lagoon design and performance presented by: dwight houweling, ph.d. envirosim associates,...
TRANSCRIPT
Lagoon Design and Performance
Presented by:
Dwight HOUWELING, Ph.D.EnviroSim Associates, Flamborough, ON
4-hour Seminar presented September 22nd, 2008at Environment Canada, Burlington, Ontario
5
Solids Separation
Solubles Particulates
Wastewater components separate through sedimentation. Settleable solids sink to the bottom layer. Soluble and fine solids remain in the top layer.
LAGOON PERFORMANCE
6
Solids Separation
Solubles Particulates
Settling removes only removes a portion of the “pollution”
Particulates
Solubles and Fine
Particulates
LAGOON PERFORMANCE
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Biological Activity
Bacteria consume soluble matter and fine particulates and then settle to bottom, which clears up water top layer
Particulates
Bacteria Consume
Solubles and Fine
Particulates
Bacteria Grow and Settle
LAGOON PERFORMANCE
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Treatment Performance
Good settling depends on: quiescent conditions (still waters), not
too much wind; Minimum depth of water above
sediment layer Good biological activity depends on:
Temperature, dissolved oxygen, other factors
LAGOON PERFORMANCE
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Treatment Performance
The biggest variable in operating lagoons in Canada is temperature change between winter and summer
Cold temperatures and ice cover will affect biology but not so much settling
LAGOON PERFORMANCE
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Winter Performance
Settling
ice
Settling is good in winter but biological activity slows down
Particulates
Solubles and Fine
Particulates
LittleBiological Activity
LAGOON PERFORMANCE
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Summer Performance
Settling
SignificantBiological Activity
Particulates
Bacteria Consume
Solubles and Fine
Particulates
Warm temperatures and sunlight allow good treatment in summer
LAGOON PERFORMANCE
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Summer Performance
Particulates
Algae
Growth of Algae is beneficial but can sometimes be excessive
LAGOON PERFORMANCE
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Summer Performance
Waterways choked with algae – while they are alive they provide beneficial oxygen but when they die they consume oxygen, which can lead to anaerobic conditions (no oxygen)
LAGOON PERFORMANCE
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Biological Activity
Biological activity is critical to the treatment performance of lagoon processes
Rate of activity is temperature dependant Bacteria do most of the work Type of biological activity depends on whether
oxygen is present (aerobic) or not (anaerobic) Aerobic activity is the most energy efficient for
life and leads to better pond performance
LAGOON BIOLOGY
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Components of interest
Suspended Solids (TSS)TSS includes human waste, pathogens,
nutrients, algae and other bacteria etc.Biochemical Oxygen Demand (BOD)
Organic Matter that depletes oxygenNutrients - EutrophicationToxicityPathogens
LAGOON BIOLOGY
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Treatment in Lagoons
What is the fate of each of the following: TSS, BOD, Ammonia, P, Pathogens?
LAGOON BIOLOGY
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Bacteria
Bacteria consume organic matter and nutrients
Algae are photosynthetic bacteria that produce oxygen
Bacteria work fastest with oxygen but can work without – which can lead to foul odours
LAGOON BIOLOGY
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Biological Activity: Big and Small
Bacteria 0.001 mm
Protozoa, Rotifers0.1 mm
Daphnia1 mm
Geese – 1 m
LAGOON BIOLOGY
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Biological activity : Oxygen
Bacteria biodegrade organic aerobically (with O2) or anaerobically (no O2)
Aerobic biodegradation is faster and produces no smells
Anaerobic biodegradation is slower and can produce foul smells
Bacteria can be strictly aerobic, strictly anaerobic or facultative (active in both conditions)
LAGOON BIOLOGY
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Biological Activity : Temperature
Bacteria are active at low temperatures (<5oC) as well as high (40oC)
Significant rates of biodegradation of wastewater occurs at temperatures >5oC
Growth slows with decreasing temperature
Net loss of bacteria when growth rate is lower than rate of (decay + predation + washout)
LAGOON BIOLOGY
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Biological Activity : Other Factors
pH – Measure of Acidity/AlkalinityToxicity – Cyanide, Heavy metals
(Copper, Chromium etc.) can inhibit growth of bacteria
Contact between bacteria, pollutants and O2 – if all the bacteria are in the bottom sediments and the O2 and pollutants are in the overlying water column then no biodegradation
LAGOON BIOLOGY
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Treatment Steps : Dilution
Sewage will be diluted in lagoon and undergo sedimentation
LAGOON BIOLOGY
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Treatment Steps : Settling
Solubles + Some Solids
Solids
Fate sewage components will depend on settleability
Interested in knowing what fractions of influent waste are soluble and particulate (solid) components
LAGOON BIOLOGY
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Treatment Steps : Biodegradability
AEROBIC REACTIONS
ANAEROBIC REACTIONS
Fate will depend on biodegradability
Most human waste will biodegrade eventually, but is it readily, slowly, very-slowly or impossibly slowly biodegradable?
