Transcript Organic and Mass Loading

LOADING RATES
Sara Heger
[email protected]
http://septic.umn.edu
LOADING RATES - THE THOUGHT
PROCESS
 The system should last a long time
 The wastewater plugs the soil over the long term
 Designing the system for plugging is CRITICAL
HOW DOES SOIL TREAT WASTEWATER?
Well
Horizontal
Setback
Aerobic soil
Groundwater
Aerobic soil is needed to treat – remove pathogens –
and disperse the treated wastewater back into the
environment
WHAT ARE AEROBIC SOIL CONDITIONS?
Pores filled primarily with air (oxygen)
Aerobic organisms present
Pores are open – not smeared
Air can move through pores – not
compacted
Soil is NOT saturated or likely to become
saturated
SOIL PROPERTIES THAT INFLUENCE
WASTEWATER TREATMENT
Wetness conditions
Water movement
Texture
Structure
Restrictive zones or horizons
Landscape
TYPES OF FLOW
Unsaturated
Saturated
 Pores air-filled
 Pores water-filled
 Flow is adjacent to particles
 Flow is in large pores
 Controlled by moisture
 Controlled by soils and
content and pore diameter
 Aerobic conditions
 Slower than saturated flow
 LTAR related to unsaturated
flow
site conditions
 May result in anaerobic
conditions
 Faster than unsaturated
flow
FLOW FROM THE TRENCH
Zone of saturated or
nearly saturated flow
Sidewall infiltration
is limited to depth of
ponding in trench
Zone of unsaturated flow,
majority of flow is vertical
Zone of saturation or a restrictive layer, flow will be down
hill
Cross-section conventional septic
system drainfield trench
Regulations vary:
Vertical separation
distance :
2-3’
The thickness of air
filled soil required
between the base
of the drainfield
4” Dia. Perforated
PVC Pipe
and the water table.
Native Backfill
Filter Fabric
12”
Crushed Stone
W
WT
wt
WASTEWATER TREATMENT AND
RENOVATION IN SOILS
Controlling Factors :
Environmental
•
Temperature, moisture, and oxygen levels
Wastewater characteristics
Loading rates; wastewater strength
• Types of pollutants
•
WASTEWATER TREATMENT AND
RENOVATION IN SOILS
Controlling Factors:
Soil properties
Physical - filtration and sedimentation
• Chemical - adsorption/precipitation (surface
•
area)
• Biological - uptake, incorporation, predation,
and transformations
TIME IS NEEDED FOR
TREATMENT REACTIONS


Biochemical processes depend on detention
time
Detention time is closely related to

hydraulic loading rates

rate of wastewater movement through soils

soil texture, structure, and density have a huge
influence on detention and reaction times
SOIL PHYSICAL
PROPERTIES - TEXTURE
The relative proportion of soil separates
(sand, silt & clay) in a soil.
Texture influences:
•Soil permeability and moisture content
•Biomat formation
•Treatment of effluent
•System construction
- Soil smearing and compaction
SOIL STRUCTURE & WATER
MOVEMENT
Void spaces between soil peds transmit air and water.
Type of structure determines:
• Direction of voids (soil pores)
• Direction of water movement
• Relative rate of water movement
• Retention time for treatment processes
Biomat begins to grow as drainfield
trench receives more wastewater
Native Backfill
2-3’
Filter Fabric
T1
Biomat begins as
incomplete layer
at end of trench
4” Dia. Perforated
PVC Pipe
closest to D-Box
where most of the
loading is taking place.
12”
Crushed Stone
Trench with a fully-developed biomat
T m (mature)
Even distribution
of wastewater has
occurred due to
biomat acting as
a membrane-type
filter.
Native Backfill
2-3’
Filter Fabric
12”
4” Dia. Perforated
PVC Pipe
Crushed Stone
Drainfield Trench
BIOMAT ACTING AS A MEMBRANE FILTER
T s (steady state)
Soil under biomat is aerobic
and air filed.
