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Secondary treatment is widely used in sewage treatment and is also applicable to many agricultural and industrial wastewaters. Secondary treatment systems are classified as fixed-film or suspended-growth systems, and as aerobic versus anaerobic.
Since the systems are staged, the culture of the later stages can be acclimated to the slowly degraded materials. [8]: Ch 2 The discs consist of plastic sheets ranging from 2 to 4 m in diameter and are up to 10 mm thick. Several modules may be arranged in parallel and/or in series to meet the flow and treatment requirements.
The aeration stage and the disinfecting stage are the primary differences from a traditional septic system; in fact, an aerobic treatment system can be used as a secondary treatment for septic tank effluent. [1] These stages increase the initial cost of the aerobic system, and also the maintenance requirements over the passive septic system.
Activated sludge tank at Beckton sewage treatment plant, UK.The white bubbles are due to the diffused air aeration system. The activated sludge process is a type of biological wastewater treatment process for treating sewage or industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa.
Constructed subsurface flow wetlands are meant as secondary treatment systems which means that the effluent needs to first pass a primary treatment which effectively removes solids. Such a primary treatment can consist of sand and grit removal, grease trap, compost filter, septic tank , Imhoff tank , anaerobic baffled reactor or upflow ...
The basic national standard for U.S. municipal treatment plants is the Secondary Treatment Regulation. [2] Most plants in the U.S. must meet this secondary treatment standard. The permit authority (state agency or EPA) can compel a POTW to meet a higher standard, if there are applicable water quality standards for the receiving water body.
Extended aeration agitates all incoming waste in the sludge from a single clarifier. The combined sludge starts with a higher concentration of inert solids than typical secondary sludge and the longer mixing time required for digestion of primary solids in addition to dissolved organics produces aged sludge requiring greater mixing energy input per unit of waste oxidized.
Industrial facilities may generate the following industrial wastewater flows: [citation needed] Manufacturing process wastestreams, which can include conventional pollutants (i.e. controllable with secondary treatment systems), toxic pollutants (e.g. solvents, heavy metals), and other harmful compounds such as nutrients