Water and Wastewater Pre-Treatment Process
The pre-treatment process is one of the most important steps in the overall water and wastewater treatment process. The purpose of the pre-treatment stage is to remove disturbing factors such as some impurities, solids, suspended colloidal particles, and living organisms in the wastewater. One of the most important benefits that this process gives us is to ensure the final water quality is up to our standards. Pre-treatment processes allow your water and wastewater quality to be protected from factors such as seasonal changes, industrial pollution, and severe weather conditions. If we want to point out some of the advantages of using pre-treatment processes on a case-by-case basis, the following will be included:
Helps to have a continuous and reliable water flow
Increases the lifespan of reverse osmosis membranes used in later stages
Ensures standard quality of water sent to reverse osmosis or electrodeionization process
Increases the life cycle of general treatment plant processes and thus helps reduce final costs
Pre-Treatment Methodes
In general, wastewater in the local water supply system usually turns into a sludge form due to the presence of various raw tissue compositions. The pre-treatment process protects water and sewage transmission systems, including pipes, from hazards such as clogging and potential sediments.
Pre-treatment processes are classified into different types depending on the type and method or materials that will be removed in the end, but in general, pre-treatment processes in the water and wastewater industry can be divided into two general models:
Physical and Chemical processes (Physicochemical)
Biological processes
Physical and Chemical processes (Physicochemical)
Contaminated water usually has different suspended particles that are divided into four different categories based on size. Particles smaller than 0.08 micrometers are usually dissolved in wastewater, particles between 0.08 and 1 micrometer are colloidal particles, particles 1 to 100 millimeters in size are super colloid particles, and finally, particles larger than 100 micrometers are suspended in wastewater and can be deposited if at rest.
We will need physical and chemical processes to separate such particles. At this stage, colloidal particles are usually removed from the wastewater. Some perceptible particles can be removed by simple physical processes, but colloidal particles that are simply not visible to the naked eye are removed from the wastewater by a physicochemical process. For this purpose, various chemicals such as coagulants are used. These substances are added to the affluent and cause the physical state of the colloidal particles to change and form sedimentable colloidal clots by sticking together. Eventually, the particles that settle will be easily separated from the wastewater. In the physical and chemical pretreatment stage, the use of membranes is considered the most common method.
Zirsakht Tadbir Arian (ZETA) Company also pre-treats wastewater at this stage using the best and latest membrane separation and filter technologies. Softening silica removal (silicon dioxide, a common compound in rocks, sand, and mineral grains) with the help of up-to-date equipment is another service of this company. In general, the pre-purification services of ZETA Company are composed of two main parts in order to apply the pre-purification process. These two parts are filtration and separation and removal of silica. Various methods are used to remove silica from the wastewater composition, including ion exchange removal, softening by factors such as lime, reverse osmosis, ultrafiltration, and electrical coagulation.
Chemical Water Treatment Process
Softening Silica Removal
The method of softening and then separating silica is one of the common methods of removing it from the effluent, which is also used by Zirsakht Tadbir Arian (ZETA)Company. This method usually uses agents such as lime (calcium hydroxide) to remove or reduce the hardness of water by precipitating hardeners such as magnesium carbonate and calcium carbonate. After the addition of effective agents, silica is usually absorbed into the structure of calcium hydroxide and magnesium hydroxide and forms a bulk. The bulk is then separated from the effluent by a membrane or various filters. Depending on the concentration of silica in the wastewater, the amount of additives to it also changes, and the team of engineers at ZETA Company, taking advantage of up-to-date knowledge and appropriate equipment, undertake all the steps of silica removal.
Physical Water Treatment Process
Filtration
The method of softening and then separating silica is one of the common methods of removing it from the effluent, which is also used by Zirsakht Tadbir Arian (ZETA) Company. This method usually uses agents such as lime (calcium hydroxide) to remove or reduce the hardness of water by precipitating hardeners such as magnesium carbonate and calcium carbonate. After the addition of effective agents, silica is usually absorbed into the structure of calcium hydroxide and magnesium hydroxide and forms a bulk. The bulk is then separated from the effluent by a membrane or various filters. Depending on the concentration of silica in the wastewater, the amount of additives to it also changes, and the team of engineers at ZETA Company, taking advantage of up-to-date knowledge and appropriate equipment, undertake all the steps of silica removal.
Different types of membranes:
Ceramic membrane is a type of synthetic membrane that is made of inorganic materials such as aluminum oxide. This model of membrane can be useful for filtration operations at very high temperatures due to its high thermal resistance. In addition, the use of this type of membrane is recommended when hazardous substances such as acids or strong solvents are present in the wastewater.
