Sewage treatment
Abstract：Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and houhold wage, both runoff (effluents) and domestic. It includes physical, chemical, and biological process to remove physical, chemical and biological contaminants. Its objective is to produce a waste stream (or treated effluent) and a solid waste or sludge suitable for discharge or reu back into the environment. This material is often inadvertently contaminated with many toxic organic and inorganic compounds.
Key words: Sewage treatment, fixed-film and 库氏呼吸suspended-growth, Activated sludge
Origins of wage踏破贺兰山缺
Sewage is created by residences, institutions, and commercial and industrial establishments. Raw influent (wage) includes houhold waste liquid from toilets, baths, showers, kitchens, sinks, and so forth that is dispod of via wers. In many areas, wag
e also includes liquid waste from industry and commerce. The paration and draining of houhold waste into greywater and blackwater is becoming more common in the developed world, with greywater being permitted to be ud for watering plants or recycled for flushing toilets. A lot of wage also includes some surface water from roofs or hard-standing areas. Municipal wastewater therefore includes residential, commercial, and industrial liquid waste discharges, and may include stormwater runoff. Sewage systems capable of handling stormwater are known as combined systems or combined wers. Such systems are usually avoided since they complicate and thereby reduce the efficiency of wage treatment plants owing to their asonality. The variability in flow also leads to often larger than necessary, and subquently more expensive, treatment facilities. In addition, heavy storms that contribute more flows than the treatment plant can handle may overwhelm the wage treatment system, causing a spill or overflow. It is preferable to have a parate storm drain system for stormwater in areas that are developed with wer systems.
As rainfall runs over the surface of roofs and the ground, it may pick up various contamin
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ants including soil particles and other diment, heavy metals, organic compounds, animal waste, and oil and grea. Some jurisdictions require stormwater to receive some level of treatment before being discharged directly into waterways. Examples of treatment process ud for stormwater include dimentation basins, wetlands, buried concrete vaults with various kinds of filters, and vortex parators (to remove coar solids).
Process overview
Sewage can be treated clo to where it is created (in ptic tanks, biofilters or aerobic treatment systems), or collected and transported via a network of pipes and pump stations to a municipal treatment plant (e werage and 召集读音pipes and infrastructure). Sewage collection and treatment is typically subject to local, state and federal regulations and standards. Industrial sources of wastewater often require specialized treatment process (e 同音不同字的词语Industrial wastewater treatment).
Conventional wage treatment may involve three stages, called primary, condary and tertiary treatment. Primary treatment consists of temporarily holding the wage in a quie
scent basin where heavy solids can ttle to the bottom while oil, grea and lighter solids float to the surface. The ttled and floating materials are removed and the remaining liquid may be discharged or subjected to condary treatment. Secondary treatment removes dissolved and suspended biological matter. Secondary treatment is typically performed by indigenous, water-borne micro-organisms in a managed habitat. Secondary treatment may require a paration process to remove the micro-organisms from the treated water prior to discharge or tertiary treatment. Tertiary treatment is sometimes defined as anything more than primary and condary treatment. Treated water is sometimes disinfected chemically or physically (for example by lagoons and microfiltration) prior to discharge into a stream, river, bay, lagoon or wetland, or it can be ud for the irrigation of a golf cour, green way or park. If it is sufficiently clean, it can also be ud for groundwater recharge or agricultural purpos.
Pre-treatment
Pre-treatment removes materials that can be easily collected from the raw wastewater be
fore they damage or clog the pumps and skimmers of primary treatment clarifiers (trash, tree limbs, leaves, etc).睡不着觉是什么原因引起的
Screening
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The influent wage water is strained to remove all large objects carried in the wage stream. This is most commonly done with an automated mechanically raked bar screen in modern plants rving large populations, whilst in smaller or less modern plants a manually cleaned screen may be ud. The raking action of a mechanical bar screen is typically paced according to the accumulation on the bar screens and/or flow rate. The solids are collected and later dispod in a landfill or incinerated.
Grit removal
Pre-treatment may include a sand or grit channel or chamber where the velocity of the incoming wastewater is carefully controlled to allow sand, grit and stones to ttle.
Primary treatment
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In the primary dimentation stage, wage flows through large tanks, commonly called "primary clarifiers" or "primary dimentation tanks". The tanks are large enough that sludge can ttle and floating material such as grea and oils can ri to the surface and be skimmed off. The main purpo of the primary dimentation stage is to produce both a generally homogeneous liquid capable of being treated biologically and a sludge that can be parately treated or procesd. Primary ttling tanks are usually equipped with mechanically driven scrapers that continually drive the collected sludge towards a hopper in the ba of the tank from where it can be pumped to further sludge treatment stages. Grea and oil from the floating material can sometimes be recovered for saponification.
