drinking water standards improve and water quality monitoring becomes more intensive, membrane treatment processes such as reverse osmosis (RO) are being implemented to address specific water quality issues as part of a water treatment strategy. While RO has become well-established in the water treatment industry, there are several technical considerations that that must be dealt with to ensure successful implementation. This is particularly important when integrating RO into an existing treatment system. Technical considerations include: Source supply capacity, hydraulics of pumping in series Method of control of various system pumps (pressure, level, sequence) Feasibility of using VFD s for selected pumps Post-membrane (RO) treatment for suitable water quality Water wasted by small-capacity RO systems is significant, impacting system s ability to meet peak instantaneous demands Blending an option to reduce system cost and moderate impact of de-mineralized water Relevant water quality parameters include Langelier Index LI (most important), alkalinity, TDS or conductivity, ph, sodium, SDI to monitor RO and post RO treatment performance Use potassium chloride rather than sodium chloride for softener regeneration (KCl is 3X cost) 20

21 Technical Considerations for Implementing Membrane Treatment Duplex Ultra-Filtration Membranes Well Pressure Tanks FM Flow Meter Duplex Softener Duplex Organics Filter Cartridge Filters (2) A Well Pump Pressure Tank Additional Pressure Tanks Solenoid Valve RO System (8 TFC Modules) Duplex UV Units A S P RO Pump RO Reject Stream (30-40% Qin) Neutralizing Filter SIMPLIFIED PROCESS FLOW DIAGRAM Treated Water Storage Tank P System Pump Treated Water to Plumbing 21

22 Technical Considerations for Implementing Membrane Treatment RO System - Flow Meters RO System Frame Mounted Package System 22

23 Technical Considerations for Implementing Membrane Treatment 140 Water Supply System - Pump Curves Head (m) VFD for RO pump? affinity laws state that matching flow rate of well pump would require head to be reduced below osmotic pressure of membrane (75% Q 56% H) Flow (L/min) RO Pump at 56% speed Well Pump Original RO Pump New RO Pump 23

24 Technical Considerations for Implementing Membrane Treatment Summary of RO Water Quality Parameter ODWQS AO / OG Raw Groundwater RO Permeate Water Post RO Water (following neutralization) Total Dissolved Solids (Average mg/l +/- 1 S.D.) Langelier Index (LI) (Average +/- 1 S.D.) Alkalinity (Average mg/l +/- 1 S.D.) 500 mg/l 800 +/ / /- 116 no standard No testing / / to 500 mg/l 257 +/ / /- 15 ph (Average +/- 1 S.D.) 6.5 to / / / Sodium (Average mg/l +/- 1 S.D.) 20 / 200 mg/l 48 +/ / /- 3 Langelier Index (LI) is a composite parameter, primarily a measure of the degree of calcium carbonate saturation, but also takes into account, alkalinity, ph, calcium concentration, TDS, and water temperature. Measured in a lab. It is a calculated parameters and is unitless. LI = 0 is neutral LI < 0 tends to be aggressive LI > 0 tends to be scale forming. Above table presents average results from monthly water quality testing from the time the RO system was put into service in September 2010 until September

25 Taste and Odour (T&O) Control Introduction Hydrogen sulphide (H 2 S) is a unique water quality parameter in that human olfactory senses (smell, taste) may be more sensitive that current scientific analytical test methods for detection of this substance. Therefore, conducting a taste and odour survey when selecting treatment technologies for H 2 S removal is critical for producing finished water of acceptable quality for customers. Background Hydrogen sulphide (H 2 S) may be present in some groundwater, emitting as characteristic rotten egg taste and odour. The detection limit for H 2 S by common analytic test methods is mg/l to mg/l. Research conducted jointly in 1998 by the American Public Health Association (APHA), American Water Works Association (AWWA), and Water Environment Federation (WEF) Research indicates that humans can detect H 2 S down to concentrations in the range of to 0.25 ug/l or 2 orders of magnitude more sensitive than analytical methods. Even given the subjective nature of quantifying human sensory detection limits, standard analytical methods have a Method Detection Limit (MDL) of 20% to 40% of the aesthetic objective (AO) of mg/l. 25

26 H 2 S in Groundwater Supplies - Sulfate (SO 4 2- ): Taste and Odour (T&O) Control - Naturally occurring anion present in many groundwater supplies across Ontario - Indirectly responsible for taste and odour problems (i.e. smell of rotten eggs) from its reduction to hydrogen sulfide (H 2 S) - Conversion to H 2 S: SO organic matter S 2- + H 2 O + CO 2 S 2- + H + HS - (aq) HS - + H + H 2 S (gas) - Reactions occur under anaerobic conditions in the presence of decaying organic matter 26

