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Primary Treatment:

Primary treatment is the first process that takes place, its usually the operation performed to remove those materials that separate easily. The web definition of primary treatments: the first stage of waste water treatment, consisting of the removal of a substantial amount of suspended matter by using, sedimentation, flocculation, screening or similar methods.

Sedimentation takes place in a settling or a clarifier. It allows many suspended particles to settle out of water or waste water while slowing going through tank and providing a source of purification. A large about sludge is usually found at the bottom of the tank and is periodically removed. 

Flocculation is the action of binding large particles into clumps. Its where colloids from into flakes or floc, colloids are usually dissolved into a liquid, they do this by genitally missing the coagulated water this is also called the hydrodynamic process. Flocs or flakes are supposed to grow to either 0.1 or 2.0mm so that it can be removed by sedimentation.   

Screening, removes relatively solids in a primary treatment facility.  It is most commonly used by food processing plants and reduces the amount of solids being discharged. During the screening treatment, wood, dead animals, and rocks get in the way and have to be removed to keep the process going.

Secondary Treatment:

After the Primary treatment it goes through the secondary treatment The secondary treatment, also called activated sludge process,  is designed to remove biological content from the sewage such as, human waste, food, soap, detergent. In these process remove up to 90% of the waste water by adding in small microorganisms in the sewage which absorbs the organic material in the water, this is what the microorganisms live off of, the organic matter is they're food supply there are two types of this method, the first method is the activated sludge where the bacteria is free floating. The second method is that the bacteria is attached to a membrane that the water filters through allowing them to end waste  After the microorganisms have done their jobs the water is moved to an area to be disinfected of harmful bacteria  or anything else  that might be harmful, after this they are moved to a side river or lake to be held there.

Tertiary Treatment:

Advanced/tertiary wastewater treatment is additional treatment that follows primary and secondary treatment process. It removes stubborn contaminates that secondary treatment was not able to clean up and household sewage. More tha one tertiary treatment process may be used at any treatment plant. If disinfection is practiced, it is always the final process. Tertiary treatment technologies can be extensions of conventional secondary biological treatment to further stabilize oxygen-demanding substance in the wastewater, or to remove nitrogen and phosphorus. It may also involve physical-chemical separation techniques such as carbon adsorption, precipitation, membranes for advanced filtration, and reverse osmosis. The goal for the tertiary treatment is to remove no-biodegradable toxic organic pollutants, disable disease causing organisms and viruses, and other synthetic pollutants. They are removed by activated  carbon filter. Phosphate is removed by precipitation as calcium phosphate and nitrogen is removed volatilization as ammonia.

Waste water treatment plants using current biological treatment systems can produce a high quality effluent but, typically require further treatment for reuse application. A bioprocess tertiary membrane system is the perfect solution for reuse quality water.

Activated Sludge:

Activated sludge is the second part of the waste water treatment process. Activated sludge works by adding air or oxygen to the liquor. After a certain period of time the activated sludge absorbs more and more material to become larger and more dense which caused it to sink down the liquor absorbing all the harmful materials on its way down the main objective activated sludge has is to remove all harmful microorganisms from the soon to be treated water. 

Advantage /Disadvantage

Advantages

• Capable of removing 97% of suspended solids
• Biological nitrification without adding chemicals
• Oxidation and nitration achieved
• Biological phosphorous removal
• Solids and liquids separation
• Removes organics
• Cost effective
• Easily maintained mechanical work
• Self sustaining system

Disadvantages

• Cleaning is a hassle
• Most plants need at least three tanks
• Temperature changes affect the tank greatly

Activated sludge is a suspended process, and a suspended process is when the biomass is mixed with the sewage. The other secondary process is a fixed film process. This is when the biomass grows on the media and the sewage passes over the surface. Types of systems include Trickling filters and rotating biological contractors.

What activated sludge does

Activated sludge does many things in the waste water treatment process. Activated sludge oxidizes biological matter, ammonia, and nitrogen. It also removes phosphate, it drives away carbon dioxide, nitrogen, ammonia, etc. All in all activated sludge leaves a very low amount of dissolved or suspended material and it is very easy to floc and settle making it a very efficient way of cleaning water. Activated sludge is also a process that has bacteria clump together which is called a floc and feed off of the wastewater. This is done by introducing air into the wastewater. This is supposed to settle some of the healthy brown sludge at the bottom to sort the sludge from the rest of the wastewater, this is known as mixed liquor. Mixed Liquor is a combination of wastewater and organic materials (flocs).When this happens the microorganisms eat and stabilize the organic materials in the water. Types of bacteria in the water include: Fungi, Rotifers, and protozoan. Bacteria make up much of the activated sludge. This process is supposed to allow the flocs to sink to the bottom of the tank and allow the rest of the wastewater to be filtered.

