Print version CEE/EHS 597B Meeting #2: Treatment for Small Water Systems Dave Reckhow David Reckhow CEE/EHS 597B 1
Purposes for Water Treatment • Disinfection • Removal of Turbidity • Removal of Color, and Tastes & Odors • Removal of Iron & Manganese • Hardness removal • Protection from Toxic Organics and Inorganics David Reckhow CEE/EHS 597B 2
Drinking Water Treatment Processes • Gas Transfer (stripping) • Oxidation • Coagulation & Flocculation • Sedimentation or Flotation • Softening • Adsorption • Disinfection David Reckhow CEE/EHS 597B 3
Source Waters • Groundwaters • Reservoirs & lakes – constant quality – less variation than rivers • seasonal blooms of alae • Rivers in nutrient rich reservoirs – variable quality • oxygen can be depleted • storm events, runoff from bottom; causing Fe/Mn problems – increases in turbidity, pathogens, coliforms • reservoir turnover in fall • Wastewater inputs & spring • Agricultural runoff • Accidental spills David Reckhow CEE/EHS 597B 4
SWTR • Multiple Barrier Concept Source Water Protection – Filtered Systems: Filtration Disinfection – Unfiltered Systems: Including wellhead Source Water Protection protection Disinfection 2 different ones David Reckhow CEE/EHS 597B 5 5
Log Removal • Meaning of “Log Removal or Inactivation” – Removal: remove organisms from the water – Inactivation: make organisms non-infectious by use of disinfection – Let N 0 be the number concentration of microorganisms in raw water – Let N be the number concentration of microorganisms after treatment – N/N 0 = fraction remaining after treatment – 100 x (N 0 – N)/N 0 = percent removal (or inactivation) – Log (N 0 /N) = the log removal (or inactivation) – Relation between % removal and log removal: % Removal Log Removal N, if N 0 = 10,000/L 90 1 1000 99 2 100 99.9 3 10 99.99 4 1 David Reckhow CEE/EHS 597B 6
SWTR (cont.) • Requirements for Filtered Supplies Log 10 Removal Allowed Remaining Log 10 By Filtration Inactivation by Type of Disinfection Filtration Giardia Viruses Giardia Viruses Conven- 2.5 2.0 0.5 2.0 tional Direct 2.0 1.0 1.0 3.0 • Requirements for Unfiltered Supplies The TT approach, rather than MCL – Meet source water quality criteria – Provide all Pathogen removal by Disinfection Requires • 3 log Giardia , 4 log viruses a certain David Reckhow CEE/EHS 597B 7 CT
Treatment vs Sources • Surface water • Groundwater – Major water quality – Major water quality concerns concerns • Pathogens • Fe/Mn • Turbidity • Hardness • Color & TOC • Arsenic, perchlorate • Taste & odor • VOCs & pesticides – Typical treatment – Typical treatment • “conventional” • Disinfection only coagulation-filtration • Softening • Some use advanced treatment • Aeration • Pressure filtration David Reckhow CEE/EHS 597B 8
Simple Groundwater systems • “Groundwater Treatment Process” – From RCAP reading, pg 10-11 The focus of this period Will be discussed in period #10 by Kumpel & Ford David Reckhow Will be discussed in period #5 by David Boutt CEE/EHS 597B 9
Groundwater Treatment • More realistically, there are many options or needs: a. Fe/Mn removal b. Precip. Softening c. Ion exchange d. Simple disinfection From: Water and Wastewater Technology by Hammer and Hammer, 6 th edition (2008) H&H, fig 7-25, pg.250 David Reckhow CEE/EHS 597B 10
Surface Water • Again from RCAP, pg/ 14-15 David Reckhow CEE/EHS 597B 11
Conventional Treatment • Coagulation & solids separation – rapid mix, flocculation, settling, filtration • Disinfection – including clearwell for contact time H&H, Fig 7-1, pp.210 • Most common for surface water Corrosion Control Fluoride Coagulant Disinfectant Dist. Clear Sys. well raw water rapid flocculation Settling Filtration mix David Reckhow CEE/EHS 597B 12
Overview of “conventional” treatment Direct Filtration coagulant Settling Water Rapid Filtration Flocculation Mix Supply Flotation Coagulation Dissolved Organics Settleable Unstable Stable Particles Particles Particles David Reckhow CEE/EHS 597B 13
Conventional “plus” • common to include preoxidation or pre- disinfection with conventional treatment – helps with removal of metals & organics by coagulation – achieves more complete disinfection Corrosion Control Fluoride KMnO 4 , Cl 2 Coagulant Disinfectant Dist. Sys. Clear well raw water rapid flocculation Settling Filtration Pre-oxidation/ disinfection mix David Reckhow CEE/EHS 597B 14 Sludge
