Sewage Disposal and Wastewater Treatment PDF

Sewage Disposal and Wastewater Treatment SEWAGE DISPOSAL  process of removing and destroying or converting the noxious substance of sewage or wastewater especially by ammonification and nitrification through bacterial action. Sewage Di...

Sewage Disposal and Wastewater Treatment SEWAGE DISPOSAL  process of removing and destroying or converting the noxious substance of sewage or wastewater especially by ammonification and nitrification through bacterial action. Sewage Disposal Methods  Through sewer systems - standard in built-up areas (cities and industrial areas)  On-site sewerage treatment - usually found in residential, rural areas  Chemical toilets - used by airplanes, long-distance vehicles (trains, caravans, buses) Sewage Treatments  Consists of primary (physical) and secondary (chemical and biological) treatment  Two types of systems: o On-site sewage treatment o Off-site sewage treatment Off-Site Sewage Treatment Systems  Usually for urban areas, where houses and buildings are arranged along a street, each with a household sewer pipeline connected to a communal sewer leading to a wastewater treatment location, then via a main fallout, to rivers and other irrigation areas  Can be restricted to primary level treatment, which includes: degreasing, grit removal, sludge thickening and digestion  After treatment, the water is usually dumped into the ocean or a perennial river outfall, and is considered to still be raw sewage  Only when it passes through secondary treatment does it become acceptable by standards that it is equal to natural river water Treatment Plants  Work to separate the wastewater into supernatant liquid and sludge  Supernatant liquid, after further treatment, is then discharged to rivers, waterways, oceans, and aquifers, while sludge is dried and deposited into ponds and settling beds or used as a fertilizer On-Site Sewage Treatment  Multi-stage systems that collect, treat and disperse water generated by a home or business   Wastewater is treated and discharged to the soils rather than collected and transported to a wastewater treatment plant Steps of On-Site Wastewater Treatment 1. Identifying the source - Discharge sources for residential areas include plumbing fixtures, toilets, laundry, and dishwater; Commercial wastewater comes from restaurants, manufacturing plants, and businesses 2. Collection and Storage of Wastewater - Solid rigid pipe collects wastewater from plumbing fixtures and appliances, laid at a downward slope leading to the pre-treatment plant 3. Pre-treatment of Wastewater - Involves removing contaminants from the wastewater to prepare it for final treatment, using components like trash tanks, septic tanks and processing tanks 4. Final Treatment and Dispersal of Wastewater - Final removal of contaminants takes place and the water can be safely dispersed into the environment, often through a gravity flow system Stages of On-Site Wastewater Treatment 1. Bar Screening - Removal of large objects that can damage equipment 2. Screening - Removal of grit through a grit chamber 3. Primary Clarifier - Separation of solid organic matter from wastewater 4. Aeration - Air is pumped into a tank to encourage NO3 development (from NH3) and provide oxygen for bacterial growth 5. Secondary Clarifier - Treated wastewater is pumped into a secondary clarifier to allow any remaining organic sediment to settle out 6. Chlorination - Chlorine is added to kill any remaining bacteria in the contact chamber 7. Water Analysis and Testing - Proper pH level, ammonia, nitrates, phosphates, dissolved oxygen, and residual chlorine levels are tested to conform to the plant's NPDES permit 8. Effluent Disposal - After meeting all permit specifications, clean water is reintroduced into the environment The Septic Tank Septic Tank System  Private septic tank systems treat wastewater underground, used in rural regions without municipal sewage systems  Septic tanks break down biodegradable waste from a home's or business's sewage system  Septic systems handle bathroom, kitchen, and laundry wastewater using nature and technology Types of Septic Tank Systems 1. Conventional System 2. Alternative Systems: o Aerobic Treatment Unit (ATU) o Mound o Sand Filter o Peat Moss Aerobic Treatment Unit (ATU)  Break down solid waste using oxygen, producing "cleaner" wastewater than conventional septic systems  Aerobic bacteria in the septic tank need oxygen to grow and thrive, decomposing household and business waste Mound  Used when the drain field is elevated or there is little soil for treatment  Employs a sand-filled mound atop natural soil over a drain field, to clean wastewater as it passes through the sand layer and into the soil Sand Filter  Similar to mound systems, employs a layer of sand and a pump to cleanse and disperse wastewater where soil is limited  One of the most common septic systems used when conventional systems lack sufficient soil Peat Moss  Used in systems that rely on peat moss between the septic system's pump tank and drainfield  Wastewater is mostly treated by the peat prior to entering the drainfield, beneficial in areas with limited