Organic and Mass Loading

Loading Rates

Sara Hegersheger@umn.eduhttp://septic.umn.edu

Loading Rates - The Thought ProcessThe system should last a long timeThe wastewater plugs the soil over the long termDesigning the system for plugging is CRITICAL

How does soil treat wastewater?GroundwaterWellAerobic soilAerobic soil is needed to treat remove pathogens and disperse the treated wastewater back into the environmentHorizontalSetbackSoil and Site. Lindbo et al. DRAFT1/28/20133The important factor is aerobic soil. This is where the treatment occurs. The goal for an installer is to preserve the soil properties to ensure the soil stays aerobic. So what are aerobic soil conditions?What are aerobic soil conditions?Pores filled primarily with air (oxygen)Aerobic organisms presentPores are open not smearedAir can move through pores not compactedSoil is NOT saturated or likely to become saturated

Soil and Site. Lindbo et al. DRAFT1/28/20134Aerobic conditions as described. Proper treatment is attained through aerobic conditions.Soil properties that influence wastewater treatmentWetness conditionsWater movement TextureStructureRestrictive zones or horizonsLandscapeSoil and Site. Lindbo et al. DRAFT1/28/20135There are several properties of soils that need to be consider in order to evaluate the soils for on-site wastewater treatment.

Lets consider the soil now.Types of FlowUnsaturatedSaturatedPores air-filledFlow is adjacent to particlesControlled by moisture content and pore diameter Aerobic conditions Slower than saturated flowLTAR related to unsaturated flow

Pores water-filledFlow is in large poresControlled by soils and site conditionsMay result in anaerobic conditionsFaster than unsaturated flowSoil and Site. Lindbo et al. DRAFT1/28/20136Start with the 2 types of flow; saturated and unsaturated. Each are related to different soil conditions. Here again we need to stress treatment over disposal. If all we wanted was disposal we would strive for saturated flow. LTARs are set to promote unsaturated flowFlow from the trenchZone of saturated or nearly saturated flowZone of unsaturated flow, majority of flow is verticalZone of saturation or a restrictive layer, flow will be down hillSidewall infiltration is limited to depth of ponding in trenchSoil and Site. Lindbo et al. DRAFT1/28/20137Flow from the trench is not a simple one dimensional flow. Side walls only play a role to the depth at which they are ponded. In a conventional system this should be minimal. It will be more important in serial distribution. Once flow leaves the zone of saturation it will become unsaturated flow. Although matric potential can draw the flow in any direct (highest potential to lowest potential) the majority of the flow is still vertical. Once the water/effluent reaches the ground water (or restrictive) the flow will become gradient driven, generally lateral.

Regulations vary: Vertical separationdistance :The thickness of airfilled soil required between the baseof the drainfield and the water table. WWT wtWastewater treatment and renovation in soilsControlling Factors : Environmental Temperature, moisture, and oxygen levelsWastewater characteristics Loading rates; wastewater strength Types of pollutantsWastewater treatment and renovation in soilsControlling 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 - TextureThe relative proportion of soil separates (sand, silt & clay) in a soil.Texture influences:Soil permeability and moisture content Biomat formationTreatment of effluentSystem construction - Soil smearing and compactionSoil structure & water movementVoid 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 1Biomat begins asincomplete layer at end of trench closest to D-Boxwhere most of the loading is taking place.

Trench with a fully-developed biomat T m (mature)Even distributionof wastewater hasoccurred due to biomat acting as a membrane-typefilter.

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 ValuesHydraulic FlowOrganic Loading18Wastewater also is made up of two values, one is flow, one is organic loading. Wastewater quantity is the flow that will be entering a wastewater treatment system. Hydraulic Flow Wastewater Loading Wastewater quantityHydraulic loadingResidential 120-150 gallons per bedroomWastewater qualityOrganic loadingResidential 300 mg/lOxygen demandResidential and commercial facilities

20The required size and capability of an onsite wastewater treatment system is dependent on the wastewaters quality, or strength, the oxygen demand the constituents will generate, and the daily wastewater flow.We will describe wastewater loading in a couple different ways mainly in relation to:

Weve already spent some time discussing Wastewater Quantity which is the Hydraulic loading and Wastewater Quality which relates to Organic loadingWe will then discuss the difference between Residential and commercial facilities.

