Civil Engineering and Architecture

 

Water Supply & Wastewater Treatment

Public Water System - Community owned potable water distribution system.

Hard Water - Drinking water, usually from a groundwater source, that is high in dissolved minerals, most commonly calcium, magnesium, and iron.

Head - Water pressure

Head Loss - Energy loss in hydraulic systems due to friction.

Potable Water - Raw or treated water that is considered safe to drink.

Static Head Pressure - The water pressure within a pipe when the water is not moving.

Flow Rate - The rate at which water or wastewater moves through a treatment system or pipe network.

Total Dynamic Head (TDH) - The pressure within a pipe system with the water in motion. TDH = Static head minus head loss.

Water Supply:
 Click on the images below...

Water TowerWell Water

Water Supply:

  • Required Minimum Pressure = 40psi
  • 1psi = 2.31' of water
  • 1 mile = 5,280'
     
  • Actual pressure = static pressure – head loss (all expressed in psi)

  • Static pressure = (elevation of water level – elevation of water discharge point) ÷ 2.31 ft/psi

  • Static Water Head = WSEL at Tower - Elevation water supply at discharge point
  • Static Water Pressure = Static Water Head * (psi/2.31')
  • Actual Head = Static Head - Head Loss
  • Actual Pressure = street pressure - static difference - head loss
     
  • Calculate the equivalent length of the fittings:
  • Calculate total length of pipe:
  • Select Hazen-Williams coefficient:
     
  • Head Loss:

  • hf = 10.44 * L * Q1.85
                  C1.85 * d4.8655

  • hf is head loss due to friction, feet
  • L is the length of pipe, feet
  • Q is the flowrate of water through the pipe, gpm
  • C is the Hazen-Williams coefficient
  • d is the diameter of the pipe, inches

Waste Water Management:

A civil (environmental) engineer must decide how to manage the wastewater by considering three broad categorical options:

Reuse: wastewater that can be used again without treatment of any kind.

Recycling: wastewater that is treated either on-site or off-site and used again. 

Discharge/treatment: wastewater that is simply discharged from the structure for treatment either on-site or off-site. 

Percolation Test: The ability of the native soil to permit water or wastewater to infiltrate (or percolate) is critical to the design.

Wastewater - The spent or used water from an individual household, a community, or commercial establishment, which contains dissolved and suspended matter that is harmful to human health and the environment. Wastewater requires treatment to remove bacteria and pathogens, either through an onsite decentralized wastewater treatment system or a centralized municipal sewage system, before it can safely be released into the environment. Household wastewater includes liquid-solid mixtures from toilets, sinks, showers, bathtubs, washing machines, dishwashers, and other drains.

Waste Treatment Engineer - The profession that is responsible for designing and analyzing waste water treatment facilities, such as sanitary waste, disposable waste, and water treatment facilities.

Water Management Engineer - A profession that studies the use of hydraulic and hydrologic principles to design drainage systems, detention and retention ponds, navigational waterways, dams, and lakes.

Publicily Owned Treatment Works (POTW) - Municipal owned water treatment or wastewater treatment facility.

Public Sanitary Sewer System - Community owned wastewater system.

Wastewater Management

Septic System - A method to handle raw sewage on site; consists of piping from the structure to the tank, a tank to hold sewage where bacteria breaks it down, and a drain field where liquid is dispersed

Septic - An anaerobic condition of water and wastewater.

Septage - The biodegradable waste from septic tanks and similar treatment systems. Septage includes the sediments, water, grease, and scum pumped from a septic tank.

Pump Stations - Pumps, typically housed in buildings, which add energy to water distribution and sanitary sewer systems.

Septic System

Distribution Box is used to divide the wastewater effluent flow among multiple distribution lines in the infiltration bed.

The absorption, leach, or infiltration field is located in permeable, unsaturated soil or imported fill material. Septic tank effluent flows out of the distribution box and into perforated pipes that distribute the wastewater over the field area

Septic tank: The septic tank is a pre-cast, concrete structure that is designed to retain wastewater long enough to trap floating material (oil, grease, and floating debris) and settle solid particles. The floating material is called the scum layer and the settled solids form the sludge layer.

Septic Tank

Waste Water Management:

  • Total Daily Wastewater Flow = Flowrate per customer x number of customers + flowrate per employee x number of employees
  • Slope = Change in Elevation ÷  Length of Pipe
     
  • Septic Tank Sizing & Layout:
    Hydraulic detention time = liquid volume ÷ flowrate
     
  • Total volume = liquid volume ÷ [1-scum / solids volume as a fraction]
     
  • Liquid volume = (hydraulic detention time) * (wastewater flow rate)
     
  • Infiltration Field Sizing & Layout:
    Infiltration Area = trench area = wastewater flow rate ÷  hydraulic loading rate
     
  • Trench Length = infiltration area ÷  trench width