Wastewater Collection (Sewer Alternatives)

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Wastewater Collection (Sewer Alternatives) Outline

Wastewater Collection (Sewer Alternatives)

Sewer Basics  Collection and transport of wastewater from each home/building to the point where treatment occurs.  Wastewater Characterization • Solids• Liquids  Pipe System • Plastic• Ductile iron• Concrete/lined

Satel ite Wastewater Management  Also called “decentralized” or “distributed”  Undertaken by utilities for a variety of reasons:  Economics  To reuse water locally  To avoid expanding “centralized facilities  As communities expand, the distances from the new developments to existing wastewater treatment facilities becomes so great as to not be economically feasible  Sustainable  Cost Effective, good for the public and the environment

Col ection System Alternatives 1. Conventional Gravity sewers 2. Septic Tank Effluent Gravity (STEG) 3. Septic Tank Effluent Pump (STEP) 4. Pressure Sewers with Grinder Pumps 5. Vacuum Sewers

Conventional Gravity vs. Pressure Sewers

Sewer Alternatives and Characteristics

Conventional Gravity Sewer  Large pipe (8” minimum), manholes spaced 300-500 feet  Designed to transport solids  Minimum velocity >2 fps (to avoid the deposition of solids) Max velocity = 15 fps  Infiltration and Inflow (I & I)  Uniform Slope between manholes • Sewer size Minimum slope (feet/100 ft) • 8-inch 0.40 • 10-inch 0.28 • 12-inch 0.22 • 14-inch 0.17 • 16-inch 0.14 • 18-inch 0.12 • 24-inch 0.08

Conventional Gravity Sewer

Conventional Gravity Sewer Alignment: 24-inch sewers (or smaller) should be laid with straight alignment between manholes. Changes in pipe size: When a smaller sewer joins a larger one (at a manhole), the invert (bottom) of the larger sewer should be lowered sufficiently to overcome head losses. An approximate method is to place the 0.8 depth point of both sewers at the same elevation. 0.8 depths are aligned Sewer Materials: many types, materials and bedding shall prevent damage from external loads, and joints shall prevent leakage

Manholes * Located at changes in sewer size, direction, or slope * Or every 300-500 feet * Provides access for maintenance (cleanout, etc.) * Problematic because of Infiltration and Inflow (I&I)

Conventional Gravity Sewer Bedding: specified by an engineer for pipe type and anticipated loads

Conventional Gravity Sewer Backfill: suitable material, free of debris, stones, etc. DO NOT DISTURB SEWER ALIGNMENT Separation from Water Lines: • 10 feet horizontal• Water line 18-inches above sewer

Crown Corrosion H S + H O    H SO 2 2 2 4 H SO 2 4 H S 2

Estimating Flowrate  Equivalent Dwelling Unit (EDU)  A residence with a given number of people (say 3.5) Represents the average household flowrate  Design Peak Flowrate (DPF)  Flowrate expected in the collection system, assuming a given number of EDUs are discharging at the same time  Typical values for systems with >50 EDUs is 0.35 to 0.5 gal/min-EDU  Total DPF Q = 0.5 N DP

Septic Tank Effluent Gravity STEG  Small diameter plastic pipe Conveys effluent from a septic tank • with an effluent filter  No solids to transport (no minimum velocity required) Can be installed at variable (flat) grades No manholes Air-release valves needed at high points

Septic Tank Effluent Gravity STEG

STEG Sewer Components

Pipe Size and Velocity

Septic Tank Effluent Pump STEP  High-head turbine pump used to pump screened septic tank effluent into a pressurized collection system.  Small diameter, plastic pipe (2-inch)  No Solids transport (no minimum velocities required)  Installed shallow  Can follow terrain  Air-release valves incorporated

STEP Components  Building sewer (from house to septic tank) Septic Tank (or interceptor tank) Vaults/pump basins (effluent filter and pump) Pumps (submersible, high-head, turbine) Service lateral (1.25-inch typical) Check Valves (at pump outlet and at edge of property)

Septic Tank Effluent Pump STEP

STEP System Design Data

STEP System Interceptor Tank

Pressure Sewer with Grinder Pumps  Discharge pump with chopper blades in a small pump basin  Small diameter, pressure line, installed shallow  Solids and greases are transported  Relatively simple installation  Somewhat higher O&M  No I&I

Pressure Sewer Grinder Pump basin

Grinder Pump Basin

Vacuum Sewer  Central vacuum source maintains a vacuum on a small diameter sewer  Pulls wastewater to a central location  Ideal application: • Flat terrain• High water table• 70-100 connections to be economical

Vacuum Sewer

Vacuum Sewer Components

Vacuum Station