Wastewater quantity and quality are actually interrelated parameters that cannot be totally separated. We will discuss them separately but need to keep this interrelationship in mind.

Across the nation there are a few states that are now making a real clear statement as what is domestic waste. Because our regulations across the nation, simply address domestic waste. Residential waste. They dont address commercial waste. And thats the real challenge here, is how do we take it from where were at to where we know we have to be? So what were saying in some states is that when we call it domestic waste, then the highest BOD5. Its 300 ml per liter, not every state identifies that. Importance of hydraulic loadThe daily flow must not exceed the systems hydraulic capabilityHydraulic 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 soilEffluent surfacing 21The two most significant impacts of hydraulic overload are in components that have particular hydraulic detention time necessary to provide the treatment. This is particularly important in tanks such as septic tanks or grease traps. If the water flows through too fast then the solids wont have time to settle. Also if water moves too fast solids might get stirred up. The other aspect of excessive hydraulic loading rates are the soil acceptance rates. The soil must be able to accept the water from the treatment system. Too much useClean waterGroundwater drainageFooting drainCooling waterWater treatmentToo much useOver useWash dayCleaning serviceChange in useMaster bathAdded bedroom

Leaky ComponentsTanksPipingTreatment ComponentsSystem measurementMeasured Flows? How often is it Measured?Annually plus---Average < 70%Monthly70-75%Weekly80%DailyActual useSurge flow is determined by measuring flow daily over an extended period of time

24Now if I come back in 30 days after that hour meter is installed, I have a 30-day average. If I want to know what the peak flow is, I need to read it every day. That way I can determine what the peak flow is. Maybe one day a month, maybe one day a week, its not uncommon that our average flow will be far below design. But our peak one-day of flow might be twice the design, so you really need to look for what is that peak flow.

An accurate surge flow can only be determined by measuring the flow through the system on a daily basis over an extended period of time. If the flow is only measured once every month, then only the 30-day average daily flow can be determined. If the peak hourly flow needs to be determined, then the flow must be measured every hour. What is needed to Calculate Hydraulic LoadingCycle counter readingDose VolumeTime between readings (actual operation)Elapsed time meterPump RateChange in value = Total number of unitsMinutesHoursTime between readings (actual operation)Water MeterPresent and last readingTime between readings Pump delivery rate

25Should use CC and ETM together to maximize the amount of information that can be collected. Wastewater Quantity - Surges Surge flowsDaily WeeklySeasonalFlow equalization?

26Peak flows are a part of any treatment system because human activity directly relates to the generation of wastewater in a facility. The graph shows the discharge rate from a facility with respect to time of day. Daily flow initiates about 6:00 am and tails off after 10:00 pm. The daily wastewater flow has two peak flows associated with activities in the morning and activities in the evening. Households that do not have anyone at home during the day will have less flow during the mid part of the day.

Weekly - peak flows are associated with facilities that have varying flows throughout the day. Can you think of facilities that may have varying flows through out the week? Churches tend to be the best example of peak flows because of the loading on Sundays. They may have additional flows during the week based on activities in the church.

Seasonal peak flows are associated with facilities used more on a seasonal basis. What types of facilities would have seasonal peaks? Summer camps, ski resorts, state parks, etc.

