What is the chemical treatment process of wastewater?
Wastewater Chemical Treatment Processes. Chemical precipitation is the most common method for removing dissolved metals from wastewater solution containing toxic metals. To convert the dissolved metals into solid particle form, a precipitation reagent is added to the mixture. A chemical reaction, triggered by the reagent,...
What are the 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.
What is industrial wastewater treatment for inorganics?
Industrial wastewater treatment for inorganics can be as simple as settling or filtration and as complex as multistage chemical precipitation or ion exchange processes.
How do oxidizing agents work in wastewater treatment?
With the introduction of an oxidizing agent during chemical oxidation, electrons move from the oxidant to the pollutants in wastewater. The pollutants then undergo structural modification, becoming less destructive compounds. Alkaline chlorination uses chlorine as an oxidant against cyanide.
What is removed during secondary wastewater treatment?
Secondary Treatment The secondary stage of treatment removes about 85 percent of the organic matter in sewage by making use of the bacteria in it. The principal secondary treatment techniques used in secondary treatment are the trickling filter and the activated sludge process.
What are the 4 stages of wastewater treatment?
Four common ways to treat wastewater include physical water treatment, biological water treatment, chemical treatment, and sludge treatment. Let us learn about these processes in detail.
What are the 3 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.
What is removed during primary wastewater treatment?
Primary treatment removes material that will either float or readily settle out by gravity. It includes the physical processes of screening, comminution, grit removal, and sedimentation.
What are the 5 stages of wastewater treatment?
Treatment StepsStep 1: Screening and Pumping. ... Step 2: Grit Removal. ... Step 3: Primary Settling. ... Step 4: Aeration / Activated Sludge. ... Step 5: Secondary Settling. ... Step 8: Oxygen Uptake. ... Sludge Treatment.
What is primary secondary and tertiary wastewater treatment?
Wastewater is treated in 3 phases: primary (solid removal), secondary (bacterial decomposition), and tertiary (extra filtration).
What is meant by secondary treatment?
Secondary treatment is the second step in most waste treatment systems during which bacteria consume the organic parts of the wastes. This is accomplished by bringing the sewage, bacteria and oxygen together in trickling filters or within an activated sludge process.
What is the first stage of water treatment?
CoagulationCoagulation is often the first step in water treatment. During coagulation, chemicals with a positive charge are added to the water. The positive charge neutralizes the negative charge of dirt and other dissolved particles in the water.
What is done during second stage of primary treatment?
Answer: 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 preliminary wastewater treatment?
Preliminary treatment is used to remove screenings and grit that enters a wastewater treatment plant from a sewered system. Preliminary treatment will have little effect on pathogens in the liquid wastestream.
Which process is used in tertiary treatment?
Several tertiary treatment processes can be employed depending on the purpose, with some of the most used being the following: membrane separation processes (microfiltration, ultrafiltration, and reverse osmosis), adsorption (activated carbon), ion exchange, disinfection (chlorination), advanced oxidative processes ( ...
How many stages of wastewater treatment are there?
Wastewater treatment facilities involve natural, chemical, and physical processes that allow for development and growth. There are three different stages of wastewater treatment each one, working together removing organic and inorganic loadings that would pollute the receiving streams in our environment. What are the 3 Stages of Wastewater Treatment?
How does secondary treatment remove organic matter?
The secondary stage of treatment removes about 85 percent of the organic matter in sewage by making use of the bacteria that is naturally found in it. Increased oxygen encourages the growth of bacteria, which consume and breakdown the complex organic compounds.
How is wastewater treated?
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. The resulting “sludge” is then fed into a digester, in which further processing takes place. This primary batch of sludge contains nearly 50% of suspended solids within the wastewater. Again as you can see the principle of Wastewater treatment is to separate the solids from the liquid and the more the operation separates the solids from the liquid the cleaner the Wastewater becomes.
What is the main objective of wastewater treatment?
The main objective of Wastewater Treatment is to separate solids from liquid then to treat both turning the solids into nonhazardous Bio-solids and water into non-threatening environmentally safe water to add back to the environment where it came from with the intention of using it again. 1. Primary Wastewater Treatment.
Why is aeration used in sewage treatment?
We will use this type to talk about. The secondary stage of treatment removes about 85 percent of the organic matter in sewage by making use of the bacteria that is naturally found in it. Increased oxygen encourages the growth of bacteria, which consume and breakdown the complex organic compounds.
