what is removed during secondary wastewater treatment

What is secondary wastewater treatment?

Secondary Wastewater treatment is the second stage of wastewater treatment. In primary treatment, suspended solids, colloidal particles, oil, and grease are removed. In secondary treatment, biological treatment is done on the wastewater to remove the organic matter present.

What is the process of wastewater treatment?

Oct 16, 2009 · The secondary treatment is designed to remove soluble organics from the wastewater. Secondary treatment consists of a biological process and secondary settling is designed to substantially degrade the biological content of the sewage such as are derived from human waste, food waste, soaps and detergent.

What are the different types of wastewater treatment?

Mar 23, 2017 · The main objective of secondary treatment: To remove most of the fine suspended and dissolved degradable organic matter that remains after primary treatment, so that the effluent may be rendered suitable for discharge. Conventional secondary treatment can reduce the BOD's

What happens to the water after the secondary treatment process?

Secondary wastewater treatment processes use microorganisms to biologically remove contaminants from wastewater. Secondary biological processes can be aerobic or anaerobic, each process utilizing a different type of bacterial community. Coupled anaerobic–aerobic processes may also be employed under certain circumstances.

What is removed in secondary treatment?

Secondary treatment removes the soluble organic matter that escapes primary treatment. It also removes more of the suspended solids. Removal is usually accomplished by biological processes in which microbes consume the organic impurities as food, converting them into carbon dioxide, water, and energy…

What is removed in the secondary clarifiers?

The wastewater is pumped through a vertical pipe into the feed well. The speed of the incoming water is slowed, and the water evenly distributes around the tank. The skimmer arm is used to remove the floating solids such as scum and grease from the secondary clarifier.

What happens during the step of secondary wastewater treatment?

During secondary treatment, water flows through a secondary sedimentation tank that allows both solid wastes and microorganisms to form clumps and settle out of the water that is being treated. This step in the process of wastewater treatment uses various types of bacteria to treat water.Sep 30, 2014

What is removed during wastewater treatment?

Suspended solids that pass through screens and grit chambers are removed from the sewage in sedimentation tanks. These tanks, also called primary clarifiers, provide about two hours of detention time for gravity settling to take place. As the sewage flows through them slowly, the solids gradually sink to the bottom.

What are secondary clarifiers?

secondary clarifiers is to separate biological floc from the treated liquid waste stream. Secondary clarifiers are most often discussed in conjunction with suspended growth biological wastewater treatment systems.

How much Bod does the secondary treatment remove?

85 percentPrimary treatment typically removes about one-third of the BOD and one-half of the suspended solids in domestic wastewaters. Combined primary and secondary treatment is required to achieve 85 percent reduction in both BOD and suspended solids concentration to meet the regulatory definition of secondary treatment.

What is grit removal?

Grit removal is the process used to remove sand, silt and grit from water. Grit (and sand) removal is often found in the headworks of wastewater treatment plants (WWTP).

What steps are taken during secondary treatment of waste water Why secondary treatment is called biological treatment?

Secondary treatment of wastewater works on a deeper level than primary level. It is called as biological treatment because it is designed to substantially degrade the biological content of the waste through aerobic biological processes. This step removes the dissolved organic matter by the use of biological agents.

What is the expected BOD removal after both primary and secondary treatment?

A sewage treatment plant providing both primary and secondary treatment is expected to remove at least 85 percent of the BOD and suspended solids from domestic sewage.

What is removed from wastewater during the first stages of water treatment?

Primary treatment (stage 1) This is when wastewater is temporarily held in large sedimentation tanks to remove settleable solids. With gravity, heavier solids sink to the bottom while lighter solids rise to the top. Chemicals can also be added as coagulants to remove more solids.Mar 7, 2021

What is not removed in wastewater treatment?

Biological stages in wastewater treatment plants are not able to remove substances such as drugs, found in the wastewater of medical centers, or halogenated compounds and cyanides from industrial wastewater.Jul 26, 2013

How is nitrate and phosphate removed from wastewater?

