WASTEWATER TREATMENT Aeration Tanks use the connection between oxygen and wastewater to their advantage. The wastewater is either transported down slats, slowly, while oxygenated air flows up through the wastewater, or oxygenated air is bubbled through the wastewater. Either way, the oxygenated air causes the biological matter to oxidize while the volatile organics are stripped from the water. top Collection Systems are conduits for the transportation of sewage or other waste liquids including storm, surface, and ground water drainage. Collection systems can use gravity as their main source of energy for transportation of wastewater. The sewer system has to have a constant gradient and constructed in a straight line so the wastewater flows directly to the treatment facility. Other collection systems that contain lifts and separators for solids and liquids are more easily installed and contain mechanisms to force sewage through the collection system. top Filters aid in the removal of suspended solids in wastewater through filtration, chemical sorption, and assimilation. top Filter Media may include sand, anthracite, and activated carbon. Sand and anthracite are used to intercept the larger particles to be removed and activated carbon is used as the adsorbent for smaller particles, such as colloids, bacteria and viruses, in the filtering process. top Grit Chambers are part of the preliminary treatment of the wastewater after the screening devices. They are also called aerated grit chambers. Aerating, meaning that air is bubbled up the wall of the chamber, forces the grit to the other side of the chamber where it is collected. top Primary Clarifiers, also known as primary sedimentation basins, retain the influent for a period long enough to allow most of the solids to be settled to the bottom of the tank. This mass is raw sludge. Scrapers and pumps, at the bottom of the clarifier, remove the sludge. Surface skimming collects the materials, like oil and grease, which rise to the surface. top Rotating Biological Reactors degrade contaminants in water with microorganisms. Contaminated water is circulated in an aeration basin where a microbial population aerobically degrades organic matter and produces carbon dioxide, water, and new cells. The cells form a sludge, which is settled out in a clarifier, and is either recycled out to the aeration basin or discarded.top Screening Devices are used primarily to remove large objects that may interfere with the following treatment processes. Large grit particles are removed with the screens to prevent rapid corrosion to the following units. They also remove logs, shoes, and other large objects that may interrupt the flow. top Secondary Clarifiers, also known as secondary sedimentation basins, remove suspended solids that could not be settled in the primary clarification process. Following the aerobic treatment of the suspended solids, the wastewater is sent to the secondary clarifier to be settled. top Sludge Dewatering thickens the sludge by removing the water, therefore making it easier to remove and transport. Anaerobic Treatment causes the sludge to separate as it forms biogas that can be used for energy. The biogas is then stored in a gas dome, where anaerobic digested volatile solids form sludge on the bottom of the unit. A layer of scum forms on the top of the water and water forms in the center to be sent back to the influent. top Stabilization Ponds hold waste that has been treated or decomposed to the extent that if released the waste would not cause a nuisance or odors. top Trickling Filters and Media provide aerobic treatment of the wastewater. Generally, wastewater is pumped from a compartment of the septic tank and dispersed over a media bed in which it is aerated. The wastewater is then allowed to drain back into the septic tank. Trickling filters contain either rock or plastic media. These media remove organics by adsorption. top WATER TREATMENT Activated Carbon is applied in adsorption in both powdered and granular form within carbon columns. Activated carbon removes color, taste and odor from drinking water. It is a very porous substance with a high surface area to volume ratio. The high surface area is ideal for maximum particulate adsorption to the carbon's surface. top Air Stripping is a process used by water treatment facilities to rid the water of dissolved contaminants. It reduces the concentration of taste and odor-causing substances, such as hydrogen sulfide, by allowing a stream of the influent flow over planks while air is propelled up into the tank. This causes the water to separate from the gaseous contaminants, which are then released into the air and out of the water. top Carbon Adsorption takes advantage of the large surface area provided by the activated carbon by using the particles' attractive forces to hold the contaminants to any surface of contact. top Chemical Storage is an important factor in water treatment. Alum and other coagulants need to be stored and accessed by the clarifiers to form settleable particles. Chlorine is also stored in both liquid and solid form at a water treatment facility to provide disinfection for the public. top Clarifiers, also known as settling tanks and sedimentation basins, are used to settle the large particles of debris that are not filtered through the screening devices. In a clarifier, coagulation and flocculation are used to remove the particles. The settling basins can be rectangular or circular. The parameters