Meeting Filtration and Disinfection By-Product Rules with

Modified Slow Sand Filtration Clean and Safe Drinking Water Workshop Newfoundland and Labrador 2011 Robert (Bob) A. LeCraw - MS Filter Systems Inc. Brian Jobb – Walkerton Clean Water Centre.

Slow Sand Filtration Why resurgence in popularity? • • • • •

Meets ALL regulatory requirements Low O & M costs / lowest life-cycle costs Relatively low operator skill level Simple process - no coagulation chemicals Serviceable by local trades

BASIC SLOW SAND FILTER

Water Level over sand Inlet Schmutzdecke

Sand

Overflow

Outlet

BASIC SLOW SAND FILTER

Inlet

Schmutzdecke scraped off

Sand

Overflow

Outlet

Modified Slow Sand Filtration

= Conventional Slow Sand Filtration (Simple Operation – Low O & M Cost)

+ Additional Unit Processes (Water Quality-Dependent)

Modified Slow Sand Filtration Unit Processes Can Include: • Ozonation and/or AOP (oxidation) • Roughing filtration (solids removal) • Post-treatment BAC filtration (additional biofiltration stage) • Post-treatment limestone contactor (corrosion) • Post-treatment disinfection (required)

Modified Slow Sand Filter SPLITTER BOX

OVERFLOW

INJECTOR

ROUGHING FILTER

SLOW SAND FILTER

OZONE CONTACTOR

OZONATORS

Plan

DE-GAS AND OZONE DESTRUCT

CLEAR PVC

SPLITTER BOX VENT

OVERFLOW

OZONATORS

ROUGHING FILTER SLOW SAND FILTER

INJECTOR OZONE CONTACTOR

DRAIN

Profile

Ozone Application

Modified Slow Sand Filtration Coagulation Chemicals Not Used • Natural Organic Colour = Large Complex Molecules - Not Biodegradable (DBP Precursors) • Complex Organics Oxidized into assimilable organic carbon (AOC) • Resulting “AOC” = More Bio-available Food Source for Microorganisms • Coagulants = 80 to 95% of sludge therefore no Coagulant = far less sludge

Modified Slow Sand Filtration Enables treatment of poor quality source water • Pre-Ozonation • Converts TOC to AOC; Oxidizes Fe, Mn • Powerful Disinfectant • Roughing filter with GAC cap • Extends range of raw water turbidity • Package Plant with “Automated” Cleaning • Effective for a broad spectrum of pathogens and contaminants

Slow Sand Filtration Slow Sand Meets Regulatory Requirements • •

Health Canada Treatment Guidelines USEPA – Slow Sand Plants Average 3-log removal of Cryptosporidium oocysts

•

Ontario MOE: Roughing Filter + Slow Sand (No Ozone) = 2.5-log Giardia removal credit

•

Documented ability to remove protozoan cysts and oocysts; > 5-log removal reported

Protozoan Cyst / Oocyst Removal • Recent Cryptosporidium oocyst removals reported for slow sand filtration: • 4.0 – 4.7 log (Anderson & Huck, 2005) • 4.0 log (DeLoyde, 2007) • 4.7 log (Hijnen et al, 2007) • 5.3 log (Dullemont et al, 2006) • Giardia cyst removal generally better than Cryptosporidium oocyst removal

Protozoan Cyst / Oocyst Removal • High cyst / oocyst removals consistent with earlier literature on slow sand filtration • Cyst / oocyst removal occurs in upper layers of the slow sand filter • Predation and/or biodegradation • Very low risk of delayed breakthrough

Bacteria / Virus Removal • Minimum 4.0 log reovirus removal reported • Poliovirus removal significantly better than MS2 bacteriophage removal • Bacillus spores and E. coli similar; consistently >2.5 log removal reported • Removal efficiencies organism-specific • Required post-treatment disinfection generally effective for bacteria and viruses

REMOVAL OF: Pharmaceuticals Personal Health Care Products & Endocrine Disrupting Compounds (= “PPHCPs” & “EDCs” ) and Other Exotic Compounds

PPHCPs & EDCs • Analytical capabilities for contaminants in drinking water are constantly improving • Reasons for concern: • Pharmaceuticals often engineered to target specific organs • Certain EDCs and pharmaceuticals have a nonlinear dose-response • Physiological effect becomes greater as the dose is reduced

PPHCPs & EDCs • Biological filtration reported to remove many common compounds including: • Certain classes of antibiotics (tetracycline, quinolone, and macrolides) • Acetaminophen, caffeine, DEET, ibuprofen • Certain polar pharmaceuticals are not effectively removed by biological filtration

Tastes & Odours Biological Filtration Alone • Geosmin / 2-MIB removed from 25 ng/L to threshold odour level with biologicallyactive GAC filters • 100 ng/L influent concentrations of geosmin reduced by ~ 60% • 100 ng/L influent levels of 2-MIB reduced by ~ 40% (1 ng/L = 1 ppt)