Amount of organic material
removed from underside of
biomat membrane by soil
aerobic bacteria roughly
equals amounts added from
septic tank.
0.5 – 4 ft
Organic inputs
from septic tank
via perforated pipe
gas & oxygen
moves through
filter fabric and
from sidewalls
Lower part of crushed
stone is saturated and
anaerobic
When organic inputs exceed removals and all
soil pore spaces are clogged by organic
material, then hydraulic failure occurs.
ALL SYSTEMS
HAVE TWO VALUES
Hydraulic Flow
Organic Loading
HYDRAULIC FLOW
WASTEWATER LOADING
Wastewater quantity
 Hydraulic loading
 Residential 120-150
gallons per bedroom
Wastewater quality
 Organic loading
 Residential – 300 mg/l
 Oxygen demand
Residential and
commercial facilities
IMPORTANCE OF HYDRAULIC LOAD
 The daily flow must not exceed the system’s hydraulic capability
 Hydraulic detention time (HDT)
 Example: solids are not able to settle in a septic tank if the water moves through too
quickly.
 Hydraulic overload of the soil
 Effluent surfacing
TOO MUCH USE
 Clean water
 Groundwater drainage
 Footing drain
 Cooling water
 Water treatment
 Too much use
 Over use
 Wash day
 Cleaning service
 Change in use
 Master bath
 Added bedroom
LEAKY COMPONENTS
MEASURED FLOWS? HOW OFTEN IS IT
MEASURED?
 Annually plus-- Average < 70%
 Monthly
 70-75%
 Weekly
 80%
 Daily
 Actual use
 Surge flow is determined
by measuring flow daily
over an extended period
of time
WHAT IS NEEDED TO CALCULATE
HYDRAULIC LOADING
 Cycle counter reading
 Dose Volume
 Time between readings (actual operation)
 Elapsed time meter
 Pump Rate
 Change in value = Total number of units
 Minutes
 Hours
 Time between readings (actual operation)
 Water Meter
 Present and last reading
 Time between readings Pump delivery rate
WASTEWATER QUANTITY - SURGES
Surge flows
 Daily
 Weekly
 Seasonal
Flow equalization?
ORGANIC LOADING
COMMERCIAL WASTEWATER
Strength
Usually greater
than residential
Operation based
Food preparation
Restrooms
Laundry
HIGH STRENGTH WASTEWATER
CIDWT glossary definition
1) Influent having




BOD5 > 300 mg/L,
and/or TSS > 200 mg/L,
and/or fats, oils, and grease (FOG) > 50 mg/L entering a pretreatment
component
2) Effluent from a septic tank or other pretreatment component
that has:




BOD5 > 170 mg/L,
and/or TSS > 60 mg/L,
and/or (FOG) > 25 mg/L and is applied to an infiltrative surface.
Local code definitions may vary
RESTAURANT RESULTS - MINNESOTA
Type of
Restaurants BOD5
Restaurant Sampled, # mg/L
Fast Food
8
1286
TSS
mg/L
202
FOG
mg/L
282
Service
5
1130
213
219
Golf Club
4
1010
142
200
Bar
3
874
184
132
RESTAURANT DATA - LESIKAR 2004 STUDY
28 restaurants located in Texas
Sampled during June, July, and August
2002
12 samples per restaurant and 336
total observations
Most conclusive study to date
31
PERCENT OF DATA CAPTURED
(28 RESTAURANTS)
(GEOMETRIC MEAN PLUS ONE STD. DEV.)
Parameter
Value (mg/L)
% Data Covered
BOD5
1523
82
TSS
664
87
FOG
197
81
Lesikar et. al (2006)
SUMMARY STATISTICS
Raw Data
Mean
1,584
BOD5
Std. Dev.
2,902
(mg/l)
Geometric Mean
932
Geo. Mean + Std Dev.
