Septic Tank Systems and Components PDF

Septic Tank Definition: – buried, watertight container that collects wastewater from homes. – buried, watertight receptacles designed and constructed to receive wastewater from the structure to be served How It Works: Receives Wastewater: Collects water from toilets and sinks. Separates Solids a...

Septic Tank Definition: – buried, watertight container that collects wastewater from homes. – buried, watertight receptacles designed and constructed to receive wastewater from the structure to be served How It Works: Receives Wastewater: Collects water from toilets and sinks. Separates Solids and Liquids: 1. Sludge: Heavy solids settle at the bottom. 2. Scum: Lighter materials float on top. Digests Organic Matter: Bacteria break down some sludge. Stores Waste: Holds sludge and scum until pumped out. Discharges Clarified Liquid: The middle layer flows out for further treatment in a drain field. The diagram depicts the structure and function of a septic tank, which is used for on-site sewage treatment. Here's a breakdown of the key components shown: 1. Inlet: Wastewater enters the septic tank from the house through this pipe. It carries the waste from toilets, sinks, and other household drains. 2. Scum Layer: This is the top layer that consists of lighter materials such as oils, fats, and grease. These substances float to the top and form a scum layer. 3. Baffle: This internal structure directs the flow of incoming wastewater to prevent disruption of the layers inside the tank. It helps separate the tank into two compartments and ensures proper settling of solids.  4. Effluent Layer: This is the middle layer, consisting of the liquid portion of the wastewater. Effluent is the partially treated wastewater that eventually flows out of the septic tank. 5. Sludge: Heavier materials in the wastewater, such as solids and dirt, settle at the bottom of the tank to form sludge. This sludge will need to be periodically removed from the tank. 6. Effluent Filter (Optional): This filter, located near the outlet, helps prevent larger particles from leaving the tank and clogging the dispersal system. 7. Outlet: The treated effluent (liquid waste) exits the septic tank through the outlet pipe. From here, it moves on to further treatment or a dispersal system, such as a drain field or leach field, where it is absorbed into the ground. 8. Access Risers: These provide access to the interior of the tank for inspection, cleaning, and maintenance purposes. How It Works: Wastewater enters the tank through the inlet. Inside, it separates into three layers: scum (top), effluent (middle), and sludge (bottom). Effluent passes through the outlet, potentially through a filter, and moves into the dispersal system, where it is absorbed and treated by the soil. The septic tank retains solids and sludge, which accumulate at the bottom and need periodic pumping. The number of compartments or specific configurations might vary depending on regional or state requirements. How Septic Tanks and Leach Fields Work: Process Overview 1. Wastewater Entry: Household wastewater (sewage) flows into a septic tank. 2. Separation of Waste: Inside the tank, solid waste settles at the bottom, forming a layer called sludge. This sludge needs to be pumped out periodically. 3. Liquid Waste Treatment: The remaining liquid, now partially treated, moves from the septic tank to a leach field. 4. Leach Field: The leach field consists of perforated pipes buried in the ground. Here, the liquid is naturally absorbed into the soil, where it undergoes further treatment by microorganisms. Summary: Wastewater flows into the septic tank, where solids settle and some treatment occurs. Effluent moves to the distribution box, which directs it into the drain field. In the drain field, effluent is absorbed and filtered by the soil, completing the treatment process. Parts of Conventional Septic Tank System: 1. Septic Tank: Receives household wastewater. Solids settle at the bottom (sludge), while lighter materials float (scum). 2. Distribution Box: Distributes partially treated liquid (effluent) evenly into the drain field. 3. Septic Drain Field (Leach Field): A network of perforated pipes that allows effluent to seep into the soil for further natural treatment. Summary: Wastewater enters the septic tank, where solids settle.  Effluent moves to the distribution box and is spread into the drain field. The soil further purifies the effluent before it reaches groundwater. Septic Drain Field (Leach Field) Components: 1. Distribution Pipe: Carries effluent from the septic tank to the drain field. 2. Gravel: Surrounds the distribution pipes, aiding in filtration and distribution of wastewater. 3. Hay, Straw, or Building Paper: Acts as a barrier to prevent soil clogging while allowing effluent to seep through. 