keith allen, p.e., bcee water/wastewater august 6, 2015 groundwater
TRANSCRIPT
KEITH ALLEN, P.E . , BCEEWATER/WASTEWATER
AUGUST 6 , 2015
Groundwater
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
Treatment Micro org inorg CO2 CH4 NO3
Aeration X* X X X
Oxidation/disinfection
X X
Sedimentation X X* X
Filtration X X* X
Membranes X X X X
Softening X X X
Ion exchange X X X X
Gac/Pac X X
Conventional X X X
health treatment technologies
Treatment iron Mn hardness TDS H2S Color
Aeration X* X* X
Oxidation/Disinfection
X* X* X
Sedimentation X X X* X* X*
Filtration X X X* X* X*
Membranes X X X X X
Softening X X X X X
Ion exchange X X X X
Gac/Pac X
Conventional X X X X X
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 filtrationIon 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 MagnesiumProperly softened water will have a residual
hardness of 50 mg/l to 80 mg/lIon 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 MgDemineralizes by removing Fe, Mn, F, &
NaGood for small systemsNo break in pressure
Ion Exchange Cycles
Organic Matter
All natural waters contain organic materialOrganic matter simply contains carbonSources 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
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 formulationsIs 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 oilReacts with free chlorine to form disinfection
byproductsProducts formed
Trihalomethanes Haloacetic Acids
Byproducts can cause cancer and birth defects
Modes of transmission include ingestion, absorption through skin, and breathing
Breakpoint Chlorination
0
0.1
0.2
0.3
0.4
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Ch
lori
ne
Res
idu
al
Chlorine Added
Destruction of Chlorine
by Reducing Compounds
Formation of Chloro-organicCompounds 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 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
Developed by American Water Works Association with funds from the U.S. Environmental Protection Agency, Published 2015
Powdered Activated Carbon (PAC)
dist.
PAC PACPAC PAC
IntakePAC
B/W
Application Point
Intake PAC Contactor
Rapid Mix
Flocculation Sedimentation
Contact Time (min)
varies 15 – 90 < 5 30 - 60 120 - 240
Mixing poor excellent very good
moderate none
PAC removal
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 settlingdisinfection& storage
distribution
coagulant
GAC filter-adsorber
Granular Activated Carbon (GAC): Filter Adsorber (FA)
Conventional treatment with additional GAC filter
disinfectant
rapid mix
flocculation settlingrapid media
filtration
disinfection& storage
Dist.
coagulant
Conventional treatment
GAC filtration
Granular Activated Carbon (GAC): Post Filter Adsorber (PFA)
Application EBCT(min)
TOC Removal
(%)
Media Life Media size Limitations
Post-Filter Adsorber
5 - 30 10 - 70 2 - 24 months
12x40ES=
0.65 mm
•Cost/space/hydraulic head•Oxidant compatibility
Granular Activated Carbon (GAC): TOC Breakthrough Curves
1.0D
OC
C/C 0
Operation time, t
5-15% non-adsorbable
10-15% biodegradable
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