Estimating peaks We can estimate the peak flows by evaluating the time period when the greatest activity will be occurring in a facility. We can estimate the runoff period from a facility by evaluating the time period when the facility is open. Restaurants will have some additional time with wastewater generation tied to food preparation and clean-up following the close of business. Organic loadingCommercial WastewaterStrengthUsually greater than residentialOperation basedFood preparationRestroomsLaundry

28Commercial Wastewater treatment systems have special considerations regarding the sizing of an advanced wastewater treatment system.The type of business is a key consideration when estimating the wastewater stream i.e. restaurant, video store, sandwich shop, laundry, business offices, etc. Strength of wastewater is an important consideration when designing a commercial operation because the wastewater strength is Usually greater than residential. The facility advanced treatment system needs to be sized based on both the hydraulic and organic load. The approach requiring the greatest amount of capacity should determine the appropriate size for the system. The type of Operation affects the wastewater strength. Again, a restaurant, video shop, school, bakery, office building will all have different considerations when evaluating the wastewater stream for treatment. High Strength WastewaterCIDWT glossary definition1) 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 vary29In general weve said that high strength wastewater has constituent levels that are higher than residential quality. The Onsite Consortium glossary defines high strength wastewater to be either an influent with BOD greater than 300 mg/l, TSS greater than 200 mg/L and/or Fog higher than 50 mg/L that is entering a pretreatment component, so raw wastewater. It can also be an effluent from a septic tank or other treatment unit that has BOD5 > 170 mg/L, and/or TSS > 60 mg/L, and/or (FOG) > 25 mg/L. This definition may not hold true in every jurisdiction so it is important to familiarize yourself with the local code. Restaurant Results - MinnesotaFOGmg/LTSSmg/LBOD5 mg/LRestaurants Sampled, #Type of Restaurant1321848743Bar20014210104Golf Club21921311305Service28220212868Fast FoodRestaurant Data - Lesikar 2004 Study28 restaurants located in Texas Sampled during June, July, and August 200212 samples per restaurant and 336 total observationsMost conclusive study to date31Percent of Data Captured (28 Restaurants)(Geometric Mean plus One Std. Dev.)ParameterValue (mg/L)% Data CoveredBOD5152382TSS66487FOG19781Lesikar et. al (2006)Summary Statistics

Lesikar et. al (2006)Wastewater Organic RatesType of Facility Flow(gal/cap/day) lbs. BOD5(cap/day) Apartments - multiple family 75.175Boarding houses 50.140Bowling alleys - per lane (no food) 75.150Campgrounds - per tent or travel trailer site - central bathhouse 50.130Churches per seat 5.020Dwellings - single family 75.170Dwellings - small, and cottages, with seasonal occupancy 50.140Factories - gallons, per person, per shift (no showers) 25.073Add for showers 10.010Laundromats 400VariesOffice (no food) 15.050Schools boarding 100.208Schools - day (without cafeterias, gyms, or showers) 15.031Schools - day (with cafeterias, but no gyms or showers) 20.042Schools - day (with cafeterias, gyms, and showers) 25.052Stores - per toilet room 400.83234Wastewater Organic Rates are available for some facilities on a mass basis.

This table presents information regarding mass loading rates for different types of facilities which is noted by the class in the left column. As we move to the right across the table we are provided additional information regarding the loading assumptions presented in this table. Again, the hydraulic loading is increased for different economic classifications for housing. The low cost subdivisions have an estimated hydraulic load of 70 gallons per person per day, while higher cost subdivisions have a hydraulic load of 100 gallons per person per day.

The BOD loading in pounds per person per day is in the right two columns. The first column presents an average organic loading on a per person basis of 0.17 lbs per person per day. The second column presents a distinction regarding the use of a garbage disposal in the residence. The organic loading increases with an anticipated greater use of a garbage disposal.

This table presented in Goldstein and Moberg (1973) is used as an example to discuss organic loading rates. It is not presented as an authoritative source of information on this subject. You will need to check with your local regulations, regulatory authority, or the manufacturer of the product you are planning to use in a specific facility to determine appropriate sizing guidance.

Effluent Constituent ConcentrationsSourceOxygen DemandBOD5, (mg/L)Total Suspended Solids, TSS(mg/L)NitrogenTotal N(mg/L)Fecal Coliform (org. /100 mL)Septic Tank1140-20050-10040-100106-108AerobicTreatment Unit5-505-100 25-60103-104 Sand Filter 2-155-2010-50101-103

Foam or Textile Filter5-155-1030-60101-103

1Siegrist, 2001 35Field testing of treatment systems generate data related to the Effluent Constituents under a broad range of operational situations.