Advanced Oxidation processes

Advanced oxidation processes are applied in water treatment after the waste water has been screened and bulk sludge and solid contaminates have been removed. It works by weaking the bonds between organic and chemical contaminants and the water with the use of chemicals like hydrogen peroxide and hydroxyl radicals and the use of UV radiation. This chemicals are specifically tailored to weaken and break down the bonds formed with water molecules at a faster rate than exposure to oxygen. The application of UV radiation generates the process of UV photolysis which speeds the effect of the hydroxyl radicals and increase the rate of decay in the chemical bonds causing the water to oxidize much more rapidly and completely. The advanced oxidation process is used during the secondary treatment stage to remove biologically toxic and non-degradable materials such as aromatics and pesticides.

How it works

UV oxidation is a destruction process that oxidized organic and explosive constituents in waste water by the addition of strong oxidizers and irradiation with UV light. Oxidation of target contaminates is caused by direct reaction with the oxidizers. UV photolysis, and through synergistic action of UV light, in combination with ozone, and/or hydrogen peroxide. If complete mineralization occurs, the final products of oxidation are carbon dioxide, water and salts.

The main advantage of UV oxidation is that it is a destructive process, as opposed to air stripping, or carbon absorption, for which contaminants are extracted and concentrated in a separate phase.

Ø  A process that utilizes UV light rays to activate ozone into a Hydroxyl radical, which is a stronger and faster oxidizer than ozone.

Ø   The ozone or Hydroxyl radical enters the water through a venturi  or a compressor, which bubbles the gas into the water.

Ø  The amount of water being treated determines the kind of ozone generator used, for high volumes or high concentrations corona generators are used, for low volumes of water or low concentrations UV is used.

Ø   UV light is mainly for disinfection only and only works if the water has good turbidity,  ozone however removes minerals such as iron among other things as well as odor, so its best to use both for the treatment.

Ø  This is an ozone generator, one of the key components use in the advanced oxidation process.

Ø  After the ozone has been made a venturi compressor is used to put the ozone into the water.

Ø  The ozonated  water then enters the stainless- steel contact tank where it remains for 3-4 minutes “contact time” for effective mixing and transfer of ozone to the water. 

Oxidizers

Here are some of the applicable oxidizers in order of strength

ü    Fluoride

      Hydroxyl Radical*

ü    Ozone

ü    Hydrogen Peroxide*

      Permanganate

      Chlorine

      Bromine 

      Iodine

      Oxygen*

Pros and Cons

Chlorine Treatment

During the main process of water treatment chlorine are used in the disinfection stage of the process. This stage comes before the finished water storage cycle and after the disinfectant fluoride.

The Disinfection Basin Cycle

Disinfection, sometimes referred to loosely as chlorination, is a necessary part of the water treatment process. It kills pathogens, and it produces chemical byproduct. Disinfection typically done by adding small amounts of a chlorine- based disinfectant to water. It destroys water-borne microbes, bacteria, and viruses – organisms that can cause serious illnesses or death. Typhoid and cholera,  which have killed hundreds of thousands of people in global epidemics, have been controlled in the world through the addition of disinfectant to drinking water.

Key pollutants That Are Removed During This Step

The advantage of chlorination is that it continues to kill bacteria as water moves through pipes to the tap. Chlorine has the major advantage of ensuring clean water right up to the tap, whereas the action of other disinfectants - such as ozone, ultraviolet light and ultra filtration - is only temporary. In addition to purifying water, chlorine helps remove tastes and odors, controls the growth of slime and algae in mains pipes and storage tanks, and helps to remove unwanted nitrogen compounds from water.

Major Disadvantages of Using Chlorine as a Disinfectant

The major disadvantage is the possibility of disinfection by – products. Excess chlorine in water can combine with organic material in the water to from substances such as Trihalomethanes, which can cause liver, kidney, or central nervous system problems, and are linked to an increased risk of cancer over a lifetime exposure. See disinfection Byproducts sub page for more information.

Other Forms of Disinfectant During The Water Treatment Process

Ultraviolet Light

Ultraviolet germicidal irradiation (UVGI) is a sterilization method that uses ultraviolet (UV) light at sufficiently short wavelength to break down microorganisms. Using a UVGI device in certain environments like circulating air or water systems creates a deadly effect on microorganisms such as pathogens, viruses and molds that are in these environments. Coupled with a filtration system, UVGI can remove harmful micro-organisms from these environments. There are potential dangers that come with this disinfectant. At certain wavelength (including UVC) UV is harmful to humans and other forms of life. In most UVGI systems the lamps are shielded or are in environments that limit exposure, such as a closed water tank or closed air circulation system, often with interlocks that automatically shut off the UV lamps if the systems is opened for access by human beings. Limited exposure mitigates the risk of danger.

Disinfection Byproducts