Examples:ProteinsCarbohydratesToilet PaperWoodPlastic
LAGOON BIOLOGY
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Treatment Steps : Gas Transfer
Ammonia can be removed by volatilization but it depends on pH
Useful to know what pH is…
NH3NH+4 + H+
LAGOON BIOLOGY
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Total Influent COD
Biodegradable COD
Unbiodegradable COD
Soluble Readily Biodegradable
Particulate Slowly Biodegradable
Soluble Unbiodegradable
Particulate Unbiodegradable
Influent Fractions
COD (Chemical Oxygen Demand) is a measure of all the organic matter in a sample
LAGOON SAMPLING
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Suspended Solids (TSS)
Suspended solids cause turbidityRemoving suspended solids means
removal of BOD, pathogens, metals, and other componentsTurbidity used as criteria for safe drinking
waterSuspended solids can clog receiving
waters, block light penetration, muddy stream bottoms
LAGOON SAMPLING
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Suspended Solids (TSS)
Suspended solids block light penetration
Changing the environment of receiving waters
LAGOON SAMPLING
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Biochemical Oxygen Demand (BOD5)
BOD is a measurement of the amount of biodegradable organic matter
Typically a 5-day test (BOD5) Units are mg O2/L because we are interested
in knowing the amount of oxygen depleted after biodegradation of the organic matter
BOD discharge can be associated with a depletion in dissolved oxygen (DO) concentrations in receiving waters
Without DO, fish die + bad smells
LAGOON SAMPLING
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Biochemical Oxygen Demand (BOD5)
Case study – shows DO “sag” due to BOD discharge
http://www.oxscisoft.com/hermes/casestudies.htm
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Nutrients: N and P
Nitrogen (N) and especially phosphorus (P) are limiting elements for growth of algae in most Canadian lakes and rivers
Human waste contain N and PDetergents contain PLead to eutrophication of receiving
waters
LAGOON SAMPLING
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Toxicity: Ammonia
Sewage can contain toxic componentsIn domestic wastewater the principle
source of toxicity is ammoniaIndustrial effluents and landfill leachates
can contain toxic elements including metals
A government study found that ammonia was the principle source of toxicity in the Saint-Lawrence river (SLV 2000)
LAGOON SAMPLING
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Toxicity: Ammonia
Toxicity of ammonia to fish is dependant on pH
Ammonia can interfere with disinfection of drinking water
LAGOON SAMPLING
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Seasonal Factors
TemperatureBiologyTurnover Ice Cover
SunlightPhotosynthesis affects pH and DOpH has an important effect on effluent
toxicity!!!
LAGOON SAMPLING
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Seasonal Factors
Jan Apr Jul Oct Jan0
2
4
6
8
10
12
14
16E
fflu
en
t a
mm
on
ia (
mg
N/L
)
Averages of 3-years of measurements effluent of 1st lagoon at Drummondville (2000-2003)
Snowmelt Dilution
Biological Activity
(nitrification)
LAGOON SAMPLING
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COD test
Readily Biodegradable
Slowly Biodegradable
Soluble Unbiodegradable
Particulate Unbiodegradable
+
Inorganic Suspended Solids
Chemical Oxygen Demand
LAGOON SAMPLING
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BOD5 test
Biochemical Oxygen Demand
Readily Biodegradable
Slowly Biodegradable
Soluble Unbiodegradable
Particulate Unbiodegradable
+
Inorganic Suspended Solids
LAGOON SAMPLING
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TSS test
Total Suspended Solids
Readily Biodegradable
Slowly Biodegradable
Soluble Unbiodegradable
Particulate Unbiodegradable
+
Inorganic Suspended Solids
LAGOON SAMPLING
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NH3 test
TotalAmmoniaNitrogen
Organic Nitrogen
(Particulate & Soluble)
Colorimetric analysis
LAGOON SAMPLING
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PO4 test
Colorimetric analysis
Phosphate
Organic Phosphorus
(Particulate & Soluble)
LAGOON SAMPLING
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E. coli
CFU/100 mL
Readily Biodegradable
Slowly Biodegradable
Soluble Unbiodegradable
Particulate Unbiodegradable
+
Inorganic Suspended Solids
Important to know because of effect on human health but not a large contributor to oxygen demand
LAGOON SAMPLING
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Case Study: Role of Algae