A study by Siegrist (2001) evaluated effluent quality from a septic tank. The biochemical oxygen demand in the septic tank effluent ranged from 140 to 200 mg/L. The Total Suspended Solids concentration ranged from 50 to 100 mg/L in the septic tank effluent. The total nitrogen concentration in septic tank effluent ranged from 40 to 100 mg/L. The fecal coliform concentration in the septic tank effluent ranged from 1,000,000 to 100,000,000 organisms per 100 milliliters of effluent.

The biochemical oxygen demand of the Advanced Treatment Unit effluent to be 25 mg/L or less while the total suspended solids concentration should be less that 30 mg/L. These criteria for advanced treatment units specify the effluent concentrations of BOD and TSS to be greatly reduced compared to septic tank effluent. The total nitrogen concentration in advanced treatment unit effluent as measured by Siegrist (2001) ranged from 25 to 60 mg/L which showed a lower range than septic tank effluent. The fecal coliform concentration in the advanced treatment unit ranged from 1000 to 10,000 organisms per 100 milliliters. Therefore, the advanced treatment process reduces the fecal coliform concentration in the effluent. However, a disinfection treatment process would be needed to further treat the effluent for surface application or discharge.

What's Next? Mass loadingNow that we know the hydraulic and organic values, we combine the two to determine the mass load36Now that we know the Flow and the Biological values, we combine the two to determine the mass loadThe organic loading is much more significant when converted to a mass loading rather than a concentration.Mass LoadingCalculate mass loading to a systemConcentration of constituent in the wastewaterMass loading based on number of peopleMass (lb) = C (mg/l) x Q (gpd) x 0.00000834Mass (lb) = P (# of people) x OL (lbs per capita- day)

37Now we will consider different methods to Calculate the mass loading to an onsite wastewater treatment system. We have two different ways to determine this mass loading:Concentration of constituent in the wastewater, and Mass loading based on number of people.

The equation for calculating mass loading based on concentration is:Mass (lb) = C (mg/l) x Q (gpd) x 0.00000834This equation uses the conversion factor of 0.00000834 which represents the relationship of 1 mg/L concentration of a constituent equals 8.34 pounds of that constituent in one million gallons of water. The equation for calculating mass loading based on people and organic load is:Mass (lb) = P (# of people) x OL (lbs per capita- day)We use the number of people using a facility and their organic loading to the facility to determine the mass loading to the system.Mass Loading CalculationResidential strengthCalculate mass loading to a systemConcentration in wastewaterVolume of wastewaterMass (lb) = 140(mg/l) x 200(gpd) x 0.00000834Mass (lb) = 0.23 lbs per day

Commercial strengthMass (lb) = C (mg/l) x Q (gpd) x 0.00000834Mass (lb) = 500(mg/l) x 600(gpd) x 0.00000834Mass (lb) = 2.5 lbs per day

38An example of a Mass Loading Calculation is described on this slide.

We will go through a procedure to Calculate the mass loading to a system when we have information describing the Concentration of a constituent in the wastewater and the volume of wastewater flowing through a facility.

For example a facility has a wastewater constituent concentration of 500 mg/L in the wastewater and the facility has an average daily flow of 600 gallons per day. The 500 mg/L concentration is placed in the C location in the equation and the 600 gpd is placed in the Q location.

Mass (lb) = C (mg/l) x Q (gpd) x 0.00000834

Mass (lb) = 500(mg/l) x 600(gpd) x 0.00000834

These numbers are then multiplied together with the conversion factor to calculate a loading to the facility. For this example the mass loading is 2.5 lbs per day.

