Waste Water Disposal Plumbing Systems CNST 305 Environmental Systems 1 Dr. Berryman 2aWaste Water Disposal and Storm Drainage Chapter 4, 7; Appendix A (Wentz) and (Toa) 4.11 Analysis and Design of Construction Systems - Mechanical (3 hrs)

Individual Waste Treatment Individual Usually residential or small commercial use or areas that have no access to municipal treatment plant Primary system - settling of solids with anaerobic digestion Secondary –filtering process of liquid waste Tertiary – disinfect ion w/ chlorine

Primary Treatment Septic Tanks* Commonly precast concrete Contains two chambers or a baffle Raw sewage settles anaerobic digestion proceeds Liquid move toward outlet. Solid continue to sink and decompose. About 70% purified, liquid move to the secondary system Individual - Primary *1000 – 1200 gallon tanks for a family of 4

Individual – Primary (cont.) Improvements on Primary System Increase digestion rates Oxygenate the tank for aerobic digestion Keep temperature of tank around 92 o F Drawbacks – energy intensive, costly, and requires more maintenance.

Individual – Secondary System Drain Fields Mounds Seepage Pits Evaporation Tanks (or lagoons) Sand Filter

Drain Field Must have porous soils Relatively inexpensive to install and operate Trench construction (1-3 ft width) Washed gravel or stone Perforated pipe Manufactured Tiles

Drain Field – “Perc” Test Length of drain tile determined by Percolation test Test pit dug 12 – 36 inches Filled with water Number of minutes it takes for the water level to drop 1 inch Use table to determine length

Mounds with Leach Beds May require special approval (newness) An option for high water tables Little more expensive to install Sizing same as drain fields Absorption area has to be 50% larger

Seepage Pits Strictly Controlled Outlawed in some codes Appropriate for porous soils Must have a deep water table

Evaporation Pits Areas having very slow soil percolation rates Sewage directly into the lagoon aerobic and anaerobic decomposition Minimum size lot area for lagoon construction is 3 acres enclosed with a 4 foot high fence signs stating: NO TRESPASSING--WASTE LAGOON

Sand Filter Use in non-porous soils More expensive Requires disinfection (tertiary system) before releasing into environment

Individual – Tertiary System Rare usage on residential applications Most common is disinfection for environmental release chlorine Use extensively on large scale treatment plants

Cost Comparisons Relative costs of home sewage treatment systems as compared to the septic tank- absorption field system (assumed to be $2,500 in spring, 1980). SOURCE:

Sewage Treatment Plants Similar to individual Three stages of treatment Primary treatment includes: Sedimentation and retention ponds for raw sewage Aeration ponds Skimming ponds Scum removal of floating partially treated sewage Sludge removal Secondary treatment includes: Suspension ponds – alum/filtration process Tertiary treatment Disinfection by chemical addition FILM

Next time Storm Drainage 2aWaste Water Disposal and Storm Drainage Chapter 4, 7; Appendix A (Wentz) and (Toa) 4.11 Analysis and Design of Construction Systems - Mechanical (3 hrs)