PPHCPs & EDCs

• Ozone + biofiltration effective treatment for most PPHCPs and EDCs (80 different compounds – Westerhoff, 2003) • Many compounds not removed by biological treatment were oxidized by ozone (synergy) • Oxidation byproducts of EDCs and PPHCPs were removed or reduced by biological filtration

Microcystins •

•

•

Biological and slow sand filtration effective at reducing microcystin-LR Ozone very effective at removing moderate and high levels of microcystins The combination of ozone with biological (slow sand) filtration provides two levels of protection

Modified Slow Sand Filtration Removal of AOC (or BDOC) following ozonation is very important: • Can lead to regrowth • May increase DBPs • Biological treatment very effective • TOC removals using O3 + biofiltration similar to alum coagulation • Excellent DBP precursor removal

TTHMFP Reduction BLANDFORD, MA PILOT STUDY TTHM Formation 120

Raw

TTHM (µg/L)

100

80

SSF No O3 60

40

O3 + SSF 20

0 0

50

100

150

200

Time (hours)

3-Day SDS

7 Day TTHMFP

Raw

HAA5 Blandford MA Pilot Study 100 90

HAA5 Concentration (ug/L)

80 70 Stage 1 DBPR MCL - 60 ug/L HAA5

60

Raw T1-Post O3 T1-Post SSF T2-Post O3 T2-Post GAC

50 40 30 20 10 0 0

20

40

60

80

100

Time (hours)

120

140

160

180

Source: Tighe & Bond

Developments in Ozone-Assisted Biofiltration u

Blandford, MA - Actual operating data, August 2007

THMs

µg/L

HAA5

µg/L

Chloroform

27

MCAA

ND

BDCM

3.8

DCAA

0.98

DBCM

0.73

TCAA

0.58

Bromoform

ND

MBAA

ND

31.53 DBAA

ND

Total THM

Total HAA5

1.54

SERPENT RIVER ONTARIO PILOT STUDY Treated Water Chlorinated

Typical Filter Ripening Period Plant 1: Turbidity (NTU)

T u rb id ity ( N T U )

Max Raw Turbidity 2.0 NTU 2 1.9 Turbidity Meters First Clean 1.8 w ere installed 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1 0.9 0.8 0.7 0.6 Ozone off 0.5 0.4 0.3 Filter Break-in (Ozone 0.2 Filter Break-in (Ozone 0.1 0 31-Jul-02 7-Aug-02 14-Aug-02 21-Aug-02 28-Aug-02 4-Sep-02 11-Sep-02 18-Sep-02 25-Sep-02 2-Oct-02 0.3 m /hr

Plant Effluent

Date

0.4 m /hr

Raw

9-Oct-02

16-Oct-02

0.6 m /hr

Typical Filtered Turbidity

O & M / Life-Cycle Costs Slow Sand Filtration = Low O & M Costs: •

Engineering Costs (1 - 2 % of total)

•

Construction Costs (6 - 18 % of total)

•

Operations and Maintenance Costs (80 - 93% of total life cycle cost)

LIFE CYCLE COST

80 – 93% of Total Life-cycle Costs

Source: Consulting Engineers of Canada

O & M / Life-Cycle Costs Common Problems for Small Systems: • Limited Resources for O & M (Capital Cost Usually Subsidized) • Operator has Multiple Responsibilities • Expensive Service Calls by OEM • Complex Treatment Chemical Systems

O & M / Life-Cycle Costs Common Problems for Small Systems: • Attracting and Retaining Skilled Operators • Overall Shortage of Qualified Operators (35% Eligible to Retire Within 10 Years) • With most Technologies Operators must also be Electronics Technicians • Comparatively Low Compensation and High Level of Responsibility

Summary- Conventional Slow Sand • Meets Regulatory Requirements for Filtration • Safe, Simple Operation • Very Low O & M Costs • No Coagulant Chemical Addition Minimal Sludge Generation • Passive - Operator Friendly Process

Summary- Conventional Slow Sand • Excellent removal of cysts / oocysts • Mechanisms = straining and predation • Mainly in upper layers of filter • Ability to remove or reduce certain common PPHCPs, EDCs, microcystins and taste and odour causing compounds • BUT Limited to very good quality raw water sources

Summary- Modified Slow Sand • Ozone = excellent disinfectant for pathogenic cysts, bacteria and viruses • Ozone converts stable DOC to AOC removed by biofiltration / slow sand filtration • Ozone oxidizes many contaminants not removed by biological processes alone

Summary- Modified Slow Sand Ozone + biofiltration removes or significantly reduces: • • • • •

Most PPHCPs, EDCs and pesticides Microcystins (Toxic Algal Metabolites) Geosmin / 2-MIB (Taste & Odour) Iron and manganese TOC and DBP precursors

Provides an Excellent Barrier to Pathogens and Contaminants, including DBPs

Questions?