Mass (lb) = 2.5 lbs per day

This calculation can be used to calculate a loading for any constituent that is known on a concentration basis. Some example constituents could be BOD, Nitrogen, and Phosphorous. Other constituents may be a concern in specific locations.Mass LoadingCalculate mass loading to a systemNumber of peopleOrganic loading rateMass (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

39The equation for calculating mass loading based on people and organic load is:Mass (lb) = P (# of people) x OL (lbs per capita- day)We use the number of people using a facility and their organic loading to the facility to determine the mass loading to the system.Water Saving DevicesDecrease water quantityAssuming no change in mass loadWastewater strength increases

40Water saving devices only change the hydraulic loading. The mass loading will not change although with less dilution water, the concentrations will increase.Water Saving Device ExampleExample 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?41This example shows how using water saving devices effect the TSS loading of a system. We are going to assume that a family of 4 produces .56 pounds of TSS per day. Their flow began as 75 gals per day per person before they switched to water saving devices. The flow per person dropped to 60 gallons per person per day. 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 L42The loading remains constant even with water saving devices. Calculating the concentrations for the different flow values show that the concentration increases when the flow decreases although the overall loading is the same. What's Next? Contour loading rateNow that we know the flow and the biological values, we combine the two to determine the mass load43Now that we know the Flow and the Biological values, we combine the two to determine the mass loadThe organic loading is much more significant when converted to a mass loading rather than a concentration.Much More WaterSoil TextureApproximate Natural Recharge to Groundwater (ft/year)Recharge to Groundwater from absorption area* of SSTS - based on of design flow (ft/year)Sand1.030Sandy Loam0.519Loam0.415Silt Loam0.312Clay Loam0.2511Much More WaterSoil TextureTypical Saturated Hydraulic Conductivity(in/day)Effluent Loading rate from SSTS - based on of design flow(in/day)Sand9601Sandy Loam300.6Loam100.5Silt Loam100.4Clay Loam10.36Much More WaterIt 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 ReviewActually 2 Loading Rates:Infiltration/Absorption LoadingAmount of Effluent/Soil TextureOrganic Loading RateContour/Mounding Loading RateTwo Loading RatesInfiltration CapacityTwo Loading RatesDisperses 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 biomatoxygenSo What is the Problem?Breakout in downslope areasWhat Affects Mounding?Loading RateSoil Texture (hydraulic conductivity)Restrictive LayersDepth to Periodically Saturated SoilDepth to Regional Watertable

What Affects Mounding?Distance to Surface WaterSlopeLandscape PositionSystem Geometry55Mounding and septic systemsLow surface areaHigh surface areaSandy SoilHeavy SoilContour 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 systemsContour linesDrainageDirection of groundwater flowContour LoadingSoil treatment area(Drainfield)This traditional design uses many short trenches for the system. The lateral flow away from the system has to pass through a narrow window down slope.DrainageDirection of groundwater flowContour LoadingSoil treatment area(Drainfield)Perhaps 1 or 2 long trenches can over come the limitation of the down slope window. Unfortunately, drainfield configuration is rarely this simple as it is generally constrained by lot size and shape.What's Next? How these factors impact loading rates and treatment 61Now that we know the Flow and the Biological values, we combine the two to determine the mass loadThe organic loading is much more significant when converted to a mass loading rather than a concentration.

Horizontal flow123Contour loadingZone 3 is criticalSo zone 3 is the critical zone when on a sloping site. All effluent must move through it . If the zone is too small, like a partially closed window, less effluent can pass; this may result in saturation and a reduction in treatment.Lateral flow

213On any given septic system 3 zones of infiltration or infiltrative surfaces need to be considered. Zone 1 is the trench bottom and biomat, zone 2 is the most limiting zone below the trench, and zone 3 is the window or horizontal zone that water must move through as it moves down gradient from the system. The ability to keep the system aerobic will depend on not exceeding the hydraulic conductivity of the most limiting of these layers. Therefore, the most limiting layer is the one that must be considered for design purposes.Soil Treatment SystemsSoil treatmentBiomat restrictive layer at infiltrative surfaceBiofilm biological layer developing on soil particlesBiozone active biological treatment volume in the soil

64Soil Treatment Systems provide the final treatment and dispersal of effluent into the soil. We need to evaluate how soil treatment systems interact with higher quality effluent.

