KEITH ALLEN, P.E., BCEE WATER/WASTEWATER AUGUST 6, 2015 Groundwater

Groundwater treatment issues  Aesthetic – iron, manganese, hardness, total dissolved solids, hydrogen sulfide, organic color  Health related – microorganisms (bacteria), organic matter (chemicals), Inorganic chemicals, carbon dioxide (Corrosion), methane, nitrates Aesthetic contaminants cause customer complaints  Taste  Odor  Color Health related contaminants are potentially harmful

TreatmentMicroorginorgCO2CH4NO3 AerationX*XXX Oxidation/ disinfection XX SedimentationXX*X FiltrationXX*X MembranesXXXX SofteningXXX Ion exchangeXXXX Gac/PacXX ConventionalXXX health treatment technologies

TreatmentironMnhardnessTDSH2SColor Aeration X* X Oxidation/ Disinfection X* X SedimentationXXX* FiltrationXXX* MembranesXXXXX SofteningXXXXX Ion exchangeXXXX Gac/PacX ConventionalXXXXX Aesthetic treatment technologies

Iron and manganese Manganese - Secondary limit is 0.05 mg/l  Causes discoloration(black like motor oil), turbidity, deposits, and taste  Effects taste of drinks made with the water (tea, coffee)  Usually accompanied by iron causing “brownish” stain  More difficult to remove than iron Iron – Secondary limit is 0.3 mg/l  Causes discoloration(orange like rust), turbidity, deposits, and taste similar to Manganese  Effects taste of drinks made with the water (tea, coffee)  Supports growth of iron bacteria usually in the distribution system

Iron and Manganese Control Oxidation, detention, filtration  Oxidation by aeration, chlorine, or both  pH should be above 7.5 for Fe and 8.3 for Mn  Used most when Fe and Mn are only treatment issues Water softening (Lime/Soda Ash) Manganese greensand filtration Ion exchange  Sodium cycle  Acid cycle Sequestration by polyphosphates

Iron and Manganese Control Rate of oxidation  pH  Chlorine dosage  Temperature  Mixing conditions  30 minute detention time 1 mg/l KMnO4 will oxidize 1.06 mg/l Fe & 0.52 mg/l Mn  Stronger oxidant than chlorine  Reaction is not as pH dependent as Chlorine  Overfeed can turn water pink

Corrosion Control Natural Draft Aerators  Uses trays filled with coke or other media  Water flows over media  Turbulence exposes water to surrounding air  Air adds oxygen resulting in oxidation (Fe &Mn)  Oxygen replaces gases removed (CO2, H2S, CH4)  Efficiency based on ambient air temperature  Slat trays (6) recommended with high iron and manganese  Easily cleaned  Loading rate 10 gallons/square feet

Coke Tray Aerators

Natural Draft Aerator

Corrosion Control Mechanical draft  Induced or forced  Completely sealed  Highly efficient  Media usually plastic balls or triangles  Good for low iron/manganese waters  When iron/manganese higher  Reduce efficiency by changing media to plastic or redwood slats  Provide easy access for cleaning  Loading rate 20 gallon/square foot  Can become plugged  Inspected regularly

Aerators

Pressure Filter

Solids Contact Basin (Clarifier)

Filter Plant Types – Conventional, Direct, Slow Sand, & Diatomaceous

Lime/Soda Ash Softening Hardness – caused by metal ions (Ca,Mg)  Carbonate hardness associated with alkalinity usually in the form of bicarbonates.  Removed by lime addition  ph is raised to about 9.6 for Calcium bicarbonate  Excess lime is added for a ph of 10.4 or higher to remove magnesium bicarbonate.  Recarbonation is required prior to filtration to prevent incrustation and clogging

Lime/Soda Ash Softening Non-carbonate hardness associated with other constituents such as sulfates and chlorides  Soda Ash must be added to remove noncarbonate compounds associated with calcium  Soda Ash and “excess” lime must be added to remove noncarbonate compounds associated with Magnesium Properly softened water will have a residual hardness of 50 mg/l to 80 mg/l Ion exchange may be more cost effective for noncarbonate hardness removal

Lime – Soda Ash Softening Processes

Water Treatment - Ion Exchange Used selectively to replace one ion by another Process must be reversible so that exchanged medium can be regenerated and used again Softens by removing Ca and Mg Demineralizes by removing Fe, Mn, F, & Na Good for small systems No break in pressure

Ion Exchange Cycles

Organic Matter All natural waters contain organic material Organic matter simply contains carbon Sources and types of organic matter in groundwater  Organic Color  Bio-film  Bearing lubricant  Methane  Other natural hydrocarbons

Organic Matter Sources and types of organic matter in groundwater  Contamination  VOC’s  IOC’s  SOC’s Note: most hydrocarbons and VOC’S are easily removed by Aeration

Organic Matter

Cause of Organic color Humic acids, fulvic acids, tannins, etc. Caused by microbiological decay of plants and animals Complex chemical compounds which have widely varying formulations Is characterized by TOC (total organic carbon), DOC (dissolved organic carbon), NOM (natural organic material) and AOC(Assimilated organic carbon) Is typically not harmful