3,834
Mean
1,030
T SS
Std. Dev.
7,113
(mg/l)
Geometric Mean
257
Geo. Mean + Std Dev.
7,370
Mean
4,520
FOG
Std. Dev.
51,400
(mg/l)
Geometric Mean
108
Geo. Mean + Std Dev.
51,508
Mean
18
Flow
Std. Dev.
11
(gal/seat)
Geometric Mean
15
Geo. Mean +Lesikar
Std Dev.
26
et. al (2006)
Trimmed Data
1,040
690
833
1,523
358
430
234
664
123
107
90
197
18
10
15
25
WASTEWATER ORGANIC RATES
Type of Facility
Flow
(gal/cap/day)
lbs. BOD5
(cap/day)
Apartments - multiple family
75
.175
Boarding houses
50
.140
Bowling alleys - per lane (no food)
75
.150
Campgrounds - per tent or travel trailer site - central bathhouse 50
.130
Churches – per seat
5
.020
Dwellings - single family
75
.170
Dwellings - small, and cottages, with seasonal occupancy
50
.140
Factories - gallons, per person, per shift (no showers)
25
.073
Add for showers
10
.010
Laundromats
400
Varies
Office (no food)
15
.050
Schools – boarding
100
.208
Schools - day (without cafeterias, gyms, or showers)
15
.031
Schools - day (with cafeterias, but no gyms or showers)
20
.042
Schools - day (with cafeterias, gyms, and showers)
25
.052
Stores - per toilet room
400
.832
EFFLUENT CONSTITUENT
CONCENTRATIONS
Source
Oxygen
Demand
BOD5, (mg/L)
Total
Suspended
Solids, TSS
(mg/L)
Nitrogen
Total N
(mg/L)
Fecal
Coliform (org.
/100 mL)
Septic Tank1
140-200
50-100
40-100
106-108
Aerobic
Treatment
Unit
5-50
5-100
25-60
103-104
Sand Filter
Foam or
Textile Filter
1Siegrist,
2001
2-15
5-20
10-50
101-103
5-15
5-10
30-60
101-103
Now that we know the hydraulic and
organic values, we combine the two
to determine the mass load
WHAT'S NEXT?
MASS LOADING
MASS LOADING
Calculate mass loading to a system
Concentration of constituent in the
wastewater
Mass loading based on number of people
Mass (lb) = C (mg/l) x Q (gpd) x 0.00000834
Mass (lb) = P (# of people) x OL (lbs per capita- day)
MASS LOADING CALCULATION
Residential strength
 Calculate mass loading to a system
 Concentration in wastewater
 Volume of wastewater
 Mass (lb) = 140(mg/l) x 200(gpd) x 0.00000834
 Mass (lb) = 0.23 lbs per day
Commercial strength
 Mass (lb) = C (mg/l) x Q (gpd) x 0.00000834
 Mass (lb) = 500(mg/l) x 600(gpd) x 0.00000834
 Mass (lb) = 2.5 lbs per day
MASS LOADING
Calculate mass loading to a system
 Number of people
 Organic loading rate
 Mass (lb) = P (# of people) x OL (lbs per capita- day)
 Mass (lb) = 5 (# of people) x 0.17 (lbs per capita- day)
Mass (lb) = 0.85 lbs per day
lbs BOD5/cap/day
Class
Subdivisions, Higher Cost
Subdivisions, Average
Subdivisions, Low Cost
Motels, Hotels, Trlr. Pks.
Persons Per Unit gal/cap/day Average
3.5
100
0.17
3.5
90
0.17
3.5
70
0.17
2.5
50
0.17
with Garbage BOD5
Grinder (mg/L)
0.25
205
0.23
220
0.20
290
0.20
400
WATER SAVING DEVICES
Decrease water quantity
Assuming no change in
mass load
Wastewater strength
increases
WATER SAVING DEVICE EXAMPLE
 Example 4.2 Increasing concentration of TSS
 A 4 person household produces 0.56 lbs/day TSS without water saving
devices (75 gpd/person).