Where is digested sludge sent?
The water is sent to the Headworks and the digested sludge is sent to Drying Beds or landfills. Sometimes the Gas made up of Methane is simply burned off. Digested sludge is passed through a dewatering step; the dried solids are disposed of, and the water is sent back to secondary treatment.
Where is the preliminary treatment located?
Stage 1.- Includes Preliminary Treatment is located at what is called the Headworks in the Primary Wastewater Treatment part of a plant. It involves the first couple of processes in a Conventional Wastewater Treatment Plant. Where inorganic material that won’t degrade in the Biological System is separated from the Wastewater. It’s a treatment process that is a vital part of the process and one that is often overlooked and the least pleasant part of the operation.
What happens after a wastewater treatment plant meets all permit specifications?
After meeting all permit specifications, clean water is reintroduced into the environment. Although testing is continuous throughout the wastewater treatment process to ensure optimal water flow, clarification and aeration, final testing is done to make sure the effluent leaving the plant meets permit specifications.
What is the process of removing large items from the influent?
Removal of large items from the influent to prevent damage to the facility’s pumps, valves and other equipment .#N#The process of treating and reclaiming water from wastewater (any water that has been used in homes, such as flushing toilets, washing dishes, or bathing, and some water from industrial use and storm sewers) starts with the expectation that after it is treated it will be clean enough to reenter the environment.#N#The quality of the water is dictated by the Environmental Protection Agency (EPA) and the Clean Water Act, and wastewater facilities operate to specified permits by National Pollutant Discharge Elimination System (NPDES). According to the EPA, The Clean Water Act (CWA) establishes the basic structure for regulating discharges of pollutants into the waters of the United States and regulating quality standards for surface waters. Under the CWA, EPA sets wastewater standards for industry. The EPA has also developed national water quality criteria recommendations for pollutants in surface waters. EPA's National Pollutant Discharge Elimination System (NPDES) permit program controls discharges.#N#As an example of expected standards, the Biochemical Oxygen Demand (BOD) of average wastewater effluent is 200 mg/L and the effluent after treatment is expected to be >30 mg/L. It is crucial a wastewater facility meets these expectations or risk stiff penalty.#N#The physical process of wastewater treatment begins with screening out large items that have found their way into the sewer system, and if not removed, can damage pumps and impede water flow. A bar screen is usually used to remove large items from the influent and ultimately taken to a landfill.
Why is wastewater pumped into a secondary clarifier?
Treated wastewater is pumped into a secondary clarifier to allow any remaining organic sediment to settle out of treated water flow. As the influent exits the aeration process, it flows into a secondary clarifier where, like the primary clarifier, any very small solids (or fines) sink to the bottom of the tank.
What is activated sludge?
These small solids are called activated sludge and consist mostly of active bacteria. Part of this activated sludge is returned to the aeration tank to increase the bacterial concentration, help in propagation, and accelerate the breakdown of organic material. The excess is discarded.
What is the function of an aeration tank?
The primary function of the aeration tank is to pump oxygen into the tank to encourage the breakdown of any organic material (and the growth of the bacteria), as well as ensure there is enough time for the organic material to be broken down.
What is a bar screen in wastewater treatment?
A bar screen is usually used to remove large items from ...
Where do organics sink in a clarifier?
Solids known as organics/sludge sink to the bottom of the tank and are pumped to a sludge digestor or sludge processing area, dried and hauled away. Proper settling rates are a key indicator for how well the clarifier is operating.
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.
Why is secondary wastewater treatment important?
Completing secondary wastewater treatment allows for safer release into the local environment, reducing common biodegradable contaminants down to safe levels.
What is biofiltration?
Biofiltration uses sand filters, contact filters or trickling filters to ensure that any additional sediment is removed from the wastewater.
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 are the stages of water treatment?
Several processes are at your disposal for implementing the various preparation stages of water treatment: Physical processes for mechanical preparation such as aeration, sedimentation or thermal influence. This also includes the use of screens, filters and sieves. Biological processes such as anaerobic wastewater ...
How is wastewater treated?
To achieve this, the wastewater is guided into a screening plant, where a screen or sieve drum filters out coarse impurities such as leaves, paper or textiles . Various screens, from coarse screens with several centimetres gap width, to fine screens with a gap width of a few millimetres, through which the water flows at different speeds, filter out the coarse materials step-by-step. The mechanically-recovered screen debris is dewatered and disposed of in an incineration plant.