Soil treatment is accomplished by the soil microbes converting the wastewater constituents to materials that are not harmful such as organic material and gases. These microbes are the workers converting the wastewater and we will discuss descriptive terms representing this microbial population in the soil.Biomat restrictive layer at infiltrative surface. Generally a function of organic loading that causes a biologically active layer at the soil interface that restricts water movement. This biomat contains suspended solids filtered from the wastewater in addition to the microbes feeding on the waste materials. The biomat is the critical mechanism for distribution of effluent in gravity distribution trenches.Biofilm biological layer developing on soil particles. These microbes attach themselves to the soil surface. As the water moves through the soil under unsaturated flow conditions, it is in contact with the biofilm. The wastewater constituents included pathogens are removed.Biozone active biological treatment volume in the soil. This soil volume contains the soil particles, microbial growth on the soil particles and oxygen in the soil pores for aerobic treatment of the wastewater. This soil volumes needs to retain the effluent for a sufficient time to facilitate removal of the wastewater constituents.

Infiltrative Surface Sized by the loading rate in gpd/ft2Loading rate determined byNatural soil propertiesSeparation distanceNatural site conditionsModified site conditions (drainage)

Soil and Site. Lindbo et al. DRAFT1/28/201365The overall area of infiltrative surface is determined by the LTAR. LTAR is determined by the soil and site conditions. If the soil properties after change without changes to the LTAR (size of infiltrative surface) the overall system performance will be affected.Long Term Acceptance RateDesign parameter expressing the rate that effluent enters the infiltrative surface of the soil treatment systemMeasured in volume per area per time, e.g. gallons per square foot per day (g/ft2/day)Determined by evaluatingTexture StructurePercolation rateEffluent qualityDosing methodTheoretical Hydraulic Acceptance

Long Term Acceptance RateTimeAcceptance Rate67This slide was developed from research data on biomat development on the top of soil columns overtime. The wastewater being added to the soil had a strength equivalent to septic tank effluent. What Controls Loading Rate?Infiltrative surface biomat/soil interfaceLeast permeable layer in profileHorizontal hydraulic conductivity above the least permeable layer

Soil and Site. Lindbo et al. DRAFT1/28/201368LTAR is controlled by several factors.Biomat InfluencesSystem: FoodHydraulic loadingOrganic loadingSite: OxygenSoil typeTextureStructureSeparationDepthResting PressurizationGeometry [Width]The BiomatHigher Quality Effluent DistributionDistribution of higher quality effluent Lower organic loadingNo biomat formationGreater soil acceptance rate

70Distribution of higher quality effluent Advanced treatment units improve the effluent quality distributed into the soil. Lower organic loading The concentration of BOD5, TSS and FOG are greatly reduced in the effluent but not totally removed. The effluent still serves as a food source for biological treatment. No biomat formation Generally, a biomat is associated with a higher organic loading to the infiltrative surface. Greater soil acceptance rate is achieved because of the lack of biomat at the infiltrative surface. Higher Quality Effluent DistributionPressure distribution Distributes effluent in space and time Facilitates unsaturated zone below infiltrative surfaceBiozone Effluent treatmentBiofilm development on particlesTime for soil treatment

71High Quality Effluent Distribution distributes effluent in the soil to provide final treatment. Higher quality effluent still contains small concentrations of organic material and potentially pathogens if a disinfection system was not used prior to distribution.Pressure distribution utilizes a network of piping and orifices in the piping to uniformly distribute effluent into the soil. Distributes effluent in space and time The distribution network covers the absorptive surface or soil treatment area to accept and treat the wastewater thus accomplishing the distribution in space. Distribution in time is achieved through the use of a control panel to periodically dose effluent through the distribution network and out into the soil. The rest period between doses facilitates the effluent distribution in the soil. Facilitates unsaturated zone below infiltrative surface The rest period in the pressure dosing cycle allows water movement to be converted from saturated flow conditions to unsaturated flow conditions in the soil. Properly matching the total hydraulic load and the dose volume to the soil on the site will assist in not moving effluent through the soil under saturated conditions.Biozone the biozone provides the remaining effluent treatment. The effluent is distributed into the soil and slowly moves through the soil under unsaturated conditions to achieve the treatment.Biofilm development on soil particles is the microbes in the soil that convert the remaining contaminants in the effluent to harmless materials. Time for soil treatment is one of the most critical factors when evaluating the soils ability to renovate effluent. The effluent must stay in the aerobic biozone for a sufficient amount of time to allow the microbes to convert the contaminants. The dosing and resting components of the pressure distribution cycle need to be properly matched to the soil to achieve the time for treatment.

