9/11/2017 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 1
9/11/2017 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 – increases in turbidity, Fe/Mn problems pathogens, coliforms • reservoir turnover in fall • Wastewater inputs & spring • Agricultural runoff • Accidental spills David Reckhow CEE/EHS 597B 4 2
9/11/2017 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 3
9/11/2017 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 • Aeration treatment • Pressure filtration David Reckhow CEE/EHS 597B 8 4
9/11/2017 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 5
9/11/2017 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 6
9/11/2017 Overview of “conventional” treatment Direct Filtration coagulant coagulant Settling Settling Water Water Rapid Rapid Filtration Filtration Flocculation Flocculation Supply Supply Mix Mix Flotation 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. Clear Sys. well raw water rapid flocculation Settling Filtration Pre‐oxidation/ disinfection mix David Reckhow CEE/EHS 597B 14 Sludge 7
9/11/2017 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. Clear Sys. well Dissolved Air raw water rapid flocculation Filtration mix Flotation 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. Clear Sys. well raw water rapid flocculation Filtration mix David Reckhow CEE/EHS 597B 16 Sludge 8
9/11/2017 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‐ Pre‐ Lime & Lime & coagulant coagulant Soda Ash Soda Ash oxidant oxidant Settling Settling Water Water Supply Supply Rapid Rapid Flocculation Flocculation Mix Mix Flotation Flotation Chlorine Chlorine Intermediate Intermediate Filtration Filtration GAC GAC Ozonation Ozonation Clear Well Ads. Ads. To the distribution system David Reckhow CEE/EHS 597B 18 9
9/11/2017 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 10
9/11/2017 Disinfection • Kill or inactivate pathogens – Bacteria, viruses protozoa • Methods – Heat: boil water – Expose to UV light Small scale, for emergencies – 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 11
9/11/2017 Point of Addition of Disinfectants DAF Pre‐Disinfectant Coagulant Direct Filtration Settling Rapid Mix Flocculation 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 • Aeration treatment • Pressure filtration David Reckhow CEE/EHS 597B 24 12
9/11/2017 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 0.8 0 =HOCl/C T Fraction of total ( ) 1 =OCl - /C T 0.7 Although both hypochlorous acid and hypochlorite are 0.6 disinfectants, hypochlorous 0.5 0.4 acid is much more powerful. The equilibrium reaction is: 0.3 0.2 [ ][ ] H OCl 0.1 8 7 . 5 3 . 16 10 10 K a x [ ] 0.0 HOCl 4 5 6 7 8 9 10 11 pH David Reckhow CEE/EHS 597B 26 13
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