why is air along with microorganisms bubbled into rhe sewage treatment?
Answers
if this ans helped u mark it brainliested
Every day, wastewater goes down toilets and drains in homes, schools, businesses and factories and then flows into New York City's sewer system. Runoff from rain and melting snow, street and sidewalk washing, and other outdoor activities flows into catchbasins in the streets and from there into the sewers. In some New York City neighborhoods, runoff from the streets is carried by separate storm sewers directly to local streams, rivers and bays. In most areas of the City, sanitary and industrial wastewater, rainwater and street runoff are collected in the same sewers and then conveyed together to the City's treatment plants. This is known as a combined sewer system. Sometimes, during heavy rains or snow, combined sewers fill to capacity and are unable to carry the combined sanitary and storm sewage to the plants.When this occurs the mix of excess storm water and untreated sewage flows directly into the City's waterways. This is called combined sewer overflow (CSO). Approximately 70 percent of the City sewers are combined.
Wastewater treatment plants, also called sewage treatment plants or water pollution control plants, remove most pollutants from wastewater before it is released to local waterways. At the plants, physical and biological processes closely duplicate how wetlands, rivers, streams and lakes naturally purify water. Treatment at these plants is quick, taking only about seven hours to remove most of the pollutants from the wastewater. In the natural environment this process could take many weeks and nature alone cannot handle the volume of wastewater that New York City produces.
At the City's wastewater treatment plants, wastewater undergoes five major processes: preliminary treatment, primary treatment, secondary treatment, disinfection and finally, sludge treatment. Primary and secondary treatments remove about 85% to 95% of pollutants from the wastewater before the treated wastewater is disinfected and discharged into local waterways. Sludge, the byproduct of the treatment process, is digested for stabilization and is then dewatered for easier handling. The resulting material, known as biosolids, is then applied to land to improve vegetation or processed further as compost or fertilizer. (See illustration — “Diagram of Treatment Process” on page 16-17.)
Preliminary treatment
Several stories underground, wastewater flows into the plants from sewers connected to New York City's homes and businesses. The incoming wastewater, called influent, passes through screens consisting of upright bars, spaced one to three inches apart. These bars remove large pieces of trash including rags, sticks, newspaper, soft drink cans, bottles, plastic cups and other similar items. This protects the main sewage pumps and other equipment. The garbage is transported to landfills. The main sewage pumps then lift the wastewater from the screening chamber to the surface level of the plant.
back to top
Primary treatment
Next, the wastewater enters primary settling tanks, also called sedimentation tanks, for one to two hours. The flow of the water is slowed, allowing heavier solids to settle to the bottom of the tank and the lighter materials to float. At the end of the process, the floatable trash, such as grease and small plastic material, rises and is skimmed from the top of the tanks surface.
The settled solids, called primary sludge, are then pumped through cyclone degritters — devices that use centrifugal force to separate out sand, grit (such as coffee grinds) and gravel. This grit is removed, washed and taken to landfills.
The degritted primary sludge is pumped to the plant's sludge handling facilities for further processing. The partially treated wastewater from the primary setting tanks then flows to the secondary treatment system.
back to top
Secondary treatment
Secondary treatment is called the activated sludge process. This is because air and “seed” sludge from the plant treatment process are added to the wastewater to break it down further. Air pumped into large aeration tanks mixes the wastewater and sludge that stimulates the growth of oxygen-using bacteria and other tiny organisms that are naturally present in the sewage. These beneficial microorganisms consume most of the remaining organic materials that are polluting the water and this produces heavier particles that will settle later in the treatment process.Wastewater passes through these bubbling tanks in three to six hours.
The aerated wastewater then flows to the final settling tanks which are similar to the primary settling tanks. Here the heavy particles and other solids settle to the bottom as secondary sludge. Some of this sludge is re-circulated back to the aeration tanks as “seed” to stimulate