Transcript DRINKING WATER TREATMENT

Drinking Water
&
Wastewater
Regulation and Treatment
Drinking Water Regulations
• 1893 - Interstate Quarantine Act
– Result: Prohibition of Common Drinking Cup on Interstate
Carriers – created a market for Dixie® cups
• 1914 - Microbiological Standard
– 2 coliforms / 100 ml
• 1925 - New Microbiological Standard
– 1 coliform / 100 ml
• 1942 - Maximum Concentrations for Constituents:
Lead
Selenium
Copper
Zinc
Phenolics*
Fluoride
Barium
Magnesium
Chloride
Total Solids
Arsenic
Hexavalent Chromium
Iron + Manganese
Sulfate
Alkalinity
*Phenol = carbolic acid, addition of methyl group forms cresols, o, m, or p
Drinking Water Regulations
1962 Limits for:
Alkyl benzene sulfonates (synthetic detergents)
Carbon-chloroform extract (organic residues)
[Adsorption on activated carbon, chloroform extraction, gravity quantification]
Barium
Nitrate
Cadmium
Silver
Cyanide
Radioactivity
Safe Drinking Water Act of 1974
Enacted over concern about organic materials in drinking water
Established Maximum Contaminant Levels (MCLs) for several
substances [Enforceable]
Federal Guidelines - Secondary MCLs (SMCLs), [Nonenforceable]
1975 - National Interim Primary
Drinking Water Regulations
Amended repeatedly, now include:
• Microbiological Contaminants
– Total and Fecal coliforms, E. coli, Turbidity
• Radioactive Contaminants
– Beta/photon emitters, Alpha emitters, Combined radium
• Inorganic Contaminants
– 15 elements or materials
• Synthetic Organic Contaminants including
Pesticides and Herbicides; Volatile Organics
– 54 compounds and groups of compounds
Drinking Water Treatment
CLEAN
DRINKING WATER
DELIVERED TO CUSTOMERS
SAMPLING
PROGRAM
DISINFECTION
FLUORIDATION
GROUNDWATER
SOURCES
SURFACE WATER
SOURCES
Groundwater Treatment Options
WATER TO
SYSTEM
AQUIFER
FILTRATION
AQUIFER
IRON & MANAGNESE
REMOVAL
SOFTENING
AERATION
AQUIFER
AQUIFER
Surface Water Treatment Options
WATER TO
SYSTEM
WATER
SOURCE
FILTRATION
FILTRATION
WATER
SOURCE
COAGULATION &
FLOCCULATION
INTAKE
SYSTEM
WATER
SOURCE
Drinking Water Treatment
Units or Processes
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INTAKES
AERATION
COAGULATION & FLOCCULATION
CLARIFICATION
FILTRATION
DISINFECTION
SOFTENING
TASTE & ODOR CONTROL
IRON & MANGANESE REMOVAL
TRACE METALS & ORGANICS
AERATION
(Usually for Groundwater)
• ADDS OXYGEN
• REMOVES:
– Carbon Dioxide
– Methane
Hydrogen Sulfide
Taste & Odors
• REMOVAL MAY BE BY:
– Oxidation
• Iron & Manganese
Volatilization
Organics
Coagulation, Flocculation & Clarification
Coagulation changes the electrical charge of suspended
particles and colloids; allows attachment to each other.
Coagulants are usually cations: Alum, Ferric Sulfate, Lime
(CaO)
Chemical/Physical process of mixing special purpose
chemical from flow and removing the resulting product
– Silts/Clays, Viruses, Bacteria
– Fulvic & Humic Acids, Minerals, Organic Particulates
Flocculation is the agglomeration of particles into settleable
particles
Clarification - sedimentation of floc particles, allows longer
filter runs, settling velocity of the floc allows particle
removal before the water leaves the basin
Drinking Water Filtration
• Rapid Sand Filters are most commonly used for
surface water
• May be gravity or pressure flow
– Some States prohibit pressure flow
• Fine-to-course (back wash result)
• Course-to-fine (multi-media)
– Anthracite, Sand, Course Garnet, Fine Garnet
• Rapid Sand filters may clean 1 - 2 gpm/ft2
• Alternatives include: microscreens, diatomaceous
earth filters, cartridge filters
DISINFECTION
• CT concept is the current basis for disinfection theory:
CT = K
C = disinfectant concentration
T= contact time
K= proportionality constant, variable with different organisms
Ohio regulation = 30 min contact time, 0.2 mg/l Cl2 residual
• Chlorination is most common in the U.S.