Dissolved Air Flotation (DAF) • uses very small air bubbles to cause “floc” to float, instead of relying on gravity to make them sink Corrosion Control Fluoride Coagulant Disinfectant Dist. Sys. Clear well Dissolved Air raw water rapid flocculation Filtration Flotation mix David Reckhow CEE/EHS 597B 15 Sludge
Direct Filtration • No settling or flotation – goes “directly” from flocculation to filtration – works well for some low color, low turbidity waters Corrosion Control Fluoride Coagulant Disinfectant Dist. Sys. Clear well raw water rapid flocculation Filtration mix David Reckhow CEE/EHS 597B 16 Sludge
Ozone Plant • Many types – Simplest type: ozone, non-filtration shown below • examples: MWRA (Boston), Portland ME Cl 2 O 3 Cl 2 NH 3 Dist. Sys. David Reckhow CEE/EHS 597B 17
An advanced water treatment process Direct Filtration Pre- Lime & coagulant Soda Ash oxidant Settling Water Supply Rapid Flocculation Mix Flotation Chlorine Intermediate Filtration GAC Ozonation Clear Well Ads. To the distribution system David Reckhow CEE/EHS 597B 18
Disinfection • 1-2 punch of filtration & chlorination Greenberg, 1980, Water Chlorination, Env. Impact & Health Eff., Vol 3, pg.3, Ann Arbor Sci. US Death Rates for Typhoid Fever David Reckhow CEE/EHS 597B 19 Melosi, 2000, The Sanitary City, John Hopkins Press
Disinfection of PWS • One of the greatest achievements in public health during the 20 th century – US Centers for Disease Control (CDC) • One of the greatest engineering feats of the 20 th century – National Academy of Engineering David Reckhow CEE/EHS 597B 20
Disinfection • Kill or inactivate pathogens – Bacteria, viruses protozoa • Methods – Heat: boil water Small scale, for emergencies – Expose to UV light – Add Chemical Oxidants Slowly becoming more common • Chlorine (Cl 2 , HOCl or OCl - ) • Chloramines (NH 2 Cl or NHCl 2 ) • Ozone (O 3 ) By far the most common • Chlorine Dioxide (ClO 2 ) • Primary purpose for drinking water treatment David Reckhow CEE/EHS 597B 21
Application Points • Primary Disinfection – removal or inactivation of pathogens by “treatment technique” or TT approach • CT concept – done in the treatment plant, sometimes as a first step – can be: free chlorine, ozone, chlorine dioxide or UV light • Secondary Disinfection – Added as the last step just prior to entry into distribution system – intended to maintain a residual of disinfectant throughout the distribution system • Minimize growth on pipe walls, some protection against re- contamination, or maybe just a “sentinel” – usually free or combined chlorine, sometimes chlorine dioxide David Reckhow CEE/EHS 597B 22
Point of Addition of Disinfectants DAF Pre-Disinfectant Coagulant Direct Filtration Settling Flocculation Rapid Mix Intermediate Disinfectant Post-disinfectant Filtration Dist. GAC Sys. Ads. Clearwell David Reckhow CEE/EHS 597B 23
Treatment vs Sources • Surface water • Groundwater – Major water quality – Major water quality concerns concerns • Pathogens • Fe/Mn • Turbidity • Hardness • Color & TOC • Arsenic, perchlorate • Taste & odor • VOCs & pesticides – Typical treatment – Typical treatment • “conventional” • Disinfection only coagulation-filtration • Softening • Some use advanced treatment • Aeration • Pressure filtration David Reckhow CEE/EHS 597B 24
Forms of Chlorine applied to water • Chlorine gas – Cl 2 Traditional method • Sodium Hypochlorite liquid (Hypo) – NaOCl Becoming more common • Calcium Hypochlorite solid – Ca(OCl) 2 • Other forms – Organic-N based compounds and resins David Reckhow CEE/EHS 597B 25
Chlorine Cont. ↔ + - HOCl H + OCl The hypochlorous acid 1.0 ionizes to hypochlorite. 0.9 α 0 =HOCl/C T 0.8 Fraction of total ( α ) α 1 =OCl - /C T 0.7 Although both hypochlorous 0.6 acid and hypochlorite are 0.5 disinfectants, hypochlorous 0.4 acid is much more powerful. 0.3 The equilibrium reaction is: 0.2 + − [ H ][ OCl ] 0.1 − − = = = 8 7 . 5 K a 3 . 16 x 10 10 [ HOCl ] 0.0 4 5 6 7 8 9 10 11 David Reckhow CEE/EHS 597B 26 pH
Question • At pH 8.5, the percent of the total free chlorine that is in the most effective form is: A. 0% B. 9% C. 27% D. 50% E. 73% F. 91% G. 100% David Reckhow CEE/EHS 597B 27
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