Presentation on theme: "LOADING RATES Sara Heger"— Presentation transcript:
LOADING RATES Sara Heger firstname.lastname@example.org 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? Groundwater Well Aerobic soil Aerobic soil is needed to treat – remove pathogens – and disperse the treated wastewater back into the environment Horizontal Setback
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 UnsaturatedSaturated Pores air-filled Flow is adjacent to particles Controlled by moisture content and pore diameter Aerobic conditions Slower than saturated flow LTAR related to unsaturated flow Pores water-filled Flow is in large pores Controlled by soils and site conditions May result in anaerobic conditions Faster than unsaturated flow
FLOW FROM THE TRENCH Zone of saturated or nearly saturated flow Zone of unsaturated flow, majority of flow is vertical Zone of saturation or a restrictive layer, flow will be down hill Sidewall infiltration is limited to depth of ponding in trench
Regulations vary: Vertical separation distance : The thickness of air filled soil required between the base of the drainfield and the water table. W WT wt
WASTEWATER TREATMENT AND RENOVATION IN SOILS 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 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
T 1 Biomat begins as incomplete layer at end of trench closest to D-Box where most of the loading is taking place.
Trench with a fully-developed biomat T m (mature) Even distribution of wastewater has occurred due to biomat acting as a membrane-type filter.
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.
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
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
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
COMMERCIAL WASTEWATER Strength Usually greater than residential Operation based Food preparation Restrooms Laundry
HIGH STRENGTH WASTEWATER CIDWT glossary definition 1) Influent having BOD 5 > 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: BOD 5 > 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 - MINNESOTAFOGmg/LTSSmg/L BOD 5 mg/L Restaurants Sampled, # Type of Restaurant 1321848743Bar 20014210104 Golf Club 21921311305Service 28220212868 Fast Food
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 BOD 5 152382 TSS66487 FOG19781 Lesikar et. al (2006)
WASTEWATER ORGANIC RATES Type of Facility Flow(gal/cap/day) lbs. BOD 5 (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 Laundromats400Varies 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
WHAT'S NEXT? MASS LOADING Now that we know the hydraulic and organic values, we combine the two to determine the mass load
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 O L (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 O L (lbs per capita- day) Mass (lb) = 5 (# of people) x 0.17 (lbs per capita- day) Mass (lb) = 0.85 lbs per day
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 ____ 0.56 lbs/day___ = 224 mg 300 gal x 0.00000834 L 300 gal x 0.00000834 L TSS Concentration (after) = ____ 0.56 lbs/day___ = 280 mg 240 gal x 0.00000834 L 240 gal x 0.00000834 L
WHAT'S NEXT? CONTOUR LOADING RATE Now that we know the flow and the biological values, we combine the two to determine the mass load
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) Sand1.030 Sandy Loam0.519 Loam0.415 Silt Loam0.312 Clay Loam0.2511
MUCH MORE WATER Soil Texture Typical Saturated Hydraulic Conductivity (in/day) Effluent Loading rate from SSTS - based on ½ of design flow (in/day) Sand9601 Sandy Loam300.6 Loam100.5 Silt Loam100.4 Clay Loam10.36
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?
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 Low surface area High surface area Sandy SoilHeavy Soil
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
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/ft 2 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/ft 2 /day) Determined by evaluating Texture Structure Percolation rate Effluent quality Dosing method
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 (BOD 5 ) 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/ft 2 lbs of BOD 5 / ft 2 /day lbs of TSS/ ft 2 /day lbs of O&G/ ft 2 /day Sands1.20.00170.000650.00025 Fine sands0.60.000870.000330.00013 Sandy loam0.780.00110.000420.00016 Loam0.60.00070.000270.0001 Silt loam0.50.00060.000240.00009 Clay loam, clay 0.450.000350.000130.00005
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 BOD 5 effluent of 400 mg/L Based on hydraulic loading Ra = 0.50 gal / ft 2 -day Drainfield = 400 gal/day = 800 ft 2 0.50 gal/ft 2 -day Based on organic loading R OL = 0.0006 lbs/ft 2 - day BOD 5 lbs/d = 400 mg/L x 400 gal/d x 0.00000834 = 1.33 lbs/d Drainfield = 1.33 lbs/day = 2217 ft 2 0.0006 lbs/ft 2 -day
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