What are the two types of wastewater treatment?
Firstly, problematic substances are removed from the water. This is done with cleaning, iron removal, manganese removal, sterilisation, desalination or softening .
How are phosphates removed from wastewater?
Phosphates are removed with a chemical precipitation or flocculation process. The phosphate precipitation is partly triggered by the addition of aluminium or iron salts in the sand collector or in the secondary wastewater treatment tank. The metal-phosphate flocks that are formed during this secondary clarification are then taken out of the wastewater together with the activated sludge. Depending on the mode of operation, the phosphate can also be "fished" with the help of microorganisms from the wastewater. In this case we speak of a biological phosphorus elimination, which is, however, still rarely used.
What is the purpose of return sludge?
The other part of the sludge, also known as "return sludge" is returned to the aeration tank to ensure that there are enough microorganisms in the aeration tank to break down the dirt. After biological treatment, approximately 90% of the wastewater is cleaned of biodegradable substances.
What is the name of the tank that cleans wastewater?
In most wastewater treatment plants, the water pre-purified in the mechanical treatment stage now reaches what are known as aeration tanks, which are often designed as circulation tanks. This is where the biological cleaning takes place.
What is the process of converting methane gas into electricity?
A pump transports the fresh sludge to what is known as a digestion tower. In the digestion tower, methane gas is produced in four phases (hydrolysis, acidification, acetone gene and methanogene phase); it is converted into electricity in a block heating plant and can be used to supply the plant with energy.
How does wastewater treatment work?
In small communities, wastewater treatment facilities may consist of individual septic systems, simple collection systems that directly discharge effluent to surface waters, or municipal lagoons that are emptied annually. These facilities usually treat and disperse the waste as close as possible to its source, thus minimizing operational costs and maintenance requirements. The longer the waste can sit in a lagoon before being discharged, the less likely it will be to contaminate drinking water sources. Some communities store the waste in lagoons, but others release the waste directly into water sources.
Which act regulates the release of toxic substances into the environment?
The Fisheries Act prohibits the release of harmful substances into waters that fish live in. The Canadian Environmental Protection Act governs the release of toxic substances into the environment and allows the federal government to develop regulations for the use of toxic substances.
How to reduce pressure on septic system?
Following some water conservation practices can greatly reduce pressure on your septic system. For more information about conserving water, see the fact sheet about Water Consumption. Here are a few things that you can do to care for your septic system: 1 Do not use your drain or toilet as a garbage disposal; avoid putting dental floss, diapers, coffee grounds and paper towel down the drain, as they can clog up your septic system. 2 Spread your loads of laundry out over the week. When too much water is added to the septic tank, it does not have time to treat wastes, and you could be flooding your drainfield with wastewater. 3 Plant grass on your drainfield, but keep trees and shrubs away from it, because roots can clog the system and cause damage. 4 Do not drive on your drainfield, because this can compact the soil and damage the septic system components.
Why is oxygen important in wastewater treatment?
The oxygen helps the bacteria to digest the pollutants faster. The water is then taken to settling tanks where the sludge again settles, leaving the water 90 to 95 percent free of pollutants. The picture below shows the settling tanks in the Winnipeg Wastewater Treatment Plant.
How is sludge treated?
The sludge that is removed from the settling tanks and the scum that is skimmed off the top during the primary steps are treated separately from the water. Anaerobic bacteria (anaerobic bacteria do not require oxygen) feed off of the sludge for 10 to 20 days at temperatures around 38 degrees Celsius. This process decreases the odour and organic matter of the sludge, and creates a highly combustible gas of methane and carbon dioxide, which can be used as fuel to heat the treatment plant. Finally, the sludge is sent to a centrifuge, like the one shown in the picture below. A centrifuge is a machine that spins very quickly, forcing the liquid to separate from the solid. The liquid can then be processed with the wastewater and the solid is used as fertilizer on fields.
Why is commercial wastewater not sent to public wastewater treatment plants?
Commercial and industrial waste is not sent directly to public wastewater treatment plants, because the public wastewater treatment system cannot effectively remove all of the contaminants. Wastewater from commercial and industrial processes is usually divided into the following four categories and dealt with accordingly:
What are the different levels of wastewater treatment?
There are several levels of wastewater treatment; these are primary, secondary and tertiary levels of treatment. Most municipal wastewater treatment facilities use primary and secondary levels of treatment, and some also use tertiary treatments.