 Then that family switches to water savings devices, and so they only use
60 gpd/person.
 What is the change in TSS concentration after water saving devices are
installed?
EXAMPLE CONT.
TSS Concentration (before) =
____ 0.56 lbs/day___ = 224 mg
300 gal x 0.00000834
L
TSS Concentration (after) =
____ 0.56 lbs/day___ = 280 mg
240 gal x 0.00000834
L
Now that we know the flow and the
biological values, we combine the
two to determine the mass load
WHAT'S NEXT?
CONTOUR LOADING RATE
MUCH MORE WATER
Soil Texture
Approximate
Natural
Recharge to
Groundwater
(ft/year)
Recharge to
Groundwater from
absorption area* of
SSTS - based on ½ of
design flow (ft/year)
Sand
1.0
30
Sandy Loam
0.5
19
Loam
0.4
15
Silt Loam
0.3
12
Clay Loam
0.25
11
MUCH MORE WATER
Soil Texture
Typical
Saturated
Hydraulic
Conductivity
(in/day)
Effluent Loading
rate from SSTS
- based on ½ of
design flow
(in/day)
Sand
960
1
Sandy Loam
30
0.6
Loam
10
0.5
Silt Loam
10
0.4
Clay Loam
1
0.36
MUCH MORE WATER
 It appears to be OK to use conventional soil loading rates for sizing the
infiltration areas for both septic systems and MSTS (i.e. getting the
effluent from the media into the soil)
 The question is what does the effluent do once it gets into the soil?
STOP TO REVIEW
 Actually 2 Loading Rates:
 Infiltration/Absorption Loading
 Amount of Effluent/Soil Texture
 Organic Loading Rate
 Contour/Mounding Loading Rate
TWO LOADING RATES
Infiltration Capacity
TWO LOADING RATES
Disperses
WHAT IS GW MOUNDING?
Simply, the rise in the groundwater when water is added by man.
SO WHAT IS THE PROBLEM?
 Reduce the unsaturated zone for pathogen removal
SO WHAT IS THE PROBLEM?
 Impede oxygen transfer needed to breakdown the biomat
oxygen
SO WHAT IS THE PROBLEM?
Breakout in downslope areas
WHAT AFFECTS MOUNDING?
•Loading Rate
•Soil Texture (hydraulic conductivity)
•Restrictive Layers
•Depth to Periodically Saturated Soil
•Depth to Regional Watertable
WHAT AFFECTS MOUNDING?
•Distance to Surface Water
•Slope
•Landscape Position
•System Geometry
MOUNDING AND SEPTIC SYSTEMS
Sandy Soil
Low surface area
Heavy Soil
High surface area
CONTOUR LOADING RATE (OR LINEAR)
Amount of wastewater applied daily along
the landscape contour.
It is expressed in gallons per day per linear
foot along the contour (gpd/ft of contour)
Mounding is dealt with by limiting contour
loading rates to 12 gal/linear foot
MOUNDING AND SEPTIC SYSTEMS
CONTOUR LOADING
Contour lines
Drainage
Soil treatment area
(Drainfield)
Direction of groundwater flow
CONTOUR LOADING
Drainage
Direction of groundwater flow
WHAT'S NEXT?
