Why Ban Screens Are Important In Wastewater Technology
Screens are one of the first steps in a wastewater treatment process. They remove large solids from the water, allowing for more comprehensive steps that include biological degradation, chemical additions, disinfection and other processes.
Coarse screens remove debris from wastewater flow to help protect pumping and other equipment. This is a valuable preliminary treatment step to avoid clogged pumps and costly repair costs down the road. Wastewater from human activity contains rags, textiles and plant debris that can clog or jam equipment. Screens are then positioned along the channel to catch these materials. Manual bar screens represent the workhorse of many small wastewater facilities and can be used to control the entry of large solids into a treatment facility. These screens have vertical bars spaced 1 to 2 inches apart to catch the debris. These coarse screens can be hand raked or operated with automated screening heads such as rakes, combs and scrapers. However, the wet material they collect tends to be smelly and attract vermin and odor complaints from the public.
In addition to providing protection for downstream equipment, fine screens can remove rags, paper, plastics, latex, tins, containers and wood from the wastewater flow. They also prevent pipe blockages, damage and wear-tear on the plant’s piping and equipment. Typically used in the inlet works of treatment plants, fine screenings remove non-biodegradable wastes that can clog pumps, pipes and equipment. These include rags, sticks, leaves, food particles and plastics.
A sedimentation tank is a large tank that allows suspended particles in water to settle. It is usually rectangular with a sloped floor that allows gravity to move the suspended particles to the bottom of the tank before water is drawn out at the outlet. There are many options when it comes to designing a sedimentation tank. For example, it is possible to use inclined plates or tubes that provide more settling surface area and decrease the amount of time it takes for particles to settle. Another option is to add flocculants or coagulants to the liquid in order to increase the settling velocity and reduce the amount of time it takes for suspended solids to settle. Adding these reagents to the water also allows for easier separation of the settling particles from the water. This is an important step in the wastewater treatment process.
Burial is a common method for smaller plants to dispose of screenings. This consists of adding a cover of approximately 6 inches of soil over the top to prevent flies and odors. Despite the hype, burial is not a practical solution for all wastewater treatment facilities. It can create a significant drain on a plant’s water budget and the earthwork required to build a pit large enough to accommodate the buried screenings is no small feat. The best practice is to bury screenings in a manner that minimizes the need for earthwork and to use an alternative disposal system such as incineration or digestion when possible. This is a better alternative to the open-area dumping of screenings that has been proven to produce significant health risks.