soil depth or high groundwater How a Conventional Septic System Works  Septic tanks are underground, watertight containers often built of concrete, fiberglass, or polyethylene  The drain field is an open, covered trench dug into relatively dry ground, with perforated pipes to allow the water to escape into the ground and be absorbed, purified, and distributed throughout the soil before entering the groundwater system Types of Septic Tanks 1. Concrete Septic Tank 2. Steel Septic Tank 3. Plastic or Fiberglass Septic Tank Concrete Septic Tank  Can crack, rust, or even separate due to low-quality concrete mix and inadequate maintenance  Cracks allow waste to leak out or groundwater to seep in, causing complications Steel Septic Tank  The weakest and least popular option, enduring only 20-25 years before corroding  The steel tank lid may corrode and collapse under weight Plastic or Fiberglass Septic Tank  More resistant to rust, corrosion, and cracking than steel or concrete  But their lightweight construction makes them prone to structural damage Septic Tank Design  Users and sludge removal intervals determine septic tank capacity, with sludge removal every 2 years  95-150 liters of human waste, including kitchen garbage, is produced daily  Septic tanks have 23cm brick or RCC walls, 15cm cement concrete 1:2:4 foundation floors, and all corners are rounded  Impermo, Cem-seal, Acidproof, etc. are added to cement mortar at 2% by weight to prevent concrete leakage  The septic tank floor slopes 1:10-1:20 toward the inlet side floor Partition or Baffle Wall  A permanent partition may divide a septic tank above 2000 liters into two chambers, with the first chamber's capacity double that of the second Cover and Access Holes  Each septic tank compartment must have a 445x610mm rectangular access aperture or a 500mm circuit opening Pipe Ventilation  Septic tanks must have 50mm ventilation pipes enclosed in a protective mesh cage to keep mosquitoes out Septic Tank Construction  The tank's base must be watertight and sturdy enough to maintain the tank's weight, walls, and interior during earthquakes  Brick walls must be at least 200mm thick and plastered with a cement mortar ratio of 1:3; Stone masonry walls must be at least 370mm thick  Septic tanks have 75-100mm RCC slabs on top, with 500mm manholes for inspection and desludging Designing a Septic Tank  Example: A small house of 20 people with a secure water supply from the municipal headwork at a rate of 120 liters/person/day  Quantity of water supplied = 120 x 20 = 2400 liters/day  Considering 80% of water supplied becomes sewage, the quantity of sewage produced = 2400 x 0.8 = 1920 liters/day  Considering a detention time of 24 hours, the quantity generated during the detention time/tank capacity = 1920 liters   Considering the deposited sludge rate as 30 liters/capita/year and a cleaning period of 1 year = 30 x 20 x 1 = 600 liters  Total Required capacity of the tank = Capacity for sewage + Capacity for sludge = 1920 + 600 = 2520 or 2.52 cubic meters  Considering the tank's depth of 1.3 meters, the tank's surface area = 2.53/1.3 = 1.94 m^2  Considering length to width is 1:3, the Length x Width = 1.94 m^2, so B = sqrt 1.94/3 = 0.8 m  The dimension of the septic tank will be 2.412m x 0.804m x (1.53+0.3)m overall depth Waste Pipes  Smaller in size than the soil pipe due to the type of waste it receives from various plumbing fixtures  Suspended materials found in the water waste include grease, lint, matches, hair, and garbage General Conditions for Good Waste Pipes 1. Making the right choice of materials based on the character of the waste and the service it is intended for 2. Conservative use of fittings to ensure smooth flow 3. Right slope or grade of the pipelines, ideally 2% slope 4. Proper manner of joining pipes as recommended by manufacturers Recommended Size of Waste Pipes 1. Sink Waste - Minimum 38mm or 1 1/2", but practice is to use 50mm or 2" pipe 2. Slope Sink - 75 or 100mm for traps installed on floors, 75mm for traps installed on walls 3. Scullery Sink - 50mm 4. Panty Sink - 38mm 5. Factory Wash Up Sink - 50mm 6. Bathtub - 38mm min to 50mm 7. Lavatories - 50mm 8. Shower Bath - 50mm 9. Urinal - 50mm 10. Laundry Tub - 38mm to 50mm 11. Drinking Fountain - 32mm 12. Lavatory Waste - 50mm 13. Hospital Fixtures - 50mm House Drain  That portion of the plumbing system that receives discharges of all soil and waste stacks within the building, and conveys the same to the House Sewer  Can be installed underground, suspended below the floor or inside the ceiling Types of House Drain  1. Combined Drain - Receives discharge of sanitary waste as well as storm water 2. Sanitary Drain - Receives the discharge of sanitary domestic waste only 3. Storm Drain - Conveys all storm clear water or surface water waste except sanitary wastes 4. Industrial Drain - Receives discharges from industrial equipment containing objectionable acid wastes Determining the Size of House Drain  The Unit System is the most practical method, based on Fixture Unit load discharges for sanitary drain, or roof area that accumulates major rainfall for storm drain  No water closet shall