Phosphate and nitrate pollutants can be removed by chemical precipitation, biological treatment, membrane processes, electrolytic treatment, ion-exchange and adsorption process to remove these pollutants from water sources effectively.Dec 24, 2016

What is the purpose of sewage treatment?

The purpose of the sewage treatment is to remove the solids present in the sewage. ROLE OF MICROORGANISMS. Microorganisms are unicellular microscopic living things. They multiply by binary division of cells within 10 to 20 minutes. They require oxygen for their respiration.

What is secondary treatment?

The secondary treatment is designed to remove soluble organics from the wastewater. Secondary treatment consists of a biological process and secondary settling is designed to substantially degrade the biological content of the sewage such as are derived from human waste, food waste, soaps and detergent.

What is activated sludge?

The activated sludge process (ASP) is an aerobic biological wastewater treatment process that uses microorganisms, including bacteria, fungi, and protozoa, to speed up decomposition of organic matter requiring oxygen for treatment.

What is the only thing to be provided for the respiration of aerobic organisms?

The organic solids present in the wastewater serve as food for the aerobic microorganisms. The only thing to be provided is the DO , which is essential for the respiration of the aerobic organisms.

What is suspended growth?

In suspended growth systems the microorganisms responsible for treatment are maintained in liquid suspension by appropriate mixing methods. Typically, suspended growth systems require smaller footprints than fixed film systems for an equivalent capacity. There are a number of biological processes. The most common is activated sludge process in which microbes, also known as biomass, are allowed to feed on organic matter in the wastewater and remain in suspension. The make-up and dynamics of the microbial population is a function of how the ASP is operated.

What are the end products of anaerobic and aerobic processes?

Under aerobic conditions, if completely oxidized, organic matter is transformed into non-hazardous products. But an anaerobic process can produce methane (CH 4 ), which is explosive, and ammonia (NH 3) and hydrogen sulfide (H 2 S), which are toxic.

What are the two types of biological processes?

TYPES OF BIOLOGICAL PROCESSES. There are two types of biological treatment process; aerobic and anaerobic. Aerobic process means that oxygen is present for the microbes for respiration. Anaerobic process means that the process proceeds in the absence of DO.

What is secondary treatment in wastewater?

Once wastewater has gone through the Primary treatment stage the Effluent will undergo a secondary treatment in order to remove both small suspended solids and BOD 5 (five day biochemical oxygen demand [2]) that pass through the primary treatment stage. All secondary treatment systems use a biological process to break down organic matter. Microorganisms are introduced to the wastewater and consume the organic matter, oxygen is delivered to the system ensuring microorganism survival. Oxygen delivery differs among the various systems. This biological process occurs naturally in nature, but is accelerated in secondary treatment systems. Typically 85% of BOD and suspended solids are removed during this process. Water exiting secondary treatment will still carry nitrogen, phosphorus, heavy metals, Pathogens, and bacteria. For further removal of pollutants the water is transported to a tertiary treatment [3] system and disinfection. There are a variety of secondary treatment processes; the following are conventional processes used by treatment plants:

What is secondary effluent?

The secondary effluent that settles will either enter a digester or re-enter the trickling system. Secondary effluent that re-enters the trickling filter serves several purposes, the following are examples; 1. further treatment, 2. preventing the microorganism from drying out, and 3. diluting or supplementing primary effluent.

What is the process of trickling filter?

Process: When primary effluent is transported to a trickling filter system the wastewater is dispensed upon a bed of media, such as rocks, stones, plastics, or salts. The most modern trickling filters use a type of rockwool. The effluent flows through the material at slow enough rates to allow microbial growth on the surface of the media (and within the fibres of the media, in the rockwool types) creating a layer of film. The spacing of the media allows air to circulate throughout the trickling system. Once microbial growth takes place additional wastewater flow has contact with microorganisms; this contact ensures that the organic matter in the primary treatment effluent is broken down. The biofilm that falls off the media flows through the bed of material and will be transported to the secondary settling tank to remove excess microorganisms. The secondary effluent that settles will either enter a digester or re-enter the trickling system. Secondary effluent that re-enters the trickling filter serves several purposes, the following are examples; 1. further treatment, 2. preventing the microorganism from drying out, and 3. diluting or supplementing primary effluent. Figure 2 provides a visual layout of a trickling filter system.