A hollow fiber membrane is a type of membrane that has a semi-permeable filter in the form of a hollow fiber. This model of membranes, which are considered as artificial membranes, are used in liquid and gas filtration processes. This model of membrane usually has holes with a medium size for holes and is used to separate medium and large particles.
A tubular membrane is actually a tube in which different membranes are placed. The body of the pipe can be made of different materials depending on the type of process. Because the location of tubular membranes is inside a tube, the flow in a tubular membrane is usually inside out. The diameter of such a membrane is usually between 5 and 15 mm. Zirsakht Tadbir Arian Company perfroms the filtration process with two different filtration processes; That is, direct filtration (UF) and side stream filtration (MBR).
Direct filtration is the separation by means of a tubular membrane and the ultrafiltration process by applying high pressure to the filtered fluid. The tubular membranes used in this process are resistant to various types of sediments and prevent possible clogging of the piping and water supply system. On the other hand, a side stream filtration is actually a form of filtration that is based on two different models:
- Immersed method in which the membrane of the corresponding tube is placed inside the tank.
- Side stream method in which the mentioned tube membrane is located outside the tank.
Although less energy is consumed in the immersed method than in the side stream method, one of the important advantages of the side stream method is that in processes where the wastewater has a high velocity or flow rate, this model of membrane requires a lower surface to perform operations and it could lead to lower costs for the maintenance. In addition to the above, wastewater with a high concentration of solids is separated with the help of sidestream method with higher efficiency.
Biological Water Treatment Process
Filtration
Another type of pre-treatment process occurs at the stage of biological processes. During such processes, in fact, the purpose of separation is the decomposition of organic matter in wastewater with the help of natural processes and is planned based on biological science and biochemistry. The biological pre-treatment process relies on the decomposition of organic waste by bacteria, nematodes (tapeworms), and other small organisms through cellular reactions. Sewage usually contains a bulk of organic matter such as garbage, waste, and semi-digested foods, and may sometimes contain pathogenic organisms, heavy metals, and various toxins. Biological processes are usually considered to be more common than other methods due to their lower cost. These processes are usually divided into two general categories, aerobic and anaerobic. It is clear that in aerobic processes, the decomposition of organic waste material is done by living organisms in the presence of oxygen, but in anaerobic processes in the absence of oxygen.
Different biological processes in the pre-treatment stage will be different depending on the type of wastewater, but the main and basic stages and processes that are also provided by Zirsakht Tadbir Arian (ZETA) Company are as follows:
Membrane bioreactors are reactors in which biological reactions take place in the pre-treatment process. These reactors typically use membrane processes such as microfiltration or ultrafiltration. In this system, the membrane filtration process is combined with a biological treatment process such as activated sludge process and form a membrane bioreactor system that will be able to treat industrial and miscellaneous wastewater. In this system, a membrane is usually used to separate the activated sludge from the outlet stream of the bioreactor and return the microorganisms to the aeration tank. The difference between the bioreactors used at this stage and conventional reactors is the type of catalyst used in them. Such reactors use microorganisms or enzymes from biological metabolism to accelerate the decomposition process.
A2O processes are actually simple processes that take place in order to separate the nitrogen and phosphorus from wastewater. In this process, oxygen tanks are used to perform the process of nitrification. In short, such systems use oxygen tanks to perform several series of chemical reactions to absorb and then separate nitrogen and sometimes phosphorus.
Amino acid processes are used to remove protein from wastewater. Numerous studies have shown that large amounts of organic matter are found in various wastewaters that have a protein structure. Inorganic substances in wastewater are easily separated by various processes such as nitrification, but organic compounds are somewhat resistant to this model of separation and tend to remain in the effluent. Due to the fact that amino acids often have an enzymatic and protein structure, so they can also be effective in separating organic compounds from wastewater.
A moving bed biofilm bioreactor is a system consisting of an aeration tank that acts similar to an activated sludge tank in bioreactors. In this system, special plastic carriers are placed to provide the surface area required for the growth of biofilm in the reactor. The advantage of this type of reactor compared to membrane bioreactor is that less space is used in this reactor than the space required for activated sludge tank in membrane bioreactor because the biomass formed has a much higher concentration and in short It has a denser structure. In addition, the efficiency of the whole system does not depend much on the efficiency of the final stage of sludge separation. In general, this model of reactors has shown high potential for the separation of micro-pollutants such as pharmaceuticals, phosphorous and organic pesticides.
Series discontinuous reactor systems are also a set of reactors based on activated sludge processes used for biological separation and treatment of wastewater. In this system, oxygen is bubbled into the wastewater through the wastewater and activated sludge to help reduce of organic matter. The treated effluent in this system may be suitable for discharge into surface waters or for use on agricultural land.
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