Sewage is added to lagoon and bacteria use the oxygen to degrade organic matter (COD) Oxygen is replenished by algae at the surface of the lagoon using energy from the sun Oxygen is initially depleted because bacteria use oxygen faster than algae can produce it
LAGOON SAMPLING
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Case Study: Role of Algae
Oxygen is depleted faster at night when algae cannot produced oxygen If lagoon is loaded heavily so that bacteria use oxygen faster than algae
can replenish it, oxygen will drop to zero and anaerobic conditions will exist, leading to odours
LAGOON SAMPLING
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Case Study: Role of Algae
Algae tend to increase the pH in the lagoon which favours volatile form of ammonia
NH4+ ↔ NH3 + H+
Ammonia exists in equilibrium between non-volatile (NH4+) and volatile
(NH3) forms. At neutral pH, the non-volatile form is dominant
LAGOON SAMPLING
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Types of Lagoons
FacultativeOxygen input from algae and wind is
significantOdours generated in bottom layer are
eliminated in overlying aerobic layer
LAGOON DESIGN
O2 O2
O2O2
O2
ANAEROBIC
52
Types of Lagoons
AnaerobicOxygen input is relatively insignificant
(organic load is too high)
LAGOON DESIGN
ANAEROBIC
Odours
53
Facultative Lagoon – Process Operation
Aerobic and Anaerobic Zones allow for varied biology
Water Column is aerobicSediments are anaerobicExchanges between Sediments and
Water Column can be significantRelease of soluble organic matter and
nutrients from sediments (Benthic Load)
LAGOON DESIGN
54
Facultative Lagoon – Design Criteria
Low Organic Load Hydraulic Detention Time : several days Depth (shallow to maximize A:V) L:W ratio (Plug flow vs. Complete Mix) Freeboard Inlet and outlet size, placement, depth
(distribution boxes to avoid a jet) Clay or geomembrane lining to limit seepage
LAGOON DESIGN
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Anaerobic Lagoon – Process Operation
Deep to minimize the effect of oxygen transfer across the lagoon surface
Both Water Column and Sediments are anaerobic
Significant gas production leads to odour problems
Should be upstream of an aerobic process
LAGOON DESIGN
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Anaerobic Lagoon – Design Criteria
High Organic Load Hydraulic Detention Time Depth (deep) L:W ratio Freeboard Inlet and outlet size, placement, depth
(distribution boxes to avoid a jet) Clay or geomembrane lining to limit seepage
LAGOON DESIGN
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Aerated – process operation
Supply of DO allows for biological activity in winter
Influent has heat input which may keep lagoon from freezing over
If rate of feed is low relative to volume, freeze over is likely
LAGOON DESIGN
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Aerated – Design Criteria
Similar to facultative lagoon except:Greater Depth is allowed because natural
surface aeration is not important to treatment
Energy for aeration can increase operation costs significantly
LAGOON DESIGN
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Seasonal Discharge
If lagoon freezes over and no aeration, minimal biological activity and poor treatment
Seasonal discharge is a good option in these cases to avoid discharging poor quality water in winter
LAGOON DESIGN
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Seasonal Discharge – Design Criteria
Hydraulic Detention Time : several months Depth : deep lagoons are good for storage in
water but shallow lagoons favour aerobic activity in summer
Freeboard Inlet and outlet size, placement, depth are
important for controlling discharge Clay or geomembrane lining to limit seepage
LAGOON DESIGN
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Seasonal Factors
TemperatureBiologyTurnover Ice Cover
SunlightPhotosynthesis affects pH and DOpH affects volatility and toxicity of ammonia
LAGOON DESIGN
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Alberta Design Criteria
Unaerated sewage lagoons in Alberta have no effluent requirements
Design must include 2 or 4 anaerobic cells with 2-day retention time in each cell
1 facultative cell with a 2 month retention time 1 storage cell with a 12 month retention time Lagoons are to be drained between late spring
and fall and discharge period should not exceed 3 weeks. i.e. Discharged once per year
LAGOON DESIGN
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Alberta Design Criteria
Anaerobic cells are 3 m deep and designed for desludging.