4. Soil: Absorbs and further treats the effluent through natural filtration. Summary: Effluent flows through the distribution pipe into the gravel. Gravel filters and distributes the wastewater. Hay or straw prevents clogging, while soil absorbs and treats the effluent. Importance of Septic Tank Sludge Removal: Prevent System Strain: Excess sludge increases pressure, risking system failure. Avoid Blockages: Accumulated sludge can lead to blocked drains and toilets. Protect Drain Field: Overflowing sludge contaminates the drain field, causing premature failure. Ensure Effluent Quality: High sludge levels degrade effluent quality, risking health and environmental safety. Products of Septic Tanks: 1. Scum: Substances lighter than water (oil, grease, fats) float to the top, forming a scum layer. 2. Sludge: The "sinkable" solids (soil, grit, bones, unconsumed food particles) settle to the bottom of the tank, forming a sludge layer. Anaerobic bacteria work here. 3. Effluent: The clarified wastewater left over after the scum has floated to the top and the sludge has settled to the bottom. It flows through the septic tank outlet into the drain field. Summary: Scum: Rises to the top. Sludge: Sinks to the bottom. Effluent: Flows out for further treatment. Key Parameters in Septic Tank Function: 1. Effective Volume Definition: The liquid volume in the clear space between the scum and sludge layers. 2. Retention Time Definition: The time water spends in the tank from inlet to outlet. Formula: Retention Time (days) = Effective Volume (gal) / Flow Rate (gal/day)​ Design Guidelines: Minimum Retention Time: At least 24 hours, allowing one-half to two-thirds of the tank volume for sludge and scum.  Ordinary Conditions: Ideally, a tank should provide 2 to 3 days of retention time with routine maintenance. Importance of Parameters: Effective Volume: Determines how much liquid can be treated. Retention Time: Ensures adequate separation of solids, preventing blockages and ensuring proper treatment. Summary: Effective Volume: Space between scum and sludge layers. Retention Time: Duration wastewater remains in the tank. Constructed Wetlands: Artificially created water bodies designed for wastewater treatment. Design: Typically consist of long, narrow trenches or channels to promote plug flow conditions. Basin Depth: Usually a 1-meter deep basin, sealed with clay or another lining to prevent percolation into groundwater. Soil and Vegetation: The basin is filled with soil, in which reeds are planted to aid in the treatment process. Summary: Artificial Water Bodies: Created for wastewater treatment. Trenches/Channels: Designed for effective flow. 1-Meter Deep Basin: Sealed to protect groundwater. Reeds in Soil: Essential for filtration and treatment. NOTE: – They are effective for removing various contaminants from wastewater (BOD, TSS, nitrogen and phosphorus, metals, trace organics and pathogens). – Typically, a septic tanks (primary settling basin) or anaerobic reactors is used before water enters constructed wetlands for effective sewage treatment (PRECEDING TREATMENT) Two Main Operational Considerations: 1. Mosquito control 2. Plant harvesting. Plants Used for Constructed Wetlands: – macrophytes 1. Bulrush 2. Phragmites 3. Cattail 4. Canna Lily 5. Duckweeds 6. Reeds Common Characteristics of Emergent Aquatic Macrophytes: Rooted in Water: These plants have roots that grow underwater while their stems and leaves extend above the water surface.  Adaptation to Wet Conditions: They thrive in shallow water and are well-suited for environments with fluctuating water levels. Reasons for Use in Constructed Wetlands: Filtration: Their root systems help filter pollutants and sediments from wastewater. Nutrient Uptake: They absorb excess nutrients (like nitrogen and phosphorus) from the water, improving water quality. Habitat Support: Provide habitat for aquatic organisms and contribute to biodiversity. Oxygen Production: Some species release oxygen into the water, enhancing aerobic conditions beneficial for microbial activity. 2 Systems of Constructed Wetlands: 1. Free Water Surface (FWS) Systems Description: Shallow water depths with an exposed surface. Functionality: Water flows above ground, allowing for natural aeration. 2. Subsurface Flow (SSF) Systems Description: Water flows laterally through sand or gravel below the surface. Functionality: Wastewater is filtered as it passes through the media. Design Considerations for Constructed Wetlands: a. Detritus Removal: Importance: Prevents aging of the wetland. Methods: Options include harvesting or burning detritus. b. Wildlife Enhancement: Open Water Surface: 25 to 35% of the wetland surface should be open water, with a depth no greater than five feet. Emergent Vegetation: Should comprise 65 to 75% of the surface area, with water depth of less than two feet. c. Mosquito Control: Design Requirement: Minimize hydraulically static areas to prevent mosquito breeding. d. Maximum Hydraulic Design Loading: Flow Rate: 25,000 gallons per acre per day. e. Minimum Detention Time: Recommended: 7 days; Optimal: 14 days for effective treatment. f. Recommended Depth of Flow: Range: Between 6 and 24 inches. Optimum Depth: 9 inches. g. Configuration: Shape: Rectangular configuration enhances treatment efficiency. Length to Width Ratio: Should be between 5:1 and 10:1. Wildlife Support: Irregular shorelines provide better habitat for wildlife. Lagoons Definition: Pond-like bodies or basins designed to receive, hold, and treat wastewater for a set period.  