How does activated sludge work?

Process: During the activated sludge process primary effluent flows into an aeration tank, where it is mixed with microorganisms. The aeration tank injects a steady supply of oxygen or air into the wastewater, ensuring that the organisms have an adequate supply of oxygen needed to breakdown the organic matter that remains in the effluent. The effluent then flows into secondary settling tanks. At this point the sludge goes in one of two directions; 1. back to the aeration tank, this is because the return sludge contains a large amount of microorganisms that will rapidly breakdown organic matter, or 2. to the sludge digester [4]. The treated water will enter the tertiary treatment stage; here it will go through the final treatment stage before it is released into a natural water system. Figure 1 is an example an active sludge system.

How deep is an oxidation pond?

Process: Oxidation ponds are large and shallow; a typical depth would range from 1-2.5m. The ponds are composed of microorganisms, which feed on the organic matter received from primary effluent. Algae are a key feature in the oxidation pond system. Algae are much like the aeration tank in the activated sludge system; they deliver a steady flow of oxygen to the bacteria. The algae require sunlight to produce oxygen via photosynthesis, reaeration created by wind delivers air flow when sunlight is not available. Overall the process is slow and requires large areas of land. Typically oxidation ponds are used in areas with small populations where land is readily available. Figure 3 shows the basics of an oxidation pond system.

How do algae produce oxygen?

The algae require sunlight to produce oxygen via photosynthesis, reaeration created by wind delivers air flow when sunlight is not available.

What is anaerobic treatment?

Anaerobic treatment is sometimes used, in the form of septic tanks and in biogas digesters. in the case of septic tanks the primary and secondary phases are combined in one unit. If biogas digesters are used for secondary treatment, the primary treatment phase is reduced or emitted (aiming to remove matter such as gravel ...

What is the material removed from wastewater?

Organic material and nutrients are removed from wastewater flowing past attached growth also known as biofilm. Packing materials used in attached growth processes include rock, gravel, slag, sand, redwood and wide range of plastic and other synthetic materials.

What is the main objective of secondary treatment?

The main objective of secondary treatment: To remove most of the fine suspended and dissolved degradable organic matter that remains after primary treatment, so that the effluent may be rendered suitable for discharge. Conventional secondary treatment can reduce the BOD's to below 20mg/l and Suspended Solids to below 30mg/l which is acceptable in ...

What is the oxidation of ammonia to nitrate?

This is achieved by oxidation of most of the ammonia to nitrate during treatment (nitrification ). 2. Nitrification: Means the oxidation of ammonia to nitrate. Nitrification is possible with aerobic biological processes.

When was the tricking filter invented?

The first tricking filter was placed in operation in England in 1893. the concept of a tricking filter was grew form the of contact frets which were water tight basins filled with broken stones. The limitation the contact filters included a relatively.

Is dissolved oxygen required in wastewater?

Are those where sufficed amount of dissolved oxygen is required into the wastewater to sustain aerobic action, as one of the major polluting effects of wastewater on streams results form the depletion of dissolved oxygen by the action of aerobic organisms in degrading the organic content of the waste. Practical aerobic biological treatment ...

What is secondary wastewater treatment?

Secondary Wastewater Treatment. Secondary wastewater treatment processes use microorganisms to biologically remove contaminants from wastewater. Secondary biological processes can be aerobic or anaerobic, each process utilizing a different type of bacterial community.

Which biological treatment processes employ organisms that function in the absence of molecular oxygen?

The wastewater flows downward over the media surface where microorganisms form a layer of biomass and consume contaminants in the water. Anaerobic – Anaerobic biological treatment processes employ organisms that function in the absence of molecular oxygen.

What is anaerobic process?

