Which treatment technologies are used in tertiary treatment of sewage?
Secondary treatment removes around 85-90 percent of BOD, TSS, and a minor amount of nitrogen, phosphorus, and heavy metals from wastewater.
Tertiary wastewater treatment is the third step of wastewater/sewage treatment, and is also known as advanced treatment. Tertiary treatment removes the nitrogen and phosphate load from the sewage. Reverse Osmosis, filtration, ion exchange, activated carbon adsorption, electro dialysis, nitrification, and denitrification, are some of the processes involved.
Treatment options in tertiary treatment are determined by the properties of the effluent, after secondary treatment as well as the type of water required at the end of the treatment. For example, if we require potable water, wastewater must be filtered and disinfected.
Technologies used in tertiary sewage treatment
Effluent polishing- It is an effective treatment for removing extra suspended particles and BOD from secondary effluent. Granular media filters, similar to those used to purify drinking water, are commonly utilized.
Polishing filters are often constructed units with tanks just above the filters to store backwash water. Effluent polishing of sewage can also be accomplished using micro strainers, similar to those used in municipal water supply treatment.
Sand Filters- Undissolved contaminants such as suspended particles, undissolved phosphate, and associated organics,are removed via sand filters. It is adaptable in terms of basic design structure to fit site-specific conditions.
Carbon Filters- Activated carbon adsorbs organics. Modifications to the fundamental design structure are possible to satisfy site-specific constraints.
Microfiltration-It is used when a solid-free wastewater for downstream facilities, such as reverse osmosis, or total removal of hazardous pollutants, is sought. It is used in metal particle recovery. It is also used in waste water treatment for metal plating, as well as sludge separation after activated sludge in a central biological STP, replacing secondary clarifier.
Ultra Filtration-It removes pollutants such as proteins and other macromolecular compounds, as well as toxic non-degradable components. It also separates heavy metals after complexation or precipitation, separates components that are not readily degradable in sewage treatment effluents that are then recycled to the biological stage.
It is a pre-treatment step prior to reverse osmosis or ion exchange.
Retention ponds-It is used to prevent downstream facilities from being flooded. It separates solid pollutants from rainfall (such as silt, organic matter, dissolved metal compounds, and nutrients). It is also used on industrial sites with heavily contaminated surfaces.
Nano Filtration –It is used to remove bigger organic molecules and multivalent ions from wastewater, in order to recycle and reuse it or reduce its volume. It increases the concentration of contaminants to the point where further destruction procedures are possible.
Reverse Osmosis (RO)-Water and dissolved components are separated down to ionic species in reverse osmosis. It is used when high purity water is required. The separated water phase is recycled and reused in processes, such as desalination, final removal of degradable components if biological treatment is not available, heavy metals, toxic components, and pollutant segregation, with the goal of concentrating or further processing.
It is frequently utilized in conjunction with other post-treatment procedures. It is used in wastewater treatment to eliminate undesirable ionic and ionisable organisms. Its biggest value is in its recovery potential.
Ion Exchange-The removal of undesirable or dangerous ionic elements of sewage and their replacement, by more acceptable ions from an ion exchange resin, where they are momentarily stored and then released into a regeneration or backwashing liquid, is known as ion exchange.
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