Secondary treatment is a step in wastewater treatment that involves the use of biological processes in order to capture all the dissolved organic materials that were not caught during the initial treatment. Microbes take these organic substances as food, transforming them to water, energy and carbon dioxide.
What is the second stage of wastewater treatment?
Secondary Wastewater Treatment 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 are the objectives of secondary treatment of waste water?
Objectives of Secondary Treatment of waste water 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.
What happens to wastewater in a wastewater treatment plant?
Wastewater entering the treatment plant includes items like wood, rocks, and even dead animals. Unless they are removed, they could cause problems later in the treatment process. Most of these materials are sent to a landfill. 2. Pumping
What is the final step in the secondary treatment process?
The final step in the secondary treatment stage is to settle out the biological floc or filter material in a secondary sedimentation tank (SST) or secondary clarifier and produce sewage water containing very low levels of organic material and suspended matter
What are the steps involved 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 the main goal of secondary wastewater treatment?
The objective of secondary treatment is the further treatment of the effluent from primary treatment to remove the residual organics and suspended solids.
What is a secondary treatment system?
Secondary treatment system is a wastewater treatment system which produces treated wastewater of secondary standard, i.e. 20 mg/L of Biochemical Oxygen Demand (BOD), 30 mg/L of Total suspended solids (TSS) and 10 cfu/100 mL of Escherichia (E) coli.
What happens during secondary treatment of wastewater sewage?
Secondary treatment is the removal of biodegradable organic matter (in solution or suspension) from sewage or similar kinds of wastewater. The aim is to achieve a certain degree of effluent quality in a sewage treatment plant suitable for the intended disposal or reuse option.
What happens in secondary sedimentation tank?
The Secondary Sedimentation Tanks are circular tanks equipped with rotating mechanical sludge and scum collectors. Appurtenant systems include spray systems for moving scum and for odor control, and pumps for draining tanks. Sedimentation Tank No. 1 is 75 feet in diameter with side water depth of 9 feet.
What is secondary waste?
Secondary waste is waste generated from different sources and of different nature, i.e. waste generated in a process that is known as a waste treatment operation; it includes residual materials originating from recovery and disposal operations, such as incineration and composting residues.
What is the purpose of secondary wastewater treatment quizlet?
The purpose of secondary treatment is to remove the suspended solids that did not settle out in the primary tanks and the dissolved BOD that is unaffected by physical treatment.
What happens in the secondary stage of wastewater treatment class 7?
Secondary treatment is a biological process. The screened water is passed on to sedimentation tanks to obtain clarified water. The water is passed on to aeration tanks to speed up the process of treatment of water by blowing air through it. Biogas is obtained at this stage.
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:
Why is secondary treatment important?
Secondary treatment of sewage and other wastewater is the stage of wastewater treatment designed to substantially degrade the biological content of the sewage.
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.
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 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 suspended process?
Suspended processes, particularly activated sludge, are most common in medium to large-scale plants; fixed film methods such as roughing filters need less maintenance and control, and are more resilient, and are appropriate where cost and maintenance are major issues. Anaerobic treatment is sometimes used, in the form of septic tanks ...
When did the Clean Water Act start?
In response to the escalating pollution of natural bodies of water, the Federal Government passed the Clean Water Act [1] in 1972 . This act required that wastewater treatment plants operate with a secondary treatment system.
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 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.
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.
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 secondary treatment?
Secondary treatment is a step in wastewater treatment that involves the use of biological processes in order to capture all the dissolved organic materials that were not caught during the initial treatment.
Is wastewater a solid?
Total solids in wastewater can be categorized as inorganic and organic. When it comes to the size, it can be divided into suspended, colloidal and dissolved solids. The main purpose of the initial or primary treatment is to eliminate the suspended solids as much as possible.
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 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 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 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 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.
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 ...
Why is it important to operate a wastewater treatment plant?