discharge into a drain less than 75 mm or 3 inches pipe diameter, and no more than 2 water closets shall discharge into any 75 mm horizontal soil branch, house drain or house sewer Grade Slope of House Drain  House drain must produce the necessary velocity and discharge capacity at certain inclination, ideally 2% slope, to attain scouring action  Exceptions may be made when the depth of the sewer line in relation to the depth of the basement floor is low, or for long sewer lines that require lower pitch but not less than 1% House Sewer  That portion of the horizontal drainage system, which starts from the outer face of the building and terminates at the main sewer in the street or septic tank  The Main Sewer line is financed and maintained by the government, and houses along the street with main sewer line are required to connect their house sewers to the public sewer line House Connection of House Sewer  The house sewer pipe is connected to the Main Sewer by boring a small hole through the concrete pipe, using a sharpened steel chisel or electric drill  The House Sewer pipe is connected to the Main Sewer entering at 45 degrees angle or directly from the top Size of a House Sewer  Old practice was to use 150 mm or 6 in. diameter cement/vitrified clay pipe for house sewer  For plastic pipe or equivalent interior surface texture, the diameter can be reduced to 100 mm, subject to standard rules Storm Drain   The unit of the plumbing system that conveys rain or storm water to a suitable terminal, normally discharged into a street gutter and carried to a natural drainage terminal Types of Storm Drain Pipes 1. Reinforced Concrete Pipe 2. High Density Polypropylene Smooth Interior 3. PVC - Polyvinyl Chloride 4. High-Density Polyethylene Smooth Interior Parts of a Drainage System  Inlets - Openings that allow stormwater to flow into the storm drainage system (curb opening, grate, slotted, combination)  Culverts - Massive pipes that carry stormwater underground to a local pond, treatment plant, or other destination  Manholes - Openings to access confined spaces for inspection, maintenance and system upgrades  Trunk Line - The main pipeline that carries the stormwater away Classification of Storm Drains 1. Inside Storm Drain - Located under the basement floor or within the walls of the building 2. Outside Storm Drain - Installed outside the foundation wall of the building 3. Overhead Storm Drain - Adopted when the street drainage is higher in elevation than the basement floor, to avail of gravity flow Sizing a Storm Drain Considerations:  Rainfall over a given period, whether constant or heavy showers  Varying roof areas, slope, and distance traveled before reaching conductors  Height of the building contributing to velocity of water falling into vertical pipe conductors  Use of proper fittings and avoiding short offsets Grade Change of Direction  Storm drain installed with a slope of not more than 2% per meter run  Combination of Y and ⅛ bend or a long radius fitting is appropriate for any change in direction Plumbing Ventilation  Plumbing vent, or vent stack, regulates the air pressure within the home's plumbing system  Allows fresh air into the system, improving pipe drainage and water flow Why is Ventilation Necessary?  Drainage and vent systems work together to move waste and water efficiently out of the home  Without proper ventilation, the systems work against each other, causing plumbing issues Venting Methods  Conventional Venting (Individual Venting)  Common Venting  Wet Venting  Circuit Venting  Combination Waste and Vent  Island Fixture Venting  Waste Stack Venting  Single-Stack Venting Trap Seal Loss  Main ways for trap-seal loss are self-siphonage, induced-siphonage, and compression  Can be caused by poor practice, not following regulations, or improper pipework design and installation Retardation of Flow  Retarded water flow inside the pipe is the result of improper atmospheric conditions due to insufficient ventilation or incorrect installation of fittings  Can be corrected by providing ventilation pipes to equalize or balance the air pressure inside the plumbing installation Soil Vent Pipe  Vertical pipe that removes sewage and greywater from a building, often attached to the exterior  Allows odors to be released above the building and facilitates aerobic sewage digestion Drain Waste Vent (DWV) System  Allows air to enter the plumbing system to maintain proper air pressure and enable the removal of sewage and greywater  Drain refers to water from fixtures, waste refers to water from toilets Main Vent  Pipe that runs from a plumbing fixture up through the roof, allowing air pressure to escape the plumbing system Unit Venting  Vent that allows gases in the sewage drainage system to discharge to the outside and sufficient air to enter, reducing air turbulence Types of Vents  Individual Vent  Stack Vent  Vent Stack  Circuit Vent  Relief Vent  Looped Vent  Wet Vent Table: Recommended Waste Pipe Sizes Fixture Minimum Pipe Size Sink Waste 38mm (1 1/2") Slope Sink 75-100mm Scullery Sink 50mm Panty Sink 38mm Factory Wash Up Sink 50mm Bathtub 38-50mm Lavatories 50mm Shower Bath 50mm Urinal 50mm