What is primary treatment in sewage treatment?
Primary treatment is aimed at the removal of fine suspended organic solids that cannot be removed in the preliminary treatment. Primary treatment basically involves the process of sedimentation or settling. In the normal process of sewage treatment, sedimentation is usually carried out twice-once before the secondary treatment, referred to as primary sedimentation, and then after the secondary treatment is complete, a process known as secondary sedimentation. It is sometimes necessary to use chemical coagulants to facilitate or aid sedimentation, and this process is referred to as chemical precipitation or coagulation-aided sedimentation.
How to remove pathogenic organisms from water?
The pathogenic organisms can also be removed by mechanical means, during the course of waste water treatment. The processes involving screens (coarse and fine), grit chambers and sedimentation can partly remove the disease- causing organisms.
What is sequencing batch reactor?
The processes namely aeration and sedimentation are carried out in both the systems . The major difference is that while in the conventional activated sludge system, aeration and sedimentation occur simultaneously in separate tanks, these two processes are carried out sequentially in the same tank in SBR. Thus, the sequencing batch reactor may be regarded as fill- and-draw activated sludge process.
Why is phosphorus important in sewage treatment?
Thus, during the normal secondary treatment process, 10-30% of the sewage phosphorus is utilized by the microorganisms for growth and energy purposes. Phosphorus removal from waste water is required to control eutrophication and to maintain water quality.
How often is sedimentation done in sewage treatment?
In the normal process of sewage treatment, sedimentation is usually carried out twice-once before the secondary treatment, referred to as primary sedimentation, and then after the secondary treatment is complete, a process known as secondary sedimentation.
What are the most commonly used coagulants in sewage treatment?
The most commonly used coagulants in sewage treatment are alum (alluminium sulfate) iron salts (ferric sulfate, ferrous sulfate, ferric chloride), lime and soda ash (sodium carbonate), sodium silicate and sodium aluminate.
What are the biological processes of sewage?
The biological treatment processes of sewage are broadly classified as aerobic, anaerobic and pond processes . Depending on the nature of the use of the microorganisms, the biological processes are categorized as suspended growth systems and attached growth systems.
What are the parameters of industrial wastewater treatment?
Typical parameters requiring treatment in industrial wastewater include suspended solids, dissolved metals, nitrate, ammonia, arsenic, and sulfate. This article will be a high-level examination of the treatment options available for inorganic contaminants. The same basic steps can be followed in selecting a process for most industrial wastewater ...
What is biological treatment?
Biological Treatment. Biological treatment processes include attached growth, suspended growth, and membrane bioreactors. Attached growth processes are most common, but membrane bioreactors are a growing application. Biological treatment can be used to remove ammonia, nitrate, selenium, sulfate, and dissolved metals.
What is the process of oxidation and reduction?
Oxidation/reduction processes are used to transform contaminants into less soluble or more easily removed forms. For arsenic removal, oxidizing agents such as chlorine/sodium hypochlorite, hydrogen peroxide, ozone, or permanganate are commonly added. Conversely, reducing agents such as sodium bisulfite or metabisulfite may be added to remove contaminants such as chromium and selenium. Oxidation and reduction are typically rapid reactions but, since they require chemical addition, will increase the total dissolved solids (TDS) in treated water.
What is suspended growth?
Suspended growth is often used for removal of nutrients (nitrogen and phosphorus). When properly designed, these systems can be used for both nitrification (ammonia removal) and denitrification (nitrate removal). Nitrification is an aerobic process, while denitrification is anaerobic.
What is the process of sulfide precipitation?
Sulfide precipitation, which can achieve lower levels than hydroxide precipitation, is typically used as a “polishing” step to meet low metals concentrations. Sodium sulfide or sodium hydrosulfide (NaHS) is typically used. This process requires only small quantities of reagent and a short retention time. The process is typically done at neutral-to-high pH to avoid generating dangerous H2S gas.
What is ion exchange resin?
Specific ion exchange resins from several manufacturers are available to remove dissolved metals, arsenic, and nitrate (Figure 2). In this process, sodium or chloride ions are exchanged for the target contaminants. Resin is relatively expensive but has a long life and can be chemically regenerated (either on-site or off-site). The waste stream from ion exchange is typically much less than that generated by RO.
What is a logical starting point for a water treatment project?