– Effective, low cost, proven technology
– Reactions with natural aquatic organics produce
trihalomethanes -- suspected carcinogens
• Ozonation is popular in France, Germany, Canada, and Russia
• Chlorine Dioxide gaining acceptance in Europe and U.S.
Chlorine Chemistry
Cl2 + H2O -----> H+ + Cl- + HOCl
HOCl = Hypochlorous Acid, is the most active ingredient,
concentration is pH dependent; dissociates to:
H+ + OCl
Active against (listed in decreasing order):
Bacteria
Viruses
Protozoans (cysts)
Chlorine reacts with Ammonia (NH3) to produce mono,
di, and trichloroamines
NH2Cl
NHCl2
NCl3
Chlorine Residuals & Chlorine Demand
-
• Free Chlorine: Cl2, HOCl, OCl
• Combined Chlorine: Chloramines
• Free Chlorine has strong disinfecting powers but is
quickly dissipated
• Combined Chlorine is slower acting but remains in
solution longer and provides longer-term protection
• Chlorine Demand = the difference between the amount
of chlorine applied and the amount of free, combined,
or total chlorine remaining at the end of the contact
period
• Anything oxidizable can produce a chlorine demand,
including pathogens, organics, particulates, sulfides,
ammonia, etc.
Alternative Disinfectants
Ozone
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O3, powerful oxidant, alternative to chlorine
Effective at low doses
Expensive (capital and operating costs)
Produces no residual
Chlorine Dioxide
– ClO2, an unstable gas, produced at the point of
use from sodium chlorite, NaClO2
– Nearly as effective as chlorine, does not react
with ammonia to produce chloramines, or with
other organics to form trihalomethanes
BIOFILMS
• In many environments, microorganisms form,
and exist in, complex, protective layers called
biofilms
• Biofilms may form in any part of a drinking
water distribution system. Cooling towers can
support robust biofilms.
• Disinfectants may be unable to attack or
completely remove the organisms in biofilms
• Most biofilms are made up of non-pathogenic
organisms; however, pathogens may be
protected in such an environment
Softening
Reduction in dissolved calcium and magnesium reduces
deposits in distribution system - scale formation
(CaCO3)
Hard water reacts with soap to form films that are
difficult to remove
Hard water deposits form scale in boilers
Softening also removes some trace inorganics – Pb, Cd,
Ag, Ba, Cr, As, Hg, and Ra
Lime-soda process adds quick lime (CaO) or hydrated lime
[Ca(OH)2], precipitating calcium carbonate (CaCO3)
Ion-exchange removes Ca2+ and Mg2+ and replaces them with
Na ions; often used in homes
Taste & Odor Control
• Very low concentrations of metals, salts, or
organics may produce detectable levels in
sensitive people - iron, copper, manganese, and
zinc, magnesium chloride and bicarbonate,
chlorinated organics; fungal and algal metabolites;
hydrogen sulfide, other sulfur compounds
• Activated carbon is often very effective in
removing organics
• Oxidation (chlorine, chlorine dioxide, ozone)
Iron & Manganese Removal
Iron and manganese cause staining and leave noticeable
residuals at very low concentrations
Fe >0.2 mg/l Mn >0.1 mg/l
Iron promotes growth of “iron bacteria” in mains that increase
friction and power consumption
Oxidation produces less soluble compounds and precipitation
is often used for removal
Trace Metals
Iron, Cadmium, Lead, Copper, Zinc may come from the
plumbing system; others may be from the aquifer
Corrosion control processes may be the most effective means
of reducing these concentrations - precipitation of a layer of
calcium carbonate often provides a nonreactive surface
Turbidity
A measure of suspended particulates in water - clays,
microorganisms, organics
Highly turbid waters are difficult to disinfect because of high
demands - large amounts of materials to be oxidized;
organisms protected from exposure to disinfectants
Coagulation and flocculation, and filtration are common
removal methods
Trace Organics
Solvents, hydrocarbons, etc. may come from the aquifer
Modified organics may be the result of disinfection processes
Humic and fulvic acids are poorly defined and are common in
natural waters
TOC and TOX are broad tests of water quality
Precipitation, filtration, adsorption, and oxidation may all
remove some of the materials
Fluoridation
• The fluoridation process was very
controversial when initially implemented
• Low concentrations (1 - 2 mg/l) of fluoride
provide strong protection against tooth
decay
• Slightly higher concentrations (> 4 mg/l)
can cause discoloring of teeth
CROSS CONNECTIONS
– Accidental contamination of drinking water can
occur during routine plumbing modification,
sewer backups, floods, earthquakes, careless
homeowners, etc.