Lining: Often lined with clay or artificial material to prevent leaks into groundwater. Treatment Processes: Wastewater is treated through a combination of: Physical, Biological, Chemical processes. Aeration: Some systems use aeration devices to add oxygen, enhancing treatment efficiency and reducing land area needs. Additional Treatment or Polishing: Wastewater leaving a lagoon may require further treatment or “polishing” to remove: Disease-causing organisms, Nutrients Design Considerations for Lagoons: A. Total Organic Loading: Limit: Maximum of 20 pounds of BOD5 per acre per day. B. Liquid Retention: Minimum Retention: Design for a minimum liquid retention of 180 days based on average flow rate. C. Depth Requirements: Minimum Depth: At least 2 feet. Maximum Depth: Should not exceed 6 feet. The table shows lagoon health based on water color: 1. Bright Green: Great – Healthy lagoon with plenty of green algae. 2. Dull Green: Not good – Poor water quality, undesirable algae dominate. 3. Tan/Brown: Questionable – Soil or red algae present, uncertain conditions. 4. Gray/Black: Very bad – Anaerobic, poor wastewater treatment, likely odors. 3 Types of Lagoon Designs: Types of Lagoon Designs 1. Anaerobic Lagoons Function: Treat wastewater without aeration, allowing organic matter to ferment into simple organic acids and methane. Usage: Commonly used for high-strength wastewater, especially from food processing, as a first-stage treatment. Problems in Anaerobic Lagoons: 1. Acid Lock: Fermentation produces acids that lower pH, inhibiting methanogen growth. 2. Low COD Removal: Nutrient limitations or chemical inhibitors can slow bacterial growth, leading to poor organic matter breakdown. 3. Low Methane Production: Nutrient deficiencies or inhibitors may limit methane generation. 4. High Odor Generation: Anaerobic processes produce odorous compounds like hydrogen sulfide and volatile acids. 2. Facultative Lagoons Definition Facultative Lagoons: Wastewater treatment systems that can be actively aerated or rely on oxygen diffusing from the air into the surface water. Facultative lagoons effectively treat wastewater by utilizing a combination of aerobic and anaerobic processes. Key Features Bacterial Activity: Contains both aerobic and anaerobic bacteria, aiding in the removal of contaminants. Layer Structure: Aerobic Layer: Top layer with oxygen from air and algae. Facultative Layer: Middle layer where both aerobic and anaerobic processes occur. Anaerobic Layer: Bottom layer where organic matter is fermented. Benefits Nitrification: Aerobic bacteria convert ammonia to nitrite and nitrate. Efficient COD Removal: Volatile acids are converted to carbon dioxide and water. Problems in Facultative Lagoons Foaming: Caused by surfactants or filamentous bacteria under low oxygen conditions. Dispersed Biomass: High suspended solids due to toxic compounds or rapid bacterial growth. Inversion of Water Layers: Wind or temperature changes can mix layers, disrupting treatment processes. Loss of Nitrification: Sensitive to toxins, low pH, and nutrient deficiencies, leading to potential washout of nitrifying bacteria. 3. Aerated Lagoons Definition Aerated Lagoons: Wastewater treatment systems that use surface aerators to mix water and increase dissolved oxygen levels. Key Features Mixing: Aerators create a mixed zone, but complete mixing is rare, leading to anaerobic processes in the sediment and "dead zones." Efficiency: Effective at removing COD (Chemical Oxygen Demand) and nitrification due to higher biomass production from aerobic bacteria. Common Problems Low COD Removal: Lack of essential nutrients or inhibitors can slow bacterial growth, leading to insufficient organic matter breakdown. Foaming: Caused by surfactants or filamentous bacteria due to low dissolved oxygen or unbalanced nutrients. Dispersed Biomass: High suspended solids may result from toxic compounds or rapid bacterial growth. Pass-through of Compounds: Essential bacteria for degrading certain chemicals may be absent or insufficient, leading to incomplete treatment. Dissolved Oxygen Requirements Minimum Level: Aeration equipment must maintain a minimum dissolved oxygen level of 2 mg/L at all times, depending on BOD loading and suspended solids concentration.