Sewage Treatment

Sewage Pollutants & Treatment Process

To first understand sewage treatment (water pollution control, wastewater treatment, etc.) we first need to know a little about what sewage is, what it contains, and what its harmful effects are.

  1. Sewage contains about 99% water & 1% solid material. The water is the method of transporting the solid material to where it can be treated.
  2. If sewage is not treated it can:
    1. Cause diseases such as diarrhea, dysentery, cholera, & typhoid;
    2. Create bad odors & visible contamination;
    3. Use up dissolved oxygen in rivers, lakes, & oceans that aquatic animals require;
    4. Kills animals, birds, fish & other water life;
    5. Possibly contaminating drinking water supplies.
  3. Sewage may contain any or all of the following pollutants:
    1. Oxygen demanding wastes;
    2. Disease causing agents;
    3. Nutrients;
    4. Synthetic organic chemicals;
    5. Inorganic chemicals & minerals;
    6. Heat;
    7. Sediment/silt;
    8. Radioactive substances.
  4. Pollutants can come from:
    1. Homes:
      1. Improper disposal of household hazardous chemicals, paints, solvents, motor oil, old medications, personal care products, etc.
    2. Industrial/commercial sources:
      1. Factories, mines, refineries, power plants, service stations, laundromats, restaurants, etc.
    3. Farms:
      1. Fertilizers, animals, insecticides, etc.
      2. Large contributors of non point source pollution w/manure runoff.
    4. Air:
      1. When it rains it causes air pollutants/nutrients to return to the ground, rivers, lakes, etc.
    5. Wildlife:
      1. Animals, birds, etc.
      2.  Allowing grazing cattle, horses, ect. to have standing access to rivers & streams.
  5. Sewage treatment plants speed up the natural processes by which water purifies itself, using pipes, tanks, screens, and other processes by directing the flow of sewage to the right process at the right time. Years ago before the tremendous growth in population, it was felt that nature would clean the fast moving bodies of water, like the Sugar River, without the help of man. An old popular saying in the sanitary engineering field was, "The solution to pollution lies in its dilution". Now today with a greatly increased population, man must assist nature, for obvious reasons.
  6. There are two major types of treatment plants:
    1. Biological plants where the bacteria within the sewage uses up or consumes other bacteria (Newport's system);
    2. Physical chemical plants where chemicals are used to help settle out the bacteria and other harmful chemicals and/or materials in the sewage.
  7. There are three main stages of treatment variations exist:
    1. Primary used in Newport:
      1. Screens out or grinds up coarse materials such as rags, sticks, stones, etc;
      2. Removes grit, sand, small stones, etc;
      3. Removes some settleable solids & floating scum.
    2. Secondary used in Newport:
      1. Bacteria and air are mixed together in the correct amounts to use up or consume the dissolved and suspended matter that can not be removed in the primary stage;
      2. Additional settleable solids are removed and in some instances, nutrients are reduced &/or removed.
    3. Disinfection used in Newport:
      1. Use of ultraviolet disinfection, to achieve a pathogen kill, water passes at close range through banks of illuminated UV bulbs;
      2. There are several other types of disinfection available such as chlorine gas, hypochlorite, & ozone.