A logical starting point is to examine the regulations that determine (or are interpreted to determine) an industrial facility’s discharge limits. These limits then form the basis for all of the water treatment work that follows. Effluent limits allow the environmental professional to specify treatment goals and process design criteria.
What is the primary objective of wastewater treatment?
The primary objective of wastewater treatment processes is to purify the water and make certain that it is safe for subsequent use once it has been returned to the environment as part of the water cycle. Wastewater treatment involves a number of stages involving processes that are mechanical (physical)-based, biological-based, chemical-based, ...
How is wastewater treated?
First, the wastewater is directed to a screen or a sieve drum that filters out impurities that are relatively coarse, such as leaves, textiles, paper, or other large materials. A series of screens are used with various degrees of fineness from several centimeters down to a few millimeters to screen out coarse contaminants in the water. The speed with which the wastewater flows through the screens at each step is carefully controlled to assure the effectiveness of the screening process. Any debris that has been collected on the screens is sent to other process steps where the material gets dewatered and then incinerated.
How does coagulation work?
This chemical process involves destabilizing wastewater particles so that they aggregate during chemical flocculation. Fine solid particles dispersed in wastewater carry negative electric surface charges (in their normal stable state), which prevent them from forming larger groups and settling. Chemical coagulation destabilizes these particles by introducing positively charged coagulants that then reduce the negative particles’ charge. Once the charge is reduced, the particles freely form larger groups. Next, an anionic flocculant is introduced to the mixture. Because the flocculant reacts against the positively charged mixture, it either neutralizes the particle groups or creates bridges between them to bind the particles into larger groups. After larger particle groups are formed, sedimentation can be used to remove the particles from the mixture.
How does chemical stabilization work?
Chemical Stabilization. This chemical wastewater treatment process works in a similar fashion as chemical oxidation. Sludge is treated with a large amount of a given oxidant, such as chlorine. The introduction of the oxidant slows down the rate of biological growth within the sludge and also helps deodorize the mixture.
How to remove metals from wastewater?
Chemical precipitation is the most common method for removing dissolved metals from wastewater solution containing toxic metals. To convert the dissolved metals into solid particle form, a precipitation reagent is added to the mixture. A chemical reaction, triggered by the reagent, causes the dissolved metals to form solid particles. Filtration can then be used to remove the particles from the mixture. How well the process works is dependent upon the kind of metal present, the concentration of the metal, and the kind of reagent used. In hydroxide precipitation, a commonly used chemical precipitation process, calcium or sodium hydroxide is used as the reagent to create solid metal hydroxides. However, it can be difficult to create hydroxides from dissolved metal particles in wastewater because many wastewater solutions contain mixed metals.
How does slowing down wastewater work?
A further slowing of the wastewater speed is performed by widening the basin as the water enters a primary treatment tank. The slower velocity permits finer particles to settle out into a sludge that accumulates to the bottom of the tank. This last treatment tank represents the end of the mechanical wastewater treatment process. Removed sludge is sent to a digestion tower where any organic material is converted into methane gas and can be used to produce electrical energy to power the processing plant.
What is redox reaction?
Redox reactions are used for the treatment of potable water. Chlorinated hydrocarbons and pesticides can be effectively removed from wastewater by the use of ozone and hydrogen peroxide treatments. Advanced oxidation processes are also used for the degradation of drug substances like antibiotics or cytostatic drugs that might be found in the water. Reduction processes can also be used for the transformation of heavy metal ions into sulfides.
Why Treat Wastewater?
It's a matter of caring for our environment and for our own health. There are a lot of good reasons why keeping our water clean is an important priority:
Wastewater treatment
The major aim of wastewater treatment is to remove as much of the suspended solids as possible before the remaining water, called effluent, is discharged back to the environment. As solid material decays, it uses up oxygen, which is needed by the plants and animals living in the water.
Stage One — Bar Screening
Stage Two — Screening
Stage Three — Primary Clarifier
Stage Four — Aeration
Stage Five — Secondary Clarifier
- Treated wastewater is pumped into a secondary clarifier to allow any remaining organic sediment to settle out of treated water flow. As the influent exits the aeration process, it flows into a secondary clarifier where, like the primary clarifier, any very small solids (or fines) sink to the bottom of the tank. These small solids are called activat...
Stage Six — Chlorination
Stage Seven — Water Analysis & Testing
Stage Eight — Effluent Disposal