27 Taste and Odour (T&O) Control Historical Raw Water Chemistry Parameter ODWQS AO In Service ( ) Concentration in Raw Water Testing (2000) Testing (2008) Testing (2009) ph 6.5 to H 2 S (mg/l) 0.05 <0.03 to to to Fe 2+ (mg/l) ~ 0.37 <0.10 to Mn 2+ (mg/l) ~ to Average % Removal for Key Parameters Parameter Calculated % Removal Greensand Catalox Fe 2+ 89% 87% Mn 2+ 78% 75% H 2 S 94% 96% (not detected) (not detected) 27

28 Taste and Odour (T&O) Control Blank Prepared H2S Sample Cells 28

29 Taste and Odour (T&O) Control Pilot Testing Apparatus 2 Greensand Filter Media Filter Effluent Polishing With GAC Contactors 29

30 Taste and Odour (T&O) Control - Based on Standard Method 2160C Flavour Rating Assessment - 19 participants - Smell, taste and rate each sample, and provide written comments Rating Rating Description I would be very happy to accept this water as my everyday drinking 1 water 2 I would be happy to accept this water as my everyday drinking water 3 I am sure that I could accept this water as my everyday drinking water 4 I could accept this water as my everyday drinking water 5 Maybe I could accept this water as my everyday drinking water 6 I don t think I could accept this water as my everyday drinking water 7 I could not accept this water as my everyday drinking water 8 I could never drink this water 9 I can t stand this water in my mouth and I could never drink it 30

31 Taste and Odour (T&O) Control Sample No. 1 Sample Description Blended Sample: 50% (by volume) Filtered Water from Filter 2, and 50% (by volume) Treated Municipal Water 2 Filtered Water from Filter 2 3 Filtered Water from Filter 1 with post GAC polishing, and rechlorination to approx. 0.5 mg/l 4 Filtered Water from Filter 1 5 Filtered Water from Filter 2 with post GAC polishing, and rechlorination to approx. 0.5 mg/l 6 Treated Municipal Water 7 Blended Sample : 50% (by volume) Filtered Water from Filter 1, and 50% (by volume) Treated Municipal Water 31

32 Taste and Odour (T&O) Control Average Score Sample Description Overall Assessment 2.5 Treated Municipal Water Filtered Water from Filter 2 with post GAC polishing, and re-chlorination to approx. 0.5 mg/l Filtered Water from Filter 1 with post GAC polishing, and re-chlorination to approx. 0.5 mg/l Blended Sample: 50% (by volume) Filtered Water from Filter 2, and 50% (by volume) Treated Municipal Water high acceptability 6.1 Filtered Water from Filter Blended Sample: 50% (by volume) Filtered Water from Filter 1, and 50% (by volume) Treated Municipal Water low acceptability 6.3 Filtered Water from Filter 1 32

33 Taste and Odour (T&O) Control Score +14 Sample Description Filtered Water from Filter 1 with post GAC polishing, and re-chlorination to approx. 0.5 mg/l Overall Assessment +12 Filtered Water from Filter 2 with post GAC polishing, and re-chlorination to approx. 0.5 mg/l +10 Treated Municipal Water high acceptability -21 Blended Sample : 50% (by volume) Filtered Water from Filter 1, and 50% (by volume) Treated Municipal Water -29 Blended Sample: 50% (by volume) Filtered Water from Filter 2, and 50% (by volume) Treated Municipal Water -32 Filtered Water from Filter 2 low acceptability -37 Filtered Water from Filter 1 33

34 Taste and Odour (T&O) Control Sulfide Concentration (mg/l) ODWQS AO = 0.05 mg/l Threshold Taste/Odour Concentration of H 2 S (gas) Run Time (hrs) Filter 1 Filter 2 Raw Water 34

35 Conclusions Taste and Odour (T&O) Control - Results of onsite pilot testing indicated that both filter media performed very well; reducing sulfide concentrations to non detect limits in all filter effluent samples - Results of the subsequent taste and odour survey, however, indicated that a post-filtration polishing step is required to produce aesthetically pleasing water - In other words, the qualitative analysis significantly changed the recommended option for full scale treatment at the subject well - Pilot treatability studies for reduction of H 2 S (gas) should therefore consider including a qualitative analytical component 35

36 Thank You For Attending. Questions? 36