Anaerobic processes are generally used to treat high-strength wastewaters where it is impractical to utilize aerobic processes or where producing a biofuel gas is desired .

Where do microorganisms grow?

Microorganisms grow on the surface of the discs where aerobic biological degradation of the wastewater pollutants takes place. Trickling filter – An attached-growth process where wastewater is distributed over a fixed bed of media such as rocks, gravel, plastic substrate, etc.

Is wastewater aerobic or anaerobic?

Coupled anaerobic–aerobic processes may also be employed under certain circumstances. Aerobic – Aerobic biological processes are common in municipal wastewater treatment. In an aerobic system, the organic contaminants are converted to carbon dioxide, water, additional microorganisms, and other end products.

What is primary wastewater treatment?

The primary wastewater process utilizes equipment to break up larger particles and then uses sedimentation or a floating process for extraction. Many treatments that use the primary method then proceed to the secondary treatment process.

How is wastewater treated?

The primary treatment of wastewater occurs through sedimentation with filtering out large contaminant particles within the liquid. The contaminants separate as they are passed through several tanks and other filters. Leftover sludge filters through a digester to suspend solids from the wastewater.

How to get rid of sediment in sewage?

The first is biofiltration that uses filters with sand, contact filters or trickling filters that remove sediment from the sewage. Aeration is the next step. It mixes the wastewater with a microorganism solution. Then, this treatment uses an oxidation pond to pass the wastewater through a body for up to two or three weeks.

What is the process of removing impurities from water?

The removal in the secondary wastewater treatment process generally occurs through a biological process with consumption of impurities in water by microbes, converting the matter into energy, carbon dioxide gases, and water. AOS can help with municipal wastewater treatment services in both primary and secondary processes.

What is primary treatment?

Through the primary treatment, it is possible to remove materials that float and settle on top of water. Through primary treatment, it is possible to implement screening water treatment, reduce particles to fragments, remove grit and initiate sedimentation. The primary treatment pushes sewage through screens into the comminutor for grip disposal ...

What is the difference between primary and secondary treatment?

The principal difference in primary and secondary treatment is the process that breaks down the sewage in wastewater. In the primary method, the waste processes through a physical procedure with equipment and filtration. While secondary treatment may use similar items, this method uses biological treatment through microbes.

What is the difference between filtration and sedimentation?

Another difference between these processes is how much time they take to complete.

What is the most effective method of secondary treatment of wastewater?

This method of secondary treatment of wastewater employs sand filters, contact filters, or trickling filters to ensure that additional sediment is removed from wastewater. Of the three filters, trickling filters are typically the most effective for small-batch wastewater treatment.

What is primary treatment of wastewater?

Primary treatment of wastewater involves sedimentation of solid waste within the water. This is done after filtering out larger contaminants within the water. Wastewater is passed through several tanks and filters that separate water from contaminants.

What is the third step in wastewater management?

This third and last step in the basic wastewater management system is mostly comprised of removing phosphates and nitrates from the water supply. Substances like activates carbon and sand are among the most commonly used materials that assist in this process.

How long does it take for a wastewater solution to be aerated?

The resulting mixture is then aerated for up to 30 hours at a time to ensure results.

What is the process of removing sediment from a wastewater system?

1. Biofiltration. Bio filtration uses sand filters, contact filters or trickling filters to ensure that any additional sediment is removed from the wastewater. 2. Aeration. Aeration is a lengthy process which increases oxygen saturation by introducing air to wastewater.

What are the stages of wastewater treatment?

What Are the Three Stages of Wastewater Treatment? There are three main stages of the wastewater treatment process, aptly known as primary, secondary and tertiary water treatment. In some applications, more advanced treatment is required, known as quaternary water treatment.

Where is wastewater held?

During primary treatment, wastewater is temporarily held in a settling tank where heavier solids sink to the bottom while lighter solids float to the surface. Once settled, these materials are held back while the remaining liquid is discharged or moved through to the more rigorous secondary phase of wastewater treatment.

What is tertiary treatment?

