wastewater

Information about wastewater

Published on November 9, 2007

Author: Samantha

Source: authorstream.com

Content

The Basics of Centralized Sewer Systems:  The Basics of Centralized Sewer Systems Types of Systems --Sanitary Sewer System and a separate Stormwater Sewer System --Combined Sewer System What are the advantages and disadvantages of each? The Basic System Laterals  Submains  Trunk Sewers  Treatment Plant Designed to flow half-full, at a slope of 0.5-2.0% (2 ft.ps), Who is responsible for these different pieces? Manhole covers: Changes in direction, Confluence of major lines, and at specified intervals on straight lines Gravity Mains vs. Force Mains: Uses, Advantages, Disadvantages? Tallahassee’s Sewer System Estimated 675 miles in length (100 of FM), 15,000 manholes, 85 pumping stations Lake Bradford Road Wastewater Treatment Plant (1934) Capacity to treat 4 ½ million gpd Thomas P. Smith Wastewater Treatment Plant (1966-1992) Capacity to treat 27.5 million gpd (Peak of 55 mil.) F Wastewater Treatment:  Wastewater Treatment Major Elements to be Removed Suspended solids, Biological oxygen demand (BOD), nitrogen, phosphorous, and colliform bacteria Major Stages of Treatment Primary Treatment (Reduce Solids 50-60%, BOD 30-50%) Bar screens, Comminutor, Grit chamber (Settling tank) Secondary Treatment (Solids 85-95%, BOD 80-95%, Col. 90-95%) Trickling filter, Activated sludge, Water treatment ponds Advanced Treatment (Solids ~100%, BOD ~99%, Col. ~99%) Land Application, Coagulation-sedimentation, Adsorption, Electrodialysis Outputs of Treatment Effluent: Sprayed on fields, Treated to make potable Sludge (Treated Biosolids) Old Way: Burned, Landfilled, Dumped in ocean (illegal now) New Way: Fertilizer, Dewater and treat (then reuse) the water, Digestion in heated sludge tanks, Process and reuse the methane gas F Slide3:  Wastewater Package Plants Package Plants: Intermediate sized biological wastewater treatment systems. They are designed and engineered specifically for areas that are temporarily or permanently outside the reach of municipal waste disposal systems. Pre-built at the factory and shipped to the project site as a self-contained unit requiring only minimal field assembly. Typically PPs handle between 3,000-500,000 gpd, usually designed for between 10 and 500 dwelling units. Advantages 1) Service areas not serviced by municipal sewer relatively cheaply 2) Make land available for development where water and roads exist 3) Plants are easy to operate, many are manned for 2-3 hours per day 4) Superior to septic tank systems in treatment and cost Disadvantages 1) Promotes leapfrog development 2) Often poorly operated and maintained 3) Allows development in undesirable areas (from view of planners) For more info go to: http://www.epa.gov/owm/mtb/package_plant.pdf Slide4:  Example Package Plant Slide5:  Wastewater: Septic Tanks Over 100 years old; rapidly spread in usage (Created in 1860s, Came to the US in 1884) Septic Tank System The Septic Tank: A large container to hold solid wastes 1) tank stores 2) tank distributes 3) tank provides a place for bacterial digestion Tanks designed to hold wastewater for at least 24 hours before flowing into the drainfield. Piping: A perforated 4-inch pipe in a specially dug trench Drainfield: A trench dug to capture and treat effluent as of flows out of the septic tank. Trench has gravel in it to help with percolation Basically a system that provides Primary and Secondary Treatment. 1) Solids settle, Greases float 2) Effluent is cleaned by settling/floating, bacterial digestion, percolation and infiltration into the ground F Slide6:  Wastewater: Septic Tank Issues Septic Tanks are a mixed blessing because while they brought the convenience of indoor plumbing to rural areas, they also brought problems associated with their use in dense urban areas. A centralized sewer system can be designed on the concept of the “average user”. What needs to be determined is the projected number of “average users” and then the size of the system can be determined. -A septic tank cannot be designed for the “average user”. A septic tank must be designed for the “worst condition” or the 99th percentile of users. “To have a 99% chance of performing satisfactorily, a septic tank system must be designed for those families in the top 1% with respect to water use.” Research in the 1970s and 1980s found that most systems fail in twenty years due to poor construction or a lack of maintenance. Septic systems have “a distressing perversity with regard to predictability of performance.” In terms of their economy, septic tanks are cheaper only in the short run. Studies have shown that centralized sewer systems are less expensive in the long run (over 60 years). Septic tanks become economical at very low densities (approximately 3 acre lots). F Slide7:  Wastewater: Septic Tank Successes Why are Septic Tanks so important historically? --Provided the convenience and safety of interior plumbing to rural areas --Helped to foster suburbanization/rural growth --Brought wastewater treatment to undeveloped areas In recent years, septic tanks have become more and more safe because: 1.      Better septic tank technology (better materials, better builders) 2.      Better understanding of septic tank problems 3.      Better regulations (permitting and building), Better enforcement 4. Specialized firms for septic tank work Septic Tank Administration A permit is required for septic tanks. Location of drainfield is the KEY. Inspected every 3-5 years (3 is best) Clean out annually, especially when you have a garbage disposal When failure occurs: --Must hook up to sewer line if available ($) --Must dig new drainfield (if there is room) ($$) --If no room for new drainfield, must clean out entire old drainfield ($$$$$) F Slide8:  Wastewater: Planning Considerations Important Legislation Federal Water Pollution Control Act (1972) Clean Water Act (1977) Water Quality Act (1987) Resource Conservation and Recovery Act (1976) Determining Sewer System Size and Type --Building a system of appropriate capacity --Cost factors --Balancing cost and treatment levels Linkage of Sewer System Planning and Comprehensive Planning --Federal monies and federal requirements Siting Sewer Facilities --Ideally at the lowest point in the area --Away from residential/commercial areas --Good transportation access --Soil considerations Importance of Maintenance --EPA study showed that while most needs are for new facilities, retrofitting and repairing older facilities are very expensive, so maintenance is essential. F

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