By operating your wastewater plant in a safe way, you can help ensure you are running a more effective wastewater treatment plant, while keeping your facility, your employees, and the environment safe.
What is the last step of primary treatment?
The last step of primary treatment involves sedimentation, which causes the physical settling of matter. Sedimentation often uses chemicals like flocculants and coagulants.
What is added to wastewater to remove pathogens?
During this part of the wastewater treatment process, chemicals like chlorine and sodium hypochlorite are added to the wastewater to remove harmful pathogens that cause cholera, polio, typhoid, and other diseases.
Why is wastewater treatment important?
The proper treatment of wastewater is essential not only for the environment; due to the use of several chemicals throughout the process, a safe process also keeps employees and your facility safe. Wastewater treatment is usually broken down ...
What is primary treatment?
Primary Treatment. During primary treatment, 40-50% of solids are removed from wastewater. This process usually involves large screens that let water pass through, but not floatable trash and other pollutants. These materials are collected and then properly disposed of.
How much impurity can tertiary treatment remove?
It is not as common as the other two steps, but tertiary treatment is capable of removing over 99% of all impurities from wastewater. Unfortunately, tertiary wastewater treatment is also relatively expensive.
Where can wastewater be returned?
Once the wastewater finishes its treatment, it can be returned safely to waterways in the vicinity where it will become a part of the natural environment and provide a home for fish and other types of water-based plants and animals.
What is the pretreatment stage in a wastewater treatment plant?
Many plants also add a pretreatment stage before the primary treatment process. In a standard municipal sewage treatment plant model, the wastewater flows into pretreatment tanks before undergoing primary and then secondary treatment.
What are the effects of pumping untreated sewage back into the environment?
Pumping untreated sewage back into the environment has a devastating ecological effect. The contaminants in sewage can kill plants and animals or make habitats unsafe to live in and water sources hazardous to drink. Contaminated wastewater from many industries, including the oil and gas industry, can have these adverse consequences.
How does activated sludge treatment work?
Plants typically also use activated sludge treatment, which is one of the most common aerobic processes. It works by using aeration and flocculation together. As we have seen, wastewater flows into an aeration tank and becomes mixed with water during aeration.
What is the process of removing solid particles from wastewater?
1. Pretreatment. Pretreatment primarily uses physical processes like filtration and settling to remove larger solid particles from the wastewater. During pretreatment, wastewater flows into the treatment tanks and basins as an influent. Large bar screens filter out larger items like tree limbs, leaves, and plastic debris.
How much of the world's wastewater is untreated?
Worldwide, however, the practice of treating wastewater is not as common. According to the United Nations, about 80% of the world’s wastewater is untreated when it returns to the environment. Wastewater treatment is essential for several reasons.
Why is wastewater treatment important?
Wastewater treatment is vital for healthy communities and ecosystems. It provides clean, healthful water for industrial and municipal use, cuts down on disease transmission, and helps ensure a green, thriving environment for the coming generations.
Where does municipal sewage come from?
This sewage comes from sinks, showers, toilets in structures like houses, apartments, restaurants, hospitals and office buildings.
What is wastewater treatment?
wastewater treatment. In wastewater treatment: Wastewater treatment and disposal. …as a first step before secondary treatment. Secondary treatment removes more than 85 percent of both suspended solids and BOD. A minimum level of secondary treatment is usually required in the United States and other developed countries.
What percentage of solids and BOD must be removed?
When more than 85 percent of total solids and BOD must be removed,…. Read More. In wastewater treatment: 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 ...
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...
Activated Sludge
- 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 secondar…
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, i…
Oxidation Ponds
- 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 alg…
See Also
External Links
- Wikipedia:Sewage treatment#Secondary treatment
- Clean Water Act- US EPA
- -An Overview of Tertiary Treatment
- [https://www.daviddarling.info/encyclopedia/A/AE_anaerobic_digestion.html-Anaerobic Digestion