Many of our daily chores such as bathing, doing laundry, flushing toilets, repairing meals, washing dishes and other activities generate wastewater. Few people give thought to where wastewater goes after it disappears down the drain.
Domestic wastewater (i.e. sewage) must be properly treated because it contains excessive nutrients, harmful bacteria/viruses and household chemicals that may contaminate the land and waters of our state and threaten public health.
Read Also : Wastewater Treatment Options
In the developed countries, the technology and the resources available are often adequate to properly treat their wastewaters; you may need to think of this and search for cities that have witnessed breakdown of their municipal treatment plants of recent.
Wastewater Treatment Objectives
The basic objectives of wastewater treatment include the followings:
Remove sediments
Remove organic matter (BOD)
Remove nutrients (N and P)
Remove or inactivate pathogens
The objectives vary with level. Table 13 below shows the specific objective of water treatment at different levels.
Table 13: Levels of Water Treatment and their Objectives
| Level | Objective |
| Pre-treatment | Remove sand, grit and large objects |
| Primary | Remove suspended particles by sedimentation. Remove BOD, N, P and pathogens |
| Secondary | Remove dissolved solids, BOD, N and P by biological degradation (use of bacteria) |
| Tertiary | Additional treatment, specific to situations (e.g. nutrients, organics and colloids) |
| Disinfection | Remove inactive pathogens |
Operations of a Wastewater Treatment Plant
Wastewater is about 99 percent water by weight and is generally referred to as influent as it enters the wastewater treatment facility. “Domestic wastewater” is wastewater that comes primarily from individuals, and does not generally include industrial or agricultural wastewater.
At wastewater treatment plants, this flow is treated before it is allowed to be returned to the environment, lakes, or streams. There are no holidays for wastewater treatment, and most plants operate 24 hours a day.
Wastewater treatment plants operate at a critical point of the water cycle, helping nature defend water from excessive pollution. Most treatment plants have primary treatment (physical removal of floatable and settle able solids) and secondary treatment (the biological removal of dissolved solids).
On-Site Disposal and Treatment System
This is a system that requires that the municipal wastewater, commonly known as sewage is treated on the site. Each on-site sewage disposal system is designed for a specific site and a specific volume of wastewater. Each site is different and must be evaluated individually.
Site evaluation information includes: soil conditions, topography, lot size and location, estimated water usage, depth of the groundwater tables, seasonal high water tables, water-well locations (yours and your neighbours’), location of creeks, rivers, springs, ponds and lakes, or other factors that may affect the type of system you select.
It is possible that no system can be approved if adverse environmental and/or physical conditions exist on the site. Soil conditions are determined by conducting a soil percolation test or soil profile description.