In the case of water treated by municipalities, tertiary treatment also involves the removal of pathogens, which ensures that water is safe for drinking purposes.

What is primary treatment of sewage?

Primary treatment of sewage by quiescent settling allows separation of floating material and heavy solids from liquid waste. The remaining liquid usually contains less than half of the original solids content and approximately two-thirds of the BOD in the form of colloids and dissolved organic compounds.

What is secondary treatment?

Secondary treatment is designed to substantially degrade the biological content of the sewage which are derived from human waste, food waste, soaps and detergent. The majority of municipal plants use aerobic biological processes as a secondary treatment step. To be effective, the biota require both oxygen and food to live.

What is an MBR system?

Membrane bioreactors (MBR) are activated sludge systems using a membrane liquid-solid phase separation process. The membrane component uses low pressure microfiltration or ultrafiltration membranes and eliminates the need for a secondary clarifier or filtration. The membranes are typically immersed in the aeration tank; however, some applications utilize a separate membrane tank. One of the key benefits of an MBR system is that it effectively overcomes the limitations associated with poor settling of sludge in conventional activated sludge (CAS) processes. The technology permits bioreactor operation with considerably higher mixed liquor suspended solids (MLSS) concentration than CAS systems, which are limited by sludge settling. The process is typically operated at MLSS in the range of 8,000–12,000 mg/L, while CAS are operated in the range of 2,000–3,000 mg/L. The elevated biomass concentration in the MBR process allows for very effective removal of both soluble and particulate biodegradable materials at higher loading rates. Thus increased sludge retention times, usually exceeding 15 days, ensure complete nitrification even in extremely cold weather.

How does an aerated lagoon work?

Aerated lagoons are a low technology suspended-growth method of secondary treatment using motor-driven aerators floating on the water surface to increase atmospheric oxygen transfer to the lagoon and to mix the lagoon contents. The floating surface aerators are typically rated to deliver the amount of air equivalent to 1.8 to 2.7 kg O 2 / kW·h. Aerated lagoons provide less effective mixing than conventional activated sludge systems and do not achieve the same performance level. The basins may range in depth from 1.5 to 5.0 metres. Surface-aerated basins achieve 80 to 90 percent removal of BOD with retention times of 1 to 10 days. Many small municipal sewage systems in the United States (1 million gal./day or less) use aerated lagoons.

How much BOD is in secondary treated sewage?

Secondary treated sewage is expected to produce effluent with a monthly average of less than 30 mg/l BOD and less than 30 mg/l suspended solids. Weekly averages may be up to 50 percent higher.

How is primary clarifier effluent discharged?

Primary clarifier effluent was discharged directly to eutrophic natural wetlands for decades before environmental regulations discouraged the practice. Where adequate land is available, stabilization ponds with constructed wetland ecosystems can be built to perform secondary treatment separated from the natural wetlands receiving secondary treated sewage. Constructed wetlands resemble fixed-film systems more than suspended growth systems, because natural mixing is minimal. Constructed wetland design uses plug flow assumptions to compute the residence time required for treatment. Patterns of vegetation growth and solids deposition in wetland ecosystems, however, can create preferential flow pathways which may reduce average residence time. Measurement of wetland treatment efficiency is complicated because most traditional water quality measurements cannot differentiate between sewage pollutants and biological productivity of the wetland. Demonstration of treatment efficiency may require more expensive analyses.

What is a cyclic activated sludge system?

One type of system that combines secondary treatment and settlement is the cyclic activated sludge (CASSBR), or sequencing batch reactor (SBR). Typically, activated sludge is mixed with raw incoming sewage, and then mixed and aerated. The settled sludge is run off and re-aerated before a proportion is returned to the headworks.

Brief History

Brief Explanation

• Once wastewater has gone through the Primary treatment stage the Effluent will undergo a secondary treatment in order to remove both small suspended solids and BOD5 (five day biochemical oxygen demand) that pass through the primary treatment stage. All secondary treatment systems use a biological process to break down organic matter. Microorganisms...

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Activated Sludge

Trickling Filter

Oxidation Ponds

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