FOAMING AGENTS
– Surfactants (the active part of detergents) can
get into surface water through incomplete
sewage treatment
– Groundwater sources include septic tank
systems
Nitrate & Nitrite
• Nitrate is common in natural waters at 1 to 2 mg/l
• Nitrate (NO3) is reduced to nitrite (NO2) in the
digestive system - reduction is more complete in
infants than adults - because of more alkaline
conditions in system
• Excess nitrite produces methemoglobinemia in
infants by oxidizing hemoglobin to
methemoglobin which cannot carry oxygen
• Nitrosamines formation (suspected carcinogens)
can also occur from nitrate or nitrite
• TOTAL DISSOLVED SOLIDS
– High TDS may increase corrosivity because of
increase conductance
– High sodium may be of health concern
• CORROSIVITY
– Decreases life of plumbing system
– Solubilized metals, perhaps in toxic quantities - lead
and cadmium are of most concern
– Copper, iron, and zinc produce tastes and stains
– Corrosion can shield microorganisms from
disinfection processes
– Water may be characterized as passive or aggressive
CLEAN WATER ACT - Background
• Rivers and Harbors Act of 1899
– Prohibited discharge of refuse without a permit from
the Secretary of the Army
• Water Pollution Control Act of 1948
– Gave primary responsibilities to the States
– Provided construction funds, Money never
appropriated
• Water Pollution Control Act Amendments of 1956
– Authorized Grants for construction
– Provided funds for research into Health Effects
• Other minor Acts in 1961, 1965, 1966, 1970
• Federal Water Pollution Control Act - 1972 - PL 92-500
– Goal of “fishable/swimmable” water
– Construction Grants for Sewage Treatment Facilities
• BPT - Best Practicable Treatment
• BAT - Best Available Treatment
– Concentrated on Oxygen Demand, Suspended Solids
– 1976 - NRDC v. Train - Consent Decree - resulted in...
• Clean Water Act - 1977 - PL 95-217
• Wetlands Resources Act - 1986
• Water Quality Act Amendments of 1987
– Required EPA regulations on storm water runoff
– Required State nonpoint source management programs
TITLE I -RESEARCH AND RELATED
PROGRAMS
• Sec. 101 - Declaration of Goals and Policy -Objective: Restore and maintain the chemical, physical,
and biological integrity of the Nation's waters.
• Goals:
1. Eliminate pollutant discharges into navigable
waters by 1985.
2. Interim goal to protect fish, shellfish, and wildlife
and provide for recreation in and on the water by
July 1, 1983.
3. Prohibit the discharge of toxic pollutants in toxic
amounts.
TITLE III - STANDARDS AND ENFORCEMENT
• 304 - Information and Guidelines - provides for
development of water quality criteria. Defines
conventional pollutants - including, but not limited to,
biological oxygen demand, suspended solids, fecal
coliforms, and pH, --- specifically excluded thermal.
• 305 - Water Quality Inventory - requires States to
provide a water quality description, an inventory of
point-source dischargers, and an estimate of costs of
improving quality.
• 306 - National Standards of Performance - requires a list
of categories of sources and establishment of new source
performance standards for those categories
TITLE IV: PERMITS AND LICENSES
Sec 402 - National Pollutant Discharge Elimination
System - (NPDES) establishes requirements for
issuing permits and State implementation of the
program.