Calculating Soil Mass Loading rate200 (GPD) X 140 (BOD5) X 0.00000834 = 0.23 pounds/dayFor Soil Loading0.23 / absorption area square feet = lb/day/square foot729The next thing that we would look at is now that we have a better understanding of the biological side of this system and we know that they hydraulic side of this system, we are moving across the nation and to get a better understanding is to look at the mass loads of what we are saying is the mass load is the combination of the flow that a BOD fiber organic loading times a million to 8.4 so that would be 200 gallons per day times 140 milligrams per liter BOD5 times and this is kind of an equation, .00000834. Thats to the water. 834 times a million. Multiply that flow time BOD plus the equation will give you a mass load of the average BOD is about .23 pounds per day. Thats pretty much agreed upon across the nation. That .23 pounds per day is what we would consider the healthy system. A really healthy system. A system that has .23 pounds per day would have a very long life generally speaking. You can also take that loading of .23 pounds per day or whatever that is, it could be a lot more than and divide it into the absorption area so you would have your organic loading to the foot of the absorption area. And thats another thing that well get into is looking at what is the maximum organic loading per foot. But that is how you figure mass load. Its flow times the biological side times the equation of 50834 will give you .23 pounds per day. Now what were saying here, and this is really important, this is what we know to be a tank thats probably getting that 70% reduction, not the 20%, so this is a tank thats working very well and with this, this is what we are looking for, the good, you have to understand a tank thats working well before you can understand one thats working poorly. Organic Loading to Soil (MN Values) Soil Texture GroupLoading Rategpd/ft2lbs of BOD5/ ft2/daylbs of TSS/ ft2/daylbs of O&G/ ft2/daySands1.20.00170.000650.00025Fine sands0.60.000870.000330.00013Sandy loam0.780.00110.000420.00016Loam0.60.00070.000270.0001Silt loam0.50.00060.000240.00009Clay loam, clay0.450.000350.000130.00005Residential soil treatment areaSoil absorption area based on hydraulic loadingA = Q / Loading Rate (soil hydraulic)Soil absorption area based on organic loadingA= organic loading/loading rate (soil organic)Residential drainfield area requirementsExample: 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 loadingRa = 0.50 gal / ft2-dayDrainfield = 400 gal/day = 800 ft2 0.50 gal/ft2-day

Based on organic loadingROL = 0.0006 lbs/ft2- dayBOD5 lbs/d = 400 mg/L x 400 gal/d x 0.00000834 = 1.33 lbs/dDrainfield = 1.33 lbs/day = 2217 ft2 0.0006 lbs/ft2 -dayThe PartsSoil: Texture, Structure & SeparationSets: Water & Oxygen flowpondingThe SystemFlow pattern in a gravity trenchBiomat Growth (t = 0 = start )

Unsaturated flowSaturated flow77Effluent is added to the system and the biomat will start to develop.This development is a factor of the waste strength in the effluent. The more BOD the faster development of the Biomat.

In a gravity fed system wastewater always enters the beginning part of each trench. If the applied wastewater cannot infiltrate the soil within the first few meters of the length of the trench, it will flow by gravity along the trench until the surface area of infiltration matches the ratio of the volume of applied wastewater and the average infiltration rate of wastewater into the soil from the bottom and side walls of the trench. As the time progresses, due to the ponding of wastewater at the beginning of the trench, a biological mat (also called biomat, clogging mat or biological clogging mat) will be created at the interface of gravel and soil in the trench (see Siegrist, 1986). With time, this biological mat may eventually cover the entire length of the trench and result in a substantial reduction in the infiltration capacity of the trenches. Surfacing of wastewater over the drain field and/or backing of sewage into the dwelling occurs when the trenches of a septic system fill up and the volume of wastewater applied daily to the trenches can no longer infiltrate the soil within each 24-h period.