Facultative cell are a maximum depth of 1.5 m Storage cell are a maximum depth of 3 m and
is intended to act as a facultative cell. Slope of cell walls is 3:1 Wastewater lagoons in Alberta must be lined
to control seepage
LAGOON DESIGN
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Sludge Accumulation Slows down
Solids accumulate in the lagoon sediments Rate of accumulation gradually slows due to
digestion
Sludge Accumulation in Lagoon
Volatile Solids (tons) VS (tons)
Jan-02Jan-01Jan-00Jan-99Jan-98
Vo
lati
le S
oli
ds
(M
etr
ic T
on
s)
2,000
1,800
1,600
1,400
1,200
1,000
800
600
400
200
0
Drummondville, QC WWTP
LAGOON DESIGN
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Quebec Design Criteria
Facultative lagoons are designed based on loading rates of 22 to 12 kg BOD5/ha/d in northern regions.
In general, design is for only seasonal discharge: in spring and fall.
Discharge should not be less than 3 weeks after the ice-melt. Systems generally comprise 2 cells in series or in parallel. Discharge should allow at least 0.3 m of liquid in the lagoon
below which solids entrainment in the effluent can be significant. For systems with continuous discharge in summer, at least 3
cells are recommended which respect the loading rates recommended above.
LAGOON DESIGN
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Quebec Design Criteria
As is the case for Alberta, operational requirements are specified rather than effluent requirements.
MENV guide suggests design gives effluent BOD5 of 20-40 mg/L and TSS of 20-100 mg/L (depending on presence of algae)
Data from installations in Quebec in 1990 had an average of 400 to 20 000 CFU/100 mL
Sampling at least once per month of continuous discharge, discharge must be made during allowed periods and beginning and end of discharge must be noted.
LAGOON DESIGN
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Quebec Design Criteria
Discharge must be conducted in such a way as to limit solids entrainment and to limit erosion from the lagoon
Sludge must be removed before it reaches the bottom of the effluent weir
Geotechnical stability of the lagoon berm should be inspected visually (fissures, sloughing)
Need for lining to control seepage depends on conditions of site and potential impacts to drinking water supplies
LAGOON DESIGN
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Lagoon Design
Poor design can lead to problems:Poor effluent qualityFoul OdoursExcessive sludge accumulationUncontrolled dischargeUncontrolled seepage
LAGOON DESIGN
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Exfiltration Lagoons
Seepage through berm adds a third treatment mechanism:
1. Settling
2. Biodegradation
3. Filtering Rate of seepage from lagoon will
impact treatment performance significantly
LAGOON DESIGN
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Exfiltration Lagoons
“Most of the communities have a dumping lagoon that exfiltrates through the sand and gravel of a berm down a wetland slope anywhere from a few hundred metres to several kilometres long. The wetlands are lush and green with vegetation that thrives on the wastewater while helping to treat it. What we’re finding is that in smaller communities, such as Chesterfield Inlet or Whale Cove, it works very well. The water that reaches the ocean is of very high quality.”
-Brent Wootton, senior scientist with the Centre for Alternative Wastewater Treatment at Fleming College Daily Commercial News and Construction Record, May 9, 2008, Reed Construction Data, Markham, ON
LAGOON DESIGN
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Sewage Lagoon at Whale Cove, NU
wetland
Downstream wetland provides further treatment beyond the lagoon
LAGOON DESIGN
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Exfiltration Lagoon Performance
Why wetlands do or do not work is a current topic of study. Important factors include:
Loading (kg BOD5/m2)TemperatureRate of Seepage over YearExfiltration or uncontrolled runoffRetention time in downstream wetlands
LAGOON DESIGN
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Operation and Sampling
What do we sample for?
What do the tests tell us?
Sampling plan to characterize Lagoon Behaviour Impact on receiving waters.
LAGOON SAMPLING
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Mass Balances
Propose a sampling campaign to characterize the removal of COD, N, and P for the following lagoon system.
*Flow In = Flow Out + Accumulation
82
Sludge Production
After 5 years, the seasonal discharge lagoon at Exampleville is 60% full of sludge. The seasonal discharge lagoon at Pleasanthamlet 100 km away is only 25% full after 10 years.
•How can this be?•What information would you need to investigate your assumptions?•Plan a sampling campaign to investigate your claims
After 10 years After only 5 years
Low TSS High TSS
83
Ammonia discharge
Local residents notice a fish kill in the river two years in a row in early June. The munipality’s lagoon discharges continuously into a wetland 500 meters from the river.
•Could effluent from the lagoon be responsible for the fish kill?•Can you offer an explanation for the fish kill?•What information would you need to investigate your assumptions?•Plan a sampling campaign to investigate your claims