Problem with Organic color Dingy to dark appearance (weak tea) At high levels can resemble motor oil Reacts with free chlorine to form disinfection byproducts Products formed  Trihalomethanes  Haloacetic Acids Byproducts can cause cancer and birth defects Modes of transmission include ingestion, absorption through skin, and breathing

Breakpoint Chlorination Chlorine Residual Chlorine Added Destruction of Chlorine by Reducing Compounds Formation of Chloro-organic Compounds and Chloramines Destruction of Chloramines and Chloro- organic Comp. Formation of Free Chlorine and Presence of Chloro-organic Compounds not Destroyed

Reactions with free chlorine Free chlorine reacts first with reducing agents such as iron, manganese, sulfides, and most inorganic reactants leaving little or no combined residual Second reaction is with some nitrogenous organic material and all free ammonia that may be present. This reaction is almost instantaneous. Remaining free chlorine reacts with remaining organic material such as organic color and bacteria (this is oxidizing stage not kill stage) If free chlorine is measured – no ammonia is present

Reactions with free chlorine CL2 + Ammonia = Inorganic Chloramine  Inorganic monochloramine is desired residual  No inorganic chloramine remains after breakpoint CL2 + DON = Organic Chloramine  No credited residual for disinfection  Approximately 0.8 mg/l organic chloramine/mg/l DON  Organic chloramine residual can remain indefinitely Organic Nitrogenous material (DON for reaction purposes) is present in almost all plant and animal waste and remains

Avoiding disinfection by products THM’s are usually formed slowly and can take up to seven days to fully form. HAA’s are usually formed quickly and then degrade over time. Limiting chlorine residual to just disinfection dose will limit the formation of byproducts Limiting detention time by flushing the distribution system routinely will limit THM formation. Use booster chlorination to target areas where residual cannot be maintained.

Avoiding disinfection by products If the easy stuff doesn’t work  Alternative Oxidants  Chloramines  Chlorine Dioxide  Ozone  Combined Disinfection or Treatment processes  Ozone and Free Chlorine  Ozone and chloramines  Chlorine Dioxide and Free Chlorine  Chlorine Dioxide and Chloramines  Ozone and BAF (bacteriologically active filters)  Ozone, aeration and free Chlorine

Avoiding disinfection by products If the easy stuff doesn’t work (continued)  Removal of Precursors (organic matter)  Membranes processes RO NF UF MF ED EDR  Adsortion processes GAC PAC

Avoiding disinfection by products If the easy stuff doesn’t work (continued)  Removal of Precursors (continued)  Conventional Treatment  Softening  Removal of THM’s and HAA’s  Aeration  Adsorption Processes GAC PAC  Membranes  Conventional Treatment  Softening

Alternative Disinfection Chloramines Chloramines  ammonia & chlorine combined in 4/1 ratio  Does not promote THM formation  Less effective than free-chlorine  Persistent residual  Controls microbial growth (biofilm)  Can lead to nitrification problems in distribution system

Powdered Activated Carbon (PAC) dist. PAC Intake PAC B/W Application Point IntakePAC Contactor Rapid Mix FlocculationSedimentation Contact Time (min) varies15 – 90< Mixingpoorexcellentvery good moderatenone PAC removal Developed by American Water Works Association with funds from the U.S. Environmental Protection Agency, Published 2015

Conventional treatment with filter media replaced with GAC disinfectant rapid mix flocculation settling disinfection & storage distribution coagulant GAC filter- adsorber Granular Activated Carbon (GAC): Filter Adsorber (FA) Developed by American Water Works Association with funds from the U.S. Environmental Protection Agency, Published 2015

Conventional treatment with additional GAC filter disinfectant rapid mix flocculation settling rapid media filtration disinfection & storage Dist. coagulant Conventional treatment GAC filtration Granular Activated Carbon (GAC): Post Filter Adsorber (PFA) ApplicationEBCT (min) TOC Removal (%) Media LifeMedia sizeLimitations Post-Filter Adsorber months 12x40 ES= 0.65 mm Cost/space/hydraulic head Oxidant compatibility

Granular Activated Carbon (GAC): TOC Breakthrough Curves

Membrane Processes Types of membranes  Polymeric  Organic material with low flux and permeability  Used routinely for all membrane operations (RO, NF, UF, MF)  Ceramic AlO3  Inorganic material with higher flux and permeability  Used for UF and MF  AlO3  ZrO3  TiO3  SiC

Polymeric membrane

Ceramic membrane

Membrane Processes Benefits of ceramic membranes  –Mechanical strength  –Chemical and thermal resistance  –Longer operational life  –High flux and low fouling  General considerations Potential limitations  –High initial capital cost  –Lack of operational experience in the US

Membrane Processes General considerations  Corrosion control treatment will be necessary after most membrane processes unless split treatment or selective treatment is used  Membranes are physical barriers, if broken, treatment ceases

Contact Information Questions? Contact Information Keith Allen, P.E., BCEE