Flow pattern in a gravity trench Biomat Growth (t = growth)

Unsaturated flow78The biomat will develop along the bottom of the systems first. The front edge of the flow is high- saturated and under the biomat the flow is unsaturated.Flow pattern in a gravity trench Biomat Growth (t=mature)

Mature BiomatSHLR~ Trench flow = SHLR x Area79A mature biomat extends along the bottom of the system and will begin to develop along the sidewalls. This will appear as ponded effluent in the system. When the biomat is developed the flow under the trench is unsaturatedThis is the key to treatmentIf the system is too small the biomat will be a problem and hydraulic failure will occurFlow pattern with Pressure Distribution

Unsaturated flow created by the use of pump80Instead of relying on the biomat to produce unsaturated flow, in a pressure distribution system the rate of application is controlled by a pump. This produces a loading rate that maintains unsaturated flow. If the loading is to high an anaerobic biomat will form and the system will fail.Pressure distribution moves the spreading to the pump and soil receives the effluent at a rate that the soil can accept the effluent in unsaturated flowPressure distribution

Loading maintains Unsaturated conditions81SummaryAerobic soil conditions are necessaryAll wastewater has two valuesHydraulicOrganicMass loading should be considered particular with HSWCLR is an important variable to consider to minimize mounding

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Crushed Stone
Filter Fabric
12
2-3
4 Dia. PerforatedPVC Pipe
Native Backfill

Biomat begins to grow as drainfield trench receives more wastewater
Crushed Stone
Filter Fabric
12
2-3
4 Dia. PerforatedPVC Pipe
Native Backfill

University of Rhode Island
Conventional Septic System Drainfield Trench
Crushed Stone
Filter Fabric
12
2-3
4 Dia. PerforatedPVC Pipe
Native Backfill

University of Rhode Island
Conventional Septic System Drainfield Trench
Lower part of crushed stone is saturated andanaerobic
gas & oxygen moves through filter fabric and from sidewalls
0.5 4 ft
Organic inputsfrom septic tank via perforated pipe

Sheet1Raw DataTrimmed DataBOD5 (mg/l)Mean1,5841,040Std. Dev.2,902690Geometric Mean932833Geo. Mean + Std Dev.3,8341,523TSS (mg/l)Mean1,030358Std. Dev.7,113430Geometric Mean257234Geo. Mean + Std Dev.7,370664FOG (mg/l)Mean4,520123Std. Dev.51,400107Geometric Mean10890Geo. Mean + Std Dev.51,508197Flow (gal/seat)Mean1818Std. Dev.1110Geometric Mean1515Geo. Mean + Std Dev.2625

ClassPersons Per Unitgal/cap/daylbs BOD5/cap/day

Averagewith Garbage GrinderBOD5(mg/L)

Subdivisions, Higher Cost3.51000.170.25205

Subdivisions, Average3.5900.170.23220

Subdivisions, Low Cost3.5700.170.20290

Motels, Hotels, Trlr. Pks.2.5500.170.20400

Apartment Houses2.5750.170.25225

Resorts, Camps, Cottages2.5500.170.20400

Hospitalsper bed2000.300.35200

Factories or Officesper person200.06-360

Factories with showersper person250.07-340

Restaurantsper meal50.020.06450

soil comp0.250.250.020.48

Sheet1Water25%Air25%Organic2%Minerals48%

Chart26050352650332520322319.518241917162017.51615181615.414.81615.414.814.715.2514.7514.614.514.914.714.614.414.814.714.514.4

SandLoamSilt/Clay LoamClay

Sheet2timeSandLoamSilt/Clay LoamClay1605035262503325203322319.51842419171652017.516156181615.414.871615.414.814.7815.2514.7514.614.5914.914.714.614.41014.814.714.514.4

Sheet3