are the same for both rectangular and circular sedimentation basins. top Ozone Treatment is used after clarification and filtration to destroy microorganisms, pathogens, and industrial pollutants quickly through disinfection. Ozone, a highly volatile gas, is injected in the water with a venturi or a diffuser. The water is exposed only 15 minutes at a time, leaving no residue, as chlorination does. top Pumps in a water treatment facility are used to retrieve untreated potable water. Raw surface water enters the plant through a low lift pump. Ground water enters the plant through a high lift pump. The pumps force the water up to filtering devices above the ground. The designated heights of the filtering devices provide the water with enough velocity to travel throughout the different processes of the treatment facility. top Reverse Osmosis, also known as hyperfiltration, has the best purification capability for drinking water. Reverse osmosis removes ions from water including salt from seawater, particles, and bacteria by use of membrane filtration. top Screening Devices are used in the first stage of the water treatment process. Their purpose is to filter out large objects before the water is sent to settling tanks. top UV & Ionizing Radiation passes a flow of water under a bank of lamps that produce electromagnetic radiation to kill microorganisms, thus reducing color, taste and odor. It leaves no residue as chlorination does. However, the water does lose its disinfecting capability when it leaves the plant, where chlorination holds it's residual for further disinfections. top WATER RESOURCES Bridge Piers: These structures provide added support for stationary and mobile loads on long bridges. Piers can also be used for measuring depth of flow in an underlying channel. Key issues involved in the design of bridge piers include the shape, size and orientation with respect to flow direction. top Dams: These are structural barriers built to obstruct or control the flow of water in rivers and streams. They are designed to serve two broad functions. The first is the storage of water to compensate for fluctuations in river flows or in demand for water and energy. The second is the increase of hydraulic head, or the difference in height between water levels in the lake created upstream of the dam and the downstream river. By creating additional storage and head, dams are able to generate electricity, supply water for agricultural, industrial, and household needs, control the impact of floodwaters, and enhance river navigation. They can be simultaneously operated in a manner that augments downstream water quality, that enhances fish and wildlife habitat, and that provides for a variety of recreational activities such as fishing, boating, and swimming.top Erosion and Scour: These terms refer to the detachment and transport of sediment particles as a result of flowing water. These processes can occur over land or within rivers and streams and ultimately result in the deposition of transported sediment at downstream locations. The movement of sediment can lead to the loss of significant soil volumes throughout a watershed, the instability of channel beds and banks, the undercutting of bridge pier and abutment foundations, the reduction of stream conveyance and reservoir storage capacity, the damaging aquatic habitat, and the increase of turbidity and inhibition of photosynthesis. top Open Channels: These consist of a natural or man-made structure that contains, restricts and directs the flow of water or wastewater. The surface of the liquid is exposed to the atmosphere, and therefore, flow is often referred to as free surface flow. The design and analysis of channels includes the solution of relationships between bed and bank roughness, channel geometry, and flow velocity. Free surface flows are driven by gravity and can vary in both time and space.top Spillways: These are conveyance structures, often associated with dams, that release diverted waters, or surplus and flood waters that cannot be contained upstream of the dam. top Stormwater Systems: The management of stormwater, or flow resulting from rain or snowfall, is a major consideration for most municipalities. Urban stormwater drainage systems include streets, curbs and gutters, storm sewer networks, ditches, channels, streams and culverts. These systems are designed to collect and convey runoff to a stream in a manner that safely prevents ponding of water in streets, homes and properties. top Watershed: A term that refers to the land that contributes runoff to a given stream or river location. They vary greatly in size and characteristics, but can often be delineated by considering the topography of the land. Once rain or snow has fallen on a sloped surface, the primary processes involved with flow on a watershed basis include overland or sheet flow, in which runoff first forms a thin layer of water and becomes more concentrated en route to larger gullies, streams and rivers; infiltration of water to the subsurface; and interception or depression storage, in which flow collects in puddles or larger storage areas. top Weir: This is a man-made structure that is built perpendicular to a river or stream to restrict the flow of water. Weirs come in a variety of shapes and sizes, and their primary use is for flow measurement. Once the weir has been calibrated, volumetric flowrate in the river or stream can typically be determined by a simple measurement of flow depth at the weir. top