– Excludes: Irrigation return flows, Storm water
runoff from Oil, Gas and Mining operations
– Anti-Backsliding - renewed permits must be as
stringent as the original
– Storm water is included by October 1, 1993
ADDITIONS, AMENDMENTS
• LIMITATIONS ON DISCHARGE OF RAW
SEWAGE BY NEW YORK CITY
– North River Plant - required to have advanced
preliminary treatment by Aug, 1986
– Red Hook Plant - required advanced preliminary
treatment by Aug, 1987
• BOSTON HARBOR AND ADJACENT
WATERS
– Authorization for constructing waste treatment
works for providing secondary treatment
Oil Pollution Act
• Revised penalties for oil discharges
– Administrative penalties of $125,000 for
violations of regulations or discharges
– Civil penalties of $25,000/ day for discharges,
or $1,000/ barrel of oil
– Gross negligence or misconduct minimum
penalty of $100,000
CONVENTIONAL POLLUTANTS
• Several are “Empirical,” derived by experimentation
• Biological Oxygen Demand - test using microorganisms that
measures oxygen uptake over five days
• Suspended Solids - quantified by filtration of a sample and
drying and weighing the filter
• Fecal Coliform Bacteria - microbial analysis dependent upon
incubation conditions and selective media
• pH - measured directly
• Oil and Grease - derived by extraction of a water sample with
a solvent and either an infra-red (IR) measure of the solvent,
or a gravimetric measure of the residue
Pretreatment Regulations
Industrial discharges into POTWs (40 CFR 403)
– POTWs with flows > 5 million gpd, or smaller
POTWs with significant industrial discharges must
establish local pretreatment programs
– National standards must be enforced
– Hazardous wastes are the focus of regulation
– Significant industrial users must meet reporting
requirements:
• Users subject to categorical pretreatment standards
• Users of > 25,000 gpd of processed wastewater
• Users that make up >5% average organic capacity
• Other users with a reasonable potential to adversely
effect the POTW’s operation
Wastewater Treatment
• Collection System
– Sewage
• Domestic (sanitary)
• Industrial
• Mixed
– Stormwater
• Separate Systems
• Combined Systems
• Infiltration (20 to 3,000 gal/acre/day)
Unit Operations & Unit Processes
• Unit Operations - Treatment methods using
physical forces
• Screening
Mixing
• Sedimentation
Flotation
• Aeration (gas transfer)
Flocculation
Filtration
• Unit Processes - Treatment methods using
chemical or biological reactions
• Precipitation
• Biodegradation
Adsorption Disinfection
Nutrient Removal
Treatment Levels
• Primary Treatment - (preliminary), physical unit
operations
– Removal of constituents that cause maintenance or
operational problems -- debris, grit, oil and grease,
• Secondary Treatment - chemical and biological
unit processes
– Removal of biodegradable organics and suspended solids
• Tertiary Treatment - (advanced), combinations of
all three methods
– Removal of residual nutrients, toxics, specific
contaminants
Typical Treatment Process
Influent
Sludge
Disposal
Bar
Screen
Grit
Chamber
Anaerobic
Digester
Primary
Clarifier
Activated
Sludge Unit(s)
Sludge
Return
Disinfection
Effluent
Secondary
Clarifier
Industrial Wastewater
Treatment - Differences
• Equalization - hydraulic residence time at
least equal to activated sludge unit, may be
several times longer
• Oil Separation
– Dissolved Air Flotation, Dissolved Gas Flotation
– Corrugated Plate Interceptors
• Sludges may be hazardous by regulation
Design Criteria
• Flow Rate
Peak Hour
Maximum Month
Minimum Day
Maximum Day
Minimum Hour
Minimum Month
• Mass Loading
Maximum Day
Maximum Month
Minimum Day
Sustained Peaks
Minimum Month
Wastewater
Daily Flow Pattern
Midnight
Noon
Midnight
Reactor Types
• Homogeneous Reactions:
– Batch Reactor
– Plug-Flow Reactor
– Complete-Mix Reactor, Stirred Tank Reactor
– Complete-Mix Reactors in Series • May be significantly more effective than the same
volume in a single unit
– Arbitrary -Flow Reactor
• Heterogeneous Reactions:
– Packed-Bed Reactor
– Fluidized-Bed Reactor
Mass-Balance Analysis
Accumulation = Inflow - Outflow + Generation
V dC/dt = QCo - QC + V(-kC)
V = volume of reactor
dC/dt = rate of change of reactant concentration within reactor
Q = volumetric flow rate into/out of reactor
Co = reactant concentration in influent
C = reactant concentration in reactor and effluent
k = first-order reaction-rate constant
Mass Balance Applications
• Model constituent biodegradation or removal
(volatilization, precipitation, etc.)
• Model solids (sludge) formation
Common Operational and
Design Practices
• Gravity flow through system
– Only pump the water one time
• Parallel units
– Allow operational flexibility and maintenance
• Minimize human contact with materials
SIMPLIFIED TREATMENT FLOW
Fairborn Plant
Raw
Sewage
Grit
Tanks
Digesters
Landfill
Oxidation
Ditches
Sludge
Return
Disinfection
Effluent to
Mad River
Clarifiers
Fairborn NPDES Permit Requirements
• Sampling Stations
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Plant Outfall
Waste Sludge
Raw Sewage Influent
Upstream at State Route 235
Downstream - 200 ft south of lift station at River
Mile 8.6
• Samples:
– Composite samples of at least three grab samples
proportionate in volume to the sewage flow rate at
the time of sampling...intervals of at least 30 min.,
but not more than 2 hours
Fairborn
Performance Statistics
• Average Daily Flow (mgd)
• Average Influent:
– Suspended Solids
– BOD
– Ammonia
• Average Effluent:
– Suspended Solids
6 mg/l
– BOD
3 mg/l
– Ammonia
0.1 mg/l
3.795
198 mg/l
143 mg/l
16 mg/l
97%
98%
99%