HOW THESE FACTORS
IMPACT LOADING RATES
AND TREATMENT
CONTOUR LOADING
ZONE 3 IS CRITICAL
1
Horizontal flow
2
3
LATERAL FLOW
1
2
3
SOIL TREATMENT SYSTEMS
Soil treatment
 Biomat – restrictive layer
at infiltrative surface
 Biofilm – biological layer
developing on soil
particles
 Biozone – active biological
treatment volume in the
soil
INFILTRATIVE SURFACE
Sized by the loading rate in gpd/ft2
Loading rate determined by
Natural soil properties
Separation distance
Natural site conditions
Modified site conditions (drainage)
LONG TERM ACCEPTANCE RATE
 Design parameter expressing the rate that effluent enters the infiltrative
surface of the soil treatment system
 Measured in volume per area per time, e.g. gallons per square foot per
day (g/ft2/day)
 Determined by evaluating
 Texture
 Structure
 Percolation rate
 Effluent quality
 Dosing method
THEORETICAL HYDRAULIC ACCEPTANCE
Sand
Loam
Silt/Clay Loam
Clay
WHAT CONTROLS LOADING RATE?
Infiltrative surface – biomat/soil interface
Least permeable layer in profile
Horizontal hydraulic conductivity above the least
permeable layer
BIOMAT INFLUENCES
 System: Food
 Hydraulic loading
 Organic loading
 Site: Oxygen
 Soil type
 Texture
 Structure
 Separation
 Depth
 Resting
 Pressurization
 Geometry [Width]
HIGHER QUALITY EFFLUENT
DISTRIBUTION
 Distribution of higher quality
effluent
 Lower organic loading
 No biomat formation
 Greater soil acceptance rate
HIGHER QUALITY EFFLUENT
DISTRIBUTION
Pressure distribution
 Distributes effluent in
space and time
 Facilitates unsaturated
zone below infiltrative
surface
Biozone
 Effluent treatment
 Biofilm development on
particles
 Time for soil treatment
CALCULATING SOIL
MASS LOADING RATE
200 (GPD) X 140 (BOD5) X 0.00000834 =
0.23 pounds/day
For Soil Loading
0.23 / absorption area square feet =
lb/day/square foot
ORGANIC LOADING TO SOIL (MN VALUES)
Soil Texture
Group
Loading
Rate
gpd/ft2
lbs of
BOD5/
ft2/day
lbs of
TSS/
ft2/day
lbs of
O&G/
ft2/day
Sands
1.2
0.0017
0.00065
0.00025
Fine sands
0.6
0.00087
0.00033
0.00013
Sandy loam
0.78
0.0011
0.00042
0.00016
Loam
0.6
0.0007
0.00027
0.0001
Silt loam
0.5
0.0006
0.00024
0.00009
Clay loam,
clay
0.45
0.00035
0.00013
0.00005
RESIDENTIAL SOIL TREATMENT AREA
Soil absorption area based on hydraulic
loading
A = Q / Loading Rate (soil hydraulic)
Soil absorption area based on organic
loading
A= organic loading/loading rate (soil organic)
RESIDENTIAL DRAINFIELD AREA
REQUIREMENTS
Example: Size a soil trench system in silt loam soils for a
system that is treating 400 gpd with BOD5 effluent of 400
mg/L
Based on hydraulic loading
Ra = 0.50 gal / ft2-day
Drainfield = 400 gal/day
= 800 ft2
0.50 gal/ft2-day
Based on organic loading
ROL = 0.0006 lbs/ft2- day
BOD5 lbs/d = 400 mg/L x 400 gal/d x 0.00000834 = 1.33 lbs/d
Drainfield =
1.33 lbs/day
= 2217 ft2
0.0006 lbs/ft2 -day
THE PARTS
Water
Oxygen
FLOW PATTERN IN A GRAVITY TRENCH
 Biomat Growth (t = 0 = start )
FLOW PATTERN IN A GRAVITY TRENCH
 Biomat Growth (t = growth)
FLOW PATTERN IN A GRAVITY TRENCH
 Biomat Growth (t=mature)
FLOW PATTERN WITH
PRESSURE DISTRIBUTION
PRESSURE DISTRIBUTION
SUMMARY
 Aerobic soil conditions are necessary
 All wastewater has two values
 Hydraulic
 Organic
 Mass loading should be considered particular with HSW
 CLR is an important variable to consider to minimize mounding
QUESTIONS – SEPTIC.UMN.EDU