G6 Flashcards
Wastewater/Sewage Treatment
process that involves the purification of water contaminated with various pollutants and contaminants before it is released back into the environment or reused for different purposes.
Stages of Wastewater Treatment
Primary Treatment
Secondary Treatment
Tertiary Treatment
Primary Treatment
- initial phase of sewage treatment where wastewater is held in a basin for solids to settle at the bottom and lighter substances to rise to the top.
- removes settleable solids and the separation of oil and lighter materials. Removing around 50 to 90 percent of solids and floatable materials from the wastewater.
Determine and Explain the Steps/Processes involving Primary Treatment
a. Screening - Screens are made of long, closely spaced, narrow metal bars. They block floating debris such as wood, rags, and other bulky objects that could clog pipes or pumps.
b. Comminution - A comminutor may be used to grind and shred debris that passes through the screens. Shredded material is removed later by sedimentation or flotation processes.
c. Grit Removal - Grit chambers are long narrow tanks that are designed to slow down the flow so that solids such as sand, coffee grounds, and eggshells will settle out of the water. Grit causes excessive wear and tear on pumps and other plant equipment. Its removal is particularly important in cities with combined sewer systems, which carry a good deal of silt, sand, and gravel that wash off streets or land during a storm.
d. Sedimentation - Suspended solids that are removed from the sewage in sedimentation tanks or primary clarifiers. Provide about two hours of detention time for gravity settling to take place. As the sewage flows through them slowly, the solids gradually sink to the bottom. The settled solids (primary sludge) moved along the tank bottom by mechanical scrapers. Sludge is collected in a hopper, where it is pumped out for removal.
Secondary Treatment
focuses on removing dissolved and suspended biological matter using microorganisms in a controlled environment.
- break down organic components in the sewage.
- eliminate contaminants that were not fully removed during the primary treatment.
Determine and Explain the Steps/Processes involving Secondary Treatment
a. Biofiltration - A trickling filter consists of a bed of stones that is about 6 feet tall are used in biofiltration to ensure that any excess sediment is extracted from the wastewater. The bacteria congregate on these stones and begin to multiply and evolve until all of the organic matter in the sewage has been consumed.
b. Activated Sludge Process - The air and sludge are allowed to come into close contact with the bacteria during this process and then passed into the settling tank. The entire setup is left alone for several hours, during which time the bacteria decompose the organic matter into toxic by-products. The sludge, which has been activated by billions of bacteria, is returned to the aeration tank to handle fresh sewage.
c. Oxidation Ponds - Also known as lagoons or stabilisation ponds, are large, shallow ponds that use the interaction of sunlight, bacteria, and algae to treat wastewater. Algae use the sun’s energy, as well as carbon dioxide and inorganic compounds released by bacteria in the water, to release oxygen which is needed by aerobic bacteria. Dredging is needed to remove sludge deposits in the pond.
d. Rotating Biological Contacter - In this treatment system a series of large plastic disks mounted on a horizontal shaft are partially submerged in primary effluent. As the shaft rotates, the disks are exposed alternately to air and wastewater, allowing a layer of bacteria to grow on the disks and to metabolize the organics in the wastewater.
Tertiary Treatment
- also known as polishing
- final stage of wastewater treatment that further cleans the water to meet specific quality standards
- crucial for producing water suitable for drinking or returning to the environment without causing harm.
